JP5772392B2 - Electric field probe and electric field measuring device - Google Patents

Description

  The present case relates to an electric field probe and an electric field measurement device for detecting an electric field.

  Conventionally, with the spread of mobile communication systems such as wireless communication and optical wireless communication, the EMC standard for electromagnetic compatibility (EMC) of electronic devices such as home appliances, computers, aircraft equipment, and mobile phones has been around the world. Is being developed. The EMC standard defines an evaluation scale relating to the influence of electromagnetic waves radiated from electronic devices, and has been established in various ways as an international standard, a regional standard that complies with this standard, and a national standard.

  The electromagnetic compatibility of electronic devices is mainly evaluated from two aspects. One is evaluation of resistance to external electromagnetic waves, and the other is evaluation of electromagnetic wave noise intensity radiated from an electronic device to the outside. The former is subject to evaluation of the susceptibility (sensitivity) to influence from other devices, and the latter is subject to evaluation of the susceptibility (influence) to other devices. In other words, it is intended to improve the operational stability in an electromagnetic environment where a plurality of electronic devices are mixed by ensuring the performance of these both side surfaces.

  On the other hand, recent electronic devices tend to be less resistant to external electromagnetic waves as well as external electromagnetic waves due to higher density of electronic circuits, higher operating frequency, lower operating voltage, etc. is there. For example, it is known that the sensitivity of a television antenna may be reduced due to electromagnetic wave noise generated from a wireless module in a mobile phone compatible with one-segment broadcasting (one-segment partial reception service for digital terrestrial television broadcasting).

Further, when electromagnetic waves for call transmission / reception are mixed in the image processing circuit, flickering or noise may occur on the display screen. Thus, the phenomenon in which electromagnetic waves generated in electronic devices affect their performance is called self-poisoning (or intra EMC).
In order to prevent self-poisoning, it is important not only to consider conventional electromagnetic compatibility, but also to accurately grasp the intensity of electromagnetic waves generated by electronic devices and the position of the source. In particular, a measurement technique that accurately visualizes the state of the electromagnetic field in the vicinity of the electromagnetic wave generation source is desired.

  As a technique for grasping the electric field in the near field, a technique using an electric field probe and a measuring instrument (such as a spectrum analyzer or an oscilloscope) is known. That is, a change in an electric field is detected in a non-contact state with respect to an electromagnetic wave radiation source using a coaxial probe, and this is analyzed by a measuring instrument (for example, see Patent Document 1). By measuring the intensity distribution of the electric field, it becomes easy to observe the radiation state of the electromagnetic wave, which can be used for, for example, circuit design of a printed circuit board and selection of electronic components.

JP 2007-278820 A

  However, the electric field probe itself that detects the electric field may disturb the electric field to be detected. In other words, the coaxial electric field probe has a structure in which the electric field strength is detected by the central conductor inserted in the outer conductor that defines the reference potential (ground), so that the electric field applied to the central conductor is changed by the conductive outer conductor. As a result, an accurate electric field strength cannot be detected. In fact, the actual measurement result of the electric field intensity using the electric field probe does not necessarily coincide with the theoretical electric field distribution obtained by simulation such as the finite difference time domain method (FDTD method). The degradation phenomenon of measurement accuracy due to the invasiveness of an electric field probe is one of the concerns in the field of conventional electromagnetic field analysis. Therefore, the development of a highly non-invasive electric field probe is awaited.

  In addition, the direction of the electric field vector in the near field of the electronic device is not necessarily a radiation direction centering on the radiation source of the electromagnetic wave. For example, in a microstrip line structure used for connecting high-frequency circuits and components, a ground plane (ground pattern) is provided on the back side of the substrate on which the signal line is provided, so the traveling direction of the lines of electric force radiated from the signal line Is curved toward the substrate surface, and its curvature varies greatly depending on the positional relationship with the signal line. On the other hand, since the electric field probe cannot identify the gradient (direction) of the electric field acting on the tip of the electric field probe, it is difficult to specify the position of the electromagnetic wave radiation source from the measurement result by the electric field probe.

If the x-axis and y-axis are set in the direction parallel to the plate surface of the microstrip line structure substrate and the z-axis is set in the direction perpendicular to the plate surface, the position of the radiation source is the most in the xy plane. It is considered that the electric field component in the z-axis direction corresponds to a large coordinate. In other words, if the electric field component in the z-axis direction is accurately grasped, the position of the radiation source is also specified.
However, not only the z-axis direction component but also the x-axis and y-axis direction electric field components act on the tip of the electric field probe, and an electric field reflecting the triaxial electric field component is detected. In other words, there is an actual situation that the accurate z-axis component value becomes unclear due to the presence of the x-axis component and the y-axis component of the electric field, which makes it difficult to specify the position of the radiation source.

