Application of active dual-mode microwave microfluidic sensor in liquid dielectric constant detection

Abstract

The application discloses application of an active double-mode microwave micro-flow sensor to liquid dielectric constant detection. The double-mode resonant unit is formed by a microstrip line and a split ring resonator, and has high and low resonant frequency points. The low-frequency resonant frequency point moves to a low frequency with the increase of the dielectric constant, and the high-frequency frequency point moves to a high frequency with the increase of the dielectric constant, thereby effectively increasing the sensitivity of the passive resonant unit. A negative impedance circuit is embedded at the rear end of the microwave passive sensor to form an oscillator, namely a microwave passive resonator and a radio frequency amplifier, and the oscillation frequency changes with the change of the dielectric constant of the material to be detected, and the change of the dielectric constant is mapped to the change of the oscillation frequency. The relationship between the dielectric constant and the resonant frequency is converted to the relationship between the dielectric constant and the direct current voltage through a demodulation circuit. The application has the advantages of high sensitivity, low price, convenience for carrying, etc., and is a high-performance and low-cost system-level detection device which will play an important role in the detection field of liquid materials.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology and relates to the application of active dual-mode microwave microfluidic sensors in the detection of liquid dielectric constant. In particular, it relates to a miniaturized active microwave sensor based on injection-locked oscillation technology for measuring the dielectric constant of liquids of different concentrations. Background Technology

[0002] Water quality has always been a major concern in people's lives and work, as it is fundamental to our well-being. In the industry, many technologies for water quality testing have emerged, such as photochemical analysis, electrochemical analysis, and chromatographic analysis. These technologies primarily focus on physicochemical monitoring, utilizing various chemical analysis methods and related instruments to monitor water quality. However, the aforementioned testing methods suffer from low accuracy. Therefore, improving testing accuracy has become a common focus for both academia and industry.

[0003] Currently, scholars worldwide have proposed numerous techniques for detecting the dielectric constant of liquids, primarily including those based on passive and active microwave devices. Microwave-based detection methods are increasingly favored due to their ease of measurement, portability, small size, light weight, and high sensitivity. In passive microwave-based detection, the main focus is on improving the resonant unit to confine more electric fields, thereby indirectly increasing detection sensitivity. Currently proposed resonant units mainly include split-ring resonators (SRR), complementary split-ring resonators (CSRR), electric-LC (ELC), magnetic-LC (MLC), spoofsurface plasmon polaritons (SSPP), and improved structures based on these resonant units. The split-ring resonator is based on the principle that the electric field can be effectively concentrated at the opening of the split ring, so this location is considered the induction region. The complementary split-ring resonator detects the dielectric constant of a liquid based on the principle that the electric field can be maximally confined at the gap. Electric LC and magnetic LC are also complementary, but under microstrip line excitation, this structure produces two resonance modes. Artificial surface plasmon resonances (ASPRIs) are a novel type of resonant unit structure. The resonant units constructed from ASPRs exhibit metamaterial properties, namely the slow-wave effect. Because ASPR-constructed resonant unit structures have higher relative permittivity and permeability values ​​compared to traditional resonant structures, it can be deduced that the electromagnetic wave propagation speed in this structure is slower. Furthermore, ASPRs are periodic structures, which can also achieve a good electric field concentration effect, making them convenient for dielectric constant detection. In the detection based on active microwave devices, scholars both domestically and internationally have proposed many innovative technical solutions, mainly including microwave sensors based on phase-locked loop (PLL) technology and oscillation sensor technology based on feedback loops. Microwave sensor designs based on phase-locked loop (PLL) technology are relatively complex and require the development of related software programs. Oscillation sensing technology based on feedback loops requires the design of a feedback network as a self-injected signal to excite a normal oscillation frequency.

