A high-resolution double-entry cavity sensor based on microwave negative resistance circuit compensation

Abstract

This invention proposes a high-resolution dual-entry cavity sensor based on negative resistance compensation, comprising a passive resonant cavity, a microfluidic chip, and a negative resistance compensation circuit. It utilizes a common metal layer between two resonant cavities to isolate them from each other while requiring only one negative resistance compensation circuit to compensate for the energy of both cavities. By etching a microstrip line + stripline structure on the common metal layer to connect a negative resistance compensation circuit designed with transistors and diodes, simultaneous and independent energy compensation for the two resonant cavities is achieved, thereby improving the quality factor at their corresponding resonant frequencies and enhancing detection sensitivity. Simultaneously, embedding two microfluidic chips in the gap region where the electric field strength of the resonant cavity is strongest gives the proposed sensor both extremely high resolution and high sensitivity, improving the overall performance of the sensor. The sensor is suitable for detecting trace amounts of solute in liquid solvents, particularly for characterizing the concentration of glucose solutions.

Description

Technical Field

[0001] The invention belongs to the field of microwave sensors, and in particular relates to a high-resolution sensor suitable for detecting ultra-low concentration glucose solutions. Background Art

[0002] Currently, diabetes has become one of the mainstream epidemics in the world. As of 2014, the number of diabetes patients has reached 422 million. And the incidence of diabetes is still increasing year by year. At the same time, diabetes can cause many complications such as end-stage renal disease, heart disease, stroke and blindness. At present, diabetic patients mainly monitor their blood sugar levels through blood glucose meters and blood glucose test strips. However, each time the patient needs to prick his finger to collect blood samples for monitoring blood sugar concentration. Such a day-to-day operation is painful for patients.

[0003] Nowadays, microwave sensors have great potential for non-invasive, label-free and real-time measurement. Microwave sensors are widely used in agriculture, biopharmaceuticals, and electrical fields. There are also many reports on the use of microwave sensors for in vivo blood glucose monitoring and in vitro glucose concentration measurement.

[0004] Although diabetes is caused by excessively high levels of glucose in the human blood, this is only compared to normal people. In fact, the glucose content in human blood is very small. In order to use microwave sensors to monitor such ultra-low concentration glucose solutions, microwave sensors need to have greater sensitivity and extremely high resolution.

[0005] Generally, a microwave passive sensor is combined with a microfluidic chip to monitor the glucose solution. The microfluidic chip is generally loaded in the area where the electric field strength of the microwave resonator is the strongest, which ensures that a high sensitivity can be achieved even when the required sample volume is as small as possible. However, the sensitivity of a general planar structure microwave sensor is generally low because its strong electric field is mostly concentrated in the middle dielectric layer of the dielectric substrate and is difficult to be utilized. However, the reentrant cavity used in the present invention makes full use of the strong electric field area of ​​the resonant cavity, making its sensitivity higher than that of a planar structure.

[0006] The high resolution of a microwave sensor is often closely related to the quality factor of the sensor itself. Specifically, the higher the quality factor corresponding to the resonator, the higher the resolution. The present invention uses the technology of a negative resistance compensation circuit to compensate the energy of the resonant cavity, thereby improving the quality factor of the resonant cavity. Moreover, the present invention only requires a simple operation of adjusting the bias voltage of the transistor and the varactor diode in the negative resistance compensation circuit to greatly improve the quality factor of the resonant cavity, thereby realizing ultra-low concentration monitoring of the glucose solution. Summary of the invention

[0007] The present invention proposes a high-resolution double-entry cavity sensor based on negative resistance compensation, which improves the quality factor of the two corresponding resonant frequencies by simultaneously and independently performing energy compensation on the two resonant cavities, and improves the detection sensitivity, thereby enhancing the overall performance of the sensor.

[0008] The technical solution of the present invention is as follows:

[0009] A high-resolution double-entry cavity glucose sensor based on negative resistance compensation, the sensor comprising a passive resonant cavity, a microfluidic chip and a negative resistance compensation circuit.

[0010] The passive resonant cavity is composed of two upper and lower reentrant resonant cavities formed in four longitudinally stacked dielectric substrates. The two reentrant resonant cavities are respectively formed in the first and second upper dielectric substrates and the third and fourth lower dielectric substrates. Each dielectric substrate has a three-layer structure of a top metal layer, an intermediate dielectric layer and a bottom metal layer. The two reentrant resonant cavities are longitudinally isolated by the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate in direct contact, so that the electromagnetic field is confined in their respective cavities.

[0011] The microfluidic chip has two pieces, which are respectively embedded in two reentrant resonant cavities and located in the gap area where the electric field intensity of each resonant cavity is the strongest.

[0012] A cavity feeding structure and a negative resistance compensation circuit connection port of two reentrant resonant cavities are formed on the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate in contact with each other, wherein the cavity feeding structure is connected to a vector network analyzer through an adapter, and the negative resistance compensation circuit is connected to the two reentrant resonant cavities through the negative resistance compensation circuit connection port, and energy compensation of the two resonant cavities is achieved simultaneously and independently by adjusting the bias voltage of the triode and the varactor diode in the negative resistance compensation circuit.

[0013] During measurement, one of the cavities is selected as the sensing cavity and the other cavity is selected as the reference cavity.

[0014] The above is the overall structure of the present invention, and the specific structure of the present invention is further described as follows:

[0015] The passive resonant cavity is composed of four dielectric substrates stacked vertically, wherein the first and second dielectric substrates at the top constitute an upper reentrant resonant cavity, and the third and fourth dielectric substrates at the bottom constitute a lower reentrant resonant cavity. Rectangular grooves and gradient microstrip lines are etched on the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate to form a cavity feeding structure and a negative resistance compensation circuit connection port. Each dielectric substrate is composed of a top metal, an intermediate dielectric layer and a bottom metal.

[0016] The intermediate dielectric layers of the four dielectric substrates are periodically arrayed with metallized through holes near the edges of the two reentrant resonant cavities. The metallized through holes connect the top metal and the bottom metal to form equivalent metal walls of the two reentrant resonant cavities.

