Multi-port network circuit and high sensitivity fluid sensor

Abstract

The present application relates to a kind of multi-port network circuit and high sensitivity fluid sensor, including Butler matrix circuit, differential module, input end power divider, reference end quadrature coupler and port group for being connected with external;Input end power divider has first output port and second output port, first output port is connected to differential module, second output port is connected to reference end quadrature coupler;Reference end quadrature coupler is connected to the first input port of Butler matrix circuit;The output port of differential module is connected to the second input port of Butler matrix circuit;Differential module includes output power divider, reference path composite left-right hand transmission line, fourth quadrature coupler, sensing path composite left-right hand transmission line and microstrip line;The isolation end D of fourth quadrature coupler is connected to the first output power divider sensing path input port of output power divider via sensing path composite left-right hand transmission line.The present application enhances the phase sensitivity of fluid sensor.

Description

Technical Field

[0001] This invention relates to the field of fluid sensor technology, specifically to multi-port network circuits and high-sensitivity fluid sensors. Background Technology

[0002] Fluid concentration, as a crucial indicator, impacts industrial production, environmental safety, and public health, making its detection technology a long-standing hot topic in the sensor field. In gas sensing, detecting the concentration of volatile organic compounds (VOCs) is of great significance. Firstly, VOCs are often flammable and explosive, requiring concentration monitoring in factories to prevent serious accidents. Secondly, VOCs are toxic, and accidental inhalation can harm workers' health. Furthermore, in agricultural production, some VOCs can be used to reflect the growth or disease status of crops and livestock, aiding in production and management. In liquid sensing, real-time monitoring of the water content in emulsified oil helps prevent equipment wear and facilitates oil changes. In petroleum processing, the water content of oil is also measured, serving as a criterion for process quality. Therefore, the demand for fluid concentration detection is high, making the development of a highly sensitive, reliable, and stable sensor essential.

[0003] Currently, various fluid detection methods have been reported, such as spectroscopic detection, semiconductor metal oxide detection, resistive detection, conductive polymer detection, and microwave detection. Metal oxide detection methods offer high sensitivity, but require high-temperature operating environments. While conductive polymer detection methods do not require high temperatures, they lack stability. Microwave detection methods, due to their low cost, stable response, and ability to operate at room temperature, have become a highly promising approach, and microwave-based sensors are widely used in the measurement of liquids, solids, displacement, and gases. In recent years, among the numerous microwave technologies applied to fluid sensing both domestically and internationally, microwave multi-port fluid detection technology is particularly novel. The characteristics of multi-port technology are low cost and stable reliability. Microwave multiport circuits developed based on multiport technology are often used in the sensing field as an alternative to vector network analyzers for low-cost offline measurements. In addition, multiport technology is also a key technology in phased array radar and millimeter-wave transceivers. Research on multiport technology started earlier abroad, and its applications are more mature. However, in the field of fluid sensing, existing fluid sensors based on multiport technology, both domestically and internationally, mainly focus on improving fluid sensing resolution, with relatively little research on enhancing sensitivity. Sensitivity is also crucial for sensor performance; good sensitivity helps enhance the sensor's detection accuracy in stable environments and improves the stability and reliability of sensing equipment.

[0004] Therefore, it is necessary to develop a new multi-port network circuit and a high-sensitivity fluid sensor. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-port network circuit and a high-sensitivity fluid sensor, which can enhance the sensitivity of the sensor.

[0006] In a first aspect, the present invention provides a multi-port network circuit comprising a Butler matrix circuit, a differential module, an input power divider, a reference quadrature coupler, and a port group for external connection; the input power divider has a first output port and a second output port, wherein the first output port is connected to the differential module via a microstrip line, and the second output port is connected to the reference quadrature coupler; the reference quadrature coupler is connected to the first input port of the Butler matrix circuit; and the output port of the differential module is connected to the second input port of the Butler matrix circuit.

[0007] The differential module includes an output power divider, a reference path composite left-handed and right-handed transmission line, a fourth quadrature coupler, a sensor path composite left-handed and right-handed transmission line, and a microstrip line. The isolation terminal D of the fourth quadrature coupler is connected to one end of the sensor path composite left-handed and right-handed transmission line via a microstrip line and a tapered microstrip line. The other end of the sensor path composite left-handed and right-handed transmission line is connected to the first output power divider sensor input port of the output power divider via a tapered microstrip line and a microstrip line, forming a sensor branch. The through terminal D of the fourth quadrature coupler is connected to one end of the reference path composite left-handed and right-handed transmission line via a microstrip line and a tapered microstrip line. The other end of the reference path composite left-handed and right-handed transmission line is connected to the second output power divider sensor input port of the output power divider via a tapered microstrip line and a microstrip line, forming a reference branch. The signal in the sensor branch has a 90° phase delay compared to the reference branch.

[0008] Optionally, the reference path composite left- and right-handed transmission line and the sensing path composite left- and right-handed transmission line have the same structure, wherein the reference path composite left- and right-handed transmission line includes interdigitated capacitors, microstrip inductors, and virtual ground capacitors.

[0009] One end of the microstrip inductor is connected to the arm of the interdigitated capacitor, and the other end of the microstrip inductor is connected to the virtual ground capacitor.

