CN106546826B

CN106546826B - Radio frequency sensor

Info

Publication number: CN106546826B
Application number: CN201610880142.0A
Authority: CN
Inventors: 刘伟娜; 詹华伟; 杨新伟; 刘海瑞
Original assignee: Henan Normal University
Current assignee: Henan Normal University
Priority date: 2016-10-09
Filing date: 2016-10-09
Publication date: 2019-12-24
Anticipated expiration: 2036-10-09
Also published as: CN106546826A

Abstract

The invention discloses a radio frequency sensor, which comprises a single-sided copper-coated dielectric plate, wherein two ports of the sensor are etched on the single-sided copper-coated dielectric plate, a sector radiation surface of a 180-degree coplanar waveguide-groove line back-to-back inverse balun, an isolation resistor of the 180-degree inverse power divider, the 180-degree coplanar waveguide-groove line back-to-back inverse balun, an output part of the 180-degree inverse power divider, an inverted U-shaped groove line and a lead wire welded with each discontinuous part, the output parts of two identical 180-degree inverse power dividers are respectively connected with the inverted U-shaped groove line and the 180-degree inverse balun, and input ports of the two power dividers are also input and output ports of the whole sensor. The sensor designed by the invention adopts gold plating treatment, so the sensor can also be used for testing corrosive chemical solution and has wide practicability.

Description

Radio frequency sensor

Technical Field

The invention relates to a technology for measuring the change of material parameters under microwave frequency, in particular to a high-sensitivity radio frequency sensor for measuring the change of dielectric constant under microwave frequency.

Background

The change of the dielectric constant of a substance is an important parameter reflecting the change of the transmission characteristics of electromagnetic waves in different substances. At present, the measurement of medium parameter change under microwave frequency is expanded to a plurality of fields, such as cytomology, electromagnetic compatibility, microwave chemistry and the like, and great economic benefit is obtained. For example, in the field of cell molecular characterization, bilayer lipid membranes and the like have been studied by changing the electrical parameters of the medium. The method for measuring the dielectric constant change of a substance mainly comprises a transmission/reflection method, a free space method, a resonant cavity method and the like, and the basic idea is to measure the scattering parameters of the substance to be measured through different testing devices and then finish the extraction of the dielectric constant by combining an algorithm. Among the many test methods, the transmission/reflection method is most widely used, but has a limitation in measuring a change (particularly, a weak change) in dielectric constant, which is expressed in that the background noise of the transmission line itself easily overwhelms the changed test information. In order to improve the sensitivity of the measurement of the dielectric constant change, new research ideas are continuously proposed, wherein a typical representative method is to adopt a cancellation type sensor, that is, a radio frequency sensor is designed by adopting the concept of canceling two paths of signals with the same amplitude and opposite phases, and the signals of the two paths on the sensor are cancelled to realize high-sensitivity measurement. The literature entitled "a simple, tunable, and high throughput radio-frequency sensor" has proposed a broadband testing technique based on this idea, but it is not possible to integrate, nor to construct future micro-analyzers.

Disclosure of Invention

The invention provides a cancellation type radio frequency sensor with simple structure and convenient use, aiming at overcoming the defect and the defect of low sensitivity in the traditional dielectric constant change measurement.

The invention has the technical scheme that the radio frequency sensor is formed by etching a single-sided copper-clad plate, and is characterized in that two identical 3dB 180-degree reverse phase Wilkinson power dividers, an inverted U-shaped groove line and a 180-degree reverse phase balun form a basic structure of the sensor. Specifically, the ports of the inverted U-shaped slot line and the 180-degree inverse balun are respectively connected to the output ports of two identical 180-degree inverse power splitters, so that the whole sensor is a two-port network, and the inverted U-shaped slot line and the 180-degree inverse balun respectively form two branches of the sensor, which are called a reference branch and a measurement branch. Ideally, when the sensor is empty, i.e. neither branch contains any substance, the signals of the two branches can just completely cancel, i.e. the transmission parameter of the sensor is 0, so that the own background signal of the whole device is eliminated. When two branches are provided with substances with slightly different dielectric constants, namely discontinuous structures are loaded on the sensor, and the discontinuous structures influence scattering parameters of two ports of the sensor. The invention reflects the change condition of the dielectric constant of the measured substance of the two branches by the change (including amplitude change and phase change) of the scattering parameters of the two ports of the test sensor.

