Reflection coefficient measurement device
Patent Information
- Application Number
- PCT/JP2025/008773
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-03-10
- Publication Date
- 2026-09-17
Smart Images
Figure JP2025008773_17092026_PF_FP_ABST
Abstract
Description
Reflectance coefficient measuring device
[0001] This invention relates to a reflection coefficient measuring device used in dielectric spectroscopy measurements.
[0002] As the population ages, addressing lifestyle-related diseases is becoming a major challenge. Blood tests, such as those for blood glucose levels, require blood sampling, which places a significant burden on patients. For this reason, non-invasive device-based concentration measurement devices that do not require blood sampling are attracting attention. One such non-invasive device is one that utilizes dielectric spectroscopy. Dielectric spectroscopy involves irradiating the skin with electromagnetic waves, utilizing the interaction between the target blood component (e.g., glucose molecules) and water to cause the electromagnetic waves to be absorbed, and observing the amplitude and phase of the electromagnetic waves.
[0003] Conventional devices include those using a coaxial probe that irradiates the object to be measured with electromagnetic waves ranging from microwaves to millimeter waves. Figure 20 shows the configuration of a dielectric spectroscopy measuring device using a coaxial probe. The dielectric spectroscopy measuring device consists of a coaxial probe 1000 with an open end on the end facing the object to be measured, a sensor unit 1001, and a vector network analyzer (VNA) 1002.
[0004] In reflectance measurements, which calculate the reflection coefficient by measuring the incident voltage and reflected voltage, it is known that drift errors in the reflection coefficient occur due to fluctuations in ambient temperature and vibrations and stresses applied to the measurement cable. Generally, as shown in Figure 20, the sensor unit 1001 is connected to the coaxial probe 1000, and the sequential calibration function of the sensor unit 1001 is used to calibrate fluctuations occurring in the VNA 1002 and the measurement cable with each measurement. Such a sequential calibration function can reduce cable instability and system drift errors.
[0005] Furthermore, a calibration device has been proposed that generates multiple states such as open, short, and loaded at the output port of a VNA, measures these multiple states using the VNA, and calculates the calibration coefficient of the VNA based on the measurement results. In addition, a planar dielectric spectroscopic sensor has been proposed in which a first via and a plurality of second vias arranged in a circle around the first via are formed on a dielectric substrate, and the reflection coefficient is measured using a pseudo-coaxial line structure made up of these vias as a coaxial probe. (Patent Document 1)
[0006] Furthermore, conventionally, a dielectric spectroscopy measuring device has been proposed that integrates a pseudo-coaxial sensor and a configuration for sequential calibration on the same substrate, with the aim of performing dielectric spectroscopy measurements with high accuracy while sequentially calibrating the drift error of the reflection coefficient (Patent Document 2). Figure 21 shows the configuration of the dielectric spectroscopy measuring device disclosed in Patent Document 2.
[0007] The dielectric spectroscopy measuring device consists of a sensor unit 1 and a reflection coefficient measuring unit 2. A VNA is used in the reflection coefficient measuring unit 2, for example. The sensor unit 1 includes a dielectric substrate 10, a coaxial probe 11, a switch 12, an RF terminal 14, a control terminal 15, and a load unit 16. The coaxial probe 11, the switch 12, the RF terminal 14, the control terminal 15, and the load unit 16 are mounted on the dielectric substrate 10. The coaxial probe 11 includes antenna sections 110, 111, an open section 112, and a short section 113. In the example disclosed in Patent Document 2, a pseudo-coaxial line structure is adopted to form the antenna sections 110, 111, the open section 112, and the short section 113.
[0008] The antenna sections 110 and 111 have a pseudo-coaxial line structure with an open end on the side that contacts the sample to be measured. The open section 112 has a pseudo-coaxial line structure with an open end on the side that contacts the air. The short section 113 has a pseudo-coaxial line structure with conductivity between the central conductor and the ground at its tip. The load section 16 formed on the dielectric substrate 10 is composed of a resistor formed between the signal line and the ground and terminates the signal line.
[0009] Furthermore, a switch 12, an RF terminal 14, and a control terminal 15 are mounted on the dielectric substrate 10. The antenna sections 110, 111, the open section 112, the short section 113, and the load section 16 are each connected to the selection terminal of the switch 12. This allows the switch 12 to select one of the antenna sections 110, 111, the open section 112, the short section 113, and the load section 16. The control terminal of the switch 12 is connected to the control terminal 15.
[0010] The reflection coefficient measurement unit 2 outputs a control signal to the switch 12 via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12 so that one of the short section 113, the open section 112, and the load section 16 is connected to the RF terminal of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 connects the short section 113, the open section 112, and the load section 16 to the RF terminal of the reflection coefficient measurement unit 2 in order and performs reflection measurements for each. Then, the reflection coefficient measurement unit 2 calculates a calibration coefficient (S-parameter of the error circuit present in the reflection coefficient measurement unit 2) from the results of the reflection measurements. By calculating the calibration coefficient in this way, it becomes possible to calculate the reflection coefficient with the measurement error of the reflection coefficient measurement unit 2 removed.
