Microstrip microwave sensor system based on embedded interdigital structure and applications thereof

Abstract

The application discloses a microstrip microwave sensor system based on embedded interdigital structure and application thereof. The application forms a common main channel gap by extending the second microstrip line to pass through the upper and lower parts of the interdigital structure, and the electric field is mainly bound to the main channel gap area; the interdigital structure can generate two odd mode resonance modes through the electromagnetic mutual coupling effect between the sub-gap and the main channel gap; the odd mode 1 resonance mode is used to realize the detection of the dielectric constant of micro-flow liquid. By adding active radio frequency circuit devices and analog low frequency devices, a detection system is formed, which can convert the change relation between the dielectric constant and the resonance frequency into the relation between the dielectric constant and the direct current voltage, and further summarize the related mathematical model, so as to achieve the purpose of predicting the dielectric constant of unknown concentration liquid. The detection system has the advantages of low manufacturing cost, convenient carrying, high sensitivity and the like, and will play an important role in the field of liquid material detection.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of microwave technology, and relates to a microstrip microwave sensor system based on embedded interdigital structure and application thereof, in particular to a microstrip microwave sensor system based on embedded interdigital structure and application thereof in measuring dielectric constants of different concentrations of liquid. BACKGROUND

[0002] In the field of detecting dielectric constants of solutions with different concentrations, many detection technologies and methods have emerged, such as spectroscopy, electrochemical detection method, optical fiber sensing technology and microwave sensing technology. Among them, the microwave sensor technology has attracted great attention and research due to its advantages of convenient detection, high sensitivity, low processing and manufacturing cost and easy to carry.

[0003] To date, scholars worldwide have conducted extensive and in-depth research on microwave sensors, proposing many innovative design ideas and structures. These can be broadly categorized into two main approaches: the first approach starts with the structure of passive resonant units, continuously optimizing and improving the structure to better confine the electric or magnetic field strength, thereby enhancing detection sensitivity; the second approach embeds active circuitry into microwave sensors to create a system-level detection device. The first approach, through the development of passive resonant units, has led to the emergence of many novel resonant unit structures, including: split-ring resonators (SRR), complementary split-ring resonators (CSRR), electric-LC (ELC), spoof surface plasmon polaritons (SSPP), substrate integrated waveguides (SIW), half-mode substrate integrated waveguides (HMSIW), stepped impedance resonators (SIR), and their related improved structures. These passive resonators are all based on the resonant unit, introducing novel branch structures to maximize the confinement of the electric field, allowing more electric field lines to pass through the detected material. The second approach, building upon the first, embeds active circuitry to create a system-level detection device. This active circuitry transforms the relationship between the dielectric constant and resonant frequency at different concentrations into a relationship between the dielectric constant and DC voltage, thus synthesizing a mathematical model to predict the dielectric constant of liquids of unknown concentrations. The first approach, relying solely on passive resonant units for dielectric constant detection, while having lower manufacturing costs, relies on expensive vector network analysis and is inconvenient to carry, resulting in inconvenient detection. The second approach, using an active radio frequency system, eliminates the reliance on expensive vector network analysis, leading to lower manufacturing costs, greater portability, and more convenient detection. This invention not only improves the microwave passive resonant unit to enhance the electric field confinement capability but also embeds an active radio frequency circuit system to create a highly sensitive system-level detection device.

[0004] This invention proposes a microstrip microwave sensor system based on an embedded interdigital structure, which mainly consists of two parts: an improved microstrip structure with an embedded interdigital structure and an active sensor system.

[0005] This improved microstrip structure with embedded interdigitated structure is derived from the traditional standard 50-ohm microstrip line. By widening the middle section of the standard microstrip line and then etching the interdigitated structure, the electric field confinement is enhanced, thereby improving detection sensitivity. Compared to the traditional interdigitated structure, this invention introduces a novel interdigitated structure, mainly in three aspects: First, structurally, by extending the middle etched gap of the lower half of the interdigitated structure to connect with the upper half, a common main etched channel is formed, and the electric field is mainly confined within the main etched channel region; second, in terms of generated modes, through the electromagnetic coupling between the sub-slits and the main channel slits, the novel interdigitated structure can generate two odd-mode resonant modes, namely odd-mode 1 and odd-mode 2; third, high Q-value characteristics. The odd-mode 1 resonant mode of the novel interdigitated structure proposed in this invention has high notch characteristics and a high Q-value, which is more conducive to the detection of the dielectric constant of microfluidic liquids. This invention utilizes odd-mode 1 resonant mode for the detection of the liquid dielectric constant.