[0010] Optionally, the Butler matrix circuit includes a first orthogonal coupler, a second orthogonal coupler, a third orthogonal coupler, a microstrip line with an electrical length of 180°, and a first resistor;

[0011] The input terminal A of the first quadrature coupler serves as the first input port of the entire Butler matrix circuit, used to receive input signals. The through terminal A of the first quadrature coupler is connected to the input terminal B of the second quadrature coupler via a microstrip line with an electrical length of 180°. The coupling terminal A of the first quadrature coupler is connected to the input terminal C of the third quadrature coupler. The isolation terminal A of the first quadrature coupler is connected to one end of a first resistor, and the other end of the first resistor is grounded. The through terminal C of the third quadrature coupler is connected to the isolation terminal B of the second quadrature coupler. The isolation terminal C of the third quadrature coupler serves as the second input port of the Butler matrix circuit, used to receive the output signals of the differential module. The signal is fed in from the input terminal A of the first quadrature coupler and the isolation terminal C of the third quadrature coupler, and then output from the through terminal B, the coupling terminal B of the second quadrature coupler, and the coupling terminal C of the third quadrature coupler.

[0012] Optionally, the first output port of the input power divider is connected to the input port D of the fourth quadrature coupler of the differential module via a microstrip line; the second output port of the input power divider is connected to the reference quadrature coupler via a microstrip line; and the reference quadrature coupler is connected to the input terminal A of the first quadrature coupler in the Butler matrix circuit.

[0013] Optionally, a first gap exists between the first output port and the second output port in the input power divider;

[0014] There is a second gap between the first output power divider sensor input port and the second output power divider sensor input port in the output power divider.

[0015] A second resistor is welded at both the first and second gaps; this improves the isolation between the two signals of the power divider.

[0016] Optionally, the isolation terminal A of the first orthogonal coupler is welded with a 50Ω matching load to absorb power reflected due to mismatch at the port.

[0017] Optionally, the port group includes:

[0018] The main input port is used to connect a single-frequency signal source. This main input port is connected to the input port E of the input power divider.

[0019] The first matching port is used to connect a 50Ω matching load, and this first matching port is connected to the isolation terminal D of the fourth quadrature coupler.

[0020] The second matching port is used to connect a 50Ω matching load. This second matching port is connected to the isolation terminal F of the reference quadrature coupler.

[0021] The reference output port is used to connect to the power detector. This reference output port is connected to the coupling terminal F of the reference quadrature coupler.

[0022] The third output port is used to connect to the power detector, and this third output port is connected to the coupling terminal C of the second quadrature coupler.

[0023] The fourth output port is used to connect to the power detector, and this fourth output port is connected to the coupling terminal B of the second quadrature coupler;

[0024] The fifth output port is used to connect to the power detector, and this fifth output port is connected to the through-hole B of the second quadrature coupler.

[0025] Optionally, the fourth quadrature coupler is a 4.77dB quadrature coupler, and the isolation terminal D and the through terminal D of the fourth quadrature coupler 23 output signals with a power distribution ratio of 2:1, and the amplitude ratio is... Applying this 4.77dB quadrature coupler to the differential module makes the ratio of the sensing branch signal power to the reference branch signal power 2:1, and the amplitude ratio is... According to Matlab simulations, when the phase change range of the composite left and right hand transmission lines in the sensing path is within 50° under the configuration of the differential module, the vector superposition signal output by the power divider in the differential module can produce a larger phase change.

[0026] Secondly, the high-sensitivity fluid sensor described in this invention employs a multi-port network circuit as described in this invention, wherein the multi-port network circuit is disposed on a circuit medium board.

[0027] Optionally, it also includes:

[0028] A microfluidic channel is mounted on a circuit substrate and located directly above the differential module. A groove is formed at the bottom of the microfluidic channel, and through holes are provided at both ends of the groove, with the top of the through holes extending to the upper surface of the microfluidic channel.

[0029] A fluid base assembly includes fluid bases equal in number to the number of through holes. Each fluid base is installed above the through hole of a microfluidic channel. Each fluid base has a flow channel hole, one end of which is connected to the corresponding through hole, and the other end of which is a fluid inlet or outlet.

[0030] In implementing this high-sensitivity fluid sensor, the analyte fluid is injected into two microfluidic channels: the sensing branch and the reference branch. The concentration of the analyte fluid changes in the sensing branch's microfluidic channel, while the concentration in the reference branch remains constant. When the analyte fluid concentration changes, its dielectric constant changes. This change in dielectric constant disturbs the electric field in the interdigital capacitance region of the CRLH-TL, causing a change in the S21 phase of the CRLH-TL. During this process, the phase of the CRLH-TL in the sensing branch changes while the phase of the reference branch remains unchanged. This results in a larger phase change in the vector superposition signal ultimately output by the output power divider in the differential module. The function of the microfluidic channels is to ensure that the fluid concentration changes in the sensing branch within the same circuit, while the fluid concentration in the reference branch remains unchanged.

