OCSRR-Based Microfluidic Differential Microwave Sensor and Its Design Method

Abstract

The present invention discloses a microfluidic differential microwave sensor based on OCSRR and its design method, which at least includes a measurement unit and a reference unit. The measurement unit and the reference unit adopt the same structure, and measurement OCSRR particles and reference OCSRR particles are respectively arranged therein. Among them, the measurement unit is used to generate a first signal according to the fluid under test flowing through it, and the reference unit is used to generate a second signal according to the reference fluid flowing through it. The first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particles, and then the sensing information is obtained through the differential information of the two to extract the complex permittivity of the liquid sample. By testing the sensor designed by the present invention, the experimental results are in good agreement with the simulation results. Compared with the existing similar sensors, this sensor can suppress the influence of environmental factors, and the average sensitivity is as high as 0.88%.

Description

Technical Field

[0001] The present invention relates to the field of microwave radio frequency sensing, and particularly to a microfluidic differential microwave sensor based on OCSRR and a design method thereof. Background Art

[0002] In the past decade, microwave sensors, as a relatively reliable type of sensor, have been increasingly widely used. In the field of medical biology, microwave sensors can detect the culture status of biological tissues. In environmental monitoring, microwave sensors can be used to detect environmental temperature, humidity, and soil water content, etc. In physics, microwave sensors can be used to restore parameters such as object displacement and rotation angle. In industrial production, microwave sensors can be used to characterize the dielectric properties of solids and liquid chemicals. Among them, since microwave microfluidic sensors do not require labeling protocols or biological markers, it is no longer necessary to consume a large amount of reagents, solutions, and time for studying liquid chemicals or biological liquids, which greatly reduces the cost of extracting liquid parameters. Most of the currently developed microwave sensors use complementary split ring resonator (CSRR) structures and stepped impedance resonator (SIR) structures. Among them, the electric field distribution of the SIR structure is not concentrated, so a relatively large amount of liquid samples are required for each measurement, making it difficult to be applied in practice. Although the electric field of the CSRR structure is relatively concentrated, it uses a coupling form in transmission, which will affect the sensitivity. In practical applications, a high sensitivity is required for measurement because chemistry and biology have extremely high precision requirements for the liquid concentration. In addition, the non-invasiveness of the sensor is also a very important indicator. Losing too much liquid sample during measurement is undoubtedly a great waste for industry.

[0003] In view of the defects existing in the current technology, it is necessary to conduct research to realize a high-quality microwave sensor with non-invasiveness, high sensitivity, and low manufacturing and measurement costs, so that it can generate value in practical applications. Summary of the Invention

[0004] In order to overcome the defects existing in the prior art, the present invention proposes a microfluidic differential microwave sensor based on OCSRR and its design method, that is, a microfluidic differential microwave sensor is realized based on an Open complementary splitring resonator (OCSRR). The differential form is used to suppress the test errors brought by environmental factors (such as humidity and temperature); a new OCSRR structure is used to increase the resonance frequency, while reducing the physical size of the sensor and the cost of the sensor; in addition, the OCSRR structure can generate a strong and concentrated electric field on the left side of the outer ring, which greatly improves the sensitivity of the sensor; the use of a hexagonal and rectangular combined OCSRR structure is beneficial to reducing the capacitance of the OCSRR structure itself and can further improve the sensitivity of the sensor.

[0005] To solve the existing technical difficulties, the technical solution of the present invention is as follows:

[0006] A microfluidic differential microwave sensor based on OCSRR includes at least a measurement unit and a reference unit. The measurement unit and the reference unit adopt the same structure, and measurement OCSRR particles and reference OCSRR particles are respectively arranged therein. Among them, the measurement unit is used to generate a first signal according to the fluid under test flowing through it, and the reference unit is used to generate a second signal according to the reference fluid flowing through it. The first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particles, and then the sensing information is obtained through the differential information of the two.

[0007] The measurement unit at least includes an input microstrip line, a signal access microstrip line, an output microstrip line, measurement OCSRR particles and a fluid channel. Among them, the fluid channel is connected to the measurement OCSRR particles and is used to flow in the fluid.

[0008] The input microstrip line and the output microstrip line are connected to the measurement OCSRR particles through the signal access microstrip line in the middle. The output microstrip line is connected to a 50Ω resistor and grounded at the center of the dielectric plate.

