Differential active microwave microfluidic sensor

Abstract

The application belongs to the technical field of microwave sensing, and particularly relates to a differential active microwave micro-flow sensor. The differential active microwave micro-flow sensor comprises a top metal layer, a middle dielectric layer and a bottom metal layer; the top metal layer comprises a microstrip line structure and an active amplification circuit; the bottom metal layer comprises a metal sheet and a grooved metal SLSP structure; the grooved metal SLSP structure is a spiral ring structure, and is a plan view pattern composed of two Archimedes spiral lines; a micro-fluidic chip made of polydimethylsiloxane (PDMS) is placed in the area, and an injection liquid is in the chip, and a vector network analyzer (VNA) is used to measure a sensor S parameter curve. The sensor provided by the application has very high sensitivity and Q value, so that the accuracy of measurement is ensured, and therefore the sensor is very suitable for measuring dielectric constant.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave sensing, and particularly relates to a differential active microwave micro-flow sensor. BACKGROUND

[0002] Accurate measurement of dielectric constant of dielectric material plays an important role in healthcare, food safety, and industrial manufacturing. In recent years, planar microwave resonant sensors have been widely used in biological medicine, food safety, environmental pollution monitoring and other fields due to their passive, low cost, small size, high reliability, high sensitivity and non-invasive advantages. In a microwave resonant sensor, the resonant frequency and the quality factor are related to the relative dielectric constant and the electrical loss, respectively. That is, when a sample to be measured is placed on the sensor, the resonant frequency will move downward due to the increase of the sensor resonant cavity capacitance, and the quality factor will decrease due to the dielectric loss of the sample.

[0003] The resonant frequency and the quality factor are two key parameters of a microwave resonant sensor, which determine the sensitivity and measurement accuracy of the sensor. The resonant frequency is related to the relative dielectric constant of the material sample to be measured. When the sample to be measured is placed on the sensor, the resonant frequency will change because the dielectric constant of the sample to be measured is different from that of air or other environments. Therefore, the greater the change in the resonant frequency, the higher the sensitivity of the sensor, that is, the more accurate the dielectric properties of the sample to be measured can be detected. However, the performance of the sensor is often affected by environmental factors such as temperature, humidity, etc., which can increase the measurement error and instability of the sensor. Therefore, a differential sensor is designed to eliminate the influence of these environmental factors and improve the measurement accuracy and reliability of the sensor. Meanwhile, a higher quality factor can produce a stronger resonant response. The change in the quality factor is related to the electrical loss of the sample to be measured. Therefore, when the sample to be measured is placed on the sensor, the change in the quality factor also affects the sensitivity and measurement accuracy of the sensor. The higher the quality factor of the sensor, the higher the measurement accuracy, and also has higher sensitivity. However, the unloaded Q value of the passive SLSP resonator is usually limited, and the resolution of the sensor is generally not high.

[0004] Therefore, in order to solve the above problems, it is necessary to design a differential active microwave micro-flow sensor based on artificial local surface plasmon resonator, which can improve the sensitivity and quality factor of the sensor, and thus improve the practicality of the miniaturized sensor. SUMMARY

[0005] The present invention aims to overcome the problems of existing SLSP sensors, which are often limited by the no-load Q value, resulting in low sensor resolution, low quality factor, and low sensitivity. It provides a differential active microwave microfluidic sensor that can improve the sensitivity and quality factor of the sensor, thereby improving the practicality of miniaturized sensors.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] A differential active microwave microfluidic sensor includes a passive resonator and an active amplifier circuit; the passive resonator is a two-port device, which includes a microstrip line structure, a dielectric layer, a metal sheet, and two grooved metal SLSP structures from the top to the bottom.

[0008] The microstrip line is disposed on the upper surface of the dielectric layer; the microstrip line structure includes a first microstrip line, a second microstrip line, a third microstrip line, a fourth microstrip line, and a fifth microstrip line; wherein the first microstrip line is symmetrically arranged, the second and third microstrip lines are symmetrically arranged, the fourth and fifth microstrip lines are symmetrically arranged, one end of the first microstrip line is connected to the midpoint of the second microstrip line, and the other end of the first microstrip line serves as an input / output port; the fifth microstrip line has rounded corners, one end of the fifth microstrip line is connected to the second microstrip line, and the other end of the fifth microstrip line is connected to the third microstrip line; a gap is provided between the first and third microstrip lines, and they are arranged parallel to each other; a gap is provided between the second and fourth microstrip lines, and they are arranged parallel to each other.

