CN112798870A - Microwave differential sensor based on substrate integrated waveguide reentry type resonant cavity and microfluidic technology - Google Patents
Microwave differential sensor based on substrate integrated waveguide reentry type resonant cavity and microfluidic technology Download PDFInfo
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Abstract
A microwave differential sensor based on substrate integrated waveguide dual-in type resonant cavity and microfluidic technology comprises two resonant cavities and a microfluidic chip; the two cavities are composed of an upper cover plate and a lower bottom plate which are overlapped. The middle medium layers of the upper cover plate and the lower bottom plate respectively comprise a plurality of metal through holes which are used for connecting the top metal layer and the bottom metal layer, and the bottom metal of the second layer plate and the top metal of the third layer plate are etched to form a feeder line with a gradually changed appearance. An annular groove is formed in each cavity, and a capacitor column is formed in the middle of each cavity and corresponds to the micro-channel of the chip. The two cavities are respectively used as a sensing resonant cavity and a reference resonant cavity. The sensor is characterized in that two reentrant resonators are skillfully and longitudinally combined, the advantages of high concentration of resonant cavity electric fields and accurate control of trace fluid by a micro-fluidic chip are combined by utilizing a naturally existing metal wall and a special excitation mode between resonant cavities, and the microwave differential sensor which is compact in structure, free from interference of factors such as temperature and humidity, mutually independent in components and capable of being used for liquid dielectric characterization is formed.
Description
Technical Field
The invention belongs to the field of sensors, and particularly relates to a microwave differential sensor combining a resonant cavity and a microfluidic technology.
Background
With the rapid development of microwave technology in various industries (such as military, medicine, food, chemical and meteorology fields), various types of radio frequency microwave devices are gradually developed and applied, and meanwhile, because the electromagnetic properties of the magnetic medium materials used by the high-frequency devices greatly influence the performance parameters of equipment devices, the research on the electromagnetic properties of the magnetic medium materials is paid attention.
There are many methods for measuring the dielectric constant, and the methods are mainly classified into a resonance method and a non-resonance method, and the most typical method of the resonance method is a resonance cavity method. Most material characterization sensors convert the dielectric constant change of the measured sample into a resonant frequency shift, and the main disadvantage of such sensors is the cross-sensitivity to environmental factors (e.g., temperature, differential, etc.), which may cause unnecessary measurement errors and mis-calibration of the sensor. When the environmental condition introduces common mode effect, the differential measurement is an effective method for eliminating measurement error caused by environmental factors. Frequency division based microwave differential sensors are typically comprised of two sensing elements, one of which serves as the sensing and the other as the reference. In the existing differential microwave sensor based on the resonance principle, the following disadvantages basically exist: the coupling between the two sensing elements reduces the sensitivity to small disturbances; the combination of resonators is mostly done in the horizontal direction; the method of enlarging the distance between the components to avoid the coupling between the sensing elements makes the relative size of the overall structure large and also makes the structure less compact.
In addition, simply placing the two resonant cavities used as reference and sensing vertically is difficult to solve the feeding problem, because the common coplanar waveguide feeder line cannot provide equal power for the two cavities simultaneously, the two cavities are unbalanced, and the strip line is directly used, so that the actual process cannot obtain better transmission response. The design of the structure solves the problems and simultaneously manufactures the microwave sensor which can provide resolution ratio for a large dielectric constant measuring range.
Disclosure of Invention
The invention provides a microwave differential sensor based on a substrate integrated waveguide reentry type resonant cavity and a microfluidic technology. The whole differential sensor takes one resonant cavity as a reference and the other resonant cavity as a sensing test cavity, so that the measurement error caused by environmental factors can be eliminated, and the dielectric property of a detected object can be accurately characterized. Meanwhile, the invention utilizes two substrate-based integrated waveguide reentrant resonant cavities, and good electromagnetic shielding is provided between the two cavities, so that coupling between sensing elements is avoided, and the relative size of the whole structure is greatly reduced by adopting a specially designed feeding mode.
