JP7630728B2 - Power Transmission Coil - Google Patents

Description

The present disclosure relates to a power transmission coil of a transmitting coil or a receiving coil in a magnetic field coupling type power transmission device that uses electromagnetic induction to transmit power from a transmitting coil to a receiving coil in a non-contact manner, i.e., transmit power.

Magnetic field coupling type power transmission is known in which a portable device such as a mobile phone, headset, digital camera, or digital video has a receiving coil, and power is transmitted from a transmitting coil to the receiving coil to contactlessly power or charge the portable device.
In recent years, research has been conducted not only on small devices such as portable devices, but also on large devices and applications that handle large amounts of power, such as automatic transport robots and electric vehicles.
When transmitting power from the transmitting coil to the receiving coil, some of the power transmitted from the transmitting coil is not received by the receiving coil and is radiated into the air, acting as an interference wave to surrounding devices, which adversely affects the surrounding devices.

Patent Document 1 discloses an antenna (corresponding to a power transmission coil) for use in a portable device that transmits power and that can suppress emitted radiation noise without significantly reducing power transmission efficiency.
The antenna shown in Patent Document 1 is a composite antenna consisting of a planar coil and a loop coil, and the resonant frequency of the resonant circuit consisting of the inductance of the loop coil and the tuning capacitance is adjusted to a frequency that is more than twice the driving frequency of the planar coil.

JP 2012-115069 A

The inventors attempted to verify the antenna disclosed in Patent Document 1 from the viewpoint of power transmission efficiency, and found that when the impedance Z _loop at the drive frequency of the loop coil is small, the power at the drive frequency of the planar coil is not necessarily received by the receiving coil with high transmission efficiency.
Furthermore, at frequencies below the resonant frequency of the loop coil, the impedance Z _loop of the loop coil becomes capacitive, and the magnetic flux from the planar coil and the magnetic flux radiated from the loop coil due to the current induced in the loop coil by this magnetic flux reinforce each other.
In other words, in this frequency range, the loop coil cannot suppress radiated interference waves, and if the capacitance C of the capacitor is determined so that the resonant frequency of the loop coil is sufficiently higher than the drive frequency, the frequency range in which radiated interference waves can be suppressed becomes narrow.

That is, in the antenna disclosed in Patent Document 1, if we consider a series resonant circuit consisting of resistance R of a loop coil, self-inductance L, and capacitance C of a capacitor, the impedance Z _loop of the loop coil is expressed by the following equation (1).

In equation (1), j is the imaginary unit, and ω is the angular frequency.
If the capacitance C is determined so that the loop coil resonates at a frequency twice the fundamental frequency, Z _loop is expressed by the following equation (2).
The fundamental wave referred to here is the driving wave in Patent Document 1, and refers to the fundamental frequency component of a high-frequency signal transmitted (or received) by a power transmitting circuit (or a power receiving circuit) connected to the planar coil.

In equation (2) , ω ₀ is the fundamental wave angular frequency.
Since the real part does not depend on frequency, the imaginary part of the impedance Z _loop of the loop coil at the fundamental wave angular frequency ω ₀ is expressed by the following equation (3).

As is clear from equation (3), when the self-inductance L of the loop coil at the fundamental wave angular frequency ω ₀ is small, the impedance Z _loop of the loop coil at the fundamental wave angular frequency ω ₀ does not become sufficiently large, and a current is easily induced in the loop coil.
As a result, conductor loss occurs in the loop coil, and if the loop coil is provided on a dielectric substrate, dielectric loss occurs due to the material of the dielectric substrate, resulting in a decrease in the power transmission efficiency of the drive frequency power.

On the other hand, in order to make the imaginary part of the impedance Z _loop of the loop coil at the fundamental wave angular frequency ω ₀ sufficiently large, it is also possible to determine the capacitance C of the capacitor so that the resonant frequency of the loop coil is sufficiently higher than the fundamental wave frequency.
However, as is clear from the above formula (1), in a frequency band below the resonant frequency of the loop coil, the imaginary part of the impedance Z _loop of the loop coil becomes a negative value, and the impedance Z _loop of the loop coil becomes capacitive.

If the impedance Z _loop of the loop coil is a capacitive impedance, the magnetic flux from the planar coil and the magnetic flux radiated from the loop coil due to the current induced in the loop coil by this magnetic flux will reinforce each other, and at frequencies below the resonant frequency of the loop coil, the loop coil will not be able to suppress radiated interference waves, and the frequency range in which radiated interference waves can be suppressed will be narrowed.
In short, suppression of radiated interference waves and making the resonant frequency of the loop coil sufficiently higher than the fundamental wave frequency cannot be achieved at the same time.

The present disclosure has been made in consideration of the above-mentioned points, and aims to obtain a power transmission coil that does not affect the power transmission efficiency of the power transmitted by the coil transmitting power, and suppresses unnecessary radiation waves due to frequencies other than the fundamental frequency of the electromagnetic field formed by the power transmission coil, that is, the fundamental frequency transmitted by a power transmission circuit connected to the power transmission coil when the power transmission coil is a power transmission coil, or the fundamental frequency received by a power receiving circuit connected to the power receiving coil when the power transmission coil is a power receiving coil.

The power transmission coil according to the present disclosure comprises a power transmission coil for transmitting power, a loop conductor having a slit, and a resonant circuit connected between both open ends of the slit of the loop conductor, the resonant circuit having a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel and a second inductor connected in series to the parallel resonant circuit , and a shield conductor arranged at a position where the electromagnetic fields formed by the power transmission coil intersect when the power transmission coil transmits power.

According to the present disclosure, it is possible to suppress unnecessary radiation waves due to frequencies other than the fundamental frequency of the electromagnetic field formed by the power transmission coil without affecting the power transmission efficiency of the power transmitted by the power transmission coil.

1 is a configuration diagram showing a power transmission coil according to a first embodiment; 3 is an equivalent circuit diagram of a shield conductor in the power transmission coil according to the first embodiment. FIG. 4 is a diagram showing the phase of the impedance of a shield conductor relative to the frequency of the power to be transmitted in the power transmission coil according to the first embodiment. FIG. 4 is a diagram showing power transmission efficiency versus frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. 5A to 5C are diagrams illustrating the suppression effect with respect to the frequency of transmitted power in the power transmission coil according to the first embodiment. 4 is a diagram showing the absolute value of the impedance of a shield conductor versus the frequency of the power to be transmitted in the power transmission coil according to the first embodiment; FIG. 4 is a diagram showing the radiation efficiency versus frequency of transmitted power in the power transmission coil according to the first embodiment. FIG. FIG. 11 is a configuration diagram showing a power transmission coil according to a second embodiment. FIG. 11 is a configuration diagram showing a power transmission coil according to a third embodiment. FIG. 13 is a configuration diagram showing a power transmission coil according to a fourth embodiment. FIG. 13 is a configuration diagram showing a power transmission coil according to a fifth embodiment. FIG. 13 is a configuration diagram showing a power transmission coil according to a sixth embodiment. 13 is a diagram showing the phase of the impedance of a shield conductor relative to the frequency of the transmitted power in a power transmission coil according to embodiment 6. FIG.

Embodiment 1.
A power transmission coil according to a first embodiment will be described with reference to FIGS. 1 to 7. FIG.
The power transmission coil according to the first embodiment is a power transmission coil or a power receiving coil in a magnetic field coupling type power transmission device that uses electromagnetic induction to transmit power from a power transmission coil to a power receiving coil in a non-contact manner, that is, transmits power.
In this disclosure, the power transmitting coil and the power receiving coil are collectively referred to as a power transmission coil, and the power transmission coil refers to either the power transmitting coil or the power receiving coil.

When transmitting power from the power transmitting coil to the power receiving coil in a non-contact manner, the power receiving coil is placed opposite a position where electromagnetic induction occurs with the power transmitting coil, that is, a position where the electromagnetic fields generated by the power transmitting coil interlink.
At the fundamental frequency of the high-frequency signal transmitted to the transmitting coil by the transmitting circuit connected to the transmitting coil, the transmitting coil and the receiving coil are in a resonant relationship, so the receiving coil efficiently receives power at the fundamental frequency, but for unwanted waves at frequencies other than the fundamental frequency, the coupling between the transmitting coil and the receiving coil is small, so power reception is suppressed.

The explanation of the present disclosure will show an example in which the power transmission coil is applied to a power transmission coil, but even if the power reception coil is applied to the power transmission coil, the configuration will be similar to that of the power transmission coil, based on the same concept.
In addition, the power transmission coil of the power transmission coil and the power receiving coil of the power receiving coil are collectively referred to as power transmission coils, and in the case of a power transmission coil, the power transmission coil refers to the power transmission coil, and in the case of a power receiving coil, the power transmission coil refers to the power receiving coil.

