CN113740353B - Differential humidity sensor based on substrate integrated waveguide dual-entry resonant cavity - Google Patents
Differential humidity sensor based on substrate integrated waveguide dual-entry resonant cavity Download PDFInfo
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Abstract
A differential humidity sensor based on a substrate integrated waveguide dual-entrance resonant cavity is characterized in that two re-entrance resonant cavities are longitudinally combined together and respectively serve as a sensing resonant cavity and a reference resonant cavity, a sensitive material capable of adsorbing water molecules in humid air is deposited in a groove region of the sensing resonant cavity, and the water molecules are diffused into the sensitive material to cause the change of intrinsic characteristics of the sensitive material, so that the interaction between a strong induction electric field and a moisture absorption material is excited in the sensing resonant cavity. The interaction between the strong induced electric field and the humid air medium is excited in the reference resonant cavity, and the metal grids corresponding to the two cavities, the middle air-filled medium substrate and the capacitor column metallized through holes are utilized, so that the humidity sensor which has the advantages of compact structure, free inlet and outlet of humid air, strong up-and-down circulation, rich water molecules of the humid air, sufficient reaction with the moisture absorption material in the cavity and mutually independent components and parts, high sensitivity and high resolution is obtained.
Description
Technical Field
The invention belongs to the field of sensors, and particularly relates to a microwave passive sensor suitable for detecting air relative humidity.
Background
Humidity is an important index in environmental quality monitoring, and humidity detection has great significance in various laboratories and industrial applications, such as electronic equipment manufacturing, food processing, medical storage, pharmaceutical manufacturing, large-scale equipment operation and the like, which have high requirements on environmental humidity. Therefore, the research and development of the high-performance humidity sensor have high practical value in various fields.
Traditional humidity sensors such as resistive sensors, capacitive sensors and piezoelectric sensors all work at lower frequencies and cannot be directly applied to modern radio frequency sensing detection systems. In order to solve the problem, scientific research personnel have recently proposed the design scheme of the microwave passive humidity sensor. Microwave passive humidity sensors are favored for their low cost, high design flexibility, ease of integration with rf sensing detection systems, and other advantages. However, the currently reported microwave passive humidity sensing and monitoring devices still have the problems of large relative size, low sensing sensitivity, low quality factor and the like, and the practical application range of the devices is severely limited. Frequency division based microwave differential sensors typically consist of two sensing devices, one of which serves as the sensing and the other as the reference. And most of the components are combined in the horizontal direction, so that the relative size of the whole structure is large, and the structure is not compact enough.
The applicant has proposed a humidity sensor based on a substrate integrated waveguide re-entry resonant cavity, which has low circulation of a wet air medium, is unable to freely enter and exit, is slow in response and recovery during humidity sensing, and has low resolution because an air through hole is small and the inside of the cavity is a closed structure.
Disclosure of Invention
The invention provides a differential humidity sensor based on a substrate integrated waveguide dual-entrance resonant cavity, which solves the problem that humid air circulates up and down in two resonant cavities, so that the high quality factor characteristic of the resonant cavity is well maintained, and the high-resolution detection of the relative humidity of the air is realized.
The design idea of the invention is to vertically place the resonant cavities for sensing and reference, and longitudinally provide equal power for the two cavities simultaneously by adopting a special feed line structure of coplanar waveguide and strip line. The two resonant cavities are vertically arranged, and the naturally-existing metal walls have good electromagnetic shielding performance, but simultaneously isolate the possibility of up-and-down circulation of humid air.
The technical scheme of the invention is as follows:
a differential humidity sensor based on a substrate integrated waveguide dual-in type resonant cavity comprises two resonant cavities which are superposed up and down and two feeder lines; the resonant cavity is composed of three medium substrates of an upper layer, a middle layer and a lower layer, and each medium substrate comprises a top metal layer, a middle medium layer and a bottom metal layer.
The resonant cavity of the upper resonant cavity is surrounded by a circle of metalized through holes, the metalized through holes are etched at the same positions of the middle dielectric layers of the three dielectric substrates, and the top metal layer and the bottom metal layer are connected to be equivalent to the metal wall of the resonant cavity.