The technical scheme of the invention is as follows:
a microwave differential sensor based on a substrate integrated waveguide reentrant resonant cavity and a microfluidic technology comprises two substrate integrated waveguide reentrant resonant cavities which are overlapped up and down and two microfluidic chips which are respectively embedded in the resonant cavities. The resonance cavity is formed by overlapping an upper cover plate and a lower bottom plate, and the middle micro-channel of the micro-fluidic chip is spiral.
The upper cover plate and the lower bottom plate respectively comprise a three-layer structure of a top metal layer, a middle medium layer and a bottom metal layer, and a plurality of rows of metal through holes which are symmetrical along a longitudinal axis and a transverse axis are distributed at the position, close to the edge, of the middle medium layer of each laminate plate and are used for connecting the top metal layer and the bottom metal layer, so that the four-side metal wall of the resonant cavity is formed by the four-side metal wall.
An upper cover plate of the resonant cavity is etched from bottom metal to part of the middle medium layer in an area surrounded by the metal wall to form a groove, and the micro-fluidic chip is embedded in the groove; the lower cover plate is etched from the top metal layer to part of the middle medium layer to form a ring groove, the size of the periphery of the ring groove is the same as that of the periphery of the groove, and the ring groove and the groove form a resonant cavity together; and the central area of the ring groove which is not etched is provided with metal through holes distributed in an array manner to form a capacitor column.
The bottom cover plate of the resonant cavity is etched from the top metal to part of the middle medium layer in the area defined by the metal walls to form a groove, the microfluidic chip is embedded in the groove, the upper cover plate is etched from the bottom metal to part of the middle medium layer to form a ring groove, the size of the periphery of the ring groove is the same as that of the periphery of the groove, and the two layers form another resonant cavity together; and the central area of the ring groove which is not etched is provided with metal through holes distributed in an array manner to form a capacitor column.
The positions of the capacitance columns are the areas with the strongest electric fields in the respective cavities, and the micro-channels of the micro-fluidic chip are distributed corresponding to the areas with the strongest electric fields respectively; the radiuses of the capacitor columns in the two resonant cavities are different, the cavity with the large radius of the capacitor column is a sensing resonant cavity, and the cavity with the small radius of the capacitor column is a reference resonant cavity; the bottom metal and the top metal, which are in direct contact between the two resonator cavities, longitudinally isolate the two cavities so that the electromagnetic field is well confined in the respective cavities.
The left end and the right end of the upper layer cover plate and the lower layer bottom plate of the resonant cavity are wider than those of the upper layer cover plate and the lower layer bottom plate of the resonant cavity and serve as feeder line setting areas, and two feeder lines which are symmetrical about a longitudinal axis are arranged in the left area and the right area of the top layer metal layer of the upper layer cover plate and are used for feeding excitation signals into the resonant cavity from two sides. The feeder adopts a microstrip line and strip line structure form; the feeder line with the same structure is also arranged at the position, overlapped with the feeder line, of the bottom metal layer of the lower bottom plate of the resonant cavity, and the feeder line provides equal power for the longitudinal cavities, so that the two cavities can resonate simultaneously.
Furthermore, the metal through holes of the metal wall surrounding the resonant cavity are distributed close to the edge positions of the upper cover plate and the lower bottom plate and are symmetrical along the longitudinal axis and the transverse axis, the resonant cavity is also symmetrical along the longitudinal axis and the transverse axis, namely the resonant cavity can be in various shapes symmetrical along the longitudinal axis and the transverse axis, but preferably, the groove and the ring groove are both circular, and the resonant cavity is also formed to be circular.
Furthermore, the feed structure has five parts, the first part is a gradient microstrip line, the second part is a rectangular strip line connected with the gradient microstrip line, the third part is a trapezoid directly connected with the rectangular strip line, the fourth part and the fifth part are welding-free terminal connector grounding devices arranged for meeting the feed requirement, and the fourth part and the fifth part are two whole bodies which are positioned at two sides of the first part and are symmetrical relative to the first part and are composed of a triangle and a rectangle.
