CN117849465A - Complex dielectric constant broadband test device and test method for substrate surface - Google Patents
Complex dielectric constant broadband test device and test method for substrate surface Download PDFInfo
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- 239000000523 sample Substances 0.000 claims abstract description 40
- 230000008878 coupling Effects 0.000 claims abstract description 31
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- 229910052751 metal Inorganic materials 0.000 claims abstract description 14
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- 230000005284 excitation Effects 0.000 claims abstract description 11
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- 238000004364 calculation method Methods 0.000 claims description 6
- 239000004020 conductor Substances 0.000 claims description 4
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- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 claims description 2
- 230000021615 conjugation Effects 0.000 claims description 2
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- 238000005516 engineering process Methods 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
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- 238000003825 pressing Methods 0.000 description 1
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- 230000005855 radiation Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
- G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
- G01R27/2617—Measuring dielectric properties, e.g. constants
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Abstract
The invention aims to provide a complex dielectric constant broadband testing device for the outside of a substrate surface, and belongs to the technical field of electromagnetic parameter testing of microwave and millimeter wave materials. The device comprises a cylindrical resonant cavity shell, wherein a plurality of gaps penetrating through the bottom wall are formed in the bottom of the cylindrical resonant cavity shell, a sample is placed at the bottom of the cavity, and the bottom outside the cavity is connected with a vacuumizing device, so that the sample is completely attached to the bottom surface of the cylindrical resonant cavity, and the precision of a test result is improved; meanwhile, a central feeding mode is adopted, a coupling hole coaxial with the resonant cavity is respectively arranged at the centers of the top wall and the bottom wall of the cylindrical resonant cavity, a metal probe is arranged in the coupling hole, and the metal probe does not extend into the cylindrical resonant cavity. Compared with the mode of inserting the magnetic excitation rings at two sides of the cavity, the feed structure has the advantage that ultra-wideband testing of the substrate to be tested at 1-60 GHz can be realized.
Description
Technical Field
The invention belongs to the technical field of electromagnetic parameter testing of microwave and millimeter wave materials, and particularly relates to a broadband testing device and a testing method for complex dielectric constants outside a substrate surface.
Background
With the continuous development and technical innovation of the electronic industry, the importance of microwave dielectric substrate materials is increasingly highlighted, for example, in the design of radar antenna communication systems and microwave circuits, the dielectric constant of the microwave dielectric substrate has an important influence on various performance indexes. Currently, most microwave dielectric substrates are composite materials, and therefore they generally have anisotropy, i.e., there is a difference in dielectric constant between the horizontal and normal directions of the substrate. When a microwave dielectric substrate is used to design a microwave circuit, the dielectric properties of the substrate in the normal direction will affect the characteristic impedance and the electrical length of the circuit, and further affect the performance of the whole circuit system, so how to obtain the out-of-plane complex dielectric constant of the microwave dielectric substrate has become one of the key problems.
Currently, the common methods for obtaining the complex permittivity outside the dielectric substrate are a parallel plate capacitor method and a strip line resonator method. The parallel plate capacitor method is to clamp a sample material to be measured between two electrodes to form a capacitor, and calculate a dielectric constant by using a capacitance value obtained by measurement, and is simple to operate, but is generally only suitable for low frequencies, the frequency range is 20Hz to 1GHz, and large errors are easily generated due to the influences of air gaps and electrode polarization effects. For example, in 2017, yang Chenguang of southeast university designs a novel parallel plate capacitor test fixture, the applicable frequency range is 10 kHz-100 MHz, the thickness of a test sample is 0.1-10 mm, and the test samples are medium-loss and high-loss samples. The strip line resonator method takes a sample to be measured as a dielectric material of a strip line, and the complex dielectric constant of the dielectric material to be measured can be calculated by measuring the resonant frequency and the quality factor; however, the loss of the strip line resonator comprises dielectric loss, conductor loss and radiation loss, with the increase of frequency, the signal loss gradually increases and the higher order resonant mode overlaps with the main mode due to the surface roughness of the conduction band, and the measurement error gradually increases, and the frequency range to which the method is generally applicable is within 20 GHz. For example, in 2018, zhang Yonghua et al built a strip line resonator test system, studied a high frequency printed board substrate, and measured its complex dielectric constant at 7-14 GHz, but the error of the measurement result of the loss tangent value at each frequency point was large. Both methods have similar characteristics, namely low precision and suitability for medium and low frequencies.
