Material complex permittivity testing device and method with wide loss testing range

Abstract

The application provides a material complex permittivity testing device and method with a wide loss testing range, and belongs to the technical field of microwave testing. The device is characterized in that: a center hole and a plurality of eccentric holes are arranged on the center and radial direction of the top end surface of the cylindrical cavity; the sample to be tested is loaded at the center hole or the eccentric hole of the cylindrical cavity, so that the TM 0n0 mode in the cylindrical cavity can be excited, thereby realizing the measurement of the permittivity of the sample to be tested; and the perturbation algorithm is established when the sample to be tested is placed in the eccentric hole, so that the same cylindrical cavity can meet the testing requirements of the complex permittivity of high, medium and low loss materials.

Description

Technical Field

[0001] This invention belongs to the field of microwave testing technology, specifically relating to a device and method for testing the complex permittivity of materials with a wide loss testing range. Background Technology

[0002] The complex permittivity (including dielectric constant and loss tangent) is the most important fundamental parameter characterizing the dielectric properties of materials, and its accurate measurement is crucial for the research and application of dielectric materials. The cylindrical cavity resonance method is a commonly used method for testing the complex permittivity of materials, offering advantages such as test stability and high accuracy. However, the cylindrical cavity resonance method is limited by the requirements for establishing the resonance state and the disturbance of the cavity field after material loading, and is generally only used for testing medium- and low-loss materials.

[0003] Currently, the method for testing the complex permittivity of medium- and low-loss materials based on cylindrical cavity resonance is relatively mature. In the patent "High-Temperature Testing System and Method for Complex Permittivity in Oxygen-Deprived Environment" (CN 104360172B), a TM method with a heterodyne mode suppression structure is proposed. 0n0 A cylindrical cavity is used to test the complex dielectric constant of cylindrical materials based on the perturbation method. In the patent "Wideband Test Structure and Test Method for Dielectric Constant of Planar Dielectrics" (publication number CN 113655287A), a TM with radial slits is proposed. 0n0 A cylindrical cavity was constructed to test the complex permittivity of rectangular sheet materials using a perturbation method. The TM model was developed in the literature "High-Temperature Testing System for Complex Permittivity of Cylindrical Cavity". 010 A cylindrical cavity was modeled, and low-loss temperature-dependent dielectric property testing of materials was achieved based on the accurate field solution method. In the paper "An accurate radially stratified approach for determining the complex permittivity of liquids in an acylindrical microwave cavity," a method based on TM was proposed. 0n0 A method for testing the complex permittivity of materials in cylindrical cavities was developed, and tests were conducted on medium- and low-loss liquids such as cyclohexane and n-butanol.

[0004] When testing medium- and low-loss materials as described above, TM 0n0 All cylindrical cavities require the sample to be placed in the center of the cavity, while TM... 0n0 The mode has the maximum electric field strength at the center of the cylindrical cavity. If a high-loss sample is loaded at this location, the cylindrical cavity TM will be damaged unless the lateral dimension of the sample is reduced. 0n0The mode cannot oscillate, thus making it impossible to test the complex permittivity. However, reducing the lateral size of the sample would pose significant challenges to sample fabrication, requiring very fine samples to meet the testing requirements. This limits the ability of the cylindrical cavity resonator method to test the complex permittivity of high-loss materials.

[0005] Therefore, how to design the sample loading method so that it is based on TM 0n0 The cylindrical cavity mold can be used for high, medium and low loss materials at the same time, and the testing of the complex permittivity of wide loss materials has become a research focus. Summary of the Invention

[0006] To address the problems existing in the background art, the present invention aims to provide a material complex permittivity testing device and method with a wide loss testing range. This device utilizes a central hole and multiple eccentric holes set at the center of the top end face of a cylindrical cavity and in the radial direction. The sample to be tested is loaded at the central hole or eccentric holes of the cylindrical cavity, allowing the TM (tumor thyristor) within the cylindrical cavity to... 0n0 The mode can oscillate, thereby enabling the measurement of the dielectric constant of the sample under test; at the same time, a perturbation algorithm is established when the sample under test is placed in an eccentric hole, so that the same cylindrical cavity can simultaneously meet the requirements for testing the complex dielectric constant of high, medium and low loss materials.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A material complex permittivity testing device with a wide loss testing range includes a cylindrical cavity, several plug seats, and a sample holder. The sample holder has a similar structure to the plug seats, except that it has a central sample through-hole for placing the sample to be tested. A central through-hole is provided at the center of the upper end face of the cylindrical cavity, and several eccentric through-holes are provided in the same radial direction. The plug seats and sample holder are placed in the central through-hole or the eccentric through-holes. The bottom surface of the plug seats and sample holder is flush with the bottom of the upper end face of the cylindrical cavity, and their dimensions are adapted to the dimensions of the central through-hole and the eccentric through-holes, so that after the plug seats and sample holder are placed on the cylindrical cavity, the cylindrical cavity forms a complete and closed cavity.