When the power transmission coil is a power transmission coil, the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed by the power transmission coil, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit connected to the power transmission coil.
When the power transmission coil is a receiving coil, the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed in the receiving coil by receiving power through electromagnetic induction with the power transmission coil, and is the fundamental frequency of the high-frequency signal received by the receiving circuit connected to the receiving coil.
To avoid complicating the explanation, hereinafter, the explanation will be given as a power transmission coil.

As shown in FIG. 1 , the power transmission coil includes a power transmission coil 1 and a shield conductor 2 .
When the present disclosure is applied to a power receiving coil, the power receiving coil includes a power receiving coil and a shield conductor.
A high-frequency signal having mainly fundamental frequency components transmitted from a power transmission circuit 3 is input to the power transmission coil 1 .
Based on the high-frequency signal input from the power transmission circuit 3, the power transmission coil 1 forms an electromagnetic field around the power transmission coil 1, and the formed electromagnetic field links with the power receiving coil (not shown) placed in the opposing position, forming an electromagnetic field in the power receiving coil and transmitting power to the power receiving coil by electromagnetic induction.

The power receiving coil that receives the power transmitted from the power transmitting coil 1 supplies the power to a load (not shown) such as a rechargeable battery connected thereto via a power receiving circuit (not shown).
A capacitor for impedance matching is connected between the power transmission coil 1 and the power transmission circuit 3. This impedance matching capacitor is omitted from the illustration as it is included in the power transmission circuit 3.
The power transmission coil 1 is a coil having a planar pattern wound a plurality of times on the surface of a dielectric substrate (not shown).

The shield conductor 2 is disposed on the outside of the power transmission coil 1 .
The shield conductor 2 may be disposed inside the power transmission coil 1, or above or below it.
The shield conductor 2 includes a loop conductor 21 and a resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel.

In the shield conductor 2, the resonant circuit 22 places the loop conductor 21 in an essentially electrically open state for the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, and a current of opposite phase to the high-frequency current flowing in the power transmission coil 1 is induced in the loop conductor 21 for unwanted waves of frequencies other than the fundamental frequency, in this example, unwanted waves of frequencies more than twice the fundamental frequency.
When a current is induced in the loop conductor 21 , a magnetic field is generated around the loop conductor 21 by the induced current.
In addition, even for frequencies less than the fundamental frequency, a current is induced in the loop conductor 21 as an unwanted wave, and a magnetic field is formed around the loop conductor 21 by the induced current.

The magnetic field formed by the high-frequency current of harmonic frequency flowing through the power transmission coil 1 and the magnetic field formed by the high-frequency current of opposite phase induced in the loop conductor 21 are substantially in opposite phase and cancel each other out.
In other words, the shield conductor 2 has the characteristic that a current is unlikely to be induced in the loop conductor 21 at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, but a current is induced in the loop conductor 21 at frequencies other than the fundamental frequency, particularly the frequencies of unwanted waves whose radiated interference waves are to be suppressed.

As a result, the shielding conductor 2 does not affect the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1, i.e., the fundamental frequency of the transmitted power, and weakens the electromagnetic field formed around the power transmission coil 1 for unwanted wave frequencies.
In short, a decrease in power transmission efficiency is avoided for the fundamental frequency of the transmitted power, and radiation noise caused by currents of unwanted wave frequencies flowing through the power transmission coil 1 is suppressed by radiation from high-frequency currents of the opposite phase induced in the loop conductor 21.
In this disclosure, power transmission efficiency is defined as the ratio of the power supplied to the power transmitting coil 1 to the power received and output by the power receiving coil.

The loop conductor 21 is disposed at a position where it is linked with the electromagnetic field generated by the power transmission coil 1 when the power transmission coil 1 transmits electric power.
The loop conductor 21 is a conductor having a loop-shaped planar pattern wound once on the surface of the dielectric substrate so as to surround the outer periphery of the power transmission coil 1 .
The loop conductor 21 is a parasitic conductor having a slit 211 formed at the end of the loop.

The loop conductor 21 is disposed outside the power transmission coil 1 .
The loop conductor 21 only needs to be located close enough to the power transmission coil 1 so that a sufficient current is induced in the loop conductor 21 by linkage with the electromagnetic field formed by the power transmission coil 1, and may be located inside the power transmission coil 1, or above or below the power transmission coil 1. The loop conductor 21 does not need to be on the same plane as the power transmission coil 1.
The thickness of the loop conductor 21 is greater than the thickness of the power transmission coil 1. In other words, the line width of the loop conductor 21 is greater than the line width of the power transmission coil 1.

The inductor 221 and the capacitor 222 connected in parallel form a parallel resonant circuit 22 .
The parallel resonant circuit 22 is connected between both open ends of the slit 211 of the loop conductor 21 .
That is, one terminal of inductor 221 is electrically connected to one open end of slit 211, and the other terminal is electrically connected to the other open end.
Similarly, one terminal of the capacitor 222 is electrically connected to one open end of the slit 211, and the other terminal is electrically connected to the other open end.
The inductor 221 and the capacitor 222 are formed on the surface of a dielectric substrate by commonly known methods.

The parallel resonant circuit 22 increases the impedance of the shielding conductor 2 at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 to reduce the induced current, and reduces the impedance of the shielding conductor 2 at frequencies other than the fundamental frequency, i.e., the frequencies of radiated interference waves, which are unwanted waves that we wish to suppress, to make it easier for a current to be induced.
The resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 .
In this example, the frequency of the spurious wave to be suppressed is set to a frequency that is at least twice the fundamental wave frequency f _0. However, the frequency is not limited to twice the fundamental wave frequency.

Moreover, the inductance L of the inductor 221 and the capacitance C of the capacitor 222 that configure the parallel resonant circuit 22 are values that satisfy ω ₀ C=1/ω ₀ L.
ω ₀ is the fundamental frequency of the electromagnetic field formed by the power transmitting coil 1 , and is the angular frequency at the fundamental frequency of the high-frequency signal transmitted by the power transmitting circuit 3 connected to the power transmitting coil 1 .
This point will be explained in more detail below.

An equivalent circuit diagram of the shield conductor 2 is shown in FIG.
In FIG. 2, R _L denotes the resistance of the impedance of the loop conductor 21 , L _L denotes the inductance of the impedance of the loop conductor 21 , L denotes the inductance of the inductor 221 , and C denotes the capacitance of the capacitor 222 .
The impedance Z of the shield conductor 2 is expressed by the following equation (4).

The condition for increasing the impedance Z of the shield conductor 2 and reducing the induced current at the fundamental frequency _f0 (angular frequency is _ω0 ) of the electromagnetic field formed by the power transmission coil 1 is equal to the condition for a parallel resonant circuit consisting of the inductance L of the inductor 221 and the capacitance C of the capacitor 222 to resonate, which is when the inductance L and the capacitance C satisfy the following equation (5).

When equation (5) is satisfied, the third term in equation (4) becomes infinite, and the shield conductor 2 is electrically open, that is, it is equivalent to the loop conductor 21 being open in the parallel resonant circuit 22.
Therefore, no current is induced in the loop conductor 21 at the fundamental frequency f ₀ of the electromagnetic field formed by the power transmission coil 1 , which has an angular frequency ω ₀ .
As a result, power of fundamental frequency f ₀ transmitted from the power transmitting coil 1 to the power receiving coil is not affected by the shield conductor 2 and is received by the power receiving coil, so power transmission efficiency does not decrease.

Next, a method for determining the inductance L of the inductor 221 and the capacitance C of the capacitor 222 will be described.
As described above, the resonant frequency at which the parallel resonant circuit consisting of the inductor 221 and the capacitor 222 resonates must match the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1. Therefore, the inductance L and the capacitance C have a degree of freedom within a range that satisfies the following equation (6).

On the other hand, the effect of weakening the electromagnetic field by the shield conductor 2 can be obtained only when the impedance Z of the shield conductor 2 is inductive.
The phase of the impedance Z of the shield conductor 2 constituting the equivalent circuit shown in FIG. 2 changes as shown in FIG.
In Figure 3, the horizontal axis indicates the transmission frequency of the power supplied to the power transmission coil 1, and the vertical axis indicates the phase of the impedance Z of the shield conductor 2. Frequency F1 is the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1, and frequency F2 is the frequency at which the imaginary part of the impedance Z of the shield conductor 2 shown in the above equation (4) becomes 0, i.e., the resonant frequency of the shield conductor 2.
As is clear from FIG. 3, the effect of weakening the electromagnetic field by the shield conductor 2 can be obtained for frequencies less than the fundamental frequency f ₀ (F1) and frequencies equal to or greater than the resonant frequency F2 of the shield conductor 2.

Therefore, the condition for making the impedance Z of the shield conductor 2 inductive in order to suppress radiated interference waves at frequencies equal to or higher than the resonant frequency F2 of the shield conductor 2 is expressed by the following equation (7), where the resonant frequency F2 of the shield conductor 2 is f ₀ ×B.