One of the purposes of the present case was invented in view of such problems, and is to improve the measurement accuracy of the electric field.
In addition, the present invention is not limited to the above-described purpose, and is an operational effect derived from each configuration shown in “Mode for Carrying Out the Invention” to be described later. It can be positioned as a purpose.

The disclosed electric field probe includes a center conductor, a first dielectric portion made of a dielectric material and provided on the outer periphery of the center conductor, and an outer conductor provided on the outer periphery of the first dielectric portion. In addition, a second dielectric portion formed by coating a dielectric material having a relative dielectric constant larger than that of the dielectric material forming the first dielectric portion is provided on the outer peripheral surface on the front end side of the outer conductor.

  According to the disclosed technology, the detection accuracy of the electric field can be improved.

It is a figure which illustrates the composition of the electric field measuring device concerning an embodiment. It is a figure which illustrates the electric field probe of this electric field measuring apparatus, (a) is a longitudinal cross-sectional view [BB sectional drawing of (b)], (b) is a transverse sectional view [AA sectional drawing of (a). ]. It is a typical perspective view for demonstrating the numerical analysis model of the electric field measurement by this electric field probe. It is a graph of the calculation result of electric field distribution by numerical analysis. It is a longitudinal cross-sectional view which shows this electric field probe and the electric force line of the vicinity. It is a figure which shows a coincidence with the theoretical value of the estimated value of the electric field strength by this electric field probe, (a)-(d) shows the coincidence when using dielectrics having different relative permittivity and loss respectively. (E) is a perspective view showing a model of an electric field probe, and (f) is a legend showing the relationship between each hatching in the graph and the total sum of absolute value errors. It is a schematic diagram which shows the electric field distribution in the near field of a microstrip line, (a) is an electric field distribution at the time of using a comparative probe, (b) is an electric field distribution at the time of using the electric field probe as a modification. Show. Each of (a), (b), (c), (d), and (e) is a longitudinal sectional view illustrating an electric field probe of an electric field measuring device as a modification.

  Hereinafter, embodiments of an electric field probe and an electric field measurement device will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention of excluding various modifications and technical applications that are not explicitly described in the embodiment. In other words, the present embodiment can be implemented with various modifications (combining the embodiments and modifications) without departing from the spirit of the present embodiment.

[1. Device configuration]
FIG. 1 is a perspective view illustrating the configuration of an electric field measurement apparatus 10 according to the embodiment. This electric field measuring device 10 measures an electric field in the vicinity of electronic devices such as a printed circuit board 12 on which electronic components are mounted, a home appliance that incorporates an electronic circuit, a computer, a wireless transmission / reception device, a mobile phone, and the like. A spectrum analyzer 6 (measuring device) and an electric field probe 1 are provided.

  The characteristics of an electric field and a magnetic field due to electromagnetic waves radiated from electronic devices greatly vary depending on the distance from the radiation source. A range having a distance smaller than one wavelength of the electromagnetic wave is called a near field, and a range having a distance larger than this is called a far field. The electric field measuring apparatus 10 is suitable for use in measuring the electric field strength in the near field of electronic equipment, but can also be applied to the measurement in the far field.

  The spectrum analyzer 6 is a device that measures and displays the frequency spectrum of an input high-frequency signal. Here, the voltage signal input from the electric field probe 1 is a measurement target of the spectrum analyzer 6. The spectrum analyzer 6 displays the intensity for each frequency spectrum of the signal input from the electric field probe 1 on the display.

  The electric field probe 1 is a coaxial probe that detects an electric field in a non-contact state with an object to be searched, and outputs a signal corresponding to a change in electric field intensity that has acted near the tip of the electric field probe 1. As shown in FIGS. 2A and 2B, the electric field probe 1 includes a central conductor 2, a first dielectric part 3, an outer conductor 4, and a second dielectric part 5.

  The center conductor 2 is a core wire made of, for example, a copper wire, and is arranged at the center of the electric field probe 1. The center conductor 2 is preferably formed of a material with low conductor loss, and the surface of the center conductor 2 may be subjected to silver plating in consideration of the skin effect.

  The outer conductor 4 is a portion formed as a hollow cylindrical conductor and disposed coaxially with the central conductor 2. The outer conductor 4 is arranged so that its central axis coincides with the central axis C of the central conductor 2, and is fixed integrally with the central conductor 2 via the first dielectric portion 3 with the central conductor 2 inserted inside. Is done. The outer conductor 4 has a function of defining a reference potential (ground) of an electric field input to the central conductor 2. As with the central conductor 2, it is preferable to form the outer conductor 4 with a material having a low conductor loss.

