Method and device for measuring complex dielectric constant of wave-transmitting material based on radiometer

Abstract

The invention discloses a method and a device for measuring complex permittivity of a wave-transmitting material based on a radiometer, and belongs to the technical field of passive microwave / millimeter wave remote sensing and detection. The method comprises the steps that N (N > = 3) material samples with different thicknesses are prepared, the thicknesses are recorded as d [d1, d2, d3..., dN], and the thicknesses of the samples should be smaller than the skin depth of the materials, so that it is guaranteed that electromagnetic waves can effectively penetrate through the samples; measuring the linear polarization transmittances of the material samples with all the thicknesses under the incident angle theta, and recording the linear polarization transmittances as gamma [gamma 1, gamma 2, gamma 3... gamma N]; fitting an output loss index factor Q (epsilon r, theta) and a Fresnel reflectivity Tp (epsilon r, theta) by using a fitting algorithm according to a calculation formula of the transmissivity of the wave-transparent material; and calculating a complex dielectric constant epsilon r by using Q (epsilon r, theta) and Tp (epsilon r, theta). The unique solution of the complex dielectric constant of the wave-transparent material can be obtained, and accurate measurement of the complex dielectric constant of the wave-transparent material is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of passive microwave / millimeter wave remote sensing and detection, and more specifically, relates to a method and device for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer. Background Art

[0002] In nature, all substances with a physical temperature above absolute zero radiate energy in the form of electromagnetic waves, and their frequency range covers almost the entire band, and different substances have different radiation spectra. Millimeter wave radiation detection technology has the advantages of all-day, quasi-all-weather operation, concealment, and good penetration, and has important applications in remote sensing, target detection, and human safety inspection.

[0003] Electromagnetic parameters (including complex relative permittivity and complex relative permeability) are the core parameters that describe target material information. Most common artificial and natural targets are non-magnetic materials with a complex permeability of 1. In this case, the complex permittivity is the main electromagnetic parameter that reflects the material differences. Targets of different materials exhibit different millimeter-wave radiation characteristics due to their different complex permittivity. Accurate complex permittivity can better achieve the classification and even identification of targets, which will help promote the application of millimeter-wave radiation measurement in the fields of human security inspection, ground object monitoring, military target detection, etc., and provide theoretical and methodological support for the acquisition of target information.

[0004] At present, the commonly used complex dielectric constant measurement methods include the resonance method and the free space method. The test principle of the resonance method is to compare the resonant frequency and quality factor of the resonant cavity before and after the target is placed, and obtain the complex dielectric constant of the target by inverting the difference between the two. The resonance method is not suitable for measuring dielectric materials with large losses, and it cannot perform broadband sweep frequency measurement; the free space method uses a vector network analyzer to measure the reflection coefficient of the sample to be tested in free space and then invert the complex dielectric constant. However, because the S parameter measurement value of the free space method is a complex number, phase ambiguity will occur during the inversion process, and the inversion result has a multi-value problem. In addition, the price of a high-frequency vector network analyzer such as a W-band is more than one million, which is expensive. Therefore, it is extremely urgent to propose a complex dielectric constant measurement method for wave-transmitting materials that can obtain a unique definite solution and is suitable for different degrees of loss, as well as a measurement device with a simple structure and relatively low cost. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present invention is to provide a method and device for measuring the complex dielectric constant of wave-transmitting materials based on a radiometer, aiming to propose a method for measuring the complex dielectric constant of wave-transmitting materials that can obtain a unique definite solution and a measuring device with simple structure and low cost.

[0006] To achieve the above object, the present invention provides a method for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer, comprising the following steps:

[0007] (1) Take N samples of the wave-transmitting material to be tested with different thicknesses, and record the thickness as d[d1, d2, d3…, d N ], the sample thickness is less than the skin depth of the wave-transmitting material to be tested; wherein N is an integer greater than or equal to 3;

[0008] (2) At the incident angle θ, the p-polarized transmittance of samples of all thicknesses is measured and recorded as γ[γ1,γ2,γ3…,γ N ]; where p is h or v, indicating horizontal polarization or vertical polarization, respectively;

[0009] (3) According to the following formula, the output loss index factor Q and Fresnel reflectivity T are fitted. p ;

[0010]

[0011] (4) Lianli T p and Q to solve for the complex refractive index:

[0012]

[0013] A + 2 =A - 2 +n' 2 -n" 2 -sin 2 θ

[0014]

[0015] The complex dielectric constant is obtained, which is expressed as:

[0016] ε r =ε r '-jε r ”

[0017] ε r '=n' 2 -n" 2

[0018] ε r ”=2n'n”

[0019] where λ is the free space wavelength, n' and n" are the real and imaginary parts of the complex refractive index, respectively.