In order to achieve the above purpose, the present invention adopts the technical scheme formed by the following technical measures. The sensor adopts a single-sided copper-clad plate, wherein the 3dB Wilkinson 180-degree reverse phase power divider consists of a slot line and an asymmetric coplanar strip line, and the 180-degree reverse phase balun consists of a coplanar waveguide, a fan-shaped radiation surface and a slot line.

The radio frequency sensor provided by the invention has the obvious advantages of being used for measuring the dielectric constant change of a substance: can be used for measuring the change of electrical parameters of massive solid, powder and liquid; the demand on the tested material is little; the device has higher sensitivity and wider test bandwidth, and can sensitively sense the weak change of the dielectric constant; and has the characteristics of on-line and real-time measurement. The sensor designed by the invention adopts gold plating treatment, so the sensor can also be used for testing corrosive chemical solution and has wide practicability.

Description of the drawings;

figure 1 is a schematic view of the structure of the present invention,

FIG. 2 is a schematic view of a slotline and asymmetric coplanar stripline structure,

figure 3 is a schematic diagram of scattering parameters of the sensor under no-load conditions,

FIG. 4 is a graph showing scattering parameters at a variation of the real part of the dielectric constant of two branches of 3,

FIG. 5 is a diagram of scattering parameters for a variation of the imaginary part of the dielectric constant in both branches of 0.3,

FIG. 6 is a graph showing scattering parameters measured in two branches of a solution of deionized water and 0.05% by mol alcohol,

fig. 7 is a graph showing the sensitivity of the sensor in measuring changes in dielectric constant in comparison to a conventional transmission line.

The specific implementation mode is as follows:

the embodiments are described in detail in connection with the above drawings,

a radio frequency sensor comprises a single-sided copper-coated dielectric plate 1, two ports 2 etched with the sensor, a fan-shaped radiation surface 3 of a 180-degree coplanar waveguide-groove line back-to-back phase-reversal balun, an isolation resistor 4 of the 180-degree phase-reversal power divider, a 180-degree coplanar waveguide-groove line back-to-back phase-reversal balun 5, an output part 7 of the 180-degree phase-reversal power divider, an inverted U-shaped groove line 8 and leads 6 welded to discontinuous parts. As can be seen from fig. 1, the output parts 7 of two identical 180-degree inverse power dividers are respectively connected to the inverted U-shaped groove line 8 and the 180-degree inverse balun 5, and the input ports (combining ports) of the two power dividers (combiners) are also input and output ports of the whole sensor. The 180-degree reverse phase power divider port is composed of slot lines, namely 2 and 7 parts in figure 1, and the lambda/4 part, namely 10 part in figure 1, is composed of asymmetric coplanar strip lines. The structure diagrams of the two transmission lines are shown in fig. 2, wherein (a) is the structure diagram of a slot line, and (b) is the structure diagram of an asymmetric coplanar strip line, wherein 1 is a medium of a single-sided copper-clad plate, and 2 is a copper-clad plate of 17um of a medium plate. During testing, two ports 2 shown in figure 1 are connected with two ports of a vector network analyzer, a test substance is placed in parts 8 and 9 shown in figure 1, and the change condition of the parameter of the substance placed in the parts 8 and 9 is reflected by analyzing the change of scattering parameters of the two ports of the sensor under the conditions of no load and load.

This embodiment simulates the entire measurement system using a Finite Element (FEM) numerical method. The model structure of the measurement system shown in fig. 1 is constructed according to actual dimensions, and the electric field distribution and scattering parameters S of the measurement system under no-load (no material is placed in the parts 8 and 9 of fig. 1) are simulated firstly₁₁，S₂₁As shown in fig. 3. As can be seen in FIG. 3, S₁₁The frequency band of ≤ 13dB is 3GHz-4.8GHz, and S is in the frequency band range of 3.8GHz-4.8GHz₂₁Less than or equal to-25 dB, and transmission coefficient S of the sensor at 4.1GHz₂₁As low as-48 GHz and therefore, in the 3.8GHz-4.8GHz range, the transmission coefficient of the sensor under no load is very low, i.e. the background noise of the sensor is very small. When a substance is placed on the sensor 8 or 9 as shown in fig. 1, this discontinuity will greatly affect S, corresponding to the addition of a discontinuity on the sensor₁₁，S₂₁This variation is manifested not only in the amplitude but also in the phase of the scattering parameter. The invention tests the change of the dielectric constant of the substance by the microwave transmission principle.