Furthermore, the first part of the gradually-changed microstrip line of the feed structure is obtained by gradually changing a rectangular transmission line with the length of 8mm, the width of 3mm and the characteristic impedance of 50 Ω, the width of the microstrip line at the feed port is 0.6mm, the microstrip line gradually increases from the feed port to the center of the cavity, gradually changes to the width of 3mm after the length of 4mm, at the moment, the gradually changing is suspended, and gradually changes to the width of 1.11mm after the length of 1.5mm and 2.5mm from the width of 3 mm. The reason that the width of the feed port of the feeder line is gradually changed to 0.6mm is to more directly connect with an external welding-free terminal connector for actual test, which is beneficial to the actual test.
Further, the length of the rectangular strip line of the second part of the feed structure is 2mm, the width is 1.11mm, the trapezoid of the third part of the feed structure is a structure of strip line-to-substrate integrated waveguide, the upper bottom of the trapezoid is connected with the rectangular strip line of the second part and is 1.11mm, the lower bottom of the trapezoid is 5.55mm, and the height is 13mm, and the trapezoid is used for feeding signals into the cavity and improving transmission response; the same structure is etched at the position where the bottom layer metal of the lower bottom plate of the upper resonant cavity body is contacted with the top metal of the cover plate of the lower resonant cavity body.
Furthermore, the lower bottom plate of the resonant cavity is etched from the top metal to the bottom metal at the position corresponding to the feeder line area arranged on the upper cover plate to form a notch for installing the welding-free terminal connector.
Furthermore, the upper cover plate of the upper resonant cavity and the bottom cover plate of the lower resonant cavity are provided with liquid inlet and outlet holes communicated with micro channels of respective micro-fluidic chips. The liquid inlet and outlet holes can be open through holes symmetrically arranged along the diagonal line of the resonant cavity, and a tube seat is correspondingly arranged above each through hole and used for connecting out a flexible guide tube to realize the injection and extraction of the liquid medium to be detected.
The beneficial effects of the invention are as follows:
1. the two substrate integrated waveguides are skillfully combined longitudinally, the cavity with the column with the larger radius has a lower frequency point and is used for sensing, and the cavity with the column with the smaller radius has a higher frequency point and is used for reference. In addition, the planar structure of the substrate integrated waveguide reentrant cavity also makes it easier to integrate with other planar circuit structures. Because the two resonant cavities are longitudinally combined and a natural metal wall exists between the two resonant cavities, the electromagnetic isolation is excellent, so that the mutual coupling of the sensing elements is avoided, and the whole structure is very compact.
The invention adopts a differential structure form, can perform differential measurement on the dielectric constant of the liquid medium, and eliminates the influence of environmental factors by adopting a relative measurement mode. Compared with a method for preventing coupling by pulling the ground distance of the sensing element away, the method has the advantages that the relative size is greatly reduced, and the frequency point of the resonator can be reduced by increasing the radius of the central capacitance column according to the characteristics of the reentrant cavity, namely the wavelength of the corresponding frequency point is increased, so that the relative size of the structure is reduced. The invention has compact structure, light and thin volume and easy processing and manufacturing, can be realized by utilizing the existing very mature standard printed circuit board process and photoetching process, and effectively reduces the manufacturing cost.
2. The feeder line adopts a structure of 'microstrip line + strip line' and a technology that the strip line is connected with the substrate integrated waveguide, can provide equal power for two longitudinal cavities simultaneously, can greatly reduce insertion loss, solves the problem that the good feeding effect is difficult to achieve due to the vertical arrangement of two microwave resonant cavities, enables the structure to obtain better transmission response, and simultaneously does not reduce the sensitivity of the sensor to small disturbance. The invention can obtain enough Q value, and the quality factor is increased along with the enlargement of the measuring range, so the invention is still applicable to the measurement of higher dielectric constant.