[0017] The first dielectric substrate of the upper reentrant resonant cavity is etched upward from the bottom metal to part of the middle dielectric layer in the area where the equivalent metal wall is formed to form a circular groove, and the first microfluidic chip is embedded in the circular groove. The second dielectric substrate etches the top metal to the middle dielectric layer so that an annular groove is formed on the top metal, and the outer periphery of the annular groove is the same size as the outer periphery of the circular groove. Metallized through holes are periodically distributed in the middle dielectric layer in the central area of ​​the annular groove to connect the top metal and the bottom metal of the first dielectric substrate to form a first capacitor column.

[0018] The fourth dielectric substrate of the lower reentrant resonant cavity is etched downward from the top metal to part of the middle dielectric layer in the area where the equivalent metal wall is formed to form a circular groove, and the second microfluidic chip is embedded in the circular groove; the third dielectric substrate etches the bottom metal to the middle dielectric layer so that an annular groove is formed on the bottom metal, and the outer periphery of the annular groove is the same size as the outer periphery of the circular groove, and metallized through holes are periodically distributed in the middle dielectric layer in the central area of ​​the annular groove to connect the bottom metal and the top metal of the third dielectric substrate to form a second capacitor column.

[0019] The positions of the first capacitor column and the second capacitor column are both the areas with the strongest electric field in their respective cavities, and the microchannels of the first and second microfluidic chips correspond to the areas with the strongest electric field respectively; the radii of the capacitor columns corresponding to the two resonant cavities are different, the radius of the capacitor column corresponding to the upper reentrant resonant cavity is larger, and the radius of the capacitor column corresponding to the lower reentrant resonant cavity is smaller; the bottom metal and the top metal in direct contact between the two reentrant resonant cavities separate the two cavities in the longitudinal direction, which makes the electromagnetic fields well confined in their respective cavities and difficult to interfere with each other.

[0020] The first dielectric substrate of the upper reentrant resonant cavity and the fourth dielectric substrate of the lower reentrant resonant cavity are both provided with open through holes symmetrically arranged along the diagonal of the resonant cavity for connecting the inlet and outlet holes in their respective microchannels. There is a base above the two through holes for connecting a polytetrafluoroethylene hose, and the introduction and outlet of the glucose solution are achieved through the polytetrafluoroethylene hose.

[0021] The cavity feeding structure and the negative resistance compensation circuit connection port both adopt a "microstrip line + stripline" transition structure, wherein the cavity feeding structure is connected to the vector network analyzer through an SMA adapter, and the negative resistance compensation circuit connection port is connected to the negative resistance compensation circuit through a direct integration method.

[0022] After the cavity feeding structure passes through the gradient microstrip line, it is necessary to etch rectangular grooves with corresponding upper and lower positions and the same shape and area on the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate; after the negative resistance compensation circuit connection port passes through the gradient microstrip line, it is also necessary to etch rectangular grooves with corresponding upper and lower positions and the same shape and area on the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate.

[0023] The negative resistance circuit includes a resistor, a capacitor, an inductor, a transistor and a varactor diode; the inductor L n One end is connected to the base b of transistor BFP420, and the other end is directly grounded; the collector c of transistor BFP420 is connected to the capacitor C d1 One end is connected to the inductor L c1 One end of the capacitor C d1 The other end of the resistor R c As a DC bias resistor, one end is connected to the inductor L c1 The other end of the resistor R c The other end is connected to the voltage source V c The positive pole of the voltage source V c The negative pole of the transistor BFP420 is directly grounded; the emitter e of the transistor BFP420 is connected to the inductor L c2 and capacitor C d2 One end of the resistor R e With inductance L c2 The other end of the resistor R e The other end is connected to the voltage source V e The negative pole of the voltage source V e The positive electrode of the resistor R0 is directly grounded; one end of the resistor R0 and the capacitor C d2 The other end of the resistor R0 is connected to the cathode of the variable capacitance diode SMV1405 and the inductor L c3 The anode of the variable capacitance diode SMV1405 is directly grounded; the inductor L c3 The other end of the bias The positive pole is connected to the voltage source V bias The negative pole is directly grounded.

[0024] The equivalent circuit models of the two passive resonant cavities are two corresponding RLC parallel networks, and the vector network port impedances connected to the cavity feeding structure are equivalent to Z IN and Z OUT, and the cavity feeding structure is equivalent to an ideal three-port transformer, the corresponding transformation ratio is T1 and T2, and the port structure used to connect the negative resistance compensation circuit is also equivalent to an ideal three-port transformer, the corresponding transformation ratio is T3 and T4. The negative resistance compensation circuit is equivalent to a negative resistance plus capacitance, and the corresponding impedance form can be written as -R+1 / jωC R form.

[0025] After the passive resonant cavity and the negative resistance compensation circuit are connected through the negative resistance compensation circuit port, the bias voltage V of the diode SMV1405 is adjusted. bias Can change the imaginary part of the negative resistance compensation circuit output (i.e. 1 / jωC R size) but has little effect on the real part of the output (i.e., the size of -R); adjust the bias voltage V of the transistor BFP420 e The output real and imaginary parts of the negative resistance compensation circuit can be changed, but the real part is mainly affected. In order to use the negative resistance compensation circuit to compensate for the energy loss of the passive resonant cavity and thus improve the quality factor of the two resonant cavities at the resonant frequency, the present invention changes V bias 、V e , so that the real part (-R) and imaginary part (1 / jωC) of the output of the negative resistance compensation circuit R ) is to be compared with the real part (R L ) and the imaginary part (X L ) is zero. At the same time, the present invention first selects a specific diode bias voltage V bias To determine the energy compensation of the two passive reentrant resonant cavities to improve their quality factor, and then adjust the bias voltage V of the triode e To obtain the best compensation effect corresponding to the selected resonant cavity and thus obtain the maximum quality factor. In order to more easily realize energy compensation of two resonant cavities simultaneously by a negative resistance compensation circuit, the present invention adjusts the size of the resonant cavity and the capacitor column so that the difference between the resonant frequencies of the two resonant cavities is 71.4MHz.

