Multi-layer medium thickness and dielectric constant estimation method based on time domain analysis method

Abstract

The invention belongs to the technical field of microwave measurement, and particularly relates to a multilayer medium thickness and dielectric constant estimation method based on a time domain analysis method.The method comprises the steps that wide-band S parameter measurement is conducted on the basis of a reflectometer, then a waveform on a time domain is obtained through Fourier inverse transformation, the time domain waveform is analyzed, and the thickness and dielectric constant of a multilayer medium are estimated. And calculating the thickness and dielectric constant of the material. According to the method, layer-by-layer separation is carried out on a dielectric material by utilizing the physical significance of the discontinuity of a measured medium in a time domain, the thickness and the dielectric constant of the outermost single-layer medium are firstly calculated, and then the thickness and the dielectric constant of each layer of medium inside are analyzed from outside to inside. According to the invention, the thickness and dielectric constant of the multi-layer medium can be measured at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave measurement, and is a method for estimating the thickness and dielectric constant of multi-layer dielectrics based on time-domain analysis method. Background Art

[0002] The measurement of the electromagnetic parameters of dielectrics usually adopts the network parameter method that can be measured in a wide frequency band. This method regards the dielectric as a single-port or two-port network, measures its network parameters such as scattering parameters and complex reflection coefficients, and then calculates the electromagnetic parameters of the dielectric material according to the measured scattering parameters. When processing the measured scattering parameters, there are problems of complex calculation process, large calculation amount and multi-valuedness of the measurement results in directly calculating the electromagnetic parameters through frequency-domain data. The conventional time-domain analysis method uses the time-domain gating method to window the time-domain waveform of the discontinuity point, then converts it to the frequency domain to calculate the modulus value of the reflection coefficient, and then infers the dielectric constant of the dielectric from the relationship between the reflection coefficient and the wave impedance in the case of perpendicular incidence of the plane wave on the ideal dielectric boundary plane, and finally calculates the thickness of the dielectric by combining the dielectric constant with the time difference of the time-domain discontinuity point. This method has many error factors and is greatly affected by the test bandwidth. Insufficient bandwidth will cause the time-domain waveforms of the discontinuity points to overlap, resulting in the inability to perform time-domain gating. Moreover, in order to reduce the influence of side lobes, ringing effects, etc. during the time-frequency transformation process, window functions with different attenuation coefficients are added to the signal, and there will also be time reading errors in calculating the time difference of the time-domain discontinuity point. If the dielectric is a multi-layer dielectric or a lossy dielectric, the calculation error and calculation difficulty will be greatly increased, and the calculation accuracy will also be reduced.

[0003] The existing time-domain analysis methods mainly focus on the case of single-layer dielectrics, and measure the thickness and dielectric constant. For example, the method for estimating the dielectric constant of dielectrics based on the time-domain analysis method uses a vector network analyzer to measure the S parameters of two test systems as references, subtracts the antenna standing waves from the two sets of data respectively and then performs a division operation, then converts the data to the time domain, calculates the thickness of the dielectric through comparative analysis, and then reads the time consumed by the electromagnetic wave in the dielectric plate from the time relative position difference at the discontinuity of the device under test, and calculates the dielectric constant according to this time and the obtained dielectric thickness. This method is only applicable to single-layer dielectrics and cannot measure the thickness and dielectric constant of the dielectric simultaneously. Summary of the Invention

[0004] The present invention aims to provide a method for estimating the thickness and dielectric constant of multi-layer dielectrics based on time-domain analysis. This method measures the S-parameters in a wide frequency band based on a reflectometer, then uses the inverse Fourier transform to obtain the waveform in the time domain, analyzes the time-domain waveform, and calculates the thickness and dielectric constant of the material. By using the physical meaning of the discontinuity of the measured dielectric in the time domain, the dielectric materials are separated layer by layer. First, the thickness and dielectric constant of the outermost single-layer dielectric are calculated, and then the internal dielectric conditions are analyzed from the outside to the inside. The present invention aims to calculate the thickness and dielectric constant of a multi-layer dielectric plate by using relevant theories of digital signal processing.

