Dielectric spectroscopic sensor and method for measuring reflection coefficient

Abstract

This dielectric spectroscopic sensor (1) comprises a control unit (10) and a measurement unit (20). The control unit (10) has a storage device (11) and a computation unit (12). The measurement unit (20) has an oscillator (21), a receiver (22), a signal separator (23), and a measurement unit (24). A measurement result obtained by the measurement unit (20) is stored by the storage device (11) and is subjected to a computation by the computation unit (12) in the control unit (10), and a control signal obtained through the computation is sent from the control unit (10) to the measurement unit (20).

Description

Dielectric spectroscopy sensor, method for measuring reflection coefficient

[0001] The present invention relates to a dielectric spectroscopy sensor and a method for measuring a reflection coefficient.

[0002] As the aging population advances, responding to adult diseases has become a major issue. Tests for blood glucose levels, etc., require blood sampling, which places a heavy burden on patients. For this reason, non-invasive element concentration measuring devices that do not require blood sampling are attracting attention.

[0003] Known non-invasive constituent concentration measurement devices use electromagnetic waves in the microwave to millimeter wave band because they scatter less in vivo than optical methods such as near-infrared light, and the energy of one photon is low. Examples of non-invasive constituent concentration measurement devices include those using a resonant structure, as described in Non-Patent Document 1. In this device, a measurement sample is brought into contact with a device with a high Q factor, such as an antenna or resonator, and frequency characteristics around the resonant frequency are measured. Because the resonant frequency is determined by the complex dielectric constant of the device's surroundings, the constituent concentration can be estimated from the resonant frequency shift by predicting the correlation between the resonant frequency shift and the constituent concentration.

[0004] Another known method using microwave-millimeter wave electromagnetic waves is dielectric spectroscopy, as described in Patent Document 1. In dielectric spectroscopy, electromagnetic waves are irradiated into the skin, absorbed by the blood component being measured, e.g., glucose molecules, in accordance with the interaction between the molecules and water, and the amplitude and phase of the electromagnetic waves are observed. The dielectric relaxation spectrum is calculated from the amplitude and phase of the observed electromagnetic waves at different frequencies. The dielectric relaxation spectrum is generally expressed as a linear combination of relaxation curves based on the Cole-Cole equation, and the complex dielectric constant is calculated. In measuring biological components, for example, the amount of blood components, such as glucose and cholesterol, contained in the blood is correlated with the complex dielectric constant, and the complex dielectric constant is measured as an electrical signal (amplitude, phase) corresponding to this change. A calibration model is constructed by measuring the correlation between changes in complex dielectric constant and component concentration in advance, and the component concentration is calibrated from changes in the measured dielectric relaxation spectrum. Regardless of which method is used, improved measurement sensitivity can be expected by selecting a frequency band that is strongly correlated with the target component. Therefore, it is important to measure the change in dielectric constant in advance using broadband dielectric spectroscopy.

[0005] Among dielectric spectroscopy methods, methods using a coaxial probe (open-ended coaxial probe or open-ended coaxial line) as described in Non-Patent Documents 2 and 3 and Patent Document 2 allow for the use of readily available samples such as water for calibration of the measuring instrument. Furthermore, the dielectric constant of a sample can be measured by contacting the probe end with the sample without requiring special processing of the material. Therefore, this method is suitable for measuring the dielectric constant of samples whose electrical properties need to be evaluated without processing, such as living organisms, fruits, soil, and hydrogels. To measure these dielectric constants, a reflected signal measuring instrument as described in Non-Patent Document 1 or a general-purpose measuring instrument such as a portable vector network analyzer is used. Generally, when considering the practical application of these devices, it is desirable to stop radio wave emission when not in contact with a living organism, taking into consideration the possibility that radio wave leakage when not in contact with a sample may affect external devices.

[0006] JP 2013-32933 A Japanese Patent No. 6771372 A

[0007] 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. 2195-2203,2013J 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, 1989T.P. Marsland, and S. Evans “Dielectric measurements with an open-ended coaxial probe”, IEE Proceedings, Vol. 134, No. 4, 1987

[0008] However, with conventional dielectric spectroscopy sensors, it is difficult to set the thresholds for determining contact with air and contact with a living body. Conventional dielectric spectroscopy sensors do not implement control to directly detect the contact state between the sensor and the sample during measurement, but instead perform control to repeat measurements at certain time intervals. This poses the problem of making it difficult to stop radio wave emission if the sensor suddenly falls off the object being measured.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a dielectric spectroscopy sensor that can reduce the impact on peripheral devices by immediately stopping the emission of radio waves when the probe falls off the sample to be measured, and a method for measuring a reflection coefficient using a dielectric spectroscopy sensor.

