JP2016211976A - Dielectric spectroscopy sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform broadband dielectric spectroscopic measurement without changing a sample installation site.SOLUTION: A dielectric spectroscopy sensor comprises a substrate 11 designed to operate as an ATR prism on which an MSL structure is provided, and a part of strip wires 12 of the MSL structure are formed in a grid shape set with intervals so as to operate as a wire grid polarizer. This reduces the reflection of a terahertz wave at a strip wire 12 interface, thereby performing spectroscopic measurement at a microwave-millimeter-wave band using the MSL in addition to allowing spectroscopic measurement using the prism at a terahertz wave band. Thus, broadband dielectric spectroscopic measurement can be performed without changing the installation site of a sample.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for noninvasively measuring the concentration of blood components such as humans and animals, and more particularly to a dielectric spectroscopic sensor.

  As aging progresses, the response to adult diseases has become a major issue. Tests such as blood glucose levels are a heavy burden on patients because they need to collect blood. Therefore, a non-invasive component concentration measuring apparatus that does not collect blood has attracted attention.

  An apparatus using dielectric spectroscopy has been proposed as a noninvasive component concentration measuring apparatus. Dielectric spectroscopy irradiates the skin with electromagnetic waves, absorbs the electromagnetic waves according to the interaction of blood components to be measured, for example, glucose molecules and water, and observes the amplitude and phase with respect to the frequency of the electromagnetic waves. The dielectric relaxation spectrum is calculated from the amplitude and phase with respect to the frequency of the observed electromagnetic wave. In general, the complex dielectric constant is calculated by expressing as a linear combination of relaxation curves based on the Cole-Cole equation. In the measurement of biological components, for example, the complex dielectric constant has a correlation with the amount of blood components such as glucose and cholesterol contained in blood, and is measured as an electrical signal corresponding to the change. A calibration model is constructed by measuring the correlation between the complex dielectric constant change and the component concentration in advance, and the component concentration is calibrated from the measured change in the dielectric relaxation spectrum.

  As a conventional measurement method, there is a dielectric spectroscopic device using a micro strip line (MSL) in a microwave to millimeter wave frequency band (see Patent Document 1). As described in Non-Patent Document 1, an impedance analyzer (Impedance Analyzer: IA) or a vector network analyzer (Vector Network Analyzer: VNA) is connected to an MSL on which a measurement sample is placed on a strip conductor, and a background component and a target component The concentration of the target component in the measurement sample mixed with is measured. The complex permittivity is calculated from the impedance when connected to IA, and from the S parameter when connected to VNA. A coplanar waveguide (CPW) is also used in place of the MSL.

  In the frequency band of terahertz waves having a frequency higher than that of millimeter waves, there is a dielectric spectroscopic device using photoelectric conversion (photomixing). This dielectric spectroscopic device photoelectrically converts an optical signal obtained by combining two continuous light waves having different frequencies to generate a terahertz wave, irradiates the object to be measured with the generated terahertz wave, and transmits or transmits the object to be measured. In this configuration, the reflected terahertz wave is received and the reference light synthesized by modulating the phase of one of the two continuous light waves is input to perform homodyne mixing.

In the terahertz wave band, an attenuated total reflection (ATR) method using a prism is suitable for measuring a liquid sample. When the sample is placed on the prism and electromagnetic waves are incident on the sample at an angle greater than the critical angle, the electromagnetic waves are totally reflected at the sample-prism interface. When electromagnetic waves are totally reflected at the sample-prism interface, an evanescent wave is generated from the prism toward the sample at the sample-prism interface, causing interaction with the sample. The critical angle θ _c and the penetration depth dp of the evanescent wave in the sample direction can be calculated by the following equations.

ここで、ｎ_１，ｎ_２はそれぞれプリズムと試料の屈折率、λは入射する電磁波の波長を表す。非特許文献２に示されるように、リファレンス信号と測定信号のスペクトルの強度及び位相差から複素誘電率が計算される。

Here, n ₁ and n ₂ represent the refractive indexes of the prism and the sample, respectively, and λ represents the wavelength of the incident electromagnetic wave. As shown in Non-Patent Document 2, the complex dielectric constant is calculated from the spectrum intensity and phase difference between the reference signal and the measurement signal.