[0004] The aforementioned microwave sensors based on passive resonant units require expensive vector network analyzers, which is not conducive to portable detection. Microwave sensors based on active devices can eliminate the dependence on expensive vector network analyzers and are easier to manufacture into portable instruments for easy portability. This invention utilizes the dual-mode nature of passive microstrip sensors and, based on an active reflective oscillator using injection-locked oscillation technology, further embeds a demodulation circuit to transform the relationship between dielectric constant and resonant frequency into a relationship between dielectric constant and voltage, thereby achieving the purpose of detecting the dielectric constant of liquids. The sensor proposed in this invention mainly consists of key components such as a passive microwave resonant unit, a reflective oscillator, a power divider, a low-noise amplifier, a mixer, a delay line, and an analog low-pass filter, which is a major innovative highlight of this invention. Among these, the passive microwave resonator adopts a combination of a microstrip line and a split-ring resonator, that is, part of the microstrip line structure coincides with one side of the split-ring resonator, thus generating two resonant modes: Mode 1 and Mode 2. The opening gap of the resonant ring can be used as the sensing area; to improve detection sensitivity, an interdigital capacitor structure is embedded in the opening. When the liquid to be tested is placed in the sensing area, the resonant frequency of mode 1 shifts to a lower frequency, and the resonant frequency of mode 2 shifts to a higher frequency, so the detection sensitivity will be further improved. This is the second innovation of the present invention. When the liquid to be tested is placed in the sensing area, the resonant frequency of the oscillator will change accordingly. After the demodulation circuit, the relationship between the dielectric constant and the resonant frequency will be transformed into the numerical relationship between the dielectric constant and the voltage. This is the third innovation of the present invention. Summary of the Invention

[0005] The main objective of this invention is to address the shortcomings of existing technologies by proposing an active dual-mode microwave microfluidic sensor based on injection-locked oscillation technology. This sensor can improve detection accuracy by utilizing the dual-mode of a novel resonant unit, and it can also convert the relationship between dielectric constant and resonant frequency into a numerical relationship between dielectric constant and voltage based on the principle of demodulation circuitry, thereby obtaining the dielectric constant value of the liquid to be detected. Furthermore, it eliminates the dependence on expensive vector network analyzers and is easy to carry.

[0006] This invention is implemented according to the following technical solution:

[0007] The application of a dual-mode microwave microfluidic sensor in the detection of liquid dielectric constant: The dual-mode microwave microfluidic sensor includes a cascaded 50-ohm load (1), a microwave passive resonant unit (2), an RF amplifier (3), a power divider (4), two parallel branches, a downconverter (8), a low-pass filter (9), a baseband amplifier (10), and an oscilloscope (11); The two parallel branches include an upper branch and a lower branch, wherein the upper branch includes a cascaded first RF amplifier (5) and a delay line (7), and the lower branch includes a second RF amplifier (6); The microwave passive resonant unit (2) and the RF amplifier (3) constitute a reflective oscillator.

[0008] The microwave passive resonant unit (2) includes a top layer (12), a middle layer (24), and a bottom layer (25);

[0009] The top layer (12) includes an input port (13), an output port (14), an excitation microstrip line, a resonant unit, and an interdigital capacitor (22); the excitation microstrip line includes a first part (15), a second part (16), and a third part (17); the resonant unit includes a vertical first part (18), a vertical second part (19), a horizontal first part (20), and a horizontal second part (21); the input port (13) is connected to one end of the first part (15) of the excitation microstrip line, the other end of the first part (15) of the excitation microstrip line is connected to one end of the second part (16) of the excitation microstrip line and one end of the vertical first part (18) of the resonant unit, and the other end of the second part (16) of the excitation microstrip line is connected to one end of the third part (17) of the excitation microstrip line and one end of the vertical first part (18) of the resonant unit. One end of the second part (19) is connected, and the other end of the third part of the excitation microstrip line is connected to the output port (14). The other end of the vertical first part (18) of the resonant unit is connected to one end of the horizontal first part (20) of the resonant unit. The other end of the vertical second part (19) of the resonant unit is connected to one end of the horizontal second part (21) of the resonant unit. The other end of the horizontal first part (20) of the resonant unit and the other end of the horizontal second part (21) of the resonant unit form an interdigital capacitor (22). The electric field is mainly concentrated in the gap of the interdigital capacitor (22) as the sensing area. A polydimethylsiloxane PDMS (26) is placed directly above the sensing area. The PDMS (26) structure has microfluidic channels with the same structure as the interdigital capacitor (22) and the same gap size, which are used to hold the liquid to be detected (27).

