Microstrip microwave sensing system based on high-sensitivity parallel stepped impedance resonator transmission coefficient phase and application

Abstract

The invention discloses a microstrip microwave sensing system based on a high-sensitivity parallel stepped impedance resonator transmission coefficient phase and application, the size of a parallel stepped impedance transmission line in the sensor is obtained through quantitative analysis according to a transmission line model, the transmission coefficient of the transmission line sensor is firstly obtained, the phase of the transmission coefficient is calculated, and the phase of the transmission coefficient is calculated; and according to a sensitivity formula, deriving the transmission coefficient phase relative to the electrical length of the induction zone, and finally determining the parameter value of the stepped impedance transmission line according to the extreme value relation of a derivative function. The parallel stepped impedance transmission line sensor is combined with a radio frequency amplifier to design a reflection type radio frequency oscillator, a demodulation circuit is built, and the change relation between the dielectric constant and the oscillation frequency is converted into the relation between the dielectric constant and the direct current voltage, so that the dependence on an expensive vector network analyzer is eliminated. The detection system has the advantages of low manufacturing cost, convenience in carrying, convenience in detection and the like, and plays an important role in the detection fields of materials, biological medicines, chemistry and the like.

Description

Technical Field

[0001] The invention belongs to the field of microwave technology and relates to a microwave microstrip sensing system, in particular to a microstrip microwave sensing system based on a high-sensitivity parallel step impedance resonator transmission coefficient phase and its application in measuring the dielectric constant of liquids with different concentrations. Technical Background

[0002] Microwave microstrip sensors are increasingly being used in the detection of dielectric constants of liquids and solids due to their high sensitivity, simple and convenient processing and manufacturing, low cost, easy integration and portability.

[0003] So far, domestic and foreign scholars have proposed many high-sensitivity resonant units to address the sensitivity of microwave sensors. Starting from the initial split-ring resonator (SRR) design, the electric field of the split-ring resonator is mainly concentrated at the opening of the resonant ring, and the intensity of the bound electric field is relatively small at this time; in order to improve the binding ability of the electric field, the interdigital capacitance (IDC) is added at the opening of the resonator to achieve high-intensity binding of the electric field; the complementary split-ring resonator is etched at the bottom of the dielectric substrate to form a complementary split-ring resonator. resonator, CSRR), at this time the electric field is mainly bounded in the slot of the etched complementary split ring. By improving the straight slot of the complementary split ring resonator into a meandering slot structure, the structural unit can greatly improve the ability of the electric field to be bound. In order to achieve the purpose of multi-parameter detection, a multi-mode resonator unit structure is proposed, such as an electric-LC (ELC) resonant structure. In order to improve the binding ability of the electric field, the electric-LC structure is etched to the bottom of the dielectric substrate to form a magnetic-LC (MLC) resonant structure. At this time, the electric field is mainly bounded in the slot of the middle vertical arm of the magnetic-LC resonator. In order to improve the detection sensitivity, the meander trough structure is added to the middle arm of the resonator, which can not only realize the high-intensity binding of the electric field, but also realize the dual-mode detection function; in order to suppress the adverse effects of external environmental factors such as temperature, humidity, air pressure and other changes on the detection of microstrip sensors, a differential microwave microstrip sensor structure is proposed. The most common is the power splitter / combiner structure, which uses one branch of the power splitter / combiner structure as a reference unit and the other branch as a detection unit. During detection, the response of the reference unit can be detected at all times, thereby eliminating the error and improving the detection sensitivity. However, the resonant unit structure of the above-mentioned microwave microstrip sensors adopts a qualitative improvement method to improve the detection sensitivity, and no quantitative analysis of the specific parameters of the resonator is performed.

