CN115372716A

CN115372716A - Dielectric constant measuring sensor based on resonance method

Info

Publication number: CN115372716A
Application number: CN202211023099.8A
Authority: CN
Inventors: 张丹; 赵亮; 查放; 叶明旭; 吴昊; 卢梦明; 杭杰; 凡磊; 芮珍珍
Original assignee: Anhui East China Institute of Optoelectronic Technology
Current assignee: Anhui East China Institute of Optoelectronic Technology
Priority date: 2022-08-25
Filing date: 2022-08-25
Publication date: 2022-11-22

Abstract

The invention discloses a dielectric constant measuring sensor based on a resonance method, which consists of three layers, namely a metal patch layer, a dielectric layer and a ground layer; the metal patch layer comprises a square metal patch, so that an electric field is concentrated in a complementary square spiral resonator area; the ground plane has etched a CSSR for resonance; when liquid or powder MUT is measured, a square container is loaded above the CSSR; when the sensor resonates, the electric field is concentrated on the resonant unit; the dielectric constant measuring sensor based on the resonance method can measure the dielectric constant of solid, liquid or powder MUT, has high sensitivity, can detect the dielectric constant variation as low as 0.01, and has almost no influence on the test result of the invention when the thickness of the MUT reaches a certain value.

Description

Dielectric constant measuring sensor based on resonance method

Technical Field

The invention relates to the technical field of microwaves, in particular to a dielectric constant measuring sensor for solid, liquid or powder materials based on a resonance method.

Background

With the wide application of radio frequency technology and microwave circuit in various fields such as food, aviation, microelectronics, etc., how to accurately and rapidly obtain the dielectric properties of materials has become an important research topic in the technical fields of microwave circuit, microwave communication, microwave biology, microwave electromagnetism, etc. The dielectric constant is an important parameter for describing the electromagnetic properties of the material, and the larger the dielectric constant is, the better the insulating property of the material is. Microwave refers to electromagnetic wave with frequency of 300MHz-300GHz, and can be used to measure dielectric constant of the tested sample (MUT) mainly because the absorption of microwave by the medium is proportional to the dielectric constant of the medium. There are many methods for measuring the dielectric constant, which can be divided into two categories, resonance method and non-resonance method. The resonance method is to generate resonance through a specific structure and disturb the electric field distribution surrounding the surface of the sensor; when MUTs with different dielectric constants are loaded, the contact between the MUTs and the resonant cells disturbs the electric field distribution again, so that the sensor has different frequency responses. Microwave sensors based on resonance methods have become a hot point of research in recent years due to their small size, high accuracy, and fast nondestructive and rapid detection speed.

Most microwave sensors are researched by solid-state MUT or liquid-state MUT, wherein the solid-state MUT is most obviously developed and can be applied to the development and design of various radio frequency microwave circuits and basic devices; liquid state is more of interest for electrolyte solutions; while the discussion of the powdery MUT is rare, it is also very important to detect the moisture content in powdery drugs, foods, and the like. In addition, most sensors can only study MUTs in one state, and two to three sensors may be needed to detect MUTs in various states, such as solid, liquid and powder, which increases the cost.

Disclosure of Invention

The invention aims to realize a miniaturized sensor which can simultaneously detect MUT in various states of solid, liquid and powder and improve the practicability of the sensor.

In order to achieve the purpose, the invention adopts the technical scheme that: the dielectric constant measuring sensor based on the resonance method is characterized in that the upper surface of a dielectric layer is a metal patch layer, the lower surface of the dielectric layer is a ground layer, the metal patch layer is composed of a micro-strip transmission line and a square metal patch in the middle of the micro-strip transmission line, a CSSR (complementary square spiral resonator) is arranged on the ground layer, and SMA connectors are welded at two ends of the micro-strip transmission line.

The edge of the upper surface of the medium layer is surrounded by a circle of surrounding barrier, and the surrounding barrier and the medium layer form a container for storing the material to be detected.

The enclosure is made of PTFE plates, the thickness of the enclosure is 0.8-1.2mm, and the size of a container formed by the enclosure and the medium layer is 40mm multiplied by 25mm multiplied by 10mm.

The metal patch layer and the grounding layer are both metal copper foils, and the thickness range is 0.014mm to 0.02mm.

The size of the square metal patch is 6mm multiplied by 6mm.

The dielectric layer is an FR4 substrate with the dielectric constant of 4.4, the loss tangent value of 0.02 and the thickness of 1.6 mm.

The CSSR is etched in the center of the ground plane and is used to create resonance.

The CSSR structure size is 6mm multiplied by 6mm, and the width of the etching groove is 0.5mm.