[0010] The intermediate layer (24) is a dielectric substrate;

[0011] The bottom layer (25) is a metal layer;

[0012] The specific methods for detecting the dielectric constant of liquids include:

[0013] Step S1: Calculate the expression for the DC voltage of the oscilloscope under no-load conditions:

[0014] S1-1: When the microwave passive resonant unit (2) is in an unloaded state, the reflective oscillator oscillates out an unloaded oscillation frequency f0 and obtains an oscillation signal x0 with the simplified mathematical formula A·cos(2πf0t), where A is the initial amplitude and t is time;

[0015] S1-2: When the above oscillation signal x0 passes through the power divider (4), it is divided into two paths. The simplified mathematical formula is as follows: Signal x1;

[0016] S1-3: The two signals x1 pass through the first RF amplifier (5) and the second RF amplifier (6) respectively, and obtain the simplified mathematical formulas as follows: The RF signals x2 and x3, where B is the gain of the RF amplifier; when the upper branch RF signal x3 passes through the delay line (7), the simplified mathematical formula is: RF signal x4;

[0017] S1-4: When the RF signals x2 and x4 of the upper and lower branches simultaneously enter the downconverter (8), the simplified mathematical formula is obtained as follows: RF signal x5;

[0018] S1-5: The radio frequency signal x5 enters the low-pass filter (9), and the simplified mathematical formula is obtained as follows: DC signal x6;

[0019] S1-6: The DC signal x6 enters the baseband amplifier (10), and the simplified mathematical formula is: The DC signal x7, where C is the amplification factor of the baseband amplifier (10);

[0020] S1-7: The DC signal x7 is detected by the oscilloscope, and the DC voltage value is displayed.

[0021] S2. Creating a standard curve:

[0022] S2-1: When detection liquids with different dielectric constants are placed into the microfluidic channel (23), the resonant frequency of the reflective oscillator will change, denoted as f. i At this time, the expression for DC voltage is:

[0023] S2-2: By comparing the DC voltage displayed on the oscilloscope under no-load and detection conditions, a standard curve of the mathematical relationship between dielectric constant and DC voltage is obtained through fitting.

[0024] S3. Dielectric constant detection of the liquid to be tested:

[0025] When the liquid to be tested is placed into the microfluidic channel (23), the oscilloscope displays the corresponding DC voltage value. Substituting this value into the standard curve above, the dielectric constant of the liquid to be tested is finally calculated.

[0026] Preferably, the overall microwave sensor has dimensions of Lx = 25 mm and Ly = 40 mm.

[0027] Preferably, the width of the first part (15) of the excitation microstrip line is W0 = 1.67 mm, and the length of the first part (15) of the excitation microstrip line is L0 = 13 mm;

[0028] Preferably, the width of the second part (16) of the excitation microstrip line is W0 = 1.67 mm, and the length of the second part (16) of the excitation microstrip line is L0 = 10 mm;

[0029] Preferably, the width of the third part (17) of the excitation microstrip line is W0 = 1.67 mm, and the length of the third part (17) of the excitation microstrip line is L0 = 13 mm;

[0030] Preferably, the width of the vertical first part (18) of the resonant unit is W1 = 2mm, and the length of the vertical first part (18) of the resonant unit is L1 = 10mm;

[0031] Preferably, the width of the vertical second part (19) of the resonant unit is W1 = 2 mm, and the length of the vertical second part (19) of the resonant unit is L1 = 10 mm;

[0032] Preferably, the width of the first transverse portion (20) of the resonant unit is W2 = 2.5 mm, and the length of the first transverse portion (20) of the resonant unit is L2 = 5.8 mm;

[0033] Preferably, the width of the second transverse part (21) of the resonant unit is W2 = 2.5 mm, and the length of the second transverse part (21) of the resonant unit is L2 = 5.8 mm;

[0034] Preferably, the overall width of the interdigital capacitor structure (22) is W3 = 2.4 mm, the overall length of the interdigital capacitor structure (22) is L3 = 3.85 mm, and the gap width of the interdigital capacitor is 0.2 mm;

[0035] Preferably, the length, width and height of the PDMS(26) structure are 6.83 mm, 4.4 mm and 5 mm, respectively;

[0036] Preferably, the width of the microfluidic channel in the PDMS(26) structure is 0.2 mm.