[0004] Based on this, the present invention designs a microstrip microwave sensing system with high sensitivity from the perspective of quantitative analysis, and applies it to the detection of the dielectric constant of liquids. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art and propose a microstrip microwave sensing system and application based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator. The optimal parallel step impedance transmission line size of the sensor is determined by quantitative analysis based on the transmission line model. First, the transmission coefficient of the transmission line sensor is obtained, and then the phase of the transmission coefficient is calculated. Then, according to the sensitivity calculation formula, the transmission coefficient phase is derived with respect to the electrical length of the sensing area, and finally, according to the maximum value relationship of the derivative function, the various parameter values ​​of the step impedance transmission line are finally determined. With the parallel step impedance transmission line sensor as the load, a reflective radio frequency oscillator is designed based on the negative impedance principle using a high-frequency electron migration device. Finally, a demodulation circuit is built using a power divider, a phase shifter, a mixer and a low-pass filter to convert the relationship between the dielectric constant and the oscillation frequency into the relationship between the dielectric constant and the DC voltage, thereby getting rid of the dependence on expensive vector network analyzers.

[0006] The present invention is implemented according to the following technical solutions:

[0007] A microstrip microwave sensing system based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator. The system uses a high-sensitivity parallel step impedance transmission line as a load network, and combines an RF amplifier to form a reflective RF oscillator. The relationship between the dielectric constant and the transmission coefficient phase is converted into the relationship between the dielectric constant and the oscillation frequency, and a cascade demodulation circuit is used to convert the oscillation frequency into a DC voltage, where:

[0008] The reflective RF oscillator comprises a 50 ohm load, a high-sensitivity parallel step impedance transmission line sensor and a RF amplifier connected in sequence, wherein the high-sensitivity parallel step impedance transmission line sensor comprises a top layer, a middle layer and a bottom layer, wherein the top layer and the bottom layer are both metal layers, the middle layer is a dielectric substrate, and the metal layer of the top layer is a second-order step impedance transmission line, comprising a microstrip line with a first standard characteristic impedance of 50 ohms, a microstrip line with a second standard characteristic impedance of 50 ohms, a first section of the step impedance transmission line, a second section of the step impedance transmission line, a transmission line in the induction area, a copper foil at the end of the step impedance transmission line and a metal grounding via; a microstrip line with a first standard characteristic impedance of 50 ohms and a second A microstrip line with a standard characteristic impedance of 50 ohms is connected, and the connection point is connected to one end of the first section of the step impedance transmission line. The first section of the step impedance transmission line, the second section of the step impedance transmission line, the sensing area transmission line, and the copper foil at the end of the step impedance transmission line are sequentially connected along the length direction of the first section of the step impedance transmission line. The metal grounding via is located in the middle of the copper foil at the end of the step impedance transmission line, and passes through the middle layer and the bottom layer, and is connected to the copper foil at the end of the step impedance transmission line and the metal layer of the bottom layer; wherein the structural parameters of the first section of the step impedance transmission line and the second section of the step impedance transmission line are obtained by performing quantitative analysis based on the transmission line model so that the phase change rate of the sensor transmission coefficient is maximized.

[0009] In the above technical solution, further, the microstrip line with the first standard characteristic impedance of 50 ohms is completely consistent with the microstrip line with the second standard characteristic impedance of 50 ohms in size; the width of the first section of the step impedance transmission line is greater than the width of the second section of the step impedance transmission line, the width of the second section of the step impedance transmission line is greater than the width of the sensing area transmission line, and the lengths of the first section of the step impedance transmission line and the second section of the step impedance transmission line are equal and less than the length of the sensing area transmission line.

[0010] Furthermore, the demodulation circuit includes a first power divider, a second power divider, a third power divider, a first phase shifter, a second phase shifter, a first mixer, a second mixer, a first low-pass filter, and a second low-pass filter; the output signal of the reflection-type RF oscillator is divided into two by the first power divider, one signal enters the second power divider and is divided into two, and the other signal is divided into two by the third power divider, forming a total of four branch signals, wherein the first branch signal passes through the first phase shifter and enters the local oscillator port of the first mixer, the second branch signal enters the signal port of the first mixer, the third branch signal passes through the second phase shifter and enters the local oscillator port of the second mixer, and the fourth branch signal enters the signal port of the second mixer; the output signal of the first mixer outputs a first DC voltage signal after passing through the first low-pass filter, and the output signal of the second mixer outputs a second DC voltage signal after passing through the second low-pass filter.

[0011] Furthermore, the radio frequency amplifier adopts a high-frequency electron mobility transistor.

