Reflectance coefficient measuring device

Abstract

Provided is a reflectance coefficient measuring device comprising: antenna units (110, 111); an open unit (112); a short unit (113); a load unit (114); a switch (12a); and a reflectance coefficient measuring unit that controls the switch (12a) to sequentially connect the antenna units (110, 111), the open unit (112), and the short unit (113) to its port and measure respective reflectance coefficients. The reflectance coefficient measuring unit controls the switch (12a) to sequentially connect the short unit (113), the open unit (112), and the load unit (114) to its port to perform respective reflection measurements, and performs calibration on the basis of measurement results to remove measurement errors of reflectance coefficients.

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 in the microwave to millimeter wave range. Figure 21 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 21, 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, in addition to the antenna used to measure the sample, a device has been proposed that uses three types of calibration covers: an open type with an open end, a short-circuit type with a short-circuited open end, and a loaded type with a load connected to the open end (Patent Document 1). Also, a calibration device has been proposed that generates multiple states such as open, short-circuited, and loaded for the output port of a VNA, measures multiple states with the VNA, and calculates the calibration coefficient of the VNA based on the measurement results (Patent Document 2). Moreover, 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 3).

[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 4). Figure 22 shows the configuration of the dielectric spectroscopy measuring device disclosed in Patent Document 4.

[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 4, 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 23 is a plan view of the dielectric substrate 10, and Figure 24 is a bottom view of the same part as in Figure 23, viewed from below. Figure 25 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] A connection point exists between the multilayer wiring board on which the coaxial probe 11 (antenna sections 110, 111, open section 112, short section 113) is formed and the dielectric substrate 10 on which the multilayer wiring board is mounted. On the other hand, as shown in Figure 22, there is no connection point between the multilayer wiring board and the dielectric substrate 10 in the load section 16 mounted on the dielectric substrate 10. Therefore, since the reflection from the connection point is different between the coaxial probe 11 and the load section 16, an error occurs in the reflection coefficient calculated by calibration, resulting in the problem that the dielectric constant of the sample cannot be accurately measured.

[0014] Reflection characteristics of coaxial probe 11 and commercially available coaxial probe (S parameter S) １１ Figures 26 and 27 show the following. In Figure 26, 700 is the S of a commercially available coaxial probe. １１ The amplitude component, 701 is the S of the coaxial probe 11. １１ This shows the amplitude component. 800 in Figure 27 is the S of a commercially available coaxial probe. １１ The phase component, 801 is the S of the coaxial probe 11. １１ This shows the phase component. As shown in Figures 26 and 27, it can be seen that there is a difference in the reflection characteristics between the coaxial probe 11 and a commercially available coaxial probe.

[0015] Japanese Patent Publication No. 5499379, Japanese Unexamined Patent Publication No. 2005-99038, Japanese Patent Publication No. 6771372, International Publication WO2023 / 223541

[0016] The present invention was made to solve the above problems and aims to provide a reflection coefficient measuring device that can reduce the measurement error of the reflection coefficient.

[0017] The reflection coefficient measuring device of the present invention comprises: an antenna portion formed on a substrate with an open end on the side in contact with the sample to be measured; an open portion formed on the substrate with an open tip; a short portion formed on the substrate with a central conductor and ground being electrically connected at the tip; a load portion formed on the substrate and configured to terminate a signal line; a switch configured to select one of the antenna portion, the open portion, the short portion, and the load portion; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the antenna portion, the open portion, and the short portion to its own port and measure the reflection coefficient of each, wherein the reflection coefficient measuring unit controls the switch to sequentially connect the short portion, the open portion, and the load portion to its own port 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.

[0018] According to the present invention, by forming the antenna section, open section, short section, and load section on the same substrate, the reflection from the connection point of the wiring between the substrate and the switch can be made identical for all of the antenna section, open section, short section, and load section, so that the measurement error of the reflection coefficient can be reduced by calibration. As a result, in the present invention, the dielectric constant of the sample can be accurately measured using the measurement result of the reflection coefficient.