[0009] The metal sheet has the same shape as the dielectric layer and is disposed on the lower surface of the dielectric layer; two grooved metal SLSP structures are etched on the metal sheet, and the two grooved metal SLSP structures are arranged symmetrically; each grooved metal SLSP structure is coupled to the third microstrip line and the fourth microstrip line.

[0010] Preferably, each grooved metal SLSP structure includes a spiral arm composed of an Archimedean spiral; the center of each grooved metal SLSP structure is aligned in planar position with the center of the gap between the fourth microstrip line and the fourth microstrip line axis.

[0011] Preferably, the dielectric layer uses a Rogers 4350 series dielectric substrate; the dielectric substrate has a dielectric constant of 3.66, a loss tangent of 0.004, and a thickness of 0.762 mm.

[0012] Preferably, the input / output ports are used to connect to an SMA connector; the SMA connector is connected to a vector network analyzer.

[0013] Preferably, the first microstrip line has a length of 15 mm and a width of 2.79 mm.

[0014] Preferably, the lengths of the second, third, and fourth microstrip lines are 18.72 mm, 7.86 mm, and 5.5 mm, respectively.

[0015] Preferably, the widths of the second, third, and fourth microstrip lines are 1.64 mm, 1.64 mm, and 0.5 mm, respectively.

[0016] Preferably, each grooved metal SLSP structure is provided with a microfluidic chip for measuring the dielectric constant of the liquid; each microfluidic chip is provided with a microfluidic channel for storing the liquid; wherein, the microfluidic channel in one microfluidic chip is used for measurement, and the microfluidic channel in the other microfluidic chip is used as a reference.

[0017] Preferably, the active amplifier circuit includes a transistor ATF54143, resistors R1, R2, and R3, capacitors C1, C2, C3, and C4, and inductors L1, L2, L3, L4, L5, and L6; wherein the gate G of transistor ATF54143 is connected to one end of capacitor C3 and one end of inductor L3; the other end of capacitor C3 is connected to one end of inductor L5; the other end of inductor L3 is connected to one end of capacitor C1, one end of resistor R3, and one end of resistor R2; the other end of resistor R3 is connected to the other end of capacitor C1 and grounded; transistor ATF54143... The drain D of the capacitor is connected to one end of capacitor C4 and one end of inductor L4, respectively, and serves as the output of the amplifier circuit. The other end of capacitor C4 is connected to the other end of inductor L6. The other end of inductor L4 is connected to one end of capacitor C2 and one end of resistor R1. One end of inductor L1 is connected to the other end of inductor L5 and grounded, and the other end of inductor L1 is connected to the source S1 of transistor ATF54143. One end of inductor L2 is connected to the other end of capacitor C2 and grounded, and the other end of inductor L2 is connected to the source S2 of transistor ATF54143. The other end of resistor R1 is connected to the other end of resistor R2 and then connected to the positive terminal of the power supply. The other end of inductor L6 is grounded.

[0018] Compared with the prior art, the beneficial effects of this invention are: (1) Compared with the existing SLSP sensor, this invention significantly improves the sensitivity and quality factor of the sensor when performing dielectric characterization on samples of different concentrations, and can accurately detect the dielectric constant of the sample; (2) The sensor of this invention adopts a T-type microstrip line coupled deep subwavelength SLSP resonator, which effectively improves the coupling strength between the microstrip line and the SLSP resonator, so that the electric field is tightly bound to the edge of the slot ring of the SLSP; (3) This invention also adopts a differential structure design, which effectively eliminates the interference of surrounding environmental factors and avoids the error generated during measurement; (4) This invention also adds an active amplifier circuit to improve the quality factor of the sensor. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a differential active microwave microfluidic sensor in this invention;

[0020] Figure 2 This is a schematic diagram of one structure of the top layer of the differential active microwave microfluidic sensor in this invention;

[0021] Figure 3 This is a schematic diagram of the underlying structure of the differential active microwave microfluidic sensor in this invention;

[0022] Figure 4 This is a schematic diagram of one parameter of the first three resonant points S of the differential active microwave microfluidic sensor in this invention;

[0023] Figure 5 This is a schematic diagram of the electric field intensity distribution in this invention;

[0024] Figure 6 This is a schematic diagram of the structure of the PDMS and microfluidic channel in this invention;

[0025] Figure 7 for Figure 6 A corresponding top view;

[0026] Figure 8 This is a schematic diagram of a three-dimensional hierarchical layout of the differential active microwave microfluidic sensor in this invention;

[0027] Figure 9 This is a schematic diagram showing the relationship between the transmission coefficients of the two sensing units and the dielectric constants of the test liquids of different concentrations after the first and second sensing units are simultaneously placed with microfluidic chips in this invention.

