Liquid and powder material measurement system and calibration method based on transmission reflection method

Abstract

The invention discloses a liquid and powder material measuring system and calibration method based on a transmission reflection method, and belongs to the technical field of testing. According to the system, a customized container is adopted as a clamp and is matched with the corrugated horn antenna to complete GRL calibration, a calibration end face extends to the position of the inner surface of the container, and then the dielectric constant and the magnetic conductivity of liquid and powder materials are calculated through a transmission reflection method. According to the invention, the process of removing the influence of the container through a hierarchical algorithm in the prior art can be avoided, and the calibration port directly extends to the internal surface of the container, so that the test steps are simplified, and the error rate is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of testing technology, and particularly relates to a measurement system and calibration method for liquid and powder materials by a transmission reflection method. Background Art

[0002] Electronic materials can be divided into solid materials and liquid materials according to their forms. Since most liquid materials have large losses, there are few means to measure their electromagnetic parameters, especially in the millimeter wave band, the measurement methods are more limited. Currently, the most widely used method for testing the electromagnetic parameters of liquid materials is the coaxial probe method. The test frequency of this method is up to 40 GHz at most, but the calibration operation is cumbersome and the measurement accuracy is low. Another available method is the transmission reflection method. In this method, low-loss materials such as polytetrafluoroethylene and quartz are used as containers for containing liquids or powders, and the electromagnetic parameters of the material to be measured are solved by using the layered material test algorithm. The layered material test needs to first measure the electromagnetic parameters of the container material or assume that the electromagnetic parameters of the container are known, and on this basis, the electromagnetic parameters of the material to be measured are deduced. This method not only introduces errors in multiple measurements, but also cannot eliminate the errors caused by multiple reflections between the container and the sample.

[0003] Microwave dielectric materials are widely used in fields such as communication, radar, biomedicine, and chemical industry. With the continuous development of technology, more attention has been paid to liquid and powder materials. As one of the important characteristics of liquid and powder materials, the dielectric constant is required by more and more research. In industrial development, the purity of gasoline can be detected by measuring the dielectric constant of ethanol; the water content in the air and environment can be detected by measuring the dielectric constant of the liquid, so as to judge the environmental quality.

[0004] The methods for testing the electromagnetic parameters of materials can be divided into the resonance method and the network parameter method according to the principle. The network parameter method can perform swept-frequency measurement in a wide frequency band. The sample and its sensor are regarded as a single-port or two-port network, and the electromagnetic parameters of the dielectric material are calculated by measuring the network parameters. The resonance method can only perform point-frequency measurement. By placing the sample in a resonant cavity, the electromagnetic parameters of the dielectric material are calculated by using the change in the electromagnetic field characteristics in the cavity with and without the sample. The resonance method is mainly used to test low-loss materials, while most liquid materials have high losses and are not suitable for this method. Moreover, when testing at high frequencies, liquids and powders need to be made; in the network parameter method, the transmission reflection method and the probe method are two commonly used methods for testing liquid materials. Among them, the coaxial probe method has low measurement accuracy, and the fixture of the transmission reflection method is made of low-loss materials such as polytetrafluoroethylene and quartz, and the electromagnetic parameters of the material to be measured are solved by using the layered material test algorithm.

[0005] In the currently existing transmission reflection test methods for testing liquids or powders, Zhang Xiansheng of the Shandong Institute of Automation developed a terahertz free space test system, and the system block diagram is as Figure 1As shown in the figure; the system adopts a combination of an antenna and a lens fixture. By obtaining the S-parameter matrices in three states: air, an empty sample box, and a sample box with a sample to be measured, the S-parameters of the sample to be measured itself are calculated. Then, using the NRW algorithm, the dielectric properties of the sample to be measured are inversely calculated. Among them, the thicknesses of the sample and the sample box are required in the calculation process, and the dielectric constant of the sample is calculated through a layering algorithm.

[0006] The free-space measurement system constructed by Jiangsu University presses the powder sample into a container, and both the antenna and the carrier box loaded with the object to be measured are placed in a metal shielding box. The transmitting antenna and the receiving antenna are located at the upper and lower ends respectively, while the carrier box is located in the middle. The design model of this system is as Figure 2 shown. When measuring the dielectric constant of the powder by microwave transmission sweep frequency, the main observation object is the transmission coefficient S21. The sweep frequency range of the device is set at 800 MHz to 4.4 GHz, and the lowest valley point frequency (i.e., the point corresponding to the first resonance peak frequency) in this frequency band is taken to calculate its dielectric constant.