[0031] The beneficial effects of this invention are:

[0032] (1) The multi-port network circuit integrating two CRLH-TLs (i.e., composite left-handed and right-handed transmission lines, including a reference path composite left-handed and right-handed transmission line and a sensing path composite left-handed and right-handed transmission line) and a differential module provided by this invention enhances the sensor sensitivity by improving the circuit topology and based on the principle of signal vector superposition within the differential module. Furthermore, the provided topology integrates the composite left-handed and right-handed transmission lines with the multi-port circuit, achieving system integration and miniaturization. This invention employs dual-path microfluidic technology, using one fluid path as a reference and the other as a sensor, combined with the characteristics of the differential module circuit, to enhance the phase sensitivity of the fluid sensor. Simulation results show that the phase sensitivity of this invention is approximately twice that of a single CRLH-TL.

[0033] (2) The multi-port network circuit proposed in this invention is optimized on the circuit, so it is not limited to liquid sensing, but can also be coated with sensitive material in the interdigitated capacitor area for gas sensing, and has good robustness for a variety of sensing objects.

[0034] (3) The multi-port circuit provided by this invention has significant economic advantages. The multi-port circuit provided by this invention can inverse the change in the detected fluid concentration simply by the change in the output voltage of the power detector. The voltage value is very easy to detect and record with current technology. For example, a data acquisition card plus LabVIEW can complete the accurate real-time recording of the voltage value. Therefore, this invention can perform offline measurement without complex detection instruments, greatly reducing the cost of fluid detection.

[0035] (4) The present invention is based on a single-frequency sensing method, so only a single-frequency signal source is needed, avoiding the use of a wideband signal source, which is more conducive to integration.

[0036] (5) This invention is an integration of passive circuits and is not based on resonance, which means that this invention has good stability. Attached Figure Description

[0037] Figure 1 This is a three-dimensional exploded view of the high-sensitivity fluid sensor proposed in the embodiments of this application;

[0038] Figure 2 This is a schematic diagram of a multi-port circuit board proposed in the embodiments of this application;

[0039] Figure 3 This is a schematic diagram of the differential module circuit proposed in the embodiments of this application;

[0040] Figure 4 This is a schematic diagram of the composite left and right hand transmission line in the embodiments of this application;

[0041] Figure 5 This is a schematic diagram of the Butler matrix circuit in an embodiment of this application;

[0042] Figure 6 This is a schematic diagram of a coplanar waveguide feeder wire used for connecting solderless joints in an embodiment of this application;

[0043] Figure 7 This is a three-dimensional perspective view of the microfluidic channel in the embodiments of this application;

[0044] Figure 8 This is a schematic diagram representing the vector superposition principle of the differential module in the embodiments of this application;

[0045] Figure 9 This is a phase curve diagram of the differential module output when the fourth orthogonal coupler in the differential module takes different power distribution ratios;

[0046] Figure 10 This is a graph showing the derivative of the output phase of the differential module with respect to the phase of the sensing branch when the fourth orthogonal coupler in the differential module has different power distribution ratios.

[0047] Figure 11 This is a simulation of the insertion loss curves at each output port of a multi-port circuit when the dielectric constant of the material in the microfluidic circuit of both the sensing branch and the reference branch is 2.

[0048] Figure 12 It is a line graph comparing the simulated phase of the composite left- and right-handed transmission line and the simulated phase extracted from the multi-port circuit;

[0049] Figure labeling: 1. Butler matrix circuit; 11. First quadrature coupler; 111. First weld; 112. Input terminal A; 113. Through terminal A; 114. Coupled terminal A; 115. Isolation terminal A; 12. Second quadrature coupler; 121. Input terminal B; 122. Through terminal B; 123. Coupled terminal B; 124. Isolation terminal B; 13. Third quadrature coupler; 131. Isolation terminal C; 132. Coupled terminal C; 2. Differential module; 21. Output power divider; 211. Second weld; 212. Sensor input port of the first output power divider; 213. Reference input port of the second output power divider; 22. Composite left and right hand transmission line of the reference path; 221. Interdigitated capacitor; 222. Microstrip inductor; 223. Virtual ground capacitor; 25. Tapered microstrip 1. Line; 23. Fourth orthogonal coupler; 231. Input port D; 232. Straight-through port D; 233. Isolation port D; 234. Isolation port D; 24. Sensor path composite left and right hand transmission line; 3. Input power divider; 31. Input power divider weld; 32. First output port; 33. Second output port; 34. Input port E; 4. Reference orthogonal coupler; 41. Isolation port F; 42. Input port F; 43. Straight-through port F; 44. Coupled port F; 5. PTFE insulating adhesive; 6. Microfluidic channel; 61. Groove; 62. Tapered through hole; 7. Fluid base; 81. Total input port; 82. Second matching port; 83. Reference output port; 84. First matching port; 85. Fifth output port; 86. Fourth output port; 87. Third output port. Detailed Implementation

[0050] The following description, with reference to the accompanying drawings and preferred embodiments, illustrates the implementation of the technical solution of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0051] like Figure 2 As shown in the embodiment of this application, a multi-port network circuit is disposed on a circuit medium board. The multi-port network circuit includes a Butler matrix circuit 1, a differential module 2, an input power divider 3, a reference quadrature coupler 4, and a port group for external connection.

