Dielectric constant measurement device

Abstract

A dielectric constant measurement device comprising: a probe (1); a pressure sensor (15) disposed at a tip of the probe (1); a dielectric constant measurement unit for calculating a dielectric constant of a measurement target (100) by irradiating the measurement target (100) with electromagnetic waves via the probe (1); and a pressure measurement unit for calculating a pressing pressure applied from the probe (1) to the measurement target (100) on the basis of an output of the pressure sensor (15). The probe (1) includes an electromagnetic wave irradiation portion (13) provided at a central portion of the tip, and a protrusion (14) provided on an outer peripheral portion of the tip. The pressure sensor (15) is disposed on an end surface of the protrusion (14).

Description

Dielectric constant measuring device

[0001] The present invention relates to a dielectric constant measuring device.

[0002] The coaxial probe method is chosen as a method for measuring the dielectric constant of living skin because it allows non-invasive measurements without damaging the skin and because it can irradiate radio waves in a higher frequency band than other methods. With the coaxial probe method, it is known that the strength of the pressure applied to the object to be measured affects the dielectric constant measurement results (Non-Patent Document 1, Non-Patent Document 2).

[0003] In the technique disclosed in Non-Patent Document 2, as shown in Fig. 11, a measurement object 100 (e.g., beef liver) placed on a measurement table 101 is pressed by a coaxial probe 102 for measuring the dielectric constant, and the change in mass of the entire measurement table is measured by a load cell provided on the measurement table 101. Based on the measurement results, the pressure P applied to the measurement object 100 from the coaxial probe 102 is calculated using equation (1).

[0004]

[0005] In equation (1), m is the mass of the entire measurement table when pressed by the coaxial probe 102, m ｓａｍｐｌｅ is the mass of the measurement object 100, m ｓｅｔｕｐ is the mass of the measurement table 101, etc., g is the gravitational constant, and A is the area of ​​the tip of the coaxial probe 102. In the technology disclosed in Non-Patent Document 2, by measuring the mass simultaneously with the irradiation of radio waves from the coaxial probe 102, a system is constructed that can measure the dielectric constant by the coaxial probe method and simultaneously continuously measure pressure.

[0006] In the technology disclosed in Non-Patent Document 2, the area value of the tip of the coaxial probe 102 is used to calculate the pressure. However, because the measurement stage 101 is in contact with the bottom surface of the measurement target 100, there is a possibility that the pressure cannot be calculated correctly using equation (1). When measuring the dielectric constant of a living subject using the coaxial probe method, the burden on the living subject changes depending on the pressure applied to the skin from the coaxial probe 102. Therefore, in order to measure the pressure value and its changes in detail, it is considered necessary to measure the mass at a position close to the coaxial probe 102 and the skin.

[0007] Furthermore, with the technology disclosed in Non-Patent Document 2, there is a possibility that the mass cannot be measured correctly if the centers of gravity of the coaxial probe 102, the measurement target 100, and the measurement table 101 do not coincide. For this reason, the technology disclosed in Non-Patent Document 2 can be applied when the measurement target is stationary, but when a living body is used as the measurement target, conditions such as keeping the living body still are required, which poses the problem that it is not suitable for long-term measurements.

[0008] Yusuke Sato et al., "In-vivo Measurement of Complex Permittivity of Human Skin Tissue Using an Open-Ended Coaxial Probe," IEEJ Transactions on Electrical Engineering, Vol. 131, No. 12, pp. 2040-2045, 2011. G. Maenhout, T. Markovic, I. Ocket, B. Nauwelaers, "Effect of Open-Ended Coaxial Probe-to-Tissue Contact Pressure on Dielectric Measurements," Sensors 2020, 20, 2060, <https: / / doi.org / 10.3390 / s20072060>

[0009] The present invention has been made to solve the above-mentioned problems, and aims to provide a dielectric constant measuring device that can measure the dielectric constant of an object to be measured and at the same time measure the pressing pressure from the probe to the object to be measured more appropriately and for a longer period of time than conventional methods.

