Dielectric Spectroscopy Sensor

Abstract

The present invention is provided with: a connection line path (11); a transmission line path (14) to which an impedance conversion unit (12) is connected; and a measurement surface (13) that is brought into direct or indirect contact with a measurement target M, and outputs electromagnetic waves to the measurement target. The connection line path (11) has a first characteristic impedance that is the same as that of a dielectric spectroscopic system (20). The end of the impedance conversion unit (12) located closer to the connection line path (11) has the first characteristic impedance, and the end thereof located closer to the measurement surface (13) has a second characteristic impedance different from the first characteristic impedance.

Description

[Technical field]

[0001] The present invention relates to a dielectric spectroscopy sensor. [Background technology]

[0002] Testing blood glucose levels and other constituent concentration tests requires the sampling of blood, which places a heavy burden on patients. For this reason, non-invasive constituent concentration measuring devices that do not require blood sampling have been put to practical use.

[0003] As a non-invasive element concentration measurement device, a method using electromagnetic waves in the microwave to millimeter wave band has been proposed. This method has the advantage that there is less scattering in the body and the energy of one photon is low compared to optical methods such as near-infrared light.

[0004] As a method using electromagnetic waves in the microwave to millimeter wave band, a method using a resonant structure disclosed in Non-Patent Document 1 has been proposed. In Non-Patent Document 1, a measurement sample is brought into contact with a device with a high Q value, such as an antenna or a resonator, and frequency characteristics around the resonant frequency are measured. Since the resonant frequency is determined by the complex dielectric constant around the device, the component concentration can be estimated based on the resonant frequency shift by predicting the correlation between the resonant frequency shift and the component concentration in advance.

[0005] As another method using microwave-millimeter wave electromagnetic waves, dielectric spectroscopy has been proposed as disclosed in Patent Document 1. In dielectric spectroscopy, electromagnetic waves are irradiated into the skin of a human or animal, and the electromagnetic waves are absorbed according to the interaction between the blood components to be measured, for example, glucose molecules and water, and the amplitude and phase of the electromagnetic waves are observed. A dielectric relaxation spectrum is calculated from the amplitude and phase of the observed electromagnetic waves relative to the frequency. The dielectric relaxation spectrum is generally expressed as a linear combination of relaxation curves based on the Cole-Cole equation, and a complex dielectric constant is calculated.

[0006] The complex dielectric constant correlates with the amount of blood components such as glucose and cholesterol contained in blood. A calibration model can be constructed by measuring the correlation between the change in complex dielectric constant and the component concentration in advance, and the component concentration can be calibrated based on the change in the measured dielectric relaxation spectrum. Regardless of which method is used, it is expected that the measurement sensitivity will be improved by selecting a frequency band that is highly correlated with the target component, so it is necessary to measure the change in dielectric constant in advance using broadband dielectric spectroscopy.

[0007] Among dielectric spectroscopy, the method using a coaxial probe (open-ended coaxial probe or open-ended coaxial line) as shown in Non-Patent Documents 2, 3 and Patent Document 2 can use easily available samples such as water to calibrate the measuring instrument. In addition, it is possible to measure the dielectric constant of the sample by contacting the sample to be measured with the probe end without requiring special processing of the material. For this reason, it is suitable for measuring samples such as living organisms, fruits, and soil, whose electrical properties are to be evaluated without processing them. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2013-32933 A [Patent Document 2] Patent No. 6771372 [Non-patent literature]

[0009] [Non-Patent Document 1] M. Hofmann, G. Fischer, R. Weigel, and D. Kissinger, “Microwave-Based Noninvasive Concentration Measurements for Biomedical Applications”, IEEE Trans. Microwave Theory and Techniques, Vol.61, No.5, pp. 2195-2203,2013 [Non-Patent Document 2] J P. Grant, R N. Clarke, G T. SYymm and N M. Spyrou, “A critical study of the open-ended coaxial line sensor technique for RF and microwave complex permittivity measurements”, J. Phys.E: Sci. Instrum,Vol.22, pp. 757-770,1989 [Non-Patent Document 3] TP Marsland, and S. Evans“Dielectric measurements with an open-ended coaxial probe”, IEE Proceedings, Vol. 134, No.4,1987 Summary of the Invention [Problem to be solved by the invention]

[0010] However, when measuring the dielectric constant using a transmission line such as a coaxial sensor, it is necessary to match the characteristic impedance between the transmission line and the dielectric spectroscopy system to which the transmission line is connected in order to reduce loss due to reflection. For example, if the characteristic impedance of the dielectric spectroscopy system is 50 Ω, it is necessary to set the wire structure of the transmission line so that the characteristic impedance of the transmission line is 50 Ω. This causes a problem in that the measurement sensitivity of the reflected wave by the dielectric spectroscopy sensor is limited.