In the resonant cavity region of the upper resonant cavity, the middle dielectric layer of the upper dielectric substrate is provided with metal through holes distributed in an array manner, a rectangular metal is reserved on the bottom metal layer in the corresponding metal through hole array region, the rest of the rectangular metal is etched away, the rectangular metal and the metalized through holes jointly form a capacitor column structure of the resonant cavity, and the capacitor column is located in the region with the strongest electric field in the cavity. The middle medium substrate is completely dug through from the top metal layer to the bottom metal layer in the resonant cavity region to form an air filling region; and the lower dielectric substrate is etched from the top metal to part of the middle dielectric layer in the resonant cavity region to form a groove, and the surface size of the groove is the same as that of the rectangular metal surface to form a sensing function region. And etching the metallized through hole array around the groove in the middle dielectric layer of the lower dielectric substrate to form a metal grid.
The lower resonant cavity and the upper resonant cavity are symmetrical and have the same structure, the capacitor columns in the two resonant cavities have different sizes, the cavity with the large size of the capacitor column is a sensing resonant cavity, and the cavity with the small size of the capacitor column is a reference resonant cavity.
The bottom and top layers of metal and the metal grid, which are in direct contact between the upper and lower resonant cavities, longitudinally isolate the cavities so that the electromagnetic fields are well confined in the respective cavities.
The upper resonant cavity and the lower resonant cavity realize the free inlet and outlet of the humid air through the metalized through holes of the respective capacitor columns, the metal grating and the air filling type medium substrate.
The feeder lines are arranged on the bottom layer metal and the top layer metal which are in direct contact between the upper resonant cavity and the lower resonant cavity and are symmetrically distributed along the transverse axis.
The beneficial effects of the invention are as follows:
1. the two substrate integrated waveguides are skillfully combined longitudinally, the cavity with the capacitor column with the larger size has a lower frequency point and is used for sensing, and the cavity with the capacitor column with the smaller size has a higher frequency point and is used for reference.
The invention adopts a differential structure form to carry out differential sensing detection on the environmental humidity, and deposits a sensitive material which can absorb water molecules in humid air in a sensing function area of a sensing resonant cavity, namely a groove area, wherein the water molecules are diffused into the sensitive material to cause the change of intrinsic characteristics, for example, the effective dielectric constant of the material is obviously improved, thereby the interaction between an electric field and a moisture absorption material is strongly induced in the cavity of the sensing resonant cavity; the moisture absorption material is not deposited in the sensing function area in the reference resonant cavity, and only the interaction between the strong induced electric field and the humid air medium is excited, so that the sensing sensitivity of the sensor is obviously improved.
2. According to the differential humidity sensor provided by the invention, a humid air medium enters the resonant cavity through the metalized through hole of the reentrant capacitor column, and water molecules of humid air can be better enriched in a sensing function area in the resonant cavity by utilizing a space provided by an air filling area of the intermediate medium substrate, so that a humidity sensing function is realized. Meanwhile, each metal through hole of the metal grating corresponds to each other in the vertical direction one by one, so that the humid air can flow up and down in the two resonant cavities.
It is worth noting that the metal through holes forming the reentrant capacitance column and the metal grating only allow the wet air to enter and exit, while the electromagnetic waves in the two resonant cavities cannot leak from the metallized through holes, the metal grating avoids the mutual coupling between the sensing elements of the two cavities, and the metallized through holes of the reentrant capacitance column avoid the radiation of the electromagnetic waves to the free space, so that the electromagnetic fields are well constrained in the respective cavities. Because the diameters of the metallized through holes are all smaller than lambda/2, the distance between the adjacent through holes is larger than 60/lambda (lambda is the wavelength corresponding to the working frequency point of the resonant cavity), and the porosity is smaller than fifty percent, the design requirements of the metal grating theory on the diameter, the distance and the porosity of the through holes are met. The resonant cavity can still be considered a closed structure for electromagnetic waves. The characteristic can well maintain the high quality factor characteristic of the resonant cavity, thereby realizing the high-resolution detection of the relative humidity of the air.
3. The feeder line of the invention adopts a structure of 'coplanar waveguide + strip line' and a technology that the strip line is connected with the substrate integrated waveguide, thereby not only providing equal power for two longitudinal cavities, but also greatly reducing insertion loss. Compared with the complex feeder line design for two vertically placed microwave differential sensors, the feeder line is designed in an integrated structure, the coplanar waveguide is used for replacing the microstrip line, and the strip line is formed by extending the coplanar waveguide, so that a good feeding effect can be achieved, and the structure can obtain better transmission response.