[0020] Furthermore, the step (2) specifically includes:

[0021] (21) Align the radiometer with the center of the wave-transparent material to be measured, and the angle between the center of the radiometer and the normal of the wave-transparent material to be measured is equal to θ; place the first radiation source on the back of the wave-transparent material to be measured as the background radiation source, measure for a time equal to T, and record the horizontal polarization output voltage V of the radiometer during this time object_black ;

[0022] (22) Keep the first radiation source stationary, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, denoted as V black ;

[0023] (23) Reposition the wave-transparent material to be tested to the same position as (21), remove the first radiation source, and replace it with the second radiation source. The second radiation source serves as the background radiation source. Record the horizontal polarization output voltage of the radiometer within time T, which is recorded as V object_mental ;

[0024] (24) Keep the second radiation source stationary, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, denoted as V mental ;

[0025] (25) Take the M data in the middle of the data length T / t and calculate the transmittance at the incident angle θ according to the following formula:

[0026]

[0027] Where t is the radiometer integration time, i is the i-th block of samples, 1≤i≤N, j is the j-th data, 1≤j≤M, and γ is an M×N matrix.

[0028] Furthermore, the first radiation source is an absorbing material, and the second radiation source is a metal plate.

[0029] Furthermore, the real and imaginary parts of the M complex dielectric constants are obtained and averaged:

[0030]

[0031]

[0032] The average result ε r 'As the final inversion result of the real part of the complex dielectric constant, ε r ” as the final inversion result of the imaginary part of the complex dielectric constant.

[0033] Furthermore, the surface roughness s of the wave-transmitting material to be tested satisfies:

[0034]

[0035] Where λ is the free space wavelength.

[0036] Furthermore, the algorithm used in step (3) is the Levenberg-Marquardt algorithm.

[0037] Furthermore, the beneficial effect achieved by the present invention is that by measuring the transmittance of the target with a radiometer to invert the complex dielectric constant, a relatively accurate and unique solution can be obtained; the measurement steps are simple, time and labor are saved, and the cost of measuring instruments and equipment is low.

[0038] Furthermore, there is no requirement for the size of the incident angle, but in the case of large incident angles, when measuring thicker samples, it is necessary to pay attention to the fact that the main beam of the radiometer may be projected on the edge, and the edge is also within the observation field of view. The radiation characteristics on the thickness surface are inconsistent with the positive surface of the wave-transparent material to be measured. At this time, a "measurement window" can be constructed using absorbing materials. The "measurement window" is to use absorbing materials to enclose the edge of the measurement object and fix the effective radiation area, thereby achieving control of the effective radiation area. The size of the sample can also be appropriately increased to avoid this error.

[0039] Furthermore, the beneficial effect achieved by the present invention is that the present invention can be applied to dielectric materials with different loss levels, as long as the thickness of the sample to be tested is less than the skin depth in the frequency band to be tested.

[0040] Another aspect of the present invention provides a complex dielectric constant measurement device based on a radiometer, comprising a sample holder, a radiometer and a processor;

[0041] The sample fixture is used to make the incident beam incident on the sample at an incident angle θ, wherein the sample is N pieces of wave-transmitting materials to be tested with different thicknesses, and the thickness is recorded as d[d1, d2, d3…, d N ], the sample thickness is less than the skin depth of the wave-transmitting material to be tested; N is an integer greater than or equal to 3;

[0042] The radiometer is used to measure the radiation of the transmitted beam and measure the p-polarization transmittance of samples of all thicknesses, which is recorded as γ[γ1,γ2,γ3…,γ N ]; where p is h or v, indicating horizontal polarization or vertical polarization, respectively;

[0043] The processor is used to fit the output loss index factor Q, the Fresnel reflectivity T according to the following formula p ;

[0044]

[0045] Lian Li T p and Q to solve for the complex refractive index:

[0046]

[0047] A +2 =A - 2 +n' 2 -n" 2 -sin 2 θ

[0048]

[0049] The complex dielectric constant is obtained, which is expressed as:

[0050] ε r =ε r '-jε r ”

[0051] ε r '=n' 2 -n" 2

[0052] ε r ”=2n'n”

[0053] where λ is the free space wavelength, n' and n" are the real and imaginary parts of the complex refractive index, respectively.