[0028] Figure 10 This is a schematic diagram of an active amplifier circuit according to the present invention;

[0029] Figure 11 This is a data comparison diagram of the differential active microwave microfluidic sensor before and after amplification in this invention.

[0030] In the figure: 1. Dielectric layer; 2. SMA connector; 3. First microstrip line; 4. Second microstrip line; 5. Third microstrip line; 6. Fourth microstrip line; 7. Fifth microstrip line; 8. Metal sheet; 9. Grooved metal SLSP structure; 10. Microfluidic channel. Detailed Implementation

[0031] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0032] Example:

[0033] like Figures 1 to 3 As shown, the present invention provides a differential active microwave microfluidic sensor, including a passive resonator and an active amplifier circuit; the passive resonator is a two-port device, which includes a microstrip line structure, a dielectric layer 1, a metal sheet 8, and two grooved metal SLSP structures 9 from the top layer to the bottom layer;

[0034] The microstrip line is disposed on the upper surface of the dielectric layer; the microstrip line structure includes a first microstrip line 3, a second microstrip line 4, a third microstrip line 5, a fourth microstrip line 6, and a fifth microstrip line 7; wherein the first microstrip line is symmetrically arranged, the second and third microstrip lines are symmetrically arranged, the fourth and fifth microstrip lines are symmetrically arranged, and one end of the first microstrip line is connected to the midpoint of the second microstrip line, and the other end of the first microstrip line serves as an input / output port, which is used to connect to an SMA connector 2, and the first microstrip line is soldered to the SMA connector; the SMA connector is connected to a vector network analyzer; the fifth microstrip line has rounded corners, one end of the fifth microstrip line is connected to the second microstrip line, and the other end of the fifth microstrip line is connected to the third microstrip line; a gap is provided between the first and third microstrip lines, and they are arranged in parallel; a gap is provided between the second and fourth microstrip lines, and they are arranged in parallel.

[0035] The metal sheet has the same shape as the dielectric layer and is disposed on the lower surface of the dielectric layer; two grooved metal SLSP structures are etched on the metal sheet, and the two grooved metal SLSP structures are arranged symmetrically; each grooved metal SLSP structure is coupled to the third microstrip line and the fourth microstrip line.

[0036] Each grooved metal SLSP structure includes a spiral arm composed of an Archimedean spiral; the center of each grooved metal SLSP structure is aligned in planar position with the center of the gap between the fourth microstrip line and the fourth microstrip line axis.

[0037] The dielectric layer uses a Rogers 4350 series dielectric substrate; the dielectric substrate has a dielectric constant of 3.66, a loss tangent of 0.004, and a thickness of 0.762 mm.

[0038] like Figure 4 The diagram shown is a schematic diagram of the S-parameters of the sensor at the first three resonant points provided in an embodiment of the present invention.Figure 5 A schematic diagram of the electric field intensity distribution at the corresponding resonance points. The region with the strongest electric field at the first resonance point is more concentrated and has a stronger electric field distribution.

[0039] The sensor design of this invention was carried out in the three-dimensional electromagnetic simulation software Ansys HFSS environment, and the relevant dimensions were obtained through the software, as shown in the table below.

[0040] Table 1 Simulation Parameters of Differential Active Microwave Microfluidic Sensor

[0041] Parameter l m ]]> ​ [l2] [l3] w m ]]> w1 Value (mm) 15 18.72 7.86 5.5 2.79 1.64 Parameter w2 w3 s r Value (mm) 1.64 10 4 1

[0042] like Figure 6 The diagram shows the PDMS and microfluidic channel of this invention. The microfluidic channel 10 is composed of polydimethylsiloxane (PDMS) material. The PDMS is designed as a ring to bond with the SLSP sensor. When analytes with different dielectric constants flow into the microfluidic channel, the resonant frequency shifts. The relative shift of the frequency points characterizes the sensor's sensitivity. The PMDS thickness is 5 mm, and the channel width and thickness are 1 mm and 0.4 mm, respectively. Figure 7 As shown, the detailed parameter design of the microfluidic channel is as follows: R = 6.7 mm, r1 = 2 mm, r2 = 3.2 mm, d = 1 mm.