[0009] Furthermore, the cross-sections of the central through hole and the eccentric through hole are regular shapes, such as rectangles or circles, preferably circles.

[0010] Furthermore, the plug seat and sample holder are composed of two concentric cylinders, forming an overall "T" shape. When the plug seat and sample holder are placed in the central through hole or the eccentric through hole, the first cylinder is exposed outside the upper end face of the cylindrical cavity, and the second cylinder is placed inside the central through hole or the eccentric through hole, with the height of the second cylinder being the same as the thickness of the upper end face of the cylindrical cavity.

[0011] Furthermore, the position of the eccentric through-hole should be such that the electric field intensity at its axis decreases proportionally along the radial direction, that is, the distance R between the axis of the m-th eccentric through-hole (counting radially outward from the center of the upper end face of the cylindrical cavity) and the axis of the cylindrical cavity. m Calculated by the following formula:

[0012]

[0013] Where J0 is the 0th order Bessel function, u 01 Let J0 be the first root, R be the radius of the cylindrical cavity, n be the number of eccentric through holes, and m = 1, 2, ..., n.

[0014] Furthermore, the number n of eccentric through holes is preferably 2 or 3.

[0015] Furthermore, in order to prevent energy from radiating from inside the cylindrical cavity to the outside, if the cross-section of the sample through-hole is circular, its radius should be less than one-quarter of the wavelength corresponding to the working frequency of the cylindrical cavity, and the height of the sample through-hole should be greater than its diameter.

[0016] Furthermore, the height of the sample to be tested should be such that it is placed inside the sample through hole. When the sample holder is placed inside the central through hole or the eccentric through hole, the bottom surface of the sample to be tested is in contact with the bottom inner wall of the cylindrical cavity, and the top surface extends beyond the sample through hole.

[0017] This invention also provides a testing method based on the above-mentioned material complex permittivity testing device with a wide loss testing range, comprising the following steps:

[0018] Step 1: Place plugs in both the central through-hole and the eccentric through-hole of the cylindrical cavity to form a complete and closed cavity. Then, measure the TM of the cylindrical cavity in the empty cavity state. 010 The mode's resonant frequency f0 and quality factor Q0;

[0019] Step 2: Select a sample holder that matches the size of the sample to be tested. After inserting the sample into the sample through-hole of the sample holder, insert the entire sample into the central through-hole and all the eccentric through-holes of the cylindrical cavity in sequence. The bottom surface of the sample should be in contact with the inner wall of the bottom of the cylindrical cavity. When the sample holder is placed in the central through-hole or an eccentric through-hole, plugs should be placed in the other through-holes. Observe and record the TM value when the sample is inserted into the central sample hole and the eccentric sample hole respectively. 010 The shape of the resonant peak and the resonant frequency of the mode;

[0020] Step 3: Combine TM in cavity state 010 The resonant frequency of the mode is calculated by the frequency offset of the sample under test when it is placed in each through-hole;

[0021] Step 4: First, determine whether the resonance peak is complete based on its shape. If the resonance peak is complete, then determine whether the offset corresponding to the resonance peak is less than a set threshold. If the offset measured at the through hole corresponding to only one sample is less than the set threshold, then the through hole position is taken as the optimal sample hole. If the offset measured at the through holes corresponding to several samples is less than the set threshold, then the through hole position with the smallest offset is selected as the optimal sample hole.

[0022] Step 5: Place the sample to be tested in the optimal sample well selected in Step 4, and place the plugs in the remaining positions. Measure the TM value at this time. 010 resonant frequency f in mode s And quality factor Q s ;

[0023] Step 6: Calculate the relative complex permittivity ε of the sample under test based on the perturbation method. r The specific formula is as follows:

[0024]

[0025] Where, ε' r ρ is the relative permittivity of the sample under test, tanδ is the loss tangent of the sample under test, ε0 is the vacuum permittivity, μ0 is the vacuum permeability, L is the height of the cylindrical cavity, ΔV is the spatial region occupied by the sample under test within the cylindrical cavity, and E is the relative permittivity of the sample under test. z Let be the electric field along the z-direction (the height of the cylindrical cavity) in the hollow state. In the hollow state, along the cylindrical cavity directional magnetic field

[0026]

[0027] A is a constant coefficient, J1 is a first-order Bessel function, u 01 Let J0 be the first root of the 0th-order Bessel function, R be the radius of the cylindrical cavity, and r be the radial direction in the cylindrical coordinate system.