[0010] One aspect of the present invention is a dielectric spectroscopy sensor comprising a control unit and a measurement unit, wherein the control unit has a storage device and a computing unit, and the measurement unit has an oscillator, a receiver, a signal separator, and a measurement unit, and the control unit stores the measurement results obtained by the measurement unit in the storage device and processes them in the computing unit, and sends a control signal obtained by the processing from the control unit to the measurement unit.

[0011] One aspect of the present invention is a method for measuring a reflection coefficient using a dielectric spectroscopy sensor of one aspect of the present invention, comprising: step A measuring a reference signal for measuring the reflection characteristics of an object to be measured; step B measuring a measurement signal indicating the reflection characteristics of the object to be measured; step C determining a threshold value of the measurement signal at the timing of measuring the measurement signal; step D stopping the oscillation of radio waves when the measurement signal exceeds the threshold value, or stopping the oscillation until a signal input to resume measurement is received; and step E terminating the measurement when it is confirmed that the reflection coefficient of the object to be measured has exceeded the threshold value of the measurement signal.

[0012] According to the present invention, it is possible to provide a dielectric spectroscopy sensor that can reduce the impact on peripheral devices by immediately stopping the emission of radio waves when the probe falls off the sample to be measured, and a method for measuring a reflection coefficient using the dielectric spectroscopy sensor.

[0013] 1 is a schematic diagram showing the basic configuration of a dielectric spectroscopy sensor according to one embodiment of the present invention; FIG. 2 is a flowchart of a first method of a reflection coefficient measurement method according to one embodiment of the present invention; FIG. 3 is a flowchart of a second method of a reflection coefficient measurement method according to one embodiment of the present invention; FIG. 4 is a diagram showing the results of measuring the dielectric constant of a living body; FIG. 5 is a diagram showing the results of measuring the reflection coefficient of air or a living body using a reflection coefficient measurement method according to one embodiment of the present invention; FIG. 6 is a diagram showing changes in the electric field strength of an instrument main transformer when a process to stop oscillation when a threshold is exceeded is performed and when not performed using a reflection coefficient measurement method according to one embodiment of the present invention; and FIG. 7 is a flowchart of a conventional reflection coefficient measurement method.

[0014] [Dielectric Spectroscopy Sensor] Fig. 1 is a schematic diagram showing the basic configuration of a dielectric spectroscopic sensor according to an embodiment of the present invention. As shown in Fig. 1, the dielectric spectroscopic sensor 1 of this embodiment includes a control unit 10 and a measurement unit 20.

[0015] The control unit 10 includes a storage device 11 and a computing unit 12 .

[0016] For example, a memory, a hard disk, etc. can be used as the storage device 11. For the computing unit 12, a microcomputer, a central processing unit (CPU), an FPGA (Field Programmable Gate Array), etc. can be used.

[0017] The control unit 10 may be, for example, a device such as a personal computer (PC) or a smartphone that is independent of the measurement unit 20 .

[0018] The measurement unit 20 includes an oscillator 21 , a receiver 22 , a signal separator 23 , and a measurement unit 24 .

[0019] The oscillator 21 may be, for example, a voltage-controlled oscillator, a crystal oscillator, a phase-locked loop oscillator, or an oscillator using OE (Electro-Optical) conversion using a photomixer. The oscillator 21 transmits an electromagnetic wave.

[0020] The receiver 22 may be, for example, a diode detector, an RMS (RMS detector), a mixer, an IQ mixer, etc. The receiver 22 measures the voltage, power, phase, etc. of the radio waves that reach the receiver 22.

[0021] For example, a directional coupler, a circulator, a switch, etc. can be used as the signal separator 23. The signal separator 23 separates the electromagnetic wave transmitted from the oscillator 21 into a reference signal and a measurement signal.

[0022] For example, a coaxial probe, or a transmission line, antenna, resonator, or the like that can provide an equivalent effect can be used as the measurement unit 24. By placing a sample under test (DUT) in the measurement unit 24, the reflection characteristics of the sensor change depending on the dielectric constant of the DUT, and the change in the reflection characteristics or the dielectric constant of the sample is measured.

[0023] In the dielectric spectroscopy sensor 1 of this embodiment, the measurement unit 20 may be an oscillator, a receiver, a general-purpose measuring instrument such as a signal generator or a spectrum analyzer, or a vector network analyzer that integrates an oscillator, a signal separator, and a receiver.