  When the electric field probe 1 is a semi-rigid coaxial probe, the outer conductor 4 may be formed of a copper tube. When the electric field probe 1 is a flexible coaxial probe, the outer conductor 4 may be formed of a braided copper wire or the like.

  The first dielectric portion 3 is a layer made of a dielectric material (insulator) filled between the central conductor 2 and the outer conductor 4. The relative dielectric constant of the first dielectric part 3 is set according to the characteristic impedance required for the electric field probe 1. The characteristic impedance is determined by the ratio between the inner diameter of the outer conductor 4 and the outer diameter of the center conductor 2 and the relative dielectric constant of the first dielectric portion 3.

  The first dielectric part 3 is preferably formed of a substance having a low dielectric loss, and for example, it is conceivable to use a fluorine resin or polyethylene having a low chemical activity. Further, when air is used as an insulator, the first dielectric portion 3 may be omitted. In this case, if the center conductor 2 is fixed to the outer conductor 4 via an arbitrary insulator, the space between the center conductor 2 and the outer conductor 4 functions as a dielectric layer.

  The second dielectric portion 5 is a hollow cylindrical member made of a dielectric material having a relative permittivity (relative permittivity with respect to an AC electric field) larger than that of air and loaded on the outer peripheral surface of the outer conductor 4. The inner diameter of the second dielectric part 5 is formed so as to coincide with the outer shape of the outer conductor 4, and the second dielectric part 5 is fixed in a state where its inner cylindrical surface is in contact with the outer peripheral surface 4 b of the outer conductor 4. Is done. The second dielectric portion 5 is provided so as to cover at least the outer peripheral surface 4b at the end portion of the outer conductor 4 on the front end 4a side. The contact state between the outer conductor 4 and the second dielectric portion 5 may be a close fitting state or may be slidably contacted.

  The material of the second dielectric part 5 may be the same as the material of the first dielectric part 3, but may be different, and is preferably a material having a high relative dielectric constant. The greater the relative permittivity, the stronger the electric field correcting action near the tip of the electric field probe 1. The relative permittivity here is a relative permittivity with respect to an AC electric field in a high frequency range. In the present embodiment, in consideration of the frequency dependence characteristics of the relative permittivity, a material having a relative permittivity greater than that of air with respect to electromagnetic waves in a high frequency range of 500 [MHz] or higher is used. More preferably, a material having a relative dielectric constant larger than that of air with respect to electromagnetic waves in a high frequency range of 1 [GHz] or more is used.

  Focusing on the tip shape of the electric field probe 1, as shown in FIG. 2A, the tip 2a of the center conductor 2, the tip 3a of the first dielectric part 3, the tip 4a of the outer conductor 4, and the second dielectric part 5 are used. All the tips 5a are located on the same plane, so that the tip of the electric field probe 1 is formed flat. That is, the end surfaces of the center conductor 2, the first dielectric portion 3, the outer conductor 4, and the second dielectric portion 5 are all coincident. Focusing on the cross-sectional shape of the electric field probe 1, as shown in FIG. 2B, the central conductor 2, the first dielectric part 3, the outer conductor 4 and the second dielectric part 5 are all arranged concentrically. ing.

[2. Numerical analysis]
[2-1. Theoretical value]
FIG. 3 illustrates a microstrip line 9 (electromagnetic wave transmission path) prepared as a numerical analysis model for electric field measurement by the electric field probe 1 described above. The microstrip line 9 is obtained by providing a linear conductor line 7 on the upper surface of a substrate 8 made of a dielectric. The entire bottom surface of the substrate 8 is a ground layer 13. In this numerical analysis, the substrate 8 of the microstrip line 9 has a square shape of 200 [mm] square, its thickness (distance between the conductor line 7 and the ground layer 13) is 1 [mm], and the width of the conductor line 7 is 2 [mm] was set, and the conductor line 7 was terminated at the end of the substrate. The relative dielectric constant of the substrate was 4.

FIG. 4 shows the numerical analysis result of the electric field distribution when a high frequency voltage of 1 [GHz] is applied to the microstrip line 9. Here, the y-axis (x = 0) is set at the center of the conductor line 7, the x-axis is set in the horizontal direction orthogonal thereto, and the z-axis is set in the vertical direction. In addition, in the horizontal plane with a height of 1 mm from the plate surface, the position directly above the conductor line 7 (x = 0) is the starting point of the analysis position, and the scanning direction is the x-axis direction (increase direction of x) It was.
As shown by the thick solid line in FIG. 4, the theoretical value of the electric field strength by numerical analysis takes the maximum value at the distance x = 0, and decreases as the distance x increases. Also, the minimum value at x = x _1, takes a maximum value at x = x _2, greatly attenuated in farther than the distance x _2.