[0028] Furthermore, if the sample to be tested is placed in the central through hole, then ∫ in equation (2) ΔV |E z | 2 The dv item should be rewritten as:

[0029]

[0030] If the sample to be tested is placed in an eccentric through hole, then in equation (2) ∫ ΔV |E z | 2 The dv item should be rewritten as:

[0031]

[0032] In the formula, s is the number of longitudinal segments of the sample to be tested, which is a positive integer.

[0033] Furthermore, the threshold value set in step 4 is preferably 5‰.

[0034] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0035] This invention provides a complex permittivity testing device suitable for wide-loss materials. The device has a central through-hole and an eccentric through-hole, and different through-holes can be selected to establish resonance conditions according to the loss range of the cylindrical sample. The testing method is based on the perturbation method to solve the complex permittivity of the sample. For the case of eccentric placement of the cylindrical sample, the equivalent calculation of the integral is achieved by dividing the sample along the longitudinal direction, and a solution model for the complex permittivity of the sample under eccentric placement is established. This device and method extend the upper limit of the loss tangent test range of the cylindrical cavity resonance method, so that the same cylindrical cavity can simultaneously meet the testing requirements of complex permittivity of high, medium and low loss materials. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the complex permittivity testing device for wide-loss materials according to the present invention.

[0037] Figure 2 This is an overall schematic diagram of the cylindrical sample to be tested being placed on the cylindrical cavity according to the present invention.

[0038] Figure 3 This is a schematic diagram of the cross-section of the cylindrical sample to be tested in this invention when it is placed eccentrically.

[0039] Figure reference numerals: 1 is cylindrical cavity, 2 is T-shaped plug seat, 3 is T-shaped sample holder, 4 is central through hole, 5 is eccentric through hole, 6 is sample hole, and 7 is cylindrical sample. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0041] A complex permittivity testing device suitable for wide-loss materials is shown in the schematic diagram below. Figure 1As shown, the system includes a cylindrical cavity 1, several plug seats, and a sample holder. The plug seats and sample holder are composed of two concentric cylinders, forming a "T" shape. The T-shaped sample holder 3 is similar in structure to the T-shaped plug seat 2, except that it has a sample through hole 6 in the center for placing the sample to be tested. A circular central through hole 4 is provided at the center of the upper end face of the cylindrical cavity, and several circular eccentric through holes 5 are provided in the same radial direction. The plug seats 2 and sample holder 3 are placed in the central through hole 4 or the eccentric through holes 5. The bottom surface of the plug seats and sample holders is flush with the bottom of the upper end face of the cylindrical cavity 1, and their dimensions are adapted to the dimensions of the central through hole 4 and the eccentric through holes 5, so that after the plug seats and sample holders are placed on the cylindrical cavity, the cylindrical cavity forms a complete and closed cavity.

[0042] When the plug seat 2 and the sample holder 3 are placed in the central through hole 4 or the eccentric through hole 5, the first cylinder is exposed outside the upper end face of the cylindrical cavity, and the second cylinder is placed in the central through hole 4 or the eccentric through hole 5, and the height of the second cylinder is the same as the thickness of the upper end face of the cylindrical cavity 1.

[0043] Example 1

[0044] The cylindrical cavity was set with a radius R = 124 mm and a height L = 19 mm, and the inner wall was coated with silver; the cylindrical test samples had the same dimensions (radius a = 3 mm, length 40 mm) and the same relative permittivity (ε'). r =9.5), and the loss angle tangent is in two intervals: 0.05~0.3 and 0.4~1.

[0045] The radius of the sample through-hole is 'a', which is less than one-quarter of the wavelength corresponding to the working frequency, and the height is 15 mm, which is greater than the diameter of the sample through-hole.

[0046] The number of eccentric sample holes is set to 2, and their positions should ensure that the electric field strength at their axis decreases proportionally along the radial direction. That is, the distance R between the axis of the m-th eccentric sample hole counting outwards radially and the axis of the cylindrical cavity is... m Calculated by the following formula:

[0047]

[0048] Where m is 1 or 2, J0 is the 0th order Bessel function, and u 01 =2.4048 is the first root of J0.

[0049] Calculations show that R1 = 62.3 mm, corresponding to an electric field strength at the axis of the eccentric sample hole that is 2 / 3 of that at the axis of the cylindrical cavity; R2 = 93.4 mm, corresponding to an electric field strength at the axis of the eccentric sample hole that is 1 / 3 of that at the axis of the cylindrical cavity. A schematic diagram of the cylindrical sample to be tested placed on the cylindrical cavity is shown below. Figure 2 As shown.