[0010] The dielectric constant measuring device of the present invention comprises a probe for irradiating electromagnetic waves onto a measurement object, a pressure-sensitive sensor installed at the tip of the probe facing the measurement object, a dielectric constant measuring unit configured to irradiate electromagnetic waves onto the measurement object via the probe and calculate the dielectric constant of the measurement object based on the reflected waves reflected by the measurement object and received by the probe, and a pressure measuring unit configured to calculate the pressing pressure from the probe to the measurement object based on the output of the pressure-sensitive sensor, wherein the probe comprises an electromagnetic wave irradiating unit that protrudes from the center of the tip so as to come into contact with the measurement object, and a protrusion provided on the outer periphery of the tip, and the pressure-sensitive sensor is installed on the end face of the protrusion facing the measurement object.

[0011] According to the present invention, by installing a pressure sensor in the probe, it is possible to measure the dielectric constant of the object to be measured and at the same time measure the pressure applied from the probe to the object to be measured more appropriately and for a longer period of time than conventionally possible.

[0012] FIG. 1 is a cross-sectional view of a coaxial probe of a dielectric constant measuring device according to an embodiment of the present invention. FIG. 2 is a bottom view of a coaxial probe of a dielectric constant measuring device according to an embodiment of the present invention. FIG. 3 is a block diagram showing the configuration of a dielectric constant measuring device according to an embodiment of the present invention. FIG. 4 is a diagram showing an example of measurement results of dielectric constant and pressure. FIGS. 5A and 5B are cross-sectional views showing the arrangement of pressure-sensitive sensors when only pressure measurements are experimentally performed. FIG. 6 is a diagram showing the deviation between the dielectric constant of a measurement object when a pressure-sensitive sensor is not arranged and the dielectric constant when a pressure-sensitive sensor is arranged. FIG. 7 is a diagram explaining the arrangement of pressure-sensitive sensors according to an embodiment of the present invention. FIG. 8 is a bottom view showing another configuration of a coaxial probe according to an embodiment of the present invention. FIG. 9 is a bottom view showing another configuration of a coaxial probe according to an embodiment of the present invention. FIG. 10 is a block diagram showing an example configuration of a computer that realizes a dielectric constant measuring device according to an embodiment of the present invention. FIG. 11 is a diagram showing the configuration of a conventional dielectric constant measuring device.

[0013] Fig. 1 is a cross-sectional view of a coaxial probe of a dielectric constant measuring device according to an embodiment of the present invention, and Fig. 2 is a bottom view of the coaxial probe as seen from the side of the object to be measured. A coaxial probe of a dielectric constant measuring device generally has a structure in which a coaxial structure part consisting of a center conductor and a surrounding dielectric protrudes from the tip part on the side of the object to be measured in order to ensure close contact with the object to be measured.

[0014] In this embodiment, the coaxial probe 1 also comprises a center conductor 10, a dielectric 11 surrounding the center conductor 10, and an outer conductor (ground conductor) 12 surrounding the dielectric 11. The coaxial probe 1 has a structure in which a coaxial structure 13 (electromagnetic wave irradiating portion) consisting of the center conductor 10, the dielectric 11, and the outer conductor 12 protrudes from the tip end on the measurement object 100 side. Furthermore, in this embodiment, a protrusion 14 is provided on the outer periphery of the coaxial probe 1. A pressure sensor 15 is installed on the end face of the protrusion 14 facing the measurement object 100.

[0015] If the height H1 of the coaxial structure 13 protruding from the end face 120 of the outer conductor 12 on the side of the object to be measured 100 in a direction perpendicular to the surface of the object to be measured 100 facing the coaxial probe 1 is taken as the height H1, the height H2 of the protrusion 14 is lower than the height H1 of the coaxial structure 13. While the pressure sensor 15 is shown enlarged in FIG. 1 for ease of understanding, it is a thin-film sensor with a thickness of, for example, approximately 0.3 mm. To prevent gaps from forming between the coaxial structure 13 and the object to be measured 100 and between the pressure sensor 15 and the object to be measured 100 when the coaxial probe 1 is pressed against the object to be measured 100, it is desirable that the total height H3 of the protrusion 14 and the pressure sensor 15 be approximately the same as the height H1 of the coaxial structure 13.