[0026] When measuring glucose solution, the present invention selects one of the cavities to load glucose solutions of different concentrations in its microfluidic channel as the sensing cavity each time, and deionized water is loaded in the microfluidic channel of the other cavity as the reference cavity. When performing specific tests, first, the two microfluidic channels are filled with deionized water to determine the initial resonant frequency f0 of the two resonant cavities. Then, by adjusting the bias voltage of the varactor diode and the triode, the quality factor corresponding to the selected sensing cavity is greatly improved, ensuring that the ultra-low concentration of glucose solution can be detected. However, at this time, the quality factor at the resonant frequency of the reference cavity remains basically unchanged or is improved to a limited extent. The glucose solution is gradually pumped into the microfluidic channel of the sensing cavity at a constant flow rate by an injection pump, and then the LabVIEW software is used to record in real time the change process of the resonant frequency of the sensing cavity when the glucose solution replaces the deionized water. When the glucose solution enters the microfluidic channel of the sensing cavity, the resonant frequency of the sensing cavity will gradually increase. As the deionized water is gradually replaced by the glucose solution, the resonant frequency change of the sensing cavity will gradually converge to f s In the present invention, the difference between the final convergence frequency of the sensing cavity and the initial resonance frequency of the sensing cavity (Δf = f s -f0) to characterize glucose solutions of different concentrations. This long-term real-time continuous measurement makes the measured data more accurate. Each concentration of glucose solution is repeatedly measured multiple times using the method described. Moreover, by adjusting the bias voltage of the varactor diode and the triode, the resonant frequency point with improved quality factor is selectively changed, and the two resonant cavities do not interfere with each other, thereby achieving the alternate measurement of the two cavities by using the two cavities as mutual sensing and reference cavities.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The present invention integrates two substrate integrated waveguide reentrant resonant cavities vertically, and embeds the microfluidic chip into the gap area with the largest electric field intensity of the resonant cavity, so that the cavity electric field area of ​​the resonant cavity is fully utilized to improve the sensitivity of the resonant cavity. At the same time, the negative resistance compensation circuit technology is used to compensate the energy of the passive resonant cavity, thereby greatly improving the quality factor (102009) at the corresponding resonant frequency of the passive resonant cavity. The overall performance of the sensor in terms of resolution and sensitivity has been greatly improved. The lowest concentration limit of the glucose solution that the sensor proposed in the present invention can detect is 1mmol / L, and the sensor can also clearly distinguish between 1mmol / L and 2.5mmol / L glucose solutions.

[0029] 2. The present invention cleverly designs the microchannel on the microfluidic chip into a ring shape. When the liquid to be tested enters the channel, it is directly divided into two by using the structure of the ring channel, which can quickly fill the entire channel to improve the response speed of the sensor. At the same time, compared with other structures, the use of the ring channel reduces the path for the glucose solution to flow due to the simple channel structure, so that after each test, the residual liquid can be completely extracted to ensure the accuracy of the measurement results. Moreover, the depth and width of the microchannel are optimized to ensure that after it is embedded in the resonant cavity, the entire sensor has the highest sensitivity without affecting the matching of the resonant cavity as a whole with the negative resistance compensation circuit. In addition, the introduction of microfluids has greatly improved the performance of the sensor in terms of sensitivity, resolution, and response speed.

[0030] 3. The core components of the negative resistance compensation circuit proposed in the present invention are a transistor BFP420 and a varactor diode SMV1405. The adjustment of the real and imaginary parts of the output of the negative resistance compensation circuit is determined by the bias voltage of the transistor and the diode. Through a specific combination of diodes and transistor bias voltages, a negative resistance compensation circuit is realized to simultaneously and independently realize the energy compensation of two resonant cavities, thereby greatly improving the quality factor of the two resonant cavities at the corresponding resonant frequency. In order to realize the function of a negative resistance compensation circuit to simultaneously and independently realize the energy compensation of two resonant cavities in the present invention, in addition to introducing transistors and diodes, it is also necessary to design the length, width and geometry of the metal in the negative resistance compensation circuit. The components (transistors, varactor diodes, etc.) in the negative resistance compensation circuit need to be connected through metal conductors. The structural parameters (length, width and geometry) of these metals will have a greater impact on the performance of the negative resistance compensation circuit, so a special design is required and cannot be selected at will. Through its optimized design, when adjusting the bias voltage of the diode, only the output imaginary part of the negative resistance compensation circuit will be affected (1 / jωC R ), but has little effect on the real part (-R) of the output of the negative resistance compensation circuit. When adjusting the bias voltage of the transistor, it mainly affects the real part (-R) of the negative resistance compensation circuit, but has little effect on the imaginary part (1 / jωC R ) is very little affected. At the same time, the real and imaginary parts of the output of the negative resistance compensation circuit are also affected by the frequency. The combination of the two realizes a negative resistance compensation circuit that can selectively match the output impedance (R L +jX L ) are matched with each other to improve the quality factor at the desired resonant frequency of the resonant cavity.

[0031] 4. The present invention ingeniously etches rectangular grooves with the same upper and lower positions and consistent structural parameters on the metal layer commonly stacked between the two cavities. When the two rectangular grooves are stacked vertically, a "stripline" structure is formed. At the same time, a rectangular plus trapezoidal gradient "microstrip line" structure is etched on the top metal of the third dielectric substrate. The "microstrip line" structure is directly integrated with the metal that forms the "stripline" structure on the top metal of the third dielectric substrate. In this way, the special negative resistance compensation circuit connection port of "stripline + microstrip line" is formed on the common metal layer between the two cavities, and this special structure does not affect the electromagnetic isolation between the two resonant cavities, so that the resonant characteristics between the two resonant cavities will not interfere with each other, but it can ensure that the single negative resistance compensation circuit placed on the third dielectric substrate can simultaneously and independently compensate energy to the two resonant cavities. The use of the special "stripline + microstrip line" structure realizes the function of a negative resistance compensation circuit to simultaneously and independently improve the quality factor of the corresponding resonant frequency of the two resonant cavities. At the same time, the non-interference characteristics of the two resonant cavities can be used to refer to each other and the two resonant cavities can be used as sensing cavities to alternately measure the glucose solution, making the measured data more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a cross-sectional schematic diagram of the sensor proposed by the present invention;