[0011] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a dielectric spectroscopic sensor capable of improving measurement sensitivity. [Means for solving the problem]

[0012] A dielectric spectroscopy sensor of one embodiment of the present invention is a dielectric spectroscopy sensor connected to a dielectric spectroscopy system having a first characteristic impedance, and has a transmission line having a first end which has the first characteristic impedance and a second end which has a second characteristic impedance different from the first characteristic impedance, the first end being connected to the dielectric spectroscopy system and the second end being a measurement surface for measuring the dielectric constant of a measurement object. Effect of the Invention

[0013] According to the present invention, it is possible to improve the measurement sensitivity. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a block diagram showing the configuration of a dielectric spectroscopy sensor according to a first embodiment of the present invention and its peripheral devices. [Figure 2A] FIG. 2A is an explanatory diagram showing the configuration of a connecting line and an impedance transforming portion. [Figure 2B] FIG. 2B is a cross-sectional view of the connecting line and the impedance transforming portion. [Diagram 3] FIG. 3 is a graph showing the amount of change in the S11 parameter or admittance on the complex plane when the dielectric constant changes from "εs" to "εs+Δεs." [Figure 4] FIG. 4 is a graph showing the relationship between the frequency of the signal applied to the measurement surface and the measurement sensitivity. [Diagram 5] FIG. 5 is a graph showing another relationship between the frequency of the signal applied to the measurement surface and the measurement sensitivity. [Figure 6] FIG. 6 is a cross-sectional view showing another configuration of the impedance transforming portion. [Figure 7]FIG. 7 is a block diagram showing the configuration of the dielectric spectroscopy sensor according to the second and third embodiments of the present invention and its peripheral devices. [Figure 8A] FIG. 8A is an explanatory diagram showing the configuration of a transmission line according to the second embodiment. [Figure 8B] FIG. 8B is a cross-sectional view of the transmission line shown in FIG. 8A. [Figure 9A] FIG. 9A is a perspective view showing the configuration of the measurement surface side of the dielectric spectroscopy sensor according to the third embodiment. [Figure 9B] FIG. 9B is a perspective view showing the configuration of the line pattern side of the dielectric spectroscopy sensor according to the third embodiment. [Figure 10] FIG. 10 is a graph showing the relationship between frequency and characteristic impedance. [Figure 11] FIG. 11 is an explanatory diagram showing a metal pattern provided in the dielectric spectroscopy sensor according to the third embodiment. [Figure 12] FIG. 12 is an explanatory diagram showing a modified example of the metal pattern provided in the dielectric spectroscopy sensor according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Description of the First Embodiment] Fig. 1 is a block diagram showing the configuration of a dielectric spectroscopy sensor according to a first embodiment of the present invention and its peripheral devices. As shown in Fig. 1, a dielectric spectroscopy sensor 100 according to this embodiment is connected to a dielectric spectroscopy system 20 and receives a radio frequency (RF) signal output from the dielectric spectroscopy system 20. The dielectric spectroscopy sensor 100 outputs an electromagnetic wave toward a measurement object M, receives a reflected wave thereof, and transmits it to the dielectric spectroscopy system 20. The measurement object M is, for example, human skin, an animal, fruit, soil, etc. The dielectric spectroscopy system 20 may be, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor), a memory, a storage (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device, an input device, and an output device.

[0016] The dielectric spectroscopy sensor 100 includes a connection line 11, an impedance converter 12, and a measurement surface 13. The connection line 11 and the impedance converter 12 form a transmission line .

[0017] FIG. 2A is an explanatory diagram of the connecting line 11 and the impedance transforming portion 12, and FIG. 2B is a cross-sectional view of the connecting line 11 and the impedance transforming portion 12 cut along the longitudinal direction.

[0018] As shown in FIG. 2A, the connecting line 11 and the impedance transforming section 12 have a long coaxial cable structure, one end of which is the measurement surface 13 and the other end of which is connected to a high-frequency connector 11a.