[0016] The protrusion 14 may be made of metal and integrally molded with the external conductor 12, or may be made of resin, for example. The resin protrusion 14 may be fixed to the external conductor 12, and the pressure sensor 15 may be fixed to the protrusion 14 by, for example, adhesive.

[0017] 3 is a block diagram showing the configuration of the dielectric constant measuring device according to this embodiment. The dielectric constant measuring device comprises a coaxial probe 1, a pressure sensor 15 provided on the coaxial probe 1, a vector network analyzer (VNA) 2, a resistance meter 3, and a computer (PC) 4. The VNA 2 and a dielectric constant calculation section 40 of the PC 4 constitute a dielectric constant measuring section 400. The resistance meter 3 and a pressure calculation section 41 of the PC 4 constitute a pressure measuring section 401.

[0018] To measure the dielectric constant and pressure, the tip of the coaxial probe 1 is pressed against the measurement object 100 as in the conventional method. The VNA 2 measures the reflection coefficient when an electromagnetic wave is irradiated from the coaxial probe 1 to the measurement object 100. 200 in Figure 1 represents the electromagnetic wave irradiated to the measurement object 100. The resistance meter 3 measures the resistance value of the pressure-sensitive sensor 15.

[0019] The permittivity calculation unit 40 of the PC 4 calculates the complex permittivity of the object 100 based on the reflection coefficient measured by the VNA 2. The pressure calculation unit 41 of the PC 4 calculates the pressure applied to the object 100 based on the resistance value measured by the resistance meter 3.

[0020] In this way, in this embodiment, it is possible to simultaneously measure the dielectric constant of the measurement object 100 and the pressure applied from the coaxial probe 1 to the measurement object 100. In this embodiment, a resistive pressure sensor 15 is used, but if, for example, a piezoelectric pressure sensor 15 is used, a voltmeter may be used instead of the resistance meter 3. The voltmeter measures the output voltage of the pressure sensor 15. The pressure calculation unit 41 calculates the pressure based on the voltage measured by the voltmeter.

[0021] A capacitance-type pressure sensor 15 may be used instead of the resistance-type pressure sensor 15. When a capacitance-type pressure sensor 15 is used, a capacitance meter may be used instead of the resistance meter 3. The capacitance meter measures the capacitance of the pressure sensor 15. The pressure calculation unit 41 calculates the pressure based on the capacitance measured by the capacitance meter. An optical pressure sensor 15 may also be used.

[0022] Fig. 4 shows an example of the results of simultaneous and continuous measurement of the dielectric constant and pressure using the skin of a person being measured as the measurement object 100. In Fig. 4, 400 indicates the dielectric constant (real part) of the measurement object 100, and 401 indicates the pressure applied from the coaxial probe 1 to the measurement object 100. Here, electromagnetic waves with a frequency of 1.058 GHz were irradiated onto the measurement object 100.

[0023] The pressing pressure was kept almost constant from the start of measurement (0 minutes) to 60 minutes. During this period, the dielectric constant rose sharply and then remained almost constant. When the pressing pressure was increased after 60 minutes, the slope of the increase in the dielectric constant became steeper. The result that the dielectric constant increased as the pressing pressure increased is consistent with the result in Non-Patent Document 2. It was confirmed that this example allows the dielectric constant and pressure to be measured simultaneously.