[0006] The active sensor system of this invention mainly includes active radio frequency (RF) devices and low-frequency analog devices, namely a power divider, a low-noise amplifier, a delay line, a down-converter, a low-pass filter, and an analog baseband amplifier. The working principle of this active sensor system can be briefly described as follows: When a signal source emits a specific frequency signal, it is split into two RF signals by the power divider, namely branch 1 and branch 2. The RF signal of branch 1 passes through a passive resonant unit, which changes the amplitude and phase of the RF signal. Then, the RF signal of branch 1 passes through a delay line, which changes the phase of the RF signal. Next, the RF signals of branch 1 and branch 2 pass through the down-converter, outputting a 2x frequency RF signal and a zero-IF signal (DC voltage). Immediately afterward, the 2x frequency signal is filtered out by the low-pass filter, leaving only the DC voltage. Finally, the DC voltage is amplified by the baseband amplifier, and the reading of the DC voltage is measured using a multimeter. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing an improved microstrip microwave sensor system based on an embedded interdigital structure. The passive resonant unit of this sensor is an improvement upon the traditional standard 50-ohm microstrip line structure. By widening the width of the middle portion of this standard 50-ohm microstrip line to etch an interdigital structure, the embedding of the interdigital structure allows for greater confinement of the electric field, thereby improving detection sensitivity. Compared to the traditional interdigital structure, this invention introduces a novel interdigital structure, mainly in three aspects: First, structurally, by extending the middle etched gap of the lower half of the interdigital structure to connect with the upper half, a common main etched channel is formed, and the electric field is primarily confined within the main etched channel region. Second, in terms of generated modes, through the electromagnetic coupling between the sub-slits and the main channel slits, the novel interdigital structure can generate two odd-mode resonant modes, namely odd-mode 1 and odd-mode 2. Third, high Q-value characteristics: the odd-mode 1 resonant mode of the novel interdigital structure proposed in this invention exhibits high notch characteristics and a high Q-value, which is more conducive to the detection of the dielectric constant of microfluidic liquids. This detection system is constructed by adding active radio frequency devices and low-frequency analog devices. The relationship between dielectric constant and resonant frequency is transformed into the relationship between dielectric constant and DC voltage, thereby establishing a mathematical model to predict the dielectric constant of liquids with unknown concentrations, eliminating the reliance on expensive vector network analysis.

[0008] This invention is implemented according to the following technical solution:

[0009] In the first aspect, the present invention provides an improved microstrip microwave sensing system based on an embedded interdigital structure, which is a system-level detection device, including a signal generator (1), a power divider (2), two parallel branches, a mixer (7), a low-pass filter (8), a baseband amplifier (9), and a multimeter (10) cascaded in sequence.

[0010] The two parallel branches include a first branch and a second branch; the first branch includes a first RF amplifier (3), a microstrip microwave passive resonant unit (5) with an embedded interdigital structure, and a delay line (6) cascaded in sequence; the second branch includes a second RF amplifier (4);

[0011] The signal generator (1) emits a radio frequency signal of a specific frequency, which is split into two by the power divider (2). The radio frequency signal of the first branch passes through the first radio frequency amplifier (3), the microwave passive resonant unit (5) and the delay line (6) in sequence. At this time, the amplitude and phase of the radio frequency signal are changed by the microstrip microwave passive resonant unit (5) and the delay line (6). The radio frequency signal of the second branch passes through the second radio frequency amplifier (4). The output radio frequency signal of the first branch is used as the input signal of the mixer (7), and the output radio frequency signal of the second branch is used as the local oscillator signal of the mixer (7). The signal output by the mixer (7) is a 2 times frequency radio frequency signal and a zero intermediate frequency DC signal. Then it passes through the low-pass filter (8). At this time, the 2 times frequency radio frequency signal is filtered out by the low-pass filter (8), leaving only the zero intermediate frequency DC signal. Then the DC signal is amplified by the baseband amplifier (9), and finally the amplified DC signal is measured by the multimeter (10).

[0012] The microstrip microwave passive resonant unit (5) with embedded interdigital structure includes a top layer (21), a middle layer (22), and a bottom layer (23);

[0013] The top layer (21) is a metal layer; the metal layer is based on the traditional standard 50-ohm microstrip line, and the linewidth of the middle part of the microstrip line is widened to facilitate the etching of interdigital structures (219), so that the electric field is more confined to the interdigital structure region, which can be used as the sensing region for liquid detection; the metal layer includes an input port (211), a first microstrip line (213), a second microstrip line (214), a third microstrip line (220) and an output port (212) connected in sequence; the second microstrip line (214) has an interdigital structure (219) etched at its center;

[0014] The first microstrip line (213) is connected to the second microstrip line (214), and a first small slit (215) and a second small slit (216) are etched at the connection point; the third microstrip line (220) is connected to the second microstrip line (214), and a third small slit (217) and a fourth small slit (218) symmetrically formed at the connection point;

[0015] The interdigitated structure (219) includes upper and lower parts, and a third etched slit (2193) connecting the upper and lower parts. The upper part includes a first etched slit (2191), a sixth etched slit (2196), and a fifth etched slit (2195), and the lower part includes a second etched slit (2192), a fourth etched slit (2194), and a seventh etched slit (2197). The first etched slit (2191) is located at the upper end of the interdigitated structure (219). The second etched slit (2192) is located at the lower end of the interdigitated structure (219), and the first etched slit (2191) and the second etched slit (2192) are connected by the third etched slit (2193), forming an "I" shape. The fourth etched slit (2194) is located on the side of the second etched slit (2192) facing the first etched slit (2191) and is connected to the second etched slit (2197). The fifth etched slot (2192) is directly connected to the first etched slot (2191) and is spaced apart from it; the fifth etched slot (2195) is located on the side of the first etched slot (2191) facing the second etched slot (2192) and is directly connected to the first etched slot (2191) and is spaced apart from it; the sixth etched slot (2196) is located on the side of the second etched slot (2192) facing the first etched slot (2191) and is directly connected to the second etched slot (2192) and is spaced apart from it; the seventh etched slot (2197) is located on the side of the first etched slot (2191) facing the second etched slot (2192) and is directly connected to the first etched slot (2191) and is spaced apart from it.