[0033] Figure 2 Schematic diagram of an equivalent circuit model of the sensor proposed by the present invention;

[0034] Figure 3 It is a schematic diagram of an equivalent circuit model of a microwave negative resistance compensation circuit proposed by the present invention;

[0035] Figure 4 is a three-dimensional schematic diagram of the sensor proposed by the present invention;

[0036] Figure 5 is a layered schematic diagram of the sensor proposed by the present invention;

[0037] FIG6( a ) is a front view of the first dielectric substrate 1 - 1 of the sensor proposed by the present invention;

[0038] FIG6( b ) is a schematic diagram of the back side of the first dielectric substrate 1 - 1 of the sensor proposed by the present invention;

[0039] FIG. 7( a ) is a front view of the second dielectric substrate 1 - 2 of the sensor proposed by the present invention;

[0040] FIG. 7( b ) is a schematic diagram of the back side of the second dielectric substrate 1 - 2 of the sensor proposed by the present invention;

[0041] FIG8( a ) is a front view of the third dielectric substrate 2 - 1 of the sensor proposed by the present invention;

[0042] FIG8( b ) is a schematic diagram of the back side of the third dielectric substrate 2 - 1 of the sensor proposed by the present invention;

[0043] FIG8(c) is an enlarged schematic diagram of the feeding structure 3-2-2 on the top metal layer of the third dielectric substrate 2-1 of the sensor proposed by the present invention;

[0044] FIG8(d) is an enlarged front view of the feeding structures 3-2-3 and 3-2-4 on the top metal layer of the third dielectric substrate 2-1 of the sensor proposed by the present invention;

[0045] FIG8( e ) is an enlarged three-dimensional schematic diagram of the cavity feeding structure 3 - 1 and the negative resistance compensation circuit connection port 3 - 2 proposed by the present invention;

[0046] FIG9( a ) is a front view of the fourth dielectric substrate 2 - 2 of the sensor proposed by the present invention;

[0047] FIG9( b ) is a schematic diagram of the back side of the fourth dielectric substrate 2 - 2 of the sensor proposed by the present invention;

[0048] Fig.10 It is a three-dimensional schematic diagram of the microfluidic chip proposed by the present invention;

[0049] Fig.11 It is a front schematic diagram of the microfluidic chip proposed by the present invention;

[0050] Fig.12 is a transmission response curve diagram of the sensor proposed by the present invention under different transistor and diode bias voltages;

[0051] Fig.13 It is a schematic diagram of the relationship between the transmission curve of the sensor proposed by the present invention in different modes and the dielectric constant of the sample to be tested;

[0052] Fig.14 It is a schematic diagram of the relationship between the transmission response curve and glucose solutions of different concentrations when the sensor negative resistance compensation circuit proposed by the present invention performs energy compensation. DETAILED DESCRIPTION

[0053] In order to better explain the design process and purpose, the present invention is further described below in conjunction with embodiments and drawings:

[0054] like Figures 1 to 11 As shown, this embodiment proposes a high-resolution double-entry resonant cavity sensor based on microwave negative resistance compensation for measuring glucose solution, which is composed of two re-entry resonant cavities, two microfluidic chips and a negative resistance compensation circuit.

[0055] The two reentrant resonant cavities are formed by vertically stacking the first to fourth dielectric substrates 1-1, 1-2, 2-1, 2-2, wherein two microfluidic chips 1-1-2, 2-2-1 are embedded in the first and second dielectric substrates 1-1, 2-2. The above four dielectric substrates all have a three-layer structure of a top metal layer, a middle dielectric layer and a bottom metal layer.

[0056] The above-mentioned microfluidic chip is etched respectively in order to be embedded in the first and second dielectric substrates 1-1 and 2-2. A circular groove is etched upward from the bottom metal in the central area of ​​the first dielectric substrate 1-1, and the area of ​​the groove is the same as the area of ​​the first microfluidic chip 1-1-2, and the depth of the groove is the same as the thickness of the microfluidic chip. The first microfluidic chip 1-1-2 is embedded in the circular groove with its front side facing upward, and the front side of the chip is bonded to the groove of the first dielectric substrate 1-1 with insulating glue, the purpose of which is to seal the microchannel and prevent the leakage of the liquid to be tested. Similarly, a circular groove is etched downward from the top metal in the central area of ​​the fourth dielectric substrate 2-2, and the area of ​​the groove is the same as the area of ​​the second microfluidic chip 2-2-1, and the depth of the groove is the same as the thickness of the microfluid. The front side of the second microfluidic chip 2-2-1 is embedded and placed in the circular groove with its front side facing downward, and the front side of the chip is bonded to the groove of the fourth dielectric substrate 2-2 with insulating glue, the purpose of which is to seal the microchannel and prevent the leakage of the liquid to be tested.

[0057] In this embodiment, preferably, the corresponding groove depths of the first and fourth dielectric substrates 1-1 and 2-2 are both 1 mm, and the corresponding groove radius is 18 mm. Moreover, the parameters of the two microfluidic chips 1-1-2 and 2-2-1 are the same.

[0058] In the actual structure, the four dielectric substrates are fixed by screws with a radius of 0.8 mm. The screws are located outside the resonant cavity and do not affect the resonant characteristics of the resonant cavity.

[0059] In this embodiment, the intermediate dielectric layer materials of the four dielectric substrates are all made of F4BM265, which has a relative dielectric constant of 2.65, a relative magnetic permeability of 1, and a loss tangent of 0.0015.

[0060] The length and width of three of the four dielectric substrates are the same, and preferably both are 52 mm, but the length and width of the third dielectric substrate 2-1 used to place the negative resistance compensation circuit are 114 mm and 76 mm respectively, and the thickness of each dielectric substrate is 1.5 mm.

[0061] The intermediate dielectric layers of the above four dielectric substrates have periodically arrayed metallized through holes 1-1-1 near the edge of the resonant cavity, and the metallized through holes 1-1-1 connect the top and bottom metals of each dielectric substrate, so as to form an equivalent metal wall of the resonant cavity. In this embodiment, as a preferred embodiment, the radius of the metallized through hole is 0.4 mm, and the distance between the centers of two adjacent metallized through holes is 1.4 mm.

