CN108226650B

CN108226650B - Broadband dielectric constant measuring device

Info

Publication number: CN108226650B
Application number: CN201711366266.8A
Authority: CN
Inventors: 刘伟娜; 牛有田
Original assignee: Henan Normal University
Current assignee: Henan Normal University
Priority date: 2017-12-18
Filing date: 2017-12-18
Publication date: 2023-04-11
Anticipated expiration: 2037-12-18
Also published as: CN108226650A

Abstract

The invention discloses a broadband dielectric constant measuring device, which comprises a coplanar waveguide transmission line, and a composite branch node I and a composite branch node II which are serially loaded in the middle conduction band of the coplanar waveguide transmission line and have two symmetrical structures, wherein the composite branch node I consists of a branch node with a triple structure, the branch node with the triple structure comprises a coplanar waveguide with an open terminal and two slot line branch nodes with short terminals, the coplanar waveguide with the open terminal is connected with the two slot line branch nodes with the short terminals in parallel, a test area for placing a sample to be tested is arranged on the composite branch node I, and the composite branch node II consists of a right-angle bent slot line gap. The testing device has simple structure and high sensitivity, belongs to broadband measurement, adopts the traditional etching process to process the composite branch joint I and the composite branch joint II on the testing device, has low price and low processing difficulty, is convenient for batch production, and can realize online real-time broadband detection.

Description

Broadband dielectric constant measuring device

Technical Field

The invention belongs to the technical field of microwave measuring devices, and particularly relates to a broadband dielectric constant measuring device.

Background

With the continuous and dramatic development of microwave technology in the fields of biology, cytology, food chemical industry, electromagnetic compatibility and the like, many emerging interdisciplines, such as microwave chemistry and electromagnetic field biomedicine, are developed. However, due to the insufficient research on the interaction mechanism of microwave and biological medium or chemical substance, the application of microwave technology in the above-mentioned field still faces many technical barriers. The electrical parameters of biological media or chemical substances are important parameters reflecting the interaction of microwaves with them, and studies on non-thermal effects in the fields of biology, such as thermal denaturation of proteins, double plasma membranes, single cell properties, and microwave chemistry, have been conducted by analyzing the changes in dielectric properties of biological or chemical substances.

Generally, the dielectric property measurement method of a sample can be divided into a resonance method and a non-resonance method, and the resonance method is characterized by high sensitivity and accurate accuracy, but belongs to a narrow-band test. The non-resonance method is characterized by simple equipment and low test sensitivity, but belongs to broadband test. The non-resonant method is the main method for realizing broadband detection, and the transmission/reflection method is most widely applied to the non-resonant method. In the transmission/reflection method, a broadband measurement method based on a coplanar waveguide transmission line is developed greatly, and the basic idea is to place a measured sample on the coplanar waveguide transmission line, invert the dielectric property of the measured sample by measuring two-port scattering parameter information and combining with a de-embedding technology or other algorithms (such as a neural network algorithm). In order to achieve high test sensitivity, various methods have been proposed, and the document "Haase N M N, fuge G, trieu H K, et al, miniatured Transmission-Line Sensor for Broadband Dielectric Characterization of Biological Liquids and Cell cations [ J ]. IEEE Transactions on Microwave Theory and Techniques, 2015, 63 (10): 3026-3033" reports that the Dielectric Characterization of Broadband liquid Biological media is achieved by loading a microfluidic channel, which requires special processes, which increases the difficulty and cost of processing, and is not suitable for wide popularization.

In view of the above, the present invention provides a dual-frequency broadband detection sensor based on a transmission/emission method, which is based on a coplanar waveguide transmission line, and has two composite stubs with symmetrical structures loaded on a middle guide strip of the coplanar waveguide transmission line, so that the detection sensitivity is greatly improved.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a broadband dielectric constant measuring device which is simple in structure and high in detection sensitivity, and the measuring device can be used for detecting the dielectric constant of fluid, solid powder and blocky solid.