[0012] Furthermore, the method for determining the structural parameters of the first section of the step impedance transmission line and the second section of the step impedance transmission line is specifically as follows:

[0013] Firstly, the transmission coefficient of the parallel step impedance transmission line sensor is obtained, and the phase of the transmission coefficient is calculated. Then, according to the sensitivity formula, the transmission coefficient phase is derived with respect to the electrical length of the transmission line in the sensing area. According to the maximum value relationship of the derivative function, the structural parameters of each section of the parallel step impedance transmission line are finally determined so as to maximize the rate of change of the transmission coefficient phase.

[0014] The application of the microstrip microwave sensing system described in any of the above items is used to detect the dielectric constant of the liquid.

[0015] Furthermore, a PTFE substrate for containing the liquid to be tested is placed on the transmission line of the sensing area, and a microfluidic channel structure for containing the liquid to be tested is formed inside the PTFE substrate. Furthermore, the detection method includes the following:

[0016] Step S1: Calculate the output signal of the sensor system in a no-load state;

[0017] Step S2: preparing a standard curve: injecting liquid solutions with different known dielectric constants into the PTFE substrate, obtaining the output signal of the system, fitting it to obtain mathematical expressions of different dielectric constants and output signals, and obtaining a standard curve;

[0018] Step S3: Dielectric constant detection of the liquid to be detected: After the liquid to be detected is injected into the PTFE substrate, the output signal obtained is brought into the standard curve obtained in S2 to deduce the dielectric constant of the liquid to be detected.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention is based on the traditional step impedance transmission line, and is formed by connecting a standard 50 ohm microstrip line in parallel with a multi-step step impedance transmission line. According to the transmission line mathematical model, the mathematical expression of the transmission coefficient phase is obtained, and multiple derivatives are performed to calculate the optimal value of each segment parameter of the multi-step step impedance transmission line when the transmission coefficient phase change rate is maximized, thereby obtaining a unit structure with the maximum sensitivity and resolution.

[0021] 2. The present invention combines a high-sensitivity unit structure with a high-frequency electron mobility transistor to design a reflection-type RF oscillator. In order to improve the system's integration and portability, a demodulation circuit is added to convert the relationship between the dielectric constant and the reflection coefficient phase into the relationship between the dielectric constant and the DC voltage. This eliminates the reliance on expensive vector network analyzers and reduces detection costs.

[0022] 3. The microstrip microwave sensing system based on the transmission coefficient phase of the high-sensitivity parallel step impedance resonator of the present invention has the advantages of easy carrying, low manufacturing and processing cost, and convenient detection. Corresponding modules can be added later and integrated into the 5G wireless network to achieve the purpose of real-time remote monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the parallel second-order step impedance transmission line sensor model;

[0024] Figure 2 The system-level detection schematic diagram of the proposed microstrip microwave sensing system based on the transmission coefficient phase of the high-sensitivity parallel step impedance resonator;

[0025] FIG3 (a) is a schematic diagram of the structure of the proposed microstrip microwave sensing system unit based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator;

[0026] Figure 3 (b) is a three-dimensional view of the proposed microstrip microwave sensing system unit based on the high-sensitivity parallel step impedance resonator transmission coefficient phase;

[0027] Figure 4 The phase comparison results of the transmission coefficient of the proposed parallel step impedance transmission line sensor under two different structural parameter values ​​are shown;

[0028] Figure 5 The oscillation frequency change result of the reflection type RF oscillator when the objects to be tested with different dielectric constants are loaded;

[0029] Figure 6 The DC voltage result output by the system-level sensing detection device when the objects to be tested with different dielectric constants are loaded;

[0030] Markings in the figure: 1, 50 ohm load, 2, parallel step impedance transmission line sensor, 3, RF amplifier, 4, reflection type RF oscillator, 5, first power divider, 6, second power divider, 7, third power divider, 8, first phase shifter, 9, second phase shifter, 10, first mixer, 11, second mixer, 12, first low-pass filter, 13, second low-pass filter, 14, first multimeter, 15, second multimeter, 24, PTFE substrate, 25. Microfluidic channel, 21. Top layer, 22. Middle layer, 23. Bottom layer, 211. Input port, 212. Output port, 213. Microstrip line with a first standard characteristic impedance of 50 ohms, 214. Microstrip line with a second standard characteristic impedance of 50 ohms, 215. First section of step impedance transmission line, 216. Second section of step impedance transmission line, 217. Inductive zone transmission line, 218. Copper foil at the end of the step impedance transmission line, 219. Metal grounding via. DETAILED DESCRIPTION

[0031] In order to more clearly illustrate the problems solved by the present invention, the technical solutions adopted and the beneficial effects, the specific implementation modes of the present invention are illustrated below. The preferred implementation examples described here are only used to illustrate and explain the present invention and are not intended to limit the present invention. All modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be within the protection scope of the present invention.