In the field of 5G communications and millimeter wave radars, it is desirable to explore the behavior of dielectric substrates at higher frequencies. The cylindrical resonant cavity has the advantages of simple structure and high quality factor, is easy to perform field analysis on the cylindrical resonant cavity, has high measurement accuracy, and is commonly used for testing dielectric constants at high frequency. The traditional complex dielectric constant test of the cylindrical resonant cavity method mostly adopts a coupling mode (Kaneko, shogo, hirokazu Kawabata, and Yoshio Kobayashi. "Improved perturbation method of complex permittivity using correction charts for TM 010and TM 020modes of a circular cylindri cal cavity."2010 Asia-Pacific Microwave conference. IEEE, 2010.) that magnetic excitation rings are inserted at two sides of a cavity, and the mode limits the frequency range of the dielectric constant of the test material, and the measurement frequency cannot meet the requirement of ultra-high frequency; meanwhile, in order to reduce polarization interference caused by placing samples, the samples to be measured are usually made into a rod shape, and the length of the samples is larger than the height of the cavity. The electric field is parallel to the central axis of the rod-shaped sample during the test by the method, so that the out-of-plane complex dielectric constant of the substrate material cannot be measured.
Disclosure of Invention
Aiming at the problems existing in the background technology, the invention aims to provide a broadband testing device and a testing method for complex dielectric constants outside a substrate surface. The device comprises a cylindrical resonant cavity shell, wherein a plurality of gaps penetrating through the bottom wall are formed in the bottom of the cylindrical resonant cavity shell, a sample is placed at the bottom of the cavity, and the bottom outside the cavity is connected with a vacuumizing device, so that the sample is completely attached to the bottom surface of the cylindrical resonant cavity, and the precision of a test result is improved; and meanwhile, the coupling hole is designed to be coaxial with the cylindrical resonant cavity. The device not only can realize the test under high frequency, but also widens the frequency test range.
In order to achieve the above purpose, the technical scheme of the invention is as follows:
a complex dielectric constant broadband testing device for the outside of a substrate surface comprises a cylindrical resonant cavity 1 and a vacuum loading unit;
the center of the top wall 7 of the cylindrical resonant cavity 1 is provided with a first coupling hole 3, the center of the bottom wall is provided with a second coupling hole, the two coupling holes are coaxial with the cylindrical resonant cavity, the first coupling hole is used for placing a metal probe for excitation to generate resonance, the second coupling hole is used for placing the metal probe for receiving an excitation signal, and the metal probe does not extend into the cylindrical resonant cavity; the bottom wall of the cylindrical resonant cavity is uniformly provided with m radial slits 4 which are the same and penetrate through the lower bottom; the substrate to be tested 2 is placed at the inner bottom of the cavity of the cylindrical resonant cavity, and the side surface of the substrate to be tested is tightly contacted with the surrounding cavity wall;
the vacuum loading unit is used for vacuumizing the bottom wall of the cylindrical resonant cavity, and reducing the air gap between the substrate to be tested and the bottom wall of the cylindrical resonant cavity.
Further, the vacuum loading unit comprises a cylindrical air chamber 5, an air pipe 6 and a vacuum pump 12; the top wall of the cylindrical air chamber is a bottom wall of the cylindrical resonant cavity, and the second coupling hole penetrates through the center of the bottom wall of the air chamber and extends into the cylindrical resonant cavity; the air pipe is arranged on the side wall of the cylindrical air chamber and is connected with the vacuum pump 12.
Further, the complex dielectric constant broadband test device further comprises a pressure loading unit; the pressure loading unit comprises a pressure sensor 8, a supporting block 9, a lifting table 10and a bracket 11; the support consists of a horizontal arm, a vertical arm and a fixed arm, wherein a lifting table is arranged on the horizontal arm, one end of the horizontal arm is connected with one end of the vertical arm, the other end of the vertical arm is connected with one end of the fixed arm, and the other end of the fixed arm is arranged on the surface of the top wall of the cylindrical resonant cavity 1; the air chamber 5, the supporting block 9, the pressure sensor 8 and the lifting platform 10 are sequentially arranged from top to bottom; the cylindrical resonant cavity is tightly contacted with the cylindrical air chamber by adjusting the lifting table and matching with the fixing arm.
