Dielectric constant measurement method, dielectric constant measurement system, and dielectric constant measurement program

Abstract

This dielectric constant measurement method comprises: a step for obtaining an admittance of a calibration standard (P1) having a known dielectric constant; a step for measuring a first reflection coefficient; a step for calculating an open-state reflection coefficient of a dielectric spectral sensor (1) in an ideal open state on the basis of the first reflection coefficient and the admittance of the calibration standard (P1) obtained when the calibration standard (P1) is placed on a measurement end surface; a step for calculating a reflection coefficient of a calibration standard other than the first calibration standard on the basis of the open-state reflection coefficient and an admittance of the calibration standard other than the first calibration standard; a step for measuring a reflection coefficient of an object of interest; and a step for calculating a dielectric constant of the object of interest on the basis of the first reflection coefficient, the reflection coefficient of the calibration standard other than the first calibration standard, the reflection coefficient of the object of interest, the admittance of the first calibration standard, and the admittance of the calibration standard other than the first calibration standard.

Description

[Technical Field]

[0001] The present invention relates to a dielectric constant measurement method, a dielectric constant measurement system, and a dielectric constant measurement program. [Background technology]

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

[0003] Non-Patent Document 1 discloses that a measurement sample is brought into contact with a device with a high Q value, such as an antenna or a resonator, to measure the frequency characteristics around the resonance frequency, and the component concentration is estimated based on the amount of shift in the resonance frequency. Patent Document 1 also discloses that the complex dielectric constant is calculated by dielectric spectroscopy to measure the component concentration.

[0004] Furthermore, Non-Patent Documents 2 and 3 and Patent Document 2 disclose measuring the dielectric constant of a sample to be measured by bringing the sample into contact with the end face of a coaxial probe. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-32933 [Patent Document 2] Patent No. 6771372 [Non-patent literature]

[0006] [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]

[0007] The measurement of dielectric constant using a coaxial probe relies on the S11 parameter of a pre-measured calibration standard, and typically the S11 parameters of air, a metal plate used to short the probe, and water must be measured in advance.

[0008] However, when measuring the S11 parameter of a calibration standard using a metal plate, the coaxial probe face must be brought into precise contact with the metal plate, which requires the operator to have high technical skills or to use a measurement jig during the measurement.

[0009] Furthermore, when measuring the S11 parameter of a calibration standard using a liquid sample, it is necessary to install a temperature sensor or the like to accurately measure the temperature of the liquid, which poses the problem of increasing the size of the measurement device.

[0010] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a dielectric constant measurement method, a dielectric constant measurement system, and a dielectric constant measurement program that can easily measure the dielectric constant of an object. [Means for solving the problem]

[0011] A dielectric constant measurement method according to one aspect of the present invention is a dielectric constant measurement method for measuring the dielectric constant of an object using a dielectric spectroscopy sensor, and includes the steps of: acquiring the admittance of a first calibration standard having a known dielectric constant; measuring a first reflection coefficient of the first calibration standard; calculating an open reflection coefficient in an ideal open state of the dielectric spectroscopy sensor based on the first reflection coefficient and the admittance of the first calibration standard when the first calibration standard is installed on the measurement end face of the dielectric spectroscopy sensor; calculating a reflection coefficient of another calibration standard based on the open reflection coefficient and the admittance of the other calibration standard other than the first calibration standard; measuring the reflection coefficient of the object; and calculating the dielectric constant of the object based on the first reflection coefficient, the reflection coefficient of the other calibration standard, the reflection coefficient of the object, the admittance of the first calibration standard, and the admittance of the other calibration standard.

[0012] Another aspect of the dielectric constant measurement method of the present invention is a dielectric constant measurement method for measuring the dielectric constant of an object using a dielectric spectroscopy sensor, and includes the steps of: acquiring the admittance of a first calibration standard having a known dielectric constant; measuring a first reflection coefficient of the first calibration standard; generating a first admittance calculation formula for calculating the admittance from the dielectric constant based on the admittance of the first calibration standard and the dielectric constant; generating a second admittance calculation formula for calculating the admittance of the object based on the first reflection coefficient and the open reflection coefficient in the ideal open state of the dielectric spectroscopy sensor; and calculating the dielectric constant of the object based on the fact that the admittance calculated by the first admittance calculation formula and the admittance calculated by the second admittance calculation formula are equal.

[0013] A dielectric constant measurement system according to one embodiment of the present invention comprises a coaxial probe, a dielectric spectroscopy sensor having a measurement end face formed on the coaxial probe, and a measurement device connected to the dielectric spectroscopy sensor via a transmission line having the same characteristic impedance as the coaxial probe. The measurement device comprises a measurement unit that applies a predetermined voltage to the dielectric spectroscopy sensor and measures the reflection coefficient of an object to be measured based on the reflected signal, and a calculation unit that calculates an open-state reflection coefficient of the dielectric spectroscopy sensor in an ideal open state based on a first reflection coefficient of the first calibration standard and an admittance of the first calibration standard when the first calibration standard is installed on the measurement end face of the dielectric spectroscopy sensor, calculates a reflection coefficient of another calibration standard based on the open-state reflection coefficient and an admittance of the other calibration standard other than the first calibration standard, and calculates the dielectric constant of the object based on the first reflection coefficient, the reflection coefficient of the other calibration standard, the reflection coefficient of the object measured by the measurement unit, the admittance of the first calibration standard, and the admittance of the other calibration standard.