[0043] like Figure 8 The diagram shows a three-dimensional hierarchical layout of the present invention, in which a PDMS containing a microfluidic channel is placed on each sensing unit. The first microfluidic channel is used for measurement and can be injected with the liquid to be tested, while the second microfluidic channel is used as a reference and is not injected with the liquid to be tested.

[0044] like Figure 9 The diagram illustrates the relationship between the transmission coefficients of the first and second sensing units of this invention and the dielectric constants of the test liquids at different concentrations, after the microfluidic chip is simultaneously placed. It can be seen that as the dielectric constant of the test liquid increases from 1 to 80, the resonant frequency of the first sensing unit decreases from 0.73 GHz to 0.4 GHz, with a frequency shift of 330 MHz and a relative sensitivity of 0.57%, significantly improving sensitivity compared to existing SLSP sensors. The transmission coefficient of the second sensing unit does not change significantly. The relative change in the transmission coefficients of the two sensing units excludes interference from environmental factors.

[0045] Figure 10This is a schematic diagram of the active amplifier circuit of the present invention. The active amplifier circuit is composed of a transistor, resistors, capacitors, and inductors. The gate G of the transistor ATF54143 is connected to one end of capacitor C3 and one end of inductor L3; the other end of capacitor C3 is connected to one end of inductor L5; the other end of inductor L3 is connected to one end of capacitor C1, one end of resistor R3, and one end of resistor R2; the other end of resistor R3 is connected to the other end of capacitor C1 and grounded; the drain D of the transistor ATF54143 is connected to one end of capacitor C4 and one end of inductor L4 as the output of the amplifier circuit; the other end of capacitor C4 is connected to the other end of inductor L6; the other end of inductor L4... One end of inductor L1 is connected to one end of capacitor C2 and one end of resistor R1 respectively; one end of inductor L1 is connected to the other end of inductor L5 and grounded, and the other end of inductor L1 is connected to the source S1 of transistor ATF54143; one end of inductor L2 is connected to the other end of capacitor C2 and grounded, and the other end of inductor L2 is connected to the source S2 of transistor ATF54143; the other end of resistor R1 is connected to the other end of resistor R2 and then connected to the positive terminal of the power supply; the other end of inductor L6 is grounded; L1 = 0.45nH and L2 = 0.45nH are the conductances in series. The appropriate value of L2 can keep the resonator stable and prevent unnecessary oscillations.

[0046] The electromagnetic signal will enter the input terminal of the active amplifier circuit from the left end, be amplified, and then output from the right end. The preset values ​​of each lumped component in the bias circuit are: resistor R1 = 40Ω, R2 = 335Ω, R3 = 50Ω, input choke inductor L3 = 3.9nH, bypass capacitor C1 = 3.9pF, output choke inductor L4 = 22nH, bypass capacitor C2 = 10pF. The preset values ​​of each lumped component in the impedance matching section are: capacitor C3 = 7.1pF, capacitor C4 = 2.1pF, inductor L5 = 6.4nH, inductor L6 = 29.4nH.

[0047] Figure 11 Simulation results show that the addition of the active circuit greatly improves the quality factor Q at the resonant frequency of 0.746 GHz. In addition, different signal amplification effects can be achieved by adjusting the values ​​of the bias circuit capacitor and inductor to meet different needs.

[0048] This embodiment presents a differential active microwave microfluidic sensor based on an artificial local surface plasmon resonator. Compared with existing SLSP resonant sensors, it significantly improves the sensitivity and quality factor of the sensor when characterizing different liquid dielectric constants, and reduces the amount of liquid used by employing microfluidic channels.

[0049] Compared with existing SLSP sensors, this invention significantly improves the sensitivity and quality factor of the sensor when performing dielectric characterization on samples of different concentrations, and can accurately detect the dielectric constant of the sample. The sensor of this invention adopts a T-type microstrip line coupled to a deep subwavelength SLSP resonator, which effectively improves the coupling strength between the microstrip line and the SLSP resonator, so that the electric field is tightly bound to the edge of the SLSP slot ring. This invention also adopts a differential structure design, which effectively eliminates the interference of surrounding environmental factors and avoids errors during measurement. This invention also adds an active amplifier circuit to improve the quality factor of the sensor.