[0052] like Figure 2 In this embodiment of the application, the internal connection of the multi-port network circuit is as follows:

[0053] The input power divider 3 has a first output port 32 and a second output port 33. The first output port 32 is connected to the differential module 2 via a microstrip line, and the second output port 33 is connected to the reference quadrature coupler 4. The reference quadrature coupler 4 is connected to the first input port (i.e., input A112) of the Butler matrix circuit 1. The output port of the differential module 2 is connected to the second input port (i.e., the isolation terminal C131) of the Butler matrix circuit 1.

[0054] like Figure 2 and Figure 6 As shown, in one possible embodiment, the multi-port network circuit has a port group for external connection with seven ports: a total input port 81, a first matching port 84, a second matching port 82, a reference output port 83, a third output port 87, a fourth output port 86, and a fifth output port 85. All of the above ports are etched with coplanar waveguide feed lines to facilitate the installation of solderless SMA adapters.

[0055] In this embodiment, the circuit substrate used has a thickness of 1 mm and two 0.035 mm metal layers, with the upper metal layer serving as the circuit and the lower metal layer as the ground plane. The dielectric material used is F4BM300, which has a relative permittivity of 3.00, a permeability of 1, and a loss tangent of 0.0017. All dimensions in this multi-port network circuit are designed for a frequency of 5.8 GHz. The circuit substrate is 119.5 mm long and 90 mm wide.

[0056] In this embodiment, a 50Ω microstrip line is used, and the width of the 50Ω microstrip line is 2.6mm.

[0057] like Figure 2 and Figure 5 As shown, in one possible embodiment, the Butler matrix circuit 1 consists of a first orthogonal coupler 11, a second orthogonal coupler 12, a third orthogonal coupler 13, a microstrip line with an electrical length of 180°, and a first resistor. The third orthogonal coupler 13 is designed based on even-odd mode analysis. Preferably, both the first and second orthogonal couplers are 3dB orthogonal couplers. The third orthogonal coupler 13 is a 4.77dB orthogonal coupler. The first resistor is a 50Ω resistor.

[0058] like Figure 5As shown, in one possible embodiment, in the Butler matrix circuit 1, the input terminal A112 of the first orthogonal coupler 11 serves as the first input port of the entire Butler matrix circuit, used to receive input signals. The through terminal A113 of the first orthogonal coupler 11 is connected to the input terminal B121 of the second orthogonal coupler via a microstrip line with an electrical length of 180°. The coupling terminal A114 of the first orthogonal coupler 11 is connected to the input terminal 134 of the third orthogonal coupler 13. The isolation terminal A115 of the first orthogonal coupler 11 has a first weld 111 for connecting to one end of a first resistor, and the other end of the first resistor is grounded through a metallized via. The through terminal C133 of the third orthogonal coupler 13 is connected to the isolation terminal B124 of the second orthogonal coupler 12, and the isolation terminal C131 of the third orthogonal coupler 13 serves as the second input port of the Butler matrix circuit, used to receive the output signal of the differential module 2; thus, the Butler matrix circuit is finally formed. The Butler matrix circuit is a five-port network circuit. The signal is fed in from the input terminal A112 of the first quadrature coupler 11 and the isolation terminal C131 of the third quadrature coupler 13, and then output from the through terminal B122 and the coupling terminal B123 of the second quadrature coupler 12 and the coupling terminal C132 of the third quadrature coupler 13.

[0059] like Figure 3 As shown, in one possible embodiment, the differential module 2 consists of an output power divider 21, a reference path composite left-handed and right-handed transmission line 22, a fourth orthogonal coupler 23, a sensing path composite left-handed and right-handed transmission line 24, and a microstrip line. That is, the differential module 2 has two CRLH-TLs.

[0060] In terms of arrangement, the reference path composite left-hand transmission line 22 and the sensor path composite left-hand transmission line 24 are two identical lines arranged symmetrically in the same plane. The two ends of the reference path composite left-hand transmission line 22 are connected to the through terminal D232 of the fourth orthogonal coupler 23 and the second output power divider sensor input port 213 of the output power divider 21, respectively. The two ends of the sensor path composite left-hand transmission line 24 are connected to the isolation terminal D233 of the fourth orthogonal coupler 23 and the first output power divider sensor input port 212 of the output power divider 21, respectively. This creates two branches in the differential module 2: one branch as the reference branch and the other as the sensor branch.

[0061] In terms of internal connections, the isolation terminal D233 of the fourth orthogonal coupler 23 is connected to one end of the composite left-handed transmission line 24 of the sensing path via a microstrip line and a tapered microstrip line 25; the other end of the composite left-handed transmission line 24 of the sensing path is connected to the first output power divider sensor input port 212 of the output power divider 21 via a tapered microstrip line 25 and a microstrip line, forming a sensing branch. The through terminal D232 of the fourth orthogonal coupler 23 is connected to one end of the composite left-handed transmission line 22 of the reference path via a microstrip line and a tapered microstrip line 25; the other end of the composite left-handed transmission line 22 of the reference path is connected to the second output power divider sensor input port 213 of the output power divider 21 via a tapered microstrip line 25 and a microstrip line, forming a reference branch. The signal of the differential module 2 is finally output from one side of the single port of the output power divider 21.