[0014] One aspect of the present invention is a dielectric constant measurement program for executing the dielectric constant measurement method according to any one of claims 1 to 5 by a computer. [Effects of the Invention]

[0015] According to the present invention, it is possible to simply measure the dielectric constant of an object. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a block diagram showing the configuration of a dielectric constant measurement system according to an embodiment. [Figure 2] FIG. 2 is an explanatory diagram showing how the dielectric constant of an object is measured by the dielectric constant measurement system. [Figure 3A] FIG. 3A is an explanatory diagram schematically illustrating the calibration of a transmission line and a dielectric spectroscopy sensor. [Figure 3B] FIG. 3B is an explanatory diagram showing a transmission line, a dielectric spectroscopy sensor, and a measurement object placed on the measurement end face of the dielectric spectroscopy sensor. [Figure 4] FIG. 4 is an equivalent circuit diagram of the transmission line and the dielectric spectroscopy sensor. [Figure 5A] FIG. 5A is an equivalent circuit diagram when the measurement end face of the dielectric spectroscopy sensor is in an ideal open state. [Figure 5B] FIG. 5B is an equivalent circuit diagram when the inner conductor and the outer conductor are short-circuited at the measurement end face of the dielectric spectroscopy sensor. [Figure 6] FIG. 6 is a flowchart showing the processing procedure of the dielectric constant measuring system according to the first embodiment. [Figure 7] FIG. 7 is an explanatory diagram showing how two calibration standards are measured by the dielectric constant measurement system. [Figure 8] FIG. 8 is a graph showing the S11 parameter calculated according to this embodiment and the amplitude of S11 obtained by actual measurement. [Figure 9] FIG. 9 is a graph showing the S11 parameter calculated by this embodiment and the phase of S11 obtained by actual measurement. [Figure 10] FIG. 10 is a graph showing the dielectric constant calculated by the present embodiment and the dielectric constant calculated by the conventional method. [Figure 11]FIG. 11 is a graph showing the error between the dielectric constant calculated by this embodiment and the dielectric constant calculated by the conventional method. [Figure 12] FIG. 12 is a flowchart showing the processing procedure of the dielectric constant measuring system according to the second embodiment. [Figure 13] FIG. 13 is a block diagram showing the hardware configuration of this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] [First embodiment] The first embodiment will be described below with reference to the drawings: Fig. 1 is a block diagram showing the configuration of a dielectric constant measurement system according to the first embodiment.

[0018] As shown in FIG. 1, the dielectric constant measurement system 100 includes a dielectric spectroscopic sensor 1, a measurement device 2, and a transmission line 3 that electrically connects the dielectric spectroscopic sensor 1 and the measurement device 2.

[0019] Fig. 3A is an explanatory diagram schematically illustrating the configuration of the dielectric spectroscopy sensor 1 and the transmission line 3. As shown in Fig. 3A, the dielectric spectroscopy sensor 1 includes a coaxial probe 10, a connector 14, and a fringe 15. Fig. 3A shows the coaxial probe 10 and the fringe 15 in cross-sectional views.

[0020] The coaxial probe 10 includes an inner conductor 11 and an outer conductor 12 formed around the inner conductor 11. An insulator 13 is inserted between the inner conductor 11 and the outer conductor 12.

[0021] Connector 14 connects one end of coaxial probe 10 to one end of transmission line 3. The other end of transmission line 3 is connected to measuring device 2 shown in Figure 1. The characteristic impedance of transmission line 3 is set to be equal to the characteristic impedance of coaxial probe 10. Note that "equal characteristic impedance" means that the characteristic impedances of both are not completely identical, but may also be slightly different.

[0022] The fringe 15 is connected to the other end of the coaxial probe 10. The fringe 15 is disk-shaped. The end face of the fringe 15 is a measurement end face N1 that comes into contact with any measurement object. Measurement objects include gases such as air, liquids such as water, and solids such as metals. Measurement objects include calibration standards, which will be described later, and objects whose dielectric constants are to be measured.

[0023] FIG. 4 is an explanatory diagram showing the equivalent circuit of the dielectric spectroscopy sensor 1 and the transmission line 3. In FIG. 4, "Z0tl" indicates the characteristic impedance of the transmission line 3, and "Z0coax" indicates the characteristic impedance of the coaxial probe 10. "Yprobe(ε)" indicates the normalized admittance of the object to be measured placed on the measurement end face N1. As mentioned above, the characteristic impedances of the transmission line 3 and the coaxial probe 10 are equal, so Z0tl = Z0coax.

[0024] Returning to FIG. 1, the measurement device 2 includes a measurement unit 21, a calculation unit 22, and a storage unit .

