Microwave sensor based on differential substrate integrated waveguide reentrant cavity and microfluidics technology

Abstract

A microwave sensor based on a differential substrate integrated waveguide reentrant resonant cavity and microfluidic technology, the sensor has a superimposed upper cover plate and a lower bottom plate, the upper cover plate and the lower bottom plate both contain a top metal layer, an intermediate dielectric layer and a bottom metal layer; two resonant cavity monomers are formed side by side between the upper cover plate and the lower bottom plate, each of the resonant cavity monomers is embedded with a microfluidic chip, and the two substrate integrated waveguide reentrant resonant cavity monomers are connected in parallel and connected in series by a power divider. The present invention embeds the microfluidic chip into the substrate integrated waveguide reentrant resonant cavity based on the differential structure configuration, utilizes the advantages of differential structure compensation for environmental interference, high concentration of the reentrant resonant cavity electric field and microfluidic chip can accurately control microfluids, and obtains a high-sensitivity and high-precision sensor with little interference, non-invasive, and easy to integrate with other planar circuits.

Description

Technical Field

[0001] The invention belongs to the field of sensors, and in particular relates to a microwave sensor suitable for detecting liquid media. Background Art

[0002] The current microwave sensing detection methods for liquid media are usually divided into non-resonant transmission method and resonant method. Compared with the non-resonant transmission method, the resonant method has significant advantages such as high Q value and controllable resonant frequency. By utilizing its resonant frequency offset and scattering parameter phase amplitude change, it can achieve accurate measurement of the dielectric constant of the medium. Therefore, the detection technology solution based on microwave resonance mechanism has become a research hotspot and has attracted extensive attention from scholars at home and abroad.

[0003] However, with the continuous development of modern detection technology, microwave sensing test systems tend to be miniaturized and integrated, and higher requirements are placed on the sensitivity and anti-interference of sensors. Traditional microwave sensors have the disadvantages of large size, low test sensitivity, susceptibility to environmental factors, and pollution and waste of the tested products, so their wide application is greatly limited. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a microwave sensor based on a differential substrate integrated waveguide reentrant resonant cavity and microfluidic technology, which is used to realize the miniaturization and planarization of the sensor, effectively improve its anti-interference to the environment through the differential structure, and improve the detection sensitivity through the substrate waveguide reentrant resonant cavity structure with a strong electric field region inside. Furthermore, the microfluidic chip embedded in the resonant cavity is used to accurately control the microfluid, and the spiral structure is designed to effectively improve the sensitivity and other performance indicators of the sensor, avoiding waste and pollution of the tested product.

[0005] The technical solution of the present invention is as follows:

[0006] A microwave sensor based on a differential substrate integrated waveguide re-entrant resonant cavity and microfluidic technology, the sensor having a stacked upper cover plate and a lower bottom plate, the upper cover plate and the lower bottom plate both comprising a top metal layer, an intermediate dielectric layer and a bottom metal layer. Two resonant cavity monomers are formed side by side between the upper cover plate and the lower bottom plate, each of the resonant cavity monomers is embedded with a microfluidic chip, the two substrate integrated waveguide re-entrant resonant cavity monomers are connected in parallel and in series by a power divider to form a differential structure.

[0007] Specifically, for each resonant cavity monomer, a circle of circularly distributed metal through holes is made in the intermediate dielectric layer of the upper cover plate and the lower bottom plate to connect the top metal layer and the bottom metal layer to form a cylindrical metal wall of the resonant cavity monomer. In the cylindrical metal wall area, the upper cover plate is etched from the bottom metal upward to part of the intermediate dielectric layer to form a cylindrical groove for embedding the microfluidic chip, and the lower bottom plate is etched from the top metal downward to part of the intermediate dielectric layer to form an annular groove, the outer diameter of which is the same as the groove size of the upper cover plate, the positions are opposite, and they overlap each other to form a resonant cavity, and a short-circuit capacitor column is formed in the center of the annular groove.

[0008] For each resonant cavity monomer, two tube seats are installed above the upper cover plate for injecting and extracting the liquid medium to be measured. The two tube seats are respectively connected to the inlet and outlet of the microchannel of the microfluidic chip to achieve the connection between the microchannel and the flexible conduit.

