CN108872266B

CN108872266B - Miniature three-layer magnetic coupling microwave sensor for measuring dielectric constant

Info

Publication number: CN108872266B
Application number: CN201810419931.3A
Authority: CN
Inventors: 徐魁文; 刘洋; 赵文生; 陈世昌; 赵鹏; 王高峰
Original assignee: Hangzhou Dianzi University
Current assignee: Hangzhou Dianzi University
Priority date: 2018-05-04
Filing date: 2018-05-04
Publication date: 2021-04-20
Anticipated expiration: 2038-05-04
Also published as: CN108872266A

Abstract

The invention discloses a miniature three-layer magnetic coupling microwave sensor for measuring dielectric constant. The invention comprises an upper dielectric substrate, a top SRRs ring, a middle feed ring, a lower dielectric substrate and a bottom SRRs ring; a feed ring is printed in the center of the bottom layer of the upper-layer dielectric substrate and a feed long pin extends out; printing a coupling top layer SRRs ring at the right center of the top layer of the upper layer dielectric substrate; printing a ring of coupled bottom layer SRRs at the center of the bottom layer of the lower medium substrate, wherein the SRRs have the same size as the top layer SRRs but are opposite in opening direction; the two parallel metal strips along the top SRRs loop are the areas of maximum electric field strength where the sample to be measured is placed to maximize the sensitivity of the sensor to dielectric constant. The sensor not only has excellent performance (high Q value and high sensitivity) of accurate measurement of dielectric constant, but also has very high practicability (ultra-small electric size and strong anti-interference capability).

Description

Miniature three-layer magnetic coupling microwave sensor for measuring dielectric constant

Technical Field

The invention belongs to the technical field of microwaves, and provides a novel miniature three-layer magnetic coupling microwave sensor which is used for accurately measuring an unknown dielectric constant material.

Background

With the rapid popularization of microwave technology in the civil market, the utilization rate of microwave radio frequency devices in various electronic devices is increasing day by day, and meanwhile, because the dielectric constant of the dielectric material used by the devices has great influence on the performance of the whole devices, the precise measurement of the dielectric constant of the dielectric material is necessary.

The dielectric constant is one of the important physical properties of the electromagnetic properties of reactive materials and is an important link for the interaction between materials and electromagnetic fields. Although the dielectric constant is an intrinsic parameter of a substance, it is not a constant. It is a function of frequency and is dependent on external factors such as temperature, humidity, etc., which increase the difficulty of measuring the dielectric constant. Since the dielectric constant is a physical quantity which cannot be directly measured, only measurable physical quantities such as voltage, current, impedance and scattering parameters can be measured, and the dielectric constant of the material is inverted according to the functional relationship between the dielectric constant and the actually measurable physical quantities. In order to make an accurate measurement of the dielectric constant, high requirements are placed on the performance index of the sensor, which generally requires high sensitivity and high quality factor (Q value). In addition, the sensor should have a small size and a certain interference resistance, based on practical considerations. The anti-interference capability of the existing products for measuring the dielectric constant is basically weak, the measurement must be carried out in a microwave darkroom of a laboratory or under the condition of a low interference source, and the design of the structure mainly solves the problems and improves the practicability of the miniaturized sensor.

Disclosure of Invention

The invention aims to overcome the difficulties and the front-view challenges mentioned above and meet the requirements on the accuracy and the practicability of dielectric constant measurement, and provides a subminiature microwave sensor based on SRRs (split-ring resonators), which has a high Q value, high sensitivity and strong interference resistance. SRRs are a new type of artificial electromagnetic metamaterial, and have been widely used in various microwave devices in recent years due to their excellent characteristics.

The sensor comprises an upper-layer dielectric substrate, a top-layer split resonant ring (called a top-layer SRRs ring for short), a region with the highest electric field intensity, a middle-layer feed ring, a lower-layer dielectric substrate and a bottom-layer SRRs ring;

the top layer of the upper-layer dielectric substrate is printed with a coupling top-layer SRRs ring, and the bottom layer is printed with a middle-layer feed ring; wherein, the middle layer feed ring extends out of a feed long pin for connecting the SMA connector;

the bottom layer of the lower medium substrate is printed with a coupling bottom layer SRRs ring;

the centers of the top SRRs ring, the middle feeding ring and the bottom SRRs ring are positioned on the same straight line;

openings of the top layer SRRs ring and the bottom layer SRRs ring extend into the ring; the top layer SRRs ring and the bottom layer SRRs ring have the same size but opposite opening directions (namely, the top layer SRRs ring and the bottom layer SRRs ring are arranged in an axisymmetric mode); the inner extension part of the top SRRs loop is an area with the largest electric field intensity, a sample to be detected is placed in the area, and the sensitivity of the sensor to the dielectric constant is maximized.

The Q value of the sensor determines the measurement accuracy; the sensitivity determines the resolution of the dielectric constant measurement; miniaturization and interference rejection determine the utility of the sensor.

The working process is as follows: the invention relates to a low-radiation micro microwave sensor which is designed for accurately measuring dielectric constant of a medium, and the design of a single port depends on the frequency change of a reflection coefficient to calculate the dielectric constant. In the embodiment, the frequency with the dielectric constant of 1 is used as a reference, namely the reference frequency is measured when air is arranged above the sensor, and then the dielectric block to be measured with the same size is fixed in the area with the strongest electric field intensity on the top layer.

The invention has the beneficial effects that: the sensor has extremely high Q value and sensitivity, so that the measurement accuracy and high resolution are ensured, and meanwhile, the displacement current is reversed due to the antisymmetric design of the SRRs of the top layer and the bottom layer, so that the far-field radiation efficiency of the sensor is greatly inhibited, the anti-interference capability of the sensor is greatly improved, and the sensor has extremely high practicability due to the ultra-small size design.