Further, the number m of slits is a positive integer, preferably 6.
Further, if the slit is rectangular, the dimensions thereof are preferably 20mm long and 0.3mm wide.
Further, the top wall of the cylindrical resonant cavity can be separated from the main body of the cylindrical resonant cavity and is used for placing and taking the substrate to be measured.
Furthermore, the inner wall of the cylindrical cavity shell is polished and silver-plated so as to improve the quality factor of the resonant cavity.
Furthermore, the size of the substrate to be measured is adapted to the inner diameter of the cylindrical resonant cavity, so that an air gap between the substrate to be measured and the side wall is reduced, the thickness of the substrate to be measured is uniform, dielectric constant errors caused by uneven thickness are reduced, and the measurement accuracy is improved.
The invention also provides a complex dielectric constant test method based on the test device, which comprises the following steps:
step 1, when a substrate to be tested is not placed in a test, cavity resonance frequency f of a cylindrical resonant cavity 0 Quality factor Q 0 ；
Step 2, placing a substrate to be tested in the cylindrical resonant cavity, vacuumizing between the substrate to be tested and the bottom wall of the cylindrical resonant cavity to ensure that the substrate to be tested is completely attached to the bottom wall of the cylindrical resonant cavity, and testing the resonant frequency f of the cylindrical resonant cavity at the moment s Quality factor Q s ；
Step 3, calculating to obtain a geometric factor G according to the field distribution in the cylindrical resonant cavity ε And utilizes the geometric factor and the cavity quality factor Q 0 Equivalent surface resistance R to cavity wall S Make corrections and derive Q factor Q related to cavity wall conductor loss c And a Q factor Q related only to dielectric loss of the sample d The specific calculation formula is as follows,
wherein G is 0n0 For the geometric factor of the cavity when the substrate to be measured is not placed, omega is the angular frequency, mu 0 Is vacuum magnetic conductivity, H is total magnetic field in cavity, H t For a magnetic field tangential to the cavity wall,is cavity resonance angular frequency, L is cavity length of cylindrical resonant cavity, D is diameter, +.>In order to set the resonant angular frequency of the substrate to be tested, V is the cavity volume, S is the cavity internal surface area, and the symbol represents the conjugation, (. Cndot.) is used as the reference signal -1 Representing inversion;
step 4, according to the known in-plane complex dielectric constant epsilon || Calculating out-of-plane complex dielectric constant epsilon of the substrate to be measured by using an exceeding differential equation ⊥ The calculation formula is that,
k z tan(k z h)+ε || k z0 tan[k z0 (L-h)]＝0
wherein k is z And k z0 Is a constant parameter, p 0n Is the nth root of the Bessel function of the first kind, c is the speed of light in vacuum, h is the thickness of the substrate to be measured, j is the imaginary number, f is the resonant frequency of the resonant cavity, ω' is the real part of the angular frequency ω, ω "is the angleThe imaginary part of the frequency ω.
Further, in the step 1 and the step 2, the pressurizer is adjusted to keep the readings of the pressure sensors consistent before and after the substrate to be measured is placed.
In summary, due to the adoption of the technical scheme, the beneficial effects of the invention are as follows:
1. the invention adopts a central feeding mode, a coupling hole coaxial with the resonant cavity is respectively arranged at the centers of the top wall and the bottom wall of the cylindrical resonant cavity, a metal probe is arranged in the coupling hole, and the metal probe does not extend into the cylindrical resonant cavity. The feeding structure is more advantageous than the mode of inserting the magnetic excitation rings at two sides of the cavity, because the metal probe can generate disturbance to the field in the cavity after extending into the cavity and cannot be removed in an algorithm. The invention can realize ultra-wideband test of the substrate to be tested at 1-60 GHz.