[0005] To achieve the above-mentioned invention purpose, the technical solution of the present invention is as follows:

[0006] 1. A method for estimating multi-layer dielectric parameters based on time-domain analysis, characterized by including the following steps:

[0007] S1. Set up a dielectric parameter test system, and test the reflection coefficient S at the calibration point of the beam antenna through a vector network analyzer 11 ;

[0008] S2. Measure the antenna standing wave S 11SW ;

[0009] S3. Frequency-domain data processing:

[0010] Remove the influence of the antenna standing wave through a calibration method;

[0011] S4. Calculate the dielectric constant and thickness of the first layer of dielectric to the nth layer of dielectric in sequence:

[0012] S4.1. Convert the frequency-domain data to the time domain, and perform signal sorting on the reflected signal on the time axis to obtain multiple reflected signals;

[0013] S4.2. Calculate the dielectric constant and thickness of the first layer of dielectric:

[0014] Retain the reflected signal Г1 of the first layer of dielectric, and remove the remaining reflected signals; convert the time-domain data of the reflected signal Г1 to the frequency domain, and calculate the dielectric constant ε of the first layer of dielectric r1 ;

[0015] Measure the time difference Δt1 between the first discontinuity and the second discontinuity in the time-domain waveform, and then calculate the thickness d1 of the first layer of dielectric according to the propagation speed of electromagnetic waves in the dielectric and the dielectric constant ε of the first layer of dielectric obtained in step S4.2 r1 , and calculate the thickness d1 of the first layer of dielectric;

[0016] S4.3. Calculate the dielectric constant and thickness of the second layer to the nth layer of dielectric:

[0017] Retain the second-layer medium reflection signal Г1 and remove the remaining reflection signals; convert the time-domain data of the reflection signal Г2 to the frequency domain, and then combine it with the dielectric constant ε of the first-layer medium r1 , and calculate the dielectric constant ε of the second-layer medium r2 ;

[0018] Measure the time difference Δt2 between the second discontinuity and the third discontinuity in the time-domain waveform, and then calculate the thickness d2 of the second-layer medium according to the propagation speed of electromagnetic waves in the medium and the dielectric constant ε of the second-layer medium r2 ;

[0019] In the way of layer-by-layer peeling, in turn, according to the solution process of the parameters and thickness of the second-layer medium, the dielectric constants and thicknesses of the remaining layers of the medium are solved one by one from the outside to the inside, and the thicknesses and dielectric constants of the third, fourth... nth layers of the medium can be obtained.

[0020] As a preferred method, the operations of setting the medium parameter test system in step S1 include:

[0021] The medium parameter test system includes a vector network analyzer, a collimating antenna, a medium plate to be measured, and a metal plate; the vector network analyzer is connected to the calibration point of the collimating antenna, that is, the feed receiving port, the metal plate is closely attached to the back of the medium plate to be measured, and the collimating antenna is placed perpendicular to the medium plate; measure the reflection coefficient S at the calibration point of the collimating antenna through the vector network analyzer 11 , and record the test data as

[0022] As a preferred method, the specific operations of measuring the antenna standing wave S in step S2 11SW include:

[0023] Measure the reflection coefficient of the collimating antenna without the medium plate to be measured and the metal plate through the vector network analyzer, and this reflection coefficient is the antenna standing wave, denoted as S 11SW .

[0024] As a preferred method, the method of frequency-domain data processing in step S3 is:

[0025] Use the medium parameter test system to measure the reflection coefficient Deduct the influence corresponding to the antenna standing wave S 11SW to obtain the corresponding data, denoted as

[0026] As a preferred method, in step S4.2, perform a discrete Fourier transform on the time-domain data of the reflection signal Г1 to convert it to the frequency domain, obtain the reflection coefficient of the first layer, and combine the formula to calculate the dielectric constant ε of the first-layer medium r1 .

[0027] As a preferred method, the method for calculating the thickness d1 of the first layer of medium in step S4.2 includes:

[0028] Analyze the time-domain waveform. The first reflection peak in the time-domain waveform represents the first discontinuity of the measured material, that is, the first reflection at the interface between air and the dielectric plate; the second reflection peak represents the second discontinuity of the measured material, that is, the first reflection at the dielectric interface between the dielectric plate and the metal plate. There is a certain time difference between the first two reflections in the time domain, and this time difference is twice the time consumed by the electromagnetic wave to propagate twice the thickness of the medium. As shown in the following formula:

[0029]

[0030] where d is the thickness of the medium, c is the speed of electromagnetic wave propagation in vacuum, and ε represents the dielectric constant of the dielectric plate to be measured; according to this formula, the calculation formula is obtained

[0031] Measure the time difference Δt1 between the first discontinuity and the second discontinuity in the time-domain waveform, and then according to the dielectric constant ε of the first layer of medium obtained in step (4) r1 , using the formula where c is the speed of electromagnetic wave propagation in vacuum, the thickness d1 of the first layer of medium can be calculated.