[2-2. Comparison probe]
Next, the estimated value of the electric field intensity detected when the comparison probe 11 corresponding to the conventional coaxial probe is applied to the above numerical analysis model is numerically analyzed, and the invasiveness of the comparison probe 11 is confirmed. did. The comparison probe 11 assumed in this analysis corresponds to a structure obtained by removing the second dielectric portion 5 from the electric field probe 1 as shown in FIG.

  That is, the comparative probe 11 is a probe having the above-described center conductor 2, first dielectric portion 3, and outer conductor 4. The specifications of the comparative probe 11 were as follows: outer diameter 1 [mm], length 48 [mm], center conductor diameter 0.27 [mm], and dielectric relative permittivity 2.2. As shown in FIG. 3, the scanning direction by the comparison probe 11 was set to the x-axis direction starting from the position immediately above the conductor line 7 (x = 0). The arrangement direction of the comparative probe 11 was the z-axis direction (perpendicular to the plate surface).

As indicated by a broken line in FIG. 4, it can be read that the estimated value of the electric field intensity detected by the comparison probe 11 is greatly deviated from the theoretical value. In particular, significantly different from the distance x ₁ distance x ₃ as the minimum value of the broken line graph has the minimum value when the theoretical value is located farther than the distance x _2.

It can also be seen that the electric field strength at that position is underestimated. Further, the electric field strength attenuation effect is extremely small with respect to the subsequent increase in the distance x, and the result is as if the electric field having a constant strength is diffused over a wide range.
This is probably because the comparison probe 11 detects not only the electric field component in the z direction (Ez component) but also the electric field component in the x direction (Ex component) in the electric field of the microstrip line 9. .

[2-3. Electric field probe]
Subsequently, the estimated value of the electric field strength detected when the above-described electric field probe 1 was applied to the above numerical analysis model was numerically analyzed. The electric field probe 1 assumed here is one in which the second dielectric portion 5 is loaded on the tip of the above-described comparison probe 11. Here, the outer diameter of the second dielectric portion 5 was 11 [mm], and the length was 25 [mm]. The chemical composition of the second dielectric part 5 was a dielectric material, the relative dielectric constant was 100, and the loss was 0.

As shown by a thin solid line in FIG. 4, it can be read that the estimated value of the electric field intensity by the electric field probe 1 has a strong similarity to the theoretical value and the electric field intensity is detected with high accuracy. In particular, not only the distance x _{1 that} is the minimum value of the theoretical values almost coincides, but also the attenuation characteristics of the electric field farther than the distance x ₂ are very similar.

[2-4. Electric field correction]
The state of the lines of electric force in the vicinity of the microstrip line 9 is schematically shown in FIG. Here, the state at the moment when the charge on the conductor line 7 is positive is illustrated. When the electric field probe 1 is not present, the electric lines of force extending in the radial direction around the microstrip line 9 enter vertically toward the ground layer 13. On the other hand, when the electric field probe 1 is positioned above the conductor line 7, the lines of electric force are drawn toward the center conductor 2 below the electric field probe 1.

  At this time, if the second dielectric portion 5 is not provided around the outer conductor 4 of the electric field probe 1, the electric lines of force wrap around the surface of the outer conductor 4 as indicated by a broken line in FIG. 5. The Ex component near the outer conductor 4 (the x-axis direction component of the electric field vector) acts on the central conductor 2. As a result, the disturbance derived from the Ex component is mixed in the detection signal of the Ez component. That is, when the comparison probe 11 not provided with the second dielectric portion 5 is used, not only the Ez component of the electric field but also the Ex component is detected together, and each of these components can be identified. Can not.

On the other hand, when the electric field probe 1 loaded with the second dielectric part 5 is used, as shown by a solid line in FIG. 5, the electric lines of force are attracted to the lower surface of the second dielectric part 5, The Ex component near the outer conductor 4 is corrected in the z-axis direction.
As a result, the Ez component predominates in the electric field acting on the central conductor 2, disturbances derived from the Ex component are reduced, and the electric field probe 1 generates a voltage signal corresponding to the Ez component acting on the tip 2 a of the central conductor 2. . Therefore, in the electric field measurement of the near field of the microstrip line 9, the electric field probe 1 is not easily affected by the Ex component, and the detection accuracy of the Ez component of the electric field is improved.