[0062] The second and third dielectric substrates 1-2 and 2-1 have periodically arrayed metallized through holes 1-2-2 and 2-1-2 inside the intermediate dielectric layer in the central area of ​​the resonant cavity, and the metallized through holes connect the top metal and the bottom metal in the corresponding dielectric substrate, and the purpose is to form the first and second capacitor columns 1-2-1 and 2-1-1 of the corresponding resonant cavity. In this embodiment, as a preference, the radius of the metallized through holes 1-2-2 and 2-1-2 is 0.5 mm, the distance between the centers of two adjacent through holes is 1.7 mm, and the radii of the corresponding capacitor columns 1-2-1 and 2-1-1 are 7.5 mm and 6 mm, respectively.

[0063] The present invention arranges the cavity feeding structure 3-1 symmetrically about the longitudinal axis at both ends of the two reentrant resonant cavities, and the cavity feeding structure 3-1 is formed by connecting the strip line formed by the first feeding structure 3-2-1 and the second feeding structure 3-1-1 and the third feeding structure 3-2-2. The bottom metal of the second dielectric substrate 1-2 has a rectangular groove with the same upper and lower positions and consistent structural parameters on the top metal of the third dielectric substrate 2-1, which is used to form the first feeding structure 3-2-1 and the second feeding structure 3-1-1 to form the strip line. The two ends of the third dielectric substrate 2-1 of the reentrant resonant cavity 2 are designed to be wider than other dielectric substrates, and the third feeding structure 3-2-2 is arranged at the widened position, and connected with the strip line formed by the first and second feeding structures 3-2-1 and 3-1-1 to form the cavity feeding structure 3-1; the cavity feeding structure 3-1 provides excitation for the two longitudinal reentrant cavities, so that the two cavities can resonate at the same time.

[0064] The present invention sets the negative resistance compensation circuit connection port 3-2 at one of the other two ends of the two reentrant resonant cavities where the cavity feeding structure 3-1 is not set, and extends a portion of the third dielectric substrate 2-1 outside the cavity at this end so that it exceeds the other dielectric substrates, etches part of the metal layer at this extended portion, and sets the negative resistance compensation circuit 3-3.

[0065] The negative resistance compensation circuit connection port 3-2 is composed of a stripline structure formed by the fourth and fifth feeding structures 3-1-2 and 3-2-3 connected to a section of a gradient microstrip line 3-2-4. The stripline structure is formed by etching rectangular grooves with the same structural parameters at upper and lower positions on the top metal of the third dielectric substrate (2-1) and the bottom metal of the second dielectric substrate 1-2. The gradient microstrip line 3-2-4 is formed on the top metal of the extended part of the third dielectric substrate 2-1, and the gradient microstrip line 3-2-4 is directly connected to the negative resistance compensation circuit 3-3.

[0066] 7(b), a corresponding rectangular groove is etched on the bottom metal of the second dielectric substrate 1-2 to form a second feeding structure 3-1-1 for feeding the resonant cavity. In this embodiment, preferably, the length and width of the rectangular groove are 8 mm and 0.3 mm respectively.

[0067] 8(a), a corresponding rectangular groove is etched on the top metal of the third dielectric substrate 2-1 to form a first feeding structure 3-2-1 for feeding the resonant cavity. In this embodiment, preferably, the length and width of the rectangular groove are 8 mm and 0.3 mm respectively.

[0068] The second feeding structure 3-1-1 on the bottom metal layer of the second dielectric substrate 1-2 and the first feeding structure 3-2-1 on the top metal layer of the third dielectric substrate 2-1 have the same upper and lower positions and the same structural parameters, and together they constitute the "stripline" structure of the resonant cavity feeding.

[0069] Referring to FIG8(c), the third feeding structure 3-2-2 is composed of three parts (i.e., ①, ②, and ③ in the figure), the first part is a gradient microstrip line ①, and the second and third parts are solder-free terminal connector grounding settings ② and ③ that are symmetrical on both sides thereof for feeding. The first part of the gradient microstrip line of the third feeding structure 3-2-2 is composed of two trapezoids and a rectangle. First, the width of the microstrip line at the feeding port is 0.8 mm, and then the width gradually increases from the feeding port to the center of the resonant cavity. After a length of 6 mm, it gradually changes to 4.4 mm wide. The gradual change is paused at this time. After 1 mm, it gradually changes from 4.4 mm wide to 2.4 mm wide after a length of 5 mm. The edge of the grounding setting of the corresponding dielectric substrate 2-1 solderless terminal connector is provided with an array of metallized through holes, the radius of the metallized through hole is 0.5mm, and the difference between the centers of the two metallized through holes is 1.7mm; at the same time, in order to meet the use of the solderless terminal connector, two symmetrical screw holes are etched, with a radius of 0.99mm and a center distance of 9.53mm between the two holes. The specific shape parameters of the above solderless terminal connector are shown in Figure 8(c). The third feeding structure 3-2-2 and the "strip line" formed by the second feeding structure 3-1-1 and the first feeding structure 3-2-1 together constitute the cavity feeding structure 3-1 of the resonant cavity "microstrip line + strip line".

[0070] 7(b) and 8(a), rectangular grooves with corresponding upper and lower positions and the same shape parameters are etched on the bottom metal and top metal of the second and third dielectric substrates 1-2 and 2-1, the purpose of which is to form a "stripline" structure for connecting the negative resistance compensation circuit, that is, the "stripline" formed by the second feeding structure 3-1-1 and the first feeding structure 3-2-1. In this embodiment, as a preferred embodiment, the length of the rectangular groove is 14 mm and the width is 0.3 mm.