[0019] 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 where the switch, RF terminal, and multilayer wiring board are mounted in an embodiment of the present invention. Figure 16 is a diagram showing the reflection characteristics of a coaxial probe according to an embodiment of the present invention. Figure 17 is a diagram showing the reflection characteristics of a coaxial probe according to an embodiment of the present invention. Figure 18 is a plan view showing another configuration of the loading section according to an embodiment of the present invention. Figure 19 is a plan view showing another configuration of the loading section according to an embodiment of the present invention. Figure 20 is a block diagram showing an example of the configuration of a computer realizing a reflection coefficient measurement section according to an embodiment of the present invention. Figure 21 is a block diagram showing the configuration of a conventional dielectric spectroscopy measuring device. Figure 22 is a block diagram showing another configuration of a conventional dielectric spectroscopy measuring device. Figure 23 is a plan view of the dielectric substrate of a conventional dielectric spectroscopy measuring device. Figure 24 is a bottom view of the dielectric substrate of a conventional dielectric spectroscopy measuring device. Figure 25 is a cross-sectional view of the portion of the dielectric substrate of a conventional dielectric spectroscopy measuring device on which the switch, RF terminal, and coaxial probe are mounted. Figure 26 is a diagram showing the reflection characteristics of a conventional coaxial probe. Figure 27 is a diagram showing the reflection characteristics of a conventional coaxial probe.

[0020] 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 1 and a reflection coefficient measuring unit 2. The sensor unit 1 includes a dielectric substrate 10, a coaxial probe 11a, a switch 12a, an RF terminal 14, and a control terminal 15.

[0021] Figures 2 to 4 are cross-sectional views of the sensor unit 1. 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.

[0022] The antenna section 110 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 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, a land 1107 made of a conductor is formed on the upper surface of the insulating layer 23, a land 1108 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1109 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1101 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1100, 1101, 1107-1109 are connected by vias 1102, which are conductors that penetrate perpendicularly through the insulating layers 22-25 along the stacking direction of the conductor layers 26-30. 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. In Figure 6, multiple conductor layers and insulating layers are shown through the material.

[0023] A conductor layer 26, which serves as a ground conductor, is formed in the same layer as land 1100 but outside of land 1100. Land 1100 and the conductor layer 26 are separated by a conductor-free circular area 1103 in plan view. Similarly, a conductor layer 30, which serves as a ground conductor, is formed in the same layer as land 1101 but outside of land 1101. Land 1101 and the conductor layer 30 are separated by a conductor-free circular area 1104 in plan view.

[0024] Multiple conductor layers 27-29, which serve as ground conductors, are formed inside the multilayer wiring board 21. The conductor layers 27-29 and the lands 1107-1109 are separated by 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 the conductor-free regions 1103-1105. In the antenna section 110, the conductor layers 26-30 are connected by through-vias (through-holes) 1106.

[0025] The insulator layers 22-25, the lands 1100, 1101, 1107-1109, the via 1102 that penetrates the insulator layers 22-25 perpendicularly, the conductor layers 26-30 surrounding the via 1102, and the through via 1106 connecting the conductor layers 26-30 constitute a pseudo-coaxial line. The via 1102 and the conductor removal regions 1103-1105 are circular in plan view, and the impedance of the pseudo-coaxial line can be designed according to the sample being measured by the diameter of the via 1102, the diameter of the surrounding conductor removal regions 1103-1105, and the dielectric constant of the dielectric of the insulator layers 22-25.

[0026] 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 3) 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, a land 1117 made of a conductor is formed on the upper surface of the insulating layer 23, a land 1118 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1119 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1111 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1110, 1111, 1117-1119 are connected by vias 1112, which are conductors that penetrate perpendicularly through the insulating layers 22-25 along the stacking direction of the conductor layers 26-30. The plan view of the antenna section 111 when viewed from above is the same as in Figure 5.

[0027] 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.

[0028] The conductor layers 27-29 and lands 1117-1119 of the multilayer wiring board 21 are separated by 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.

[0029] The insulating layers 22-25, the lands 1110, 1111, 1117-1119, 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. The via 1112 and the conductor removal regions 1113-1115 are circular in plan view, and the impedance of the pseudo-coaxial line can be designed according to the sample being measured by the diameter of the via 1112, the diameter of the surrounding conductor removal regions 1113-1115, and the dielectric constant of the dielectric of the insulating layers 22-25. The shape of the antenna section 111 may be formed differently from that of the antenna section 110 to accommodate different samples.