In equation (7), L is the inductance of the inductor 221, and L _L is the inductance of the impedance of the loop conductor 21.
The radiated interference waves emitted from the power transmission coil are considered to be mainly harmonics generated at frequencies that are multiples of the fundamental frequency _f0 .
In this example, if the frequency of the spurious wave to be suppressed is set to a frequency equal to or greater than twice the fundamental wave frequency f ₀ , then in equation (7), B is set to 2 as shown in the following equation (8).

Then, the inductance L and the capacitance C are determined based on the equations (6) and (8).
As a result, the shield conductor 2 does not affect the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1, i.e., the fundamental frequency _f0 of the transmitted power, but can suppress harmonics, i.e., unwanted waves, which have frequencies more than twice the fundamental frequency _f0 .

The effect of the shield conductor 2 was verified by the results of a numerical simulation obtained by the finite element method.
In the simulation, the transmitting coil includes a transmitting coil 1, a loop conductor 21, and a shield conductor 2 including a resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel.
The receiving coil had the same components, physical size, and component values as the transmitting coil.
The power transmitting coil and the power receiving coil were placed facing each other with a gap of 5 mm between them.

In the power transmission coil, the power transmission coil 1 had a horizontal and vertical size of 40 mm x 20 mm, four turns, a line width of the power transmission coil 1 of 0.5 mm, and a distance between adjacent lines of 1.5 mm.
The loop conductor 21 had a horizontal and vertical size of 51.5 mm x 31.5 mm, one winding, and a line width of 5 mm.

The fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1, i.e., the fundamental frequency _f0 of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1, is 13.56 MHz, and the capacitance C of the capacitor 222 is set to 3,200 pF in order to increase, i.e., maximize, the amount of suppression of unwanted waves having a frequency twice the fundamental frequency _f0 .
Moreover, the inductance L of the inductor 221 is set to 43 nH, which resonates with the capacitor 222 at the fundamental frequency f ₀ (13.56 MHz).
It is assumed that materials other than the power transmission coil 1 and the loop conductor 21 are lossless.

The receiving coil is exactly the same as the transmitting coil.
Moreover, the power transmission efficiency is defined as the ratio of the power supplied from the input port to the power transmitting coil 1 to the power received by the power receiving coil and output to the output port.
It is assumed that the input port and the output port are impedance-matched with the power transmitting coil 1 and the power receiving coil, respectively, at the fundamental frequency f ₀ .

Under the above preconditions, the power transmission efficiency for the fundamental frequency of the power transmitted from the power transmitting coil to the power receiving coil was verified.
The results of the verification are shown in Figure 4.
In Figure 4, the horizontal axis indicates the transmission frequency of power transmitted from the transmitting coil to the receiving coil, the vertical axis indicates the power transmission efficiency, and curve A is the verification result when the power transmission coil of embodiment 1 is used (hereinafter referred to as this example).

For comparison, comparative example 1 was tested in which there was no shield conductor 2, i.e., a power transmission coil consisting only of a power transmission coil and a power receiving coil consisting only of a power receiving coil, and comparative example 2 was tested in which a power transmission coil with a ring-shaped loop conductor as the shield conductor and a power receiving coil with a ring-shaped loop conductor as the shield conductor were used.
Both Comparative Example 1 and Comparative Example 2 are exactly the same as this example except for the differences.
In FIG. 4, the verification results of Comparative Example 1 are shown as curve B, and the verification results of Comparative Example 2 are shown as curve C.

As is clear from FIG. 4, the power transmission efficiency for the fundamental frequency f ₀ (13.56 MHz) in this example and comparative example 1 is equal, 86.5%.
In other words, the same results were obtained in this example as in Comparative Example 1, which did not have a shielding conductor 2. It can be seen that the shielding conductor 2 in this example has no effect whatsoever on the transmission of power of the fundamental frequency f ₀ , and there is no decrease in power transmission efficiency.
On the other hand, the power transmission efficiency at the fundamental frequency f ₀ in Comparative Example 2 is 70.6% relative to the fundamental frequency f ₀ , which is a deterioration of 15.9 percentage points compared to this example and Comparative Example 1. The shield conductor made of an annular loop conductor causes a decrease in the power transmission efficiency.

As is clear from the above, it can be said that the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 in the shield conductor 2 resonates at the fundamental frequency _f0 , so that no current is induced in the loop conductor 21, and a decrease in power transmission efficiency is avoided.

FIG. 5 shows the results of verification of the suppression effect of the shield conductor 2 against unwanted waves of frequencies other than the fundamental frequency f ₀ .
FIG. 5 shows the difference in magnetic field strength between this example at a point 200 mm away from the center of the power transmission coil and that of Comparative Example 1 at a point 200 mm away from the center of the power transmission coil as the suppression effect.
In FIG. 5, the horizontal axis indicates the transmission frequency of the power transmitted from the power transmitting coil to the power receiving coil, the vertical axis indicates the suppression effect, and curve A1 is the verification result of this example.

Curve A2 shows the verification result of the shield conductor 2 (Example 2) in which the line width of the loop conductor 21 is 1 mm, the capacitance C of the capacitor 222 is 1,000 _pF in order to increase, i.e., maximize, the amount of suppression of unwanted waves at a frequency twice the fundamental frequency f0, and the inductance L of the inductor 221 is 138 nH which resonates with the capacitor 222 at the fundamental frequency _f0 .

As is clear from FIG. 5, there is no difference in magnetic field strength between this example and comparative example 1 for the fundamental frequency f ₀ (the second marker from the left in FIG. 5). In this example, the difference in magnetic field strength from comparative example 1, that is, the suppression effect, is maximum (approximately 30 dB) for a frequency of 27.12 MHz that is twice the fundamental frequency f ₀ , and a suppression effect of 10 dB to 15 dB is obtained even for frequencies exceeding twice the fundamental frequency f ₀ .

Furthermore, there is no difference in magnetic field strength between Example 2 and Comparative Example 1 for the fundamental frequency _f0 , and in Example 2, the suppression effect is maximum (approximately 25 dB) for a frequency of 27.12 MHz that is twice the fundamental frequency _f0 , and a suppression effect of 5 dB to 10 dB can be obtained for frequencies exceeding twice the fundamental frequency _f0 .
In addition, in both this example and this example 2, there is no difference in magnetic field strength from Comparative Example 1 for a power transmission frequency of 20 MHz (the third marker from the left in FIG. 5), similar to the fundamental wave frequency f ₀ .

As is clear from the above, the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 in the shield conductor 2 resonates at the fundamental frequency f ₀ of the electromagnetic field formed by the power transmission coil 1, so that no current is induced in the loop conductor 21 at the fundamental frequency f ₀ , thereby avoiding a decrease in power transmission efficiency, and the impedance of the shield conductor 2 is small for frequencies more than twice the fundamental frequency f ₀ , so that a current is induced in the loop conductor 21, and external radiation of unnecessary waves at a frequency more than twice the fundamental frequency is suppressed.

Furthermore, for frequency F1, i.e., frequencies equal to or higher than the fundamental frequency _f0 , and frequency F2, i.e., frequencies less than twice the fundamental frequency _f0 , the electromagnetic field is not weakened by the shield conductor 2, as is clear from FIG. 3, and the shield conductor 2 prevents a decrease in power transmission efficiency, as is clear from FIG. 4.
On the other hand, for frequencies less than F1 and equal to or greater than F2, as is clear from FIG. 3, the electromagnetic field is weakened by the shield conductor 2, suppressing radiated interference waves.

Therefore, for frequencies of the electromagnetic field formed by the power transmission coil 1 that are greater than or equal to frequency F1 and less than frequency F2, the electromagnetic field is not weakened by the shield conductor 2, and a decrease in power transmission efficiency can be avoided. Therefore, the power transmission coil of embodiment 1 is effective for frequencies of the fundamental wave frequency of the electromagnetic field formed by the power transmission coil 1 that are greater than or equal to frequency F1 and less than frequency F2.
This means that it is sufficient that the resonant frequency of the parallel resonant circuit 22 is lower than the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 .
That is, the resonant frequency of the parallel resonant circuit 22 is not limited to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 , but may be a frequency lower than the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 .

By making the width of the loop conductor 21 wider than that of the power transmission coil 1 and making the line width wider, for example from 1 mm to 5 mm, the inductance of the loop conductor 21 becomes smaller, so that the current induced in the loop conductor 21 becomes larger, and a greater magnetic field suppression effect is obtained for frequencies exceeding twice the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1.
In addition, since it is only necessary to reduce the inductance of the loop conductor 21, it is not limited to increasing the line width, but the thickness of the line can also be increased; in short, the thickness of the loop conductor 21 should be made thicker than the thickness of the power transmission coil 1.