[0062] like Figure 4 As shown, in one possible embodiment, since the reference path composite left and right hand transmission line 22 and the sensing path composite left and right hand transmission line 24 have the same structure, the following description will take the reference path composite left and right hand transmission line 22 as an example:

[0063] The reference path composite left- and right-handed transmission line includes interdigitated capacitors 221, microstrip inductors 222, and virtual ground capacitors 223; the specific planar structure is as follows:

[0064] The interdigital capacitor 221 contains three thin, interlaced short microstrip lines. The size of the three short microstrip lines and the spacing between adjacent short microstrip lines are exactly the same, and each is connected to the arm on its respective side at one end. The microstrip inductor 222 consists of a thin microstrip line, one end of which is connected to the arm of the interdigital capacitor 221, and the other end is connected to the virtual ground capacitor 223.

[0065] In this embodiment, the microstrip lines located at both ends of the composite left and right hand transmission lines 24 of the sensing path have an electrical length that is 90° longer than the microstrip lines located at both ends of the composite left and right hand transmission lines 22 of the reference path.

[0066] In the topology of differential module 2, after the signal is input from the input port D231 of the fourth quadrature coupler 23, there is a 90° phase difference between the through terminal D232 and the isolation terminal D233 of the fourth quadrature coupler 23. When the reference path composite left-handed transmission line 22 and the sensing path composite left-handed transmission line 24 are identical and in the same state, the sensing branch has a 90° longer microstrip line than the reference branch. Therefore, the signal in the sensing branch has an additional 90° phase delay compared to the reference branch. When the two signals are input to the output power divider 21, there will be a 180° phase difference at the input ports 212 and 213 of the first and second output power dividers on the same side of the output power divider 21. That is, the sensing branch has a 180° phase delay relative to the reference branch 22, meaning the two signals are out of phase. The final signal is output from the single-port side of the output power divider 21 and enters the isolation terminal C131 of the Butler matrix circuit. Since the reference branch signal and the sensing branch signal are out of phase, after the two signals are vector-superimposed by the output power divider 21, the signal output by the output power divider 21 in the differential module 2 is the vector superposition of the reference branch and sensing branch signals. Furthermore, due to the out-of-phase relationship of the two signals in the differential module 2, the output signal of the output power divider 21 in the differential module 2 is actually the difference between the sensing branch signal and the reference branch signal.

[0067] like Figure 2 As shown in this embodiment, the first output port 32 of the input power divider 3 is connected to the input port D231 of the fourth quadrature coupler 23 of the differential module 2 via a microstrip line. The second output port 33 of the input power divider 3 is connected to the input terminal F42 of the reference quadrature coupler 4 via a microstrip line. The through terminal F43 of the reference quadrature coupler 4 is connected to the input terminal A112 of the first quadrature coupler 11 in the Butler matrix circuit 1.

[0068] like Figure 2 As shown in this embodiment, a first gap 31 exists between the first output port 32 and the second output port 33 in the input power divider 3 of the multi-port circuit. A second gap 211 exists between the first output power divider sensor input port 212 and the second output power divider sensor input port 213 in the output power divider 21. Second resistors are soldered at both the first gap 31 and the second gap 211 to improve the isolation between the two signals of the power divider. Preferably, the second resistor is a 100Ω resistor.

[0069] like Figure 5 As shown in the embodiment of this application, the isolation terminal A115 of the first orthogonal coupler 11 in the Butler matrix circuit 1 needs to be soldered with a 50Ω matching load to absorb the power reflected due to the mismatch at the port.

[0070] like Figure 2As shown in this embodiment, the main input port 81 is used to connect a single-frequency signal source, and this main input port 81 is connected to the input port E34 of the input power divider 3. The first matching port 84 is used to connect a 50Ω matching load, and this first matching port 84 is connected to the isolation terminal D234 of the fourth quadrature coupler 23. The second matching port 82 is used to connect a 50Ω matching load, and this second matching port 82 is connected to the isolation terminal F41 of the reference quadrature coupler 4. The reference output port 83 is used to connect a power detector, and this reference output port 83 is connected to the coupling terminal F44 of the reference quadrature coupler 4.

[0071] In this embodiment of the application, a high-sensitivity fluid sensor includes the multi-port network circuit described in this embodiment. This multi-port network circuit is optimized at the circuit level, therefore it is not limited to liquid sensing; it can also be used to sense gases by coating sensitive materials on the interdigital capacitor region, exhibiting good robustness for various sensing objects.

[0072] like Figure 1 As shown, in one possible embodiment, a high-sensitivity fluid sensor, in addition to the multi-port network circuit described in the embodiments of this application, also includes a microfluidic channel 6 and a fluid base assembly. The microfluidic channel 6 is mounted on a circuit substrate and located directly above the differential module 2; a groove 61 is formed at the bottom of the microfluidic channel 6, and through holes 62 are respectively provided at both ends of the groove 61, with the top of the through holes 62 extending to the upper surface of the microfluidic channel 6. The fluid base assembly includes fluid bases 7 in number equal to the number of through holes 62. Each fluid base 7 is respectively mounted above the through holes of the microfluidic channel 6. A flow channel hole is formed on the fluid base 7, one end of which communicates with the corresponding through hole 62, and the other end of which serves as a fluid inlet / outlet.