[0024] Figures 5A and 5B show the placement of the pressure sensor when only pressure measurements were performed experimentally without dielectric constant measurements. Here, we investigated where to place the pressure sensor 15 to obtain measurement results equivalent to those of the pressure sensor 16, which measures the pressure applied from the coaxial structure 13 to the measurement target 100. Figure 5A shows the case where the pressure sensor 15 is placed in the recess between the coaxial structure 13 and the protrusion 14. Figure 5B shows the case where the pressure sensor 15 is placed on the end face of the protrusion 14, as in this embodiment. However, the total height of the pressure sensor 15 added to the protrusion 14 is approximately the same as the total height of the pressure sensor 16 added to the coaxial structure 13. Table 1 shows the pressure measurement results using the pressure sensors 15 and 16 for each of Figures 5A and 5B. The pressure values ​​represent the average of three measurements.

[0025]

[0026] 5A, the pressure value of 5.588 MPa measured by the pressure sensor 15 was smaller than the pressure value of 7.495 MPa measured by the pressure sensor 16. On the other hand, in the case of the arrangement of FIG. 5B, the pressure value of 7.584 MPa measured by the pressure sensor 15 was almost the same as the pressure value of 7.533 MPa measured by the pressure sensor 16.

[0027] From the above results, it was found that by placing the pressure sensor 15 on the end face of the protrusion portion 14 as in this embodiment, it is possible to measure a pressure equivalent to the pressing pressure from the coaxial structure portion 13 to the object to be measured 100.

[0028] The arrangement of the coaxial structure 13 and the pressure sensor 15 may adversely affect the electromagnetic wave irradiation for permittivity measurement. Therefore, the influence of the distance from the center of the coaxial probe 1 to the pressure sensor 15 on permittivity measurement was verified by electromagnetic field analysis simulation. Figure 6 shows the results of a simulation that investigated the deviation between the permittivity (real part) of the measurement object 100 when the pressure sensor 15 is not placed and the permittivity (real part) when the pressure sensor 15 is placed. The horizontal axis of Figure 6 is the distance Ds from the central axis L of the coaxial probe 1 to the pressure sensor 15, as shown in Figure 7.

[0029] When the pressure sensor 15 is sufficiently far from the central axis of the coaxial probe 1, the deviation in the dielectric constant is 0.4 or less. When the pressure sensor 15 approaches the central axis of the coaxial probe 1, the deviation in the dielectric constant rises sharply, but if the distance Ds is 0.7 mm or more, the deviation in the dielectric constant remains 0.4 or less. Therefore, it is desirable that the distance Ds be 0.7 mm or more.

[0030] As described above, in this embodiment, by installing the pressure sensor 15 on the coaxial probe 1, it is possible to simultaneously and continuously measure the dielectric constant of the measurement object 100 and the pressure applied from the coaxial probe 1 to the measurement object 100. In this embodiment, pressure can be measured more accurately than with the technique disclosed in Non-Patent Document 2. Furthermore, in this embodiment, pressure can be measured continuously even when the measurement object 100 is moving, so a measurement device suitable for long-term measurements can be realized. In this embodiment, a living organism has been described as an example of the measurement object 100, but the measurement object 100 is not limited to this and food or plants may also be used.

[0031] Furthermore, a pressure sensor 15 having a ring shape in plan view may be used, as shown in the bottom view of the coaxial probe 1 in Fig. 8. Furthermore, a plurality of pressure sensors 15 may be used, as shown in the bottom view of the coaxial probe 1 in Fig. 9. When a plurality of pressure sensors 15 are used, the pressure calculation unit 41 may calculate the average value of the pressure values ​​measured by the respective pressure sensors 15.

[0032] The dielectric constant calculation unit 40 and pressure calculation unit 41 described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in FIG.

[0033] The computer includes a CPU 300, a storage device 301, and an interface device (I / F) 302. The I / F 302 is connected to a VNA 2, a resistance meter 3, etc. In such a computer, a program for implementing the dielectric constant measuring method of the present invention is stored in the storage device 301. The CPU 300 executes the processing described in this embodiment in accordance with the program stored in the storage device 301.

[0034] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes.