[0050] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A differential active microwave microfluidic sensor, characterized in that, It includes a passive resonator and an active amplifier circuit; the passive resonator is a two-port device, which includes a microstrip line structure, a dielectric layer, a metal sheet, and two grooved metal SLSP structures from the top to the bottom. The microstrip line is disposed on the upper surface of the dielectric layer; the microstrip line structure includes two first microstrip lines, two second microstrip lines, two third microstrip lines, two fourth microstrip lines, and two fifth microstrip lines; wherein, the two first microstrip lines are arranged symmetrically along an axis, the two second microstrip lines are arranged symmetrically along an axis, the two third microstrip lines are arranged symmetrically along an axis, the two fourth microstrip lines are arranged symmetrically along an axis, and the two fifth microstrip lines are arranged symmetrically along an axis; one end of the first microstrip line is connected to the midpoint of the second microstrip line on the same side, and the other end of the first microstrip line serves as an input / output port; the fifth microstrip line has rounded corners, one end of the fifth microstrip line is connected to the second microstrip line on the same side, and the other end of the fifth microstrip line is connected to the third microstrip line on the same side; a gap is provided between the first microstrip line and the third microstrip line, and they are arranged parallel to each other; a gap is provided between the second microstrip line and the fourth microstrip line, and they are arranged parallel to each other; The metal sheet has the same shape as the dielectric layer and is disposed on the lower surface of the dielectric layer; two grooved metal SLSP structures are etched on the metal sheet, and the two grooved metal SLSP structures are arranged symmetrically; each grooved metal SLSP structure is coupled to the third microstrip line and the fourth microstrip line; Each grooved metal SLSP structure includes a spiral arm composed of an Archimedean spiral; the center of each grooved metal SLSP structure is aligned in planar position with the center of the gap between the fourth microstrip line and the fourth microstrip line axis.

2. The differential active microwave microfluidic sensor according to claim 1, characterized in that, The dielectric layer is made of a dielectric substrate; the dielectric substrate has a dielectric constant of 3.66, a loss tangent of 0.004, and a thickness of 0.762 mm.

3. The differential active microwave microfluidic sensor according to any one of claims 1-2, characterized in that, The input / output ports are used to connect to the SMA connector; the SMA connector is connected to the vector network analyzer.

4. The differential active microwave microfluidic sensor according to claim 3, characterized in that, The first microstrip line is 15mm long and 2.79mm wide.

5. The differential active microwave microfluidic sensor according to claim 1, characterized in that, The lengths of the second, third, and fourth microstrip lines are 18.72 mm, 7.86 mm, and 5.5 mm, respectively.

6. The differential active microwave microfluidic sensor according to claim 5, characterized in that, The widths of the second, third, and fourth microstrip lines are 1.64 mm, 1.64 mm, and 0.5 mm, respectively.

7. The differential active microwave microfluidic sensor according to claim 1, characterized in that, Each grooved metal SLSP structure has a microfluidic chip above it for measuring the dielectric constant of the liquid; each microfluidic chip has a microfluidic channel for storing the liquid; wherein, the microfluidic channel in one microfluidic chip is used for measurement, and the microfluidic channel in the other microfluidic chip is used as a reference.

8. The differential active microwave microfluidic sensor according to claim 1, characterized in that, The active amplifier circuit includes a transistor ATF54143, resistors R1, R2, and R3, capacitors C1, C2, C3, and C4, and inductors L1, L2, L3, L4, L5, and L6. The gate G of transistor ATF54143 is connected to one end of capacitor C3 and one end of inductor L3. The other end of capacitor C3 is connected to one end of inductor L5. The other end of inductor L3 is connected to one end of capacitor C1, one end of resistor R3, and one end of resistor R2. The other end of resistor R3 is connected to the other end of capacitor C1 and grounded. The drain of transistor ATF54143... D is connected to one end of capacitor C4 and one end of inductor L4 respectively, serving as the output of the amplifier circuit; the other end of capacitor C4 is connected to the other end of inductor L6; the other end of inductor L4 is connected to one end of capacitor C2 and one end of resistor R1 respectively; one end of inductor L1 is connected to the other end of inductor L5 and grounded, and the other end of inductor L1 is connected to the source S1 of transistor ATF54143; one end of inductor L2 is connected to the other end of capacitor C2 and grounded, and the other end of inductor L2 is connected to the source S2 of transistor ATF54143; the other end of resistor R1 is connected to the other end of resistor R2 and then connected to the positive terminal of the power supply; the other end of inductor L6 is grounded.

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