The invention adopts the following technical scheme for solving the technical problems, and the broadband dielectric constant measuring device is characterized by comprising a coplanar waveguide transmission line, and two symmetrical-structure composite branch nodes I and composite branch nodes II which are loaded in the middle of the coplanar waveguide transmission line in series, wherein the composite branch node I is composed of a triple-structure branch node, the triple-structure branch node comprises a coplanar waveguide with an open terminal and two slot line branch nodes with short terminals, the coplanar waveguide with the open terminal is connected with the two short-circuited slot line branch nodes in parallel, a test area for placing a tested sample is arranged on the composite branch node I, the composite branch node II is composed of a right-angle bending slot line gap, the composite branch node II is used for enhancing the electric field intensity on the composite branch node I and meeting impedance matching in a working frequency band so as to improve the test sensitivity and accuracy, a space is arranged between the composite branch node I and the composite branch node II for ensuring normal transmission of signals without crosstalk, and an input port and an output port of the coplanar waveguide transmission line are respectively connected with a vector network analyzer through SMA connector.

Further preferably, the sample to be tested is a massive solid and can be directly placed in the testing area, the sample to be tested is fluid or solid powder and can be loaded in the testing area through a bow-shaped micro-flow tube, and the bow-shaped micro-flow tube is adhered to the testing area through a conductive adhesive.

Preferably, the coplanar waveguide transmission line, the composite stub I and the composite stub II are formed by etching a metal layer by using a conventional etching process, the metal layer is disposed on a dielectric substrate, the dielectric substrate is made of rogers R4003C and has a relative dielectric constant of 3.38, the dielectric substrate has a thickness of 0.8mm, the widths of two signal transmission gaps and an intermediate conduction band in the coplanar waveguide transmission line are 0.15mm and 2.3mm, the widths of the gaps of the stubs in the composite stub I and the composite stub II are 0.15mm, the distance between the stub of the short-circuited slot line and the open-ended coplanar waveguide is 0.5mm, the length of the open-ended coplanar waveguide is 3mm, the length of the right-angle bent slot line is 2.7mm, and the number of right-angle bends is 5.

The measuring method of the broadband dielectric constant measuring device is characterized by comprising the following specific processes: according to the microwave transmission characteristics, microwave signals are input from an input port, pass through a composite branch section I and a composite branch section II and finally reach an output port, the composite branch section I and the composite branch section II which are loaded in series enable a test area to have a strong electric field, the measurement accuracy and sensitivity are further greatly improved, a sample to be measured is placed in the test area, equivalently, a discontinuous structure is introduced on a coplanar waveguide transmission line, the discontinuous structure is constructed into two port scattering parameters of the coplanar waveguide transmission line, the variation condition of the scattering parameters carries the dielectric characteristic information of the sample to be measured, and finally, a BP neural network method is adopted, and the dielectric characteristic of the sample to be measured is inverted based on the tested scattering parameter information containing the sample to be measured.

Compared with the prior art, the invention has the following beneficial effects: the testing device has the advantages of simple structure, high sensitivity and broadband measurement, the composite branch section I and the composite branch section II on the measuring device are processed by adopting the traditional etching process, the price is low, the processing difficulty is low, the batch production is convenient, and the online real-time broadband detection can be realized. The measuring device provided by the invention has the advantages that the composite branch joint I and the composite branch joint II are loaded, so that a test area has a very strong electric field, the impedance matching is met in a working frequency band, the sensitivity is greatly improved compared with the traditional coplanar waveguide transmission line measurement, and even the dielectric constant of a tiny sample can be measured.

Drawings

FIG. 1 is a schematic view of the structure of the measuring apparatus of the present invention;

FIG. 2 is a schematic view showing the structure of a microchannel in the measuring device of the present invention;

FIG. 3 is a graph comparing the emission coefficients of the loaded composite tributary I and II of the measuring device of the present invention;

FIG. 4 is a comparison chart of transmission coefficients of the loaded composite branch node I and the loaded composite branch nodes I and II of the measuring device of the present invention.

In the figure: the test method comprises the steps of 1-a dielectric substrate, 2-a metal layer, 3-a coplanar waveguide transmission line, 4-a signal transmission gap, 5-an intermediate conduction band, 51-a metal ground, 6-a right-angle bent type slot line gap, 61-a short-ended slot line branch section, 7-an open-ended coplanar waveguide, 8-an input port, 9-an output port and a T-test area.