[0009] As a further improvement, the OCSRR particles include an open outer ring, an open inner ring and two grounding holes.

[0010] As a further improvement, the material of the fluid channel is polydimethylsiloxane, and the structure is a cuboid, which is composed of a colloid and a microfluidic empty groove.

[0011] As a further improvement, the structures of the measurement OCSRR particles and the reference OCSRR particles are completely the same and their positions on the PCB board are completely symmetric about the center line to ensure that the dielectric properties of the two particles change in the same way when the same liquid medium is added.

[0012] As a further improvement, there is no signal coupling between the measured OCSRR particles and the reference OCSRR particles.

[0013] As a further improvement, the OCSRR particles are etched on the metal plate on the upper layer of the dielectric substrate, and the outer ring of the OCSRR particles adopts a hexagonal structure, while the inner ring of the OCSRR particles adopts a rectangular structure.

[0014] As a further improvement, the signal access microstrip line is used to connect the input microstrip line to the opening part of the OCSRR particles. Among them, the width of the signal access microstrip line should be consistent with the opening width of the OCSRR particles to ensure good signal access.

[0015] As a further improvement, the OCSRR particles form a resonant circuit, and its resonant frequency depends on the overall inductance and capacitance of the OCSRR particles. The specific expression is as follows:

[0016]

[0017] When a liquid sample is added to the fluid channel, the overall resonant frequency of the resonant circuit changes. The main reason is that the capacitance part no longer depends entirely on the capacitance of the OCSRR particles themselves, but also has a correlation with the capacitance of the liquid sample. The specific expression is as follows:

[0018]

[0019] Where L p , C p respectively represent the inductance and capacitance of the OCSRR particles; C LUT then simulates the change in the sensor capacitance when adding a liquid sample to the sensor;

[0020] The sensor sensitivity is defined as:

[0021]

[0022] Where Δf z is the shift of the resonant frequency, and Δε is the change in the dielectric constant of the dielectric sample loaded on the resonator; when the liquid sample is loaded into the fluid channel, it is equivalent to adding an additional capacitor C LUT to the sensor; from the above formula, it can be obtained that:

[0023]

[0024] Where Δε and C LUT are determined by the physical properties of the liquid sample, and f z and C R are only determined by the physical properties of the sensor; through fz and C R is the control sensitivity; when f z and C R increases, the sensitivity also increases.

[0025] As a further improvement, the total length of the fluid channel is 11 mm, the height of the fluid channel is 0.2 mm, and the width is 0.4 mm.

[0026] The present invention also proposes a design method for a microfluidic differential microwave sensor based on OCSRR, which at least includes the following steps:

[0027] Step S1: Etch two OCSRR particles with exactly the same structure on the dielectric plate, that is, measure the OCSRR particle and the reference OCSRR particle;

[0028] Step S2: Place a PDMS fluid channel on the OCSRR particle for introducing and emptying liquid samples;

[0029] Step S3: Design a signal transmission circuit, including an input microstrip line, a signal access microstrip line, and an output microstrip line. The input microstrip line and the output microstrip line are connected to the OCSRR particle through the signal access microstrip line in the middle. The output microstrip line is connected to a 50 Ω resistor and grounded at the center of the dielectric plate;

[0030] Step S4: Measure that the OCSRR particle generates a first signal according to the measured fluid flowing through its fluid channel, and the reference OCSRR particle generates a second signal according to the reference fluid flowing through its fluid channel. Among them, the first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particle;

[0031] Step S5: Obtain the first signal and the second signal and obtain the sensing information through the differential information of the two.

[0032] As a further improvement, the input microstrip line has its input end connected to the radio frequency signal output end, and its output end is respectively connected to the signal access microstrip line and the input end of the output microstrip line.

[0033] The output microstrip line has its input end respectively connected to the signal access microstrip line and the input microstrip line, and its output end is connected to a differential grounded 50-ohm resistor.

[0034] As a preferred technical solution, each differential input microstrip line is loaded with an OCSRR particle. These two OCSRR particles are exactly the same, and their positions on the PCB board also need to be completely symmetric about the center line, so as to ensure that when the same liquid medium is added, the dielectric characteristics of the two particles change identically.