3. The invention skillfully designs the micro-channel on the micro-fluidic chip into a spiral shape, places the micro-fluidic chip in a highly concentrated area of the induced electric field of the resonant cavity, and injects the medium to be tested into the micro-channel to test. By improving the depth, width, etc. of the spiral microchannel, the overall test sensitivity can be significantly increased. The polytetrafluoroethylene is used as the material of the microfluidic chip, the material has low tangent angle consumption, the high quality factor of the substrate integrated waveguide reentry cavity cannot be obviously reduced, and meanwhile, the polytetrafluoroethylene has great chemical inertness and is not easy to react with most reagents, so that the application range of the designed sensor is wide.
Drawings
Fig. 1 is a schematic cross-sectional view of a differential sensor according to the present invention;
fig. 2(a) is a schematic perspective assembly of the differential sensor proposed by the present invention;
fig. 2(b) is a schematic exploded perspective view of the components of the differential microwave sensor according to the present invention;
fig. 3(a) is a schematic front view of a first dielectric substrate of the differential sensor proposed by the present invention;
FIG. 3(b) is a schematic backside view of a first dielectric substrate of the differential sensor proposed by the present invention;
FIG. 4(a) is a schematic front view of a second dielectric substrate of the differential sensor proposed by the present invention;
FIG. 4(b) is a schematic backside view of a second dielectric substrate of the differential sensor proposed by the present invention;
FIG. 5(a) is a schematic front view of a third dielectric substrate of the differential sensor proposed by the present invention;
FIG. 5(b) is a schematic backside view of a third dielectric substrate of the differential sensor proposed by the present invention;
fig. 5(c) is an enlarged view of a feeding portion of a third dielectric substrate of the differential sensor proposed by the present invention;
fig. 6(a) is a schematic front view of a fourth dielectric substrate of the differential sensor proposed by the present invention;
fig. 6(b) is a schematic backside view of a fourth dielectric substrate of the differential sensor proposed by the present invention;
FIG. 7(a) is an overall schematic view of the microfluidic layer of the differential sensor proposed by the present invention;
FIG. 7(b) is a schematic front view of a microfluidic layer of the differential sensor proposed by the present invention;
fig. 8 is a transmission response curve of the differential sensor proposed by the present invention under different differential conditions.
Detailed Description
For better illustration of the design process and purposes, the present invention is further described below with reference to the following examples and the accompanying drawings:
as shown in fig. 1 to fig. 7(a) and fig. 7(b), the microwave differential sensor based on the substrate integrated waveguide reentry cavity and the microfluidic technology proposed by the present invention comprises two substrate integrated waveguide reentry resonant cavities and two microfluidic chips embedded in the resonant cavities.
The resonant cavity (1) is formed by overlapping an upper cover plate (1-1) and a lower bottom plate (1-2). The upper cover plate (1-1) and the lower bottom plate (1-2) both comprise three layers of structures, namely a top metal layer, a middle dielectric layer and a bottom metal layer. The resonant cavity (3) is formed by overlapping an upper cover plate (3-1) and a lower bottom plate (3-2). The upper cover plate (3-1) and the lower bottom plate (3-2) both comprise three layers of structures, namely a top metal layer, a middle dielectric layer and a bottom metal layer.
The four-layer plate with the two cavities is fixed by screws with the diameter of 2mm in an actual structure, and the screws do not influence the work of the resonant cavity.
The materials of the intermediate dielectric layers of the four-layer plates are the same, in the embodiment, the material is Rogers 4350, the relative dielectric constant is 3.66, the relative magnetic permeability is 1, and the loss tangent angle is 0.004. The four layers each have the same thickness of 1.594 mm.
The overall length and the width of the upper-layer cover plate (1-1) and the lower-layer bottom plate (1-2) are the same, and preferably, the length is 65mm, and the width is 62 mm. The overall length and width of the upper cover plate (3-1) and the lower bottom plate (3-2) are the same, and preferably, the length is 78mm and the width is 65 mm.