2. According to the invention, the bottom wall of the cylindrical resonant cavity is provided with a plurality of gaps which are communicated with the air chamber, the side wall of the air chamber is provided with the air pipe, the air pipe is connected with the vacuum pump, and the air between the sample and the bottom surface of the resonant cavity can be pumped out through the work of the vacuum pump, so that the sample and the bottom surface are completely attached. Because the air gap between the sample and the bottom wall of the resonant cavity is randomly generated no matter the volume, the position or the shape when the sample is placed at the bottom of the resonant cavity, the existing theoretical algorithm does not consider the existence of the air gap, so that the test result has errors. The invention can greatly reduce the air gap by utilizing the vacuum device, enables the sample to be flat and free of edge tilting, and realizes the improvement of the accuracy of the complex dielectric constant outside the material surface of the cylindrical resonant cavity test substrate.
3. According to the cylindrical resonant cavity shell, silver plating is carried out on the inner wall of the shell in a polishing mode, meanwhile, the top cover of the resonant cavity is in contact with the side wall in a good mode through applying pressure, the same pressure is applied before and after a sample is placed, the cavity length L can be kept unchanged during cavity calibration, the same as that after the sample is placed, the quality factor of the resonant cavity is effectively improved, and the testing with higher precision and ultra-wide frequency is achieved.
Drawings
FIG. 1 is a schematic diagram of a complex permittivity broadband test apparatus according to embodiment 1 of the present invention.
FIG. 2 is a cross-sectional view and an overall structure of a cylindrical cavity and a chamber in the complex permittivity broadband test apparatus of embodiment 1 of the present invention.
FIG. 3 is a top view of the bottom wall of a cylindrical resonator in a complex permittivity broadband test apparatus according to embodiment 1 of the present invention.
Fig. 4 is a cross-sectional view of the cylindrical resonator of comparative example 1.
FIG. 5 is a graph of S21 test obtained by the complex permittivity broadband test apparatus according to example 1 of the present invention.
Reference numerals: 1. the device comprises a cylindrical resonant cavity, 2, a substrate sample, 3, a coupling hole, 4, a bottom wall gap of the cylindrical resonant cavity, 5, an air chamber, 6, an air pipe, 7, a top wall of the cylindrical resonant cavity, 8, a pressure sensor, 9, a supporting block, 10, a z-axis lifting table, 11, a bracket, 12, a vacuum pump, 13, a pressure numerical display, 14, a side wall perforated cylindrical resonant cavity, 15, a side wall coupling hole, 16 and a rod-shaped sample filled in the side wall perforated cylindrical resonant cavity.
Detailed Description
The present invention will be described in further detail with reference to the embodiments and the accompanying drawings, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent.
Example 1
A complex dielectric constant broadband testing device for the outside of a substrate surface is shown in figure 1, and the whole structure schematic diagram of the testing device comprises a cylindrical resonant cavity 1, a vacuum loading unit and a pressure loading unit;
the center of the top wall 7 of the cylindrical resonant cavity 1 is provided with a first coupling hole 3, the center of the bottom wall is provided with a second coupling hole, the two coupling holes are coaxial with the cylindrical resonant cavity, the first coupling hole is used for placing a metal probe for excitation to generate resonance, the second coupling hole is used for placing the metal probe for receiving an excitation signal, and the metal probe does not extend into the cylindrical resonant cavity; the top view of the bottom wall of the cylindrical resonant cavity is shown in fig. 3 (seen from the top wall to the bottom wall of the cylindrical resonant cavity), 6 identical radial rectangular slits 4 penetrating through the bottom are uniformly arranged on the bottom wall of the cylindrical resonant cavity, the length of each rectangular slit is 20mm, the width of each rectangular slit is 0.3mm, and the two ends of each rectangular slit are semicircular, so that the rectangular slit is only used for actual processing; the substrate to be tested 2 is placed at the inner bottom of the cavity of the cylindrical resonant cavity, and the side surface of the substrate to be tested is tightly contacted with the surrounding cavity wall; the top wall of the cylindrical resonant cavity can be separated from the cavity body and is used for opening and taking the substrate to be tested;
the vacuum loading unit is used for vacuumizing the bottom wall of the cylindrical resonant cavity, so that an air gap between the substrate to be tested and the bottom wall of the cylindrical resonant cavity is reduced; the vacuum loading unit comprises a cylindrical air chamber 5, an air pipe 6 and a vacuum pump 12; the cross-sectional views of the cylindrical resonant cavity and the air chamber are shown in fig. 2, the schematic diagram of the whole structure is shown in fig. 2, the top wall of the cylindrical air chamber is the bottom wall of the cylindrical resonant cavity, and the second coupling hole penetrates through the center of the bottom wall of the air chamber and extends into the cylindrical resonant cavity; the air pipe is arranged on the side wall of the cylindrical air chamber and is connected with the vacuum pump 12;