[0037] The beneficial effects of this invention are as follows:

[0038] 1. This invention employs a novel microwave passive resonant unit composed of a microstrip line and a resonant unit (i.e., a split-ring resonator), which can generate two resonant modes. Furthermore, the resonant frequency at the low frequency shifts towards lower frequencies as the dielectric constant increases, while the resonant frequency at the high frequency shifts towards higher frequencies as the dielectric constant increases. This novel resonant structure can effectively improve detection sensitivity.

[0039] 2. The interdigitated structure embedded in the microwave passive resonant unit of this invention can effectively improve the detection sensitivity.

[0040] 3. The liquid dielectric constant detection system of the present invention transforms the relationship between dielectric constant and resonant frequency into the relationship between dielectric constant and DC voltage through demodulation circuit, thereby eliminating the dependence on expensive vector network analyzers and reducing detection costs.

[0041] 4. The microwave sensor of the present invention has the advantages of low cost, portability, and easy operation.

[0042] 5. The microwave sensor of this invention can be upgraded with hardware circuitry to access 5G networks for real-time, remote monitoring. Attached Figure Description

[0043] Figure 1 (a) is a schematic diagram of the system-level detection of the proposed microwave sensor;

[0044] Figure 1 (b) is a schematic diagram of the top layer of the passive resonant unit of the proposed microwave sensor;

[0045] Figure 1 (c) is a three-dimensional view of the passive resonant unit of the proposed microwave sensor;

[0046] Figure 2 (a) shows the electric field simulation results of the proposed microwave sensor in mode 1;

[0047] Figure 2 (b) shows the electric field simulation results of the proposed microwave sensor in mode 2;

[0048] Figure 3 The curves show the transmission coefficients for the two modes under different medium constants. Detailed Implementation

[0049] To more clearly illustrate the problems solved by the present invention, the technical solutions adopted, and the beneficial effects, the specific embodiments of the present invention are described below in conjunction with the figures. The preferred embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. All modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be within the protection scope of the present invention.

[0050] A microwave microfluidic sensor based on injection-locked oscillation technology and dual-mode characteristics is a system-level detection device.

[0051] like Figure 1 As shown in (a), the system-level testing equipment mainly includes a 50-ohm load 1, a microwave passive resonant unit 2, an RF amplifier 3, a power divider 4, an RF amplifier 5, an RF amplifier 6, a delay line 7, a downconverter 8, a low-pass filter 9, a baseband amplifier 10, and an oscilloscope 11. Among them, the microwave passive resonant unit 2 consists of the top layer 12, the middle layer 24, and the bottom layer 25.

[0052] like Figure 1 As shown in (a), the working principle of this system-level detection device can be described as follows: When the microwave passive resonant unit 2 is in an unloaded state, the reflective oscillator, composed of 2 and 3, oscillates at a certain resonant frequency. This oscillation signal can be simplified as A·cos(2πf0t), where A is the initial amplitude, f0 is the unloaded oscillation frequency, and t is time. When the oscillation signal passes through the power divider 4, it is split into two signals, which can be written as: After passing through radio frequency amplifiers 5 and 6 respectively, the signal can be written as In the formula, B is the gain of the RF amplifier; when the upper branch signal passes through delay line 7, the signal can be written as When the RF signals from the upper and lower branches enter the downconverter respectively, the signal at the output port of the downconverter can be written as: The signal then enters the low-pass filter, and the output signal can be written as follows: The signal then enters the baseband amplifier, and the output signal can be expressed as follows: C represents the amplification factor of the baseband amplifier; the final output DC signal can be detected by an oscilloscope and can be represented as... When the liquid being tested is placed into the microfluidic channel 23, the resonant frequency emitted by the oscillator will change, denoted as f. i Similarly, the DC signal displayed on the oscilloscope can be written as: By comparing the DC voltage expression of the oscilloscope under no-load conditions, it can be seen that the DC voltage displayed on the oscilloscope changes after the liquid to be tested is placed in the oscilloscope. By summarizing the relationship between the dielectric constant of the liquid to be tested and the DC voltage, a mathematical expression for the dielectric constant and DC voltage can be obtained.