[0035] (Supplementary Note 1) The dielectric constant measuring device of the present invention comprises a probe for irradiating electromagnetic waves onto a measurement object, a pressure-sensitive sensor installed at the tip of the probe facing the measurement object, a dielectric constant measuring unit configured to irradiate electromagnetic waves onto the measurement object via the probe and calculate the dielectric constant of the measurement object based on the reflected waves reflected by the measurement object and received by the probe, and a pressure measuring unit configured to calculate the pressing pressure from the probe to the measurement object based on the output of the pressure-sensitive sensor, wherein the probe comprises an electromagnetic wave irradiating unit that protrudes from the center of the tip so as to come into contact with the measurement object, and a protrusion provided on the outer periphery of the tip, and the pressure-sensitive sensor is installed on the end face of the protrusion facing the measurement object.

[0036] (Supplementary Note 2) In the dielectric constant measuring device according to Supplementary Note 1, the pressure-sensitive sensor is installed at a position 0.7 mm or more away from the central axis of the probe.

[0037] (Supplementary Note 3) In the dielectric constant measuring device according to Supplementary Note 1, the height of the protrusion is lower than the height of the electromagnetic wave irradiating portion.

[0038] (Appendix 4) In the dielectric constant measuring device described in Appendix 1, the probe is a coaxial probe consisting of a center conductor, a dielectric around the center conductor, and an outer conductor around the dielectric, and the electromagnetic wave irradiating part has a structure in which the center conductor, the dielectric, and a part of the outer conductor protrude from the tip.

[0039] (Supplementary Note 5) In the dielectric constant measuring device according to Supplementary Note 1, the pressure-sensitive sensor is a pressure-sensitive sensor having a ring shape in a plan view and disposed around the electromagnetic wave irradiation unit.

[0040] (Appendix 6) In the dielectric constant measuring device described in Appendix 1, the pressure sensors are installed at multiple locations on the end face of the protrusion, and the pressure measuring unit calculates the average value of the pressure obtained from the outputs of the pressure sensors.

[0041] 1...coaxial probe, 2...vector network analyzer, 3...resistance meter, 4...computer, 10...center conductor, 11...dielectric, 12...outer conductor, 13...coaxial structure part, 14...projection part, 15...pressure sensor, 40...dielectric constant calculation part, 41...pressure calculation part, 400...dielectric constant measurement part, 401...pressure measurement part.

Claims

1. A dielectric constant measuring device comprising: a probe for irradiating electromagnetic waves onto an object to be measured; a pressure sensor installed at the tip of the probe facing the object to be measured; a dielectric constant measuring unit configured to irradiate electromagnetic waves onto the object to be measured via the probe and calculate the dielectric constant of the object to be measured based on the reflected waves reflected by the object to be measured and received by the probe; and a pressure measuring unit configured to calculate the pressure applied from the probe to the object to be measured based on the output of the pressure sensor, wherein the probe comprises an electromagnetic wave irradiating unit that protrudes from the center of the tip so as to come into contact with the object to be measured, and a protrusion provided on the outer periphery of the tip, and the pressure sensor is installed on the end face of the protrusion facing the object to be measured.

2. A dielectric constant measuring device according to claim 1, wherein the pressure sensor is installed at a position 0.7 mm or more away from the central axis of the probe.

3. A dielectric constant measuring device according to claim 1, wherein the height of the protrusion is lower than the height of the electromagnetic wave irradiating portion.

4. A dielectric constant measuring device according to claim 1, wherein the probe is a coaxial probe consisting of a center conductor, a dielectric surrounding the center conductor, and an outer conductor surrounding the dielectric, and the electromagnetic wave irradiating section has a structure in which the center conductor, the dielectric, and a part of the outer conductor protrude from the tip.

5. A dielectric constant measuring device according to claim 1, wherein the pressure-sensitive sensor is a pressure-sensitive sensor having a ring shape in a plan view and installed around the electromagnetic wave irradiation unit.

6. A dielectric constant measuring device according to claim 1, wherein the pressure sensors are respectively installed at a plurality of locations on the end face of the protrusion, and the pressure measuring unit calculates the average value of the pressure obtained from the outputs of the pressure sensors.

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