[0025] The measurement unit 21 outputs a predetermined voltage to the dielectric spectroscopy sensor 1. The measurement unit 21 receives a reflected signal output from the dielectric spectroscopy sensor 1. That is, when a predetermined voltage is applied between the inner conductor 11 and the outer conductor 12 with a measurement object placed on the measurement end face N1 of the dielectric spectroscopy sensor 1, a reflected signal is generated at the measurement end face N1. The measurement unit 21 receives the reflected signal generated at the measurement end face N1. The measurement unit 21 measures the reflection coefficient of the measurement object based on the received reflected signal.

[0026] That is, the measurement unit 21 applies a predetermined voltage to the dielectric spectroscopic sensor 1 and measures the reflection coefficient of the object based on the reflected signal. Note that, hereinafter, the "reflection coefficient" may also be referred to as the "S11 parameter."

[0027] The storage unit 23 stores various arithmetic expressions used in the calculations executed by the calculation unit 22. Specifically, the storage unit 23 stores an admittance calculation expression for calculating the admittance of one object to be measured based on the dielectric constant of the object to be measured. The admittance calculation expression is, for example, Equation (9) described later.

[0028] The storage unit 23 stores a reflection coefficient calculation formula that indicates the relationship between a first reflection coefficient ("S11_load" to be described later) when a measurement object is placed on the measurement end face, the admittance of the measurement object, and the open reflection coefficient in the ideal open state of the dielectric spectroscopy sensor 1. The reflection coefficient calculation formula is, for example, formula (17) to be described later in detail.

[0029] The calculation unit 22 calculates the dielectric constant of the object placed on the measurement end face N1 by performing a calculation described later based on the reflection coefficient, admittance, and dielectric constant of each object measured by the measurement unit 21. Hereinafter, the object whose dielectric constant is to be measured will be referred to as the "object."

[0030] Specifically, the calculation unit 22 executes the following operations: calculating the open-circuit reflection coefficient using a reflection coefficient calculation formula based on the admittance of the calibration standard P1, whose dielectric constant ε is known, and the first reflection coefficient of the calibration standard P1 measured by the measurement unit 21; and calculating the reflection coefficients of the other calibration standards using a reflection coefficient calculation formula based on the open-circuit reflection coefficient and the admittances of the other calibration standards other than the calibration standard P1. The calculation unit 22 calculates the dielectric constant of the object based on the reflection coefficient of the object, the first reflection coefficient, the reflection coefficients of the other calibration standards, the admittance of the first calibration standard, and the admittances of the other calibration standards.

[0031] Next, a procedure for calculating the dielectric constant of an object using the dielectric spectroscopic sensor 1 will be described. When calculating the dielectric constant of an object using the dielectric spectroscopic sensor 1, multiple calibration standards with known dielectric constants are prepared. As an example, calibration standards P1 to P3 are prepared as shown in FIG. 1, and the dielectric spectroscopic sensor 1 is used to measure the reflection coefficients ρ1 to ρ3 of the calibration standards P1 to P3. Furthermore, as shown in FIG. 2, the object P0 is placed on the measurement end face (N1 shown in FIG. 3A) of the dielectric spectroscopic sensor 1, and the reflection coefficient ρm of the object P0 is measured. The measuring device 2 calculates the dielectric constant εs of the object P0 based on the dielectric constants ε1 to ε3 and reflection coefficients ρ1 to ρ3 of the calibration standards P1 to P3 and the reflection coefficient ρm of the object P0. This will be described in detail below.

[0032] 3B is an explanatory diagram showing a state in which a measurement object such as a calibration standard P1 is placed on the measurement end face N1 of the dielectric spectroscopy sensor 1. With the calibration standard P1 placed on the measurement end face N1, the measurement unit 21 applies a voltage of a predetermined frequency between the inner conductor 11 and the outer conductor 12. The measurement unit 21 receives a reflected wave generated at the measurement end face N1 and calculates a reflection coefficient ρ1 of the calibration standard P1 based on this reflected wave.

[0033] By performing the above operation on the other two calibration standards P2 and P3 and the object P0, the reflection coefficients ρ1 to ρ3 of the calibration standards P1 to P3 and the reflection coefficient ρm of the object P0 are obtained.

[0034] The calculation unit 22 uses the reflection coefficients ρ1 to ρ3 and ρm to calculate the dielectric constant εs of the object P0 by the coaxial probe method using the following calculation formula.

[0035] If the admittances of the calibration standards P1 to P3 and the object P0 are y1, y2, y3, and ym, respectively, the following equations (1) and (2) hold.

[0036]

number

[0037]

number

[0038] In equation (1), the reflection coefficients "ρ1 to ρ3, ρm" are measured values. "y1, y2, y3, ym" are linear maps of admittances and are indicated with the same symbols as the admittances y1, y2, y3, ym. In equation (2), "G0" is the conductance of the coaxial probe 10 in a vacuum, and "C0" is the capacitance of the coaxial probe 10 in a vacuum.