4. The double-substrate integrated waveguide reentrant resonant cavity structure provided by the invention has resonant frequency points with adjustable height, can realize flexible adjustment of working frequency points by simply adjusting and optimizing key structure parameters in the resonant cavity under the condition of not changing the overall size of the resonant cavity, and has wider application range.
Drawings
FIG. 1 is a schematic cross-sectional view of a differential humidity sensor according to the present invention;
FIG. 2 is an exploded perspective view of the components of the differential humidity sensor of the present invention;
FIG. 3 (a) is a schematic front view of a first dielectric substrate of the differential humidity sensor of the present invention;
FIG. 3 (b) is a schematic backside view of the first dielectric substrate of the differential humidity sensor of the present invention;
FIG. 4 (a) is a schematic front view of second and fifth dielectric substrates of the differential humidity sensor of the present invention;
FIG. 4 (b) is a schematic backside view of the second and fifth dielectric substrates of the differential humidity sensor of the present invention;
FIG. 5 (a) is a schematic front view of a third dielectric substrate of the differential humidity sensor of the present invention;
FIG. 5 (b) is a schematic backside view of a third dielectric substrate of the differential humidity sensor of the present invention;
FIG. 6 (a) is a schematic front view of a fourth dielectric substrate of the differential humidity sensor of the present invention;
FIG. 6 (b) is a schematic backside view of a fourth dielectric substrate of the differential humidity sensor of the present invention;
fig. 6 (c) is an enlarged view of a feeding portion of a fourth dielectric substrate of the differential humidity sensor according to the present invention;
FIG. 6 (d) is an enlarged view of the feed line of the differential humidity sensor proposed by the present invention;
FIG. 7 (a) is a schematic front view of a sixth dielectric substrate of the differential humidity sensor of the present invention;
FIG. 7 (b) is a schematic backside view of a sixth dielectric substrate of the differential humidity sensor of the present invention;
FIG. 8 (a) is a graph of the transmission response of a differential humidity sensor according to the present invention under room temperature conditions for sensing the deposition of a sensitive material in a resonant cavity and the non-deposition of a sensitive material;
FIG. 8 (b) is a graph of the relationship between the sensing resonant frequency and the relative humidity of the environment after a layer of sensitive material is deposited in the sensing resonant cavity of the differential humidity sensor according to the present invention.
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 differential humidity sensor based on substrate integrated waveguide dual-entry resonant cavity proposed by the present invention comprises two stacked resonant cavities and two feeder lines (3) of "coplanar waveguide + strip line".
The upper resonant cavity (1) is composed of an upper dielectric substrate (1-1), a middle dielectric substrate (1-2) and a lower dielectric substrate (1-3). The lower resonant cavity (2) is composed of an upper dielectric substrate (2-1), a middle dielectric substrate (2-2) and a lower dielectric substrate (2-3). Each dielectric substrate is provided with a top metal layer, a middle dielectric layer and a bottom metal layer.
The resonant cavity of the upper resonant cavity (1) is surrounded by a circle of metallized through holes (1-1-4), the metallized through holes (1-1-4) are etched at the same positions of middle medium layers of three medium substrates, and a top metal layer and a bottom metal layer are connected to be equivalent to a metal wall of the resonant cavity. And similarly, the resonant cavity of the lower resonant cavity (1) is also surrounded by a circle of metallized through holes, and the metallized through holes are etched at the same positions of the middle dielectric layers of the three dielectric substrates, connect the top metal layer and the bottom metal layer and are equivalent to the metal wall of the resonant cavity. Preferably, the diameter of the metallized through hole is 0.8mm, and the distance between two adjacent through holes is 1.3mm.
The six dielectric substrates of the two cavities are fixed by 14 screws with the diameter of 1.6mm 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 six dielectric substrates are the same, in this embodiment, the material is Rogers 4350, the relative dielectric constant of the material is 3.66, the relative magnetic permeability of the material is 1, and the loss tangent angle of the material is 0.004. The thicknesses of the intermediate medium substrates (1-2) and (2-2) are the same, and the thickness is 0.578mm. The other four dielectric substrates have the same thickness, and the thickness is 1.594mm.