[0035] As a preferred technical solution, the two ports of the OCSRR microfluidic differential microwave sensor respectively output the reflection characteristics of two OCSRR particles, one of which is used to characterize the complex permittivity of the LUT, and the other serves as a reference port. Since both microstrip lines are grounded through the holes in the middle metal patch, and a relatively large distance is left between the two metal sheets for etching the OCSRR particles, there is no coupling phenomenon between the two OCSRR particles.

[0036] As a preferred technical solution, the OCSRR microfluidic differential microwave sensor uses PDMS to fabricate the microfluidic channel. Because this material has electrical insulation, hydrophobicity, and high shear resistance, and is also relatively convenient to process, it is the best choice for fabricating the fluid channel. The cross-sectional area of the fabricated fluid channel is 0.4mm * 0.2mm, the total length of the fluid channel is 11mm, the height of the fluid channel is 0.2mm, and the width is 0.4mm. It can occupy the position with the strong electric field intensity within the largest range, resulting in the largest change in the reflection characteristics, while not wasting the liquid sample.

[0037] As a preferred technical solution, the OCSRR particles of the OCSRR microfluidic differential microwave sensor are etched on the metal plate on the upper layer of the dielectric substrate, and the outer ring of the OCSRR particles adopts a hexagonal structure to reduce the original capacitance of the OCSRR particles, and the inner ring of the OCSRR particles adopts a rectangular structure to facilitate optimizing to obtain the highest electric field intensity.

[0038] As a preferred technical solution, the differential signal access microstrip line of the OCSRR microfluidic differential microwave sensor connects the differential input microstrip line and the opening part of the OCSRR particle, and moreover, the width of the differential signal access microstrip line should be consistent with the opening width of the OCSRR particle to ensure good signal access.

[0039] As a preferred technical solution, each OCSRR particle constitutes a resonant circuit. Its resonant frequency depends on the overall inductance and capacitance of the OCSRR particle, and the specific expression is as follows:

[0040]

[0041] When a liquid sample is added to the fluid channel, the overall resonant frequency of this resonant circuit changes. The main reason is that the capacitance part no longer depends entirely on the capacitance of the OCSRR particle itself, but also has a correlation with the capacitance of the liquid sample. The specific expression is as follows:

[0042]

[0043] Wherein, L p 、C pRepresent the inductance and capacitance of the OCSRR particle respectively. C LUT Then simulate the change in the sensor capacitance when adding a liquid sample to the sensor.

[0044] This sensor is used to extract the dielectric constant of a liquid sample, so it is very important to improve the sensitivity of the sensor. The sensitivity is defined as:

[0045]

[0046] Where Δf z is the shift of the resonant frequency, and Δε is the change in the dielectric constant of the dielectric sample loaded on the resonator. When a liquid sample is loaded into the fluid channel, it is equivalent to adding an additional capacitor to the sensor (only real dielectric constants are discussed here). From the above formula, we can get:

[0047]

[0048] Where Δε and C LUT are determined by the physical properties of the liquid sample. However, f z and C R are only determined by the physical properties of the sensor. Therefore, when designing the sensor, f z and C R are the keys to controlling the sensitivity. It is not difficult to find that when f z and C R increase, the sensitivity also increases. However, when increasing f z , we need to consider the increase in the measurement difficulty and processing difficulty. When increasing C R , it is necessary to consider the influence of the capacitance of the outer ring part of the OCSRR with low electric field strength on the sensitivity. Therefore, this design obtains appropriate values of f z and C R through various considerations, which has a certain improvement in the measurement sensitivity.

[0049] Compared with the prior art, the present invention has the following technical effects:

[0050] 1. The present invention uses the OCSRR structure to replace the CSRR structure in the traditional microfluidic sensor to achieve the no-load resonant frequency of the sensor at 2.3 GHz, and uses the OCSRR structure combined with a hexagon and a rectangle to replace the traditional circular and rectangular OCSRR structure to reduce the capacitance and inductance of the OCSRR structure itself and improve the sensitivity.

[0051] 2. The present invention can be applied in the field of medical biology to detect the dielectric constant of a liquid sample, and inversely deduce the concentration of the liquid sample through the dielectric constant. The sensitivity of the present invention has a great improvement compared with the traditional invention, and the consumption of the liquid sample is extremely small, and it can play a good role in practical applications. Description of the Drawings

[0052] Figure 1 It is a schematic diagram of the working principle of a microfluidic differential microwave sensor based on OCSRR according to the present invention.