[0016] The fifth etching slot (2195) is located between the third etching slot (2193) and the fourth etching slot (2194); the sixth etching slot (2196) is located between the third etching slot (2193) and the seventh etching slot (2197);

[0017] The fourth and fifth etched slots (2194 and 2195) are arranged in a symmetrical, alternating pattern; the sixth etched slot (2196) is located at the upper right corner of the first etched slot and is directly connected to the first etched slot (2191); the seventh etched slot (2197) is located at the lower right corner of the second etched slot and is directly connected to the second etched slot (2192); the sixth and seventh etched slots (2196 and 2197) are arranged in a symmetrical, alternating pattern.

[0018] The first microstrip line (213), the second microstrip line (214), and the third microstrip line (220) are all located at the center of the dielectric substrate; the etched interdigitated structure (219) is located at the center of the second microstrip line (214), which serves to confine the electric field and enhance the detection sensitivity; the interdigitated structure (219) serves as the electromagnetic induction region, and the PDMS substrate (24) is placed on the upper surface of the interdigitated structure (219); microfluidic channels (25) are etched inside the PDMS substrate (24) to hold the detection liquid; this interdigitated structure (219) will generate two odd-mode resonance modes, namely odd-mode 1 and odd-mode 2, and odd-mode 1 is used to detect the dielectric constant of the liquid;

[0019] The intermediate layer (22) is a dielectric substrate;

[0020] The bottom layer (23) is a complete metal layer;

[0021] The length and width of the first microstrip line (213) are the same as the length and width of the third microstrip line (220); the width of the second microstrip line (214) is greater than the widths of the first microstrip line (213) and the third microstrip line (220);

[0022] A microfluidic channel (25) is cut out inside the PDMS substrate (24) to hold the liquid to be tested;

[0023] The second microstrip line (214) is extended to penetrate the upper and lower parts of the interdigital structure (219), thereby forming a common main channel gap, and the electric field is mainly confined to the main channel gap region; the sixth etched gap (2196), the fifth etched gap (2195), the fourth etched gap (2194), and the seventh etched gap (2197) serve as electromagnetic mutual coupling between the sub-gap and the main channel gap, and the interdigital structure (219) can generate two odd mode resonance modes, namely odd mode 1 and odd mode 2. The dielectric constant of the microfluidic liquid is detected by using the odd mode 1 resonance mode.

[0024] Secondly, the present invention provides the application of the above-mentioned improved microstrip microwave sensing system in measuring the dielectric constant of liquids of different concentrations.

[0025] Thirdly, the present invention provides a method for measuring the dielectric constant of a liquid based on the above-described improved microstrip microwave sensing system, wherein the method specifically comprises:

[0026] Step S1: Calculate the mathematical expression for the output signal of the baseband amplifier (9) under no-load conditions:

[0027] S11: Assume that the radio frequency signal s emitted by the signal generator (1) satisfies the following mathematical expression:

[0028] A·cos(2πf0t) Equation (1)

[0029] Where A is the amplitude of the radio frequency signal s, f0 is the frequency of the radio frequency signal s, and t is the time;

[0030] S12: The radio frequency signal s is divided into the first branch and the second branch after passing through the power divider (2). Its mathematical expression is written as:

[0031] A / 2·cos(2πf0t) Equation (2)

[0032] S13: After the RF signal of the first branch passes through the RF amplifier (3) and the RF signal of the second branch passes through the RF amplifier (4), their mathematical expressions can both be written as:

[0033] A / 2·B·cos(2πf0t) Equation (3)

[0034] Where B is the gain of the RF amplifier;

[0035] S14: The RF signal of the first branch then passes through the microstrip microwave passive resonant unit (5), and the mathematical expression of its output signal can be written as:

[0036] A / 2·B·C·cos(2πf0t-2πf0τ1) Formula (4)

[0037] Where B is the attenuation coefficient of the microstrip microwave passive resonant unit (5), and τ1 is the delay time of the microstrip microwave passive resonant unit (5).

[0038] S15: The mathematical expression of the radio frequency signal of the first branch after passing through the delay line (6) can be written as:

[0039] A / 2·B·C·cos(2πf0t-2πf0τ1-2πf0τ2) Formula (5)

[0040] Where τ2 is the delay time of the delay line;

[0041] S16: The RF signal of the first branch is used as the input port of the mixer (7), and the RF signal of the second branch is used as the local oscillator port of the mixer (7). Then the mathematical expression of the output port signal of the mixer (7) can be written as:

[0042]

[0043] Where D is the frequency conversion loss of mixer (7);

[0044] S17: The mathematical expression of the output signal of mixer (7) after passing through low-pass filter (8) can be written as:

[0045]

[0046] S18: The mathematical expression of the signal output from the low-pass filter (8) after passing through the baseband amplifier (9) can be written as:

[0047]

[0048] Where E is the multiple of the baseband amplifier;

[0049] S19: Under no-load conditions, adjust the length of the delay line so that the DC voltage output by the baseband amplifier (9) is zero volts.