[0009] Specifically, there are two power dividers, located on both sides of the resonant cavity monomer, made on the top metal of the upper cover plate, which is a Wilkinson power divider. Its three ports are connected to the circular metal ring by microstrip lines, among which port one is used to feed in the excitation signal, and port two and port three divide the power equally, and are connected to the two resonant cavity monomers by feeding lines respectively to form coplanar waveguide transmission.

[0010] There are two coplanar waveguide feeding lines on the left and right sides of the top metal layer of the upper cover plate of each resonant cavity monomer for feeding in the excitation signal.

[0011] Furthermore, the short-circuit capacitor column region includes a metal through hole for connecting the upper and lower metal layers of the short-circuit capacitor column, and the radius of the metal through hole is 0.5 mm.

[0012] Furthermore, the flow-guiding channel on the microfluidic chip is a spiral structure to increase the interaction area between the liquid medium to be measured and the induced electric field.

[0013] The beneficial effects of the present invention are as follows:

[0014] 1. The present invention designs the sensor based on the differential structure configuration, which can realize the effective compensation for the interference of the surrounding environment and greatly improve the accuracy of the measurement result.

[0015] 2. The present invention uses a substrate-integrated waveguide reentrant resonant cavity as a resonant element to design a sensor, which can be realized using the very mature standard printed circuit board process and photolithography process. Compared with the traditional waveguide resonant cavity, the present invention has a more compact structure, a lighter volume, and is easier to process and manufacture, effectively reducing the manufacturing cost. In addition, the planar structure of the substrate-integrated waveguide reentrant resonant cavity also makes it easier to integrate with other planar circuit structures.

[0016] 3. The present invention uses a microfluidic chip to introduce the detected liquid into the induced electric field area, which only requires a small amount of liquid and does not have physical contact with the sensor, thus solving the problem of traditional sensors causing contamination and waste of the detected liquid.

[0017] 4. The present invention cleverly designs the microchannel on the microfluidic chip into a mosquito coil-like spiral structure, and uses its conducting channel to introduce the measured liquid into the strong electric field area of ​​the induced electric field, which significantly improves the sensitivity of detection.

[0018] 5. The present invention adopts PMMA as the material of the microfluidic chip, and utilizes its low loss tangent angle characteristic to effectively maintain the high quality factor of the substrate integrated waveguide reentrant resonant cavity. At the same time, the excellent chemical inertness of PMMA greatly expands the application range of the designed sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the overall structure of the microwave sensor proposed by the present invention after packaging;

[0020] Figure 1 (a) is a three-dimensional exploded schematic diagram of the components of the microwave sensor proposed by the present invention;

[0021] FIG2 (a) is a schematic diagram of the overall structure of a microwave sensor substrate integrated waveguide reentrant resonant cavity monomer proposed in the present invention;

[0022] FIG2( b ) is a cross-sectional schematic diagram of a microwave sensor substrate integrated waveguide reentrant resonant cavity monomer proposed by the present invention;

[0023] FIG. 2 ( c ) is a three-dimensional exploded schematic diagram of various components of the microwave sensor substrate integrated waveguide reentrant resonant cavity monomer proposed by the present invention;

[0024] Figure 3 It is a schematic diagram of the overall structure of the upper cover plate of the microwave sensor substrate integrated waveguide re-entrant resonant cavity monomer proposed by the present invention;

[0025] Figure 3 (a) Yes Figure 3 Enlarged view of part I in the middle.