[0073] In one possible embodiment, the microfluidic channel 6 is installed directly above the reference path composite left-hand transmission line 22 and the sensing path composite left-hand transmission line 24 in the differential module 2. The microfluidic channel 6 is made of PC material by 3D printing. The groove 61 has a depth of 2mm to facilitate direct contact between the fluid and the interdigital capacitor 221. Through holes 62 are drilled at both ends of the groove 61. Preferably, the through holes 62 are tapered, and the top of the tapered through holes extends directly to the upper surface of the microfluidic channel 6. A layer of PTFE insulating adhesive 5 with a thickness of about 50 micrometers is placed between the microfluidic channel 6 and the circuit substrate to adhere the microfluidic channel 6 to the circuit substrate. The PTFE insulating adhesive 5 serves to fix the microfluidic channel 6 and ensure its airtightness. A fluid base 7 is installed on the top of the microfluidic channel 6. The fluid base 7 can be connected to an external pipe as the fluid inlet and outlet. The fluid base 7 and the microfluidic channel 6 are bonded together with adhesive. The entire microfluidic channel 6 is 38.5 mm long, 26 mm wide, and 5 mm high, with a top opening diameter of 2 mm for the tapered through-hole.

[0074] When a high-sensitivity fluid sensor is used for liquid sensing, liquids of identical concentration can be introduced beforehand into two microfluidic channels 6 in the sensing and reference branches. The liquid concentration in the sensing branch changes over time, while the liquid concentration in the reference branch remains constant. When the liquid comes into direct contact with the interdigital capacitor 221, the change in the liquid concentration in the sensing branch causes a change in its relative permittivity. This change in the relative permittivity disturbs the electric field in the region of the interdigital capacitor 221 of the composite left-handed transmission line 24 of the sensing branch, causing a change in the S21 phase of the composite left-handed transmission line 24. In the reference branch 22, since the liquid concentration remains constant, its phase also remains unchanged. This results in a larger phase change in the vector superposition signal ultimately output by the output power divider 21 in the differential module 2. The described situation can be found in [reference needed]. Figure 8 This diagram abstracts the problem into a schematic of vector superposition. For ease of explanation, the phase change caused by the dielectric constant of the composite left and right hand transmission lines 24 in the sensing path is set as... Transmitted signal S 21 Let T be the phase change of the output signal after superposition by the output power divider 21. Transmitted signal S 21 Let's call it T refIn this embodiment, since the liquid introduced beforehand is exactly the same, and the sensing branch in the differential module 2 has a fixed phase delay of 180° compared to the reference branch, the sensing branch signal is out of phase with the reference branch signal before the concentration of the liquid introduced into the microfluidic channel 6 of the sensing branch changes. When liquids of different concentrations are introduced into the microfluidic channel 6 of the sensing branch, due to the wide bandwidth transmission characteristics of the sensing branch's composite left-hand transmission line 24, the amplitude of the transmitted signal hardly attenuates, but the phase changes. This can... Figure 8 The description is T becomes T ’ Phase generation The shift in T is such that, during the aforementioned change in T, the concentration of the liquid introduced into the microfluidic channel 6 of the reference branch remains unchanged; therefore, T... ref Keeping it constant, observe T and T ref The output signal of the differential module 2 is generated due to the vector superposition effect of the output power divider 21. During the phase change of T Become A larger phase change occurred at that time. Figure 8 The middle is manifested as Significantly greater than In the embodiment, the phase change of the output signal of the differential module 2 is greater than the phase change of a single CRLH-TL in the sensing branch, which is the theoretical basis for the sensitivity enhancement proposed in this invention.

[0075] To further explain the principle of phase sensitivity enhancement and its ability to enhance sensitivity, the fourth orthogonal coupler 23, responsible for power distribution in differential module 2, is introduced and analyzed. As a preferred embodiment of the sensor sensitivity enhancement, the fourth orthogonal coupler 23 in differential module 2 is a 4.77dB orthogonal coupler, implemented as a microstrip branch-line orthogonal coupler. Its characteristic is that the isolation terminal D233 and the through terminal D232 of the fourth orthogonal coupler 23 output signals with a power distribution ratio of 2:1, and the amplitude ratio is... The fourth orthogonal coupler 23 is identical to the third orthogonal coupler 13 in the Butler matrix circuit 1, both designed using the even-odd mode analysis method. Matlab simulations show that, with the configuration of differential module 2, the power distribution ratio of this fourth orthogonal coupler 23 has a significant impact on the sensitivity enhancement effect. For example... Figure 9 and Figure 10 As shown, Figure 9 The fourth orthogonal coupler 23 in differential module 2 is shown under different power distribution ratios. Phase follows The changing curve, as shown in the simulation, exist When the change angle is less than 50°, there is a slope greater than 1, which means that within this range, differential module 2 has the ability to enhance sensitivity, and The smaller the change, the stronger the sensitivity enhancement capability. Figure 10 This also confirms this analysis. In the embodiments of this application, the power distribution ratio of the fourth orthogonal coupler 23 is 2:1 because the phase change of a single CRLH-TL is approximately 50° when the relative permittivity of the sensitive material varies from 2 to 6. To fully utilize the phase sensitivity enhancement effect of the differential module 2, combined with... Figure 9 and Figure 10 The simulation results show that a 4.77dB orthogonal coupler was selected.