JP 05-333096 A

G. R. Facer, D. A. Notterman, and L. L. Sohn, “Dielectric spectroscopy for bio analysis: From 40Hz to 26.5GHz”, Applied Physics Letters, Vol. 78, No. 7, 996 Feb. 2001 Hideki Hirori, Masaya Nagai, and Koichiro Tanaka, “Destructive interference effect on surface plasmon resonance in terahertz attenuated total reflection”, Optics Express, Vol. 13, No. 26, 10801, Dec. 2005

  However, when measuring the terahertz wave band in addition to the frequency band from microwave to millimeter wave, the measurement frequency is limited by the loss in the dielectric substrate in the conventional dielectric spectroscopic device using the MSL. It is difficult to measure the high frequency band up to the band. On the other hand, when a terahertz dielectric spectroscopy system using a prism is used in the microwave band, it is difficult to satisfy the total reflection condition at the sample-prism interface due to an increase in the dielectric constant of the measurement target.

  Therefore, in order to acquire broadband spectrum data, it is necessary to perform measurement a plurality of times by placing samples on measuring devices in each band. Since the installation location of the sample is changed for each measurement device, there is a problem that measurement reproducibility and measurement accuracy cannot be obtained due to changes in the sample temperature or drying.

  The present invention has been made in view of the above, and an object of the present invention is to perform broadband dielectric spectroscopy measurement without changing the installation location of the sample.

  A dielectric spectroscopic sensor according to the present invention includes a prism and a metal wiring of a microstrip line or a coplanar waveguide disposed on the prism, and at least a part of the metal wiring operates as a wire grid polarizer. It is characterized by having a lattice shape in which intervals are set.

  In the dielectric spectroscopic sensor, the prism is characterized in that the material on the surface on which the metal wiring is arranged has a higher dielectric constant than other parts.

  In the dielectric spectroscopic sensor, a bezel or a flow path is provided in a lattice portion of the metal wiring.

  According to the present invention, it is possible to perform broadband dielectric spectroscopy measurement without changing the installation location of the sample.

FIG. 1A is a top view of the dielectric spectroscopic sensor in the present embodiment, FIG. 1B is a cross-sectional view, and FIG. 1C is a side view. It is a figure explaining a mode that a terahertz wave enters into a dielectric spectroscopic sensor. It is sectional drawing which shows the variation of the shape of the board | substrate of a dielectric spectroscopy sensor. FIG. 4 is a cross-sectional view showing an example in which materials having different dielectric constants are used at the interface with the sample in the dielectric spectroscopic sensor shown in FIG. FIG. 5A is a top view of a modification of the dielectric spectroscopic sensor, and FIG. 5B is a cross-sectional view. FIG. 6A is a top view of another modification of the dielectric spectroscopic sensor, and FIG. 6B is a cross-sectional view. FIG. 7A is a diagram showing an example in which a dielectric spectroscopic sensor is introduced into a terahertz band dielectric spectroscopic optical system, and FIG. 7B is a diagram showing an example in which the same dielectric spectroscopic sensor is connected to a VNA. It is a graph which shows the electromagnetic field simulation result of the transmission characteristic in a microwave-millimeter wave band.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1A is a top view of the dielectric spectroscopic sensor in the present embodiment, FIG. 1B is a cross-sectional view of the dielectric spectroscopic sensor, and FIG. 1C is a side view of the dielectric spectroscopic sensor. It is.

  The dielectric spectroscopic sensor shown in the figure includes a substrate 11 operating as an ATR prism, strip wiring 12 and ground wiring 13 formed on each surface of the substrate 11, and strip wiring 12 and ground wiring 13 at both ends of the substrate 11. It has a connected connector 15. A part of the strip wiring 12 has a lattice shape, and a measurement sample is arranged on the lattice.

  As a material of the substrate 11, a material used in the ATR prism, for example, Si, ZnSe, MgO, Ge, or plastic is used. The size of the substrate 11 is several centimeters × several centimeters and several hundred μm−several centimeters thick, and a material having a high refractive index is selected according to the measurement sample. The shape of the substrate 11 is designed to operate as an ATR prism when a terahertz wave is incident from the side surface of the substrate 11 and is selected according to the measurement system of the dielectric spectroscopic apparatus. In the present dielectric spectroscopic sensor, since the substrate 11 has a structure having a prism function, the size of the prism is several centimeters × several centimeters and several hundreds μm−several centimeters thick like the size of the substrate 11.