When loop conductor 21 is formed on a dielectric substrate, a method for increasing the wire thickness of loop conductor 21 is to provide it on both the front and back surfaces of the dielectric substrate, and connect the conductor layer formed on the front surface to the conductor layer formed on the back surface with a through hole, thereby increasing the effective thickness of loop conductor 21.
In this way, by increasing the thickness direction of the loop conductor 21, it is possible to minimize the increase in the circuit area required for the power transmission coil, while obtaining the effect of suppressing unwanted waves with a frequency that is more than twice the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1.

Furthermore, by reducing the inductance L _L of the impedance of the loop conductor 21, the impedance of the shield conductor 2 can be reduced, and a current is not induced in the loop conductor 21 for the fundamental frequency f ₀ of the electromagnetic field formed by the power transmission coil 1, preventing a decrease in power transmission efficiency. A current is induced in the loop conductor 21 for a frequency that is more than twice the fundamental frequency f ₀ , and external radiation of unnecessary waves of more than twice the frequency can be suppressed.
That is, the impedance Z of the shield conductor 2 is expressed by the above equation (4), and a decrease in the inductance _LL of the loop conductor ₂₁ results in a decrease in the absolute value of the impedance of the above equation (4) at frequencies other than the fundamental frequency _f0 , where the imaginary part of the above equation (4) becomes infinite at the fundamental frequency f0.

The inductance L of the inductor 221 and the capacitance C of the capacitor 222 that configure the parallel resonant circuit 22 are set to values such that the absolute value |Z| of the impedance of the shield conductor 2 calculated by the above equation (4) is infinite at the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1, and is resistance R _L of the impedance of the loop conductor 21 at a frequency twice the fundamental frequency _f0 . FIG. 6 shows the results of a verification of the relationship between the inductance L _L of the loop conductor 21 and the absolute value |Z| of the impedance of the shield conductor 2.

6, the horizontal axis represents the value normalized by the fundamental frequency f ₀ of the electromagnetic field generated by the power transmitting coil, and the vertical axis represents the absolute value |Z| of the impedance of the shield conductor 2.
In FIG. 6, curve A3 shows the absolute value |Z| of the impedance of the normalized shield conductor 2 when the inductance _L of the loop conductor 21 is set to 10 nH, and curve A4 shows the absolute value |Z| of the impedance of the normalized shield conductor 2 when the inductance _L of the loop conductor 21 is set to 100 nH.

As shown by curves A3 and A4 in FIG. 6 , the absolute value |Z| of the impedance of the shield conductor 2 is set to infinity at the fundamental frequency _f0 and to a value that becomes the resistance _RL of the impedance of the loop conductor 21 at a _frequency twice the fundamental frequency _{f0 .} By making the inductance _LL of the loop conductor 21 smaller, for example, by making it 10nH instead of 100nH, the absolute value |Z| of the impedance of the shield conductor 2 can be significantly reduced up to below the fundamental frequency f0, for frequencies from above the fundamental frequency _f0 to below twice the fundamental frequency _f0 , and for frequencies exceeding twice the fundamental frequency f0.
As a result, by making the inductance L _L of the loop conductor 21 smaller, the current induced in the loop conductor 21 for frequencies other than the fundamental frequency f ₀ can be increased, and the effect of suppressing the magnetic field in unnecessary waves of frequencies other than the fundamental frequency f ₀ can be increased.

FIG. 7 shows the verification results of the radiation efficiency of the transmitting coil.
The radiation efficiency is the ratio of the total power radiated far away to the total power supplied from the input port to the power transmitting coil 1.
In FIG. 7, the horizontal axis represents the transmission frequency of the power transmitted from the power transmitting coil to the power receiving coil, and the vertical axis represents the radiation efficiency.

As is clear from FIG. 7, when comparing the radiation efficiency of this example with the radiation efficiency of Comparative Example 2 at a frequency of 230 MHz, a decrease in radiation efficiency of 11.9 dB is observed.
That is, in this example, not only is the magnetic field in the vicinity of the power transmission coil 1 suppressed, but radiation to distant locations is also suppressed by 10 dB or more.
As can be seen from the above simulation results, the power transmission coil according to embodiment 1 can suppress radiated interference waves to the surroundings while maintaining power transmission efficiency.

In this example, as shown in FIG. 4, the power transmission efficiency is improved to 65% when the frequency of the power transmitted from the power transmitting coil 1 to the power receiving coil is 20 MHz.
That is, in this example, the power transmission efficiency is improved by the parallel resonant circuit 22 having an inductor 221 and a capacitor 222 in the shield conductor 2 resonating with the two frequencies of 13.56 MHz and 20 MHz of the power transmitted from the transmitting coil 1 to the receiving coil.

The frequency at which the first power transmission efficiency peaks is the resonant frequency of the parallel resonant circuit, which in this example is the fundamental frequency _f0 of the electromagnetic field formed by the power transmission coil 1, and the frequency at which the second power transmission efficiency peaks can be adjusted by setting the inductance L of the inductor 221 and the capacitance C of the capacitor 222.
In short, the power transmission device to which this example is applied can efficiently transmit power at two frequencies: the fundamental frequency f ₀ of the electromagnetic field formed by the power transmission coil 1, i.e., the fundamental frequency f ₀ of the transmitted power, and other frequencies.

For example, by applying this example, i.e., a transmission coil, which has good power transmission efficiency in the two ISM bands of 6.78 MHz and 13.56 MHz, a power transmission device can be obtained that can simultaneously transmit power with a fundamental frequency of 6.78 MHz and power with a fundamental frequency of 13.56 MHz, or a wireless power transmission device that can switch between power with a fundamental frequency of 6.78 MHz and power with a fundamental frequency of 13.56 MHz.

In this case, one of the frequencies 6.78 MHz and 13.56 MHz is the first fundamental frequency, and the other frequency of 6.78 MHz and 13.56 MHz is the second fundamental frequency, both of which are fundamental frequencies, and the resonant frequency in the parallel resonant circuit 22 having the inductor 221 and the capacitor 222 is set to one of the fundamental frequencies.

Furthermore, by bringing the frequencies at which the two peaks of high power transmission efficiency occur close to each other, the peak of power transmission efficiency can be made substantially broadband with respect to the frequency of the power transmitted from the power transmitting coil.
In this case, it is possible to improve robustness against manufacturing errors in the power transmission coil, changes in the transmission/reception interval, and other environmental changes.

As described above, the power transmission coil of embodiment 1 comprises a loop conductor 21 having a slit 211, and a resonant circuit 22 connected between both open ends of the slit 211 of the loop conductor 21 and having an inductor 221 and a capacitor 222 connected in parallel, and is provided with a shield conductor 2 arranged at a position where the electromagnetic fields formed by the power transmission coil 1 intersect when power is transmitted from the power transmission coil 1 to the power receiving coil. This does not affect the power transmission efficiency of the power transmitted from the power transmission coil 1 to the power receiving coil, and suppresses unnecessary radiation waves of frequencies other than the fundamental frequency of the power to be transmitted.

In the power transmission coil according to the first embodiment, the resonant frequency of the parallel resonant circuit 22 is set to the fundamental frequency of the power transmitted from the power transmission coil 1. The inductance L of the inductor 221 and the capacitance C of the capacitor 222 that configure the parallel resonant circuit 22 are set to values that satisfy _ω0C =1/ _ω0L .

With this configuration, a current is not induced in the loop conductor 21 due to the fundamental frequency of the electromagnetic field formed by the power transmission coil, and a decrease in power transmission efficiency can be avoided.
Furthermore, the capacitance C of capacitor 222 is set to a value that suppresses unwanted waves having a frequency that is twice the fundamental frequency of the electromagnetic field formed by the power transmission coil, thereby obtaining a suppression effect against unwanted waves having a frequency that is more than twice the fundamental frequency of the electromagnetic field formed by the power transmission coil.

In other words, the parallel resonant circuit 22 resonates at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, so that no current is induced in the loop conductor 21 at the fundamental frequency of the transmitted power, thereby avoiding a decrease in power transmission efficiency, and the impedance of the shield conductor 2 is small at frequencies more than twice the fundamental frequency, so that a current is induced in the loop conductor, thereby suppressing external radiation of unwanted waves at frequencies more than twice the fundamental frequency.

Furthermore, in the power transmission coil according to embodiment 1, by setting the resonant frequency of the parallel resonant circuit 22 to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, a second peak in power transmission efficiency can be set for power at a frequency less than twice the fundamental frequency, and a second fundamental frequency can be obtained in addition to the fundamental frequency, making it possible to transmit at the two frequencies simultaneously or by switching between them.
Furthermore, by bringing the first peak of the power transmission efficiency for the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 and the second peak of the power transmission efficiency for a frequency different from the fundamental frequency close to each other, the frequency band of the transmitted power can be substantially broadened.