[0076] In the multi-port network circuit, the differential module 2 generates a higher phase sensitivity than a single CRLH-TL, and is the source of the sensitivity enhancement scheme in this embodiment. The Butler matrix circuit 1 receives the phase-sensitivity-enhanced signal from the second input port (i.e., isolation terminal C131), interferes with the signal input from the first input port (i.e., input terminal A112), and then the signals are transmitted to the third output port 87, the fourth output port 86, and the fifth output port 85 of the Butler matrix circuit 1, respectively. This process allows the three output signals to record the changes in the input signals of the first and second input ports in real time. Since the output signals of these three output ports are all generated by the interference of the two input signals, any change in the phase difference or amplitude of the two input signals will cause significant changes in the signals of the three output ports. Therefore, by monitoring the signal changes of these three output ports, the phase difference and amplitude changes of the two input signals can be inferred. In the multi-port network circuit, the signal at the first input port of the Butler matrix circuit 1 remains unchanged. Even if a slight change occurs, it will be recorded at the reference output port 83 and canceled out in the calculation. Therefore, in this embodiment, the Butler matrix circuit 1 is only used to detect the phase change of the differential module 2, and is a powerful tool for converting phase change signals into power signal changes. The reference quadrature coupler 4 is responsible for modulating the signal amplitude at the first input port and recording the power fluctuation of the signal source input to the multi-port circuit in real time through the power signal at the reference output port. The input power divider 3 provides an input interface for the multi-port network circuit and distributes the external input signal evenly between the reference quadrature coupler 4 and the differential module 2.

[0077] In this embodiment, the third output port 87, the fourth output port 86, and the fifth output port 85 are used to connect to a power detector. The power changes at the third output port 87, the fourth output port 86, the fifth output port 85, and the reference output port 83 are received by the power detector. The power detector outputs a voltage signal, and the voltage signal of the power detector has a quantitative numerical relationship with the power signal received by the power detector. The measured voltage can be used to inversely deduce the power value at the corresponding port. Therefore, the output voltage signal of the power detector represents the power output of the Butler matrix circuit port in real time. During simulation, the output power of the above three output ports and the reference output port 83 can be directly represented by the circuit's insertion loss. At the designed observation frequency, the normalized power attenuation can be directly calculated by observing the circuit insertion loss obtained from the simulation. Figure 11 As shown, the simulation of the insertion loss of the multi-port network circuit in this embodiment of the application is provided when a material with a relative permittivity of 2 is added to the CRLH-TL sensitive regions of both the sensing branch and the reference branch. The observation frequency in the figure is a pre-designed 5.80 GHz. By performing programmed calculations on the four insertion loss values ​​shown in the figure, the phase of the output signal of the differential module 2 can be extracted. Figure 12 Line graphs comparing the phase extracted by the multi-port circuit with the phase transmitted by a single CRLH-TL when the dielectric constant of the material in the sensitive region of the CRLH-TL is 2, 4, and 6 are provided. It can be clearly seen that the phase change extracted by the multi-port circuit is close to twice the phase change of a single CRLH-TL. This indicates that compared with a single CRLH-TL, the topology of the differential module 2 of this invention enhances the phase sensitivity by about 2 times, which is very beneficial for high-stability and high-sensitivity sensing.

[0078] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A multi-port network circuit, characterized in that: The system includes a Butler matrix circuit (1), a differential module (2), an input power divider (3), a reference quadrature coupler (4), and a port group for external connection. The input power divider (3) has a first output port (32) and a second output port (33), wherein the first output port (32) is connected to the differential module (2) via a microstrip line, and the second output port (33) is connected to the reference quadrature coupler (4). The reference quadrature coupler (4) is connected to the first input port of the Butler matrix circuit (1), and the output port of the differential module (2) is connected to the second input port of the Butler matrix circuit (1). The differential module (2) includes an output power divider (21), a reference path composite left-handed and right-handed transmission line (22), a fourth orthogonal coupler (23), a sensor path composite left-handed and right-handed transmission line (24), and a microstrip line. The isolation terminal D (233) of the fourth orthogonal coupler (23) is connected to one end of the sensor path composite left-handed and right-handed transmission line (24) via a microstrip line and a tapered microstrip line (25). The other end of the sensor path composite left-handed and right-handed transmission line (24) is connected to the output power divider (21), a reference path composite left-handed and right-handed transmission line (22), a fourth orthogonal coupler (23), a sensor path composite left-handed and right-handed transmission line (24), and a microstrip line via a tapered microstrip line (25). The first output power divider sensor input port (212) of the power divider (21) forms a sensing branch; the through terminal D (232) of the fourth orthogonal coupler (23) is connected to one end of the reference path composite left and right hand transmission line (22) through a microstrip line and a tapered microstrip line (25); the other end of the reference path composite left and right hand transmission line (22) is connected to the second output power divider sensor input port (213) of the power divider (21) through a tapered microstrip line (25) and a microstrip line, forming a reference branch; After the signal is input from the input port D (231) of the fourth quadrature coupler (23), there is a 90° phase difference between the through end D (232) and the isolation end D (233) of the fourth quadrature coupler (23). When the reference path composite left and right hand transmission line (22) and the sensing path composite left and right hand transmission line (24) are completely identical and in the same state, the sensing branch has a microstrip line with an electrical length of 90° longer than the reference branch, so that the sensing branch signal has an additional 90° phase delay relative to the reference branch signal. The two signals have a 180° phase difference at the first output power divider sensing input port (212) and the second output power divider sensing input port (213) of the output power divider (21), that is, the sensing branch has an additional 180° phase delay relative to the reference branch, and the two signals are out of phase. The fourth orthogonal coupler (23) is a 4.77dB orthogonal coupler. The isolation terminal D (233) and the through terminal D (232) of the fourth orthogonal coupler 23 output signals according to a power distribution ratio of 2:1, and the amplitude ratio is 1.