Specifically, the materials with the imaginary part of the dielectric constant of 0 and the difference of the real part of 3 are respectively placed in parts 8 and 9 shown in fig. 1, and the change of the scattering parameters of the two ports of the sensor is calculated by using the FEM numerical method, and the result is shown in fig. 4. It can be seen from the figure that the two-port scattering parameter of the sensor under load varies greatly compared to the no-load condition. Similarly, a substance with the same real part of dielectric constant and the difference of imaginary part of 0.02 is placed in parts 8 and 9 shown in fig. 1, and the change of scattering parameter of the sensor port is calculated by using the FEM numerical method, and the result is shown in fig. 5. Comparing figures 3, 4 and 5, the scattering parameters of the two ports of the sensor vary greatly under load and the reflection coefficient S resulting from the difference in the imaginary part of the material placed on the two branches compared to the difference in the real part of the dielectric constant of the material placed on the two branches₁₁The variation is greater. The invention reflects the change of the dielectric constant of the measured substance on the two branches according to the change of the scattering parameters under the conditions of no load and load.

The two ports of the sensor, as shown in part 2 in fig. 1, were connected to a vector network analyzer and a bottomed plastic tube having a diameter of 3mm and a length of 10mm was attached with conductive adhesive at parts 8 and 9 in fig. 1. Deionized water and a 0.05% and 1% alcohol solution were placed in each of the two plastic tubes, and the test results are shown in fig. 6. In addition, the research in the experimental process shows that the change of the dielectric constant of the sensor provided by the invention can be tested to be about 1.7 percent

Under load, the variation of the scattering parameters at the two ports of the sensor is mainly described as follows: the amplitude variation is represented by the increase of the transmission coefficient and the reflection coefficient, and the phase variation is mainly represented by the transmission coefficient S₂₁Frequency shift of resonance point, transmission coefficient S under the same test condition₂₁The variation of the phase reflects the sensitivity of the sensor, and the comparison result of the sensitivity of the sensor (sensor) and the coplanar waveguide transmission line (CPW) in terms of the variation of the test dielectric constant is shown in fig. 7. The specific implementation mode is that two same materials to be measured are respectively placed in two plastic pipes of the sensor and two gaps of the coplanar waveguide transmission line, the two selected materials are respectively deionized water and ethanol solutions with different concentrations, and the ethanol solutions with different concentrations have different dielectric constants, so that in the experimental process, the information with different dielectric constant changes is equivalently tested, and as can be seen from fig. 7, the sensor provided by the invention has higher sensitivity in measuring the dielectric constant changes than the traditional transmission line (CPW). Therefore, the sensor designed by the invention can more accurately measure the variation of the dielectric permittivity when the dielectric permittivity is slightly changed, thereby providing a powerful guarantee for more accurately obtaining the dielectric permittivity.

The above examples are merely illustrative for clarity and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. It is not necessary or necessary to exhaustively enumerate all embodiments herein, and obvious variations or modifications can be made without departing from the scope of the invention.

Claims

1. A radio frequency sensor comprises a single-sided copper-clad dielectric plate (1), two ports (2) of the sensor are etched on the single-sided copper-clad dielectric plate (1), a fan-shaped radiation surface (3) of a 180-degree coplanar waveguide-groove line back-to-back inverse balun, an isolation resistor (4) of the 180-degree inverse power divider, a 180-degree coplanar waveguide-groove line back-to-back inverse balun (5), an output part (7) of the 180-degree inverse power divider, an inverted U-shaped groove line (8) and lead wires (6) welded with discontinuous parts, the number of the 180-degree reverse-phase power dividers is two, output parts (7) are respectively connected with an inverted U-shaped slot line (8) and a 180-degree reverse-phase balun (5), input ports of the two 180-degree reverse-phase power dividers are input and output ports of the whole sensor, ports of the 180-degree reverse-phase power dividers are composed of slot lines, and a lambda/4 part is composed of asymmetric coplanar strip lines.