[0011] With the open ends of the antenna sections 110 and 111 in contact with the sample, the reflection coefficient measurement unit 2 switches switch 12 so that either of the antenna sections 110 or 111 is connected to the RF terminal of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 applies an electric field to the sample from the antenna section 110 or 111 and calculates the reflection coefficient of the sample based on the voltage amplitude and phase of the reflected wave reflected by the sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2.
[0012] Figure 22 is a plan view of the dielectric substrate 10, and Figure 23 is a bottom view of the same part as in Figure 22, viewed from below. Figure 24 is a cross-sectional view of the dielectric substrate 10 where the switch 12, RF terminal 14, and coaxial probe 11 (multilayer wiring board) are mounted. The switch 12, RF terminal 14, control terminal 15, and resistor 160 constituting the load section 16 are mounted on the bottom surface of the dielectric substrate 10. The pad of the antenna section 110 and the first select terminal of the switch 12 are connected by a microstrip line 120. The pad of the antenna section 111 and the second select terminal of the switch 12 are connected by a microstrip line 121. The pad of the open section 112 and the third select terminal of the switch 12 are connected by a microstrip line 122. The pad of the short section 113 and the fourth select terminal of the switch 12 are connected by a microstrip line 123. The pad of the load section 16 and the fifth select terminal of the switch 12 are connected by a microstrip line 124. The RF terminal 14 and the input terminal of the switch 12 are connected by a microstrip line 125. The control terminal 15 and the control terminal of the switch 12 are connected by a microstrip line 126.
[0013] In conventional devices, the penetration depth of electromagnetic waves into the sample can be varied by setting the dielectric diameter of the open end to different values in multiple antenna sections 110 and 111, making it possible to measure the dielectric constant distribution in the thickness direction of the sample. However, when the dielectric diameter of the open end is set to different values in multiple antenna sections 110 and 111, the reflection between the open end and the switch 12 will result in different results in the multiple antenna sections 110 and 111. As a result, errors occur in the reflection coefficient calculated by calibration, and there was a problem in that the dielectric constant of the sample measured at the antenna open end could not be accurately measured.
[0014] Japanese Patent No. 6771372, International Publication WO2023 / 223541
[0015] The present invention was made to solve the above problems and aims to provide a reflection coefficient measuring device that can accurately measure the reflection coefficient.
[0016] The reflection coefficient measuring device of the present invention comprises a plurality of antenna sections of a coaxial line structure, the end on the side in contact with the sample to be measured being an open end; an open section of the coaxial line structure, the tip of which is an open end; a short section of the coaxial line structure, the tip of which is electrically connected to the central conductor and the ground; a load section of the coaxial line structure configured to terminate the signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the plurality of antenna sections have different aperture diameters at their open ends, and the diameter of the central conductor of the plurality of antenna sections is set so that the reflection coefficient between the open end and the switch is the same for all of the plurality of antenna sections.
[0017] According to the present invention, by setting the diameter of the central conductor of multiple antenna sections so that the reflection coefficient between the open end and the switch matches for multiple antenna sections, the measurement error of the reflection coefficient by multiple antenna sections can be reduced. As a result, in the present invention, the dielectric constant of a sample can be accurately measured using the measurement result of the reflection coefficient, so the dielectric constant distribution of a sample in which the dielectric constant differs due to differences in material in the thickness direction can be measured with high accuracy.
[0018] Figure 1 is a block diagram showing the configuration of a reflection coefficient measuring device according to an embodiment of the present invention. Figure 2 is a cross-sectional view of the sensor section according to an embodiment of the present invention. Figure 3 is a cross-sectional view of the sensor section according to an embodiment of the present invention. Figure 4 is a cross-sectional view of the sensor section according to an embodiment of the present invention. Figure 5 is a plan view of the antenna section according to an embodiment of the present invention. Figure 6 is a plan view of the antenna section according to an embodiment of the present invention. Figure 7 is a plan view of the open section according to an embodiment of the present invention. Figure 8 is a plan view of the short section according to an embodiment of the present invention. Figure 9 is a plan view of the load section according to an embodiment of the present invention. Figure 10 is a cross-sectional view of the antenna section according to an embodiment of the present invention. Figure 11 is a bottom view of the antenna section according to an embodiment of the present invention. Figure 12 is a bottom view of the microstrip line according to an embodiment of the present invention. Figure 13 is a plan view of the dielectric substrate according to an embodiment of the present invention. Figure 14 is a bottom view of the dielectric substrate according to an embodiment of the present invention. Figure 15 is a cross-sectional view of the portion of the dielectric substrate on which the switch, RF terminal, and multilayer wiring board are mounted in an embodiment of the present invention. Figure 16 is a cross-sectional view showing another configuration of the sensor section according to an embodiment of the present invention. Figure 17 is a cross-sectional view showing another configuration of the sensor section according to an embodiment of the present invention. Figure 18 is a cross-sectional view showing another configuration of the sensor unit according to an embodiment of the present invention. Figure 19 is a block diagram showing an example of the configuration of a computer realizing the reflection coefficient measurement unit according to an embodiment of the present invention. Figure 20 is a block diagram showing the configuration of a conventional dielectric spectrometer. Figure 21 is a block diagram showing another configuration of a conventional dielectric spectrometer. Figure 22 is a plan view of the dielectric substrate of a conventional dielectric spectrometer. Figure 23 is a bottom view of the dielectric substrate of a conventional dielectric spectrometer. Figure 24 is a cross-sectional view of the portion of the dielectric substrate of a conventional dielectric spectrometer on which the switch, RF terminal, and coaxial probe are mounted.