When the power transmission coil is the power transmission coil 1, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil. However, when the power transmission coil is the power receiving coil, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed in the power receiving coil by receiving power through electromagnetic induction, and is the fundamental frequency of the high-frequency signal received by the power receiving circuit connected to the power receiving coil.
In any case, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the high-frequency signal transmitted by the power transmitting circuit 3 connected to the power transmitting coil 1 .
In short, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil.

Embodiment 2.
Second embodiment A power transmission coil according to a second embodiment will be described with reference to FIG.
The power transmission coil of embodiment 2 differs from the power transmission coil of embodiment 1 in that a second shield conductor 2A is provided, the frequency characteristics of which are different from those of the impedance of the shield conductor 2, but is otherwise the same.
In FIG. 8, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

The second shield conductor 2A is disposed outside the first shield conductor 2 .
The second shield conductor 2A may be disposed inside the first shield conductor 2, or may be disposed above or below the first shield conductor 2.
The second shield conductor 2A includes a loop conductor 21A having a slit 211A, and a parallel resonant circuit 22A connected between both open ends of the slit 211A of the loop conductor 21A and having an inductor 221A and a capacitor 222A connected in parallel.

The second shield conductor 2A is disposed at a position where it is linked with the electromagnetic field generated by the power transmission coil 1 when the power transmission coil 1 transmits power.
The loop conductor 21A is a conductor having a loop-shaped planar pattern wound once around the outer periphery of the first shield conductor 2 on the surface of the dielectric substrate.
The loop conductor 21A is a parasitic conductor having a slit 211A formed at the end of the loop.

The impedance of the second shield conductor 2A is set to a value different from that of the first shield conductor 2, and the resonant frequency of the parallel resonant circuit 22A is set to a frequency different from that of the parallel resonant circuit 22.
That is, even when the frequency of the power transmitted from the power transmitting coil 1 to the power receiving coil matches the resonant frequency of the parallel resonant circuit 22A in the second shield conductor 2A, the power transmission efficiency is improved.

As a result, in addition to the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, whose power transmission efficiency is improved by the first shield conductor 2, it becomes possible to transmit power also at frequencies whose power transmission efficiency is improved by the second shield conductor 2A.
As described in the first embodiment, the resonant frequency of the parallel resonant circuit 22 is the fundamental frequency of the electromagnetic field formed by the power transmission coil, and is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1.
The resonant frequency of the parallel resonant circuit 22A is less than twice the fundamental frequency of the electromagnetic field formed by the power transmitting coil.

The resonant frequency of the parallel resonant circuit 22A is a third frequency different from the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, at which the power transmission efficiency has a peak due to the first shield conductor 2, and the second frequency at which the power transmission efficiency has a second peak.
By providing the second shield conductor 2A, it is possible to provide a peak in power transmission efficiency also at the third frequency of the power transmitted from the power transmitting coil to the power receiving coil.

As a result, for power transmitted from the transmitting coil 1 to the receiving coil, for power having a frequency less than twice the fundamental frequency of the electromagnetic field formed by the transmitting coil 1, the first shielding conductor 2 makes it possible to set a fundamental frequency at which the power transmission efficiency has a first peak and a second frequency at which the power transmission efficiency has a second peak, and the second shielding conductor 2A makes it possible to set a third frequency at which the power transmission efficiency has a third peak.

Therefore, the power transmission coil according to the second embodiment can transmit power of three frequencies simultaneously or switch between them.
Furthermore, by setting the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 to be close to the second frequency and the third frequency, the frequency band of the power transmitted from the power transmission coil can be made wider.

Furthermore, by arranging multiple shield conductors whose parallel resonant circuits are different from each other, such as a third shield conductor, a fourth shield conductor, ... whose parallel resonant circuits have different resonant frequencies from the first shield conductor 2 and the second shield conductor 2A, and by providing multiple frequencies that each show a different peak in power transmission efficiency at frequencies less than twice the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, it is possible to further widen the bandwidth of the frequencies of the power transmitted from the power transmission coil 1 to the power receiving coil.

As described above, the power transmission coil of embodiment 2 has the same effect as the power transmission coil of embodiment 1, and also provides a wider bandwidth for the frequency of the transmitted power.

Embodiment 3.
A power transmission coil according to a third embodiment will be described with reference to FIG.
The power transmission coil of embodiment 3 differs from the power transmission coil of embodiment 1 in that the parallel-connected inductor 221 and capacitor 222 that constitute the resonant circuit 22 in the shield conductor 2 are replaced by variable inductor 223 and variable capacitor 224, respectively, and that the power transmission coil of embodiment 3 is provided with a control unit 4 that controls the variable inductor 223 and variable capacitor 224, and an operating status monitoring unit 5 that monitors the operating status, but is otherwise the same.
In FIG. 9, the same reference numerals as those in FIG. 1 designate the same or corresponding parts.

In the power transmission coil of embodiment 3, the control unit 4, which is a controller, controls the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 while satisfying the condition of the above equation (5) depending on the operating state of the transmitting coil and the receiving coil.

That is, in the operating state of the transmitting coil and the receiving coil, (a) the frequency components of the unwanted waves radiated from the transmitting coil 1 change depending on the transmission power level from the transmitting circuit 3, (b) the frequency components of the unwanted waves transmitted by the transmitting circuit 3 change due to a change in the value of the load connected to the receiving coil, and (c) even if the level of the unwanted waves transmitted from the transmitting circuit 3 is constant, a change in the load connected to the receiving coil may change the coupling between the transmitting coil and the receiving coil, causing a change in the level of interference waves radiated to the surroundings.

In the power transmission coil of embodiment 3, the operation status monitoring unit 5 monitors changes in the frequency components of unwanted waves in the operating states of the transmitting coil and the receiving coil, and the control unit 4 receives a status monitoring signal from the operation status monitoring unit 5 and outputs control signals to the variable inductor 223 and the variable capacitor 224, respectively, to change the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224.

The operation status monitoring unit 5 monitors the operation status of the power transmitting coil and the power receiving coil, and outputs a status monitoring signal to the control unit 4 .
The operation status monitoring unit 5 is an antenna that detects the intensity of the electromagnetic field due to the electromagnetic waves radiated from the power transmission coil 1, and outputs a status monitoring signal indicating the detected electromagnetic field intensity.
In addition, the operation status monitoring unit 5 is not limited to an antenna consisting of a coil with a conductor wound around it, but may be anything that can detect electromagnetic waves radiated from the power transmission coil 1. Furthermore, when focusing on unwanted waves that can become radiated interference waves in the microwave band, a dipole or monopole type antenna is preferable.

The control unit 4 receives a status monitoring signal indicating the electromagnetic field strength from the operation status monitoring unit 5, identifies the frequency that needs to be suppressed from the electromagnetic field strength indicated by the status monitoring signal, and outputs a control signal to each of the variable inductor 223 and the variable capacitor 224 to set the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to suppress unwanted waves at the identified frequency.

That is, the control unit 4 outputs control signals to each of the variable inductor 223 and the variable capacitor 224 to change the frequency at which the suppression effect shown in Figure 5 is maximized to a frequency that requires suppression based on the electromagnetic field intensity indicated by the status monitoring signal from the operation status monitoring unit 5.
As a result, it is possible to obtain the maximum radiated interference suppression effect in each operating state while suppressing deterioration of power transmission efficiency at the fundamental frequency of the electromagnetic field formed by the power transmission coil 1, which is the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1.

Although the status monitoring signal from the operation status monitoring unit 5 is output directly to the control unit 4, the status monitoring signal from the operation status monitoring unit 5 may be received by a receiver that performs analog-to-digital conversion (A/D conversion) and is placed near the operation status monitoring unit 5, and the status monitoring signal consisting of a digital signal may be transmitted to the control unit 4.
In this case, even if the antenna which is the operation status monitoring unit 5 is located away from the power transmission coil 1 and the electromagnetic field strength due to unwanted waves is very small, there is no attenuation of the high-frequency signal due to the wiring connecting the antenna and the control unit 4, and the control unit 4 can receive the status monitoring signal detected by the antenna 5 with high accuracy.

Further, the operation state monitoring unit 5 is configured with one antenna, but may be provided with a plurality of detection antennas.
In an environment where there is a metal shield around the power transmission coil, the electromagnetic field strength may vary significantly depending on the location. However, if the operation status monitoring unit 5 is configured with multiple antennas, each of the multiple antennas can be positioned in a different location, so that the frequencies that require suppression can be detected from measurements taken at various locations, and the control unit 4 can accurately identify the frequencies that require suppression.

Furthermore, each of the multiple antennas may be an antenna with a high Q value, i.e., a narrow band, suitable for each frequency of interest.
Since the sensitivity of the narrowband antenna is improved, it can detect frequencies that require suppression with high sensitivity, and the control unit 4 can specify the frequencies that require suppression with high accuracy.