[0053] Figure 2 It is a schematic structural diagram of a microfluidic differential microwave sensor based on OCSRR according to the present invention;

[0054] Figure 3 It is the OCSRR structure and its equivalent lumped element circuit model in the present invention;

[0055] Figure 4 It is a plan view of a sensor based on OCSRR in a preferred embodiment of the present invention;

[0056] Figure 5 It is an equivalent circuit model diagram of a preferred embodiment of the present invention;

[0057] Figure 6 It is the no-load transmission response and the electric field distribution at the resonant frequency of the present invention;

[0058] Figure 7 It is the reflection coefficient of a sensor based on OCSRR of the present invention for ethanol-water binary solutions with different water volume fractions;

[0059] Figure 8 It is a comparison diagram between the actual value of the relative permittivity of an ethanol-water binary solution of the present invention and the value measured using the designed sensor; Detailed Embodiments

[0060] The following are specific embodiments of the present invention and, in conjunction with the drawings, further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0061] Aiming at the defects of existing microwave sensors in the prior art, this invention focuses on improving the sensitivity and non-invasiveness of microwave sensors. The unloaded frequency of the microwave sensor is also a problem that needs to be considered first. For the selection of the unloaded frequency, first of all, the measurement should be made more convenient, that is, instruments with lower prices can be used for measurement. Secondly, the unloaded frequency has a great impact on the size of the circuit board and also has a certain impact on the sensitivity. Therefore, the selected frequency should be less than 3 GHz and greater than 2 GHz, which will neither make the circuit board size too large nor make the product applicable to most vector network analyzers. Selecting a suitable resonator structure is crucial for all indicators of the sensor. Currently, the CSRR and SIR structures are used more frequently. This invention selects the new OCSRR structure. The biggest difference between the OCSRR structure and the CSRR structure is that the CSRR structure is a defected ground structure, and the microstrip line for transmitting signals is located above the dielectric substrate, and the signal needs to be transmitted through coupling. The OCSRR structure directly digs out inner and outer rings on the upper layer of the dielectric substrate and adds a signal access line to directly access the signal into the resonant cavity, reducing signal attenuation and facilitating the observation of the change in the imaginary part of the dielectric constant. On the other hand, the inductance of the OCSRR particle is the inductance of the metal strip between the two annular grooves, and the capacitance mainly comes from the fringe capacitance generated by the metal on both sides of the two annular grooves, which can be equivalent to the fringe capacitance generated by a metal disk with a radius surrounded by a metal plane with an edge distance. Since the inductance of the CSRR is L0 / 4, the resonant frequency of the OCSRR is approximately half of the CSRR resonant frequency. Therefore, at the same center frequency, the size of the sensor with the OCSRR structure is smaller than that of the CSRR structure, which conforms to the trend of modern device miniaturization, that is, it saves materials and is convenient to carry.

[0062] At the same time, considering the influence of environmental factors on the measurement results, this invention adopts a differential structure to eliminate the influence of environmental factors such as humidity and temperature. An OCSRR particle is loaded on each differential input microstrip line. It should be noted that these two OCSRR particles are exactly the same, and their positions on the PCB board also need to be completely symmetrical about the midline, so as to ensure that when the same liquid medium is added, the dielectric characteristics of the two particles change identically.

[0063] Based on the above design considerations, this invention proposes a microfluidic differential microwave sensor based on OCSRR, see Figure 1, as shown in a schematic diagram of its principle, at least includes a measuring unit and a reference unit, the measuring unit and the reference unit adopt the same structure, and are respectively provided with measuring OCSRR particles and reference OCSRR particles, wherein the measuring unit is used to generate a first signal according to the measured fluid flowing therethrough, and the reference unit is used to generate a second signal according to the reference fluid flowing therethrough, and the first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particles and then obtain the sensing information through the differential information of the two.