Detailed Description

The details of the present invention are described in detail with reference to the accompanying drawings. As shown in fig. 1, the measuring device of the present invention is composed of a double-layer plate, the bottom layer of which is a dielectric substrate 1, the upper layer of which is a metal layer 2, a coplanar waveguide transmission line 3 etched on the metal layer 2 and including two signal transmission gaps 4, a middle conduction band 5 and a metal ground 51, a composite branch I and a composite branch II of two different structures are loaded on the middle conduction band 5 and the part far away from the feeder lines at the two ends, the composite branch I is composed of a coplanar waveguide 7 with an open end and two slot lines 61 with a short end, a test area for placing a sample to be tested is arranged on the composite branch I, the composite branch II is composed of a slot line gap 6 bent at a right angle, the number of right-angle bends is 5, the distance between the composite branch I and the composite branch II is 4.2mm, the coplanar waveguide 7 with an open end and the slot line branch 61 with two short ends in the composite branch I belong to a parallel relationship, and an input port 8 and an output port 9 of the coplanar waveguide transmission line 3 are respectively connected with a vector network analyzer through a joint.

As shown in fig. 1, a microwave signal is input from an input port, passes through a composite branch section I and a composite branch section II, and finally reaches an output port, and a test area is located on the composite branch section I, namely, a test area T shown in fig. 1; the composite branch node II is used for allocating the working frequency band of the measuring device and enhancing the electric field of a measuring area, a certain distance is kept between the composite branch node I and the composite branch node II to ensure normal transmission of signals and avoid signal crosstalk, and the distance between the composite branch node I and the composite branch node II is 4.2mm. The working frequency band of the whole device is determined by the distance between the composite branch joint I and the composite branch joint II and the size of each branch joint in the composite branch joint I and the composite branch joint II.

The tested sample is solid and can be directly placed on the measuring area T of the measuring device; if the sample to be measured is a fluid or solid powder, it can be placed in the measuring area by means of a tube, the shape of which is shown in fig. 2 and the dimensions of which can be freely tailored, the tube being selected according to the invention to have a diameter of 2mm, a height of 3mm and a length of the middle part of 3mm, and the material of the tube being selected from a plastic tube which can be attached to the measuring area of the measuring device by means of an electrically conductive adhesive.

The dielectric substrate is made of Rogers R4003C, the relative dielectric constant of the dielectric substrate is 3.38, the thickness of the dielectric substrate is 0.8mm, the width of two signal transmission gaps of the coplanar waveguide transmission line is 0.15mm, the size of a middle conduction band of the coplanar waveguide transmission line is 2.3mm, the width of each gap of a composite branch node I and a composite branch node II loaded on the dielectric substrate is 0.15mm, the distance between a short-circuited slot line branch node of a terminal and the coplanar waveguide with an open terminal is 0.5mm, the length of a right-angle bending slot line gap on the composite branch node II is 2.7mm, the length of the coplanar waveguide with the open terminal on the composite branch node I is 3mm, and the distance between the branch node of the composite branch node I and the branch node II and the two signal transmission gaps of a main transmission line (coplanar waveguide) is 0.2mm.

Fig. 3 and 4 are a comparison of scattering parameters of the proposed measuring device loading the composite branch I and loading the composite branches I and II simultaneously symmetrical to the X-axis as shown in fig. 1, and it can be seen from the figures that after the loading of the symmetrical composite branch I and the composite branch II, the reflection coefficient is improved, the operating frequency band is slightly widened, and the operating frequency is widened to 5-13GHz. As can also be seen from FIG. 3 and FIG. 4, the reflection coefficient S of the measuring device is 5-13GHz ₁₁ Less than-15 dB, transmission coefficient S ₂₁ Above-2 dB, namely the working frequency of the measuring device is 5-13GHz, belonging to broadband detection. The electric field in the test area is the strongest in the whole measuring device and reaches 10 ⁵ V, thus loading the test sample in the test area, the resulting signal can be sensitively captured by the measuring device. The size of the measuring device provided by the invention is 19.8mm 12.5mm 0.8mm, and the measuring device can be conveniently integrated with other circuit devices into a micro-analysis system, wherein D shown in figures 3 and 4 represents that the measuring device only loads the composite branch joint I, and S represents that the measuring device simultaneously loads the composite branch joint I and the composite branch joint II. Particularly, the sensor provided by the invention is composed of the coplanar waveguide transmission line, the biggest advantage is that the size of the sensor can be reasonably arranged according to the impedance characteristic of the sensor, and the impedance characteristic is that the impedance of the coplanar waveguide transmission line is determined by the ratio of the middle conduction band and the two signal transmission gaps, so the sensor can be processed into more reasonable size according to the property and the characteristic of a measured sample.