The overall length and width of the six dielectric substrates are the same, and preferably, the length and width are both 60mm.
The upper-layer dielectric substrate (1-1) of the upper resonant cavity (1) is provided with metal through holes (1-1-1) distributed in an array mode in the central area of the resonant cavity, a rectangular metal (1-1-2) corresponding to the array area of the metal through holes (1-1-1) is reserved in the bottom metal layer and is not etched, and the bottom metal layers of the rest parts in the resonant cavity are etched. The rectangular metal (1-1-2) and the metal through hole (1-1-1) jointly form a capacitance column structure (1-1-3) of the resonant cavity.
Similarly, metal through holes (2-3-1) distributed in an array mode are formed in the center area of the resonant cavity of the lower dielectric substrate (2-3) of the lower resonant cavity (2), a rectangular metal (2-3-2) corresponding to the array area of the metal through holes (2-3-1) is reserved in the top metal layer and is not etched, and the bottom metal layers of the rest parts in the resonant cavity are etched. The rectangular metal (2-3-2) and the metallized through hole (2-3-1) jointly form a capacitor column structure (2-3-3) of the resonant cavity.
Preferably, the diameter of the metal through holes (1-1-1) and (2-3-1) is 2mm, and the distance between two adjacent through holes is 3.35mm. The length and the width of the rectangular metal (1-1-2) of the upper resonant cavity (1) are both 17mm, the length and the width of the rectangular metal (2-3-2) of the lower resonant cavity (2) are both 14mm, the sizes of the capacitor columns in the two resonant cavities are different, the cavity with the large size of the capacitor column is a sensing resonant cavity, and the cavity with the small size of the capacitor column is a reference resonant cavity.
Referring to fig. 4 (a) and 4 (b), in the two resonant cavities, the intermediate dielectric substrates (1-2) and (2-2) have the same structure, and are completely dug through from the top metal layer to the bottom metal layer in the resonant cavity region to form an air filling type region, which aims to better enrich water molecules in humid air in the sensing function region in the resonant cavity, thereby realizing the humidity sensing function. Preferably, the hollowed-out air-filled region has a length and width of 34mm.
The middle dielectric layers of the lower dielectric substrate (1-3) of the upper resonant cavity (1) and the upper dielectric substrate (2-1) of the lower resonant cavity (2) are etched with rectangular grooves (1-3-1) and (2-1-1), and the purpose is to form a sensing function area. The length and the width of a rectangular groove (1-3-1) etched by a middle medium layer of a lower medium substrate (1-3) of the upper resonant cavity (1) are both 17mm, and the depth of the groove is 0.5mm; the length and the width of a rectangular groove (2-1-1) etched in a middle medium layer of an upper medium substrate (2-1) of a lower resonant cavity (2) are both 14mm, and the depth of the groove is 0.5mm.
A plurality of metalized through holes are etched in the middle medium layer of the lower medium substrate (1-3) and the upper medium substrate (2-1) around the rectangular groove (1-3-1) and the rectangular groove (2-1-1) in an array mode to form a metal grid, the metal grid (1-3-2) is connected with the bottom metal of the lower medium substrate (1-3) of the upper resonant cavity (1), the metal grid (2-1-2) is connected with the top metal of the upper medium substrate (2-1) of the lower resonant cavity (2), and the metalized through holes are in one-to-one correspondence in the vertical direction, so that humid air can fully circulate in the two resonant cavities, electromagnetic waves are shielded, and electromagnetic fields are well constrained in the cavities. The metal grids corresponding to the two cavities, the air filling area of the intermediate medium substrate and the metalized through hole of the capacitor column are utilized to realize free inlet and outlet of humid air, so that the up-and-down circulation is strong, and water molecules of the humid air can be enriched in the cavities to fully react with the moisture absorption material.
Based on the metal grating shielding theory, the design requirements on the diameter of the metalized through holes, the space between adjacent holes and the porosity are met, and preferably, the diameter of the metalized through holes is designed to be 1.2mm, and the space between adjacent through holes is designed to be 1.7mAnd m is selected. The wavelength corresponding to the working frequency point of the sensor is 47.89mm, and the diameter of the through hole is designed to meet the requirement of 1.2mm<Lambda/2 =23.94mm, the distance between adjacent holes is satisfied
The porosity is 19.56%<50 percent, thereby achieving the purpose of shielding electromagnetic waves.