[0007] The above-mentioned free-space powder and liquid test schemes respectively adopt a layering algorithm and a calculation method of resonance frequency points. The calibration method of the layering algorithm is not specifically described and should be a general calibration method for free space. At the same time, this patent realizes the test of the electromagnetic parameters of materials by calibrating and testing the S-parameters (electromagnetic parameters) of the container material of the measurement container in the empty state and testing the S-parameters of the container loaded with the powder or liquid to be measured. The calculation method of resonance frequency points can only test fixed low-frequency points, cannot perform full-frequency band sweep testing, has large test errors, and the test results are prone to fluctuations with changes in the angle and flatness of the sample placement. Summary of the Invention

[0008] In view of the above technical problems existing in the prior art, the present invention proposes a measurement system and calibration method for liquid and powder materials by transmission and reflection method, with reasonable design, overcoming the deficiencies of the prior art and having good effects.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] A measurement system for liquid and powder materials by transmission and reflection method, comprising a test antenna, two containers, and a vector network analyzer;

[0011] The test antenna is configured to transmit and receive electromagnetic wave signals;

[0012] The two containers are respectively a first container and a second container; wherein,

[0013] The interior of the first container is filled with a metal plate as a reflection calibration piece;

[0014] The second container is an empty container and is configured to load the liquid or powder material to be measured;

[0015] A vector network analyzer, connected to a test antenna, is configured to measure the transmission and reflection parameters of electromagnetic wave signals;

[0016] A time-domain filtering module is configured to perform time-domain filtering on the measured network parameters to eliminate the multiple reflection signals inside the material.

[0017] Preferably, the test antenna is a corrugated horn antenna, and the corrugated horn antenna coincides with the central axes of the first container and the second container.

[0018] Preferably, the contact surfaces of the corrugated horn antenna with the first container and the second container are provided with matching grooves, and the corrugated horn antenna is fixed to the first container and the second container through positioning pins.

[0019] Preferably, the second container is provided with a sealing ring, and its sealing performance is verified by water injection pressure test.

[0020] Preferably, the first container and the second container have the same internal space structure, are made of low-loss materials, and the thickness of the internal space is equal.

[0021] Preferably, the low-loss material is polytetrafluoroethylene or quartz; the metal plate is a smooth aluminum plate that fits tightly against the inner wall of the first container.

[0022] In addition, the present invention also mentions a calibration method, which uses a liquid and powder material measurement system of the transmission-reflection method as described above, and includes the following steps:

[0023] Step 1: Place the first container filled with a metal plate between the test antennas, collect reflection calibration data, and perform reflection calibration;

[0024] Step 2: Place the second container at the same position, collect through calibration data, and perform through calibration;

[0025] Step 3: Extend the calibration reference plane to the inner surfaces of the first container and the second container through the GRL (Generalized Roughness Length) calibration algorithm;

[0026] Step 3: Fill the second container with the material to be measured, measure the S parameters, and eliminate the multiple reflection signals through time-domain filtering processing;

[0027] Step 4: Based on the corrected S parameters, inversely calculate the electromagnetic parameters of the material to be measured through the transmission-reflection method.

[0028] Preferably, the electromagnetic parameter measurement method includes the following steps:

[0029] Step 4.1: Place the liquid or powder material to be measured in the second container;

[0030] Step 4.2: Place the second container between the test antennas;

[0031] Step 4.3: Measure the transmission and reflection parameters between the test antennas;

[0032] Step 4.4: Calculate the electromagnetic parameters of the liquid or powder material to be measured based on the measured transmission and reflection parameters.

[0033] The beneficial technical effects brought by the present invention:

[0034] The system of the present invention uses a customized container as a fixture, cooperates with corrugated horn antennas to complete GRL calibration, extends the calibration end face to the position of the inner surface of the container, and then calculates the dielectric constant and magnetic permeability of liquid and powder materials by the transmission-reflection method. The present invention can avoid the existing process of removing the influence of the container through a layering algorithm, directly extend the calibration port to the inner surface of the container, which not only simplifies the test steps but also reduces the error rate. Brief Description of the Drawings

[0035] Figure 1 It is a structural diagram of an existing free-space measurement system;

[0036] Figure 2 It is a design model diagram of an existing system;

[0037] Figure 3 It is a schematic diagram of the overall design of the present invention;

[0038] Figure 4 It is a schematic diagram of container manufacturing;

[0039] Figure 5 It is a schematic diagram of the overall container;

[0040] Figure 6 It is a schematic diagram of the container placed in a calibration aluminum plate. Detailed Embodiment

[0041] The following further elaborates on the present invention in detail in conjunction with the drawings and specific embodiments:

[0042] The present invention designs and constructs a material dielectric property test system based on the transmission reflection method, and designs a dielectric test method for liquid and powder materials by comprehensively considering factors such as calibration accuracy, test efficiency, operation convenience, and small calculation error. Two identical containers are prepared using low-loss materials such as polytetrafluoroethylene or quartz. A metal plate of equal size is placed inside one container to fill the container for reflection calibration, and the other empty container can be used for through calibration and holding the test sample. During the GRL calibration process, in the reflection state, the container with the inserted metal plate is placed in the center of the antenna, and in the through state, the empty container is placed in the same position in the center of the antenna for calibration. The calibration end face is located on the inner wall of the container, avoiding the need to use a layering algorithm to remove the influence of the container, and at the same time simplifying the test steps and calculation process, reducing the probability of error occurrence. The overall design is as Figure 3 shown.