[0032] The present invention constructs a step impedance transmission line system model based on a parallel step impedance resonator, and accurately analyzes and solves the step impedance transmission line parameters when the transmission coefficient phase change rate reaches the maximum value. Furthermore, a high-sensitivity parallel step impedance transmission line is used as a load network, and an RF active transistor is embedded to form a reflective RF oscillator, and the relationship between the dielectric constant and the phase change of the transmission coefficient is converted into the relationship between the dielectric constant and the oscillation frequency, and then a cascade demodulation circuit is connected to convert the oscillation frequency into a DC voltage. Among them, the demodulation circuit is mainly composed of a power divider, a phase shifter, a mixer, and a low-pass filter (LPF). The microwave microstrip sensor proposed by the present invention is a highly sensitive system-level detection device.

[0033] The present invention proposes a microstrip microwave sensing system based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator, which mainly includes three parts: the first part is the parallel step impedance transmission line sensor design, the second part is the reflection type radio frequency oscillator design, and the third part is the demodulation circuit design.

[0034] In order to explain the principle of quantitative analysis of multi-step step impedance transmission line sensors, the present invention takes a second-order step impedance transmission line as an example (such as Figure 1 As shown in the figure, we can quantitatively analyze the principle of designing the optimal step impedance transmission line size. Figure 1 middle, and Represent the characteristic impedance and electrical length of the sensing area respectively. The sensitivity S expression of the sensor is written as:

[0035] (1)

[0036] in, is the transmission coefficient phase of the sensor, is the dielectric constant of the object to be measured;

[0037] The input impedance of the sensing area It can be written as:

[0038] (2)

[0039] The input impedance of the parallel second-order step impedance transmission line structure can be written as:

[0040] (3)

[0041] in, is the impedance of the first section of the step impedance transmission line, is the impedance of the second section of the step impedance transmission line;

[0042] The transmission coefficient of this sensor is:

[0043] (4)

[0044] in, is the standard characteristic impedance of the transmission line;

[0045] The sensor transmission coefficient phase can be written as:

[0046] (5)

[0047] So,

[0048] (6)

[0049] By taking the derivative of formula (6), we can get:

[0050] (7)

[0051] Formula (6) can be discussed in two cases:

[0052] 1) and

[0053] function exist is monotonically increasing, then

[0054] (8)

[0055] 2) and

[0056] function exist is monotonically increasing, then

[0057] (9)

[0058] Then according to The formula is available, The larger the Therefore, the present invention uses the first case to design a parallel step impedance transmission line sensor.

[0059] According to a specific embodiment of the present invention, a microstrip microwave sensing system based on a high-sensitivity parallel step impedance resonator transmission coefficient phase is as follows: Figure 2 As shown in , 3, it is a system-level detection device.

[0060] like Figure 2 As shown, the system-level detection device includes a 50-ohm load 1, a parallel step impedance transmission line sensor 2, a radio frequency amplifier 3, a first power divider 5, a second power divider 6, a third power divider 7, a first phase shifter 8, a second phase shifter 9, a first mixer 10, a second mixer 11, a first low-pass filter 12, a second low-pass filter 13, a first multimeter 14, and a second multimeter 15. The 50-ohm load 1, the parallel step impedance transmission line sensor 2, and the radio frequency amplifier 3 are constructed into a reflection type radio frequency oscillator 4 according to the negative impedance principle. The transmitting RF oscillator 4 emits a RF signal of a fixed frequency. The RF signal enters the first power divider 5 and is divided into two. The signal of the upper branch enters the second power divider 6, and the signal of the lower branch enters the third power divider 7. One branch output by the second power divider 6 enters the first phase shifter 8, and then enters the local oscillator port of the first mixer 10. The other branch output by the second power divider 6 enters the signal port of the first mixer 10. The output signal of the first mixer 10 is filtered out of the high-frequency signal by the first low-pass filter 12, and only the DC voltage signal remains. The DC voltage signal is measured by the first multimeter 14. The output signal of one branch of the third power divider 7 enters the signal port of the second mixer 11. The other output branch of the third power divider 7 enters the second phase shifter 9, and then enters the second mixer 11. The output signal of the second mixer 11 enters the second low-pass filter 13, and the high-frequency signal is filtered out, leaving only the DC voltage signal, which is measured by the second multimeter 15.