[0019] The high-frequency connector 11a is a connector for electrically connecting to the dielectric spectroscopy system 20 shown in Fig. 1. As the high-frequency connector 11a, for example, an SMA connector, a K connector, a 2.4 mm connector, a V connector, an SMP connector, an SMPM connector, a G3PO connector, or the like can be used.

[0020] The measurement surface 13 is a surface that is brought into direct or indirect contact with or close to a measurement target M, such as human skin, during component measurement. The component to be measured is, for example, the blood glucose level of a subject.

[0021] 2A and 2B, the connecting line 11 includes an inner conductor 23, a dielectric 22 formed concentrically around the inner conductor 23, and an outer conductor 21 formed concentrically around the dielectric 22. The inner conductor 23 has a constant diameter. That is, the connecting line 11 is formed in a coaxial cable structure having the inner conductor 23 and the outer conductor 21 with constant diameters.

[0022] The impedance transformation unit 12 includes an inner conductor 33, a dielectric 32 concentrically formed around the inner conductor 33, and an outer conductor 31 concentrically formed around the dielectric 32. That is, the impedance transformation unit 12 is formed in a coaxial cable structure. The diameter of the inner conductor 33 gradually changes. Specifically, the inner conductor 33 has the same diameter as the inner conductor 23 at the connection end with the connecting line 11, and is configured so that the diameter gradually decreases toward the measurement surface 13, which is the lower end surface.

[0023] The diameter of the inner conductor 23 of the connecting line 11 is set so as to match the characteristic impedance (first characteristic impedance) of the connection end of the dielectric spectroscopy system 20 shown in Fig. 1. That is, the end (first end) of the transmission line 14 on the dielectric spectroscopy system 20 side is set to have the first characteristic impedance. Therefore, when the high-frequency connector 11a is connected to the dielectric spectroscopy system 20, the characteristic impedance is matched between the dielectric spectroscopy system 20 and the dielectric spectroscopy sensor 100. The connecting line 11 may be a coaxial cable such as a semi-rigid or soft-rigid cable.

[0024] The characteristic impedance of the impedance transforming unit 12 at the connection end on the connecting line 11 side is a first characteristic impedance that is the same as that of the connecting line 11. The characteristic impedance of the measurement surface 13, which is the lower end surface of the impedance transforming unit 12, changes because the diameter of the internal conductor 33 is smaller than the diameter of the internal conductor 23 of the connecting line 11. That is, the impedance transforming unit 12 can change the first characteristic impedance to a second characteristic impedance different from the first characteristic impedance by changing the diameter of the internal conductor 33.

[0025] That is, the transmission line 14 is formed by connecting the connecting line 11 and the impedance transformation part 12, and the connecting line 11 has a characteristic impedance of a first characteristic impedance, and one end is a first end and the other end is connected to the impedance transformation part 12. The impedance transformation part 12 has one end with the first characteristic impedance and connected to the other end of the connecting line 11, and the other end with a second characteristic impedance different from the first characteristic impedance and is the second end.

[0026] Furthermore, the impedance transformation unit 12 has a coaxial cable structure having an inner conductor 33 and an outer conductor 31 disposed outside the inner conductor 33 via a dielectric 32, and the cross-sectional area of ​​the inner conductor 33 is monotonically increased or decreased from the end connected to the connecting line 11 toward the second end, thereby making one end of the impedance transformation unit 12 a first characteristic impedance and the second end a second characteristic impedance. The conversion of the characteristic impedance will be described in detail below.

[0027] If the characteristic impedance of the coaxial cable that forms the impedance transforming portion 12 is "Zcoax", Zcoax can be expressed by the following formula (1).

[0028]

number

[0029] In formula (1), "εc" is the dielectric constant of the dielectric 32, "D" is the inner diameter of the outer conductor 31, and "d" is the outer diameter of the inner conductor 33. "log" indicates the natural logarithm. Since the inner diameter D of the outer conductor 31 of the impedance transforming unit 12 and the dielectric constant εc of the dielectric 32 are constant, the characteristic impedance at the measurement surface 13 can be set to a desired characteristic impedance by changing the inner diameter d of the inner conductor 33.

[0030] Moreover, a formula other than the above for calculating the characteristic impedance of the transmission line may be used, and the conversion efficiency of the characteristic impedance may be calculated using an electromagnetic field simulator or the like.