[0050] The testing is performed using the aforementioned material complex permittivity testing apparatus with a wide loss testing range, including the following steps:

[0051] Step 1: Install T-type plugs on all sample holes in the cylindrical cavity and measure the TM of the cylindrical cavity in the empty state. 010 The mode's resonant frequency f0 = 925.288 MHz, and its quality factor Q0 = 7904.31;

[0052] Step 2: After inserting the cylindrical sample into the sample hole of the T-shaped sample holder, insert the entire sample into the central through hole and the eccentric through hole of the cylindrical cavity respectively; the bottom of the cylindrical sample should be in close contact with the lower cavity wall of the cylindrical cavity, and the top should be higher than the top of the T-shaped sample holder; when the cylindrical sample is inserted into one sample hole, install T-shaped plugs in the other sample holes, and observe and record the TM when the sample is inserted into the central sample hole and the eccentric sample hole respectively. 010 The shape of the resonant peak and the resonant frequency of the mode;

[0053] Step 3: Combine TM in cavity state 010 The resonant frequency of the mode is calculated by the frequency offset of the sample under test when it is placed in each through-hole;

[0054] Step 4: First, determine whether the resonance peak is complete based on its shape. If the resonance peak is complete, then determine whether the offset corresponding to the resonance peak is less than 5‰. If the offset measured at only one through hole corresponding to the sample to be tested is less than 5‰, then the through hole position is taken as the optimal sample hole. If the offset measured at the central through hole and the two eccentric through holes is less than 5‰, then the through hole position with the smallest offset is selected as the optimal sample hole.

[0055] Step 5: Place the sample to be tested in the optimal sample well selected in Step 4, and place the plugs in the remaining positions. Measure the TM value at this time. 010 resonant frequency f in mode s And quality factor Q s ;

[0056] Step 6: Calculate the relative complex permittivity ε of the cylindrical sample based on the perturbation method. r The specific formula is as follows:

[0057]

[0058] Where, ε' r ρ is the relative permittivity of the cylindrical sample, tanδ is the loss tangent of the cylindrical sample, ε0 is the vacuum permittivity, μ0 is the vacuum permeability, ΔV is the spatial region occupied by the cylindrical sample within the cylindrical cavity, and E z Let be the electric field along the z-direction in the cylindrical cavity under hollow conditions. In the hollow state, along the cylindrical cavity The magnetic field in a specific direction is expressed as follows:

[0059]

[0060] A is a constant coefficient, and J1 is a first-order Bessel function;

[0061] For the case where the cylindrical sample is located in the eccentric sample hole in this embodiment, ∫ in equation (2) ΔV |E z | 2 The dv item should be rewritten as:

[0062]

[0063] In the formula, s represents the number of longitudinal subdivisions of the cylindrical sample, as illustrated in the diagram below. Figure 3 As shown, in this embodiment, s is 600.

[0064] In this embodiment, for samples with a loss tangent of 0.05 to 0.3, the optimal sample hole is the first eccentric sample hole; for samples with a loss tangent of 0.4 to 1, the optimal sample hole is the second eccentric sample hole.

[0065] The complex permittivity of the samples calculated according to the embodiments of the present invention is shown in Table 1. As can be seen from Table 1, the relative permittivity and loss tangent obtained by the test method of the present invention are basically consistent with the relative permittivity and loss tangent set by simulation, with deviations of less than or equal to 0.6% and 10%, respectively. This indicates that the test device and method of the present invention can realize the test of complex permittivity of high-loss materials, and the results are reliable.

[0066] Table 1. Calculated values ​​of resonant frequency, quality factor, and complex permittivity under different loss conditions.

[0067]

[0068] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. A device for testing the complex permittivity of materials with a wide loss testing range, characterized in that, The device includes a cylindrical cavity, several plug seats, and a sample holder. The sample holder has a similar structure to the plug seats, except that it has a sample through hole in the center for placing the sample to be tested. The cylindrical cavity has a central through hole at the center of its upper end face and several eccentric through holes in the same radial direction. The plug seats and sample holder are placed in the central through hole or the eccentric through holes. The bottom surface of the plug seats and sample holder is flush with the bottom of the upper end face of the cylindrical cavity, and their dimensions are adapted to the dimensions of the central through hole and the eccentric through holes, so that after the plug seats and sample holder are placed on the cylindrical cavity, the cylindrical cavity forms a complete and closed cavity. The position of the eccentric through-hole should be such that the electric field intensity at its axis decreases proportionally along the radial direction. The distance R between the axis of the m-th eccentric through-hole (counting outwards radially from the center of the upper end face of the cylindrical cavity) and the axis of the cylindrical cavity is... m Calculated by the following formula: (1) Where J0 is the 0th-order Bessel function, Let J0 be the first root, R be the radius of the cylindrical cavity, n be the number of eccentric through holes, and m = 1, 2, ..., n; If the cross-section of the sample through-hole is circular, its radius should be less than one-quarter of the wavelength corresponding to the working frequency of the cylindrical cavity, and the height of the sample through-hole should be greater than its diameter.