[0061] The parallel step impedance transmission line sensor 2 includes a top layer 21, a middle layer 22 and a bottom layer 23;

[0062] As shown in FIG3 (a), the top layer 21 mainly includes an input port 211, an output port 212, a microstrip line 213 with a first standard characteristic impedance of 50 ohms, a microstrip line 214 with a second standard characteristic impedance of 50 ohms, a first section of step impedance transmission line 215, a second section of step impedance transmission line 216, an induction area transmission line 217, a copper foil 218 at the end of the step impedance transmission line, and a metal grounding via 219.

[0063] The top layer 21 is a metal layer; the metal layer is composed of a microstrip line with a standard characteristic impedance of 50 ohms and a second-order step impedance transmission line with a parallel terminal short circuit. By constructing a mathematical model of the transmission line, the optimal values ​​of the length and width of the second-order step impedance transmission line are obtained to maximize the phase change rate of the transmission coefficient. The top metal layer mainly includes an input port 211, an output port 212, a microstrip line 213 with a first standard characteristic impedance of 50 ohms, a microstrip line 214 with a second standard characteristic impedance of 50 ohms, a first section of step impedance transmission line 215, a second section of step impedance transmission line 216, an induction area transmission line 217, a copper foil 218 at the end of the step impedance transmission line, and a metal grounding via 219; the microstrip line 213 with the first standard characteristic impedance of 50 ohms and the microstrip line 214 with the second standard characteristic impedance of 50 ohms are interconnected to form the entire microstrip line, Located at the far right of the microstrip microwave sensor; the first section of the step impedance transmission line 215 is located in the middle of the entire microstrip line; the second section of the step impedance transmission line 216 is directly connected to the first section of the step impedance transmission line 215; the sensing area transmission line 217 is directly connected to the second section of the step impedance transmission line 216; the copper foil 218 at the end of the step impedance transmission line is directly connected to the sensing area transmission line 217; the metal grounding via 219 is located in the middle of the copper foil 218 at the end of the step impedance transmission line, and passes through the top layer 21 and the bottom layer 23.

[0064] The PTFE substrate 24 is a container for holding the liquid to be detected, and is in the shape of a rectangular parallelepiped. A small rectangular parallelepiped microchannel 25 is dug out inside the PTFE substrate 24 to hold the liquid.

[0065] As shown in FIG3 (b), the induction zone transmission line 217 serves as an electromagnetic induction zone, and the PTFE substrate 24 is placed on the upper surface of the induction zone transmission line 217; a microfluidic channel 25 is etched inside the PTFE substrate 24 to place the detection liquid; the middle layer 22 is a dielectric substrate; the bottom layer 23 is a complete metal surface; when liquids with different dielectric constants are loaded in the induction zone, the system transmits different DC voltage signals and fits the mathematical model between the DC voltage value and the dielectric constant, so that it can be used to predict the dielectric constant value of an unknown substance.

[0066] The present invention is based on a microstrip microwave sensing system of a high-sensitivity parallel step impedance resonator transmission coefficient phase, wherein the optimal parallel step impedance transmission line size of the parallel step impedance transmission line sensor is quantitatively analyzed based on a transmission line model, firstly obtaining the transmission coefficient of the transmission line sensor, then calculating the phase of the transmission coefficient, and then according to the sensitivity calculation formula, the transmission coefficient phase is derived with respect to the electrical length of the sensing area, and finally, according to the maximum value relationship of the derivative function, the various parameter values ​​of the step impedance transmission line are finally determined. With the parallel step impedance transmission line sensor as a load, a high-frequency electron migration device ATF34143 is used, and according to the negative impedance principle, a reflective radio frequency oscillator with an operating frequency of 2.5 GHz is designed. Finally, a demodulation circuit is constructed using a power divider, a phase shifter, a mixer, and a low-pass filter to convert the changing relationship between the dielectric constant and the oscillation frequency into the relationship between the dielectric constant and the DC voltage, thereby getting rid of the dependence on an expensive vector network analyzer.