Furthermore, the antenna serving as the operation state monitoring unit 5 may be an antenna shared with a plurality of power transmission coils 1 arranged in close proximity to each other.
That is, a status monitoring signal indicating the electromagnetic field strength detected by the shared antenna is received by a control unit 4 corresponding to each of the multiple power transmission coils 1, and the frequency that needs to be suppressed is identified from the electromagnetic field strength indicated by the status monitoring signal received by the control unit 4, and a control voltage, which is a control signal that sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to suppress unwanted waves at the identified frequency, is output to each of the variable inductors 223 and variable capacitors 224 corresponding to each of the multiple power transmission coils 1.

In addition, as the antenna that is the operation status monitoring unit 5, an antenna in a wireless system installed in close proximity to the power transmission coil in embodiment 3 may be used, for example, when a power transmission coil is placed inside a room, an antenna in an entrance/exit management system that uses RFID (Radio Frequency Identification) placed at the entrance to the room.

That is, the control unit 4 receives a signal received by an antenna in the access control system as a status monitoring signal, and identifies a frequency that needs to be suppressed from the signal received by the antenna. For example, when an interference wave for the access control system is received by an antenna in the access control system, the control unit 4 identifies the frequency of the interference wave received by the antenna as a status monitoring signal to be suppressed from the electromagnetic field intensity received by the antenna in the access control system.
The control unit 4 outputs a control voltage, which is a control signal that sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to suppress the spurious waves at the specified frequency, to each of the variable inductor 223 and the variable capacitor 224 .

In addition, since the frequencies used in the access control system are specified, the control unit 4 may not specify the frequency of the interference wave for the access control system based on the electromagnetic field strength of the signal received by the antenna, but may specify a frequency other than the frequency used in the access control system that is included in the signal received by the antenna as the frequency of the interference wave for the access control system.
In a wireless system installed in close proximity, "closeness" refers to the distance that can be reached by electromagnetic waves, particularly unwanted waves, radiated from the power transmission coil 1 in the power transmission coil according to embodiment 3.

In the power transmission coil of embodiment 3, the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 is not changed, and the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed when the frequency components of the unwanted waves change in the operating state of the power transmission coil and the power receiving coil. However, it is also possible to change the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 when the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 in the operating state of the power transmission coil and the power receiving coil, that is, the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3 connected to the power transmission coil 1, is dynamically changed.

In this case, the operating status monitoring unit 5 monitors the fundamental frequency of the high-frequency signal transmitted by the power transmission circuit 3, in other words, the fundamental frequency input to the power transmission coil 1, and outputs a status monitoring signal corresponding to the fundamental frequency to the control unit 4.
The control unit 4 does not change the frequency to be suppressed, but controls the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to satisfy the condition of the above equation (5) in accordance with the angular frequency _ω0 of the fundamental frequency _f0 of the high-frequency signal transmitted by the power transmitting circuit 3, based on the state monitoring signal from the operation state monitoring unit 5.

When the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 is dynamically changed, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed to follow the dynamically changed fundamental frequency and satisfy the condition of the above equation (5), thereby suppressing deterioration of the power transmission efficiency for the power of the changed fundamental frequency.

As described above, the power transmission coil according to the third embodiment has the same effects as the power transmission coil according to the first embodiment.
Furthermore, since the parallel-connected inductor and capacitor that make up the resonant circuit are made into a variable inductor 223 and a variable capacitor 224, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 can be changed depending on the operating state of the power transmission coil, thereby obtaining a high suppression effect against unwanted waves, or suppressing deterioration of power transmission efficiency for the fundamental frequency of the power transmitted from the transmitting coil 1 to the receiving coil.

For example, when the frequency components of unwanted waves change in the operating state of the transmitting coil and the receiving coil, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed, so that the maximum suppression effect against radiated interference waves can be obtained in each operating state while suppressing deterioration of the power transmission efficiency at the fundamental frequency of the electromagnetic field formed by the transmitting coil 1, i.e., the fundamental frequency of the transmitted power.
In addition, when the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 in the operating state of the power transmission coil and the power receiving coil, i.e., the fundamental frequency of the transmitted power, is changed, the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 are changed, so that deterioration of power transmission efficiency for power of the changed fundamental frequency can be suppressed.

Embodiment 4.
A power transmission coil according to a fourth embodiment will be described with reference to FIG.
The power transmission coil of embodiment 4 differs from the power transmission coil of embodiment 3 in that, whereas the control unit 4 identifies the frequency that needs to be suppressed in response to the state monitoring signal from the operation state monitoring unit 5, and outputs a control signal to each of the variable inductor 223 and the variable capacitor 224 that uniquely changes the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 in response to the state monitoring signal from the operation state monitoring unit 5, the control unit 4 dynamically changes the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 within a range that satisfies the condition of equation (5) above, sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224, and is provided with a memory unit 6, and is otherwise the same.
In FIG. 10, the same reference numerals as those in FIG. 9 indicate the same or corresponding parts.

The control unit 4 receives a status monitoring signal indicating the electromagnetic field strength from the antenna, which is the operation status monitoring unit 5, and if the electromagnetic field strength indicated by the status monitoring signal exceeds a set threshold, dynamically changes the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 within a range that satisfies the condition of equation (5) above, until the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5 becomes equal to or less than the set threshold.

That is, even while the control unit 4 is changing the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224, it monitors the status monitoring signal indicating the electromagnetic field strength from the operation status monitoring unit 5, and outputs a control signal to each of the variable inductor 223 and the variable capacitor 224 to change the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 until the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5 becomes equal to or lower than a set threshold value.

When the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5 falls below a set threshold, the control unit 4 stops changing the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224, and stores the set values at that time in the memory unit together with information on the electromagnetic field strength indicated by the status monitoring signal from the operation status monitoring unit 5.

As described above, the power transmission coil according to the fourth embodiment has the same effects as the power transmission coil according to the third embodiment.
Furthermore, the control unit 4 constantly monitors the electromagnetic field strength indicated by the status monitoring signal from the antenna, which is the operating status monitoring unit 5, and sets the inductance of the variable inductor 223 and the capacitance of the variable capacitor 224 to set values when the electromagnetic field strength falls below a threshold value, thereby making it possible to appropriately control the suppression effect against unwanted waves.

Embodiment 5.
A power transmission coil according to the fifth embodiment will be described with reference to FIG.
The power transmission coil of embodiment 5 differs from the power transmission coil of embodiment 1 in that two slits are provided in the loop conductor, and a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel between both open ends of the slit is disposed in each slit, but is otherwise the same.
In FIG. 11, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

The loop conductor 210 has two slits 211 and 212 .
The loop conductor 210 is composed of two identically shaped conductors 210A and 210B.
The two conductors 210A and 210B are arranged to form a rectangle, and the open end of the conductor 210A and the open end of the conductor 210B face each other to form slits 211 and 212.
The loop conductor 210 composed of two conductors 210A and 210B is the same as the loop conductor 21 in the first embodiment except that a slit 212 is further formed at a position opposite to the slit 211.

In addition, the parallel resonant circuit 22 constituted by an inductor 221 and a capacitor 222 connected in parallel is electrically connected between both open ends of the first slit 211 of the loop conductor 210, similar to the parallel resonant circuit 22 in embodiment 1.
Similarly, a second parallel resonant circuit 23 formed of an inductor 231 and a capacitor 232 connected in parallel is electrically connected between both open ends of the second slit 212 of the loop conductor 210 .

Thus, the shield conductor 2 comprises a loop conductor 210, a first parallel resonant circuit 22 having an inductor 221 and a capacitor 222 connected in parallel, and a second parallel resonant circuit 23 having an inductor 231 and a capacitor 232 connected in parallel.

The impedance Z of the shield conductor 2 is expressed by the above equation (4) and is set to the same value as the impedance Z of the shield conductor 2 in embodiment 1, and the characteristics of the shield conductor 2 are set to the same as the characteristics of the shield conductor 2 in embodiment 1.
Therefore, the inductance _L1 of inductor 221 and the inductance _L2 of inductor 231 have the same value, which is 1/2 the inductance L of inductor 221 in embodiment 1, and the capacitance _C1 of capacitor 222 and the capacitance _C2 of capacitor 232 have the same value, which is twice the capacitance C of capacitor 222 in embodiment 1.

The number of slits formed in the shield conductor 2 is not limited to two, but may be three or more, and each slit is connected to a resonant circuit having an inductor and a capacitor connected in parallel.
When the number of slits is n and the number of resonant circuits is n, the inductance of the inductor of each resonant circuit is the same value, which is 1/n of the inductance L of inductor 221 in embodiment 1, and the capacitance of the capacitor of each resonant circuit is the same value, which is n times the capacitance C of capacitor 222 in embodiment 1.