[0024] The dielectric spectroscopy sensor 1 of this embodiment is used by being placed in contact with the object 100 to be measured or in the vicinity of the object 100 to be measured.

[0025] In the dielectric spectroscopy sensor 1 of this embodiment, the control unit 10 stores the measurement results obtained by the measurement unit 20 in the storage device 11 and also performs arithmetic processing on the results in the calculator 12, and sends a control signal obtained by the arithmetic processing from the control unit 10 to the measurement unit 20. As a result, the dielectric spectroscopy sensor 1 of this embodiment can be applied to applications where errors in individual sensor characteristics are likely to occur depending on the surrounding conditions, such as wearable sensors and environmental sensors, and can perform stable measurements.

[0026] [Method for measuring reflection coefficient] A method for measuring reflection coefficient according to one embodiment of the present invention is a method for measuring reflection coefficient using the dielectric spectroscopy sensor of the above-described embodiment, and includes the steps of: step A of measuring a reference signal for measuring the reflection characteristics of an object to be measured; step B of measuring a measurement signal indicating the reflection characteristics of the object to be measured; step C of determining a threshold value of the measurement signal at the timing of measuring the measurement signal; step D of stopping the oscillation of radio waves when the measurement signal exceeds the threshold value, or stopping the oscillation until a signal input for resuming measurement is received; and step E of terminating the measurement when it is confirmed that the reflection coefficient of the object to be measured has exceeded the threshold value of the measurement signal.

[0027] A first method of measuring a reflection coefficient according to this embodiment will now be described with reference to Fig. 2, which is a flowchart of the first method of measuring a reflection coefficient according to this embodiment.

[0028] 2 is a flowchart of a first method of measuring a reflection coefficient according to this embodiment. As shown in FIG. 2, in the first method of measuring a reflection coefficient according to this embodiment, measurement of the object to be measured is started (S1). First, a reference signal for measuring the reflection characteristics of the object to be measured is measured (S2). Next, a measurement signal indicating the reflection characteristics of the object to be measured is measured (S3). Next, a threshold value is determined at the timing when the measurement signal is measured (S4). The threshold value is set using, for example, the following equations (1) and (2).

[0029]

[0030]

[0031] Here, the above formulas (1) and (2) are measured using a coaxial probe at the end surface, and the dielectric constant ε ｓ The reflection coefficient S at the end face of the probe when it is brought into contact with the object to be measured is １１ (ε ｓ ) and admittance Y(ε ｓ ) is the formula.

[0032] In the above formula (2), ε ｃ is the dielectric constant of the insulator of the coaxial line, k ０ is the wave number at the measurement frequency, γ is the propagation constant in the MUT, J ０ (x) is the zeroth-order Bessel function, a and b are the outer radius of the inner conductor and the inner radius of the outer conductor of the coaxial sensor. ｓ The dielectric constant of air is 1 + 0 ｉ and the signal intensity difference when the dielectric constant of the sample to be measured, for example, the living body shown in FIG. 4, is substituted, and a certain value, for example, a threshold value S ｔｈ Here, Fig. 4 is a diagram showing the results of measuring the dielectric constant of a living body. Alternatively, as shown in Fig. 5, a plurality of frequencies may be used to calculate the gradient of the phase of the reflection coefficient in the frequency direction, and this gradient may be used as the reference value of the threshold. Here, Fig. 5 is a diagram showing the results of measuring the reflection coefficient of air or a living body using the reflection coefficient measurement method of this embodiment.

[0033]

[0034] The threshold value may be calculated using a theoretical formula or may be calculated using an actual value measured in advance in an anechoic chamber or the like.

[0035] If the threshold is exceeded, the radio wave oscillation is stopped (S7), and after a certain time has passed (S8), measurement is performed again (S2, S3).

[0036] By setting the measurement stop time tstop based on the following equation (4), the average field strength within a certain time period is kept within the weak radio standard, and the impact on peripheral devices is reduced.

[0037]

[0038] In the above formula (4), E ｗ is the electric field strength specified by the weak radio standard, tosc is the time required to measure the measurement signal, and E(t) is the electric field strength radiated to the surrounding area during measurement.

[0039] S2 and S3 are repeated, and when it is confirmed that the reflection coefficient of the object to be measured exceeds the threshold value (S4), a measurement end flag is set (S5) and the measurement is ended (S6).

[0040] A second method of measuring a reflection coefficient according to this embodiment will now be described with reference to Fig. 3, which is a flowchart of the second method of measuring a reflection coefficient according to this embodiment.