2. The multi-port network circuit according to claim 1, characterized in that: The reference path composite left and right hand transmission line (22) and the sensor path composite left and right hand transmission line (24) have the same structure. The reference path composite left and right hand transmission line (22) includes an interdigital capacitor (221), a microstrip inductor (222), and a virtual ground capacitor (223). One end of the microstrip inductor (222) is connected to the arm of the interdigital capacitor (221), and the other end of the microstrip inductor (222) is connected to the virtual ground capacitor (223).

3. The multi-port network circuit according to claim 1, characterized in that: The Butler matrix circuit (1) includes a first orthogonal coupler (11), a second orthogonal coupler (12), a third orthogonal coupler (13), a microstrip line with an electrical length of 180°, and a first resistor; The input terminal A (112) of the first quadrature coupler (11) serves as the first input port of the entire Butler matrix circuit, used to receive input signals. The through terminal A (113) of the first quadrature coupler (11) is connected to the input terminal B (121) of the second quadrature coupler via a microstrip line with an electrical length of 180°. The coupling terminal A (114) of the first quadrature coupler (11) is connected to the input terminal C (134) of the third quadrature coupler (13). The isolation terminal A (115) of the first quadrature coupler (11) is connected to one end of the first resistor, and the other end of the first resistor is grounded. The third quadrature coupler... The through terminal C (133) of (13) is connected to the isolation terminal B (124) of the second quadrature coupler (12). The isolation terminal C (131) of the third quadrature coupler (13) serves as the second input port of the Butler matrix circuit, used to receive the output signal of the differential module (2). The signal is fed in from the input terminal A (112) of the first quadrature coupler (11) and the isolation terminal C (131) of the third quadrature coupler (13), and then output from the through terminal B (122), the coupling terminal B (123) of the second quadrature coupler (12), and the coupling terminal C (132) of the third quadrature coupler (13).

4. The multi-port network circuit according to claim 3, characterized in that: The first output port (32) of the input power divider (3) is connected to the input port D (231) of the fourth orthogonal coupler (23) of the differential module (2) via a microstrip line; the second output port (33) of the input power divider (3) is connected to the reference orthogonal coupler (4) via a microstrip line; the reference orthogonal coupler (4) is connected to the input port A (112) of the first orthogonal coupler (11) in the Butler matrix circuit (1).

5. The multi-port network circuit according to claim 4, characterized in that: There is a first gap (31) between the first output port (32) and the second output port (33) in the input power divider (3); There is a second gap (211) between the first output power divider sensor input port (212) and the second output power divider sensor input port (213) in the output power divider (21). A second resistor is welded at both the first gap (31) and the second gap (211).

6. The multi-port network circuit according to claim 3, characterized in that: The isolation terminal A (115) of the first orthogonal coupler (11) is welded with a 50Ω matching load.

7. The multi-port network circuit according to claim 5, characterized in that: The port group includes: The main input port (81) is used to connect a single-frequency signal source. The main input port (81) is connected to the input port E (34) of the input power divider (3). The first matching port (84) is used to connect a 50Ω matching load, and the first matching port (84) is connected to the isolation terminal E (234) of the fourth quadrature coupler (23); The second matching port (82) is used to connect a 50Ω matching load. The second matching port (82) is connected to the isolation terminal F (41) of the reference terminal quadrature coupler (4). The reference output port (83) is used to connect to the power detector. The reference output port (83) is connected to the coupling terminal F (44) of the reference terminal quadrature coupler (4). The third output port (87) is used to connect to the power detector, and the third output port (87) is connected to the coupling terminal C (132) of the second orthogonal coupler (12); The fourth output port (86) is used to connect to the power detector, and the fourth output port (86) is connected to the coupling end B (123) of the second orthogonal coupler (12); The fifth output port (85) is used to connect to the power detector. The fifth output port (85) is connected to the through end B (122) of the second orthogonal coupler (12).

8. A high-sensitivity fluid sensor, characterized in that: The multi-port network circuit as described in any one of claims 1 to 7 is used, wherein the multi-port network circuit is disposed on a circuit medium board.

9. The high-sensitivity fluid sensor according to claim 8, characterized in that, Also includes: Microfluidic channel (6) is mounted on the circuit medium board and located directly above the differential module (2); A groove (61) is provided at the bottom of the microfluidic channel (6), and through holes (62) are provided at both ends of the groove (61), with the top of the through holes (62) extending to the upper surface of the microfluidic channel (6). The fluid base assembly includes fluid bases (7) in number equal to the number of through holes (62). Each fluid base (7) is installed above the through hole of the microfluidic channel (6). The fluid base (7) has a flow channel hole. One end of the flow channel hole is connected to the corresponding through hole (62), and the other end of the flow channel hole is a fluid inlet / outlet.

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