[2-5. Evaluation of electric field coincidence]
FIGS. 6A to 6D show simulation results obtained by estimating how the detection accuracy of the electric field changes when the composition and shape of the second dielectric portion 5 are changed. Here, the relative dielectric constant and the magnitude of loss of the second dielectric part 5 are set as shown in Table 1 below, and the simulation results in each case are shown in FIGS.

  In the above simulation, as shown in FIG. 6 (e), the dimension of the difference between the outer diameter and the inner diameter of the second dielectric part 5 is the thickness D, and the dimension in the extending direction of the electric field probe 1 is the length L. As a result, the estimated values of the electric field strength when the thickness D and the length L were changed were numerically analyzed. Further, in order to quantify the degree of coincidence between the estimated value and the theoretical value, the sum of absolute value errors between the estimated value and the theoretical value was calculated.

  The absolute value error referred to here is, for example, a parameter corresponding to the area of a region surrounded by a theoretical value graph indicated by a thick solid line and an estimated value graph indicated by a thin solid line in the graph shown in FIG. Yes, it is evaluated that the smaller the absolute value error, the more similar the shape of the graph. The magnitude relationship between the types of hatching and the absolute value error that is meant by the hatching is as shown in FIG. 6 (f). The smaller the absolute value error, the lower the density, and the thickness D and the length L The relationship between the absolute value error and the absolute value error was visualized.

  As shown in each of FIGS. 6A to 6D, when the composition of the second dielectric portion 5 is constant, the absolute value regardless of whether the thickness D and the length L are too large or too small. The error increases. This is because, when the thickness D and the length L are too small, the electric field correcting action by the second dielectric portion 5 as shown in FIG. 5 becomes weak, and the Ex component of the electric field is erroneously detected. Means that. On the contrary, when the thickness D and the length L are excessive, it is considered that the electric field correction action becomes excessive, and the original electric field of the microstrip line 9 is disturbed by the second dielectric portion 5. .

  That is, when considering the shape of the second dielectric portion 5, there are optimum values of the thickness D and the length L that minimize the absolute value error, and the thickness D and the length L are optimum values, respectively. The absolute value error increases and the degree of coincidence between the estimated value and the theoretical value decreases as the distance from the distance increases. 6A and 6B, when the relative permittivity is almost the same, the magnitude of the absolute value error is hardly influenced by the magnitude of the loss of the second dielectric portion 5. Recognize.

  On the other hand, as shown in FIGS. 6C and 6D, when the relative dielectric constant of the second dielectric portion 5 is increased, the absolute value error is totally increased regardless of the values of the thickness D and the length L. It can be determined that the degree of coincidence between the estimated value and the theoretical value increases. Therefore, it can be said that it is preferable to use a material having a large relative dielectric constant for the second dielectric portion 5 of the electric field probe 1 regardless of the magnitude of the loss.

[3. effect]
(1) According to the disclosed electric field probe 1, the outer peripheral surface 4 b on the distal end 4 a side of the outer conductor 4 is covered with the second dielectric portion 5, thereby changing the direction of the electric field acting in the vicinity of the distal end portion of the electric field probe 1. Correction can be made in the extending direction of the electric field probe 1 (that is, in the z-axis direction). As a result, the electric field component in the x-axis direction can be reduced, and the electric field strength of the measurement target can be detected with high accuracy.

(2) Also, as shown in FIG. 2 (a), the electric field probe 1 is provided such that the tip 4a of the outer conductor 4 and the tip 5a of the second dielectric part 5 are located on the same plane, The outer peripheral surface 4b of the outer conductor 4 is not exposed to the electric field. Such an end shape can make it difficult for the lines of electric force to be attracted to the outer conductor 4, and can prevent the detection result of the electric field probe 1 from being disturbed by the Ex component of the electric field. Therefore, the detection accuracy of the electric field by the electric field probe 1 can be improved.

  In addition, since the tip 4a side of the outer conductor 4 having a high density of electric lines of force is covered with the second dielectric portion 5, the influence of the Ex component of the electric field is affected even when the electric field probe 1 is brought close to the measurement object. It can be made difficult to receive. Furthermore, the accuracy of the electric field distribution measured by the spectrum analyzer 6 can be improved by the electric field detection using the electric field probe 1 having high detection accuracy of the Ez component of the electric field.

(3) Since the second dielectric portion 5 is made of a dielectric material having a relative dielectric constant larger than that of air, the electric lines of force in the vicinity of the tip portion of the electric field probe 1 can be reliably drawn. Thereby, the Ex component of the electric field in the vicinity of the outer conductor 4 can be corrected in the z-axis direction, in other words, the influence of the Ex component of the electric field can be reduced, and the electric field detection accuracy can be improved.