Researches show that the coplanar waveguide transmission line is favored by researchers in the aspect of dielectric constant measurement, and has the typical characteristics of ultra wide band and better sensitivity. The measurement principle is that when electromagnetic wave propagates along the coplanar waveguide, if other media around the coplanar waveguide are encountered, scattering parameters of two ports of the coplanar waveguide change, and the information of the change of the scattering parameters is different for different media. Namely, when a sample which is not to be measured is placed on the coplanar waveguide transmission line, namely a discontinuity structure is introduced on the transmission line, the discontinuity structure causes scattering parameters of two ports of the coplanar waveguide transmission line, and the change condition of the scattering parameters carries the information of the dielectric property of the sample, and finally, the neural network method is adopted to invert the dielectric constant of the measured sample based on the measured scattering parameter information containing the sample. The invention is based on the microwave transmission principle to realize the detection of the dielectric property of the sample. Because the strongest part of the coplanar waveguide transmission line is two signal transmission gaps, most samples must be placed on the middle guide belt of the coplanar waveguide, in order to enhance the electric field of the coplanar waveguide, two different composite structures, namely I and II, are loaded on the coplanar waveguide, the structure I consists of a coplanar waveguide with an open terminal and two slot lines with short terminals, and the structure II consists of bent slot line gaps. The measuring device designed according to the mode can greatly enhance the electric field of the measuring area, so that the measured sample can be fully influenced by electromagnetic waves, thereby improving the detection sensitivity at the expense of bandwidth, namely, the invention is still a broadband dielectric constant measuring device, and the bandwidth is 5GHz-13GHz according to the size.

The foregoing embodiments illustrate the principles, principal features and advantages of the invention, and it will be understood by those skilled in the art that the invention is not limited to the foregoing embodiments, which are merely illustrative of the principles of the invention, and that various changes and modifications may be made therein without departing from the scope of the principles of the invention.

Claims

1. A broadband dielectric constant measuring device is characterized by comprising a coplanar waveguide transmission line, and a composite branch node I and a composite branch node II which are in a symmetrical structure and are serially loaded on a middle conduction band of the coplanar waveguide transmission line, wherein the composite branch node I consists of a branch node in a triple structure, the branch node in the triple structure comprises a coplanar waveguide with an open terminal and two slot line branch nodes with short terminals, the coplanar waveguide with the open terminal is connected with the two slot line branch nodes with the short terminals in parallel, a test area for placing a tested sample is arranged on the composite branch node I, the composite branch node II consists of a right-angled bent slot line gap, the composite branch node II is used for enhancing the electric field intensity on the composite branch node I and meeting impedance matching in a working frequency band so as to improve the test sensitivity and accuracy, a space is arranged between the composite branch node I and the composite branch node II for ensuring normal transmission of signals without crosstalk, the input port and the output port of the coplanar waveguide transmission line are respectively connected with a vector network analyzer through SMA joints, the tested sample is a massive solid and can be directly placed in a test area, the tested sample is fluid or solid powder and can be loaded in the test area through a bow-shaped micro-flow tube which is pasted in the test area through conductive adhesive, the coplanar waveguide transmission line, a composite branch I and a composite branch II are etched on a metal layer by adopting the traditional etching process, the metal layer is arranged on a dielectric substrate, the material of the dielectric substrate is Rogers R4003C, the relative dielectric constant of the Rogers R4003C is 3.38, the thickness of the dielectric substrate is 0.8mm, the widths of two signal transmission gaps and a middle conduction band in the coplanar waveguide transmission line are respectively 0.15mm and 2.3mm, the gap widths of each branch in the composite branch I and the composite branch II are both 0.15mm, the distance between the short-circuited slot line branch node of the terminal and the open-circuited coplanar waveguide of the terminal is 0.5mm, the length of the open-circuited coplanar waveguide of the terminal is 3mm, the length of the right-angle bent slot line gap is 2.7mm, and the number of the right-angle bends is 5.

2. A measuring method of the broadband dielectric constant measuring device of claim 1 is characterized by comprising the following specific processes: according to the microwave transmission characteristics, microwave signals are input from an input port, pass through a composite branch section I and a composite branch section II and finally reach an output port, the composite branch section I and the composite branch section II which are loaded in series enable a test area to have an electric field, a tested sample is placed in the test area, namely a discontinuous structure is introduced on a coplanar waveguide transmission line, the discontinuous structure is constructed into two port scattering parameters of the coplanar waveguide transmission line, the variation condition of the scattering parameters carries the dielectric characteristic information of the tested sample, and finally, a BP neural network method is adopted, and the dielectric characteristic of the tested sample is inverted based on the tested scattering parameter information containing the tested sample.