[0026] FIG4 (a) is a schematic diagram of the overall structure of the microwave sensor microfluidic chip proposed in the present invention;

[0027] FIG4( b ) is a top view of the microwave sensor microfluidic chip proposed by the present invention;

[0028] Figure 5 It is a schematic diagram of the overall structure of the lower bottom plate of the microwave sensor substrate integrated waveguide re-entrant resonant cavity monomer proposed by the present invention;

[0029] Figure 6is a top view of the Wilkinson power divider proposed by the present invention;

[0030] Figure 7 It is a transmission response characteristic curve diagram of the microwave sensor proposed in the present invention to samples with different dielectric constants. DETAILED DESCRIPTION

[0031] In order to better explain the design process and purpose, the present invention is further described below in conjunction with embodiments and drawings:

[0032] like Figure 1 , Figure 1 As shown in Figure 2 (a), Figure 2 (a) and Figure 2 (b), the microwave sensor based on the differential substrate integrated waveguide re-entrant resonant cavity and microfluidic technology proposed in the present invention comprises two substrate integrated waveguide re-entrant resonant cavity monomers 1, two power dividers 3 and two microfluidic chips 2 embedded in the resonant cavity monomers.

[0033] The microwave sensor is composed of an upper cover plate 1-1 and a lower base plate 1-2. The upper cover plate 1-1 and the lower base plate 1-2 each comprise a three-layer structure, namely a top metal layer, an intermediate dielectric layer and a bottom metal layer.

[0034] The bottom metal of the upper cover plate 1-1 and the top metal of the lower bottom plate 1-2 have the same area, and the two are bonded together with conductive glue. The center axis should be aligned when bonding the upper cover plate and the lower bottom plate.

[0035] The intermediate dielectric layer material of the upper cover plate 1-1 and the lower bottom plate 1-2 is the same. In this embodiment, the material is Rogers 5880, which has a relative dielectric constant of 2.2, a relative magnetic permeability of 1, and a loss tangent of 0.0009. The thickness of the upper cover plate is 1.1 mm, and the thickness of the lower bottom plate is 1.5 mm.

[0036] Two resonant cavity monomers 1 are formed side by side between the upper cover plate 1-1 and the lower base plate 1-2, each of which is embedded with a microfluidic chip 2. The two substrate integrated waveguide re-entrant resonant cavity monomers 1 are connected in parallel and connected in series by a power divider 3 to form a differential structure.

[0037] like Figure 6As shown, the power divider is a Wilkinson power divider 3, which is made on the top metal of the upper cover plate, and its three ports are connected to the circular metal ring 3-4 by microstrip lines, wherein port 1 3-1 is used to feed the excitation signal, and port 2 3-2 and port 3 3-3 are equally divided in power, and are connected to two resonant cavity monomers 1 through feed lines 1-1-1 respectively. The metal ring 3-4 contains a 100 ohm resistor 3-5. Preferably, the outer diameter of the metal ring is 4.09 mm, the width of the microstrip line connected to port 1 3-1 is 0.93 m, and the width of the microstrip line connected to port 2 3-2 and port 3 3-3 is 1 mm.

[0038] like Figure 3 and Figure 3 As shown in (a), two feed lines 1-1-1 are engraved on the left and right sides of the top metal layer of the resonant cavity monomer 1, which are used to connect to two power dividers to form coplanar waveguide transmission. The size of the feed line 1-1-1 needs to be precisely designed to meet the requirements of input port impedance matching. Preferably, the width of the feed line 1-1-1 is 1.78mm, the depth of the feed into the resonant cavity is 8.27mm, and the gap width w between the feed line 1-1-1 and the coplanar metal of the top layer of the upper cover plate is 1mm.

[0039] Each resonant cavity monomer 1 needs to be obtained by making the following structure:

[0040] A circle of circularly arranged metal through holes 1-3 are made in the intermediate dielectric layer of the upper cover plate 1-1 and the lower base 1-2 to connect the top metal layer with the bottom metal layer, and its function is to form a cylindrical metal wall of the resonant cavity monomer 1. Preferably, the radius of the metal through hole 1-3 is 0.4 mm, and the center distance between two adjacent metal through holes is 1 mm.

[0041] like Figure 3 As shown, in the area surrounded by the cylindrical metal wall, a cylindrical groove is etched on the upper cover plate 1-1 from the bottom metal layer upward to part of the middle dielectric layer. The area of ​​the cylindrical groove is the same as that of the microfluidic chip 2, and the depth of the groove is the same as the thickness of the microfluidic chip.