[0031] Next, a procedure for setting the characteristic impedance of the measurement surface 13 to an optimal value in order to increase the sensitivity of the dielectric spectroscopic sensor 100 will be described.

[0032] First, the dielectric constant εs of the measurement object M is measured using the dielectric spectroscopic sensor 100 according to the embodiment. If the admittance of the measurement surface 13 of the dielectric spectroscopic sensor 100 is Y(εs), Y(εs) can be expressed by the following formula (2).

[0033]

number

[0034] In equation (2), “εc” is the dielectric constant of the dielectric 32, “k0” is the wave number at the measurement frequency, “εs” is the dielectric constant of the object to be measured M, “γ(εs)” is the propagation constant inside the object to be measured M, “J0(x)” is the zeroth-order Bessel function, “a” is the radius of the inner conductor 33, “b” is the radius of the outer conductor 31, and “ζ” is a weighting factor of the Hankel transformation.

[0035] The reflection coefficient S11 (hereinafter, sometimes referred to as the S11 parameter) can be measured by outputting a radio frequency (RF) signal and receiving a reflected wave from the dielectric spectroscopy system 20 shown in Fig. 1. The dielectric spectroscopy system 20 includes a radio frequency signal oscillator, a receiver, and a calculator (all of which are omitted in the figures).

[0036] The dielectric spectroscopy system 20 may be, for example, a high-frequency measuring instrument such as a vector network analyzer or a spectrum analyzer, or a reflection measurement system using a microwave IC. The dielectric spectroscopy system 20 is set to have a characteristic impedance of 50Ω at the connection, for example. The S11 parameter measured by the dielectric spectroscopy system 20 is expressed by the following formula (3).

[0037]

number

[0038] The sensitivity of the dielectric spectroscopy sensor 100 is determined by a change in the S11 parameter with respect to a change in the dielectric constant εs of the measurement object M. That is, the sensitivity is determined by the following formula (4).

[0039]

number

[0040] As can be seen from the above-mentioned formula (3), the S11 parameter of the dielectric spectroscopy sensor 100 is determined by the amount of admittance change, so the following formula (5) may be used instead of formula (4).

[0041]

number

[0042] The right side of equation (4) contains "S11(εs)," and the right side of equation (5) contains "Y(εs)." Note that "S11(εs)" and "Y(εs)" are both complex numbers.

[0043] Both equation (4) and equation (5) include the above-mentioned equation (2). In addition, the right side of equation (2) includes a logarithmic function "log(b / a)" and Bessel functions "J_0(ζa), J_0(ζb)". Therefore, by appropriately changing the values ​​of the radius "a" of the internal conductor 33 and the radius "b" of the external conductor 31 included in the impedance conversion unit 12, the sensitivity of the dielectric spectroscopy sensor 100 can be set to be high.

[0044] For example, when the impedance conversion unit 12 is not used, the characteristic impedance of the dielectric spectroscopy sensor 100 must be matched to the first characteristic impedance, and is therefore limited to, for example, 50 Ω. However, by using the impedance conversion unit 12, the characteristic impedance of the dielectric spectroscopy sensor 100 can be changed to a second characteristic impedance different from the first characteristic impedance. This makes it possible to design a highly sensitive dielectric spectroscopy sensor 100.

[0045] In addition, when the measurement target M is a low-loss material such as resin or a high-frequency substrate, the change in the real part of the dielectric constant εs is dominant over the imaginary part. Therefore, the sensitivity may be evaluated using either the amplitude or phase when the above formula (4) is expressed in feather notation, or either the real part or the imaginary part of formula (5).

[0046] When the object to be measured M has frequency dispersion and dielectric loss cannot be ignored, such as in the case of liquids containing water, organic solvents, and other biological components, the dielectric constant εs becomes a complex number, and the frequency dependence of the change in the real part and the imaginary part have different characteristics.

[0047] In this case, the change in the S11 parameter or the admittance on the complex plane when the dielectric constant changes from "εs" to "εs + Δεs" can be treated as the sensitivity, as shown in Figure 3. That is, the above-mentioned formulas (4) and (5) can be rewritten as the following formulas (6) and (7), respectively.