the pressure loading unit comprises a pressure sensor 8, a supporting block 9, a lifting table 10and a bracket 11; the support consists of a horizontal arm, a vertical arm and a fixed arm, wherein a lifting table capable of being vertically arranged on the horizontal wall is arranged on the horizontal wall, one end of the horizontal wall is connected with one end of the vertical arm, the other end of the vertical arm is connected with one end of the fixed arm, and the other end of the fixed arm is fixedly connected with the surface of the top wall of the cylindrical resonant cavity 1; the air chamber 5, the supporting block 9, the pressure sensor 8 and the lifting platform 10 are sequentially arranged from top to bottom, and the pressure sensor 8 is connected with the pressure display 13; the cylindrical resonant cavity is tightly contacted with the cylindrical air chamber by adjusting the lifting table and matching with the fixing arm.
When the air chamber is used, due to the existence of the air chamber and the vacuum pump, air between the substrate to be tested and the cylindrical resonant cavity is pumped away, and dielectric constant errors caused by an air gap are reduced; meanwhile, the same pressure is applied through the pressure loading unit before and after the sample to be measured is placed, so that the cavity length L can be kept unchanged during cavity calibration and is the same as that after the sample is placed; in addition, the top cover and the top end of the side wall of the resonant cavity can be pressed by pressurization, so that gaps are reduced, the quality factor is improved, and the precision of the complex dielectric constant outside the surface of the substrate material for testing the cylindrical resonant cavity and the improvement of the testing frequency are realized.
The complex dielectric constant test is carried out by using the out-of-plane complex dielectric constant test device, and the specific process comprises the following steps:
step 1, testing the cavity resonance frequency f of a cylindrical resonant cavity when a substrate to be tested is not placed 0 Quality factor Q 0 During test, the lifting table is required to be adjusted, and the pressure is utilized to make the roundThe top cover of the column resonator is in good contact with the side wall, and the reading of the pressure sensor is recorded at the moment;
step 2, adjusting the lifting table to open the top wall of the cylindrical resonant cavity, placing the substrate to be tested at the bottom of the resonant cavity, starting the vacuum pump to pump air between the substrate to be tested and the bottom surface of the cylindrical resonant cavity, enabling the substrate to be tested to be completely attached to the bottom surface, then placing the top wall of the cylindrical resonant cavity back to form a finished cavity, then adjusting the pressurizer to enable the reading of the pressure sensor to be consistent with that of the step 1, and testing the resonant frequency f of the cylindrical resonant cavity after the substrate to be tested is placed in the cylindrical resonant cavity s Quality factor Q s ；
Step 3, calculating a geometric factor G according to the field distribution in the resonant cavity ε And utilizes the geometric factor and the cavity quality factor Q 0 Equivalent surface resistance R to cavity wall S Make corrections and derive Q factor Q related to cavity wall conductor loss c And Q related to dielectric loss of sample only d The new angular frequency omega is calculated when the sample is loaded, and the specific calculation process is as follows:
wherein G is 0n0 For the geometric factor of the cavity when the substrate to be measured is not placed, omega is the angular frequency, mu 0 Is vacuum magnetic conductivity, H is total magnetic field in cavity, H t For a magnetic field tangential to the cavity wall,is cavity resonance angular frequency, L is cavity length of cylindrical resonant cavity, D is diameter, +.>For putting into resonance after the substrate to be measuredAngular frequency, V is cavity volume, S is cavity internal surface area, # represents conjugate, (·) -1 Representing inversion;
step 4, according to the known in-plane complex dielectric constant epsilon || Calculating the complex dielectric constant epsilon outside the substrate surface to be measured by using the transcendental differential equation ⊥ The calculation process is as follows:
k z tan(k z h)+ε || k z0 tan[k z0 (L-h)]＝0
wherein k is z And k z0 Is a constant parameter, p 0n Is the nth root of the Bessel function of the first type, c is the speed of light in vacuum, h is the thickness of the substrate to be measured, j is an imaginary number, f is the resonant frequency of the resonant cavity, ω' is the real part of the angular frequency ω, and ω "is the imaginary part of the angular frequency ω.