[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 1 is a block diagram showing the configuration of the reflection coefficient measuring device (dielectric spectroscopy measuring device) of this embodiment. The reflection coefficient measuring device consists of a sensor unit 1a and a reflection coefficient measuring unit 2. The sensor unit 1a includes a dielectric substrate 10, a coaxial probe 11a, a switch 12a, an RF terminal 14, and a control terminal 15.
[0020] Figures 2 to 4 are cross-sectional views of the sensor unit 1a. The coaxial probe 11a, switch 12a, RF terminal 14, and control terminal 15 are mounted on the dielectric substrate 10. However, the RF terminal 14 and control terminal 15 are not shown in Figures 2 to 4. The coaxial probe 11a includes antenna sections 110 and 111, an open section 112, a short section 113, and a load section 114.
[0021] The antenna section 110 has a pseudo-coaxial cable structure in which the end in contact with the sample to be measured (upper side in Figure 2) is an open end. In the antenna section 110, a land 1100 made of a conductor is formed on the upper surface of the uppermost insulating layer 22 of the multilayer wiring board 21, and a land 1101 made of a conductor is formed on the lower surface of the lowermost insulating layer 25. The lands 1100 and 1101 are connected by vias 1102, which are conductors that penetrate perpendicularly through the insulating layers 22 to 25 along the stacking direction of the conductor layers 26 to 30. Figure 5 is a plan view of the antenna section 110, and Figure 6 is a plan view of the land 1101 layer of the antenna section 110. Note that in Figure 6, multiple conductor layers and insulating layers are shown through the image.
[0022] A conductor layer 26, which serves as a ground conductor, is formed in the same layer as land 1100, but in a region outside of land 1100. Land 1100 and the conductor layer 26 are separated by a conductor-free circular region 1103 in plan view, where there are no conductors. Similarly, a conductor layer 30, which serves as a ground conductor, is formed in the same layer as land 1101, but in a region outside of land 1101. Land 1101 and the conductor layer 30 are separated by a conductor-free circular region 1104 in plan view, where there are no conductors. In this invention, the view of the sensor part 1a from above (the sample side) is considered a plan view.
[0023] Inside the multilayer wiring board 21, multiple conductor layers 27-29, which serve as ground conductors, are formed. In the layers where the conductor layers 27-29 are formed, there is a circular conductor-free region 1105 in plan view, which is a region without conductors and filled with dielectric material. Via 1102 passes through the center of conductor-free regions 1103-1105. In the antenna section 110, the conductor layers 26-30 are connected by through-vias (through-holes) 1106. The insulator layers 22-25, lands 1100, 1101, via 1102 which penetrates the insulator layers 22-25 perpendicularly, the conductor layers 26-30 surrounding via 1102, and the through-via 1106 connecting the conductor layers 26-30 constitute a pseudo-coaxial line.
[0024] The antenna section 111 has a pseudo-coaxial cable structure in which the end on the side in contact with the sample to be measured (upper side in Figure 2) is an open end. In the antenna section 111, a land 1110 made of a conductor is formed on the upper surface of the uppermost insulating layer 22 of the multilayer wiring board 21, and a land 1111 made of a conductor is formed on the lower surface of the lowermost insulating layer 25. The lands 1110 and 1111 are connected by vias 1112, which are conductors that penetrate perpendicularly through the insulating layers 22 to 25 along the stacking direction of the conductor layers 26 to 30. The plan view of the antenna section 111 when viewed from above is the same as in Figure 5. However, as will be described later, the lands 1110, 1111 and vias 1112 of the antenna section 111 have different diameters from the lands 1100, 1101 and vias 1102 of the antenna section 110.
[0025] A conductor layer 26, which serves as a ground conductor, is formed in the same layer as land 1110, but in a region outside of land 1110. Land 1110 and the conductor layer 26 are separated by a conductor-free circular region 1113 in plan view. Similarly, a conductor layer 30, which serves as a ground conductor, is formed in the same layer as land 1111, but in a region outside of land 1111. Land 1111 and the conductor layer 30 are separated by a conductor-free circular region 1114 in plan view.