[0032] As a preferred method, in step S4.3, the time-domain data of the reflected signal Г2 is subjected to discrete Fourier transform to be converted to the frequency domain, and then combined with the dielectric constant ε of the first layer of medium r1 , using the formula the dielectric constant ε of the second layer of medium can be calculated. r2 .

[0033] As a preferred method, the method for solving the dielectric constant and thickness of the remaining layers of medium in step S4.3 includes:

[0034] When calculating the dielectric constant and thickness of the nth layer of medium, the reflected signal T of the nth layer of medium n is retained, and the remaining reflected signals are removed. Then the time-domain data of the reflected signal Г n is subjected to DFT to obtain the reflection coefficient of the nth layer. Then, according to the dielectric constant ε of the (n - 1)th layer of medium rn-1 , using the formula the dielectric constant ε of the nth layer of medium can be calculated. rn . Measure the time difference Δt between the nth discontinuity and the (n + 1)th discontinuity in the time-domain waveform n , and then according to the dielectric constant ε of the nth layer of medium rn , using the formula the thickness d of the nth layer of medium can be calculated. n .

[0035] The beneficial effects of the present invention are as follows: The method of the present invention provides a new method for calculating the medium thickness and dielectric constant by time-domain analysis of S-parameters. This method is based on a reflectometer to measure the S-parameters in a wide frequency band, and then uses the inverse Fourier transform to obtain the waveform in the time domain. By analyzing the time-domain waveform, the thickness and dielectric constant of the material are deduced. In this process, using the physical meaning of the discontinuity of the measured medium in the time domain, the dielectric material is separated layer by layer. First, the thickness and dielectric constant of a single-layer medium are calculated, and then it is extended from the outside to the inside to the case of multi-layer media. Description of the Drawings

[0036] Figure 1 is the flow chart of the method for estimating the thickness and dielectric constant of multi-layer media in the embodiment;

[0037] Figure 2 is the diagram of the multi-layer medium parameter test system in the embodiment;

[0038] Figure 3 is the diagram of the test system for the thickness and dielectric constant of double-layer media in the embodiment;

[0039] Figure 4 is the time-domain waveform diagram obtained by converting the reflection coefficient measured in Embodiment 1 from the frequency domain to the time domain. Detailed Embodiments

[0040] The following specific examples illustrate the embodiments of the present invention. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0041] As Figure 1 shown, this embodiment provides a method for estimating the thickness and dielectric constant of multi-layer media based on time-domain analysis, including the following steps:

[0042] S1. Set up the medium parameter test system

[0043] Figure 2 shows the diagram of the multi-layer medium parameter test system; Figure 3 is the diagram showing the test system for the thickness and dielectric constant of double-layer media. As Figure 2 and Figure 3 shown, the medium parameter test system includes a transceiver antenna, a medium plate to be measured, and a metal reflector; connect the vector network analyzer to the calibration point of the transceiver antenna, that is, the feed receiving port. The medium plate to be measured is closely attached to the metal reflector at the back, and the transceiver antenna is placed perpendicular to the medium plate; measure the reflection coefficient S at the calibration point of the transceiver antenna through the vector network analyzer 11, the test data is recorded as

[0044] S2. Measure the antenna standing wave S 11SW ;

[0045] The reflection coefficient of the transceiver antenna without the dielectric plate under test and the metal reflector is measured by a vector network analyzer, that is, the antenna standing wave is recorded as S 11SW .