Drawings

FIG. 1 is a drawing of the overall structure and parametric notation of the present invention; wherein (a) the sensor top layer, (b) the sensor middle layer, (c) the sensor bottom layer;

FIG. 2 is a schematic of the S parameter of the present invention;

FIG. 3 is a schematic diagram of the electric field distribution of the present invention; wherein (a) the top layer and the middle layer, (b) the bottom layer;

FIG. 4 is a far field radiation efficiency diagram of the present invention;

FIG. 5 is a schematic diagram showing the relationship between the reflection coefficient and the dielectric constant of the dielectric block to be measured according to the present invention;

in the figure: 1. an upper dielectric substrate; 2. a top SRRs ring; 3. the region of maximum field strength; 4. a middle layer feed loop; 5. a lower dielectric substrate; 6. the bottom ring of SRRs.

Detailed Description

The sensor of the present invention will be further described with reference to the accompanying drawings.

As shown in fig. 1, the sensor of the invention comprises an upper dielectric substrate (1), a top SRRs ring (2), a middle feed ring (4), a lower dielectric substrate (5) and a bottom SRRs ring (6); a feed ring (4) is printed in the center of the bottom layer of the upper dielectric substrate (1) and a feed long pin is extended out for connecting an SMA connector; a coupling SRRs ring (2) is printed in the center of the top layer of the upper-layer dielectric substrate (1); printing a coupling SRRs ring (6) in the center of the bottom layer of the lower medium substrate (5), wherein the size of the SRRs is the same as that of the SRRs of the bottom layer but the opening direction of the SRRs is opposite; the two parallel metal strips along the top SRRs ring (2) are the areas (3) of maximum electric field strength where the sample to be measured is placed to maximize the sensitivity of the sensor to dielectric constant.

The design of the sensor of the invention is carried out in a three-dimensional electromagnetic simulation software HFSS environment, the relevant dimensions being determined by software optimization, as shown in table I below:

TABLEⅠ

Detail parameters of the two-layer resonator

wherein the microwave medium substrates of the upper layer and the lower layer are 40 multiplied by 1mm in size³High-frequency plate F4B (dielectric constant 2.2, permeability 1, loss tangent 0.003), all parameters being in mm.

As shown in the S parameter diagram of FIG. 2, the center resonance frequency of the sensor is 0.39GHz, the ultra-small relative size design is realized, and the corresponding electrical size reaches 0.052 lambda₀×0.052λ₀(λ₀Is the wavelength of the center frequency in free space).The-10 dB bandwidth of the sensor is 1.1MHz, and the corresponding Q value is about 345, so that the high Q value characteristic of the sensor is realized.

As shown in the electric field distribution diagram of fig. 3, the electric field distribution of the middle layer feeding ring is uniform, which indicates that the operation is in an electrically small mode at this time, and the coupling of the upper and lower layers of SRRs increases the equivalent capacitance and the equivalent inductance of the whole structure, so that the structure has an ultra-small electrical size. The top layer SRRs have stronger field strength relative to the bottom layer feed ring and the middle layer SRRs, wherein the strongest area is arranged on two parallel metal strips along the SRRs ring, so that the area where the dielectric block to be tested is preferably arranged can greatly improve the sensitivity of the sensor to dielectric constant.

As shown in fig. 4, the far-field radiation efficiency diagram has the characteristic of low radiation of SRRs, and the anti-symmetric coupling design of the upper and lower SRRs makes the far-field radiation efficiency of the sensor greatly suppressed, and the far-field radiation efficiency is less than 6.3%, so that the interference of reflected waves to measurement in the measurement process is greatly reduced, the anti-interference capability of the sensor is increased, and the precision in actual operation is improved.

As shown in FIG. 5, in the relationship between the reflection coefficient and the dielectric constant of the dielectric block to be measured, a 10 × 10 × 10mm is placed in the region with the maximum electric field intensity (the center of the top layer is selected at this time)³The reflection coefficient of the dielectric block to be measured is very sensitive to the change of the dielectric constant of the dielectric block, when the dielectric constant of the dielectric block to be measured is changed from 1 to 10, the corresponding resonant frequency of the sensor is changed from 390MHz to 333.3MHz, the relative frequency deviation reaches 14.54 percent, and the dielectric block to be measured shows excellent sensitivity to the dielectric constant.

The above results show that the sensor of the present invention not only has excellent performance (high Q value and high sensitivity) for accurately measuring the dielectric constant, but also has high practicability (ultra-small electrical size and strong anti-interference capability).

The microwave sensor has excellent performance, simple structure, double-layer PCB printing design, ultra-small electrical size and strong anti-interference capability, has the capability of accurate measurement under non-laboratory conditions, has extremely strong practicability, and can be widely popularized and used.

The above examples are not intended to limit the present invention, and the present invention is not limited to the above examples, and all that meets the requirements of the method of the present invention is within the scope of the present invention.

Claims

1. A dielectric constant measuring method is characterized in that the method takes the frequency when the dielectric constant is 1 as the reference, namely the frequency is measured when the air is arranged above a sensor, and then a dielectric block to be measured with the same size is arranged in the area with the strongest electric field intensity at the top layer of a miniature three-layer magnetic coupling microwave sensor;

the miniature three-layer magnetic coupling microwave sensor comprises an upper-layer dielectric substrate, a top-layer SRRs ring, a region with the largest electric field intensity, a middle-layer feed ring, a lower-layer dielectric substrate and a bottom-layer SRRs ring;

openings of the top layer SRRs ring and the bottom layer SRRs ring extend into the ring; the top SRRs ring and the bottom SRRs ring have the same size but opposite opening directions; wherein the inner extension part of the top SRRs ring is the area with the maximum electric field intensity.