[0053] like Figure 1As shown in (b), the microwave passive resonant unit 2 mainly includes an input port 13, an output port 14, a first part 15 of an excitation microstrip line, a second part 16 of an excitation microstrip line, a third part 17 of an excitation microstrip line, a vertical first part 18 of a resonant unit, a vertical second part 19 of a resonant unit, a horizontal first part 20 of a resonant unit, a horizontal second part 21 of a resonant unit, and an interdigital capacitor 22. The electric field is mainly concentrated at the gap of the interdigital capacitor 22, which can serve as the sensing area. The PDMS 26 structure has microfluidic channels etched inside, the same size as the gap of the interdigital capacitor, to hold the liquid 27 to be detected, and the PDMS 26 is placed directly above the interdigital capacitor 22. In the top-level 12 structure, the input port 13 is first connected to the first part 15 of the excitation microstrip line, the first part 15 of the excitation microstrip line is connected to the second part 16 of the excitation microstrip line, the second part 16 of the excitation microstrip line is connected to the third part 17 of the excitation microstrip line, the third part of the excitation microstrip line is connected to the output port 14, the first part 15 of the excitation microstrip line is connected to the vertical first part 18 of the resonant unit, the vertical first part 18 of the resonant unit is connected to the horizontal first part 20 of the resonant unit, the vertical second part 19 of the resonant unit is connected to the horizontal second part 21 of the resonant unit, and the intersection of the horizontal first part 20 and the horizontal second part 21 of the resonant unit forms an interdigital capacitor 22.

[0054] like Figure 1 As shown in (c), the intermediate layer 24 is a dielectric substrate;

[0055] like Figure 1 As shown in (c), the bottom layer 25 is a metal layer;

[0056] The overall dimensions of the microwave sensor are Lx = 25mm and Ly = 40mm.

[0057] The width of the first part 15 of the excitation microstrip line is W0 = 1.67 mm, and the length of the first part 15 of the excitation microstrip line is L0 = 13 mm.

[0058] The width of the second part 16 of the excitation microstrip line is W0 = 1.67 mm, and the length of the second part 16 of the excitation microstrip line is L0 = 10 mm.

[0059] The width of the third part 17 of the excitation microstrip line is W0 = 1.67 mm, and the length of the third part 17 of the excitation microstrip line is L0 = 13 mm;

[0060] The width of the vertical first part 18 of the resonant unit is W1 = 2mm, and the length of the vertical first part 18 of the resonant unit is L1 = 10mm;

[0061] The width of the vertical second part 19 of the resonant unit is W1 = 2mm, and the length of the vertical second part 19 of the resonant unit is L1 = 10mm;

[0062] The width of the first transverse part 20 of the resonant unit is W2 = 2.5mm, and the length of the first transverse part 20 of the resonant unit is L2 = 5.8mm;

[0063] The width of the second transverse part 21 of the resonant unit is W2 = 2.5mm, and the length of the second transverse part 21 of the resonant unit is L2 = 5.8mm;

[0064] The overall width of the interdigital capacitor structure 22 is W3 = 2.4 mm, the overall length of the interdigital capacitor structure 22 is L3 = 3.85 mm, and the gap width of the interdigital capacitor is 0.2 mm.

[0065] The length, width, and height of the PDMS26 structure are 6.83 mm, 4.4 mm, and 5 mm, respectively.

[0066] The width of the microfluidic channel in the PDMS26 structure is 0.2 mm;

[0067] A 50-ohm load 1 is connected to terminal 2 of the microwave passive resonant unit;

[0068] This system-level testing equipment contains three radio frequency amplifiers, numbered 3, 5, and 6.

[0069] This system-level testing equipment includes one power divider.

[0070] This system-level testing equipment includes one delay line 7;

[0071] This system-level testing equipment includes one down-converter.

[0072] This system-level detection device includes one low-pass filter.