[0026] In the layers of the multilayer wiring board 21 where the conductor layers 27-29 are formed, there is a circular conductor-free region 1115 in plan view, which is a region without conductors and filled with dielectric material. The via 1112 passes through the center of the conductor-free regions 1113-1115. In the antenna section 111, the conductor layers 26-30 are connected by through vias (through holes) 1116. The insulating layers 22-25, the lands 1110, 1111, the via 1112 that penetrates the insulating layers 22-25 perpendicularly, the conductor layers 26-30 surrounding the via 1112, and the through via 1116 connecting the conductor layers 26-30 constitute a pseudo-coaxial line.
[0027] The open section 112 has a pseudo-coaxial line structure in which the end on the side in contact with the dielectric (insulating layer 22) (upper side in Figure 3) is an open end. In the open section 112, the uppermost conductor layer 26 of the multilayer wiring board 21 has an opening 1127, which is a circular removal area in plan view, so that the lower insulating layer 22 is exposed to the air. A land 1120 made of a conductor is formed on the upper surface of the insulating layer 23, and a land 1121 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1120 and 1121 are connected by vias 1122, which are conductors that penetrate perpendicularly through the insulating layers 23 to 25 along the stacking direction of the conductor layers 26 to 30. Figure 7 is a plan view of the open section 112. In the open section 112, the open end is shielded by the insulating layer 22 to prevent water, dust, and other contaminants from entering the open end.
[0028] Land 1121 and the conductor layer 30 are separated by a circular conductor-free region 1123 in plan view, which has no conductors. Land 1120 and the conductor layer 27 are separated by a circular conductor-free region 1124 in plan view, which has no conductors. In the open section 112, the layers in which the conductor layers 28 and 29 are formed have a circular conductor-free region 1125 in plan view, which is a region without conductors and filled with dielectric material. Via 1122 passes through the center of the conductor-free regions 1123 to 1125. In the open section 112, the conductor layers 27 to 30 are connected by a through via 1126.
[0029] The insulating layers 23-25, the lands 1120, 1121, the via 1122 that penetrates the insulating layers 23-25 perpendicularly, the conductor layers 27-30 surrounding the via 1122, and the through via 1126 connecting the conductor layers 27-30 constitute a pseudo-coaxial line. In the open section 112, the incident signal is almost totally reflected in phase.
[0030] The short section 113 has a pseudo-coaxial line structure in which the central conductor (via) and the ground are electrically connected at the tip. In the short section 113, the uppermost conductor layer 26 of the multilayer wiring board 21 has an opening 1137, which is a circular removal area in plan view, so that the lower insulating layer 22 is exposed to the air. A land 1131 made of a conductor is formed on the lower surface of the insulating layer 25. The conductor layer 27 and the land 1131 are connected by vias 1132, which are conductors that penetrate perpendicularly through the insulating layers 23 to 25 along the stacking direction of the conductor layers 26 to 30. Figure 8 is a plan view of the short section 113.
[0031] The land 1131 and the conductor layer 30 are separated by a circular conductor-free region 1133 in plan view, which has no conductors. In the short section 113, the layers in which the conductor layers 28 and 29 are formed have a circular conductor-free region 1135 in plan view, which is a region without conductors and filled with dielectric material. The via 1132 passes through the center of the conductor-free regions 1133 and 1135. In the short section 113, the conductor layers 27 to 30 are connected by a through via 1136.
[0032] The insulating layers 23-25, the land 1131, the via 1132 that penetrates the insulating layers 23-25 perpendicularly, the conductor layers 27-30 surrounding the via 1132, and the through via 1136 connecting the conductor layers 27-30 constitute a pseudo-coaxial line. In the short-circuit section 113, the phase of the incident signal is inverted and almost total internal reflection occurs.
[0033] The load section 114 has a pseudo-coaxial line structure in which the central conductor (high-frequency signal via) and the ground are connected by a resistor at its tip. In the load section 114, the conductor layers 26, 27 and the insulating layers 22, 23 of the multilayer wiring board 21 are removed to form a cavity 1148, which is a rectangular recess in plan view for housing the resistor 1150. A land 1140 made of a conductor is formed on the upper surface of the insulating layer 24 exposed at the bottom of the cavity 1148, and a land 1141 made of a conductor is formed on the lower surface of the bottom insulating layer 25. The lands 1140 and 1141 are connected by vias 1142, which are conductors that penetrate perpendicularly through the insulating layers 24 and 25 along the stacking direction of the conductor layers 26 to 30.