[0043] When testing liquid and powder materials, in order to prevent the sample material from leaking, one set of containers needs to be sealed with a sealing ring, and the other set of containers with inserted metal plates does not need to be sealed. After the sealed container is made, it needs to be tested with water to ensure its sealing performance. The internal thickness dimensions of the two containers need to be exactly the same. The container production is as Figure 4 shown.

[0044] The metal plate is made of aluminum plate. Both the aluminum plate and the container are required to have a smooth surface and uniform thickness, as Figure 5 shown. A corrugated horn antenna is selected. The corrugated horn antenna is fixed at both ends of the guide rail through a tooling, and the centers are aligned. The container can be directly clamped by the two antennas, avoiding errors caused by the position and angle placement of the horn antenna and the container. Grooves are designed on the outer side of the container and the end face of the antenna, and the antenna and the container are fixed through positioning pins, as Figure 6 shown.

[0045] During the test process, first perform the GRL calibration by the free space method. Set up the system as Figure 3 shown. Place the fixture with the inserted metal plate in the middle of the antenna for reflection calibration, as Figure 5 shown. Then place the empty fixture in the middle of the antenna for through calibration, as Figure 6 shown. The calibration can be completed. Fill the empty sample with the sample, collect the S parameters, and calculate the electrical test characteristics of the material to be tested through the transmission reflection method. The operation process is simple and has high stability.

[0046] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A liquid and powder material measurement system using the transmission and reflection method, characterized in that, It includes a test antenna, two containers and a vector network analyzer; The test antenna is configured to transmit and receive electromagnetic wave signals; The two containers are the first container and the second container respectively; wherein, The inside of the first container is filled with a metal plate as a reflection calibration piece; The second container is an empty container, configured to hold the liquid or powder material to be measured; The vector network analyzer is connected to the test antenna and is configured to measure the transmission and reflection parameters of electromagnetic wave signals; The time-domain filtering module is configured to perform time-domain filtering on the measured network parameters to eliminate the multiple reflection signals inside the material.

2. The liquid and powder material measurement system by transmission and reflection method according to claim 1, characterized in that The test antenna is a corrugated horn antenna, and the corrugated horn antenna coincides with the central axes of the first container and the second container.

3. The liquid and powder material measurement system by transmission and reflection method according to claim 2, characterized in that, The contact surfaces of the corrugated horn antenna with the first container and the second container are provided with matching grooves, and the corrugated horn antenna is fixed to the first container and the second container through positioning pins.

4. The liquid and powder material measurement system by transmission and reflection method according to claim 1, characterized in that, The second container is provided with a sealing ring, and its sealing performance is verified by water injection pressure test.

5. The liquid and powder material measurement system by transmission and reflection method according to claim 1, characterized in that The first container and the second container have the same internal space structure, are made of low-loss materials, and the thickness of the internal space is equal.

6. The liquid and powder material measurement system by transmission and reflection method according to claim 5, characterized in that, The low-loss material is polytetrafluoroethylene or quartz; the metal plate is a smooth aluminum plate, which is closely attached to the inner wall of the first container.

7. A calibration method, characterized in that Adopt a liquid and powder material measurement system using the transmission and reflection method as described in claim 1, including the following steps: Step 1: Place the first container filled with the metal plate between the test antennas, collect reflection calibration data, and perform reflection calibration; Step 2: Place the second container at the same position, collect through calibration data, and perform through calibration; Step 3: Extend the calibration reference plane to the inner surfaces of the first container and the second container through the GRL calibration algorithm; Step 3: Fill the second container with the material to be measured, measure the S parameters, and eliminate the multiple reflection signals through time-domain filtering processing; Step 4: Based on the corrected S parameters, inversely calculate the electromagnetic parameters of the material to be measured through the transmission and reflection method.

8. The calibration method according to claim 7, wherein In step 4, the electromagnetic parameter measurement method includes the following steps: Step 4.1: Place the liquid or powder material to be measured in the second container; Step 4.2: Place the second container between the test antennas; Step 4.3: Measure the transmission and reflection parameters between the test antennas; Step 4.4: Calculate the electromagnetic parameters of the liquid or powder material to be measured according to the measured transmission and reflection parameters.

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