[0073] This system-level testing equipment includes one baseband amplifier 10;

[0074] This system-level testing equipment includes one oscilloscope 11;

[0075] This invention presents a novel microwave passive resonant unit achieved by modifying the excitation microstrip line and the split-ring resonator. This resonant unit possesses two resonant modes: the low-frequency resonant frequency shifts towards lower frequencies with increasing dielectric constant, and the high-frequency resonant frequency shifts towards higher frequencies with increasing dielectric constant, thereby improving detection sensitivity. By embedding an oscillator, the change in dielectric constant is displayed using the oscillation frequency of an active oscillator. Subsequently, a demodulation circuit is added to convert the relationship between dielectric constant and resonant frequency into a relationship between dielectric constant and DC voltage. This effectively reduces detection costs and offers the advantage of portability.

[0076] This system-level testing equipment mainly includes a 50-ohm load 1, a microwave passive resonant unit 2, an RF amplifier 3, a power divider 4, an RF amplifier 5, an RF amplifier 6, a delay line 7, a downconverter 8, a low-pass filter 9, a baseband amplifier 10, and an oscilloscope 11. The microwave passive resonant unit 2 comprises the top layer 12, the middle layer 24, and the bottom layer 25. The working principle of this system-level testing equipment can be described as follows: When the microwave passive resonant unit 2 is in an unloaded state, the reflective oscillator, composed of 2 and 3, oscillates to produce a certain resonant frequency. This oscillation signal can be simplified as A·cos(2πf0t), where A is the initial amplitude, f0 is the unloaded oscillation frequency, and t is time. When the oscillation signal passes through the power divider 4, it is split into two signals, which can be written as... After passing through radio frequency amplifiers 5 and 6 respectively, the signal can be written as In the formula, B is the gain of the RF amplifier; when the upper branch signal passes through delay line 7, the signal can be written as When the RF signals from the upper and lower branches enter the downconverter respectively, the signal at the output port of the downconverter can be written as: The signal then enters the low-pass filter, and the output signal can be written as follows: The signal then enters the baseband amplifier, and the output signal can be expressed as follows: C represents the amplification factor of the baseband amplifier; the final output DC signal can be detected by an oscilloscope and can be represented as... When the liquid being tested is placed into the microfluidic channel 23, the resonant frequency emitted by the oscillator will change, denoted as f. i Similarly, the DC signal displayed on the oscilloscope can be written as: By comparing the DC voltage expression of the oscilloscope under no-load conditions, it can be seen that the DC voltage displayed on the oscilloscope changes after the liquid to be tested is placed in the oscilloscope. By summarizing the relationship between the dielectric constant of the liquid to be tested and the DC voltage, a mathematical expression for the dielectric constant and DC voltage can be obtained. A novel microwave passive resonant unit formed by a microstrip line and a split-ring resonator generates two resonant modes. Furthermore, by adding a meandering groove structure, the capacitance of the interdigital capacitor is increased, thereby improving the sensitivity of the microwave passive resonance. By embedding an active oscillator circuit, the change in dielectric constant is expressed as a change in resonant frequency. Subsequently, by adding a demodulation circuit, the relationship between dielectric constant and resonant frequency is transformed into a relationship between dielectric constant and DC voltage. This eliminates the reliance on expensive vector network analysis, reduces manufacturing costs, and results in a smaller, more portable design.

[0077] The microwave microfluidic sensor of this invention has been optimized in commercial electromagnetic simulation software, and the specific values ​​are shown below.

[0078] The overall dimensions of the microwave sensor are Lx = 25mm and Ly = 40mm.

[0079] The width of the first part 15 of the excitation microstrip line is W0 = 1.67 mm, and the length of the first part 15 of the excitation microstrip line is L0 = 13 mm.

[0080] The width of the second part 16 of the excitation microstrip line is W0 = 1.67 mm, and the length of the second part 16 of the excitation microstrip line is L0 = 10 mm.

[0081] The width of the third part 17 of the excitation microstrip line is W0 = 1.67 mm, and the length of the third part 17 of the excitation microstrip line is L0 = 13 mm;

[0082] The width of the vertical first part 18 of the resonant unit is W1 = 2mm, and the length of the third part 18 of the excitation microstrip line is L1 = 10mm.