[0046] S3. Frequency-domain data processing

[0047] Use the reflection coefficient of the dielectric parameter test system Subtract the antenna standing wave S 11SW The obtained data is recorded as

[0048] S4. Time-frequency transformation to calculate the dielectric constant of the first layer of dielectric

[0049] Figure 4 shows the time-domain waveform obtained by converting the measured reflection coefficient from the frequency domain to the time domain. The first peak in the figure represents the reflection between air and the first layer of dielectric, the second peak represents the reflection between the first layer of dielectric and the second layer of dielectric, and the third peak represents the reflection of the metal plate. However, since the modulus of the reflection coefficient between the first layer and the second layer is This value is very small, so the second reflection is not obvious in the time domain. As Figure 4 shown, the frequency-domain data to be analyzed is converted to the time domain for analysis: Since the reflected signals in the frequency domain are signals of the same frequency and cannot be sorted by filtering, while the reflected signals are different on the time axis, so signal sorting is performed on the time axis, the reflected signal Г2 is retained, and the rest of the reflected signals are removed. Then, the time-domain data of the reflected signal Г1 is subjected to DFT to obtain the reflection coefficient of the first layer. Using the formula the dielectric constant ε of the first layer of dielectric can be calculated r1 .

[0050] S5. Time-frequency transformation to calculate the thickness of the first layer of dielectric

[0051] Analyze its time-domain waveform. The first reflection peak in the waveform represents the first discontinuity of the material under test, that is, the first reflection at the interface between air and the dielectric plate; the second reflection peak represents the second discontinuity of the material under test, that is, the first reflection at the dielectric surface between the dielectric plate and the metal plate; there is a certain time difference between the first two reflections in the time domain, and this time difference is twice the time taken for the electromagnetic wave to propagate through twice the thickness of the dielectric in the dielectric; measure the time difference Δt1 between the first discontinuity and the second discontinuity in the time-domain waveform, and then according to the dielectric constant ε of the first layer of dielectric obtained in step S4 r1 , using the formula c is the propagation speed of electromagnetic waves in vacuum, and thus the thickness d1 of the first layer of medium can be calculated.

[0052] S6. Calculate the dielectric constant of the second layer of medium

[0053] Retain the reflection signal Г2 of the second layer of medium according to step S4, and remove the remaining reflection signals. Then perform DFT on the time-domain data of the reflection signal Г2 to obtain the reflection coefficient of the second layer. Then, according to the dielectric constant ε of the first layer of medium obtained in step S4 r1 , using the formula the dielectric constant of the second layer of medium can be calculated.

[0054] S7. Calculate the thickness of the second layer of medium

[0055] Measure the time difference Δt2 between the second discontinuity and the third discontinuity in the time-domain waveform according to step S5. Then, according to the dielectric constant ε of the second layer of medium obtained in step S6 r2 , using the formula the thickness d2 of the second layer of medium can be calculated.

[0056] Similarly, for the solution of multi-layer media, the dielectric constant and thickness of each layer of medium can be solved one by one from the outside to the inside in a layer-by-layer peeling manner, and thus the thickness and dielectric constant of the third, fourth... nth layer of medium can be obtained.

[0057] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A multi-layer medium parameter estimation method based on time domain analysis, characterized in that The steps include: S1. Set up the dielectric parameter test system and test the reflection coefficient S at the calibration point of the beamforming antenna using a vector network analyzer. 11 ; S2, measure antenna standing wave S 11SW ; S3. Frequency domain data processing: Remove the influence of antenna standing waves through calibration; S4. Calculate the dielectric constant and thickness of the first to nth dielectric layers in sequence: S4.1, converting the frequency domain data into the time domain, and performing signal sorting on the reflection signal on the time axis to obtain multiple reflection signals; S4.

2. Calculate the dielectric constant and thickness of the first layer of medium: The reflection signal Г1 of the first layer of medium is retained, and the other reflection signals are removed; the time domain data of the reflection signal Г1 is converted to the frequency domain, and the dielectric constant ε of the first layer of medium is calculated r1 ; Measure the time difference Δt1 between the first discontinuity and the second discontinuity in the time domain waveform, and then calculate the dielectric constant ε of the first layer of the medium according to the speed of electromagnetic wave propagation in the medium and the dielectric constant ε of the first layer of the medium obtained in step S4.

2. r1 , calculate the thickness d1 of the first dielectric layer; S4.