[0067] Figure 4 In the figure, the simulated value of the black curve is obtained based on the optimal structure value of the sensor.

[0068] Figure 4 The phase comparison results of the transmission coefficient of the proposed parallel step impedance transmission line sensor under two different structural parameter values ​​are shown;

[0069] The sensor can be used to detect the dielectric constant of different objects, such as Figure 5 The oscillation frequency change result of the reflection type RF oscillator when the objects to be tested with different dielectric constants are loaded;

[0070] Figure 6 The DC voltage result output by the system-level sensing detection device when the objects to be tested with different dielectric constants are loaded;

[0071] During detection, the PTFE substrate 24 is placed on the upper surface of the sensing area transmission line 217. In order to facilitate the injection of the liquid to be detected, a microchannel 25 is dug out inside the PTFE substrate 24 to contain the liquid to be detected.

[0072] The detection process is:

[0073] Step S1: Calculate the mathematical expression of the output signal of the first low-pass filter 12 and the second low-pass filter 13 in the no-load state:

[0074] S11: Assume that the oscillation signal s emitted by the reflective RF oscillator 4 satisfies the following mathematical expression:

[0075] Formula (10)

[0076] in is the amplitude of the oscillation signal s, is the frequency of the oscillation signal s, and t is the time;

[0077] S12: The oscillation signal s is evenly divided into the RF signals of branch 1 and branch 2 after passing through the first power divider 5. The mathematical expression thereof is written as:

[0078] Formula (11)

[0079] S13: After the RF signal of branch 1 passes through the second power divider 6 and the RF signal of branch 2 passes through the third power divider 7, their mathematical expressions can be written as:

[0080] Formula (12)

[0081] S14: The RF signal output by the second power divider 6 passes through the first phase shifter 8, and the mathematical expression of the signal output by the second power divider 6 can be written as:

[0082] Formula (13)

[0083] in is the delay time of the first phase shifter 8;

[0084] S15: The mathematical expression of the output signal of the first mixer 10 can be written as:

[0085] Formula (14)

[0086] S16: The radio frequency signal output by the third power divider 7 passes through the second phase shifter 9, and the mathematical expression of the signal output by the third power divider 7 can be written as:

[0087] Formula (15)

[0088] in is the delay time of the second phase shifter 9;

[0089] S17: The mathematical expression of the output signal of the second mixer 11 can be written as:

[0090] Formula (16)

[0091] S18: After the signals output by the first mixer 10 and the second mixer 11 enter the first low-pass filter 12 and the second low-pass filter 13 respectively, the high-frequency signal is filtered out and the DC voltage signal is retained. The mathematical expressions of the retained DC voltage signal can be written as:

[0092]

[0093] Formula (17)

[0094] S2. Make a standard curve:

[0095] S2-1: When liquid solutions with different known dielectric constants are injected into the PTFE substrate 24, the mathematical expressions of the DC voltage output by the system are:

[0096]

[0097] Formula (18)

[0098] in It is the oscillation frequency of the reflective RF oscillator when the sensing system is loaded with liquid solutions with different dielectric constants.

[0099] S2-2: Record the DC voltage output value corresponding to the injection of liquid solutions with different dielectric constants into the PTFE substrate. By observing the data, summarize the relevant rules and use MATLAB numerical software to fit the binary polynomials of the dielectric constants of different liquid solutions and the two DC voltages, where the two DC voltages are used as independent variables and the dielectric constant is used as the dependent variable.

[0100] S3. Dielectric constant detection of the liquid to be tested:

[0101] After the liquid to be tested is injected into the PTFE substrate 24, the dielectric constant of the liquid to be tested can be calculated by substituting the obtained DC voltage into the above-mentioned standard curve equation.

[0102] According to a specific embodiment of the present invention, the microwave microfluidic sensor of the present invention is optimized in a commercial electromagnetic simulation software, and the specific values ​​are as follows.

