JPS6147386B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic transducer used in an ultrasonic diagnostic apparatus.

As is well known, an ultrasound receiver converts electrical energy into ultrasound energy using an ultrasound transducer, irradiates the subject with the ultrasound, and converts the reflected or transmitted waves back into ultrasound vibrations. The sensor receives the waves and converts them into electrical energy, and obtains information about the subject using electrical signals based on the electrical energy. An example of the configuration of such an ultrasonic transducer will be explained with reference to FIG. In the figure, a resistor 2 and a charging/discharging capacitor 6 are connected in series between a high voltage (DC voltage) application terminal 1 and a receiver 11. A thyristor 4 is connected between the input terminal) 3 and the ground terminal, and an inductor 8 for resonance frequency tuning, a damping resistor 9 for vibration suppression, and an ultrasonic vibrator 10 are connected between the tip of the capacitor 6 and the ground terminal, respectively. are connected in parallel. Next, the operation of the device will be explained with reference to the timing chart shown in FIG. First, high voltage V is applied to terminal 1.
When _H is applied, the capacitor 6 is charged via the resistor 2, and the potential at the input point 3 of the capacitor 6 is maintained at a high voltage. At this time, thyristor 4
When a trigger signal as shown in FIG. 2a is applied to the gate terminal 5 of the thyristor 4, the thyristor 4 becomes conductive every time the trigger signal reaches a high level "H". Here, the voltage at the input terminal 3 of the capacitor 6 has a sawtooth waveform as shown in FIG. 2b. Further, the waveform applied to the ultrasonic transducer 10 becomes a high voltage pulse waveform as shown in FIG. 2c due to the action of the inductor 8. The ultrasonic transducer 10 to which a voltage with such a waveform is applied will generate ultrasonic pulses due to the electrostriction effect, so when this is irradiated toward the subject, the acoustic impedance of the subject will change. A reflected wave or a transmitted wave is obtained based on the difference between the two, which is received again by the ultrasonic transducer, converted into an electrical signal, and amplified by the receiver 11 to obtain information about the object.

By the way, the ultrasonic pulse that propagates inside the subject while vibrating at a predetermined resonance frequency will attenuate depending on the length of the propagation distance due to scattering and absorption during propagation, so the received ultrasonic energy has the property of decreasing, and therefore, the receiver 11
The problem is that the signal-to-noise ratio (hereinafter referred to as S/N ratio) decreases in relation to the noise level, and therefore it is not possible to obtain a wide range of information about the subject. In order to solve this problem, there are several technical problems that are difficult to solve, as shown below.

That is, the electrical energy applied to the ultrasonic transducer 10 is high because the electrical energy charged in the capacitor 6 is instantaneously discharged by the high-speed conduction action of the thyristor 4. It is obtained by generating a pulse-like oscillating waveform of voltage. In this case, the electrostatic energy Q charged in the capacitor 6 is expressed by the following equation (1), where C is the capacitance of the capacitor 6, and V is the voltage between the terminals of the capacitor 6.

Q=1/2CV ² (1) Here, if the voltage V between the terminals of the capacitor 6 is constant, the electrostatic energy Q will be proportional to the capacitor capacitance C. Therefore, capacitor capacity C
Although it is possible to increase the emitted electrical energy and the ultrasonic energy based on this by increasing C, the value of the capacitor capacitance C cannot be increased very much for the following reasons.

For example _, the maximum voltage V ₁ charged to the capacitor 6 within the period t1 in the waveform _of FIG.
If the voltage applied to VH is _VH , it can be obtained by the following equation (2).

Therefore, the energy charged in capacitor 6
E ₁ is expressed by the following equation (3).

Here, if t ₁ and R ₁ are constant, the energy E ₁
The capacitor capacitance C ₁ at which C 1 is maximum is the optimal value for conventional equipment, and even if it is larger or smaller than this value, the emitted ultrasonic energy will not increase and the S/N ratio will decrease. .

Therefore, the conditions for increasing the emitted ultrasonic energy must satisfy the following equation (4) when the repetition period t ₁ of the trigger signal is constant.

t ₁ ≫C ₁・R ₁ ……(4) The capacitor capacity C ₁ is adjusted to satisfy this equation (4).
and charging resistance value R ₁ , the above equation (3) becomes the following equation (5)
is converted to

E ₁ ≒ 1/2C ₁・V ² _H ...(5) As is clear from this equation (5), when the high voltage V _H is constant, in order to increase the charging energy, the above equation (4) is used. It is sufficient to increase the capacitance C ₁ while satisfying the following conditions. In other words,
The purpose can be achieved by setting the resistance value R ₁ small. However, in the conventional device, the high-speed switching element 4 is composed of a thyristor or a transistor, but in this case, there are limits to the holding current of the thyristor and the maximum rated current of the transistor, so the resistance value R ₁ should not be made too small. It is not possible. Furthermore, when the switching element 4 is conductive, the current flowing into the switching element 4 flows not only from the capacitor 6 but also from the resistor 2, so if the resistance value 2 is decreased, the current flows into the switching element 4.
It is not possible to discharge the charges at a high speed, and it is not possible to increase the peak value of the pulsed voltage applied to the ultrasonic transducer 10.

In summary, in the conventional device, when the high voltage V _H is kept constant, the value of the capacitance C ₁ cannot be increased, and the value of the resistor R ₁ cannot be decreased, so the S/N ratio of the ultrasonic waves that can be received ends up being I couldn't improve it.

The present invention has been made in view of the above-mentioned circumstances, and by increasing the ultrasonic energy radiated from the ultrasonic transducer, the propagation distance of the ultrasonic waves is lengthened, and the S/S/ of the ultrasonic signals obtained from the subject is increased. It is an object of the present invention to provide an ultrasonic transducer that can improve the N ratio and obtain a wide range of information about a subject.