  The side surface of the substrate 11 on which the electromagnetic wave is incident is designed according to the electromagnetic wave incident method. As shown in FIG. 2A, when the electromagnetic wave is incident perpendicularly to the inclined surface of the substrate 11, it is designed so as to satisfy the condition of the following formula (3).

  In addition, as shown in FIG. 2B, when electromagnetic waves are incident from the horizontal direction, the design is performed so as to satisfy the following expression (4).

  An MSL structure metal wiring is formed using the top and bottom surfaces of the substrate 11. The strip wiring 12 is formed on the upper surface of the substrate 11 and is connected to the signal terminal of the connector 15. The wiring width of the strip wiring 12 is several hundred μm−several millimeters, and the wiring material is Au, Cu, Al or the like. A part of the strip wiring 12 has a lattice shape, and the size of the lattice is designed to operate as a wire grid polarizer in the frequency band (for example, terahertz wave band) of electromagnetic waves incident from the side surface of the substrate 11. For example, the conductor width is set to several μm to several tens of μm and the interval is set to several tens of μm. The ground wiring 13 is formed on the bottom surface of the substrate 11 and connected to the ground terminal of the connector 15. Note that a metal wiring having a CPW structure may be formed instead of the MSL structure.

  A connector whose coaxial size is adjusted according to the frequency band is used as the connector 15. For example, SMA connector, K connector, V connector and the like. The connection point with the MSL structure or CPW structure connector is designed to have a characteristic impedance of 50Ω.

  Next, variations in the shape of the substrate 11 will be described.

  FIG. 3 is a cross-sectional view showing variations in the shape of the substrate 11.

  FIG. 3A is a cross-sectional view of the dielectric spectroscopic sensor shown in FIG. 1, in which the opposing side surfaces of the substrate 11 are inclined.

  FIG. 3B is a cross-sectional view of the dielectric spectroscopic sensor in which the opposite side surfaces of the substrate 11 are curved. In the case of the dielectric spectroscopic sensor of FIG. 3B, it is possible to collect the terahertz wave at the same location even when the incident position of the terahertz wave is shifted.

  FIG. 3C is a cross-sectional view of the dielectric spectroscopic sensor in which the bottom surface of the substrate 11 is formed with a slope that reflects the terahertz wave incident in the horizontal direction from the side surface of the substrate 11 in the direction of the strip wiring 12. Compared with the shape of FIG. 3A, the dielectric spectroscopic sensor of FIG. 3C can reduce optical aberration when a terahertz wave is incident from the horizontal direction.

Even when the shape of the substrate 11 is a prism are different, the sample - the reflection angle at the prism interface is set to be larger than theta _c. Since terahertz waves have a larger diffraction effect than infrared rays, it is difficult to design prisms by simple ray tracing, so it is desirable to use electromagnetic field simulation.

  However, since the refractive index of the material used for the ATR prism is relatively high and the wavelength in the prism is shortened, there is a problem that the number of meshes when performing electromagnetic field simulation increases. Therefore, as shown in FIG. 4, calculation at the time of design is performed by laminating a substrate 14 of a high dielectric constant material (eg, Si) on a substrate 11 made of a low dielectric constant material (eg, a polymer such as plastic). Time can be expected to be shortened. When the substrates 11 and 14 having different dielectric constants are laminated, the substrate 11 is manufactured by an inexpensive manufacturing method such as injection molding using plastic or the like as a material, and wiring is formed on the flat substrate 14 by a normal process. , 14 is not required to form a wiring on the substrate 11, and the production of the dielectric spectroscopic sensor can be simplified.

  Next, a modified example of the dielectric spectroscopic sensor will be described.

  5 and 6 are diagrams showing modifications of the dielectric spectroscopic sensor. FIGS. 5A and 6A are top views of modified examples of the dielectric spectroscopic sensor, and FIGS. 5B and 6B are cross-sectional views of modified examples of the dielectric spectroscopic sensor.