[0048]

number

[0049]

number

[0050] Using the above equations (6) and (7), the characteristic impedance of the dielectric spectroscopic sensor 100 can be designed to maximize the sensitivity at a desired frequency, for example, in the "3 to 10 GHz" band when the measurement target is glucose molecules.

[0051] 4 is a graph showing the relationship between the frequency of the voltage applied between the inner conductor 33 and the outer conductor 31 on the measurement surface 13 and the sensitivity. The inner diameter of the outer conductor 31 is 3 mm, the dielectric constant of the dielectric 32 is 3.3, and the dielectric constant εs of the measurement object M is the dielectric constant of air.

[0052] 4, when the characteristic impedance is changed from 50Ω to 75Ω by changing the diameter of the internal conductor 33, the sensitivity is reduced. Also, when the characteristic impedance is changed from 50Ω to 25Ω, the sensitivity is increased. That is, by using the impedance conversion unit 12 to convert the characteristic impedance from 50Ω (first characteristic impedance) to 25Ω (second characteristic impedance), the measurement sensitivity of the dielectric spectroscopy sensor 100 can be increased.

[0053] 5 is a graph showing another example of the relationship between the sensitivity and the frequency of the voltage applied between the inner conductor 33 and the outer conductor 31 on the measurement surface 13. The inner diameter of the outer conductor 31 is 3 mm, the dielectric constant of the dielectric 32 is 2.1, and the dielectric constant εs of the measurement object M is the dielectric constant of pure water.

[0054] As shown in FIG. 5, the sensitivity has a peak value in the GHz band, and for example, the peak frequency when the characteristic impedance is set to 75 Ω is different from the peak frequency when the characteristic impedance is set to 150 Ω.

[0055] Therefore, the peak frequency can be shifted by changing the characteristic impedance, which makes it possible to design the sensor to have high sensitivity in a frequency band where the change in the desired component is significant, for example, in the 5 to 10 GHz band.

[0056] Since the characteristic impedance of the end face of a conventional coaxial sensor is, for example, 50Ω, the dielectric spectroscopic sensor 100 of the present embodiment can measure the dielectric constant with higher accuracy than the conventional sensor. In particular, the sensitivity can be improved significantly for materials including dielectric loss such as biological samples.

[0057] [Modification of impedance conversion section] Next, a modified example of the impedance conversion unit will be described. Fig. 6 is an explanatory diagram showing a modified example of the impedance conversion unit. As shown in Fig. 6, an impedance conversion unit 12a according to the modified example has an inner conductor 43, a dielectric 42, and an outer conductor 41 formed coaxially, similar to the first embodiment described above.

[0058] The diameter of the internal conductor 43 changes stepwise (three steps in FIG. 6). That is, in the first embodiment, the diameter of the internal conductor 33 changes continuously, whereas in the impedance conversion section 12a according to the modified example, the diameter of the internal conductor 43 changes stepwise. Even in such a configuration, the first end can have a first characteristic impedance and the second end can have a second characteristic impedance, as in the first embodiment described above.

[0059] That is, the impedance transformation unit 12a has a coaxial cable structure having an inner conductor 43 and an outer conductor 41 arranged outside the inner conductor 43 via a dielectric 42, and by gradually changing the cross-sectional area of ​​the inner conductor 43 from the end connected to the connecting line 11 toward the second end, one end of the impedance transformation unit 12 has a first characteristic impedance and the second end has a second characteristic impedance.

[0060] Thus, the dielectric spectroscopy sensor 100 of this embodiment is a dielectric spectroscopy sensor 100 connected to a dielectric spectroscopy system 20 having a first characteristic impedance, and has a transmission line 14 whose first end has a first characteristic impedance and whose second end has a second characteristic impedance different from the first characteristic impedance, with the first end connected to the dielectric spectroscopy system 20 and the second end serving as a measurement surface 13 for measuring the dielectric constant of a measurement object.

[0061] In the dielectric spectroscopy sensor 100 of this embodiment, one end of the impedance conversion unit 12 has a first characteristic impedance and the other end has a second characteristic impedance, so that the characteristic impedance can be matched between the impedance conversion unit 12 and the connecting line 11.

[0062] In addition, the characteristic impedance can be matched at the connection between the connecting line 11 and the dielectric spectroscopy system 20. This reduces the reflection loss at the connection between the transmission line 14 and the dielectric spectroscopy system 20. In addition, the characteristic impedance at the measurement surface 13 can be set arbitrarily, thereby improving the sensitivity of the dielectric spectroscopy sensor 100.