Comparative example 1
The cross-sectional view of the cylindrical resonant cavity adopted in this comparative example is shown in fig. 4, two coupling holes are provided on the side wall of the cylindrical resonant cavity, one coupling hole is used for placing a coupling ring for excitation to generate resonance, the other coupling hole is used for placing a coupling ring receiving device, and the sample to be measured is placed in the center of the resonant cavity and coaxial with the resonant cavity.
The magnetic excitation mode of the side wall opening limits the frequency range of the dielectric constant of the test material, can only measure in two modes of TM010 and TM020, and works at 2.3 octaves, so that the measurement frequency can not meet the requirement of ultra-high frequency. In addition, the sample is placed in the center of the resonant cavity and is coaxial with the resonant cavity, and the direction of the electric field is parallel to the center axis of the rod-shaped sample, so that the measurement of the out-of-plane complex dielectric constant of the substrate material cannot be satisfied.
FIG. 5 is a graph of S21 test obtained by the complex permittivity broadband test apparatus according to example 1 of the present invention. As can be seen from the graph, the material has 10 resonance peaks under the ultra-wideband of 1-60 GHz, and specific resonance frequency values are shown in Table 1.
TABLE 1
As can be seen from fig. 5 and table 1, the complex dielectric constant broadband test device of the present invention can realize measurement in 10 modes, and can work in 14.25 octaves, i.e. the measurement frequency of the device of the present invention can meet the requirement of ultra-high frequency.
While the invention has been described in terms of specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the equivalent or similar purpose, unless expressly stated otherwise; all of the features disclosed, or all of the steps in a method or process, except for mutually exclusive features and/or steps, may be combined in any manner.
Claims (10)
1. The complex dielectric constant broadband testing device for the outside of the substrate surface is characterized by comprising a cylindrical resonant cavity and a vacuum loading unit;
the center of the top wall of the cylindrical resonant cavity is provided with a first coupling hole, the center of the bottom wall of the cylindrical resonant cavity is provided with a second coupling hole, the two coupling holes are coaxial with the cylindrical resonant cavity, the first coupling hole is used for placing a metal probe for excitation to generate resonance, the second coupling hole is used for placing the metal probe for receiving an excitation signal, and the metal probe does not extend into the cylindrical resonant cavity; the bottom wall of the cylindrical resonant cavity is uniformly provided with m radial slits which are the same and penetrate through the lower bottom; placing the substrate to be tested at the inner bottom of the cylindrical resonant cavity, wherein the side surface of the substrate to be tested is tightly contacted with the surrounding cavity wall;
the vacuum loading unit is used for vacuumizing the bottom wall of the cylindrical resonant cavity, and reducing the air gap between the substrate to be tested and the bottom wall of the cylindrical resonant cavity.
2. The complex permittivity broadband testing apparatus of claim 1, wherein the vacuum loading unit comprises a cylindrical air chamber, an air tube and a vacuum pump; the top wall of the cylindrical air chamber is a bottom wall of the cylindrical resonant cavity, and the second coupling hole penetrates through the center of the bottom wall of the air chamber and extends into the cylindrical resonant cavity; the air pipe is arranged on the side wall of the cylindrical air chamber and is connected with the vacuum pump.