[0103] The dimensions of the overall microwave sensor are Lx=25mm, Ly=88mm;

[0104] The width of the microstrip line 213 with the first standard characteristic impedance of 50 ohms is 1.6855 mm, and the length of the microstrip line 213 with the first standard characteristic impedance of 50 ohms is 25.0 mm;

[0105] The width of the microstrip line 214 with the second standard characteristic impedance of 50 ohms is 1.6855 mm, and the length of the microstrip line 214 with the second standard characteristic impedance of 50 ohms is 25.0 mm;

[0106] The width of the first section of the step impedance transmission line 215 is 2.38375 mm, and the length of the first section of the step impedance transmission line 215 is 18.8424 mm;

[0107] The width of the second section of the step impedance transmission line 216 is 0.6918 mm, and the length of the second section of the step impedance transmission line 216 is 18.8424 mm;

[0108] The width of the sensing area transmission line 217 is 0.223056 mm, and the length of the sensing area transmission line 217 is 38.928 mm;

[0109] The width of the copper sheet 218 at the end of the step impedance transmission line is 1.0 mm, and the length of the copper sheet 218 at the end of the step impedance transmission line is 1.0 mm;

[0110] The length L3, width L4 and height L5 of the overall structure of the PTFE substrate 24 are 18.0 mm, 6.0 mm and 5 mm respectively;

[0111] The length L6, width L7 and height of the microchannel 25 inside the PTFE substrate 24 structure are 14.0 mm, 0.22 mm and 4.8 mm respectively.

[0112] The microwave microfluidic sensor is a system-level detection device. The optimal parallel step impedance transmission line size of the sensor is quantitatively analyzed based on the transmission line model. First, the transmission coefficient of the transmission line sensor is obtained, and then the phase of the transmission coefficient is calculated. Then, according to the sensitivity calculation formula, the transmission coefficient phase is derived with respect to the electrical length of the sensing area. Finally, according to the maximum value relationship of the derivative function, the various parameter values ​​of the step impedance transmission line are finally determined. With the parallel step impedance transmission line sensor as the load, the high-frequency electron migration device ATF34143 is used to design a reflective RF oscillator with an operating frequency of 2.5GHz according to the negative impedance principle. Finally, a demodulation circuit is built using a power divider, a phase shifter, a mixer and a low-pass filter to convert the relationship between the dielectric constant and the oscillation frequency into the relationship between the dielectric constant and the DC voltage, thereby getting rid of the dependence on the expensive vector network analyzer. The detection system has the advantages of low production cost, easy to carry, and convenient detection. It will play an important role in the detection fields of materials, biomedicine, chemistry, etc.

[0113] The above embodiments are not limitations of the present invention, and the present invention is not limited to the above embodiments. As long as the requirements of the present invention are met, they belong to the protection scope of the present invention.

Claims

1. A microstrip microwave sensing system based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator, characterized in that: The system uses a high-sensitivity parallel step impedance transmission line as a load network, combines a radio frequency amplifier to form a reflection type radio frequency oscillator, converts the change relationship between the dielectric constant and the transmission coefficient phase into the relationship between the dielectric constant and the oscillation frequency, and cascades a demodulation circuit to convert the oscillation frequency into a DC voltage, wherein: the reflection type radio frequency oscillator includes a 50 ohm load, a high-sensitivity parallel step impedance transmission line sensor and a radio frequency amplifier connected in sequence, the high-sensitivity parallel step impedance transmission line sensor includes a top layer, a middle layer, and a bottom layer, wherein the top layer and the bottom layer are both metal layers, the middle layer is a dielectric substrate, and the metal layer of the top layer is a second-order step impedance transmission line, including a microstrip line with a first standard characteristic impedance of 50 ohms, a microstrip line with a second standard characteristic impedance of 50 ohms, and a first section of step impedance transmission line, a second section of step impedance transmission line, an induction zone transmission line, a copper foil at the end of the step impedance transmission line and a metal grounding via; a microstrip line with a first standard characteristic impedance of 50 ohms is connected to a microstrip line with a second standard characteristic impedance of 50 ohms, and the connection is connected to one end of the first section of step impedance transmission line, the first section of step impedance transmission line, the second section of step impedance transmission line, the induction zone transmission line, and the copper foil at the end of the step impedance transmission line are sequentially connected along the length direction of the first section of step impedance transmission line, and the metal grounding via is located in the middle of the copper foil at the end of the step impedance transmission line, and passes through the middle layer and the bottom layer; wherein the structural parameters of the first section of step impedance transmission line and the second section of step impedance transmission line are obtained by performing quantitative analysis according to the transmission line model so that the phase change rate of the sensor transmission coefficient is maximized.