[0034] Land 1140 and the conductor layer 28 are separated by a circular conductor-free region 1143 in plan view, which has no conductor. Land 1141 and the conductor layer 30 are separated by a circular conductor-free region 1144 in plan view, which has no conductor. In the load section 114, the layer in which the conductor layer 29 is formed has a circular conductor-free region 1145 in plan view, which is a region without a conductor and filled with dielectric. Via 1142 passes through the center of conductor-free regions 1143 to 1145. In the load section 114, the conductor layers 28 to 30 are connected by through vias (through holes) 1146.
[0035] The insulating layers 24 and 25, the lands 1140 and 1141, the via 1142 that penetrates the insulating layers 24 and 25 perpendicularly, the conductor layers 28 to 30 surrounding the via 1142, and the through via 1146 connecting the conductor layers 28 to 30 constitute a pseudo-coaxial line. The land 1140 and the conductor layer 28 are connected by a resistor 1150. The load section 114 is preferable to have low signal reflection. For this reason, the resistor 1150 is selected to match the impedance of the signal line. The cavity 1148 is sealed by, for example, a glass sealing window 1149. One method for fixing the sealing window 1149 is, for example, to bond the sealing window 1149 to the conductor layer 26. Figure 9 is a plan view of the load section 114.
[0036] On the upper surface of the dielectric substrate 10, pads 40 to 44 made of a conductor and a conductor layer 45 serving as a ground conductor are formed. The pads 40 to 44 and the conductor layer 45 are separated from each other by conductor-removed regions 46 to 50 each having a circular shape in plan view with no conductor. On the lower surface of the dielectric substrate 10, pads 51 to 55 made of a conductor, a conductor layer 56 serving as a ground conductor, and microstrip lines 124, 125 are formed. As will be described later, microstrip lines other than 124 and 125 are actually formed as well. The pads 51 to 55 and the conductor layer 56 are separated from each other by conductor-removed regions 57 to 61 each having a circular shape in plan view with no conductor.
[0037] The pads 40 and 51 are connected by a via 62 which is a conductor vertically penetrating the dielectric substrate 10. The conductor layers 45 and 56 are connected by through vias (through holes) 67 which are conductors vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 40 and 51, the via 62, the conductor layers 45 and 56 around the via 62, and the through via 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line. FIG. 10 is a cross-sectional view of the antenna unit 111 as viewed from a direction different from that in FIG. 2, and FIG. 11 is a bottom view of the antenna unit 110 as viewed from below. In FIGS. 6, 10, and 11, reference numeral 120 denotes a microstrip line connecting the pad 51 of the antenna unit 110 and the switch 12a. FIG. 12 is a bottom view of the microstrip line 120 at a position away from the antenna unit 110 as viewed from below.
[0038] The pads 41 and 52 are connected by a via 63 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 41 and 52, the via 63, the conductor layers 45 and 56 around the via 63, and the through via 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line.
[0039] The pads 42 and 53 are connected by a via 64 which is a conductor vertically penetrating the dielectric substrate 10. The dielectric substrate 10, the pads 42 and 53, the via 64, the conductor layers 45 and 56 around the via 64, and the through via 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line.
[0040] The pads 43 and 54 are connected by vias 65, which are conductors that penetrate perpendicularly through the dielectric substrate 10. The dielectric substrate 10, the pads 43 and 54, the vias 65, the conductor layers 45 and 56 surrounding the vias 65, and the through vias 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line.
[0041] The pads 44 and 55 are connected by vias 66, which are conductors that penetrate the dielectric substrate 10 perpendicularly. The dielectric substrate 10, the pads 44 and 55, the vias 66, the conductor layers 45 and 56 surrounding the vias 66, and the through vias 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line. The bottom view of the antenna section 111, open section 112, short section 113, and load section 114, viewed from below, is the same as in Figure 11.
[0042] The connections between land 1101 and pad 40, land 1111 and pad 41, land 1121 and pad 42, land 1131 and pad 43, land 1141 and pad 44, and conductor layer 30 and conductor layer 45 are each connected by solder 68. In this way, a multilayer wiring board 21 with antenna sections 110, 111, open section 112, short section 113, and load section 114 is mounted on the dielectric substrate 10.
[0043] Furthermore, a switch 12a, an RF terminal 14, and a control terminal 15 are mounted on the underside of the dielectric substrate 10. The select terminal of the switch 12a is connected to the microstrip line 124, the input terminal of the switch 12a is connected to the microstrip line 125, and the ground terminal of the switch 12a is connected to the conductor layer 56, all by solder 69. The terminals of the switch 12a and the microstrip lines, which are not shown in Figure 4, are similarly connected by solder.
[0044] Figure 13 is a plan view of the dielectric substrate 10 in this embodiment, and Figure 14 is a bottom view of the same part as in Figure 13, viewed from below. Figure 15 is a cross-sectional view of the dielectric substrate 10 where the switch 12a, RF terminal 14, and multilayer wiring board 21 (coaxial probe 11a) are mounted. Note that the conductor layer 56 is omitted in Figure 14.