[0064] See also Figure 2 The figure is a three-dimensional view of a microfluidic sensor with a PDMS microfluidic channel according to an embodiment of the present invention. The input microstrip line and the output microstrip line are connected to the OCSRR particles through a signal access microstrip line, and the output microstrip line is connected to a 50Ω resistor and grounded at the center of the dielectric plate. The PDMS fluid channel of the same size is placed on two OCSRR particles, and there is a considerable gap between the two particles, so there is no coupling between the two particles. The structures on both sides are the same, ensuring that the reflection coefficients of the two resonators are completely consistent in the same environment between them. The OCSRR particle on the left is used for measurement, and the other is used as a reference. In a preferred design of the present invention, the OCSRR uses a hexagonal outer ring, which can effectively reduce the capacitance of the resonator itself when unloaded and increase the influence of the liquid sample on the resonant frequency. The rectangular inner ring is convenient for adjusting the position to obtain the maximum electric field concentration. Among them, the microfluidic channel is made of PDMS. PDMS has electrical insulation, hydrophobicity, high shear resistance and convenient processing. It is the best choice for making fluid channels. The cross-sectional area of ​​the manufactured fluid channel is 0.4mm×0.2mm, and the total length of the fluid channel is about 11mm.

[0065] See also Figure 3 The traditional OCSRR structure of this embodiment and its equivalent lumped element circuit model are shown. The OCSRR structure consists of two annular grooves hollowed out on a metal plate. Unlike the CSRR structure, the OCSRR structure is directly connected to the microstrip line through a metal strip stretched outward from the gap of the ring. In other words, the OCSRR is an open resonator, while the CSRR is a closed resonator. When used in sensors, the CSRR needs to be coupled with the microstrip line, which will cause losses during signal transmission, while the OCSRR does not have this problem. The inductance of the OCSRR particle is the inductance of the metal strip between the two annular grooves, while the capacitance mainly comes from the edge capacitance generated by the metal on both sides of the two annular grooves, which can be equivalent to a radius of R. extEdge capacitance generated when a metal disk is surrounded by a metal plane with a distance of c from its edge. Since the inductance of the CSRR is L0 / 4, the resonant frequency of the OCSRR is approximately half of the resonant frequency of the CSRR. Therefore, at the same center frequency, the size of the OCSRR structure is smaller than that of the CSRR structure sensor, which conforms to the trend of modern device miniaturization, saving materials and being convenient to carry. Therefore, the OCSRR structure is more suitable for making microwave sensors than the CSRR structure.

[0066] See Figure 4 This is the plan view of the OCSRR-based sensor of this embodiment. In this embodiment, further modifications are made on the traditional OCSRR structure by using a hexagonal outer ring. Compared with a circular outer ring, this is beneficial to increasing the position where the electric field intensity is concentrated. Compared with a rectangular outer ring, this is beneficial to achieving a smaller perimeter under the same area, reducing the capacitance of the OCSRR particle itself, and improving the measurement sensitivity. The inner ring uses a rectangle, enabling a more flexible adjustment scheme for the relative position between the inner and outer rings. And, s2 and s3 are set to values different from s1, which has a certain improvement in sensitivity. Among them, the width of s2 is greater than s1, which further reduces the internal capacitance (capacitance is inversely proportional to the distance between two dielectric plates). However, an overly large s2 will make the width of the signal access microstrip line too narrow, affecting signal transmission. The increase in the width of s3 is also beneficial to reducing the internal capacitance of the OCSRR particle. However, an overly wide s3 will cause the inner and outer rings to be connected together, resulting in signal leakage (the closure of the resonant cavity is insufficient). Ports 1 and 2 respectively output the reflection characteristics of two OCSRR particles, one of which is used to characterize the complex permittivity of the liquid sample, and the other serves as a reference port. Since both microstrip lines are grounded through the holes in the middle metal patch, and a relatively large distance is left between the two metal sheets for etching the OCSRR particles, there is no coupling phenomenon between the two OCSRR particles. These two OCSRR particles are exactly the same, and their positions on the PCB board also need to be completely symmetric about the center line to ensure that when the same liquid sample is added, the dielectric properties of the two particles change identically.

[0067] See Figure 5 This is the equivalent circuit model diagram of this embodiment. Among them, the short transmission line with characteristic impedance Z C represents the microstrip lines on both sides of the OCSRR particle. L s represents the inductance of the metal strip connecting the OCSRR particle and the microstrip line. L P , C P and R P respectively represent the inductance, capacitance, and resistance of the OCSRR particle. C LUT , R LUT , C ref and R refSimulate the changes in the capacitance and resistance of the sensor when adding a liquid sample to the sensor. Each OCSRR particle based on the OCSRR microfluidic differential microwave sensor constitutes a resonant circuit. Its resonant frequency depends on the total inductance and capacitance of the OCSRR particles, and the specific expression is as follows:

[0068]