[0042] like Figure 5 As shown, a ring groove is etched from the top metal layer to part of the middle dielectric layer on the lower bottom plate 1-2, and a circular short-circuit capacitor column 1-2-1 is formed in the center of the ring groove. The outer diameter of the ring groove is the same as the groove size of the upper cover plate, and the positions are opposite and overlapped with each other, that is, a resonant cavity monomer 1 is formed. The above two grooves do not completely etch the middle dielectric layer, and both retain a certain thickness of the middle dielectric layer for the purpose of installing the microfluidic chip.

[0043] Preferably, the depth of the cylindrical groove is 1 mm, the outer diameter of the annular groove is 24 mm, the groove depth is 1.3 mm, the radius of the short-circuit capacitor column is 6 mm, and the radius of the metal through holes 1-2-2 in the short-circuit capacitor column is 0.5 mm.

[0044] Two cylindrical tube seats 4 are installed above the upper cover plate 1 - 1 of the resonant cavity monomer 1 , and a flexible conduit is connected to each of the two tube seats for extracting or injecting the measured liquid into the microchannel of the microfluidic chip 2 .

[0045] The microfluidic chip 2 is embedded in the circular groove of the resonant cavity monomer 1 with its front side facing upwards, and the front side of the microfluidic chip is connected to the top cover plate by using insulating glue to seal the microfluidic channel and prevent leakage of the measured medium.

[0046] As shown in Fig. 4 (a) and Fig. 4 (b), a conductive mosquito coil-shaped spiral microchannel 2-1 is etched from top to bottom on the microfluidic chip 2. In this embodiment, the material of the microfluidic chip is PMMA, which can effectively maintain the high quality factor of the substrate integrated waveguide reentrant resonant cavity by utilizing its low loss tangent angle characteristic. At the same time, PMMA is extremely chemically inert, which makes the application range of the designed sensor wider.

[0047] Preferably, the thickness of the microfluidic chip 2 is 0.965 mm, the depth of the microchannel 2-1 is 0.8 mm, the width is 1.1 mm, and the spacing is 0.5 mm.

[0048] Figure 7 is a transmission characteristic curve of the microwave sensor proposed in the present invention for samples with different dielectric constants. Figure 7 As shown, when both microchannels 2-1 are completely filled with air, both reentrant resonant cavities excite strong resonance at 3.52 GHz. If the liquid to be tested is uniformly injected into one of the microchannels 2-1, and the other is still filled with air, the two reentrant resonant cavities will excite two different frequency points. The injected liquid disturbs the electromagnetic field in one of the resonant cavities, exciting a frequency point lower than 3.52 GHz, while the frequency point excited by the other resonant cavity is still 3.52 GHz. When the dielectric constant of the liquid sample to be tested increases from 2 to 10, the first frequency point value decreases from 2.66 GHz to 1.83 GHz, and the second frequency point is always 3.52 GHz. Therefore, by calculating the difference between the two frequency points, accurate detection of liquid coal quality can be achieved while avoiding environmental interference.

[0049] It can be seen that the present invention combines the differential substrate integrated waveguide reentrant resonant cavity with microfluidic technology, introduces the microfluidic chip into the substrate integrated waveguide reentrant resonant cavity, and utilizes the advantages of differential structural configuration to compensate for environmental interference, the highly concentrated electric field of the reentrant resonant cavity, and the microfluidic chip that can accurately control trace fluids, to obtain a non-invasive, reusable, high-sensitivity and high-precision sensor that is easy to integrate with other planar circuits.

[0050] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications to the invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims and equivalent technologies of the present invention, the present invention is also intended to include these changes and modifications.

Claims

1. A microwave sensor based on differential substrate integrated waveguide reentrant resonant cavity and microfluidic technology, characterized in that: The sensor comprises a stacked upper cover plate (1-1) and a lower base plate (1-2), each of which comprises a top metal layer, an intermediate dielectric layer and a bottom metal layer; two substrate integrated waveguide re-entrant resonant cavity monomers (1) are formed side by side between the upper cover plate (1-1) and the lower base plate (1-2), each substrate integrated waveguide re-entrant resonant cavity monomer (1) is embedded with a microfluidic chip (2), and the two substrate integrated waveguide re-entrant resonant cavity monomers (1) are connected in parallel and connected in series by a power divider (3) to form a differential structure; The upper cover plate (1-1) is provided with a cylindrical groove for embedding the microfluidic chip (2), the outer diameter of the cylindrical groove is the same as the size of the microfluidic chip (2), and the depth of the cylindrical groove is the same as the thickness of the microfluidic chip; There are two power dividers (3), which are located on both sides of the substrate integrated waveguide re-entrant resonant cavity monomer (1) and are manufactured on the top metal layer of the upper cover plate.