[0083] The width of the vertical second part 19 of the resonant unit is W1 = 2mm, and the length of the second part 19 of the excitation microstrip line is L1 = 10mm;

[0084] The width of the first transverse part 20 of the resonant unit is W2 = 2.5 mm, and the length of the second part 20 of the excitation microstrip line is L2 = 5.8 mm.

[0085] The width of the second transverse part 21 of the resonant unit is W2 = 2.5 mm, and the length of the second part 21 of the excitation microstrip line is L2 = 5.8 mm.

[0086] The overall width of the interdigital capacitor structure 22 is W3 = 2.4 mm, and the overall length of the interdigital capacitor structure 22 is L3 = 3.85 mm;

[0087] The length, width, and height of the PDMS26 structure are 6.83 mm, 4.4 mm, and 5 mm, respectively.

[0088] The width of the microfluidic channel in the PDMS26 structure is 0.2 mm;

[0089] This microwave microfluidic sensor is a system-level detection device, comprising a microwave passive resonant unit and an radio frequency active circuit. The microwave passive resonant unit generates two resonant modes, with the electric fields of both modes concentrated at the interdigital capacitance. Furthermore, as the dielectric constant of the covering material increases, the two resonant frequencies shift to the left and right, effectively improving detection sensitivity. The embedded oscillator transforms changes in dielectric constant into changes in the corresponding oscillation frequency. The subsequent addition of the radio frequency active circuit transforms this detection method into a system-level detection scheme, converting the relationship between dielectric constant and resonant frequency into a relationship between dielectric constant and DC voltage. This reduces reliance on vector network analyzers, lowers design and manufacturing costs, and offers advantages such as small size and portability, meeting the needs of specialized applications. The microwave microfluidic sensor proposed in this invention possesses high sensitivity and convenient detection capabilities, and will play an important role in the field of materials testing.

[0090] The above embodiments are not intended to limit the present invention, and the present invention is not limited to the above embodiments. Any embodiment that meets the requirements of the present invention is within the protection scope of the present invention.