The SMA connector is fixed at the edge of the dielectric layer and is used for connecting a vector network analyzer.

The resonance frequency of the dielectric constant measuring sensor during no-load is 2.001GHz, and the resonance frequency of the dielectric constant measuring sensor during loading is 1.885GHz.

The invention relates to a dielectric constant measuring sensor of solid, liquid or powder material based on a resonance method, wherein an electric field is concentrated on a resonance unit, in particular to a Complementary Square Spiral Resonator (Complementary Square Spiral Resonator) during resonance. When the sensor is in no-load operation, the sensor works at 2.001GHz, and the dielectric constant of the sensor can be measured by directly placing the solid MUT above the spiral structure; if a solution or powder MUT is to be measured, a container is loaded over the helix, with the resonant frequency of the sensor at 1.885GHz when the container is empty. In addition, when the thickness of the MUT reaches a certain value, the test result of the present invention is hardly affected by the thickness, and is very sensitive to frequency offset, with high sensitivity, thereby improving the accuracy of measurement.

Drawings

The following is a brief description of the contents of each figure and the symbols in the figures in the description of the invention:

FIG. 1 is a schematic diagram of a front structure of a substrate of a dielectric constant measuring sensor based on a resonance method;

FIG. 2 is a schematic diagram of a reverse structure of a substrate of a dielectric constant measuring sensor based on a resonance method;

FIG. 3 is a schematic perspective view of a dielectric constant measuring sensor based on resonance method;

FIG. 4 is a graph of the transmission coefficients of a resonant-method-based dielectric constant measuring sensor when the sensor is empty and when an empty container is loaded;

FIG. 5 shows the dielectric constant measurement sensor based on the resonance method when a solid MUT is applied (ε' _r 1-10, step 1).

FIG. 6 shows a case in which a dielectric constant measuring sensor is filled with MUT (. Epsilon. ') by the resonance method' _r =2-8, step 0.2) sensor frequency response plot;

FIG. 7 shows a case in which a dielectric constant measuring sensor is filled with MUT (. Epsilon. ') by the resonance method' _r Sensor frequency response plot of 0.01 steps, 1-1.1);

FIG. 8 shows the resonant frequency and ε 'at different thicknesses of a dielectric constant measurement sensor loaded with a solid MUT by the resonance method' _r The fitting relation graph of (1);

FIG. 9 is a graph based on the resonance methodDielectric constant measuring sensor of (1), the resonant frequency at different thicknesses when liquid or powder MUT is applied thereto, and ∈' _r The fitting relation graph of (1);

the labels in the above figures are: 1. a metal patch layer; 2. a dielectric layer; 3. a ground plane.

Detailed Description

The following description of the embodiments with reference to the drawings is provided to describe the embodiments of the present invention, and the embodiments of the present invention, such as the shapes and configurations of the components, the mutual positions and connection relationships of the components, the functions and working principles of the components, the manufacturing processes and the operation and use methods, etc., will be further described in detail to help those skilled in the art to more completely, accurately and deeply understand the inventive concept and technical solutions of the present invention.

The dielectric constant measuring sensor based on the resonance method consists of three layers, namely a metal patch layer 1, a dielectric layer 2 and a ground layer 3;

the metal patch layer 1 is an FR4 substrate and comprises a square metal patch, so that an electric field is concentrated in a CSSR area, the width of the square metal patch is 6mm, the metal patch layer 1 is metal copper with the thickness of 0.017mm, and two ends of a microstrip line in the metal patch layer 1 are connected with SMA connectors for inputting and outputting signals and measuring transmission coefficients. The SMA connector is welded with two ends of the microstrip transmission line;

the ground plane 3 is copper metal with a thickness of 0.017mm and a CSSR, which is a slot etched in the ground plane 3 as shown in fig. 2, is etched in the center of the ground plane 3 to generate resonance and concentrate electric fields by the energy coupled by the microstrip lines. The CSSR structure size is 6mm multiplied by 6mm, and the width of the etching groove is 0.5mm;

the dielectric layer 2 is an FR4 substrate with the dielectric constant of 4.4, the loss tangent value of 0.02 and the thickness of 1.6 mm; when liquid or powder MUT is measured, a square container is loaded above the CSSR, namely a circle of coaming is wound on the medium layer 2, the square container is made of PTFE (polytetrafluoroethylene) with stable performance, the size is 40mm multiplied by 25mm multiplied by 10mm, and the wall thickness is 1mm.