[0039] Here, consider the case where one of the three calibration standards P1 to P3, calibration standard P3, is a metal. In the following, the admittance "y3" of calibration standard P3 will be represented as "ys" and the reflection coefficient "ρ3" will be represented as "ρs". Since the admittance ys is ∞, the above equations (1) and (2) can be transformed into the following equations (3), (4), and (5).

[0040]

number

[0041]

number

[0042]

number

[0043] By substituting equation (4) into equation (3), the following equation (6) is obtained.

[0044]

number

[0045] That is, by using the dielectric spectroscopic sensor 1 to measure the reflection coefficients ρ1, ρ2, ρs, and ρm of the three calibration standards P1 to P3 and the object P0, and then calculating the admittances y1, y2, ys, and ym and substituting them into the above equation (6), the dielectric constant εs of the object P0 can be calculated.

[0046] However, when measuring the reflection coefficients ρ1, ρ2, and ρs of the three calibration standards P1, P2, and P3, it is necessary to accurately contact the metal or other calibration standard with the measurement end face N1, as shown in Figure 3B. This requires the operator to have advanced technical skills, or a measurement jig is required. Furthermore, if the calibration standard is a liquid, it is necessary to use a temperature sensor in combination to accurately measure the temperature of the liquid.

[0047] In this embodiment, a single calibration standard P1 is used to calculate the dielectric constant εs of the object P0. Furthermore, by using air as the calibration standard P1, the effort required to accurately contact the calibration standard P1 with the measurement end face N1 is reduced. Below, a method for calculating the dielectric constant εs of the object P0 using a single calibration standard P1 (first calibration standard) will be described.

[0048] In the equivalent circuit shown in Fig. 4, when the transmission line 3 is a microstrip line, the characteristic impedance Z0tl can be expressed by the following equation (7). Also, when the transmission line 3 is a coaxial cable, the characteristic impedance Z0tl can be expressed by the following equation (8).

[0049]

number

[0050]

number

[0051] In equation (7), "εsub" is the substrate permittivity of the microstrip line, "h" is the thickness of the substrate, and "W" is the line width. In equation (8), "εc" is the permittivity of the inner dielectric of the coaxial cable that forms transmission line 3, "D" is the inner diameter of the outer conductor of the coaxial cable, and "d" is the outer diameter of the inner conductor of the coaxial cable.

[0052] 4 are constant values ​​because they are determined when the dielectric spectroscopy sensor 1 is manufactured. As described above, the characteristic impedances Z0tl and Z0coax have the same numerical value and are set to, for example, 50 Ω, 75 Ω, and 100 Ω.

[0053] If the normalized admittance at the measurement end face N1 is "Yprobe(εs)", the normalized admittance Yprobe(εs) is expressed by the following equation (9): That is, equation (9) is an admittance calculation equation.

[0054]

number

[0055] In equation (9), "εc" is the dielectric constant of the insulator 13 provided in the coaxial probe 10, "k0" is the wave number at the measurement frequency, "εs" is the dielectric constant of the object P0, "γ" is the propagation constant inside the object P0, "J0(x)" is the zeroth-order Bessel function, "a" is the outer radius of the inner conductor 11 of the coaxial probe 10, and "b" is the inner radius of the outer conductor 12. Also, in equation (9), "ζ" represents a weighting factor for the Hankel transform.

[0056] The calculation program of the above-mentioned formula (9) is stored in the storage unit 23 shown in Fig. 1. That is, the storage unit 23 stores formula (9), which is an admittance calculation formula for calculating the admittance of one object to be measured based on the dielectric constant of the object to be measured.

[0057] Although equation (9) represents an equation when the electromagnetic wave propagating through the dielectric spectroscopy sensor 1 is only in the TEM mode, the normalized admittance may be calculated taking into account any higher order mode.

[0058] The normalized admittance Yprobe(εs) shown in Fig. 4 varies depending on the dielectric constant εs of the object P0. If the connection part between the transmission line 3 and the dielectric spectroscopy sensor 1 shown in Fig. 4 is defined as the calibration end face N2, the S11 parameter indicating the reflection coefficient is expressed by the following equation (10).

[0059]

number

[0060] In equation (10), "Zsens" represents the impedance of the dielectric spectroscopy sensor 1 as seen from the calibration end face (N2 in Figure 4). Here, we consider an ideal open state in which there is no influence of radiation or leakage electric field from the measurement end face N1, and the electromagnetic wave is completely reflected from the measurement end face N1. In the ideal open state, the equivalent circuit is Yprobe(εs) = 0, as shown in Figure 5A.

[0061] In an ideal open state, it is difficult to measure the reflection coefficient (S11 parameter) with the dielectric spectroscopy sensor 1. However, it can be calculated by using the following equations (11) and (12). That is, assuming that the measurement end face N1 is in an ideal open state, the impedance Zsens of the dielectric spectroscopy sensor 1 can be expressed by the following equation (11).

[0062]

number

[0063] In equation (11), “coth” is the hyperbolic cotangent (the reciprocal of “tanh”). Also, “j” in “jβl” is the imaginary unit, “β” is the propagation constant of the coaxial probe 10, and “l” is the line length of the coaxial probe 10.