[0050] S2. Creating a standard curve:

[0051] S2-1: When different concentrations of the liquid to be tested are injected into the PDMS substrate (24), the odd-mode 1 resonant mode will change. At this time, the mathematical expression of the DC voltage of the output signal of the baseband amplifier (9) can be written as:

[0052]

[0053] Where τ3 is the delay time when the microwave passive resonant unit is loaded with liquids of different concentrations.

[0054] S2-2: Record the DC voltage output values ​​corresponding to the liquid injection of different concentrations of liquid into the PDMS substrate, and use MATLAB numerical software to fit the mathematical expressions of the dielectric constant and DC voltage of different concentrations of liquid.

[0055] S3. Dielectric constant detection of the liquid to be tested:

[0056] After the liquid to be tested is injected into the PDMS substrate (24), the obtained DC voltage is substituted into the above standard curve equation to calculate the dielectric constant of the liquid to be tested.

[0057] The beneficial effects of this invention are as follows:

[0058] 1. Compared with the traditional interdigital structure, this invention introduces a novel interdigital structure, mainly in three aspects: First, in terms of structure, by extending the middle etched gap of the lower half of the interdigital structure to connect with the upper half of the structure, a common main etched channel is formed, and the electric field is mainly confined to the main etched channel region; Second, in terms of generated modes, through the electromagnetic coupling between the sub-gap and the main channel gap, the novel interdigital structure can generate two odd-mode resonance modes, namely odd-mode 1 and odd-mode 2; Third, in terms of high Q-value characteristics, the odd-mode 1 resonance mode of the novel interdigital structure proposed in this invention has high notch characteristics and high Q-value characteristics, which is more conducive to the detection of the dielectric constant of microfluidic liquids.

[0059] 2. This invention, based on the traditional standard 50-ohm microstrip line, widens the middle section of the microstrip line to accommodate the interdigitated structure, thus generating two odd-mode resonant modes. This invention utilizes the odd-mode 1 resonant mode to detect the dielectric constant of the liquid under test. The embedding of the interdigitated structure effectively improves the detection sensitivity.

[0060] 3. The microstrip microwave sensing system based on the embedded interdigital structure of the present invention transforms the relationship between dielectric constant and resonant frequency into the relationship between dielectric constant and DC voltage, thereby making it more convenient to detect dielectric constant values ​​of different concentrations and eliminating the dependence on expensive vector network analyzers.

[0061] 4. The microstrip microwave sensing system based on the embedded interdigital structure of the present invention has the advantages of being easy to carry, having low manufacturing and processing costs, and being convenient to detect.

[0062] 5. The microwave sensing system based on the embedded interdigital structure of the present invention can be further equipped with an additional wireless network module to access 5G / 6G networks, thereby achieving the purpose of real-time, wireless, and remote monitoring. Attached Figure Description

[0063] Figure 1 This is a schematic diagram of the system-level detection of the proposed microstrip microwave sensing system based on an embedded interdigital structure.

[0064] Figure 2 (a) is a schematic diagram of the passive resonant unit of the proposed microstrip microwave sensing system based on an embedded interdigital structure;

[0065] Figure 2 (b) is a three-dimensional view of the passive resonant unit of the proposed microstrip microwave sensing system based on an embedded interdigital structure;

[0066] Figure 3 (a) shows the electric field simulation results of the proposed microwave passive sensor in odd-mode resonance mode 1.

[0067] Figure 3 (b) The electric field simulation results of the proposed microwave passive sensor in odd-mode resonance mode 2;

[0068] Figure 4 The voltage values ​​measured by a multimeter when water and ethanol are mixed in at different volume fractions.

[0069] The diagram is labeled as follows: Signal Generator 1, Power Divider 2, First RF Amplifier 3, Second RF Amplifier 4, Microstrip Microwave Passive Resonant Unit with Embedded Interdigitated Structure 5, Delay Line 6, Mixer 7, Low-Pass Filter 8, Baseband Amplifier 9, Multimeter 10, PDMS Substrate 24, Top Layer 21, Input Port 211, Output Port 212, First Microstrip Line 213, Second Microstrip Line 214, Third Microstrip Line 220, Interdigitated Structure 219, First Small Slit 215, Second Small Slit 216, Third Small Slit 217, Fourth Small Slit 218, First Etched Slit 2191, Second Etched Slit 2192, Third Etched Slit 2193, Fourth Etched Slit 2194, Fifth Etched Slit 2196, Seventh Etched Slit 2197. Detailed Implementation

[0070] 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.

[0071] A microstrip microwave sensing and detection system based on an embedded interdigital structure is a system-level detection device.

[0072] like Figure 1 As shown, the system-level testing equipment includes a signal generator 1, a power divider 2, two parallel branches, a mixer 7, a low-pass filter 8, a baseband amplifier 9, and a multimeter 10.