[0063] In the dielectric spectroscopic sensor 100 according to the first embodiment, it is possible to improve the accuracy of the calibration curve when quantitatively measuring a desired component by improving the sensitivity of the dielectric spectroscopic sensor 100. Furthermore, it is possible to lower the detection limit.

[0064] In the dielectric spectroscopy sensor 100 of the first embodiment, the transmission line 14 is formed by connecting the impedance conversion section 12 to the connecting line 11, so that it is possible to retrofit the impedance conversion section 12 to an existing connecting line 11, thereby improving versatility.

[0065] [Description of the Second Embodiment] Next, a second embodiment of the present invention will be described. In the above-described first embodiment, an example has been described in which the transmission line 14 includes the connection line 11 and the impedance transformation section 12. The second embodiment differs from the above-described first embodiment in that the transmission line 14 has a function of transforming impedance.

[0066] 7 is a block diagram showing the configuration of a dielectric spectroscopy sensor according to the second embodiment and its peripheral devices. As shown in Fig. 7, the dielectric spectroscopy sensor 101 according to the second embodiment is connected to a dielectric spectroscopy system 20 in the same manner as in the first embodiment, and receives a radio frequency (RF) signal output from the dielectric spectroscopy system 20. The dielectric spectroscopy sensor 101 also outputs an electromagnetic wave toward a measurement object M, receives the reflected wave, and transmits it to the dielectric spectroscopy system 20.

[0067] The dielectric spectroscopy sensor 101 includes a transmission line 14 and a measurement surface 13. Fig. 8A is an explanatory diagram of the transmission line 14, and Fig. 8B is a cross-sectional view of the transmission line 14 cut along the longitudinal direction.

[0068] 8A, the transmission line 14 has a long coaxial cable structure, one end of which is the measurement surface 13, and the other end of which is connected to a high-frequency connector 14a. The high-frequency connector 14a is a connector for connecting to a dielectric spectroscopy system 20. The measurement surface 13 is a surface that is brought into direct or indirect contact with or close to a measurement target M, such as human skin, during component measurement.

[0069] The transmission line 14 includes an inner conductor 23, a dielectric 22 concentrically formed around the inner conductor 23, and an outer conductor 21 concentrically formed around the dielectric 22. That is, the transmission line 14 has a coaxial cable structure. The inner conductor 23 has a gradually changing diameter. Specifically, the diameter gradually decreases from the connection end (first end) with the high-frequency connector 14a toward the measurement surface 13 (second end).

[0070] 8B, the connection end (first end) of the transmission line 14 on the high-frequency connector 14a side has a first characteristic impedance. That is, the diameter of the inner conductor 23 of the end of the transmission line 14 on the high-frequency connector 14a side is set so as to match the characteristic impedance of the connection end of the dielectric spectroscopy system 20. When the high-frequency connector 14a is connected to the dielectric spectroscopy system 20, the characteristic impedance is matched between the dielectric spectroscopy system 20 and the dielectric spectroscopy sensor 100.

[0071] The characteristic impedance of the measurement surface 13, which is the lower end surface of the transmission line 14, changes because the diameter of the internal conductor 33 is smaller than the diameter of the internal conductor 23 of the connecting line 11. That is, by changing the diameter of the internal conductor 23, the transmission line 14 can change the first characteristic impedance to a second characteristic impedance different from the first characteristic impedance.

[0072] As with the first embodiment described above, in the second embodiment shown in Figures 8A and 8B, by adjusting the diameter of the internal conductor 23 of the transmission line 14, the characteristic impedance at the measurement surface 13 can be made a second characteristic impedance different from the first characteristic impedance, thereby improving the sensitivity of the dielectric spectroscopy sensor 101.

[0073] [Description of the Third Embodiment] Next, a third embodiment of the present invention will be described. In the third embodiment, a printed wiring board is used as the transmission line 14 shown in FIG.

[0074] 9A and 9B are perspective views showing a configuration of a dielectric spectroscopy sensor 102 according to a third embodiment. The dielectric spectroscopy sensor 102 shown in Fig. 9A and 9B has a structure in which a first substrate 61 and a second substrate 71, which are dielectric substrates, are laminated.