The present invention will be specifically explained below using Examples.

FIG. 3 is a circuit diagram showing an embodiment of the device of the present invention. In the figure, elements having the same functions as those shown in the conventional device are designated with the same reference numerals. What is different from the conventional circuit diagram in this circuit diagram is that a rectifying diode 12 is connected in the forward direction between the charging resistor 2 and the charging/discharging capacitor 6, and a connecting point 13 between the diode 12 and the charging resistor 2 is connected in the forward direction.
A switching means 15 whose ON/OFF state is controlled by a signal applied to the charging switching trigger input terminal 14 is inserted and connected between the terminal and the ground terminal, and the value of the charging resistor 2 is reduced accordingly, and The point is that the value of the charging/discharging capacitor 6 is increased. and,
The signal applied to the charge switching trigger terminal 14 is a signal that closes the switching means 15 when the thyristor 4, which is a high-speed switching element, is conductive.

The operation of such a device will be explained with reference to the timing chart of FIG. First, when high voltage V _H is applied to terminal 1, resistor 2 and diode 12
The capacitor 6 is charged through the capacitor 6, and the potential at the input point 3 of the capacitor 6 is maintained at a high voltage. At this stage, the gate terminal 5 of the thyristor 4 is connected to the
Applying an intermittent trigger signal as shown in
This thyristor 4 becomes conductive every time the trigger signal is at the "H" level. At this time, the above-mentioned figure 4 a
When a pulse voltage (b in the same figure) with a width slightly wider than the trigger pulse is applied to the control terminal 14 of the switching means 15 in synchronization with the trigger pulse of I will do it. The voltage at the connection point 13 of the switching means 15 has a sawtooth waveform that is at the "L" level only while the switching means 15 is closed, as shown in FIG. 4c.
Therefore, the voltage at the connection point 3 between the thyristor 4 and the capacitor 6 has a sawtooth waveform that is at the "L" level only while the thyristor 4 is conductive and the switching means 15 is closed, as shown in FIG. becomes. That is, immediately before the thyristor 4 becomes conductive, the switching means 15 closes and the terminal 13 is shunted to the ground potential, so the diode 12 becomes non-conductive and the capacitor 6, the potential at input point 3 is held at high potential _V2 . When the thyristor 4 is momentarily turned on by the trigger pulse shown in a above, a large current flows and the electric charge charged in the capacitor 6 is discharged. Therefore, a pulse voltage as shown in FIG. 4e is applied to the ultrasonic transducer 10. The peak value T of this pulse voltage
will show a higher value than before due to the back electromotive force based on the large current. Next, switching means 15
When the pulse voltage applied to falls to the "L" level, the switching means 15 is opened and the capacitor 6 is charged again. Ultrasonic waves are transmitted and received by repeating such operations.

In the device described above, when the thyristor 4 is conductive, the switching means 15 is closed to cut off the current from the charging resistor 2 and instantly discharge the charge in the capacitor 6. The value of can be made as small as possible, and correspondingly, the capacitance of the charging/discharging capacitor 6 can be selected to be larger than before. In other words, problems that were difficult to solve in the past are easily solved. Therefore, the energy that can be charged into the capacitor can be increased, so that the purpose can be achieved. That is, the peak value of the pulse waveform applied to the ultrasonic transducer 10 can be increased without increasing the voltage applied to the high voltage terminal 1, and the ultrasonic energy that can be irradiated can be increased, so the propagation distance of the ultrasonic wave can be increased. The resulting ultrasonic signal S/
Since the N ratio can be increased, a wide range of information about the subject can be obtained.

The present invention is not limited to the embodiments described above, and various modifications can be adopted. For example, the switching means may be a transistor 16 as shown in FIG.
Even if configured as , the same effect as described above can be obtained.

Also, as shown in FIG. 6, the switching means and the diode are removed, and a charging resistor 2 is used instead.
A switching means 17 is connected in series to the tip of the thyristor 4, and the control signal applied to the control terminal 18 of the switching means 17 is formed to be complementary to the trigger pulse applied to the control terminal 5 of the thyristor 4. , both switches 17 and 4 may be operated alternately. In this case as well, the capacitance of the charging/discharging capacitor 6 can be increased within the range of conditions such that charging is performed with a sufficiently shorter time constant than the period t ₁ of the control trigger pulse of the thyristor 4 (Fig. 4a). , it is possible to obtain the same effects as in each of the above embodiments.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional device, Fig. 2 is a timing chart for explaining its operation, Fig. 3 is a circuit diagram of an embodiment of the device of the present invention, and Fig. 4 is a diagram for explaining its operation. Timing charts, FIGS. 5 and 6 are circuit diagrams of other embodiments of the device of the present invention. 1... High voltage application terminal, 2... Charging resistor, 4
...High-speed switching element, 6... Charging/discharging capacitor, 8... Inductor, 9... Damping resistor, 10... Ultrasonic transducer, 11... Receiver, 1
2... Rectifier diode, 15... Switching means.

Claims (1)

[Claims] 1 A capacitor that charges a high voltage applied through a charging resistor, a high-speed switching element that discharges the charged charge of the capacitor, and a high-voltage pulse is applied between the terminals due to the high-speed discharge of the capacitor, which generates ultrasonic waves. In an ultrasonic transducer consisting of an ultrasonic transducer that generates an ultrasonic wave and a receiver connected to the ultrasonic transducer, a switching means is provided between the charging resistor and the capacitor, and the high-speed switching element is electrically connected. An ultrasonic transducer characterized in that the current from the charging resistor is controlled so as not to flow through the high-speed switching element.