Claims

1. The application of an active dual-mode microwave microfluidic sensor in the detection of liquid dielectric constant, characterized in that... The dual-mode microwave microfluidic sensor includes a cascaded 50-ohm load (1), a microwave passive resonant unit (2), a radio frequency amplifier (3), a power divider (4), two parallel branches, a downconverter (8), a low-pass filter (9), a baseband amplifier (10), and an oscilloscope (11); the two parallel branches include an upper branch and a lower branch, wherein the upper branch includes a cascaded first radio frequency amplifier (5) and a delay line (7), and the lower branch includes a second radio frequency amplifier (6); the microwave passive resonant unit (2) and the radio frequency amplifier (3) constitute a reflective oscillator; The microwave passive resonant unit (2) includes a top layer (12), a middle layer (24), and a bottom layer (25); The top layer (12) includes an input port (13), an output port (14), an excitation microstrip line, a resonant unit, and an interdigital capacitor (22); the excitation microstrip line includes a first part (15), a second part (16), and a third part (17); the resonant unit includes a vertical first part (18), a vertical second part (19), a horizontal first part (20), and a horizontal second part (21); the input port (13) is connected to one end of the first part (15) of the excitation microstrip line, and the other end of the first part (15) of the excitation microstrip line is connected to the second part (16) of the excitation microstrip line. One end of the resonant unit is connected to one end of the vertical first part (18), the other end of the excitation microstrip line second part (16) is connected to one end of the excitation microstrip line third part (17) and one end of the resonant unit vertical second part (19), the other end of the excitation microstrip line third part is connected to the output port (14), the other end of the resonant unit vertical first part (18) is connected to one end of the resonant unit horizontal first part (20), the other end of the resonant unit vertical second part (19) is connected to one end of the resonant unit horizontal second part (21), the other end of the resonant unit horizontal first part (20) and the other end of the resonant unit horizontal second part (21) form an interdigital capacitor (22); The electric field is mainly concentrated in the gap of the interdigital capacitor (22), which serves as the sensing area; a PDMS (26) is placed directly above the sensing area; the PDMS (26) has microfluidic channels etched inside its structure, which are the same as the structure of the interdigital capacitor (22) and have the same gap size, and are used to hold the liquid to be detected (27). The intermediate layer (24) is a dielectric substrate; The bottom layer (25) is a metal layer; The application method specifically includes the following steps: Step S1: Calculate the expression for the DC voltage of the oscilloscope under no-load conditions: S1-1: When the microwave passive resonant unit (2) is in an unloaded state, the reflective oscillator oscillates out an unloaded oscillation frequency f0 and obtains an oscillation signal x0 with the simplified mathematical formula A·cos(2πf0t), where A is the initial amplitude and t is time; S1-2: When the above oscillation signal x0 passes through the power divider (4), it is divided into two paths. The simplified mathematical formula is as follows: Signal x1; S1-3: The two signals x1 pass through the first RF amplifier (5) and the second RF amplifier (6) respectively, and obtain the simplified mathematical formulas as follows: The RF signals x2 and x3, where B is the gain of the first RF amplifier (5) and the second RF amplifier (6); when the upper branch RF signal x3 passes through the delay line (7), the simplified mathematical formula is: RF signal x4; S1-4: When the RF signals x2 and x4 of the upper and lower branches simultaneously enter the downconverter (8), the simplified mathematical formula is obtained as follows: RF signal x5; S1-5: The radio frequency signal x5 enters the low-pass filter (9), and the simplified mathematical formula is obtained as follows: DC signal x6; S1-6: The DC signal x6 enters the baseband amplifier (10), and the simplified mathematical formula is: The DC signal x7, where C is the amplification factor of the baseband amplifier (10); S1-7: The DC signal x7 is detected by the oscilloscope, and the DC voltage value is displayed; S2. Creating a standard curve: S2-1: When detection liquids with different dielectric constants are placed into the microfluidic channel (23), the resonant frequency of the reflective oscillator will change, denoted as f. i At this time, the expression for DC voltage is: S2-2: By comparing the DC voltage displayed on the oscilloscope under no-load and detection conditions, a standard curve of the mathematical relationship between dielectric constant and DC voltage is obtained through fitting. S3. Dielectric constant detection of the liquid to be tested: When the liquid to be tested is placed into the microfluidic channel (23), the oscilloscope displays the corresponding DC voltage value. Substituting this value into the standard curve above, the dielectric constant of the liquid to be tested is finally calculated.

2. The application according to claim 1, characterized in that... The width of the first part (15) of the excitation microstrip line is W0 = 1.67 mm, and the length of the first part (15) of the excitation microstrip line is L0 = 13 mm; the width of the second part (16) of the excitation microstrip line is W0 = 1.67 mm, and the length of the second part (16) of the excitation microstrip line is L0 = 10 mm; the width of the third part (17) of the excitation microstrip line is W0 = 1.67 mm, and the length of the third part (17) of the excitation microstrip line is L0 = 13 mm.

3. The application according to claim 2, characterized in that... The width of the vertical first part (18) of the resonant unit is W1 = 2mm, and the length of the vertical first part (18) of the resonant unit is L1 = 10mm; the width of the vertical second part (19) of the resonant unit is W1 = 2mm, and the length of the vertical second part (19) of the resonant unit is L1 = 10mm; The width of the first transverse part (20) of the resonant unit is W2 = 2.5 mm, and the length of the first transverse part (20) of the resonant unit is L2 = 5.8 mm; the width of the second transverse part (21) of the resonant unit is W2 = 2.5 mm, and the length of the second transverse part (21) of the resonant unit is L2 = 5.8 mm.

4. The application according to claim 3, characterized in that... The overall width of the interdigital capacitor (22) is W3 = 2.4 mm, the overall length of the interdigital capacitor (22) is L3 = 3.85 mm, and the gap width of the interdigital capacitor is 0.2 mm.

5. The application according to claim 4, characterized in that... The width of the microfluidic channel in the PDMS(26) structure is 0.2 mm.

6. The application according to claim 1, characterized in that... The length, width and height of the PDMS(26) structure are 6.83 mm, 4.4 mm and 5 mm, respectively.

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