[4. Modified example]
Regardless of an example of the disclosed embodiment, various modifications can be made without departing from the spirit of the present embodiment. Each structure and each process of this embodiment can be selected as needed, or may be combined suitably. In the following modifications, the same elements as those in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

[4-1. Composition of second dielectric part]
In the above-described embodiment, the electric field probe 1 including the dielectric material having the relative dielectric constant larger than that of the air is exemplified in the second dielectric part 5. However, the lossy material is further included in the second dielectric part 5. Thus, the detection accuracy of the electric field can be further improved.
A lossy material is a material having a function of absorbing electromagnetic waves and converting it into thermal energy, and is classified into two types, namely, a magnetic loss material and a dielectric loss material, depending on the energy conversion mechanism.

The magnetic loss material is a material that converts electromagnetic wave energy into heat by the magnetic loss ability of the magnetic material. For example, ferritic wave absorbers obtained by sintering iron oxide Fe ₂ O ₃ with divalent metal oxides such as NiO and ZnO, and powders such as silicon steel Fe-Si, permalloy Fe-Ni, and stainless steel Fe-Cr-Si. It is conceivable to use a bonded alloy-based electromagnetic wave absorber, rare earth magnet compound, or the like. Alternatively, a composite material such as rubber ferrite in which these metal powders are mixed in rubber or resin may be used. As the complex component of the relative permeability of the material used increases, the amount of electromagnetic wave energy loss increases, that is, the amount of electromagnetic wave absorption increases.

On the other hand, the dielectric loss material is a material that converts electromagnetic wave energy into heat by the dielectric loss ability of the dielectric material. For example, it is conceivable to use a radio wave absorber in which barium titanate BaTi ₃ and carbon particles are mixed in a resin, a material for a biological equivalent phantom, a polymer material, or the like. The dielectric loss material of the second dielectric portion 5 is preferably a material having a characteristic opposite to that of the low loss material applied to the first dielectric portion 3, that is, a material having a large dielectric loss. As the complex component of the relative permittivity of the material used increases, the amount of electromagnetic wave energy loss increases and the amount of electromagnetic wave absorption increases.

[4-2. Electric field vector analysis]
Here, assuming the electric field measurement using the electric field probe 14 to which the lossy material part 15 including the dielectric material and the magnetic loss material is attached instead of the second dielectric part 5, in the near field of the microstrip line 9 A change in the electric field distribution will be described.

  FIG. 7A shows the electric field distribution in a state in which the comparison probe 11 is located immediately above the conductor line 7, and FIG. 7B shows the case of the electric field probe 14 to which the lossy material portion 15 is attached. Is. 7A and 7B, the direction of the arrow indicates the direction of the electric field, and the size of the arrow indicates the electric field strength.

  When the comparison probe 11 is used, as indicated by the symbol D in FIG. 7A, the electric lines of force starting from the conductor line 7 are formed on the surface of the outer conductor 4 within the range surrounded by the broken line. The Ex component near the outer conductor 4 (the component in the x-axis direction of the electric field vector) acts on the central conductor 2. As a result, the disturbance derived from the Ex component is mixed into the detection signal generated in the central conductor 2 due to the variation of the Ez component. That is, the comparison probe 11 detects not only the Ez component of the electric field but also the Ex component.

  On the other hand, when the electric field probe 14 loaded with the lossy material part 15 is used, as indicated by the symbol E in FIG. The wraparound of the force line is suppressed, and the electric field component within the range surrounded by the broken line is reduced. In addition, since the electric field energy is converted into thermal energy by the magnetic loss ability inside the lossy material part 15, the electric field strength that has entered the inside of the lossy material part 15 is attenuated and the fluctuation of the electric field is suppressed. . Further, as in the above-described embodiment, the lines of electric force are attracted to the lower surface of the second dielectric part 5 by the action of the dielectric contained in the lossy material part 15, and the Ex component near the outer conductor 4 is in the z-axis direction. Will be corrected.

  Due to the cooperation between the correction action and the attenuation action of these electric fields, the electric field acting on the central conductor 2 is strongly dominant in the Ez component, and the electric field probe 14 responds to the change in the Ez component acting on the tip 2a of the central conductor 2. Generate a voltage signal. Thus, in the electric field measurement of the near field of the microstrip line 9, the electric field probe 14 becomes less susceptible to the Ex component and the noninvasiveness is improved.

  Thus, the lossy material included in the lossy material portion 15 can suppress electric field fluctuations outside the outer peripheral surface 4b of the outer conductor 4. Thereby, the Ex component of the electric field acting on the center conductor 2 can be attenuated, and the measurement accuracy of the electric field by the electric field probe 1 can be improved.