Referring to fig. 5 b and fig. 6 a, the differential humidity sensor is composed of a feeder structure (2-1-3) of the lower resonant cavity (2) and a feeder structure (1-3-4) of the upper resonant cavity (1) which are combined to form a coplanar waveguide + strip line feeder (3).
Referring to fig. 6 c, the feeder structure (2-1-3) of the lower resonant cavity (2) is composed of three parts, the coplanar waveguide feeder of the first part (a) is of a rhombus gradient structure, the total length is 6.2mm, the width of the feeder is 3mm, the width of the slot on two sides of the feeder is 0.35mm, the width of the rhombus feed port is 0.8mm, and the width of the feed port gradually increases from the feed port to the center of the cavity. Gradually changing the length of the paper to 3mm width after passing through 3.5mm, pausing the gradual change, gradually changing the width of the paper to 1.5mm width again after passing through 1.3mm, and gradually changing the length of the paper to 1.4mm.
The second part (B) of the feeder line structure (2-1-3) of the lower resonant cavity (2) is a conical gradual change structure and is formed by extending the first part (A) of the coplanar waveguide feeder line. The total length is 8.6mm, the feeder width is 1.5mm, the gap width of the two sides of the feeder is 0.35mm, the gap width gradually decreases after the length of 7.6mm, the gap width gradually changes from 1.5mm to 0.8mm, and the gradually changing length is 2mm.
And the third part (C) of the feeder line structure (2-1-3) of the lower resonant cavity (2) is a nonmetal through hole with the diameter of 2mm, which is symmetrically distributed along the horizontal axis, and the hole interval is 9.53mm, and is used for connecting a welding-free terminal connector.
Referring to fig. 6 d, the upper resonant cavity (1) is etched with the same feed line structure (1-3-4) as the second part (B) of the feed line structure (2-1-3) at a position where the bottom layer metal of the lower layer dielectric substrate (1-3) is in contact with the top layer metal of the upper layer dielectric substrate (2-1). The second part (B) of the feeder structure (2-1-3) and the feeder structure (1-3-4) together form a "strip line" structure.
The diamond-shaped and conical gradual change structures are used for meeting the impedance matching requirement of the input port and realizing the simultaneous excitation of two resonant cavities, thereby realizing good transmission response.
In order to use the welding-free terminal connector, rectangular gaps (1-3-5) are etched in the positions, corresponding to the first part () coplanar waveguide feeder line of the feeder line structure (2-1-3), of the upper dielectric substrate (1-1), the middle dielectric substrate (1-2), the lower dielectric substrate (1-3) and the middle dielectric substrate (2-2) and the lower dielectric substrate (2-3) of the upper resonant cavity (1) and the lower resonant cavity (2) of the differential humidity sensor from the top metal to the bottom metal. Preferably, the etching length is 15mm and the width is 6.2mm.
Fig. 8 (a) is a transmission response curve of the differential humidity sensor proposed by the present invention under room temperature conditions between the deposition and non-deposition of the sensitive material in the sensing functional region (1-3-1) of the sensing resonant cavity (1). At room temperature, the relative humidity in the room was measured to be 78.2% by a hygrothermograph. The differential humidity sensor without the deposited sensitive material excites strong resonance at 3.787GHz and 3.884GHz respectively, a layer of hygroscopic sensitive material is deposited in a sensing area (1-3-1) of the sensing resonant cavity (1), water molecules diffuse into the sensitive material to improve the effective dielectric constant of the material, and the interaction between a strong induced electric field and the hygroscopic material is excited to change the resonance frequency of the sensing resonant cavity to be reduced to 3.761GHz. And meanwhile, the resonance frequency point positioned higher is basically unchanged because the existing environmental factors are not changed. Referring to fig. 8 (b), the sensor under different relative humidity environments measures the functional relationship between the sensing resonant frequency and the environmental relative humidity after the sensing resonant cavity deposits a layer of sensitive material, when the relative humidity is increased from 41.9% to 97.3%, the resonant frequency of the sensing resonant cavity (1) is decreased from 3.77075GHz to 3.75875GHz, and the offset of the resonant frequency is 12MHz. The sensor is proved to have high sensitivity characteristic.