As described above, the power transmission coil according to the fifth embodiment has the same effects as the power transmission coil according to the first embodiment.
Furthermore, since the number of slits formed in the shield conductor 2 is multiple (n), and the number of resonant circuits connected to each slit is multiple (n), the shield conductor 2 can be made compact and can be easily mounted on a dielectric substrate.

For example, when the fundamental frequency of the electromagnetic field formed by the power transmission coil 1 is several MHz to several tens of MHz, an inductance of several hundred nH may sometimes be required to resonate a single resonant circuit having an inductor and capacitor connected in parallel at the fundamental frequency.
Inductors having a large inductance of several hundred nH are generally large.

In contrast, the power transmission coil according to embodiment 5 resonates multiple resonant circuits at the fundamental frequency, so that the inductance of each inductor can be 1/n, each inductor can be made smaller, and mountability can be improved.
Another effect is that by providing n resonant circuits, the induced electromotive force induced in the shield conductor 2 is divided by each resonant circuit, so the voltage applied to one resonant circuit becomes 1/n. Therefore, the withstand voltage required for the capacitors constituting each resonant circuit is reduced, making it possible to select smaller components and improving mountability.

Embodiment 6.
A power transmission coil according to a sixth embodiment will be described with reference to FIGS.
The power transmission coil of embodiment 6 differs from the power transmission coil of embodiment 1 in that while the resonant circuit 22 electrically connected to the slit 211 in the loop conductor 21 is a parallel resonant circuit made up of an inductor 221 and a capacitor 222 connected in parallel, the resonant circuit 22 is a circuit having a second inductor 225 further connected in series to the parallel resonant circuit made up of an inductor 221 and a capacitor 222 connected in parallel, but is otherwise the same.
In FIG. 12, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

The shield conductor 2 includes a loop conductor 21, a parallel resonant circuit formed by an inductor 221 and a capacitor 222 connected in parallel, and a resonant circuit 22 having a second inductor 225 further connected in series to the parallel resonant circuit.
One end of the parallel resonant circuit is electrically connected to one open end of the slit 211 of the loop conductor 21 , and the other end of the parallel resonant circuit is electrically connected to one end of the second inductor 225 .
The other end of the second inductor 225 is electrically connected to the other open end of the slit 211 .

The impedance Z of the shield conductor 2 is expressed by the following equation (9).
In equation (9), R _L is the resistance of the impedance of the loop conductor 21 , L _L is the inductance of the impedance of the loop conductor 21 , L is the inductance of the inductor 221 , C is the capacitance of the capacitor 222 , and L _S is the inductance of the second inductor 225 .

Comparing equation (9) with equation (4) expressing the impedance Z of the shield conductor 2 in embodiment 1, the impedance Z of the shield conductor 2 in embodiment 6 is equivalent to the impedance Z of the shield conductor 2 in embodiment 1 being increased by the inductance of the loop conductor 21 by the inductance L _S of the second inductor 225.

That is, in order to increase the inductance L _L of the loop conductor 21 itself, it is possible to, for example, narrow the width of the loop conductor 21 or increase the number of turns, but either of these methods entails an increase in the resistance component R _L of the loop conductor 21.
An increase in the resistance component _RL of the loop conductor 21 reduces the amount of suppression of spurious waves.
In contrast to this, in the sixth embodiment, the inductance of the loop conductor 21 can be increased without increasing the resistance component R _L of the loop conductor 21 .
In other words, the inductance of the loop conductor 21 can be regarded as (L _L +L _S ).

The relationship between the phase of the impedance Z of the shield conductor 2 and the assumed inductance ( _LL + _LS ) of the loop conductor 21 will be described with reference to FIG.
13, the horizontal axis indicates the value normalized by the fundamental frequency _f0 of the power transmitted from the transmitting coil to the receiving coil, and the vertical axis indicates the phase of the impedance Z of the shield conductor 2, with the normalized value f/ _f0 of 1 being the fundamental frequency _f0 of the electromagnetic field formed by the transmitting coil 1, i.e., the fundamental frequency _f0 of the transmitted power, and the normalized value f/ _f0 of 2 being twice the frequency of the fundamental frequency _f0 , which is the frequency at which the imaginary part of the impedance Z of the shield conductor 2 shown in equation (4) above becomes 0, i.e., the resonant frequency of the shield conductor 2.
Curve A5 indicates a phase curve with respect to frequency when the assumed inductance ( _LL + _LS ) of the loop conductor 21 is 10 nH, and curve A6 indicates a phase curve with respect to frequency when the assumed inductance ( _LL + _LS ) of the loop conductor 21 is 100 nH.

As is clear from FIG. 13, when the assumed inductance ( _LL + _LS ) of the loop conductor 21 is larger (100 nH), the phase change of the impedance Z of the shield conductor 2 is steep at the resonance frequency (f/ _f0 =2) of the shield conductor 2.
When the assumed inductance ( _LL + _LS ) is 100 nH, the phase of the impedance Z of the shield conductor 2 is approximately ±90° even at frequencies close to the resonant frequency of the shield conductor 2.
The most ideal condition for the mutual weakening effect between the magnetic field formed by the current flowing through the power transmission coil 1 and the magnetic field formed by the current flowing through the loop conductor 21 is a phase difference of +90°.
That is, from the viewpoint of the phase of the impedance Z of the shield conductor 2, the greater the deemed inductance (L _L +L _S ), the greater the effect of suppressing unwanted waves.

Meanwhile, in the first embodiment, as explained with reference to FIG. 6 , by reducing the inductance _L of the loop conductor 21, for example from 100 nH (curve A4) to 10 nH (curve A3), the absolute value |Z| of the impedance of the shield conductor ₂ can be significantly reduced up to the fundamental frequency _f0 , for frequencies from above the fundamental frequency _f0 to less than twice the fundamental frequency _f0 , and for frequencies above twice the fundamental frequency f0, and the effect of suppressing the magnetic field of unwanted waves of frequencies other than the fundamental frequency _f0 can be increased.

That is, in order to increase the effect of suppressing the magnetic field in unwanted waves of frequencies other than the fundamental frequency _f0 , it is better to increase the inductance L _L of the loop conductor 21 from the viewpoint of the phase of the impedance Z of the shield conductor 2, while it is better to decrease the inductance L _L of the loop conductor 21 from the viewpoint of the impedance Z of the shield conductor 2, resulting in a trade-off relationship.

In the power transmission coil of embodiment 6, the resonant circuit 22 is configured as a circuit having a second inductor 225 further connected in series to a parallel resonant circuit consisting of an inductor 221 and a capacitor 222 connected in parallel. By adjusting the inductance L _S of the second inductor 225, the apparent inductance (L _L +L _S ) of the loop conductor 21 can be adjusted. As a result, the magnetic field suppression effect of unwanted waves of frequencies other than the fundamental frequency f ₀ can be appropriately obtained from the standpoint of both the phase of the impedance Z of the shield conductor 2 and the impedance Z of the shield conductor 2.

Furthermore, by changing the inductance L _S of the second inductor 225, the inductance (L _L +L _S ) can be easily changed without changing the structure of the loop conductor 21, which makes design easy.

As described above, the power transmission coil according to the sixth embodiment has the same effects as the power transmission coil according to the first embodiment.
Furthermore, by adjusting the inductance L _S of the second inductor 225, a more appropriate suppression effect can be obtained for the magnetic field suppression effect of unnecessary waves of frequencies other than the fundamental wave frequency of the electromagnetic field formed by the power transmission coil 1.

In the power transmission coil according to embodiment 2, as in embodiment 6, the resonant circuits of both the first shield conductor 2 and the second shield conductor 2A may be a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel, and a second inductor further connected in series to the parallel resonant circuit.
Furthermore, in each of the power transmission coil according to embodiment 3 and the power transmission coil according to embodiment 4, as in embodiment 6, the resonant circuit may be a parallel resonant circuit consisting of a variable inductor and a variable capacitor connected in parallel, and a circuit having a second inductor further connected in series to the parallel resonant circuit.

Furthermore, in the power transmission coil according to embodiment 5, as in embodiment 6, each of the resonant circuits connected to each of the multiple slits in the loop conductor may be a parallel resonant circuit consisting of an inductor and a capacitor connected in parallel, and a circuit having a second inductor further connected in series to the parallel resonant circuit.

The present disclosure is not limited to the power transmission coils shown in embodiments 1 to 6, and the arrangement and shape of the components that have been changed by engineers in the relevant technical field using their ordinary technical knowledge without deviating from the perspective of the technical ideas shown in embodiments 1 to 6 are within the scope of the present disclosure.
For example, the shapes of the power transmission coil 1 and the loop conductor 21 changed by engineers in the relevant technical field using their ordinary technical knowledge without deviating from the standpoint of the technical ideas shown in embodiments 1 to 6 are within the scope of the present disclosure.