[0075] Fig. 9A is a perspective view when the first substrate 61 having a surface in contact with the measurement target M is placed on top. Fig. 9B is a perspective view when the second substrate 71 having a line surface on which lines are formed is placed on top. That is, when the dielectric spectroscopy sensor 102 in Fig. 9A is turned over, it becomes as shown in Fig. 9B.

[0076] 9A, a metal pattern 62 having a circular opening 65 is provided on the surface of a first substrate 61. The opening 65 is a region where no metal pattern is present, and is, for example, a dielectric surface.

[0077] A via 63 penetrating the first substrate 61 is provided in the center of the opening 65. In addition, a plurality of vias 64 (eight in the figure) electrically connected to the metal pattern 62 are provided along the circumference of the opening 65. That is, the dielectric spectroscopy sensor 102 according to the third embodiment forms a quasi-coaxial structure by providing a plurality of vias 64 in a circular shape around the via 63. The vias 63 and 64 are filled with a conductor. The via 63 and the plurality of vias 64 formed around it form the measurement surface 13 (see FIG. 7) that comes into contact with the measurement object M.

[0078] 9B, metal patterns 72 and 73 constituting a coplanar line are provided on the surface of second substrate 71. Metal pattern 72 (first conductor) serves as a signal line of the coplanar line, and metal pattern 73 serves as a ground line (second conductor) insulated from metal pattern 72.

[0079] That is, the transmission line 14 has a substrate 61, 71, a first conductor (metal pattern 72) formed from one end side to the other end side of the substrate surface, and a second conductor (metal pattern 73) insulated from the first conductor, and the characteristic impedance of one end side of the first conductor is set to the first characteristic impedance, and the characteristic impedance of the other end side is set to the second characteristic impedance.

[0080] 11 is an explanatory diagram showing a schematic configuration of metal pattern 72, in which metal pattern 72 serving as a signal line is formed on the front surface of dielectric 76, and metal pattern 62 connected to metal pattern 73 serving as a ground line is formed on the rear surface of dielectric 76. Metal patterns 72 and 73 shown in FIG. 9B correspond to transmission line 14 shown in FIG. 8. As the metal pattern, in addition to a coplanar line, a microstrip line, a coplanar line, a coplanar strip, or other transmission lines on a printed circuit board or a semiconductor substrate can be used.

[0081] A via 74 and a plurality of vias 75 are provided on a second substrate 71 shown in Fig. 9B in positions corresponding to the positions of the vias 63 and 64 shown in Fig. 9A. The via 74 is electrically connected to the via 63 and the metal pattern 72. The via 75 is electrically connected to the via 64 and the metal pattern 73.

[0082] 9B, the line width of the metal pattern 72 is configured so that the pattern width becomes wider in stages from one end 72a to the other end 72b. The end 72a of the metal pattern 72 is a first end connected to the dielectric spectroscopy system 20 shown in FIG. 8, and the end 72b is a second end connected to the measurement surface 13.

[0083] The characteristic impedance at the end 72a (first end) of the metal pattern 72 is set to match the first characteristic impedance of the dielectric spectroscopy system 20. Therefore, when the end 72a of the metal pattern 72 is connected to the dielectric spectroscopy system 20, the characteristic impedances are matched.

[0084] Since the line width of the metal pattern 72 changes from the end 72a to the end 72b, the characteristic impedance of the second end is a second characteristic impedance different from the first characteristic impedance. That is, by adjusting the line width of the metal pattern 72, the second characteristic impedance on the measurement surface 13 of the dielectric spectroscopy sensor 102 can be set to a desired value.

[0085] In addition, by monotonically increasing or decreasing the line width of the first conductor from one end side to the other end side of the substrate surface, the one end side of the first conductor is made a first characteristic impedance, and the other end side of the first conductor is made a second characteristic impedance.

[0086] 9A and 9B show an example in which the line width of the metal pattern 72 changes stepwise, but as shown in FIG. 12, a metal pattern 72A in which the line width changes in a tapered shape may also be used.

[0087] In the example shown in FIG. 12, the line width of the first conductor (metal pattern 72A) is changed in stages from one end to the other end of the substrate, so that one end of the first conductor has a first characteristic impedance and the other end of the first conductor has a second characteristic impedance.

[0088] If the characteristic impedance of the dielectric spectroscopy sensor 102 having the substrate structure shown in FIGS. 9A and 9B is ZMSL, the characteristic impedance ZMSL can be expressed by the following equation (8).