[0071] Referring to FIG8(d), the port corresponding to the fifth feeding structure 3-2-3 on the third dielectric substrate 2-1 is directly connected to a gradient microstrip line 3-2-4 at one end for connecting the negative resistance compensation circuit 3-3. The gradient microstrip line 3-2-4 is composed of two rectangles and a trapezoid, and is directly connected to a rectangle with a width of 3.4 mm and a length of 3 mm from the port of the fifth feeding structure 3-2-3, and the rectangle is immediately connected to a trapezoid with a lower base of 3.4 mm, an upper base of 0.8 mm, and a height of 4 mm, and the trapezoid is directly connected to the negative resistance compensation circuit 3-3 after passing through a rectangular microstrip line with a width of 0.8 mm and a length of 2 mm.

[0072] Several metallized through holes are etched on both sides of the second and third dielectric substrates 1-2 and 2-1 near the feeding structures 3-1-1, 3-2-2, 3-1-2, and 3-2-3. In this embodiment, preferably, the radius of the metallized through hole is 0.45 mm, and the distance between the centers of the two metallized through holes is 1.8 mm.

[0073] The negative resistance compensation circuit is connected to the two reentrant resonant cavities 1 and 2 through its connection port 3-2. The negative resistance compensation circuit includes a resistor, a capacitor, an inductor, a triode and a varactor diode; the inductor L n One end is connected to the base b of transistor BFP420, and the other end is directly grounded; the collector c of transistor BFP420 is connected to the capacitor C d1 One end is connected to the inductor L c1 One end of the capacitor C d1 The other end of the resistor R c As a DC bias resistor, one end is connected to the inductor L c1 The other end of the resistor R c The other end is connected to the voltage source V c The positive pole of the voltage source V c The negative pole of the transistor BFP420 is directly grounded; the emitter e of the transistor BFP420 is connected to the inductor L c2 and capacitor C d2 One end of the resistor R e With inductance L c2 The other end of the resistor R e The other end is connected to the voltage source V e The negative pole of the voltage source V e The positive electrode of the resistor R0 is directly grounded; one end of the resistor R0 and the capacitor C d2 The other end of the resistor R0 is connected to the cathode of the variable capacitance diode SMV1405 and the inductor L c3 The anode of the variable capacitance diode SMV1405 is directly grounded; the inductor L c3 The other end of the bias The positive pole is connected to the voltage source V bias The negative pole is directly grounded.

[0074] The equivalent circuit models of the two reentrant resonant cavities are two corresponding RLC parallel networks, and the vector network port impedances connected to the cavity feeding structure 3-1 are equivalent to Z IN and Z OUT , and the feed structure 3-1 is equivalent to an ideal three-port transformer, and the corresponding transformation ratios are T1 and T2, which are used to connect

[0075] The negative resistance compensation circuit port 3-2 is also equivalent to an ideal three-port transformer, and the corresponding transformation ratio is T3 and T4. The negative resistance equivalent circuit 3-3 is equivalent to a negative resistance plus capacitance, and the corresponding impedance form can be written as -R+1 / jωC R form.

[0076] After the passive resonant cavity and the negative resistance compensation circuit are connected through 3-2, the bias voltage V of the diode SMV1405 is adjusted. bias Can change the imaginary part of the negative resistance compensation circuit output (i.e. 1 / jωC R size) but has little effect on the real part of the output (i.e., the size of -R); adjust the bias voltage V of the transistor BFP420 e The output real and imaginary parts of the negative resistance compensation circuit can be changed, but the real part is mainly affected. In order to use the negative resistance compensation circuit to compensate for the energy loss of the passive resonant cavity and thus improve the quality factor of the two resonant cavities at the resonant frequency, the present invention changes V bias 、V e , so that the real part (-R) and imaginary part (1 / jωC) of the output of the negative resistance compensation circuit R ) is to be compared with the real part (R L ) and the imaginary part (X L ) is zero. At the same time, the present invention first selects a specific diode bias voltage V bias To determine whether to compensate the passive resonant cavity 1 or 2 for energy to improve the quality factor, and then adjust the bias voltage V of the transistor e To obtain the best compensation effect corresponding to the selected resonant cavity and thus obtain the maximum quality factor. In order to more easily realize energy compensation of two resonant cavities simultaneously by a negative resistance compensation circuit, the present invention adjusts the size of the resonant cavity and the capacitor column so that the difference between the resonant frequencies of the two resonant cavities is 71.4MHz.

[0077] In order to import and export the liquid to be tested, the intermediate dielectric layers of the first and second dielectric substrates 1-1 and 2-2 have two open through holes symmetrical about the diagonal line of the resonant cavity, wherein the first and second open through holes 1-1-5 and 2-2-4 are used for liquid introduction, and the third and fourth open through holes 1-1-4 and 2-2-3 are used for liquid export. In this embodiment, as a preferred embodiment, the radius of the above four open through holes is 1 mm. At the same time, the first and second tube seats 4 and 5 are installed above the through holes, and a flexible polytetrafluoroethylene catheter is connected to both tube seats for extraction and injection of the liquid to be tested. The center of the first tube seat 4 is located on the same vertical line as the center of the first and third open through holes 1-1-4 and 1-1-5. Similarly, the center of the second tube seat 5 is located on the same vertical line as the center of the second and fourth open through holes 2-2-3 and 2-2-4.

[0078] See also Fig.10 and Fig.11 , a first annular microchannel 1-1-3 for one-way flow is etched on the front of the first microfluidic chip 1-1-2, and the microchannel is symmetrical about the center, and the center of symmetry is the center of the first microfluidic chip 1-1-2. The starting point and the end point of the microchannel are both derived by circles, and the center of the circle is on the same vertical line as the center of the open through hole, and the corresponding circle radius is 0.8mm. The structures of the first and second microfluidic chips 1-1-2 and 2-2-1 are exactly the same. In this embodiment, the material of the microfluidic chip is polytetrafluoroethylene, and the dielectric constant is 2.035, the loss tangent is 0.0015, and its structural parameters are detailed in Fig.11 .

[0079] Fig.12 The transmission response curve of the sensor proposed in the present invention under different transistor and diode bias voltages. By adjusting different transistor and diode bias voltage combinations, the corresponding resonant frequencies S of the two resonant cavities can be selectively increased. 21 The quality factor of the two resonant cavities is improved by realizing a negative resistance compensation circuit that can simultaneously and independently improve the quality factors of the two resonant cavities.