[0073] The two parallel branches include a first branch and a second branch; the first branch includes a first RF amplifier 3, a microstrip microwave passive resonant unit 5 with an embedded interdigital structure, and a delay line 6 cascaded in sequence; the second branch includes a second RF amplifier 4.

[0074] The signal generator 1 emits a radio frequency (RF) signal of a specific frequency, which is split into two by the power divider 2. The RF signal of the first branch passes through the first RF amplifier 3, the microwave passive resonant unit 5, and the delay line 6 in sequence. At this time, the amplitude and phase of the RF signal are changed by the microstrip microwave passive resonant unit 5 and the delay line 6. The RF signal of the second branch passes through the second RF amplifier 4. The output RF signal of the first branch is used as the input signal of the mixer 7, and the output RF signal of the second branch is used as the local oscillator signal of the mixer 7. The signal output by the mixer 7 is a 2x RF signal and a zero-IF DC signal. Then it passes through the low-pass filter 8. At this time, the 2x RF signal is filtered out by the low-pass filter 8, leaving only the zero-IF DC signal. Then the DC signal is amplified by the baseband amplifier 9, and finally the amplified DC signal is measured by the multimeter 10.

[0075] The microstrip microwave passive resonant unit 5 is divided into a top layer 21, a middle layer 22, and a bottom layer 23;

[0076] like Figure 2 As shown in (a), the top layer 21 mainly consists of a metal layer; the metal layer includes an input port 211, a first microstrip line 213, a second microstrip line 214, a third microstrip line 220, and an output port 212 connected in sequence; the center of the second microstrip line 214 is etched with an interdigitated structure 219 serving as an electromagnetic induction region;

[0077] The interdigitated structure 219 includes upper and lower portions, and a third etched slit 2193 connecting the upper and lower portions. The upper portion includes a first etched slit 2191, a sixth etched slit 2196, and a fifth etched slit 2195, and the lower portion includes a second etched slit 2192, a fourth etched slit 2194, and a seventh etched slit 2197. The first etched slit 2191 and the second etched slit 2192 are connected by the third etched slit 2193, forming an "I" shape. The fourth etched slit 2194 is located on the side of the second etched slit 2192 facing the first etched slit 2191 and is directly connected to the second etched slit 2192, and it is also connected to the first etched slit 2191. There are gaps between them; the fifth etching gap 2195 is located on the side of the first etching gap 2191 facing the second etching gap 2192 and is directly connected to the first etching gap 2191, and there is a gap between it and the second etching gap 2192; the sixth etching gap 2196 is located on the side of the second etching gap 2192 facing the first etching gap 2191 and is directly connected to the second etching gap 2192, and there is a gap between it and the first etching gap 2191; the seventh etching gap 2197 is located on the side of the first etching gap 2191 facing the second etching gap 2192 and is directly connected to the first etching gap 2191, and there is a gap between it and the second etching gap 2192.

[0078] The fifth etching gap 2195 is located between the third etching gap 2193 and the fourth etching gap 2194; the sixth etching gap 2196 is located between the third etching gap 2193 and the seventh etching gap 2197.

[0079] like Figure 2 As shown in (b), the interdigitated structure 219 serves as the electromagnetic induction region, and the PDMS substrate 24 is placed on the upper surface of the interdigitated structure 219. Microfluidic channels 25 covering the third etched slit 2193, the fourth etched slit 2194, the fifth etched slit 2195, the sixth etched slit 2196, and the seventh etched slit 2197 are etched inside the PDMS substrate 24 to place the detection liquid. This interdigitated structure 219 will generate two odd-mode resonance modes, and the odd-mode resonance mode 1 is used to detect the dielectric constant of the liquid.

[0080] The intermediate layer 25 is a dielectric substrate; the bottom layer 23 is a complete metal surface;

[0081] Figure 3 (a) shows the electric field simulation results of the proposed microwave passive sensor resonant unit in odd mode 1.

[0082] Figure 3 (b) shows the electric field simulation results of the proposed microwave passive sensor resonant unit in odd mode 2.

[0083] During testing, the PDMS substrate 24 is placed on the upper surface of the microwave passive resonant unit structure 219. To facilitate the injection of the liquid to be tested, a microfluidic channel 25 is cut out inside the PDMS substrate 24 to hold the liquid to be tested.

[0084] This invention relates to a novel microstrip microwave sensing system based on a passive resonant unit device with an embedded interdigitated structure. This system is achieved by modifying a traditional standard 50-ohm microstrip line. The system comprises a passive microwave resonant unit and an active circuit detection system. The passive microwave resonant unit, based on a traditional standard 50-ohm microstrip line, widens the linewidth in the middle section to etch an interdigitated structure, generating two odd-mode resonant modes. The electric fields of both odd-mode resonant modes are confined to the interdigitated structure. This invention utilizes the first odd-mode resonant mode to detect the dielectric constant of liquids with different concentrations. The active circuit system transforms the mathematical relationship between dielectric constant and resonant frequency into a mathematical relationship between dielectric constant and DC voltage, thereby fitting a mathematical model to predict the dielectric constant of an unknown liquid. This detection system offers advantages such as portability, convenient detection, and low manufacturing cost.