3. Calculate the dielectric constant and thickness of the second to nth layers of dielectrics: The second layer medium reflection signal Г1 is retained, and the other reflection signals are removed; the reflection signal Г2 time domain data is converted to the frequency domain, and then combined with the first layer medium dielectric constant ε r1 , calculate the dielectric constant ε of the second layer r2 ; Measure the time difference Δt2 between the second discontinuity and the third discontinuity in the time domain waveform, and then calculate the time difference Δt2 according to the propagation speed of electromagnetic waves in the medium and the dielectric constant ε of the second layer of medium. r2 , calculate the thickness d2 of the second dielectric layer; In a layer-by-layer peeling manner, the dielectric constants and thicknesses of the remaining layers of dielectrics are solved one by one from the outside to the inside according to the solution process of the second layer of dielectric parameters and thickness, and the thicknesses and dielectric constants of the third, fourth...n layers of dielectrics can be obtained.

2. The method for estimating the thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: The operation of setting the medium parameter test system in step S1 includes: The dielectric parameter test system includes a vector network analyzer, a beamforming antenna, a dielectric plate to be tested, and a metal plate. The vector network analyzer is connected to the calibration point of the beamforming antenna, i.e., the feed receiving port. The dielectric plate to be tested is closely attached to the metal plate behind it, and the beamforming antenna is placed perpendicular to the dielectric plate. The reflection coefficient S at the calibration point of the beamforming antenna is tested by the vector network analyzer. 11 , the test data is recorded as 3. The method for estimating the thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: In step S2, the antenna standing wave S is measured. 11SW The specific operations include: The reflection coefficient of the beamforming antenna without the dielectric plate and metal plate to be tested is tested by a vector network analyzer. The reflection coefficient is the antenna standing wave, which is denoted as S 11SW .

4. A method for estimating thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: The method for frequency domain data processing in step S3 is: Reflection coefficient measured using dielectric parameter test system Deduct antenna standing wave S 11SW The corresponding impact is obtained by this, and the corresponding data is recorded as 5. A method for estimating the thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: In step S4.2, the time domain data of the reflected signal Г1 is converted to the frequency domain by discrete Fourier transform to obtain the reflection coefficient of the first layer, and combined with the formula The dielectric constant ε of the first layer of medium can be calculated r1 .

6. A method for estimating the thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: The method for calculating the thickness d1 of the first dielectric layer in step S4.2 includes: Analyzing the time domain waveform, the first reflection peak in the time domain waveform represents the first discontinuity of the material under test, that is, the first reflection at the interface between the air and the dielectric plate; the second reflection peak represents the second discontinuity of the material under test, that is, the first reflection of the dielectric surface of the dielectric plate and the metal plate; there is a certain time difference between the first two reflections in the time domain, which is twice the time it takes for the electromagnetic wave to propagate twice the dielectric thickness in the medium; as shown in the following formula: Among them, d is the dielectric thickness, c is the speed of electromagnetic wave propagation in vacuum, and ε represents the dielectric constant of the dielectric plate to be tested; according to this formula, the calculation formula is Measure the time difference Δt1 between the first discontinuity and the second discontinuity in the time domain waveform, and then use the dielectric constant ε of the first layer obtained in step (4) r1 , using the formula c is the propagation speed of electromagnetic waves in vacuum, and the thickness d1 of the first layer of medium can be calculated.

7. A method for estimating thickness and dielectric constant of a multilayer dielectric based on time domain analysis method according to claim 1, characterized in that: In step S4.3, the time domain data of the reflected signal Γ2 is converted to the frequency domain by discrete Fourier transform, and then combined with the dielectric constant ε of the first layer of medium r1 , using the formula The dielectric constant ε of the second layer of medium can be calculated r2 .

8. A method for estimating thickness and dielectric constant of a multilayer medium based on time domain analysis method according to any one of claims 1 to 7, characterized in that: Step S4.3: The method for solving the dielectric constant and thickness of the remaining layers of dielectrics includes: When calculating the dielectric constant and thickness of the n-th layer of medium, the reflected signal T of the n-th layer of medium is taken as n The remaining reflected signals are removed. n The time domain data is DFTed to obtain the reflection coefficient of the nth layer, and then the dielectric constant ε of the n-1th layer is calculated. rn-1 , using the formula The dielectric constant ε of the nth layer of medium can be calculated rn . Measure the time difference Δt between the nth discontinuity and the n+1th discontinuity in the time domain waveform n , and then according to the dielectric constant ε of the nth layer rn , using the formula The thickness d of the nth layer of medium can be calculated n .

Images