[0045] The pad 51 of the antenna section 110 and the first select terminal of the switch 12a are connected by a microstrip line 120 made of a conductor. The pad 52 of the antenna section 111 and the second select terminal of the switch 12a are connected by a microstrip line 121 made of a conductor. The pad 53 of the open section 112 and the third select terminal of the switch 12a are connected by a microstrip line 122 made of a conductor. The pad 54 of the short section 113 and the fourth select terminal of the switch 12a are connected by a microstrip line 123 made of a conductor. The pad 55 of the load section 114 and the fifth select terminal of the switch 12a are connected by a microstrip line 124 made of a conductor. The RF terminal 14 and the input terminal of the switch 12a are connected by a microstrip line 125. The control terminal 15 and the control terminal of the switch 12a are connected by a microstrip line 126.
[0046] Next, the measurement of the reflection coefficient and dielectric constant will be described. The reflection coefficient measurement unit 2 outputs a control signal to the switch 12a via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12a so that one of the antenna sections 110, 111, the open section 112, the short section 113, and the load section 114 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 outputs an RF signal by connecting the open section 112 to the port of the reflection coefficient measurement unit 2, and calculates the reflection coefficient of the open section 112 (dielectric) based on the voltage amplitude and phase of the reflected wave reflected by the open section 112 and the voltage of the incident wave measured by the reflection coefficient measurement unit 2.
[0047] Similarly, the reflection coefficient measurement unit 2 connects the short-circuit unit 113 to a port of the reflection coefficient measurement unit 2, outputs an RF signal, and calculates the reflection coefficient of the short-circuit unit 113 (the metal forming the conductor layer 27) based on the voltage amplitude and phase of the reflected wave reflected by the short-circuit unit 113 and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. Further, the reflection coefficient measurement unit 2 connects the antenna unit 110 or 111 to a port of the reflection coefficient measurement unit 2 and outputs an RF signal in a state where the open end of the antenna unit 110 or 111 is in contact with a known liquid sample (e.g., pure water), and calculates the reflection coefficient of the liquid sample based on the voltage amplitude and phase of the reflected wave reflected by the liquid sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2.
[0048] Subsequently, the reflection coefficient measurement unit 2 outputs a control signal to the switch 12a via the control terminal 15 in a state where the open end of the antenna unit 110 or 111 is in contact with the sample to be measured. Thereby, the reflection coefficient measurement unit 2 switches the switch 12a such that the antenna unit 110 or 111 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 outputs an RF signal to apply an electric field from the antenna unit 110 or 111 to the sample, and calculates the reflection coefficient of the sample to be measured based on the voltage amplitude and phase of the reflected wave reflected by the sample and the voltage of the incident wave measured by the reflection coefficient measurement unit 2. The complex permittivity can be calculated from the measured reflection coefficient as follows.
[0049]
[0050] Here, ε ＊ is the permittivity of the sample to be measured, ε Ａ ＊ is the known permittivity of the dielectric (the insulating layer 22), ε Ｂ ＊ is the known permittivity of the metal forming the conductor layer 27, ε Ｃ ＊ is the known permittivity of the liquid sample. ρ ＊ is the complex reflection coefficient, and when Γ ｉ is the reflection coefficient obtained by measurement and φ ｉ is the phase, it is represented by the following formula (2).
[0051]
[0052] ρ Ａ ＊ The measurement result for the open section 112 is ρ Ｂ ＊ The measurement result for the short section 113 is ρ Ｃ ＊ The measurement result when the open end of the antenna portion 110 or 111 is in contact with the liquid sample, ρ ＊ These correspond to the measurement results of the sample being measured. In this way, the reflection coefficient measurement unit 2 can calculate the complex dielectric constant of the sample being measured from the reflection coefficient measurement results of the dielectric, metal, and liquid samples measured in advance, the reflection coefficient measurement result of the sample being measured, and the known complex dielectric constants of the dielectric, metal, and liquid samples.
[0053] The load section 114 is used for calibrating the VNA. A one-port calibration method for a VNA using an open standard, a short standard, and a load standard as calibration standards is known as SOL calibration. In SOL calibration, three standards—an open standard, a short standard, and a load standard—are connected to the VNA port and calibration data is measured. This calibration data makes it possible to eliminate frequency response reflection tracking, directionality, and source matching of the measurement system in reflection measurements using the port to be calibrated.
[0054] In this embodiment, the reflection coefficient measurement unit 2 outputs a control signal to the switch 12a via the control terminal 15. As a result, the reflection coefficient measurement unit 2 switches the switch 12a so that one of the open section 112, short section 113, and load section 114 is connected to the port of the reflection coefficient measurement unit 2 via the RF terminal 14. The reflection coefficient measurement unit 2 connects the open section 112, short section 113, and load section 114 to the port of the reflection coefficient measurement unit 2 in order and performs reflection measurements for each. Then, the reflection coefficient measurement unit 2 calculates a calibration coefficient (S-parameter of the error circuit present in the reflection coefficient measurement unit 2) from the results of the reflection measurements. By calculating the calibration coefficient in this way, it becomes possible to calculate the reflection coefficient with the measurement error of the reflection coefficient measurement unit 2 removed. The method of calculating the calibration coefficient by SOL calibration is a well-known technique.