[0064] The above-mentioned equation (10) can be transformed into the following equation (12) using equation (11).

[0065]

number

[0066] Therefore, the S11 parameter "S11_Idealopen" at the ideal open state can be calculated using equation (12).

[0067] Next, consider the situation where the inner conductor 11 and outer conductor 12 of the coaxial probe 10 are shorted without the influence of radiation or leakage electric field from the measurement end face N1 of the dielectric spectroscopy sensor 1. In the shorted state, the equivalent circuit is Yprobe(εs) = ∞, as shown in Figure 5B. Note that the shorted state is considered to be equivalent to the case where a metal is selected as the calibration standard and the measurement end face N1 is shorted. In this case, the impedance of the dielectric spectroscopy sensor 1 is given by the following equation (13).

[0068]

number

[0069] The above equation (13) can be transformed into the following equation (14).

[0070]

number

[0071] As mentioned above, the characteristic impedance of the transmission line 3 and the characteristic impedance of the coaxial probe 10 are set to be the same. That is, assume that Z0tl = Z0coax in Figure 4. Therefore, equations (12) and (14) become the following equations (15) and (16), respectively.

[0072]

number

[0073]

number

[0074] If an arbitrary load (a load with a normalized admittance of Yprobe) is connected to the measurement end face N1 of the dielectric spectroscopy sensor 1, the above-mentioned equation (10) can be transformed into the following equation (17). Equation (17) is a reflection coefficient calculation equation. A calculation program for equation (17) is stored in the storage unit 23. That is, the storage unit 23 stores the above-mentioned equation (17) (reflection coefficient calculation equation) which indicates the relationship between the first reflection coefficient (S11_load), the admittance of the measurement object, and the open reflection coefficient in the ideal open state of the dielectric spectroscopy sensor 1 when the measurement object is placed on the measurement end face.

[0075]

number

[0076] From the relationships of the above-mentioned equations (15), (16), and (17), the S11 parameter of any calibration standard can be calculated using the S11 parameter in an ideal open state and the normalized admittance Yprobe(εs) of the measurement end face N1. The above-mentioned equations (9) and the respective calculation equations (15) to (17) are stored in the memory unit 23 shown in FIG.

[0077] Based on the above relationship, in this embodiment, the dielectric constant εs of the object P0 is measured by the processing procedure shown in Fig. 6. The procedure for calculating the dielectric constant εs of the object P0 will be described below.

[0078] FIG. 6 is a flowchart showing the processing procedure of the dielectric constant measuring method according to the first embodiment.

[0079] First, the normalized admittance of calibration standard P1 is obtained. If the admittance of the calibration standard is known, the normalized admittance is obtained based on this admittance. Alternatively, the normalized admittance is calculated by substituting the permittivity of calibration standard P1 into the admittance calculation formula shown in equation (9) above. In other words, the admittance of the first calibration standard, whose permittivity is known, is obtained.

[0080] In step ST11, the measurement unit 21 of the measurement device 2 measures the S11 parameter (S11_load; first reflection coefficient) of the calibration standard P1. That is, the first reflection coefficient of the first calibration standard is measured. The calibration standard P1 is, for example, air. Air does not require a measurement jig or temperature sensor and has high reproducibility, so measuring the S11 parameter does not require much effort. Note that the calibration standard P1 is not limited to air, and other substances may be used.

[0081] In step ST12, the calculation unit 22 calculates the normalized admittance Yprobe(εs) in the ideal open state by using the above-mentioned equation (9). The calculation unit 22 substitutes the calculated normalized admittance Yprobe(εs) into the above-mentioned equation (17), and further substitutes the "S11_load" measured in step ST11, thereby calculating the S11 parameter (S11_Idealopen) in the ideal open state.

[0082] That is, when the calibration standard P1 (first calibration standard) is placed on the measurement end face N1 of the dielectric spectroscopy sensor 1, the normalized admittance of the calibration standard P1 and the first reflection coefficient are substituted into the reflection coefficient calculation formula (17) which shows the relationship between the first reflection coefficient (S11_load), the normalized admittance of the calibration standard P1, and the open reflection coefficient (S11_Idealopen) in the ideal open state of the dielectric spectroscopy sensor 1, to calculate the open reflection coefficient (S11 parameter).

[0083] When a metal is used as the calibration standard P1, the above-mentioned equation (16) can be used instead of equation (17). That is, when the calibration standard is a metal (short circuit), equation (16) holds, and therefore S11_Idealopen can be calculated by multiplying S11_short by "-1" without calculating the normalized admittance Yprobe(εs).

[0084] In step ST13, the calculation unit 22 calculates the S11 parameter when other calibration standards, i.e., calibration standards P2 and P3, are placed on the measurement end face N1, using S11_Idealopen calculated in step ST12 and equations (16) and (17) stored in the storage unit 23. That is, the calculation unit 22 substitutes the open reflection coefficient (S11_Idealopen) and the normalized admittances of calibration standards P2 and P3 other than calibration standard P1 into the reflection coefficient calculation formula to calculate the reflection coefficients of the other calibration standards P2 and P3.