[0089]

number

[0090] In equation (8), “εsub” is the dielectric constant of the dielectric material mounted on the first substrate 61 and the second substrate 71, “h” is the thickness of the dielectric substrate, i.e., the thickness of the laminate of the first substrate 61 and the second substrate 71, and “W” is the line width of the metal pattern 72.

[0091] Then, as shown in the above-mentioned formulas (3) to (7), by setting the admittance that maximizes the sensitivity, a highly sensitive substrate-type dielectric spectroscopic sensor 102 can be formed.

[0092] As an example, when a microstrip line made with a pattern of wiring thickness 40 μm is used as an impedance conversion layer on a PCB board with a board thickness of 200 μm and a board dielectric constant of 3.55, the characteristic impedance can be converted from approximately 50 Ω to 75 Ω by reducing the line width from 400 μm to 150 μm.

[0093] 10 is a graph showing the relationship between frequency and characteristic impedance, where graph q1 shows the characteristic impedance at end 72b of metal pattern 72, and graph q2 shows the characteristic impedance at end 72a of metal pattern 72. As can be seen from graphs q1 and q2, regardless of changes in frequency, the characteristic impedance of end 72a is approximately 50Ω, and the characteristic impedance of end 72b is approximately 75Ω.

[0094] By changing the line width of the metal pattern 72, it is possible to match the characteristic impedance of the connection part between the transmission line 14 and the dielectric spectroscopy system 20, and thus to reduce the reflection loss. Note that a formula for calculating the characteristic impedance of the transmission line other than the above may be used, and the conversion efficiency of the characteristic impedance may be calculated using an electromagnetic field simulator or the like.

[0095] In the dielectric spectroscopy sensor 102 according to the third embodiment, as in the first and second embodiments, one end (first end) of the transmission line 14 has a first characteristic impedance and the other end (second end) has a second characteristic impedance, so that the characteristic impedance can be matched with the dielectric spectroscopy system 20. This makes it possible to reduce reflection loss at the connection. In addition, since the characteristic impedance at the measurement surface 13 can be set arbitrarily, it becomes possible to improve the sensitivity of the dielectric spectroscopy sensor 100.

[0096] The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the present invention. [Explanation of symbols]

[0097] 11 Connecting lines 11a high frequency connector 12, 12a Impedance conversion section 13 Measurement Surface 14 Transmission Lines 14a high frequency connector 20 Dielectric Spectroscopy System 21, 31, 41 Outer conductor 22, 32, 42 Dielectric 23, 33, 43 Inner conductor 61 First board 71 Second board 72, 72A Metal pattern (first conductor) 73 Metal pattern (second conductor) 100, 101, 102 Dielectric spectroscopy sensor M Measurement object

Claims

1. 1. A dielectric spectroscopy sensor for connection to a dielectric spectroscopy system having a first characteristic impedance, comprising: a transmission line having a first end portion set to the first characteristic impedance and a second end portion set to a second characteristic impedance different from the first characteristic impedance; the transmission line includes a connection line and an impedance transformation section, the connecting line has a characteristic impedance that is the first characteristic impedance, one end of the connecting line is connected to the first end portion, and the other end of the connecting line is connected to the impedance transforming portion, the impedance transforming section has one end which is the first characteristic impedance and is connected to the other end of the connecting line, and has the other end which is the second characteristic impedance and is the second end; The first end is connected to the dielectric spectroscopy system, and the second end is a measurement surface for measuring the dielectric constant of a measurement object. Dielectric spectroscopy sensor.

2. The impedance conversion unit is A coaxial cable structure having an inner conductor and an outer conductor disposed outside the inner conductor via a dielectric, The cross-sectional area of ​​the internal conductor is monotonically increased or decreased from the end connected to the connecting line toward the second end, thereby making one end of the impedance transforming section a first characteristic impedance and the second end a second characteristic impedance. The dielectric spectroscopy sensor of claim 1 .

3. The impedance conversion unit is A coaxial cable structure having an inner conductor and an outer conductor disposed outside the inner conductor via a dielectric, The cross-sectional area of ​​the internal conductor is changed stepwise from the end connected to the connecting line toward the second end, so that one end of the impedance transforming section has a first characteristic impedance and the second end has a second characteristic impedance. The dielectric spectroscopy sensor of claim 1 .

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