[0054] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0055] 1. The method and device for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer provided by the present invention fits the transmittance data of samples of multiple thicknesses, and then infers the complex dielectric constant of the sample to be measured based on the fitting output parameters. The fitting of multi-dimensional measurement data makes the measurement result more accurate, and the inversion method provided by the present invention can uniquely determine the solution.

[0056] 2. The method for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer provided by the present invention can be applied to dielectric materials with different loss levels, as long as the thickness of the sample to be measured is less than the skin depth in the frequency band to be measured.

[0057] 3. The measuring tool of the method for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer provided by the present invention is a radiometer. The radiometer is inexpensive, and the method only needs to measure the transmittance, incident angle and sample thickness of the sample to be measured. The measuring steps are simple, saving time and effort. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a three-layer radiation model diagram provided by the present invention.

[0059] Figure 2 This is a three-layer radiation equivalent structure diagram provided by the present invention.

[0060] FIG3( a ) is a schematic diagram of radiation measurement when an “edge problem” occurs provided by the present invention.

[0061] FIG3( b ) is a schematic diagram of a “measurement window” provided by the present invention.

[0062] FIG3( c ) is a schematic diagram of radiation measurement of the “measurement window” provided by the present invention to solve the “edge problem”.

[0063] Figure 4 A diagram of the experimental measurement scene of the complex dielectric constant of a wave-transmitting material based on a radiometer provided by the present invention. DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0065] The measurement principle can be briefly described as follows:

[0066] The electromagnetic radiation structure of the wave-transmitting material can be approximated as a three-layer radiation model, which is used to quantify and derive the overall radiation characteristics of the target, thereby establishing a more accurate radiation model of the target. First, based on the reflection and transmission theory of electromagnetic waves in a single-layer medium, combined with the principle of multiple reflections, it is applied to the three-layer medium, the radiation transmission contribution of each layer of the medium is analyzed, and the upward or downward radiation brightness temperature expression of each layer is obtained, and the final radiation brightness temperature of the air layer is obtained by summing.

[0067] like Figure 1 As shown, the radiation sources of the three-layer radiation model are mainly divided into three parts: the upward radiation and downward radiation of the second layer of the medium and the upward radiation of the third layer. The temperatures of the second and third layers of the medium are T2 and T3 respectively, which can be directly measured by the temperature sensor. Each layer of the medium is isotropic. Assume that the loss factor of the second layer of the medium is L2, the interface reflectivity of the first layer of the medium and the second layer of the medium, and the incoherent reflectivity of the interface of the second layer of the medium and the third layer of the medium are T1 and T2 respectively. It can be seen that the final radiation brightness temperature entering the first layer of the medium is calculated using the radiation transfer theory:

[0068]

[0069] Where T 2U and T 2D are the contributions of the second layer’s own upward radiation and downward radiation to the final brightness temperature, T 3U is the contribution of the third layer of medium's own upward radiation to the final brightness temperature, θ is the corresponding observation angle, and p is the polarization mode. After calculation, the final radiation brightness temperature of the first layer of medium is:

[0070]

[0071] According to the Fresnel reflectivity calculation formula, it is easy to obtain T1=T2.