The middle medium layers of the upper cover plate (1-1), the lower base plate (1-2), the upper cover plate (3-1) and the lower base plate (3-2) are etched with a plurality of metalized through holes in the central area, and the metalized through holes are uniformly distributed on the periphery of the resonant cavity and two sides of the feeder line and are used for being equivalent to the metal boundary of the resonant cavity, namely forming the metal wall of the resonant cavity. Preferably, the diameter of the metallized through holes is 0.8mm, and the distance between two adjacent through holes is 1.11 mm.
A circular groove is etched in the central area of the upper cover plate (1-1) from the bottom layer to the top, the area of the groove is the same as that of the microfluidic chip (2), and the depth of the groove is the same as that of the microfluidic chip. The micro-fluidic chip (2) is embedded into the circular groove with the right side facing upwards, and the right side of the chip is adhered into the groove of the upper cover plate (1-1) by insulating glue, and the adhesion aims to seal the micro-channel, so that the leakage of a medium to be detected is prevented. Similarly, a circular groove is etched in the central area of the lower bottom plate (3-2) from the top layer to the bottom layer, the area of the groove is the same as that of the microfluidic chip (4), and the depth of the groove is the same as that of the microfluidic chip. The microfluidic chip (4) is embedded into the circular groove with the front surface facing downwards, and the front surface of the chip is bonded in the groove of the lower base plate (3-2)) by using insulating glue, wherein the bonding purpose is to seal the micro-channel so as to prevent the leakage of the measured medium.
Correspondingly, an annular groove is etched from the top layer to the bottom layer (1-2) of the sensing cavity, namely the resonant cavity (1), around the central region, the center of the annular groove forms a circular capacitor column (1-2-1), and the reference cavity, namely the resonant cavity (3), is also provided with the same arrangement.
Preferably, the depths of the circular groove and the annular groove of the four-layer plate are both 0.85mm, and the parameters of the two microfluidic chips in the resonant cavity are also the same.
The circular capacitor column (1-2-1) area comprises a through hole array consisting of 13 metal through holes (1-2-2) for realizing the metallization of the capacitor column (1-2-1). The size parameters of the metal through holes (1-2-2) comprise the radius of the metal through holes and the center distance between adjacent metal through holes. Preferably, the radius of the metal through holes 1-2-2 is 1mm, and the center distance between two adjacent metal through holes is 3.45 mm.
The two substrate integrated waveguide reentrant type resonant cavities have different radiuses of circular capacitor columns in the central areas, and the cavity with the columns with larger radiuses is lower in frequency point and used for sensing, namely a resonant cavity (1). The cavity with the column with the smaller radius has a higher frequency point and is used as a reference, namely the resonant cavity (3), and the radiuses of the two capacitor columns are respectively 10mm and 8.5 mm.
Referring to fig. 5(c), the feeding structure (3-1-3) has five parts (i.e., the fifth part in the figure), the first part is a tapered microstrip line, the second part is a rectangular strip line connected to the tapered microstrip line, the third part is embodied as a trapezoid directly connected to the rectangular strip line, and the fourth and fifth parts are two triangles and rectangles which are symmetrical with respect to the tapered microstrip line of the first part. The first part of the gradual change microstrip line of the feed structure (3-1-3) is gradually changed by a rectangular transmission line with the length of 8mm, the width of 3mm and the characteristic impedance of 50 omega, the width of the microstrip line at the feed port is 0.6mm, then the width gradually increases from the feed port to the center of the cavity, after the length of 4mm, the microstrip line gradually changes to the width of 3mm, at the moment, the gradual change is suspended, after the length of 1.5mm, the microstrip line gradually changes from 3mm to the width of 1.11mm (after the length of 2.5 mm).
The second part of the rectangular strip line of the feed structure (3-1-3) is 2mm in length and 1.11mm in width. The third part of the feed structure (3-1-3) is a trapezoid (namely, the third section in the figure) directly connected with the strip line of the second part, the trapezoid is a structure of a strip line-to-substrate integrated waveguide, the upper bottom of the trapezoid is connected with the strip line and is 1.11mm, the lower bottom of the trapezoid is 5.55mm, the height of the trapezoid is 13mm, and the trapezoid is used for feeding a signal into the cavity to improve transmission response. The bottom metal of the plate (1-2) is in contact with the top metal of the plate (3-1) at the same position as the second and third portions.