[0069] When a liquid sample is added to the fluid channel, the overall resonant frequency of this resonant circuit changes. The main reason is that the capacitance part no longer depends entirely on the capacitance of the OCSRR particles themselves, but also has a correlation with the capacitance of the liquid sample. The specific expression is as follows:

[0070]

[0071] Among them, L p and C p respectively represent the inductance and capacitance of the OCSRR particles. C LUT then simulates the change in the capacitance of the sensor when adding a liquid sample to the sensor. Therefore, when adding liquid samples with different dielectric constants, the resonators of the OCSRR structure will generate different resonant frequencies. By measuring the resonant frequency, the dielectric constant of the liquid sample can be restored.

[0072] In addition, since this sensor is used to extract the dielectric constant of a liquid sample, it is very important to improve the sensitivity of the sensor. The sensitivity of the sensor is defined as:

[0073]

[0074] Among them, Δf is the shift of the resonant frequency, and Δε is the change in the dielectric constant of the dielectric sample loaded on the resonator. When a liquid sample is loaded into the fluid channel, it is equivalent to adding an additional capacitor to the sensor (only real dielectric constants are discussed here). From the above formula, it can be obtained that:

[0075]

[0076] Among them, Δε and C LUT are determined by the physical properties of the liquid sample. However, f z and C R are only determined by the physical properties of the sensor. Therefore, when designing the sensor, f z and C R are the keys to controlling the sensitivity. It is not difficult to find that when f z increases, the sensitivity also increases. However, when increasing f z , we need to consider the increase in the difficulty of measurement and fabrication. When C R decreases, the sensitivity increases. However, when decreasing C RWhen considering the influence of the attenuation of the electric field strength on the measurement, an appropriate f z and C R is conducive to achieving the maximum sensitivity.

[0077] See Figure 6 For the no-load transmission response and the electric field distribution at the resonant frequency of this embodiment, it can be found that there is a very dense electric field strength on one side near the outer annular groove port of the OCSRR particle. Therefore, the fluid channel is placed at this position.

[0078] See Figure 7 For the reflection coefficient of the OCSRR-based sensor of this embodiment for ethanol-water binary solutions with different water volume fractions. It can be seen that when the concentration of water in the ethanol-water binary solution gradually decreases, the resonant frequency gradually decreases from 2.05 GHz to 1.2 GHz, and the overall change in the resonant frequency exceeds 800 MHz, with relatively high sensitivity.

[0079] See Figure 8 For the comparison diagram between the actual value of the relative permittivity of the ethanol-water binary solution of this embodiment and the value measured using the designed sensor. It can be seen from the figure that the relative permittivity of the ethanol-water binary solution restored by this embodiment is very close to the actual value and can be used for actual measurement. This embodiment finally achieves only using 0.91 μL of liquid sample for each measurement, reaches a maximum change in the resonant frequency of 820 MHz, and reaches an average sensitivity of 0.88. The differential structure of this embodiment can also effectively eliminate the influence of environmental factors. Compared with the existing microwave sensors, this design has certain advantages in both sensitivity and the usage amount of liquid samples.

[0080] In order to solve the technical problems existing in the prior art, the present invention also proposes a design method for a microfluidic differential microwave sensor based on OCSRR, which at least includes the following steps:

[0081] Step S1: Etch two OCSRR particles with exactly the same structure on the dielectric substrate, that is, measure the OCSRR particle and the reference OCSRR particle;

[0082] Step S2: Place a PDMS fluid channel on the OCSRR particle for introducing and emptying the liquid sample;

[0083] Step S3: Design a signal transmission circuit, including an input microstrip line, a signal access microstrip line, and an output microstrip line. The input microstrip line and the output microstrip line are connected to the OCSRR particle through the signal access microstrip line in the middle. The output microstrip line is connected to a 50 Ω resistor and grounded at the center of the dielectric substrate;

[0084] Step S4: Measure that the OCSRR particle generates a first signal according to the fluid under test flowing through its fluid channel, and the reference OCSRR particle generates a second signal according to the reference fluid flowing through its fluid channel, wherein the first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particle;

[0085] Step S5: Obtain the first signal and the second signal and obtain the sensing information through the differential information between the two.