[0030] 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 2) 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, a land 1128 made of a conductor is formed on the upper surface of the insulating layer 24, a land 1129 made of a conductor is formed on the upper surface of the insulating layer 25, and a land 1121 made of a conductor is formed on the lower surface of the insulating layer 25. The lands 1120, 1121, 1128, and 1129 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 an insulating layer 22 to prevent water, dust, and other contaminants from entering the open end.

[0031] Between the land 1121 and the conductor layer 30, there is a circular conductor removal region 1123 without conductors in plan view that separates them. Between the land 1120 and the conductor layer 27, there is a circular conductor removal region 1124 without conductors in plan view that separates them. Between the conductor layers 28 and 29 and the lands 1128 and 1129, there is a circular conductor removal region 1125 in plan view that is a region filled with a dielectric without conductors that separates them. The via 1122 passes through the centers of the conductor removal regions 1123 to 1125. In the open portion 112, the conductor layers 27 to 30 are connected by through vias 1126.

[0032] The insulator layers 23 to 25, the lands 1120, 1121, 1128, 1129, the via 1122 that vertically penetrates the insulator layers 23 to 25, the conductor layers 27 to 30 around the via 1122, and the through via 1126 that connects the conductor layers 27 to 30 constitute a quasi-coaxial line. In the open portion 112, the incident signal is almost totally reflected in the same phase.

[0033] The short portion 113 has a quasi-coaxial line structure in which the central conductor (via) and the ground are electrically connected at the tip. In the short portion 113, an opening 1137, which is a circular removal region in plan view, is formed in the topmost conductor layer 26 of the multilayer wiring substrate 21 so that the lower insulator layer 22 is exposed in the air. A land 1138 made of a conductor is formed on the upper surface of the insulator layer 24, a land 1139 made of a conductor is formed on the upper surface of the insulator layer 25, and a land 1131 made of a conductor is formed on the lower surface of the insulator layer 25. The conductor layer 27 and the lands 1131, 1138, 1139 are connected by a via 1132, which is a conductor that vertically penetrates the insulator layers 23 to 25 along the stacking direction of the conductor layers 26 to 30. FIG. 8 is a plan view of the short portion 113.

[0034] Between the land 1131 and the conductor layer 30, there is a circular conductor removal region 1133 without conductors in plan view that separates them. Between the conductor layers 28 and 29 and the lands 1138 and 1139, there is a circular conductor removal region 1135 without conductors and filled with dielectric in plan view that separates them. The via 1132 passes through the centers of the conductor removal regions 1133 and 1135. In the short circuit portion 113, the conductor layers 27 to 30 are connected by a through via 1136.

[0035] The insulator layers 23 to 25, the lands 1131, 1138, and 1139, the via 1132 that vertically penetrates the insulator layers 23 to 25, the conductor layers 27 to 30 around the via 1132, and the through via 1136 that connects the conductor layers 27 to 30 form a pseudo coaxial line. In the short circuit portion 113, the phase of the incident signal is inverted and almost totally reflected.

[0036] The load portion 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 the tip. In the load portion 114, the conductor layers 26 and 27 and the insulator layers 22 and 23 of the multilayer wiring board 21 are removed, and a cavity 1148 which is a rectangular recess in plan view for accommodating the resistor 1150 is formed. On the upper surface of the insulator layer 24 exposed on the bottom surface of the cavity 1148, a land 1140 made of a conductor is formed, and on the lower surface of the lowermost insulator layer 25, a land 1141 made of a conductor is formed. The lands 1140 and 1141 are connected by a via 1142 which is a conductor that vertically penetrates the insulator layers 24 and 25 along the stacking direction of the conductor layers 26 to 30.