The trapezoid and the rhombus metal etching are used for meeting the requirement of input port impedance matching, and two resonant cavities can be excited simultaneously, so that excellent transmission response is realized. And thirdly, parts are formed by etching patterns on the same metal plate, namely the top metal of the upper cover plate (3-1) through a PCB process.
In addition, the fourth fifth part of the above-mentioned feeding structure (3-1-3) is a welding-free terminal connector grounding device provided for satisfying the feeding, and the specific shape parameters of the device are shown in fig. 5(c), which are two integers consisting of a triangle and a rectangle.
In order to use the welding-free terminal connector, the lower bottom plate (3-2) is etched from the top metal to the bottom metal at the position corresponding to the feed end of the upper cover plate (3-1) to form a notch, the etching length is 16.425mm, and the etching width is 6 mm.
A plurality of metalized through holes (3-1-4) are etched on two sides of a feed line on the upper cover plate (3-1), the radius of each metal through hole is 0.4mm, the distance between the centers of the through holes is 1.11mm, so that the welding-free terminal connector can be used, screw holes are also etched, the diameter of each screw hole is 1.98mm, and the distance between the two screw holes is 9.53 mm.
In order to lead out and lead out the liquid to be measured, the middle medium layers of the upper cover plate (1-1) and the lower bottom plate (3-2) are provided with two open through holes which are symmetrical about the diagonal line of the resonant cavity, and the radius of each through hole is 1 mm. The through holes are provided with pipe seats (5) and (6), the two pipe seats are connected with a flexible conduit respectively and used for extracting and injecting the liquid to be detected, the circle center of the pipe seat (5) and the circle center of the open type through hole (1-1-2) are positioned on the same vertical straight line, and similarly, the circle center of the pipe seat (6) and the circle center of the open type through hole (3-2-2) are positioned on the same vertical straight line.
Referring to fig. 7(a) and 7(b), a one-way conductive serpentine micro channel 2-1 is etched on the front surface of the micro fluidic chip (2), the micro channel is a central symmetrical pattern, and the symmetrical center is the center of the micro fluidic chip 2. Two sections of same similar-cone-shaped switching structures (2-1-1) are arranged in the starting point and the end point region of the micro-channel 2-1 and are used for preventing the sample to be detected from leaking at the starting point and the end point of the micro-channel. The circle centers of the starting point and the end point of the micro-channel 2-1 and the circle center of the open type through hole (1-1-2) are positioned on the same vertical straight line. The two microfluidic chips (4) and (2) have the same structure.
In this embodiment, the material of the microfluidic chip is polytetrafluoroethylene, and preferably, the thickness of the microfluidic chip 2 is 0.8mm, the depth of the micro channel 2-1 is 0.455mm, the width is 1.5mm, and the distance is 0.8 mm.
Fig. 8 shows the variation curve of the resonant frequency point of the microwave differential sensor pair provided by the invention for samples with different relative dielectric constants. It can be seen that when the micro channels in the two cavities are completely filled with air, the two substrate integrated waveguide re-entry type resonant cavities respectively excite strong resonance at 2.469GHz and 2.635GHz, and at this time, the electric field in the resonant cavities is strictly limited in the middle area sandwiched by the capacitor column and the upper plate. When a medium to be measured is uniformly injected into the micro-channel (2) of the cavity (1), the medium generates a polarization effect under the action of a highly concentrated electric field in the resonant cavity, so that an electromagnetic field in the resonant cavity is disturbed, the resonant frequency point of the sensor is changed finally, but the resonant point at higher frequency is unchanged all the time, because the resonant cavity (3) corresponding to the resonant cavity is not filled with any medium to be measured and the existing environmental factors are not changed, and because the two resonant cavities have natural electromagnetic isolation metal walls, the two cavities operate independently and do not interfere with each other. As shown in FIG. 8, when the relative dielectric constant of the measured medium is increased from 1 to 80, the resonant frequency point of the sensor cavity (1) is reduced from 2.469GHz to 2.083GHz, but the frequency point of the resonant cavity (2) is always unchanged, and the sensor still has resolution even if the range of the measured medium is increased.