The invention adopts a differential structure form to carry out differential sensing detection on the environmental humidity, and deposits a sensitive material (1-3-3) capable of adsorbing water molecules in humid air in a sensing functional area, namely a groove area, of a sensing resonant cavity, and refers to a figure (1) and a figure (5) a. When the sensor is exposed in a humidity environment, a humid air medium enters the resonant cavity through metallized through holes (1-1-3) and (2-3-3) of capacitor columns of an upper medium substrate of an upper resonant cavity (1) and a lower medium substrate of a lower resonant cavity (2) and is enriched in preset sensing areas (1-3-1) and (2-1-1), the diffusion of water molecules into a sensitive material can cause the change of the intrinsic characteristics of the sensitive material, for example, the effective dielectric constant of the material can be obviously improved, so that the interaction between an electric field and a moisture absorption material is strongly induced in the cavity of the sensing resonant cavity, the resonance frequency point of the sensing resonant cavity is shifted, and the shift amount is determined by the degree of the sensitive material absorbing the water molecules; the sensing function area in the reference resonant cavity is not deposited with the moisture absorption material, and only the interaction between the strong induced electric field and the humid air medium is excited, so that the resonant frequency point of the resonant cavity is shifted, and the shift amount is determined by the relative humidity of the air. The bottom layer metal, the top layer metal and the metal grating which are directly contacted with each other between the two resonant cavities longitudinally isolate the two cavities, and the metalized through holes of the reentrant capacitor columns avoid electromagnetic wave radiation to free space, so that the electromagnetic field is well bound in the respective cavities.
The sensor is formed by combining six dielectric substrates into two vertically superposed resonant cavities, and a special feed design is adopted, so that the structure is very compact. The whole differential humidity sensor takes a resonant cavity as sensing and deposits hygroscopic materials in a sensing function area; the other resonant cavity is not deposited with moisture absorption material in the sensing function area as reference. The metal grating formed by the metalized through holes in the adjacent medium substrates of the two cavities, the middle air filling type medium substrate and the metalized through holes of the reentrant capacitor column are utilized, so that the functions of free inlet and outlet of humid air, strong up-and-down circulation and full reaction of water molecules of the humid air with a moisture absorption material in the cavities are realized. Meanwhile, good electromagnetic shielding is arranged between the two cavities, so that high-sensitivity and high-resolution detection of the relative humidity of air is realized, and urgent requirements of various subject fields on high-performance air humidity sensors are met.
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 (6)
1. A differential humidity sensor based on a substrate integrated waveguide dual-entrance resonant cavity is characterized in that: comprises two resonance cavities which are superposed up and down and two feeder lines (3); the resonant cavity is composed of three medium substrates, namely an upper layer medium substrate, a middle layer medium substrate and a lower layer medium substrate, wherein each medium substrate comprises a top metal layer, a middle medium layer and a bottom metal layer;
the resonant cavity of the upper resonant cavity (1) is surrounded by a circle of first metalized through holes (1-1-4), the first metalized through holes (1-1-4) are etched at the same positions of middle medium layers of three medium substrates, and a top metal layer and a bottom metal layer are connected to be equivalent to the metal wall of the resonant cavity;
in a resonant cavity region of the upper resonant cavity (1), a middle dielectric layer of an upper dielectric substrate (1-1) is provided with second metal through holes (1-1-1) distributed in an array manner, a rectangular metal (1-1-2) is reserved in the bottom metal layer corresponding to the array region of the second metal through holes (1-1-1), the rest is etched away, the rectangular metal (1-1-2) and the second metal through holes (1-1-1) jointly form a capacitor column structure (1-1-3) of the resonant cavity, and the position of the capacitor column structure is a region with the strongest electric field in the cavity; the middle medium substrate (1-2) is completely dug through from the top metal layer to the bottom metal layer in the resonant cavity region to form an air filling region; the lower dielectric substrate (1-3) is etched from the top metal to part of the middle dielectric layer in the resonant cavity region to form a groove (1-3-1), a layer of hygroscopic sensitive material is deposited in the groove (1-3-1), the surface size of the groove is the same as that of the rectangular metal (1-1-2), and a sensing function region is formed; etching a metalized through hole array around the groove in the middle dielectric layer of the lower dielectric substrate (1-3) to form a metal grid (1-3-2);
the lower resonant cavity (2) is symmetrical to the upper resonant cavity (1) and has the same structure, the capacitor columns in the two resonant cavities are different in size, the capacitor column of the upper resonant cavity (1) is large in size and is a sensing resonant cavity, and the capacitor column of the lower resonant cavity (2) is small in size and is a reference resonant cavity;
the bottom layer metal and the top layer metal which are directly contacted between the upper resonant cavity (1) and the lower resonant cavity (2) and the metal grating longitudinally isolate the two cavities, so that electromagnetic fields are well bound in the respective cavities;
the upper resonant cavity (1) and the lower resonant cavity (2) realize the free inlet and outlet of humid air through the metalized through holes of the respective capacitor columns, the metal grids and the air filling type area;
the feeder lines (3) are arranged on the bottom layer metal and the top layer metal which are in direct contact between the upper resonant cavity (1) and the lower resonant cavity (2) and are symmetrically distributed along the transverse axis.