[0072] Simplify the model to Figure 2 , define the concepts of effective emissivity and effective reflectivity, where “effective” refers to the steady-state solution that combines all multiple reflections in the wave-transmitting material. i is the power incident on the first boundary, then the steady-state reflected and transmitted powers are:

[0073]

[0074] If the material is kept in thermodynamic equilibrium, the relationship between the effective emissivity e, the effective reflectivity ρ and the effective transmittance γ is:

[0075] e+ρ+γ=1 (1.4)

[0076] For single scattering albedo a≈0, the incoherent transmittance is:

[0077]

[0078] L2 is the power attenuation factor of the wave-transmitting material, which can be expressed by the following formula:

[0079]

[0080] k e2 =k a2 +k s2 (1.7)

[0081] χ is the actual transmission angle, k e2 , k a2 and k s2 are the extinction coefficient, absorption coefficient and scattering coefficient of the second layer of medium respectively. Here, it is assumed that the single scattering albedo a2 = k s2 / k e2 is quite small, diffuse reflection can be ignored. Absorption coefficient k a2 Also known as the power absorption coefficient, it is twice the field attenuation coefficient and is related to the dielectric constant of the medium. The specific expression is:

[0082]

[0083] Where λ is the vacuum wavelength and n" is the imaginary part of the complex refractive index.

[0084] So L2 can be expressed as:

[0085]

[0086] Peel off the sample thickness d and define the loss index factor Q:

[0087]

[0088] The solution process of the real transmission angle χ is as follows:

[0089]

[0090] in

[0091]

[0092] p=2αβ

[0093] q=β 2 -α 2 -k1 2 sin 2 θ(1.12)

[0094]

[0095] k0 is the wave number of air, and k1 is the wave number of the first layer of medium.

[0096] The combined equations (1.11) and (1.12) are simplified to:

[0097]

[0098] in

[0099]

[0100] The reflectivity T1 and T2 of the boundary are Fresnel reflectivities. The horizontal polarization Fresnel reflectivity and the vertical polarization Fresnel reflectivity can be expressed as:

[0101]

[0102] So far, based on the above principles, the present invention proposes a method for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer:

[0103] The linear polarization transmittance γ is written as e ,θ), Fresnel reflectivity T p (ε e ,θ) and sample thickness d are expressed in the form of:

[0104]

[0105] p is h or v, Q(ε e ,θ) and T(ε e ,θ) are respectively expressed by equation (1.10) and equation (1.15). It is easy to see that Q(εe ,θ) and T p (ε e ,θ) is only related to the complex dielectric constant ε r , and the incident angle θ, but has nothing to do with the sample thickness d. Therefore, when measuring the transmittance of material samples of different thicknesses at the same incident angle, Q(ε e ,θ) and T(ε e ,θ) can be regarded as a constant, which satisfies the nonlinear least squares fitting condition. In the fitting process, the algorithm used is the Levenberg-Marquardt (LM) algorithm. The transmittance measurement data vector γ[γ1,γ2,γ3…,γ N ] and the sample thickness vector d[d1,d2,d3…,d N ] is the input, where N is the number of discrete data points, Q(ε e ,θ) and T p (ε e ,θ) are the fitting output parameters, and the ranges of the fitting output parameters are set to [0,10000] and [0,1] respectively, and the initial values ​​are set to [37,0.5]. e ,θ) and T p (ε e ,θ) into equations (1.10) and (1.15) to solve the complex dielectric constant.

[0106] Taking horizontal polarization as an example, the specific steps include:

[0107] (1) Measure a target whose complex dielectric constant is ε r (ε r =ε r '-jε r ”), first prepare N (N ≥ 3) pieces of material samples with different thicknesses, and the thickness is recorded as d[d1, d2, d3…, d N ], the sample thickness should be less than the skin depth of the target to be measured to ensure that the electromagnetic wave can effectively penetrate the sample;

[0108] (2) At the incident angle θ, the horizontal polarization transmittance of the material samples of all thicknesses is measured and recorded as γ[γ1,γ2,γ3…,γ N ];

[0109] (3) Using the Levenberg-Marquardt (LM) algorithm, we input d and γ according to the following formula to fit the output loss index factor Q and surface reflectivity T h , where the ranges of the fitting output parameters are set to [0,10000] and [0,1], and the initial values ​​are set to [37,0.5];

[0110]

[0111] (4) Use numerical methods to solve the following equation:

[0112]

[0113] We get two real number solutions, denoted as n e1 and n e2 , n e1 Less than n e2 , n e2 Substitute it into the following formula to get A0:

[0114]

[0115] (5) Solve the equation using Newton's iteration method:

[0116] a6 + 6 +a5A + 5 +a4A + 4 +a3A + 3 +a2A + 2 +a1A + 1 +a0=0

[0117] in:

[0118] a6=1-T h

[0119] a5=-2cosθ(1+T h )

[0120] a4=(1-T h )cos 2 θ+2sin 2 θ(1-T h )+2P(1-T h )

[0121] a3=-4cosθsin 2 θ(1+T h )-2cosθm(1+T h )

[0122] a2=2sin 2 θcos 2 θ(1-T h )+Pcos 2 θ(1-T h )+

[0123] sin 4 θ(1-Th )+3Psin 2 θ(1-T h )+P 2 (1-T h )

[0124] a1=-2sin 4 θcosθ(1+T h )-2Pcosθsin 2 θ(1+T h )

[0125] a0=cos 2 θsin 4 θ(1-T h )+Pcos 2 θsin 2 θ(1-T h )+Psin 4 θ(1-T h )

[0126] P is expressed in terms of wavelength λ and loss index factor Q:

[0127]

[0128] The initial value of the iteration is set to A0, the absolute error limit of the root δ is set to 0.001, and the solution is recorded as A + *;

[0129] (6) A + *Bring in In, get A - *, then A + * and A - *Bring in:

[0130] A + A - =n'n"

[0131] A + 2 -A - 2 =n' 2 -n" 2 -sin 2 θ

[0132] Get the real part n' and imaginary part n" of the complex refractive index;

[0133] (7) The real and imaginary parts of the complex dielectric constant can be obtained by using the mathematical relationship between the complex refractive index and the complex dielectric constant:

[0134] ε r '=n' 2 -n"2

[0135] ε r "=2n'n";

[0136] More specifically, the specific implementation of step (2) is:

[0137] (21) Adjust the elevating bracket and the adjustable angle sample fixture so that the radiometer is aligned with the center of the wave-transmitting material to be tested, and the angle between the center of the radiometer and the normal of the wave-transmitting material to be tested is equal to θ. Place the absorbing material on the back of the wave-transmitting material to be tested as the background radiation source. The measurement time is equal to T, and the horizontal polarization output voltage V of the radiometer during this time is recorded. object_black ;

[0138] (22) Keep the absorbing material still, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, which is recorded as V black ;

[0139] (23) Place the wave-transmitting material to be tested back on the adjustable angle sample fixture in the same position as (21), remove the wave-absorbing material and replace it with a metal plate. The metal plate is tilted so that the reflected sky serves as the background radiation source. Record the horizontal polarization output voltage of the radiometer within time T, which is recorded as V object_mental ;

[0140] (24) Keep the metal plate still, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, denoted as V mental ;

[0141] (25) During the measurement process, if the radiometer integration time is ts, this means that V object_black 、V black 、V object_mental and V mental The data length is T / t. Take the middle M data and then calculate the transmittance at the incident angle θ according to the following formula.

[0142]

[0143] Where i is the i-th block of samples, j is the j-th data, and γ is an M×N matrix.

[0144] In this embodiment, the wave-transmitting materials to be tested are low-loss material PP and general loss material soda-limeglass. The sample thickness of PP is 2 mm, 10 mm, 30 mm, and 50 mm, and the sample thickness of glass is 2 mm, 3 mm, 4 mm, and 5 mm. The radiometer integration time t is 2 ms, the total measurement time T is 2 s, M is equal to 100, and the complex dielectric constant is measured at an incident angle of 50° using a 3 mm radiometer. The measurement results are:

[0145] ε PP =2.0735-0.0018j

[0146] ε soda-lime glass =6.0356-0.1332j

[0147] The reference values ​​are:

[0148] ε PP ref =2.2663-0.0024j

[0149] ε soda-lime glass ref =6.0500-0.0950j

[0150] More specifically, the incident angle in step (2) should not be too large. In the case of a large incident angle, when measuring a thicker sample, it is necessary to pay attention to the fact that the main beam of the radiometer may be projected on the edge, and the edge is also within the observation field of view. The radiation characteristics on the thickness surface are inconsistent with the positive surface of the wave-transparent material to be measured. At this time, a "measurement window" can be constructed using absorbing materials. The "measurement window" is to use absorbing materials to enclose the edge of the measurement object and fix the effective radiation area, thereby achieving control of the effective radiation area. The size of the sample can also be appropriately increased to avoid this error. Figure 3(a)-Figure 3(c) Schematic diagram of solving the "edge problem" for the measurement window.