The invention combines the substrate integrated waveguide technology and the microfluidic technology, introduces the microfluidic chip into the substrate integrated waveguide re-entry resonant cavity, and combines the method of connecting the microstrip line, the strip line and the strip line with the substrate integrated waveguide (the third step in figure 5 (c)), the natural electromagnetic isolation metal wall of the re-entry resonant cavity and the advantages of highly concentrated electric field of the re-entry resonant cavity and accurate control of trace fluid by the microfluidic chip, thereby obtaining the microwave differential sensor which has quite compact structure, is not interfered by environmental factors and can be used for liquid dielectric characterization.
The present invention is not limited to the above-described embodiments, and various modifications and variations of the invention are intended to be included within the scope of the claims and the equivalent technology of the present invention if they do not depart from the spirit and scope of the present invention.
Claims (9)
1. A microwave differential sensor based on a substrate integrated waveguide reentrant resonant cavity and a microfluidic technology is characterized in that: comprises two resonance cavities (1) and (3) which are overlapped up and down and microfluidic chips (2) and (4) which are respectively embedded in the resonance cavities; the two resonant cavities are formed by overlapping an upper cover plate and a lower bottom plate, and the upper cover plate and the lower bottom plate respectively comprise a top metal layer, a middle dielectric layer and a bottom metal layer; the upper cover plate and the lower bottom plate of each resonant cavity are respectively provided with a plurality of metal through holes for connecting the top metal layer and the bottom metal layer in the middle dielectric layer, and the metal through holes are surrounded to form a metal wall of the resonant cavity;
an upper layer cover plate (1-1) of the resonant cavity (1) is etched from bottom layer metal to part of the middle medium layer in an area surrounded by metal walls to form a groove, and the microfluidic chip (2) is embedded in the groove; the lower layer cover plate (1-2) is etched from the top layer metal downwards to a part of the middle medium layer to form a ring groove, the size of the periphery of the ring groove is the same as that of the periphery of the groove, and the ring groove and the groove form a resonant cavity together; the central area of the ring groove which is not etched is provided with metal through holes (1-2-2) distributed in an array manner to form a capacitor column (1-2-1);
a bottom cover plate (3-2) of the resonant cavity (3) is etched from the top metal to part of the middle medium layer in an area defined by the metal walls to form a groove, the microfluidic chip (4) is embedded in the groove, an upper cover plate (3-1) is etched from the bottom metal to part of the middle medium layer to form a ring groove, the size of the periphery of the ring groove is the same as that of the periphery of the groove, and the two parts form another resonant cavity together; the central area of the ring groove which is not etched is provided with metal through holes (3-1-2) distributed in an array manner to form a capacitor column (3-1-1);
the positions of the capacitor columns (1-2-1) and the capacitor columns (3-1-1) are regions with the strongest electric fields in respective cavities, and micro-channels of the micro-fluidic chip (2) and the micro-fluidic chip (4) are distributed corresponding to the regions with the strongest electric fields respectively; the radiuses of the capacitor columns in the two resonant cavities (1) and (3) are different, the cavity with the large radius of the capacitor column is a sensing resonant cavity, and the cavity with the small radius of the capacitor column is a reference resonant cavity; the bottom layer metal and the top layer metal which are in direct contact between the two resonant cavities (1) and (3) longitudinally isolate the two cavities, so that the electromagnetic field is well bound in the respective cavities;
the left and right ends of an upper layer cover plate and a lower layer bottom plate of the resonant cavity (3) are wider than those of the upper layer cover plate and the lower layer bottom plate of the resonant cavity (1) and serve as feeder line setting areas, two feeder lines (3-1-3) which are symmetrical about a longitudinal axis are arranged in the left and right areas of a top layer metal layer of the upper layer cover plate (3-1) and feed in from the two sides of the resonant cavity (3), and the feeder lines are in a microstrip line and strip line structure form; the feeder line with the same structure is also arranged at the position, overlapped with the feeder line (3-1-3), of the bottom metal layer of the lower bottom plate (1-2) of the resonant cavity (1), and the feeder line provides equal power for the longitudinal cavities, so that the two cavities can resonate simultaneously.