[0085] The working principle of the above-mentioned system-level testing equipment can be described as follows:

[0086] Step S1: Calculate the mathematical expression for the output signal of baseband amplifier 9 under no-load conditions:

[0087] S11: Assume that the radio frequency signal s emitted by signal generator 1 satisfies the following mathematical expression:

[0088] A·cos(2πf0t) Equation (1)

[0089] Where A is the amplitude of the radio frequency signal s, f0 is the frequency of the radio frequency signal s, and t is the time;

[0090] S12: The radio frequency signal s is divided into the first branch and the second branch after passing through the power divider 2. Its mathematical expression is written as:

[0091] A / 2·cos(2πf0t) Equation (2)

[0092] S13: The mathematical expressions for the RF signal of the first branch after passing through RF amplifier 3 and the RF signal of the second branch after passing through RF amplifier 4 can both be written as:

[0093] A / 2·B·cos(2πf0t) Equation (3)

[0094] Where B is the gain of the RF amplifier;

[0095] S14: The RF signal of the first branch then passes through the microstrip microwave passive resonant unit 5, and the mathematical expression of its output signal can be written as:

[0096] A / 2·B·C·cos(2πf0t-2πf0τ1) Formula (4)

[0097] Where B is the attenuation coefficient of the microstrip microwave passive resonant unit 5, and τ1 is the delay time of the microstrip microwave passive resonant unit 5.

[0098] S15: The mathematical expression for the RF signal of the first branch after passing through delay line 6 can be written as:

[0099] A / 2·B·C·cos(2πf0τ-2πf0τ1-2πf0τ2) Formula (5)

[0100] Where τ2 is the delay time of the delay line;

[0101] S16: If the RF signal of the first branch is used as the input port of mixer 7, and the RF signal of the second branch is used as the local oscillator port of mixer 7, then the mathematical expression for the output port signal of mixer 7 can be written as:

[0102]

[0103] Where D is the frequency conversion loss of mixer 7;

[0104] S17: The mathematical expression for the output signal of mixer 7 after passing through low-pass filter 8 can be written as:

[0105]

[0106] S18: The mathematical expression for the signal output from low-pass filter 8 after passing through baseband amplifier 9 can be written as:

[0107]

[0108] Where E is the multiple of the baseband amplifier;

[0109] S19: Under no-load conditions, adjust the length of the delay line so that the DC voltage output by the baseband amplifier 9 is zero volts.

[0110] S2. Creating a standard curve:

[0111] S2-1: When different concentrations of the liquid to be tested are injected into the PDMS substrate 24, the odd-mode 1 resonant mode will change. At this time, the mathematical expression for the DC voltage of the output signal of the baseband amplifier 9 can be written as:

[0112]

[0113] Where τ3 is the delay time when the microwave passive resonant unit is loaded with liquids of different concentrations.

[0114] S2-2: Record the DC voltage output values ​​corresponding to the liquid injection of different concentrations of liquid into the PDMS substrate, and use MATLAB numerical software to fit the mathematical expressions of the dielectric constant and DC voltage of different concentrations of liquid. Figure 4 The voltage values ​​measured by a multimeter when water and ethanol are mixed in at different volume fractions.

[0115] S3. Dielectric constant detection of the liquid to be tested:

[0116] After injecting the liquid to be tested into the PDMS substrate 24, the obtained DC voltage is substituted into the above standard curve equation to calculate the dielectric constant of the liquid to be tested.

[0117] The microwave microfluidic sensor of this invention has been optimized in commercial electromagnetic simulation software, and the specific values ​​are shown below.

[0118] The overall dimensions of the microwave sensor are Lx = 30mm and Ly = 50mm.

[0119] The width of the first microstrip line 213 is W0 = 1.68 mm, and the length of the first microstrip line 213 is 0.5*(Ly-L0) = 16.0 mm;

[0120] The width of the second microstrip line 214 is 15mm, and the length of the second microstrip line 214 is L0 = 18mm;

[0121] The width of the third microstrip line 220 is W0 = 1.68 mm, and the length of the third microstrip line 220 is 0.5*(Ly-L0) = 16.0 mm;

[0122] The width of the first small gap 215 is W1 = 1.0 mm, and the length of the first small gap is L1 = 2.5 mm;

[0123] The width of the second small gap 216 is W1 = 1.0 mm, and the length of the first small gap is L1 = 2.5 mm;

[0124] The width of the third small gap 217 is W1 = 1.0 mm, and the length of the first small gap is L1 = 2.5 mm;

[0125] The width of the fourth small gap 218 is W1 = 1.0 mm, and the length of the first small gap is L1 = 2.5 mm;

[0126] The overall width of the interdigitated structure 219 is L4 + 2*W2 = 8.0 mm, and the overall length of the interdigitated structure 219 is L2 = 6.0 mm;

[0127] The width of the first etched slit 2191 is W2 = 1.0 mm, and the length of the first etched slit 2191 is L2 = 6.0 mm;

[0128] The width of the second etched slit 2192 is W2 = 1.0 mm, and the length of the second etched slit 2192 is L2 = 6.0 mm;