[0085] Therefore, the S11 parameters of the calibration standards P2 and P3 can be obtained without measuring them. Alternatively, an easily measured calibration standard may be used and the S11 parameters of this calibration standard may be measured. In this case, the S11 parameters are measured for the two calibration standards P1 and P2, as shown in Figure 7.

[0086] When using two or more calibration standards, in addition to air, use a substance that has high measurement reproducibility in the measurement environment. For example, liquid samples such as water, methanol, and liquid metals are recommended. Also, if the environment is unstable in temperature and you do not want to use samples such as liquids whose dielectric constants are highly temperature-dependent as calibration standards, it is recommended to use conductors such as metal plates and liquid metals.

[0087] In step ST14, the S11 parameter of the object P0 is measured. That is, the reflection coefficient of the object P0 is measured. As a result, the S11 parameter of the calibration standard P1 obtained by measurement, the S11 parameters of the calibration standards P2 and P3 calculated by calculation, and the S11 parameter of the object P0 obtained by measurement are all obtained.

[0088] In step ST15, the calculation unit 22 calculates the dielectric constant εs of the object P0 using the aforementioned equation (6) based on the S11 parameters (reflection coefficients ρ1, ρ2, ρ3, ρm) of the calibration standards P1, P2, P3 and the object P0, and the admittances y1, y2, y3, ym of the calibration standards P1, P2, P3 and the object P0.

[0089] That is, the dielectric constant of the object P0 is calculated based on the first reflection coefficient, the reflection coefficients of the other calibration standards P2 and P3, the reflection coefficient of the object P0, the normalized admittance of the calibration standard P1, and the normalized admittance of the other calibration standards P2 and P3.

[0090] In this way, by measuring the S11 parameter of one calibration standard P1, for example the S11 parameter of water, it is possible to calculate the S11 parameter of the object P0 without actually measuring the S11 parameters of the calibration standards P2 and P3, and further to calculate the dielectric constant εs of the object P0.

[0091] 8 and 9 are graphs showing the results of estimating the S11 parameter in a short-circuit state according to this embodiment for the coaxial probe 10 in which the inner conductor 11 has an outer diameter of 3.0 mm, the outer conductor 12 has an inner diameter of 4.8 mm, the insulator 13 has a relative dielectric constant of 3.3, and the probe length is 47.1 mm.

[0092] Figure 8 is a graph showing the measured values ​​of the amplitude of the S11 parameter when the measurement end face N1 is short-circuited, and the amplitude calculated using the aforementioned equation (16). The dotted curve in the figure shows the measured values, and the solid curve shows the calculation results using equation (16). In both the solid and dotted curves, the S11 parameter fluctuates around 0 dB, and it can be said that the amplitudes of both are nearly the same.

[0093] 9 is a graph showing the measured values ​​of the phase of the S11 parameter and the phase calculated using the above-mentioned equation (16). In the graph, the dotted curve shows the measured values, and the solid curve shows the phase calculated using equation (16). In both the solid and dotted curves, the S11 parameter is approximately -180°, and it can be said that the phases of both are approximately the same. In other words, it can be seen that by adopting the method of this embodiment, the S11 parameter of the object P0 can be calculated with high accuracy.

[0094] 10 and 11 are graphs showing the results of measuring the dielectric constant using this embodiment. Fig. 10 is a graph comparing the results of measuring the reflection coefficient using air and water as calibration standards, calculating the S11 parameter for short-circuit calibration using equation (16), and calculating the dielectric constant of a glucose aqueous solution (5 g / dL) as the target (shown by the solid line) with the results of calculating the dielectric constant using equation (6) using a conventional method (shown by the dotted line). The solid and dotted lines in Fig. 10 are in good agreement.

[0095] Fig. 11 is a graph showing the error between the dotted line and the solid line shown in Fig. 10. As can be seen from Fig. 11, it can be said that dielectric constant measurement is possible with an absolute error of approximately 0.01 or less even without short-circuit calibration. By adopting the method of this embodiment, it is possible to perform dielectric spectroscopy measurement with high accuracy even without using a measurement jig, and it is clear that the dielectric constant of the target object is measured.

[0096] As described above, the dielectric constant measurement method according to this embodiment is a dielectric constant measurement method for measuring the dielectric constant of an object using the dielectric spectroscopy sensor 1, and includes the steps of acquiring the admittance of a first calibration standard having a known dielectric constant; measuring a first reflection coefficient of the first calibration standard; calculating an open reflection coefficient in the ideal open state of the dielectric spectroscopy sensor based on the first reflection coefficient and the admittance of the first calibration standard when the first calibration standard is installed on the measurement end face of the dielectric spectroscopy sensor; calculating the reflection coefficient of another calibration standard based on the open reflection coefficient and the admittance of another calibration standard other than the first calibration standard; measuring the reflection coefficient of the object; and calculating the dielectric constant of the object based on the first reflection coefficient, the reflection coefficient of the other calibration standard, the reflection coefficient of the object, the admittance of the first calibration standard, and the admittance of the other calibration standards.