[0037] Between the land 1140 and the conductor layer 28, there is a circular conductor removal region 1143 without conductors in plan view that separates them. Between the land 1141 and the conductor layer 30, there is a circular conductor removal region 1144 without conductors in plan view that separates them. In the load portion 114, in the layer where the conductor layer 29 is formed, there is a circular conductor removal region 1145 which is a region without conductors and filled with dielectric in plan view. The via 1142 passes through the centers of the conductor removal regions 1143 to 1145. In the load portion 114, the conductor layers 28 to 30 are connected by a through via (through hole) 1146.

[0038] 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.

[0039] On the upper surface of the dielectric substrate 10, conductive pads 40-44 and a conductive layer 45 that serves as a ground conductor are formed. The pads 40-44 and the conductive layer 45 are separated by conductive-free circular areas 46-50 in plan view. On the lower surface of the dielectric substrate 10, conductive pads 51-55, a conductive layer 56 that serves as a ground conductor, and microstrip lines 120 and 125 are formed. As will be described later, microstrip lines other than 120 and 125 are also formed. The pads 51-55 and the conductive layer 56 are separated by conductive-free circular areas 57-61 in plan view.

[0040] The pads 40 and 51 are connected by vias 62, which are conductors that penetrate perpendicularly through the dielectric substrate 10. The conductor layers 45 and 56 are connected by through vias (through holes) 67, which are conductors that penetrate perpendicularly through the dielectric substrate 10. The dielectric substrate 10, the pads 40 and 51, the vias 62, the conductor layers 45 and 56 around the vias 62, and the through vias 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line. Figure 10 is a cross-sectional view of the antenna section 111 viewed from a different direction than in Figure 2, and Figure 11 is a bottom view of the antenna section 110 viewed from below. In Figures 6, 10, and 11, 120 is a microstrip line connecting the pads 51 of the antenna section 110 and the switch 12a. Figure 12 is a bottom view of the microstrip line 120 viewed from below at a position away from the antenna section 110.

[0041] The pads 41 and 52 are connected by vias 63, which are conductors that penetrate perpendicularly through the dielectric substrate 10. The dielectric substrate 10, the pads 41 and 52, the vias 63, the conductor layers 45 and 56 surrounding the vias 63, and the through vias 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line.

[0042] The pads 42 and 53 are connected by vias 64, which are conductors that penetrate perpendicularly through the dielectric substrate 10. The dielectric substrate 10, the pads 42 and 53, the vias 64, the conductor layers 45 and 56 surrounding the vias 64, and the through vias 67 connecting the conductor layers 45 and 56 constitute a pseudo-coaxial line.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Similarly, the reflection coefficient measurement unit 2 connects the short circuit unit 113 to the port of the reflection coefficient measurement unit 2 to output an RF signal, and calculates the reflection coefficient of the short circuit unit 113 (the metal constituting 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 outputs an RF signal by connecting the open end of the antenna unit 110 or 111 to the port of the reflection coefficient measurement unit 2 in a state where the open end of the antenna unit 110 or 111 is in contact with a known liquid sample (for example, 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.

[0051] 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 so 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 dielectric constant can be calculated from the measured reflection coefficient as follows.

[0052]

[0053] Here, ε ＊ is the dielectric constant of the sample to be measured, ε Ａ ＊ is the known dielectric constant of the dielectric (insulating layer 22), ε Ｂ ＊ is the known dielectric constant of the metal constituting the conductor layer 27, ε Ｃ ＊ is the known dielectric constant of the liquid sample. ρ ＊ is the complex reflection coefficient. When the reflection coefficient obtained by measurement is Γ ｉ and the phase is φ ｉ , it is expressed by the following formula (2).

[0054]

[0055] 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.

[0056] 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.

[0057] 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.

[0058] As described above, in this embodiment, the antenna sections 110, 111, the open section 112, the short section 113, and the load section 114 are formed on the same multilayer wiring board 21. As a result, in this embodiment, the reflection from the connection points of the wiring between the multilayer wiring board 21 and the dielectric substrate 10 can be made the same for all of the antenna sections 110, 111, the open section 112, the short section 113, and the load section 114, so that the measurement error of the reflection coefficient measurement unit 2 can be appropriately removed by calibration. As a result, in this embodiment, the measurement error of the dielectric constant of the sample can be reduced.