[0041] 3 is a flowchart of a second method of measuring a reflection coefficient according to this embodiment. As shown in FIG. 3, in the second method of measuring a reflection coefficient according to this embodiment, measurement of the object to be measured is started (S11). First, a reference signal for measuring the reflection characteristics of the object to be measured is measured (S12). Next, a measurement signal indicating the reflection characteristics of the object to be measured is measured (S13). Next, a threshold value is determined at the timing when the measurement signal is measured (S14). The threshold value is set using, for example, the above-mentioned formulas (1) and (2).

[0042] If the threshold is exceeded, the radio wave oscillation is stopped (S17) and continues to be stopped until a signal input to resume measurement is received (S18).If a signal input to resume measurement is received, measurement is performed again (S12, S13).

[0043] In the second method, as in the first method, the measurement stop time tstop is set based on the above equation (4).

[0044] Steps S12 and S13 are repeated, and if it is confirmed that the reflection coefficient of the object to be measured exceeds the threshold value (S14), a measurement end flag is set (S15) and the measurement is ended (S16).

[0045] Here, a conventional method for measuring a reflection coefficient will be described. FIG. 7 is a flowchart of the conventional method for measuring a reflection coefficient. As shown in FIG. 7, in the conventional method for measuring a reflection coefficient, measurement of an object to be measured is started (S21). First, a reference signal for measuring the reflection characteristics of the object to be measured is measured (S22). Next, a measurement signal indicating the reflection characteristics of the object to be measured is measured (S23). Next, it is determined whether the reflection characteristics of the object to be measured have been sufficiently measured (S24). If the reflection characteristics of the object to be measured have not been sufficiently measured, S22 and S23 are repeated to repeatedly measure the reference signal and the measurement signal. After repeating S22 and S23, if it is determined that the reflection characteristics of the object to be measured have been sufficiently measured (S24), the measurement is terminated (S25).

[0046] Figure 6 shows the change in the electric field strength of the main variable of the device when the reflection coefficient measurement method of this embodiment is used, with and without the process of stopping oscillation when the threshold is exceeded. When the dielectric spectroscopy sensor falls off the object to be measured and comes into contact with air, the increase in electric field strength is suppressed, making it possible to measure the sample with minimal impact on peripheral devices.

[0047] The reflection coefficient measurement method of this embodiment can be applied to applications where errors in individual sensor characteristics are likely to occur depending on the surrounding conditions, such as wearable sensors and environmental sensors, and can measure the reflection coefficient stably.

[0048] The dielectric spectroscopic sensor and the method for measuring the reflection coefficient of the present invention can be applied to a dielectric spectroscopic sensor for a solution present in a human or an animal, and to a dielectric spectroscopic sensor for a solution or semi-solid material collected from a human or an animal.

[0049] REFERENCE SIGNS LIST 1 Dielectric spectroscopy sensor 10 Control unit 11 Storage device 12 Arithmetic unit 20 Measurement unit 21 Oscillator 22 Receiver 23 Signal separator 24 Measurement unit

Claims

1. A dielectric spectroscopy sensor comprising a control unit and a measurement unit, wherein the control unit has a storage device and a computing unit, and the measurement unit has an oscillator, a receiver, a signal separator, and a measurement unit, wherein the measurement results obtained by the measurement unit are stored in the storage device in the control unit and processed by the computing unit, and a control signal obtained by the processing is sent from the control unit to the measurement unit.

2. A method for measuring a reflection coefficient using the dielectric spectroscopy sensor of claim 1, comprising: step A of measuring a reference signal for measuring the reflection characteristics of the object to be measured; step B of measuring a measurement signal indicating the reflection characteristics of the object to be measured; step C of determining a threshold value for the measurement signal at the timing of measuring the measurement signal; step D of stopping the oscillation of radio waves when the measurement signal exceeds the threshold value, or stopping the oscillation until a signal input for restarting measurement is received; and step E of terminating the measurement when it is confirmed that the reflection coefficient of the object to be measured has exceeded the threshold value for the measurement signal.

3. The method for measuring a reflection coefficient according to claim 2, wherein in step C, the threshold value is set using the following formulas (1) and (2): (Note that equations (1) and (2) use a coaxial probe as the measurement unit, and the dielectric constant ε ｓ The reflection coefficient S at the end face of the probe when it is brought into contact with the object to be measured is １１ (ε ｓ ) and admittance Y(ε ｓ In equation (2), ε ｃ is the dielectric constant of the insulator of the coaxial line, k ０ is the wave number at the measurement frequency, γ is the propagation constant in the MUT, J ０ (x is the zeroth-order Bessel function, a and b are the outer radius of the inner conductor and the inner radius of the outer conductor of the coaxial sensor.)

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