3. The complex permittivity broadband testing apparatus of claim 1, further comprising a pressure loading unit; the pressure loading unit comprises a pressure sensor, a supporting block, a lifting table and a bracket; the support consists of a horizontal arm, a vertical arm and a fixed arm, wherein a lifting table is arranged on the horizontal wall, one end of the horizontal wall is connected with one end of the vertical arm, the other end of the vertical arm is connected with one end of the fixed arm, and the other end of the fixed arm is arranged on the surface of the top wall of the cylindrical resonant cavity; the air chamber, the supporting block, the pressure sensor and the lifting platform are sequentially arranged from top to bottom; the cylindrical resonant cavity is tightly contacted with the cylindrical air chamber by adjusting the lifting table and matching with the fixing arm.
4. The complex permittivity broadband testing apparatus of claim 1, wherein the number of radial slits m is 6.
5. The complex permittivity broadband testing apparatus of claim 4, wherein if the radial slit is rectangular, it is 20mm long and 0.3mm wide.
6. The complex permittivity broadband testing apparatus of claim 1, wherein a top wall of the cylindrical cavity is separable from the cylindrical cavity body for taking the substrate to be tested.
7. The complex permittivity broadband testing apparatus of claim 1, wherein the cylindrical cavity housing inner wall is polished silver plated.
8. The broadband test device of complex permittivity according to claim 1, wherein the size of the substrate to be tested is adapted to the inner diameter of the cylindrical cavity for reducing the air gap between the substrate and the sidewall, and the thickness of the substrate to be tested is uniform for reducing the permittivity error due to the uneven thickness and improving the measurement accuracy.
9. A testing method based on the complex permittivity broadband testing device according to any one of claims 1-8, characterized by comprising the following steps:
step 1, when a substrate to be tested is not placed in a test, cavity resonance frequency f of a cylindrical resonant cavity 0 Quality factor Q 0 ；
Step 2, placing a substrate to be tested in the cylindrical resonant cavity, vacuumizing between the substrate to be tested and the bottom wall of the cylindrical resonant cavity to ensure that the substrate to be tested is completely attached to the bottom wall of the cylindrical resonant cavity, and testing the resonant frequency f of the cylindrical resonant cavity at the moment s Quality factor Q s ；
Step 3, calculating to obtain a geometric factor G according to the field distribution in the cylindrical resonant cavity ε And utilizes the geometric factor and the cavity quality factor Q 0 Equivalent surface resistance R to cavity wall S Make corrections and derive Q factor Q related to cavity wall conductor loss c And a Q factor Q related only to dielectric loss of the sample d The specific calculation formula is as follows,
wherein G is 0n0 For the geometric factor of the cavity when the substrate to be measured is not placed, omega is the angular frequency, mu 0 Is vacuum magnetic conductivity, H is total magnetic field in cavity, H t For a magnetic field tangential to the cavity wall,is cavity resonance angular frequency, L is the cavity length of the cylindrical resonant cavity, D is the diameter,in order to set the resonant angular frequency of the substrate to be tested, V is the cavity volume, S is the cavity internal surface area, and the symbol represents the conjugation, (. Cndot.) is used as the reference signal -1 Representing inversion;
step 4, according to the known in-plane complex dielectric constant epsilon || Calculating out-of-plane complex dielectric constant epsilon of the substrate to be measured by using an exceeding differential equation ⊥ The calculation formula is that,
k z tan(k z h)+ε || k z0 tan[k z0 (L-h)]＝0
wherein k is z And k z0 Is a constant parameter, p 0n Is the nth root of the Bessel function of the first kind, c is the speed of light in vacuum, h is the thickness of the substrate to be measured, j is the imaginary number, f is the resonant frequency of the resonant cavity, ω' is the real part of the angular frequency ω, ω "is the angleThe imaginary part of the frequency ω.
10. The test method of claim 9, wherein in step 1 and step 2, the pressurizer is adjusted to maintain consistent pressure sensor readings before and after placement of the substrate under test.
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| CN118465379A (en) * | 2024-07-09 | 2024-08-09 | 电子科技大学 | Device and method for measuring complex dielectric constant based on non-radiation TM mode separation type cylindrical cavity |
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| CN118465379A (en) * | 2024-07-09 | 2024-08-09 | 电子科技大学 | Device and method for measuring complex dielectric constant based on non-radiation TM mode separation type cylindrical cavity |
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