[0129] The width of the third etched slit 2193 is W4 = 1.0 mm, and the length of the third etched slit 2193 is L4 = 6.0 mm;

[0130] The width of the fourth etched slit 2194 is W5 = 0.5 mm, and the length of the fourth etched slit 2194 is L3 = 5.0 mm;

[0131] The width of the fifth etched slit 2195 is W5 = 0.5 mm, and the length of the fifth etched slit 2195 is L3 = 5.0 mm;

[0132] The width of the sixth etched slit 2196 is W5 = 0.5 mm, and the length of the sixth etched slit 2196 is L3 = 5.0 mm;

[0133] The width of the seventh etched slit 2197 is W5 = 0.5 mm, and the length of the seventh etched slit 2197 is L3 = 5.0 mm;

[0134] The overall length, width, and height of the PDMS substrate 24 are 18.3 mm, 4.3 mm, and 5 mm, respectively.

[0135] The length, width, and height of the microfluidic channel 25 inside the PDMS substrate 24 are 6.0 mm, 4.2 mm, and 0.2 mm, respectively.

[0136] This microwave microfluidic sensor is a system-level detection device, comprising a microwave passive resonant unit and an active circuit detection system. The microwave passive resonant unit is based on a traditional standard 50-ohm microstrip line. By widening the linewidth in the middle section of the microstrip line to etch an interdigitated structure, two odd-mode resonant modes are generated. The electric fields of both odd-mode resonant modes are confined to the interdigitated structure. This invention utilizes the first odd-mode resonant mode to detect the dielectric constant of liquids with different concentrations. Combined with the active circuit system, the mathematical relationship between dielectric constant and resonant frequency can be transformed into a mathematical relationship between dielectric constant and DC voltage, thereby fitting a mathematical model to predict the dielectric constant value of unknown liquids. This detection system has advantages such as low manufacturing cost, portability, and convenient detection, and will play an important role in the detection fields of materials, biomedicine, and chemistry.

[0137] 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. An improved microstrip microwave sensing system based on an embedded interdigital structure, characterized in that... It includes a signal generator (1), a power divider (2), two parallel branches, a mixer (7), a low-pass filter (8), a baseband amplifier (9), and a multimeter (10) cascaded in sequence. The two parallel branches include a first branch and a second branch; the first branch includes a first radio frequency amplifier (3), a microstrip microwave passive resonance unit (5) with an interdigital structure embedded, and a delay line (6) cascaded in sequence; the second branch includes a second radio frequency amplifier (4). The signal generator (1) emits a radio frequency signal of a certain specific frequency, which is split into two by the power divider (2). The radio frequency signal of the first branch passes through the first radio frequency amplifier (3), the microwave passive resonance unit (5), and the delay line (6) in sequence. At this time, the amplitude and phase of the radio frequency signal are changed by the microstrip microwave passive resonance unit (5) and the delay line (6); the radio frequency signal of the second branch passes through the second radio frequency amplifier (4). The output radio frequency signal of the first branch is used as the input signal of the mixer (7), and the output radio frequency signal of the second branch is used as the local oscillator signal of the mixer (7). The signal output by the mixer (7) is a radio frequency signal of twice the frequency and a direct current signal of zero intermediate frequency. Then, it passes through the low-pass filter (8). At this time, the radio frequency signal of twice the frequency is filtered out by the low-pass filter (8), leaving only the direct current signal of zero intermediate frequency. Then, this direct current signal is amplified by the baseband amplifier (9), and finally, the amplified direct current signal is measured and obtained by the multimeter (10). The microstrip microwave passive resonance unit (5) includes a top layer (21), a middle layer (22), and a bottom layer (23). The middle layer (22) is a dielectric substrate. The bottom layer (23) is a complete metal layer. The top layer (21) is a metal layer; the metal layer includes an input port (211), a first microstrip line (213), a second microstrip line (214), a third microstrip line (220), and an output port (212) connected in sequence; an interdigital structure (219) serving as an electromagnetic induction region is etched at the center position of the second microstrip line (214). The interdigital structure (219) includes upper and lower parts and a third etching gap (2193) penetrating the upper and lower parts. The upper part includes a first etching gap (2191), a sixth etching gap (2196), and a fifth etching gap (2195), and the lower part includes a second etching gap (2192), a fourth etching gap (2194), and a seventh etching gap (2197); the first etching gap (2191) and the second etching gap (2192) are penetrated through the third etching gap (2193) and present an "I" shape; the fourth etching gap (2194) is located on the side of the second etching gap (2192) facing the first etching gap (2191) and is directly connected to the second etching gap (2192), and there is a spacing between it and the first etching gap (2191). The fifth etched slot (2195) is located on the side of the first etched slot (2191) facing the second etched slot (2192) and is directly connected to the first etched slot (2191), and there is a gap between it and the second etched slot (2192); The sixth etched slot (2196) is located on the side of the second etched slot (2192) facing the first etched slot (2191) and is directly connected to the second etched slot (2192), and there is a gap between it and the first etched slot (2191); The seventh etched slot (2197) is located on the side of the first etched slot (2191) facing the second etched slot (2192) and is directly connected to the first etched slot (2191), and there is a gap between it and the second etched slot (2192); The fifth etching slot (2195) is located between the third etching slot (2193) and the fourth etching slot (2194); the sixth etching slot (2196) is located between the third etching slot (2193) and the seventh etching slot (2197); The second microstrip line (214) is extended to penetrate the upper and lower portions of the interdigital structure (219), thereby forming a common main channel gap, and the electric field is mainly confined to the main channel gap region. The sixth etched slit (2196), the fifth etched slit (2195), the fourth etched slit (2194), and the seventh etched slit (2197) serve as electromagnetic coupling between the sub-slits and the main channel slits. The interdigital structure (219) generates two odd-mode resonance modes, namely odd-mode 1 and odd-mode 2. The odd-mode 1 resonance mode is used to detect the dielectric constant of the microfluidic liquid.