  In particular, when a magnetic loss material is used for the lossy material portion 15, the energy of electromagnetic waves can be reliably converted into heat by using the magnetic loss ability, and the Ex component of the electric field acting on the outer conductor can be reduced. Can be attenuated. Note that by increasing the complex component of the relative magnetic permeability, the influence of the Ex component on the central conductor 2 can be reduced, and the detection accuracy of the electric field can be further improved.

  On the other hand, even when a dielectric loss material is used for the lossy material portion 15, it is possible to convert electromagnetic energy using the dielectric loss ability and attenuate the Ex component of the electric field acting on the outer conductor. Can do. As in the case of the magnetic loss material, the influence of the Ex component on the center conductor 2 can be reduced by increasing the complex component of the relative permittivity, and the electric field detection accuracy can be further improved.

[4-3. Tip shape of electric field probe]
In the above embodiment, the electric field probe 1 has a flat tip formed as an example. However, as shown in FIG. 8A, the central conductor 2 is made of the first dielectric portion 3, the outer conductor 4, and the second conductor. You may make it protrude from the end surface of the dielectric part 5. FIG. In this case, it is conceivable that the end surfaces of the first dielectric part 3 and the second dielectric part 5 coincide with the end faces of the outer conductor 4 so that the inner peripheral surface and the outer peripheral surface 4b of the outer conductor 4 are not exposed. .

Here, if the amount of protrusion of the center conductor 2 from the end face of the outer conductor 4 is H ₁ and the distance from the tip 2a of the center conductor 2 to the measurement object is H ₂ , the electric field detected by the electric field probe 1 The intensity corresponds to the electric field intensity at a position where the distance from the measurement object is H ₁ + H ₂ . In this way, by projecting the center conductor 2 beyond the end face of the second dielectric portion 5, the intersection of the end face of the outer conductor 4 and the center conductor 2 (that is, the root portion from which the center conductor 2 protrudes) is provided. It is possible to detect a weak electric field that acts, and the detection sensitivity of the electric field can be improved.

Note that the end face of the second dielectric portion 5 does not necessarily coincide with the end face of the outer conductor 4. However, if the outer peripheral surface 4b of the outer conductor 4 is exposed below the tip 5a of the second dielectric part 5, the electric field correcting action by the second dielectric part 5 is weakened. Therefore, at least the tip 5a of the second dielectric part 5 is positioned on the same plane as the tip 4a of the outer conductor 4, or the tip 5a of the second dielectric part 5 extends below the tip 4a of the outer conductor 4. It is preferable to provide (that is, project so as to cover the outer peripheral surface 4b of the outer conductor 4).
The same applies to the first dielectric portion 3, and it is preferable that the tip 3 a of the first dielectric portion 3 is located on the same plane as the tip 4 a of the outer conductor 4 or extends below the tip 4 a. .

[4-4. Shape of second dielectric part]
Moreover, in the above-mentioned embodiment, although the 2nd dielectric material part 5 formed in the cylindrical shape was illustrated, the specific shape of the 2nd dielectric material part 5 is not limited to this. For example, as shown in FIG. 8B, the outer conductor 4 may have a shape in which the outer diameter is reduced toward the tip 4a side. By forming the tip of the second dielectric portion 5 thin, it is possible to easily detect an electric field in a narrow portion.

  Moreover, as shown in FIG.8 (c), it is good also as a shape where the outer diameter expanded toward the front-end | tip 4a side of the outer conductor 4. As shown in FIG. That is, the correction effect on the Ex component of the electric field that can act on the center conductor 2 can be improved by increasing the thickness of the tip of the second dielectric portion 5 that is close to the detection target (the influence of the electric field is large). This can further improve the electric field detection accuracy.

  Alternatively, as shown in FIG. 8 (d), the second dielectric part 5 may have a two-stage structure in which the electric field probe 1 is divided in the extending direction. In this case, the tip dielectric part 51 is placed on the tip side and the base dielectric part 52 is placed on the other side, and the tip dielectric part 51 side is formed of a material having a relative dielectric constant larger than that of the base dielectric part 52. To do. Alternatively, the distal dielectric part 51 side is formed of a material having a higher electromagnetic wave absorption rate than the proximal dielectric part 52. Further, when the second dielectric portion 5 is divided into a plurality of stages of three or more stages, it is considered to form the outer conductor 4 from a material having a higher relative dielectric constant or higher electromagnetic wave absorption rate toward the tip 4a side. It is done.