[0097] In the dielectric constant measurement method according to this embodiment, the reflection coefficient (S11 parameter) is measured using at least one calibration standard, and the dielectric constant εs of the object P0 can be calculated based on the measurement results. This reduces the time and effort required to install a calibration standard on the measurement end face N1 of the dielectric spectroscopy sensor 1, and enables highly accurate measurement of the dielectric constant without requiring a highly skilled operator or a measurement jig.

[0098] Since devices such as temperature sensors are not required when measuring the dielectric constant, the device scale can be reduced and the dielectric constant can be measured easily.

[0099] Using air as the calibration standard P1 reduces the effort of contacting the calibration standard P1 with the measurement end face N1 and simplifies the dielectric constant measurement process. In addition, air has high measurement reproducibility, so it is less affected by the ambient environment during measurement, enabling highly accurate dielectric constant measurements.

[0100] By using a metal as the calibration standard P1, the above-mentioned equation (17) can be changed to equation (16) to perform the calculation process of the dielectric constant, thereby reducing the calculation load on the measurement device 2.

[0101] [Description of the Second Embodiment] Next, a second embodiment will be described. The dielectric constant measurement system according to the second embodiment has the same configuration as the dielectric constant measurement system 100 shown in Fig. 1. The second embodiment differs from the first embodiment described above only in the processing procedure. Therefore, a description of the configuration of the dielectric constant measurement system according to the second embodiment will be omitted.

[0102] The processing procedure of the dielectric constant measuring method according to the second embodiment will be described below with reference to the flowchart shown in Fig. 12. Fig. 12 is a flowchart showing the processing procedure of the dielectric constant measuring method according to the second embodiment.

[0103] First, the normalized admittance of calibration standard P1 is obtained. If the admittance of the calibration standard is known, the normalized admittance is obtained based on this admittance. Alternatively, the normalized admittance is calculated by substituting the permittivity of calibration standard P1 into the admittance calculation formula shown in equation (9) above. In other words, the admittance of the first calibration standard, whose permittivity is known, is obtained.

[0104] In step ST31, the measurement unit 21 of the measurement device 2 measures the S11 parameter (S11_load; first reflection coefficient) of the calibration standard P1. That is, the measurement unit 21 measures the first reflection coefficient of the first calibration standard. The calibration standard P1 is, for example, air. Air does not require a measurement jig or a temperature sensor and has high reproducibility, so measuring the S11 parameter does not require much effort. Note that the calibration standard P1 is not limited to air, and other substances may be used.

[0105] Based on the admittance of calibration standard P1 (first calibration standard) and the dielectric constant of calibration standard P1, the above equation (9) (first admittance calculation equation), which is an equation for calculating admittance from dielectric constant, can be generated.

[0106] In step ST32, the calculation unit 22 calculates the normalized admittance Yprobe(εs) in the ideal open state by using the above-mentioned equation (9). The calculation unit 22 substitutes the calculated normalized admittance Yprobe(εs) into the above-mentioned equation (17), and further substitutes the "S11_load" measured in step ST31, thereby calculating the S11 parameter (S11_Idealopen) in the ideal open state.

[0107] That is, when the calibration standard P1 (first calibration standard) is placed on the measurement end face N1 of the dielectric spectroscopy sensor 1, the normalized admittance of the calibration standard P1 and the first reflection coefficient are substituted into the reflection coefficient calculation formula (17) which shows the relationship between the first reflection coefficient (S11_load), the normalized admittance of the calibration standard P1, and the open reflection coefficient (S11_Idealopen) in the ideal open state of the dielectric spectroscopy sensor 1, to calculate the open reflection coefficient (S11 parameter).

[0108] When a metal is used as the calibration standard P1, the above-mentioned equation (16) can be used instead of equation (17). That is, when the calibration standard is a metal (short circuit), equation (16) holds, and therefore S11_Idealopen can be calculated by multiplying S11_short by "-1" without calculating the normalized admittance Yprobe(εs).

[0109] In step ST33, the measurement unit 21 measures the S11 parameter of the object P0. That is, the measurement unit 21 measures the reflection coefficient of the object P0. Here, when the above-mentioned equation (17) is solved for Yprobe(εs), the following equation (18) is obtained.

[0110]

number

[0111] That is, it is possible to generate equation (18) (second admittance calculation equation), which is an equation for calculating the admittance of the object P0 based on the reflection coefficient (first reflection coefficient) of the calibration standard P1 and the open reflection coefficient in the ideal open state of the dielectric spectroscopy sensor 1.

[0112] In step ST34, the calculation unit 22 calculates the normalized admittance Yprobe(εs) by using S11_Idealopen in the ideal open state and the S11 parameter of the object P0 according to the above-mentioned equation (18).

[0113] Here, since both the above-mentioned equation (9) and the above equation (18) calculate the normalized admittance Yprobe(εs), they are equal. Therefore, the following equation (19) is obtained.