[0055] In the configuration described above, in this embodiment, the penetration depth of electromagnetic waves into the sample to be measured is varied by the antenna sections 110 and 111, so the aperture diameter (the dielectric diameter of the open end, which is the diameter of the conductor removal region 1103, 1113) is set to a different value for the antenna sections 110 and 111. For example, in the example in Figure 2, the aperture diameter of the antenna section 111 is smaller than the aperture diameter of the antenna section 110. However, if the aperture diameters are set to different values for the antenna sections 110 and 111, the reflection between the open end and the switch 12a will result in different results for the antenna sections 110 and 111. As a result, errors occur in the reflection coefficient calculated by calibration, and it becomes impossible to accurately measure the dielectric constant of the sample to be measured.
[0056] Therefore, in this embodiment, the lands 1110, 1111, via 1112, and pads 41, 52 of the antenna section 111 are made to have different diameters from the lands 1100, 1101, via 1102, and pads 40, 51 of the antenna section 110, so that the reflection coefficient between the open end and the switch 12a is the same for the antenna sections 110 and 111. In the example in Figure 2, the diameters of the lands 1110, 1111 of the antenna section 111 are larger than the diameters of the lands 1100, 1101 of the antenna section 110, the diameter of the via 1112 of the antenna section 111 is larger than the diameter of the via 1102 of the antenna section 110, and the diameters of the pads 41, 52 of the antenna section 110 are larger than the diameters of the pads 40, 51 of the antenna section 110.
[0057] Thus, in this embodiment, by setting the diameters of the central conductors (lands 1100, 1101, vias 1102, pads 40, 51) of the antenna section 110 and the central conductors (lands 1110, 1111, vias 1112, pads 41, 52) of the antenna section 111 to different values, the reflection coefficient between the open end and the switch 12a can be made consistent across multiple antenna sections 110, 111. As a result, in this embodiment, measurement errors due to multiple antenna sections 110, 111 can be reduced, and the dielectric constant distribution of a sample where the dielectric constant differs due to differences in material in the thickness direction can be measured with high accuracy. In the example shown in Figure 2, the diameters of via 62, which is part of the central conductor of the antenna section 110, and via 63, which is part of the central conductor of the antenna section 111, are the same, but the diameters of vias 62 and 63 may also be set to different values.
[0058] In this embodiment, microstrip lines 120-126 connecting the coaxial probe 11a and the switch 12a are formed on the lower surface of the dielectric substrate 10, but they may also be formed on the upper surface of the dielectric substrate 10. A cross-sectional view in this case is shown in Figures 16-18. The connections between the pad 40 of the antenna section 110 and the first selection terminal of the switch 12a, the pad 41 of the antenna section 111 and the second selection terminal of the switch 12a, the pad 42 of the open section 112 and the third selection terminal of the switch 12a, the pad 43 of the short section 113 and the fourth selection terminal of the switch 12a, and the pad 44 of the load section 114 and the fifth selection terminal of the switch 12a are each connected by microstrip lines formed on the upper surface of the dielectric substrate 10. Pads 51-55 and vias 62-66 are not required.
[0059] The multilayer wiring board 21 and the dielectric board 10 may be the same board. In this case, mounting of different boards using solder or the like becomes unnecessary.
[0060] The reflection coefficient measuring unit 2 described in this embodiment can be realized by a computer equipped with a CPU (Central Processing Unit), a storage device, and an interface, and a program that controls these hardware resources. An example of the configuration of this computer is shown in Figure 19.
[0061] The computer comprises a CPU 300, a storage device 301, a communication device 303, a transmitter 302, a receiver 304, a directional coupler 305, a power supply 306, a transformer 307, and a regulator 308. The transmitter 302 and the receiver 304 are connected to the sensor unit 1a via the directional coupler 305. Electromagnetic waves in the microwave band generated by the transmitter 302 are irradiated onto the sample to be measured. The signal reflected from the sample is input from the sensor unit 1a to the receiver 304 via the directional coupler 305, converted into a digital signal, and then read by the CPU 300. The CPU 300 outputs a control signal to the sensor unit 1a and controls the switch 12a to sequentially read the reflected signals from the antenna units 110, 111, the open unit 112, the short unit 113, and the load unit 114.