[0059] Reflection characteristics of the coaxial probe 11a of this embodiment and a commercially available coaxial probe (S parameter S) １１ Figures 16 and 17 show the following. In Figure 16, 500 is the S of a commercially available coaxial probe. １１ The amplitude component, 501 is the S of the coaxial probe 11a. １１ This shows the amplitude component. 600 in Figure 17 is the S of a commercially available coaxial probe. １１ The phase component, 601 is S of the coaxial probe 11a. １１ This shows the phase component. In this example, there are no major differences as shown in Figures 26 and 27, and it can be seen that the reflection characteristics are close to those of a commercially available coaxial probe.

[0060] Furthermore, in this embodiment, by placing the resistor 1150 inside the cavity 1148, the surface irregularities of the coaxial probe 11a can be eliminated, thereby facilitating contact between the antenna sections 110 and 111 and the sample.

[0061] In the examples of Figures 4 and 9, the resistor 1150 is placed on the land 1140 of the load section 114, but a configuration as shown in the plan views of Figures 18 and 19 is also possible. In Figures 18 and 19, the cavity 1148 and sealing window 1149 are omitted from the description. In the example of Figure 18, the land 1140 on the insulating layer 24 and the conductor 1152 are connected by a microstrip line 1151, and the resistor 1150 is provided to connect the conductor 1152 and the conductor layer 28. In the example of Figure 19, the resistor 1150 is provided to connect the end of the microstrip line 1151 on the opposite side of the land 1140 to the conductor layer 28.

[0062] Note that 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.

[0063] 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 20.

[0064] 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 1 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 1 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 1 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.

[0065] 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.

[0066] In the example shown in Figure 20, a direct conversion type transmit / receive configuration is shown, but a low IF (Intermediate Frequency) type transmit / receive configuration may 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. For regulator 308, a linear regulator that operates even with a low input / output potential difference is used. For power supply 306, a lithium-ion battery or the like is used.

[0067] Some or all of the above examples may also be described as follows, but are not limited to the following:

[0068] (Note 1) The reflection coefficient measuring device of the present invention comprises an antenna portion formed on a substrate, the end on the side in contact with the sample to be measured being an open end; an open portion formed on the substrate, the tip of which is an open end; a short portion formed on the substrate, the tip of which is electrically connected to the central conductor and to ground; a load portion formed on the substrate, configured to terminate a signal line; a switch configured to select one of the antenna portion, the open portion, the short portion, and the load portion; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the antenna portion, the open portion, and the short portion to its own port and measure the reflection coefficient of each; the reflection coefficient measuring unit controls the switch to sequentially connect the short portion, the open portion, and the load portion to its own port and perform reflection measurements of each; and performs calibration to eliminate the measurement error of the reflection coefficient based on the results of the reflection measurements.

[0069] (Note 2) In the reflection coefficient measuring device described in Note 1, 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.

[0070] (Note 3) In the reflection coefficient measuring device described in Note 1, the antenna section, the open section, the short section, and the load section each have a coaxial line structure in which a ground conductor is arranged around a central conductor which is a signal line.

[0071] (Note 4) 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.

[0072] 1...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, 120-126...Microstrip line, 1148...Cavity, 1150...Resistor.

Claims

1. A reflection coefficient measuring device comprising: an antenna portion formed on a substrate with an open end on the side in contact with the sample to be measured; an open portion formed on the substrate with an open tip; a short portion formed on the substrate with a central conductor and ground being electrically connected at the tip; a load portion formed on the substrate and configured to terminate a signal line; a switch configured to select one of the antenna portion, the open portion, the short portion, and the load portion; and a reflection coefficient measuring unit configured to control the switch to sequentially connect the antenna portion, the open portion, and the short portion to its own port and measure the reflection coefficient of each, wherein the reflection coefficient measuring unit controls the switch to sequentially connect the short portion, the open portion, and the load portion to its own port 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.

2. A reflection coefficient measuring device according to claim 1, 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.

3. A reflection coefficient measuring device according to claim 1, characterized in that each of the antenna section, the open section, the short section, and the load section is a coaxial line structure in which a ground conductor is arranged around a central conductor which is a signal line.

4. 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 measurement result of the reflection coefficient.

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