[0080] Fig.13 The dielectric constant ε of the sample to be measured when the sensor proposed in the present invention uses different resonant cavities as the sensing area r S when changing 21 Response curve, in which the quality factor corresponding to the passive resonator is very low, and it is difficult to determine its corresponding resonant frequency, and its corresponding resolution liquid is difficult to achieve ultra-low concentration detection of glucose solution; while connecting the negative resistance compensation circuit will not affect the sensitivity of the sensor. At the same time, the negative resistance circuit can compensate the energy of the resonant cavity and greatly improve the quality factor and resolution of the resonant cavity, thereby greatly reducing the sensor's detection limit for the concentration of glucose solution.

[0081] Fig.14 is the S corresponding to the two resonant cavities of the proposed sensor when glucose solutions of different concentrations are loaded 21 Response curve. S under each concentration of glucose solution 21The response curves are all recorded when the resonant frequency converges and stabilizes after the deionized water in the cavity is completely replaced by glucose solution, which ensures the reliability of the test results. At the same time, it can be clearly seen that the lower detection limit of the glucose solution concentration in the two resonant cavities is 1mmo / L, and the two resonant cavities corresponding to the sensor can well distinguish between 1mmol / L and 2.5mmol / L glucose solutions. This test result shows the superior performance of the proposed sensor. Due to errors in manufacturing, dielectric constant of dielectric substrate materials, etc., the actual sensor resonant frequency will deviate from the simulation result, but the actual sensor has all the functions described in the present invention.

[0082] The present invention adopts a technology combining a negative resistance compensation circuit and a re-entrant cavity for ultra-low concentration glucose solution detection, which ensures a high sensitivity of the sensor while also ensuring a high resolution. The present invention stacks two re-entrant resonant cavities together longitudinally and uses the two cavities as references and sensing cavities to measure the glucose solution multiple times during the test to ensure the accuracy of the test results. At the same time, the common overlapping metal layer between the two cavities can affect the characteristics of the two cavities, and a negative resistance compensation circuit is coupled to the two resonant cavities through a specific "microstrip line + stripline" structure to achieve simultaneous and independent energy compensation of the two resonant cavities. When measuring the glucose solution, it is only necessary to adjust the bias voltage of the transistor and the diode. At the same time, the adjustable dynamic range of the bias voltage setting of the transistor and the diode is large enough to make it easier to achieve simultaneous compensation of the two resonant cavities in actual operation.

[0083] In summary, the present invention utilizes the special structure of a common metal layer between two resonant cavities to isolate the two resonant cavities from each other, and only needs to load a negative resistance compensation circuit to achieve energy compensation for the two resonant cavities. A special structure of "microstrip line + stripline" is etched on the common metal layer to connect a negative resistance compensation circuit designed by a transistor and a diode, thereby achieving simultaneous and independent energy compensation for the two resonant cavities, thereby improving the quality factor of the two corresponding resonant frequencies. At the same time, two microfluidic chips are embedded in the gap area where the electric field intensity of the resonant cavity is the strongest, so that the proposed sensor has extremely high resolution and high sensitivity, thereby improving the overall performance of the sensor.

[0084] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications to the invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims and equivalent technologies of the present invention, the present invention is also intended to include these changes and modifications.

Claims

1. A high-resolution double-entry cavity sensor based on microwave negative resistance circuit compensation, characterized in that: The sensor comprises a passive resonant cavity, a microfluidic chip and a negative resistance compensation circuit (3-3); The passive resonant cavity is composed of two upper and lower reentrant resonant cavities formed in four longitudinally stacked dielectric substrates, the two reentrant resonant cavities are respectively formed in the first and second upper dielectric substrates and the third and fourth lower dielectric substrates, each dielectric substrate has a three-layer structure of a top metal layer, an intermediate dielectric layer and a bottom metal layer, and the two reentrant resonant cavities are longitudinally isolated by the bottom metal of the second dielectric substrate and the top metal of the third dielectric substrate in direct contact, so that the electromagnetic field is confined in the respective cavities; The microfluidic chip has two pieces, which are respectively embedded in two reentrant resonant cavities and located in the gap area where the electric field intensity of each resonant cavity is the strongest; A cavity feeding structure (3-1) and a negative resistance compensation circuit connection port (3-2) of two reentrant resonant cavities are formed on the bottom metal of the second dielectric substrate (1-2) and the top metal of the third dielectric substrate (2-1) in contact with each other, wherein the cavity feeding structure (3-1) is connected to a vector network analyzer via an adapter, and the negative resistance compensation circuit is connected to the two reentrant resonant cavities via the negative resistance compensation circuit connection port (3-2), and energy compensation of the two resonant cavities is achieved simultaneously and independently by adjusting the bias voltage of the triode and the varactor diode in the negative resistance compensation circuit; During measurement, one of the cavities is selected as the sensing cavity and the other cavity is selected as the reference cavity; The negative resistance compensation circuit (3-3) comprises a resistor, a capacitor, an inductor, a triode and a varactor diode; the inductor L n One end is connected to the base b of transistor BFP420, and the other end is directly grounded; the collector c of transistor BFP420 is connected to the capacitor C d1 One end is connected to the inductor L c1 One end of the capacitor is connected; C d1 The other end of the resistor is used as the output end of the negative resistance compensation circuit to provide negative resistance; R c As a DC bias resistor, one end is connected to the inductor L c1 The other end of the resistor is connected to R c The other end of the voltage source V c The positive pole of the voltage source is connected; V c The negative pole of the transistor BFP420 is directly grounded; the emitter e of the transistor BFP420 is connected to the inductor L c2 and capacitor C d2 One end of the resistor is connected to R e With inductor L c2 The other end of the resistor is connected to R e The other end is connected to the voltage source V e The negative pole of the voltage source is connected; V e The positive pole of the resistor is directly grounded; R 0 One end and the capacitor C d2 The other end of the resistor R 0 The other end is connected to the cathode of the varactor diode SMV1405 and the inductor L c3 connected; the anode of the variable capacitance diode SMV1405 is directly grounded; the inductor L c3 The other end of the voltage source V bias The positive pole of the voltage source is connected to V bias The negative pole is directly grounded; The cavity feeding structure (3-1) is symmetrically arranged about the longitudinal axis at both ends of the two reentrant resonant cavities, and the cavity feeding structure (3-1) is formed by connecting a strip line formed by a first feeding structure (3-2-1) and a second feeding structure (3-1-1) and a third feeding structure (3-2-2); the negative resistance compensation circuit connection port (3-2) is formed by connecting a strip line structure formed by a fourth and fifth feeding structures (3-1-2) and (3-2-3) to a section of a gradient microstrip line (3-2-4), and the strip line structure is formed by etching rectangular grooves with the same structural parameters at upper and lower positions on the top metal of the third dielectric substrate (2-1) and the bottom metal of the second dielectric substrate (1-2), and the gradient microstrip line (3-2-4) is formed on the top metal of the extended part of the third dielectric substrate (2-1), and the gradient microstrip line (3-2-4) is directly connected to the negative resistance compensation circuit (3-3).