2. A microwave differential sensor according to claim 1, wherein: the metal through holes of the metal wall which forms the resonant cavity are distributed close to the edge positions of the upper cover plate and the lower bottom plate and are symmetrical with the transverse axis along the longitudinal axis, and the resonant cavity is also symmetrical with the transverse axis along the longitudinal axis.
3. A microwave differential sensor according to claim 2, wherein: the groove and the ring groove are both circular, and the formed resonant cavity is also circular.
4. A microwave differential sensor according to claim 1, 2 or 3, wherein: the feed structure (3-1-3) is provided with five parts, wherein the first part is a gradient microstrip line, the second part is a rectangular strip line connected with the gradient microstrip line, the third part is a trapezoid directly connected with the rectangular strip line, the fourth part and the fifth part are welding-free terminal connector grounding devices arranged for meeting the feed, and the fourth part and the fifth part are two whole bodies which are positioned on two sides of the first part and are symmetrical relative to the first part and are composed of a triangle and a rectangle.
5. The microwave differential sensor of claim 4, wherein: the first part of the gradual change microstrip line of the feed structure (3-1-3) is gradually changed by a rectangular transmission line with the length of 8mm, the width of 3mm and the characteristic impedance of 50 omega, the width of the microstrip line at a feed port is 0.6mm, the microstrip line gradually increases from the feed port to the center of the cavity, gradually changes to the width of 3mm after the length of 4mm, the gradual change is suspended at the moment, and gradually changes to the width of 1.11mm from the width of 3mm to the width of 2.5mm after the length of 1.5 mm.
6. The microwave differential sensor of claim 5, wherein: the second part of the rectangular strip line of the feed structure (3-1-3) is 2mm in length and 1.11mm in width, the trapezoid of the third part of the feed structure (3-1-3) is a strip line-substrate-converted integrated waveguide structure, the upper base of the trapezoid is connected with the second part of the rectangular strip line and is 1.11mm, the lower base of the trapezoid is 5.55mm and is 13mm in height, and the trapezoid is used for feeding signals into the cavity and improving transmission response; the same structure is etched at the position where the bottom layer metal of the lower bottom plate (1-2) is contacted with the top metal of the cover plate (3-1).
7. The microwave differential sensor of claim 5, wherein: the lower-layer bottom plate (3-2) of the resonant cavity (3) is etched from top-layer metal to bottom-layer metal at a position corresponding to the region where the feeder (3-1-3) is arranged on the upper-layer cover plate (3-1) to form a notch for installing a welding-free terminal connector; preferably, the etch length is 16.425mm and the width is 6 mm.
8. A microwave differential sensor according to claim 1, 2 or 3, wherein: liquid inlet and outlet holes communicated with micro-channels of respective micro-fluidic chips are arranged on an upper cover plate (1-1) of the resonant cavity (1) and a bottom cover plate (3-2) of the resonant cavity (3); the micro-channels of the micro-fluidic chips (2) and (4) are spiral, the depth is 0.455mm, the width is 1.5mm, and the distance is 0.8 mm; preferably, the starting point and the terminal area of the micro-flow channel (2-1) and the micro-flow channel (4-1) are both provided with a section of conical-like switching structure (2-1-1) and a section of conical-like switching structure (4-1-1).
9. A microwave differential sensor according to claim 1, 2 or 3, wherein: the material of the intermediate medium layer of the upper cover plate and the lower base plate is Rogers 4350, the relative dielectric constant is 3.66, the relative magnetic conductivity is 1, and the loss tangent angle is 0.004.
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