  With such a configuration, it is possible to suppress unnecessary electric field interference on the distal end side of the electric field probe 1 as in the case shown in FIG. 8C, and the electric field detection accuracy can be further improved. The noninvasiveness can be further improved. In particular, since the electric field intensity is larger and more likely to interfere with the distal end side of the electric field probe 1, it is possible to enhance the electric field correcting action and attenuation action, which can greatly contribute to the improvement of the electric field detection accuracy.

  Moreover, as shown in FIG.8 (e), you may form the diameter reduction part 53 of the 2nd dielectric material part 5 with a material with a larger relative dielectric constant or a material with a higher absorption factor of electromagnetic waves than another site | part. Thereby, the detection accuracy of the electric field can be improved while improving the convenience of the electric field probe 1.

  Moreover, in the above-mentioned embodiment, as shown in FIG.2 (b), the center conductor 2, the 1st dielectric material part 3, the outer conductor 4, and the 2nd dielectric material part 5 illustrated what was arrange | positioned concentrically. However, the cross-sectional shape and outer shape of each of these elements are not limited to this. For example, the cross-sectional shape of each element may be a circular shape or a polygonal shape, and the three-dimensional shape of each element may be a spherical shape or an elliptical rotating body shape. Further, when a lossy material is included in the second dielectric part 5, unevenness may be provided on the outer surface of the second dielectric part 5 in consideration of radio wave absorption.

  In the above-described embodiment, the electric field measurement device 10 in which the electric field probe 1 is directly connected to the spectrum analyzer 6 is illustrated, but a specific electric field measurement method is not limited to this. For example, an amplifier or a ballast may be interposed between them, or another measurement device or computer may be connected in addition to (or instead of) the spectrum analyzer 6.

1 Electric Field Probe 2 Center Conductor 3 First Dielectric Part 4 Outer Conductor 5 Second Dielectric Part 6 Spectrum Analyzer (Measurement Device)
10 Electric field measuring device

Claims (13)

A central conductor;
A first dielectric portion made of a dielectric material and provided on the outer periphery of the central conductor;
An outer conductor provided on the outer periphery of the first dielectric portion;
A second dielectric part formed by coating a dielectric material having a relative dielectric constant larger than that of the dielectric material forming the first dielectric part on an outer peripheral surface on a front end side of the outer conductor; An electric field probe. The electric field probe according to claim 1, wherein the second dielectric portion contains a dielectric material having a relative dielectric constant larger than that of air. The electric field probe according to claim 1, wherein an end face of the second dielectric portion coincides with an end face of the outer conductor. The electric field probe according to claim 1, wherein the central conductor is provided so as to protrude from an end face of the outer conductor. The electric field probe according to claim 1, wherein the second dielectric portion contains a lossy material that absorbs electromagnetic waves. 6. The electric field probe according to claim 5, wherein the lossy material contains a magnetic loss material. The electric field probe according to claim 5 or 6, wherein the lossy material contains a dielectric loss material. The electric field probe according to any one of claims 5 to 7, wherein the second dielectric portion is set such that an absorption rate of the electromagnetic wave is higher toward an end portion side of the outer conductor. The electric field probe according to any one of claims 1 to 8, wherein the second dielectric portion has a tapered shape formed so as to be thinner toward an end portion of the outer conductor. 10. The electric field probe according to claim 1, wherein the second dielectric portion is set to have a higher relative dielectric constant toward an end portion of the outer conductor. In an electric field measurement apparatus comprising an electric field probe that outputs a signal according to electric field strength, and a measurement device that displays the intensity of the signal output from the electric field probe.
The electric field probe is
An axial center conductor;
A first dielectric portion made of a dielectric material and provided on the outer periphery of the central conductor;
An outer conductor provided on the outer periphery of the first dielectric portion;
A second dielectric portion formed by coating a dielectric material having a relative dielectric constant larger than that of the dielectric material forming the first dielectric portion on an outer peripheral surface on a front end side of the outer conductor. An electric field measuring device. A central conductor;
A first dielectric portion made of a dielectric material and provided on the outer periphery of the central conductor;
An outer conductor provided on the outer periphery of the first dielectric portion;
Ri Na covering the dielectric material on the outer surface of the distal end of the outer conductor, further comprising a second dielectric portion you containing lossy material that absorbs electromagnetic waves comprise a dielectric loss material An electric field probe. A central conductor;
A first dielectric portion made of a dielectric material and provided on the outer periphery of the central conductor;
An outer conductor provided on the outer periphery of the first dielectric portion;
Ri Na covering the dielectric material on the outer surface of the distal end of the outer conductor, as well as containing a lossy material that absorbs electromagnetic radiation, the absorption rate of the end portion side as the electromagnetic wave of the outer conductor is set higher An electric field probe comprising a second dielectric part.

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