[0086] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A microfluidic differential microwave sensor based on OCSRR, characterized in that It includes at least a measurement unit and a reference unit. The measurement unit and the reference unit have the same structure, and a measurement OCSRR particle and a reference OCSRR particle are respectively arranged therein. Wherein, the measurement unit is used to generate a first signal according to the fluid under test flowing through it, and the reference unit is used to generate a second signal according to the reference fluid flowing through it. The first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particles, and then sensing information is obtained through the differential information between the two; The measurement unit at least includes an input microstrip line, a signal access microstrip line, an output microstrip line, a measurement OCSRR particle and a fluid channel. Wherein, the fluid channel is connected to the measurement OCSRR particle and is used to flow in the fluid; The input microstrip line and the output microstrip line are connected to the measurement OCSRR particle through the signal access microstrip line in the middle. The output microstrip line is connected to a 50Ω resistor and grounded at the center of the dielectric plate; The OCSRR particle includes an open outer ring, an open inner ring and two ground holes; The measurement OCSRR particle and the reference OCSRR particle have exactly the same structure and are completely symmetric about the center line on the PCB board to ensure that the dielectric properties of the two particles change in the same way when the same liquid medium is added; The OCSRR particle is etched on the metal plate on the upper layer of the dielectric plate, and the outer ring of the OCSRR particle adopts a hexagonal structure, and the inner ring of the OCSRR particle adopts a rectangular structure.

2. The microfluidic differential microwave sensor based on OCSRR according to claim 1, characterized in that, The material of the fluid channel is polydimethylsiloxane, and the structure is a cuboid, which is composed of a colloid and a microfluidic groove.

3. The microfluidic differential microwave sensor based on OCSRR according to claim 1, characterized in that, There is no signal coupling between the measurement OCSRR particle and the reference OCSRR particle.

4. The microfluidic differential microwave sensor based on OCSRR according to claim 1, wherein The signal access microstrip line is used to connect the input microstrip line and the opening part of the OCSRR particle. Wherein, the width of the signal access microstrip line should be the same as the opening width of the OCSRR particle to ensure good signal access.

5. The microfluidic differential microwave sensor based on OCSRR according to claim 1, wherein , The OCSRR particle constitutes a resonant circuit, and its resonant frequency depends on the total inductance and capacitance of the OCSRR particle. The specific formula is as follows: ； When a liquid sample is added to the fluid channel, the total resonant frequency of the resonant circuit changes, mainly because the capacitance part no longer depends entirely on the capacitance of the OCSRR particle itself, but is also correlated with the capacitance of the liquid sample; the specific formula is as follows: ； Among them, and respectively represent the inductance and capacitance of the OCSRR particles; then simulate the change in the capacitance of the sensor when a liquid sample is added to the sensor. The sensor sensitivity is defined as: ； wherein is the offset of the resonant frequency, is the change in the dielectric constant of the dielectric sample loaded on the resonator; when a liquid sample is loaded into the fluid channel, it is equivalent to adding an additional capacitor to the sensor ; it can be obtained from the above formula that: ； wherein and are determined by the physical characteristics of the liquid sample, and are determined only by the physical characteristics of the sensor; through and is the control sensitivity; when and increase, the sensitivity also increases.

6. The microfluidic differential microwave sensor based on OCSRR according to claim 2, wherein The total length of the fluid channel is 11mm, the height of the fluid channel is 0.2mm, and the width is 0.4mm.

7. The design method of the OCSRR-based microfluidic differential microwave sensor according to any one of claims 1 to 6, characterized in that It includes at least the following steps: Step S1: Etch two OCSRR particles with exactly the same structure on the dielectric plate, that is, the measurement OCSRR particle and the reference OCSRR particle; Step S2: Place a PDMS fluid channel on the OCSRR particle to introduce and empty the liquid sample; Step S3: Design a signal transmission circuit, including an input microstrip line, a signal access microstrip line and an output microstrip line. The input microstrip line and the output microstrip line are connected to the OCSRR particle through the signal access microstrip line in the middle. The output microstrip line is connected to a 50Ω resistor and grounded at the center of the dielectric plate; Step S4: Measure that the OCSRR particle generates a first signal according to the fluid under test flowing through its fluid channel, and the reference OCSRR particle generates a second signal according to the reference fluid flowing through its fluid channel, wherein the first signal and the second signal are used to characterize the reflection characteristics of the OCSRR particle; Step S5: Obtain the first signal and the second signal and obtain the sensing information through the differential information between the two.

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