In addition to the power transmission coils shown in embodiments 1 to 6, a matching circuit connected between the power transmission coil 1 and the power transmission circuit 3 may be used to adjust impedance matching from the standpoint of power transmission efficiency.
Furthermore, the power transmission coils shown in the first to sixth embodiments may be applied to a power transmission coil that transmits power at a plurality of frequencies by combining a plurality of power transmission circuits 3 with the power transmission coil 1.

The power transmission coils shown in the first to sixth embodiments may be formed on a dielectric substrate, and may be formed together with the power transmission circuit 3 on the same dielectric substrate.
By forming the power transmission coils shown in embodiments 1 to 6 on a dielectric substrate, the cost of the power transmission coil can be reduced and the manufacturing accuracy of the dimensions of the transmission coil and loop conductor can be improved. In addition, by forming the transmission coil and transmission circuit as the power transmission coil, or the receiving coil and receiving circuit as the power transmission coil, each on the same dielectric substrate, it is possible to reduce costs and improve accuracy.

In addition, any combination of the embodiments may be used, or any component of each embodiment may be modified, or any component of each embodiment may be omitted.

The power transmission coil according to the present disclosure can be used as a transmitting coil or a receiving coil in a magnetic field coupled power transmission device for portable devices such as mobile phones, headsets, digital cameras, or digital videos, or for wireless sensors, or as a transmitting coil or a receiving coil in a magnetic field coupled power transmission device for large-scale applications that handle large amounts of power, such as factory equipment including automatic transport robots or electric vehicles.

1 Power transmission coil, 2 Shield conductor, 21, 210 Loop conductor, 211, 212 Slit, 22, 23 Resonant circuit, 221, 223, 231 Inductor, 222, 224, 232 Capacitor, 3 Power transmission circuit. 4 Control unit, 5 Operation status monitoring unit, 6 Memory unit.

Claims (21)

a power transmission coil for transmitting power;
a loop conductor having a slit, and a resonant circuit connected between both open ends of the slit of the loop conductor, the resonant circuit having a parallel resonant circuit of an inductor and a capacitor connected in parallel, and a second inductor connected in series to the parallel resonant circuit , the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power;
A power transmission coil comprising: a power transmission coil for transmitting power;
a loop conductor having a slit, and a shield conductor connected between both open ends of the slit of the loop conductor and including a resonant circuit having an inductor and a capacitor connected in parallel, the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power;
a loop conductor having a slit , and a second shield conductor connected between both open ends of the slit of the loop conductor and including a resonant circuit having an inductor and a capacitor, the frequency characteristics of the impedance in the shield conductor being different from those in the shield conductor, and the second shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil when the power transmission coil transmits power intersects with the frequency characteristics of the impedance in the shield conductor;
A power transmission coil comprising : a power transmission coil for transmitting power;
a loop conductor having a slit, and a resonant circuit connected between both open ends of the slit of the loop conductor and having a variable inductor and a variable capacitor connected in parallel, the shield conductor being disposed at a position where an electromagnetic field formed by the power transmission coil intersects when the power transmission coil transmits power;
a control unit that outputs a control signal for changing the inductance of the variable inductor and a control signal for changing the capacitance of the variable capacitor to the variable inductor and the variable capacitor, respectively;
A power transmission coil comprising : 4. The power transmission coil according to claim 1, wherein a resonant frequency of the resonant circuit in the shield conductor is a fundamental frequency of an electromagnetic field formed by the power transmission coil. 4. The power transmission coil according to claim 1, wherein the parallel-connected inductor and capacitor in the resonant circuit in the shield conductor satisfy _ω0C =1/ _ω0L , where _ω0 is the angular frequency at the fundamental frequency of the electromagnetic field formed by the power transmission coil, L is the inductance of the parallel-connected inductor, and C is the capacitance of the parallel-connected capacitor. 4. A power transmission coil as described in any one of claims 1 to 3, wherein in the inductor and capacitor connected in parallel in the resonant circuit in the shield conductor , the capacitance of the capacitor is set to a value that suppresses unwanted waves having a frequency that is twice the fundamental frequency of the electromagnetic field formed by the power transmission coil, and the inductance of the inductor is set to a value that resonates at the fundamental frequency of the electromagnetic field formed by the capacitor and the power transmission coil. 4. The power transmission coil according to claim 1, wherein the inductance of the inductor and the capacitance of the capacitor connected in parallel in the resonant circuit in the shield conductor are set so that the absolute value of the impedance of the shield conductor is infinite at the fundamental frequency of the electromagnetic field formed by the power transmission coil and is set to a value that becomes a resistance in the impedance of the loop conductor at a frequency twice the fundamental frequency. 2. The power transmission coil according to claim 1, wherein in the inductor and capacitor connected in parallel in the resonant circuit, an inductance L of the inductor and a capacitance C of the capacitor are set to values that satisfy _f0 = 1/2π√(LC) and L < 3 × (LL ₊ Ls) .
Here, _f0 is the fundamental frequency of the electromagnetic field formed by the power transmission coil, _L1 is the inductance of the loop conductor , and Ls is the inductance of the second inductor . 4. The power transmission coil according to claim 2, wherein an inductance L of the inductor and a capacitance C of the capacitor connected in parallel in the resonant circuit in the shield conductor are set to values that satisfy _f0 = 1/2π√(LC) and L < 3 × _LL .
Here, _f0 is the fundamental frequency of the electromagnetic field formed by the power transmission coil, and _L1 is the inductance of the loop conductor. A power transmission coil as described in any one of claims 1 to 3, wherein the impedance of the shield conductor becomes inductive at a frequency of unwanted waves relative to the fundamental frequency of the electromagnetic field formed by the power transmission coil, and a current of opposite phase to the current due to the unwanted waves flowing in the power transmission coil is induced in the loop conductor. 4. The power transmission coil according to claim 1 , wherein an inductance of an inductor in the resonant circuit in the shield conductor is less than three times an inductance of the loop conductor. 5. The power transmission coil according to claim 4, wherein the power transmission coil is a power transmission coil, and the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed by the power transmission coil and is the fundamental frequency of a high-frequency signal transmitted by a power transmission circuit connected to the power transmission coil. 5. The power transmission coil according to claim 4, wherein the power transmission coil is a power receiving coil, and the fundamental frequency of the electromagnetic field formed by the power transmission coil is the fundamental frequency of the electromagnetic field formed in the power receiving coil by receiving power through electromagnetic induction, and is the fundamental frequency of a high-frequency signal received by a power receiving circuit connected to the power receiving coil . 4. The power transmission coil according to claim 2 , wherein the resonant circuit is a parallel resonant circuit formed by the inductor and capacitor connected in parallel. The power transmission coil according to claim 1 , wherein a thickness of the loop conductor is greater than a thickness of the power transmission coil. 4. A power transmission coil as claimed in claim 1, wherein the loop conductor has a plurality of slits, and each of the plurality of slits is connected to a resonant circuit having an inductor and a capacitor connected in parallel between both open ends of the slit. an operation status monitoring unit that monitors an operation status of the power transmission coil and outputs a status monitoring signal to the control unit;
A control signal from the control unit is generated based on a status monitoring signal from the operation status monitoring unit.
4. A power transmission coil according to claim 3 . the operation state monitoring unit is an antenna that detects an electromagnetic field intensity due to electromagnetic waves radiated from the power transmission coil,
the status monitoring signal output by the operation status monitoring unit is a status monitoring signal indicating an electromagnetic field intensity from the antenna,
the control unit identifies a frequency that needs to be suppressed from an electromagnetic field intensity indicated by a status monitoring signal from the operation status monitoring unit;
The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor to suppress unwanted waves at the specified frequency.
20. A power transfer coil as claimed in claim 17 . the operation state monitoring unit is an antenna that detects an electromagnetic field intensity due to electromagnetic waves radiated from the power transmission coil,
the status monitoring signal output by the operation status monitoring unit is a status monitoring signal indicating an electromagnetic field intensity from the antenna,
the control signal generated by the control unit is a signal for setting an inductance of the variable inductor and a capacitance of the variable capacitor for suppressing spurious waves,
a storage unit that stores a set value of the inductance of the variable inductor and a set value of the capacitance of the variable capacitor set by the control unit together with information on the electromagnetic field intensity indicated by a state monitoring signal from the operation state monitoring unit;
20. A power transfer coil as claimed in claim 17 . the operation state monitoring unit monitors a frequency input to the power transmission coil,
the state monitoring signal from the operation state monitoring unit indicates a frequency input to the power transmission coil,
The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor according to a frequency indicated by a state monitoring signal from the operation state monitoring unit.
20. A power transfer coil as claimed in claim 17 . The control unit receives a signal received by an antenna of a wireless system installed nearby, and identifies a frequency that needs to be suppressed from the received signal;
The control signal generated by the control unit is a signal for setting the inductance of the variable inductor and the capacitance of the variable capacitor to suppress unwanted waves at the specified frequency.
4. A power transmission coil according to claim 3 .

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