  In the modification of FIG. 5, the bezel 16 is disposed at the incident position of the terahertz wave in the lattice portion of the strip wiring 12, and the flow path 17 is disposed in the modification of FIG. 6. By arranging the bezel 16 and the flow path 17, it is possible to measure a powder sample or a liquid sample. The size of the bezel 16 or the flow path 17 is about the beam diameter of the incident terahertz wave, for example, about several hundred μm to several mm. For example, glass or PDMS is used as the material of the bezel 16 and the flow path 17.

  Next, a measurement system using the dielectric spectroscopic sensor of the present embodiment will be described.

  FIG. 7A is a diagram showing an example in which a dielectric spectroscopic sensor is introduced into a terahertz-band dielectric spectroscopic optical system, and FIG. 7B is a diagram showing an example in which the same dielectric spectroscopic sensor is connected to a VNA. Although not shown, the sample is disposed on the lattice portion of the strip wiring 12 of the dielectric spectroscopic sensor.

  In FIG. 7A, the terahertz wave emitted from the THz wave oscillator 21 is focused or collimated by the lens 25A and is incident from the side surface of the substrate 11 of the dielectric spectroscopic sensor. By adjusting the antenna direction of the THz wave oscillator 21 and entering the terahertz wave in a polarization direction in which the electric field component of the terahertz wave is perpendicular to the lattice portion of the strip wiring 12, the terahertz wave is transmitted through the lattice portion. Therefore, ATR measurement is possible. The terahertz wave reflected from the sample-prism interface is emitted from the dielectric spectroscopic sensor, passes through the lens 25B, is received by the THz wave receiver 22, and a signal is transmitted to the low noise amplifier 23 and the lock-in amplifier 24.

  In FIG. 7B, the strip wiring 12 and the ground wiring 13 are connected to the VNA 31 or IA via the connector 15, and the sample placed on the strip wiring 12 is measured.

  A sample is placed on the lattice portion of the strip wiring 12, and measurement using the VNA 31 is performed in the microwave-millimeter wave band, and ATR measurement is performed in the millimeter-wave-terahertz wave band, so that dielectric spectroscopy of the same region over a wide band is performed at the same time. Can do. In addition, since the sample is arranged on the lattice portion of the strip wiring 12, the same portion is irradiated with electromagnetic waves, so that terahertz spectroscopy under microwave excitation or microwave spectroscopy under terahertz wave excitation is possible.

FIG. 8 is a graph showing electromagnetic field simulation results of transmission characteristics in the microwave-millimeter wave band. A change in S ₂₁ characteristics when an MSL having a lattice on a part of a line is provided on an Si substrate and the material in contact with the lattice is air (no data) or a liquid sample is shown. Au was used as the material for MSL, and the dielectric constant of water at 27 ° C. was used as the liquid sample.

  As described above, according to the present embodiment, the substrate 11 designed to operate as an ATR prism is provided with an MSL structure, and a part of the strip wiring 12 of the MSL structure operates as a wire grid polarizer. Since the reflection of the terahertz wave at the interface of the strip wiring 12 can be reduced by using the lattice shape with the interval set at the interval, the spectral measurement in the terahertz wave band using the prism is enabled, and the MSL Therefore, it is possible to perform broadband dielectric spectroscopic measurement without changing the installation location of the sample.

DESCRIPTION OF SYMBOLS 11 ... Board | substrate 12 ... Strip wiring 13 ... Ground wiring 14 ... Board | substrate 15 ... Connector 16 ... Bezel 17 ... Flow path 21 ... THz wave oscillator 22 ... THz wave receiver 23 ... Low noise amplifier 24 ... Lock-in amplifier 25A, 25B ... Lens 31 ... VNA

Claims (3)

Prism,
A metal strip of a microstrip line or a coplanar waveguide disposed on the prism,
A dielectric spectroscopic sensor characterized in that at least a part of the metal wiring is formed in a lattice shape in which intervals are set so as to operate as a wire grid polarizer.   2. The dielectric spectroscopic sensor according to claim 1, wherein a material of a surface of the prism on which the metal wiring is disposed has a higher dielectric constant than other portions.   The dielectric spectroscopic sensor according to claim 1, wherein a bezel or a flow path is provided in a lattice portion of the metal wiring.

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