[0062] In such a computer, the program for implementing the reflection coefficient measurement method (dielectric spectroscopy measurement method) of the present invention is stored in the storage device 301. The CPU 300 executes the control and arithmetic processing described in this embodiment according to the program stored in the storage device 301. The reflection coefficient and dielectric constant obtained by the processing are transmitted to an external computer by a communication device 303 connected to the CPU 300. As the transmitter 302, for example, a frequency synthesizer using a phase-locked circuit is used. As the receiver 304, for example, a double-balanced mixer is used. A circulator may be used instead of the directional coupler 305.
[0063] In the example shown in Figure 19, a direct conversion type transmit / receive configuration is shown, but a low IF (Intermediate Frequency) type transmit / receive configuration may also be adopted by adding a transmitter with a slightly different transmission frequency. Power supply 306 supplies power to each device. For example, a DC-DC converter is used as the transformer 307. Regulator 308 converts the input voltage from transformer 307 to a desired voltage. A linear regulator that operates even with a low input / output potential difference is used as the regulator 308. A lithium-ion battery or the like is used as the power supply 306.
[0064] In this embodiment, we have described an example in which two antenna sections 110 and 111 are provided, but it goes without saying that three or more antenna sections may also be provided.
[0065] Some or all of the above examples may also be described as follows, but are not limited to the following:
[0066] (Note 1) The reflection coefficient measuring device of the present invention comprises a plurality of antenna sections of a coaxial line structure, the end on the side in contact with the sample to be measured being an open end; an open section of the coaxial line structure, the tip of which is an open end; a short section of the coaxial line structure, the tip of which is in conductivity between the central conductor and the ground; a load section of the coaxial line structure configured to terminate the signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the plurality of antenna sections have different aperture diameters at their open ends, and the diameter of the central conductor of the plurality of antenna sections is set such that the reflection coefficient between the open end and the switch is the same for all of the plurality of antenna sections.
[0067] (Note 2) In the reflection coefficient measuring device described in Note 1, the reflection coefficient measuring unit calculates the dielectric constant of the sample based on the measurement result of the reflection coefficient.
[0068] (Note 3) In the reflection coefficient measuring device described in Note 1, the reflection coefficient measuring unit controls the switch to connect the short section, the open section, and the load section to its ports in order and perform reflection measurements on each, and performs calibration to eliminate the measurement error of the reflection coefficient based on the results of the reflection measurements.
[0069] (Note 4) In the reflection coefficient measuring device described in Note 1, the plurality of antenna sections, the open section, the short section, the load section, and the switch are arranged on the same circuit board.
[0070] (Note 5) In the reflection coefficient measuring device described in Note 4, the load section comprises a resistor configured to terminate the signal line, and the resistor is housed in a recess formed on the surface of the substrate.
[0071] (Note 6) In the reflection coefficient measuring device described in Note 1, each of the plurality of antenna sections, the open section, the short section, and the load section is a coaxial line structure in which a ground conductor is arranged around the central conductor, which is a signal line.
[0072] 1a...Sensor section, 2...Reflection coefficient measurement section, 10...Dielectric substrate, 11a...Coaxial probe, 12a...Switch, 14...RF terminal, 15...Control terminal, 21...Multilayer wiring board, 110, 111...Antenna section, 112...Open section, 113...Short section, 114...Load section.
Claims
1. A reflection coefficient measuring device comprising: a plurality of antenna sections of a coaxial line structure, the end on which it contacts the target sample is an open end; an open section of the coaxial line structure, the tip of which is an open end; a short section of the coaxial line structure, the tip of which is in conductivity between the central conductor and the ground; a load section of the coaxial line structure configured to terminate the signal line; a switch configured to select one of the plurality of antenna sections, the open section, the short section, and the load section; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the plurality of antenna sections, the open section, and the short section to its own port and measure the reflection coefficient of each, wherein the plurality of antenna sections have different aperture diameters at their open ends, and the diameter of the central conductor of the plurality of antenna sections is set such that the reflection coefficient between the open end and the switch is the same for all of the plurality of antenna sections.
2. A reflection coefficient measuring device according to claim 1, characterized in that the reflection coefficient measuring unit calculates the dielectric constant of the sample based on the reflection coefficient measurement result.
3. A reflection coefficient measuring device according to claim 1, wherein the reflection coefficient measuring unit controls the switch to sequentially connect the short section, the open section, and the load section to its own port and perform reflection measurements for each, and performs calibration to eliminate the measurement error of the reflection coefficient based on the results of the reflection measurements.
4. A reflection coefficient measuring device according to claim 1, characterized in that the plurality of antenna sections, the open section, the short section, the load section, and the switch are arranged on the same substrate.
5. A reflection coefficient measuring device according to claim 4, wherein the load portion comprises a resistor configured to terminate the signal line, and the resistor is housed in a recess formed on the surface of the substrate.
6. A reflection coefficient measuring device according to claim 1, characterized in that each of the plurality of antenna sections, the open section, the short section, and the load section is a coaxial line structure in which a ground conductor is arranged around the central conductor which is a signal line.