2. The microstrip microwave sensing system based on the transmission coefficient phase of the high-sensitivity parallel step impedance resonator according to claim 1 is characterized in that: The microstrip line with the first standard characteristic impedance of 50 ohms is exactly the same size as the microstrip line with the second standard characteristic impedance of 50 ohms; the width of the first section of the step impedance transmission line is greater than the width of the second section of the step impedance transmission line, the width of the second section of the step impedance transmission line is greater than the width of the sensing area transmission line, and the lengths of the first section of the step impedance transmission line and the second section of the step impedance transmission line are equal and less than the length of the sensing area transmission line.

3. The microstrip microwave sensing system based on the transmission coefficient phase of the high-sensitivity parallel step impedance resonator according to claim 1 is characterized in that: The demodulation circuit includes a first power divider, a second power divider, a third power divider, a first phase shifter, a second phase shifter, a first mixer, a second mixer, a first low-pass filter, and a second low-pass filter; the output signal of the reflection type radio frequency oscillator is divided into two by the first power divider, one signal enters the second power divider and is divided into two, and the other signal is divided into two by the third power divider, forming a total of four branch signals, wherein the first branch signal passes through the first phase shifter and enters the local oscillator port of the first mixer, the second branch signal enters the signal port of the first mixer, the third branch signal passes through the second phase shifter and enters the local oscillator port of the second mixer, and the fourth branch signal enters the signal port of the second mixer; the output signal of the first mixer outputs a first DC voltage signal after passing through the first low-pass filter, and the output signal of the second mixer outputs a second DC voltage signal after passing through the second low-pass filter.

4. The microstrip microwave sensing system based on the transmission coefficient phase of the high-sensitivity parallel step impedance resonator according to claim 1 is characterized in that: The radio frequency amplifier adopts a high-frequency electron mobility transistor.

5. The microstrip microwave sensing system based on the transmission coefficient phase of a high-sensitivity parallel step impedance resonator according to claim 1 is characterized in that: The method for determining the structural parameters of the first section of the step impedance transmission line and the second section of the step impedance transmission line is as follows: firstly, the transmission coefficient of the parallel step impedance transmission line sensor is obtained, and the phase of the transmission coefficient is calculated. According to the sensitivity formula , where is the transmission coefficient phase, is the electrical length of the induction zone, is the induction zone admittance, is the dielectric constant of the material to be measured. From this formula, it can be seen that in order to achieve the highest sensitivity, the first-order derivative of the transmission coefficient phase with respect to the electrical length of the transmission line in the sensing area must reach the maximum value. According to the maximum value relationship of the derivative function, the structural parameters of each section of the parallel step impedance transmission line are finally determined to maximize the rate of change of the transmission coefficient phase with respect to the electrical length of the sensing area, that is, the transmission coefficient phase with respect to the dielectric constant of the object to be measured will also be maximized, and then the sensitivity will be maximized.

6. Application of the microstrip microwave sensing system according to any one of claims 1 to 5, characterized in that: Used to detect the dielectric constant of liquids.

7. The use according to claim 6, characterized in that A PTFE substrate for containing the liquid to be tested is placed on the transmission line of the sensing area, and a micro-channel structure for containing the liquid to be tested is formed inside the PTFE substrate.

8. The use according to claim 7, characterized in that The detection method includes the following: step S1: calculating the output signal of the sensor system in a no-load state; step S2: making a standard curve: injecting liquid solutions with different known dielectric constants into a PTFE substrate to obtain the output signal of the system, fitting it to obtain mathematical expressions of different dielectric constants and output signals, and obtaining a standard curve; step S3: dielectric constant detection of the liquid to be detected: after the liquid to be detected is injected into the PTFE substrate, the output signal obtained is brought into the standard curve obtained in S2 to deduce the dielectric constant of the liquid to be detected.

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