2. The improved microstrip microwave sensing system according to claim 1, characterized in that... The first microstrip line (213) is connected to the second microstrip line (214), and a first small slit (215) and a second small slit (216) are etched on both sides of the connection point.

3. The improved microstrip microwave sensing system according to claim 1 or 2, characterized in that... The third microstrip line (220) is connected to the second microstrip line (214), and symmetrical third and fourth small gaps (217 and 218) are etched on both sides of the connection.

4. The improved microstrip microwave sensing system according to claim 1, characterized in that... The first microstrip line (213), the second microstrip line (214), and the third microstrip line (220) are all located at the center of the dielectric substrate.

5. The improved microstrip microwave sensing system according to claim 1 or 4, characterized in that... The interdigitated structure (219) is located at the center of the second microstrip line (214).

6. The improved microstrip microwave sensing system according to claim 1, characterized in that... A PDMS substrate (24) is placed on the upper surface of the interdigitated structure (219); microfluidic channels (25) are etched inside the PDMS substrate (24) to hold the liquid to be tested.

7. The improved microstrip microwave sensing system according to claim 1, characterized in that... The length and width of the first microstrip line (213) are the same as the length and width of the third microstrip line (220); The width of the second microstrip line (214) is greater than the widths of the first microstrip line (213) and the third microstrip line (220).

8. The application of the improved microstrip microwave sensing system according to any one of claims 1-7 in measuring the dielectric constant of liquids of different concentrations.

9. A method for measuring the liquid dielectric constant based on the improved microstrip microwave sensing system according to any one of claims 1-7, characterized in that... The method is specifically as follows: Step S1: Calculate the mathematical expression for the output signal of the baseband amplifier (9) under no-load conditions: S11: Assume that the radio frequency signal s emitted by the signal generator (1) satisfies the following mathematical expression: Equation (1) in Let be the amplitude of the radio frequency signal s. s is the frequency of the radio frequency signal s, and t is the time. S12: After passing through the power divider (2), the radio frequency signal s is divided into the first branch and the second branch radio frequency signals, and its mathematical expression is written as: Equation (2) S13: After the RF signal of the first branch passes through the RF amplifier (3) and the RF signal of the second branch passes through the RF amplifier (4), their mathematical expressions can both be written as: Equation (3) in, It is the gain of the radio frequency amplifier; S14: The RF signal of the first branch then passes through the microstrip microwave passive resonant unit (5), and the mathematical expression of its output signal can be written as: Equation (4) in The attenuation coefficient of the microstrip microwave passive resonant unit (5) is given. It is the delay time of the microstrip microwave passive resonant unit (5); S15: The mathematical expression of the radio frequency signal of the first branch after passing through the delay line (6) can be written as: Equation (5) in This refers to the delay time of the delay line; S16: The RF signal of the first branch is used as the input port of the mixer (7), and the RF signal of the second branch is used as the local oscillator port of the mixer (7). Then the mathematical expression of the output port signal of the mixer (7) can be written as: Equation (6) in The frequency conversion loss of the mixer (7); S17: The mathematical expression of the output signal of the mixer (7) after passing through the low-pass filter (8) can be written as: Equation (7) S18: The mathematical expression of the signal output from the low-pass filter (8) after passing through the baseband amplifier (9) can be written as: Equation (8) in This is a multiple of the baseband amplifier. S19: Under no-load conditions, adjust the length of the delay line so that the DC voltage output by the baseband amplifier (9) is zero volts; S2. Creating a standard curve: S2-1: When different concentrations of the liquid to be tested are injected into the PDMS substrate (24), the odd-mode 1 resonant mode will change. At this time, the mathematical expression of the DC voltage of the output signal of the baseband amplifier (9) can be written as: Equation (9) in Delay time for loading different concentrations of liquid onto a microwave passive resonant unit; S2-2: Record the DC voltage output values ​​corresponding to the liquid injection of different concentrations of liquid into the PDMS substrate, and use MATLAB numerical software to fit the mathematical expressions of the dielectric constant and DC voltage of different concentrations of liquid. S3. Dielectric constant detection of the liquid to be tested: After injecting the liquid to be tested into the PDMS substrate (24), the obtained DC voltage is substituted into the above standard curve equation to calculate the dielectric constant of the liquid to be tested.

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