[0114]

number

[0115] In step ST35, the calculation unit 22 calculates the dielectric constant εs of the object P0 by finding the dielectric constant εs that satisfies the above equation (19) through inverse problem analysis. That is, the calculation unit 22 calculates the dielectric constant εs of the object P0 based on the fact that the admittance calculated by the first admittance calculation equation and the admittance calculated by the second admittance calculation equation are equal.

[0116] As described above, in the dielectric constant measurement method according to the second embodiment, as in the first embodiment, the reflection coefficient (S11 parameter) is measured using at least one calibration standard, and the dielectric constant εs of the object P0 can be calculated based on the measurement results. This reduces the time and effort required to install a calibration standard on the measurement end face N1 of the dielectric spectroscopy sensor 1, and enables highly accurate dielectric constant measurement without requiring advanced technical skills from the operator.

[0117] 13, for example, a general-purpose computer system including a CPU (Central Processing Unit, processor) 901, a memory 902, a storage 903 (HDD: Hard Disk Drive, SSD: Solid State Drive), a communication device 904, an input device 905, and an output device 906 can be used for the dielectric constant measurement system 100 described above. The memory 902 and the storage 903 are storage devices. In this computer system, the CPU 901 executes a predetermined program loaded on the memory 902, thereby realizing each function of the dielectric constant measurement system 100.

[0118] The measurement device 2 may be implemented by one computer or by multiple computers, or may be a virtual machine implemented on a computer.

[0119] The program for the measuring device 2 can be stored on a computer-readable recording medium such as an HDD, SSD, USB (Universal Serial Bus) memory, CD (Compact Disc), or DVD (Digital Versatile Disc), or can be distributed via a network.

[0120] 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]

[0121] 1. Dielectric Spectroscopy Sensor 2. Measuring equipment 3 Transmission Lines 10 Coaxial Probes 11 Inner conductor 12 outer conductor 13 Insulators 14 Connectors 15 Fringe 21 Measuring part 22 Arithmetic section 23 Memory section 100 Dielectric Constant Measurement System N1 Measurement end face N2 calibration end face

Claims

1. A dielectric constant measurement method for measuring the dielectric constant of an object using a dielectric spectroscopic sensor, comprising: obtaining the admittance of a first calibration standard having a known dielectric constant; measuring a first reflection coefficient of the first calibration standard; calculating an open reflection coefficient of the dielectric spectroscopy sensor in an ideal open state based on the first reflection coefficient and the admittance of the first calibration standard when the first calibration standard is placed on the measurement end face of the dielectric spectroscopy sensor; calculating a reflection coefficient of another calibration standard other than the first calibration standard based on the open reflection coefficient and the admittance of the other calibration standard; measuring the reflection coefficient of the object; calculating a dielectric constant of the object based on the first reflection coefficient, the reflection coefficients of the other calibration standards, the reflection coefficient of the object, the admittance of the first calibration standard, and the admittance of the other calibration standards; A dielectric constant measurement method comprising:

2. The dielectric constant measuring method according to claim 1 , wherein the other calibration standard includes a metal.

3. The first calibration standard comprises water. The dielectric constant measuring method according to claim 1 or 2.

4. A dielectric constant measurement method for measuring the dielectric constant of an object using a dielectric spectroscopic sensor, comprising: obtaining the admittance of a first calibration standard having a known dielectric constant; measuring a first reflection coefficient of the first calibration standard; generating a first admittance calculation formula for calculating an admittance from a dielectric constant based on the admittance of the first calibration standard and the dielectric constant; generating a second admittance calculation formula for calculating the admittance of the object based on the first reflection coefficient and an open reflection coefficient in an ideal open state of the dielectric spectroscopy sensor; calculating a dielectric constant of the object based on the fact that the admittance calculated by the first admittance calculation formula and the admittance calculated by the second admittance calculation formula are equal; A dielectric constant measurement method comprising:

5. The first calibration standard comprises water. The dielectric constant measuring method according to claim 4.

6. a dielectric spectroscopy sensor having a coaxial probe and a measurement end face formed on the coaxial probe; a measurement device connected to the dielectric spectroscopy sensor via a transmission line having the same characteristic impedance as the coaxial probe; The measuring device is a measurement unit that applies a predetermined voltage to the dielectric spectroscopic sensor and measures a reflection coefficient of the object based on a reflected signal; calculating an open reflection coefficient of the dielectric spectroscopy sensor in an ideal open state based on a first reflection coefficient of the first calibration standard and an admittance of the first calibration standard when the first calibration standard is placed on a measurement end face of the dielectric spectroscopy sensor; calculating a reflection coefficient of another calibration standard other than the first calibration standard based on the open reflection coefficient and the admittance of the other calibration standard; a calculation unit that calculates a dielectric constant of the object based on the first reflection coefficient, the reflection coefficients of the other calibration standards, the reflection coefficient of the object measured by the measurement unit, the admittance of the first calibration standard, and the admittance of the other calibration standards; A permittivity measurement system comprising:

7. A dielectric constant measurement program that causes a computer to execute the dielectric constant measurement method according to any one of claims 1 to 5.

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