2. The substrate integrated waveguide dual-entry resonant cavity-based differential humidity sensor according to claim 1, wherein: go up resonant cavity (1) and each metal through-hole that forms the metal grating of resonant cavity (2) down on the vertical direction one-to-one for moist air can be abundant circulate in two resonant cavity, the electromagnetic wave of shielding simultaneously, makes the fine constraint of electromagnetic field in cavity separately.
3. The substrate integrated waveguide dual-entry resonant cavity-based differential humidity sensor according to claim 2, wherein: the diameter of the metalized through hole for forming the metal grid is smaller than that of the metalized through hole
The distance between adjacent through holes is larger than
，
The porosity is less than fifty percent of the wavelength corresponding to the working frequency point of the resonant cavity.
4. The substrate integrated waveguide dual-entry resonant cavity-based differential humidity sensor according to claim 1 or 2, wherein: the feeder line (3) is formed by a first feeder line structure (1-3-4) on the upper resonant cavity (1) and a second feeder line structure (2-1-3) on the lower resonant cavity (2) together, and the coplanar waveguide and the strip line are formed.
5. The substrate integrated waveguide dual-entry resonant cavity-based differential humidity sensor according to claim 4, wherein: the second feed line structure (2-1-3) is composed of three parts, wherein the coplanar waveguide feed line of the first part (A) is of a rhombic gradually-changed structure, the total length is 6.2mm, the width of the feed line is 3mm, the width of gaps on two sides of the feed line is 0.35mm, the width of a rhombic feed-in port is 0.8mm, and the width of the rhombic feed-in port gradually increases from the feed-in port to the center of the cavity; gradually changing the length of the steel wire to 3mm width after the steel wire passes through 3.5mm, pausing the gradual change, gradually changing the width of the steel wire to 1.5mm width again after the steel wire passes through 1.3mm, and gradually changing the length of the steel wire to 1.4mm;
the second part (B) of the second feed line structure (2-1-3) is a tapered gradual change structure and is formed by extending the first part (A) of the coplanar waveguide feed line; the total length is 8.6mm, the width of the feeder line is 1.5mm, the width of the gap on the two sides of the feeder line is 0.35mm, the gap gradually becomes smaller after the length of 7.6mm, the width gradually changes from 1.5mm to 0.8mm, and the length gradually changes to 2mm;
the third part (C) of the second feed line structure (2-1-3) is a non-metallized through hole with the diameter of 2mm, which is symmetrically distributed along the transverse axis, the hole spacing is 9.53mm, and the third part is used for connecting a welding-free terminal connector;
the position of the first power line structure (1-3-4) corresponds to the position of the second part of the second power line structure (2-1-3), the structure is the same, and the second part (B) of the second power line structure (2-1-3) and the first power line structure (1-3-4) jointly form a strip line structure.
6. The substrate integrated waveguide dual-entry resonant cavity-based differential humidity sensor according to claim 1, 2 or 3, wherein: the intermediate dielectric layer material of all dielectric substrates is Rogers 4350, the relative dielectric constant is 3.66, the relative magnetic permeability is 1, and the loss tangent angle is 0.004.
Priority Applications (1)
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