2. The sensor according to claim 1, characterized in that The two reentrant resonant cavities are formed by etching a plurality of metallized through holes in the intermediate dielectric layers of the respective corresponding dielectric substrates, and the metallized through holes are evenly distributed to form an equivalent metal wall of the resonant cavity; The first dielectric substrate (1-1) of the upper reentrant resonant cavity (1) is etched upward from the bottom metal to a portion of the middle dielectric layer in the area surrounded by the equivalent metal wall to form a circular groove, the first microfluidic chip (1-1-2) is embedded in the circular groove, and a metallized through hole distributed in a periodic array is provided in the central area of ​​the second dielectric substrate to form a first capacitor column (1-2-1); The fourth dielectric substrate (2-2) of the lower reentrant resonant cavity (2) is etched from the top metal layer downward to a portion of the middle dielectric layer in the area surrounded by the equivalent metal wall to form a circular groove, and the second microfluidic chip (2-2-1) is embedded in the circular groove; and metallized through holes distributed in a periodic array are provided in the central area of ​​the third dielectric substrate to form a second capacitor column (2-1-1); The positions of the first capacitor column (1-2-1) and the second capacitor column (2-1-1) are both the areas with the strongest electric field in their respective cavities, and the microchannels of the first microfluidic chip (1-1-2) and the second microfluidic chip (2-2-1) are respectively distributed corresponding to the areas with the strongest electric field; the radii of the capacitor columns in the two resonant cavities are different, the radius of the capacitor column in the upper reentrant resonant cavity (1) is larger, and the radius of the capacitor column in the lower reentrant resonant cavity (2) is smaller, and the two reentrant resonant cavities and the corresponding capacitor columns in the cavities are symmetrically distributed along the longitudinal axis and the transverse axis.

3. The sensor according to claim 1, characterized in that: The equivalent circuit models of the two reentrant resonant cavities are two corresponding RLC The impedance of the vector network ports connected to the cavity feeding structure (3-1) are equivalent to Z IN and Z OUT , and the cavity feeding structure (3-1) is equivalent to an ideal three-port transformer, and the corresponding transformation ratio is T1 and T2. The connection port (3-2) for connecting the negative resistance compensation circuit is also equivalent to an ideal three-port transformer, and the corresponding transformation ratio is T3 and T4. The negative resistance compensation circuit (3-3) is equivalent to a negative resistance plus capacitance, and the corresponding impedance form is written as -R+1 / jωC R in the form of.

4. The sensor according to claim 1, characterized in that The bottom metal of the second dielectric substrate (1-2) has a rectangular groove with the same upper and lower positions and the same structural parameters as the top metal of the third dielectric substrate (2-1), which is used to form the first feeding structure (3-2-1) and the second feeding structure (3-1-1) to form the strip line; the two ends of the third dielectric substrate (2-1) of the reentrant resonant cavity (2) are designed to be wider than other dielectric substrates, and the third feeding structure (3-2-2) is arranged at the wider position to connect with the strip line formed by the first and second feeding structures (3-2-1) and (3-1-1) to form the cavity feeding structure (3-1); the cavity feeding structure (3-1) provides excitation for two longitudinal reentrant cavities, so that the two cavities can resonate simultaneously.

5. The sensor according to claim 4, characterized in that The negative resistance compensation circuit connection port (3-2) is provided at one of the other two ends of the two reentrant resonant cavities where the cavity feeding structure (3-1) is not provided, and the third dielectric substrate (2-1) is partially extended outside the cavity at this end so as to extend beyond the other dielectric substrates, and a portion of the metal layer is etched at this extended portion to provide the negative resistance compensation circuit (3-3).

6. The sensor according to claim 1 or 2, characterized in that: The first dielectric substrate (1-1) of the upper reentrant resonant cavity (1) and the fourth dielectric substrate (2-2) of the lower reentrant resonant cavity (2) are provided with microfluidic inlet and outlet holes connected to the respective microfluidic chips; the first and second microfluidic chips (1-1-2) and (2-2-1) are provided with annular microfluidic channels, and the positions of the annular microfluidic channels correspond exactly to the areas with the maximum electric field intensity of the respective resonant cavities.

7. The sensor according to claim 1 or 2, characterized in that: The resonant cavity is circular, with a corresponding radius of 19.4 mm, and the radii of the corresponding capacitor columns (1-2-1) and (2-1-1) in the cavities (1) and (2) are 7.5 mm and 6.0 mm respectively.

8. The sensor according to claim 1 or 2, characterized in that: The intermediate dielectric layer materials of the four dielectric substrates are all F4BM, which has a relative dielectric constant of 2.55, a relative magnetic permeability of 1, and a loss tangent of 0.0015.

9. The sensor according to claim 1 or 2, characterized in that: The sensor is used for detecting liquid media, including detecting extremely trace solutes in liquid solvents, and is particularly used for characterizing the concentration of glucose solutions. When used for characterizing the concentration of glucose solutions, the resonant frequencies of the two resonant cavities can differ by 71.4 MHz by adjusting the sizes of the resonant cavity and the capacitor column.

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