2. The material complex permittivity testing device as described in claim 1, characterized in that, The cross-sections of the central through hole and the eccentric through hole are of regular shape.

3. The material complex permittivity testing device as described in claim 1, characterized in that, The cross-sections of the central through hole and the eccentric through hole are circular.

4. The material complex permittivity testing device as described in claim 1, characterized in that, The plug and sample holder are composed of two concentric cylinders, forming a "T" shape. When the plug and sample holder are placed in the central or eccentric through hole, the first cylinder is exposed outside the upper end face of the cylindrical cavity, and the second cylinder is placed inside the central or eccentric through hole, with the height of the second cylinder being the same as the thickness of the upper end face of the cylindrical cavity.

5. The material complex permittivity testing device as described in claim 1, characterized in that, The number of eccentric through holes, n, is 2 or 3.

6. The material complex permittivity testing device as described in claim 1, characterized in that, The height of the sample to be tested should be such that it is placed inside the sample through hole. When the sample holder is placed inside the central through hole or the eccentric through hole, the bottom surface of the sample to be tested should be in contact with the bottom inner wall of the cylindrical cavity, and the top surface should extend beyond the sample through hole.

7. A testing method based on the material complex permittivity testing device according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Place plugs in both the central through-hole and the eccentric through-hole of the cylindrical cavity to form a complete and closed cavity. Then, measure the TM of the cylindrical cavity in the empty cavity state. 010 The mode's resonant frequency f0 and quality factor Q0; Step 2: Select a sample holder that matches the size of the sample to be tested. After inserting the sample into the sample through-hole of the sample holder, insert the entire sample into the central through-hole and all the eccentric through-holes of the cylindrical cavity in sequence. The bottom surface of the sample should be in contact with the inner wall of the bottom of the cylindrical cavity. When the sample holder is placed in the central through-hole or an eccentric through-hole, plugs should be placed in the other through-holes. Observe and record the TM value when the sample is inserted into the central sample hole and the eccentric sample hole respectively. 010 The shape of the resonant peak and the resonant frequency of the mode; Step 3: Combine TM in cavity state 010 The resonant frequency of the mode is calculated by the frequency offset of the sample under test when it is placed in each through-hole; Step 4: First, determine whether the resonance peak is complete based on its shape. If the resonance peak is complete, then determine whether the offset corresponding to the resonance peak is less than a set threshold. If the offset measured at the through hole corresponding to only one sample is less than the set threshold, then the through hole position is taken as the optimal sample hole. If the offset measured at the through holes corresponding to several samples is less than the set threshold, then the through hole position with the smallest offset is selected as the optimal sample hole. Step 5: Place the sample to be tested in the optimal sample well selected in Step 4, and place the plugs in the remaining positions. Measure the TM value at this time. 010 resonant frequency f in mode s And quality factor Q s ; Step 6: Calculate the relative complex permittivity ε of the sample under test based on the perturbation method. r The specific formula is as follows: (2) in, The relative permittivity of the sample to be tested is denoted as . The loss tangent of the sample under test is given. The vacuum permittivity, Let L be the vacuum permeability, L be the height of the cylindrical cavity, ΔV be the spatial region occupied by the sample within the cylindrical cavity, and E be the vacuum permeability. z H represents the electric field along the height of the cylindrical cavity in its hollow state. φ This represents the magnetic field along the φ direction in the cylindrical cavity under hollow conditions. (3) A is a constant coefficient, J1 is a first-order Bessel function, u 01 Let J be the first root of the 0th-order Bessel function J0, R be the radius of the cylindrical cavity, and r be the radial direction.

8. The test method as described in claim 7, characterized in that, If the sample to be tested is placed in the central through hole, then in equation (2) The item is rewritten as: (4) If the sample to be tested is placed in an eccentric through hole, then in equation (2) The item is rewritten as: (5) In the formula, s is the number of longitudinal segments of the sample to be tested, which is a positive integer; The radius of the through-hole in the sample.

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