2. The microwave sensor according to claim 1, characterized in that: For each substrate integrated waveguide reentrant resonant cavity monomer (1), a circle of first metal through holes (1-3) distributed in a circular pattern is made in the intermediate dielectric layer between the upper cover plate (1-1) and the lower bottom plate (1-2) to connect the top metal layer and the bottom metal layer to form a cylindrical metal wall of the resonant cavity monomer; within the cylindrical metal wall region, the upper cover plate (1-1) is etched upward from the bottom metal layer to part of the intermediate dielectric layer to form a cylindrical groove to embed the microfluidic chip (2); and the lower bottom plate (1-2) is etched downward from the top metal layer to part of the intermediate dielectric layer to form an annular groove, the outer diameter of which is the same as that of the groove of the upper cover plate, and the positions are opposite and overlapped to form a resonant cavity; a short-circuit capacitor column (1-2-1) is formed at the center of the annular groove; For each of the resonant cavity monomers (1), two tube seats (4) are installed above the upper cover plate (1-1) for injecting and extracting the liquid medium to be measured. The two tube seats are respectively connected to the inlet and outlet of the microchannel (2-1) of the microfluidic chip (2) to achieve the connection between the microchannel and the flexible conduit.

3. The microwave sensor according to claim 1, characterized in that: The power divider (3) is a Wilkinson power divider, and its three ports are respectively connected to a circular metal ring (3-4) by microstrip lines, wherein port one (3-1) is used to feed in an excitation signal, and port two (3-2) and port three (3-3) equally divide the power, and are respectively connected to two substrate integrated waveguide reentrant resonant cavity monomers (1) by feed lines (1-1-1).

4. The microwave sensor according to claim 3, characterized in that: The metal ring contains a 100 ohm resistor (3-5), and the outer diameter of the metal ring is 4.09 mm; the width of the microstrip line connected to port one (3-1) is 0.93 m, and the widths of the microstrip lines connected to port two (3-2) and port three (3-3) are both 1 mm.

5. The microwave sensor according to claim 3, characterized in that: The width of the feed line (1-1-1) is 1.77 mm, the feeding depth on both sides of each resonant cavity monomer (1) is 8.7 mm, and the gap w between the coplanar metal of the feed line (1-1-1) and the top layer of the upper cover plate is 1 mm.

6. The microwave sensor according to claim 2, characterized in that: The outer diameter of the cylindrical groove in the upper cover plate (1-1) and the size of the microfluidic chip (2) are both 24 mm.

7. The microwave sensor according to claim 1 or 2, characterized in that: The material of the intermediate dielectric layer between the upper cover plate (1-1) and the lower base plate (1-2) is Rogers 5880, which has a relative dielectric constant of 2.2, a relative magnetic permeability of 1, and a loss tangent of 0.0009.

8. The microwave sensor according to claim 1 or 2, characterized in that: The thickness of the upper cover plate is 1.1 mm, and the thickness of the lower base plate is 1.5 mm.

9. The microwave sensor according to claim 2, characterized in that: The short-circuit capacitor column region includes a second metal through hole (1-2-2) for connecting the upper and lower metal layers of the short-circuit capacitor column. The radius of the second metal through hole (1-2-2) is 0.5 mm.

10. The microwave sensor according to claim 1, characterized in that: The microchannel (2-1) on the microfluidic chip (2) is spiral-shaped, the microfluidic chip substrate is made of PMMA polymer material, the thickness of the microfluidic chip (2) is 0.965 mm, the depth of the microchannel (2-1) is 0.85 mm, the width is 1.1 mm, and the spacing is 0.5 mm.

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