The working principle is as follows: when the sensor is in no-load, the CSSR is excited by a vertical electric field generated by the microstrip transmission line with the metal patch to generate resonance, and at the moment, the electromagnetic field stored in the sensor is in a balanced state; when MUT with different dielectric constant is loaded, it will change the capacitance of CSSR and generate new electromagnetic field, and these new electromagnetic field change the resonance, i.e. the resonance frequency is different at the maximum point of the insertion loss (S21), therefore the dielectric constant can be calculated by the frequency change of the transmission coefficient. When the solid MUT is measured, the reference frequency is the frequency when the dielectric constant is 1, namely the sensor is unloaded, and the frequency is equivalent to the frequency of 2.001GHz loaded with air above the sensor; if liquid or powder MUT is to be measured, the reference frequency is the frequency at which the sensor is loaded into an empty container, which is 1.885GHz.

Fig. 4 shows the resonance frequency diagrams of the sensor for measuring the dielectric constant of a solid, liquid or powder material according to the present invention based on the resonance method when the sensor is empty and when the sensor is loaded in an empty container, wherein the resonance frequencies are 2.001GHz and 1.885GHz, respectively.

As shown in FIG. 5, the dielectric constant was measured by the time when the solid MUT was loaded on the sensor (ε' _r 1-10, step 1), the resonance frequency is shifted from 2.001GHz to 1.312GHz.

As shown in FIG. 6, the container of the dielectric constant measuring sensor was filled with MUT (. Epsilon. ')' _r =2-8, step 0.2), the resonance frequency is shifted from 1.885GHz to 1.78GHz.

As shown in FIG. 7, the container of the dielectric constant measuring sensor was filled with MUT (. Epsilon. ')' _r 1-1.1, step 0.01), the resonance frequency is shifted from 1.885GHz to 1.8813GHz.

The dielectric constant measuring sensor based on the resonance method can measure the dielectric constant of solid, liquid or powder MUT, has high sensitivity, can detect the dielectric constant variation as low as 0.01, and has almost no influence on the test result of the invention when the thickness of the MUT reaches a certain value.

The invention has been described above with reference to the accompanying drawings, it is obvious that the invention is not limited to the specific implementation in the above-described manner, and it is within the scope of the invention to apply the inventive concept and solution to other applications without substantial modification.

Claims

1. Dielectric constant measuring sensor based on resonance method, its characterized in that: the upper surface of the dielectric layer is a metal patch layer, the lower surface of the dielectric layer is a ground layer, the metal patch layer is composed of a micro-strip transmission line and a square metal patch in the middle of the micro-strip transmission line, the ground layer is provided with CSSR, and SMA connectors are welded at two ends of the micro-strip transmission line.

2. The dielectric constant measuring sensor based on the resonance method according to claim 1, wherein: the edge of the upper surface of the medium layer is surrounded by a circle of surrounding barrier, and the surrounding barrier and the medium layer form a container for storing the material to be detected.

3. The dielectric constant measuring sensor based on the resonance method according to claim 2, wherein: the enclosure is made of PTFE plates, the thickness of the enclosure is 0.8-1.2mm, and the size of a container formed by the enclosure and the medium layer is 40mm multiplied by 25mm multiplied by 10mm.

4. A dielectric constant measuring sensor based on the resonance method according to claim 1, 2 or 3, characterized in that: the metal patch layer and the grounding layer are both metal copper foils, and the thickness range is 0.014mm to 0.02mm.

5. The dielectric constant measuring sensor based on the resonance method according to claim 4, wherein: the size of the square metal patch is 6mm multiplied by 6mm.

6. The dielectric constant measuring sensor based on the resonance method according to claim 1 or 5, wherein: the dielectric layer is an FR4 substrate with the dielectric constant of 4.4, the loss tangent value of 0.02 and the thickness of 1.6 mm.

7. The dielectric constant measuring sensor based on the resonance method as set forth in claim 6, wherein: the CSSR is etched in the center of the ground plane and is used to create resonance.

8. The dielectric constant measuring sensor based on the resonance method as set forth in claim 7, wherein: the CSSR structure has the size of 6mm multiplied by 6mm, and the width of the etching groove is 0.5mm.

9. The dielectric constant measuring sensor based on the resonance method as set forth in claim 1, 2, 3, 5, 7 or 8, wherein: the SMA connector is fixed at the edge of the dielectric layer and is used for connecting a vector network analyzer.

10. The dielectric constant measuring sensor based on the resonance method as set forth in claim 9, wherein: the resonance frequency of the dielectric constant measuring sensor during no-load is 2.001GHz, and the resonance frequency of the dielectric constant measuring sensor during loading is 1.885GHz.