[0151] The present invention also provides a device for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer, such as Figure 4 As shown, it includes a liftable bracket, an adjustable angle sample fixture, a radiometer, an absorbing material and a metal plate; the absorbing material and the metal plate are used to switch the radiation intensity irradiating the wave-transparent material to be measured, and the main beam after transmission is propagated to the radiometer fixed on the turntable, and the radiometer is used to perform radiation measurement on the wave-transparent material to be measured, and the complex dielectric constant of the wave-transparent material to be measured is obtained based on the radiation voltage measured by the radiometer.

[0152] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer, characterized in that: The following steps are involved: (1) Take N samples of the wave-transmitting material to be tested with different thicknesses, and record the thickness as d[d1, d2, d3…, d N ], the sample thickness is less than the skin depth of the wave-transmitting material to be tested; wherein N is an integer greater than or equal to 3; (2) At the incident angle θ, the p-polarized transmittance of samples of all thicknesses is measured and recorded as γ[γ1,γ2,γ3…,γ N ]; where p is h or v, indicating horizontal polarization or vertical polarization, respectively; (3) According to the following formula, the output loss index factor Q and Fresnel reflectivity T are fitted. p ; (4) Lianli T p and Q to solve for the complex refractive index: A + 2 =A - 2 +n' 2 -n” 2 -sin 2 i The complex dielectric constant is obtained, which is expressed as: e r =e r '-je r " e r '=n' 2 -n” 2 ε r ”2n'n” where λ is the free space wavelength, n' and n" are the real and imaginary parts of the complex refractive index, respectively.

2. The measuring method according to claim 1, characterized in that: The step (2) specifically comprises: (21) Align the radiometer with the center of the wave-transparent material to be measured, and the angle between the center of the radiometer and the normal of the wave-transparent material to be measured is equal to θ; place the first radiation source on the back of the wave-transparent material to be measured as the background radiation source, measure for a time equal to T, and record the horizontal polarization output voltage V of the radiometer during this time object_black ; (22) Keep the first radiation source stationary, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, denoted as V black ; (23) Reposition the wave-transparent material to be tested to the same position as (21), remove the first radiation source, and replace it with the second radiation source. The second radiation source serves as the background radiation source. Record the horizontal polarization output voltage of the radiometer within time T, which is recorded as V object_mental ; (24) Keep the second radiation source stationary, remove the sample, and record the horizontal polarization output voltage of the radiometer within time t, denoted as V mental ; (25) Take the M data in the middle of the data length T / t and calculate the transmittance at the incident angle θ according to the following formula: Where t is the radiometer integration time, i is the i-th block of samples, 1≤i≤N, j is the j-th data, 1≤j≤M, and γ is an M×N matrix.

3. The measuring method according to claim 2, characterized in that: The first radiation source is a wave absorbing material, and the second radiation source is a metal plate.

4. The measuring method according to claim 2, characterized in that: Get the real and imaginary parts of the M complex dielectric constants and take the average: The average result ε r 'As the final inversion result of the real part of the complex dielectric constant, ε r ” is used as the final inversion result of the imaginary part of the complex dielectric constant.

5. The measuring method according to claim 1, characterized in that: The surface roughness s of the wave-transmitting material to be tested satisfies: Where λ is the free space wavelength.

6. The measuring method according to claim 1, characterized in that: The algorithm used in step (3) is the Levenberg-Marquardt algorithm.

7. A device for measuring the complex dielectric constant of a wave-transmitting material based on a radiometer, characterized in that: Includes sample holder, radiometer and processor; The sample fixture is used to make the incident beam incident on the sample at an incident angle θ, wherein the sample is N pieces of wave-transmitting materials to be tested with different thicknesses, and the thickness is recorded as d[d1, d2, d3…, d N ], the sample thickness is less than the skin depth of the wave-transmitting material to be tested; N is an integer greater than or equal to 3; The radiometer is used to measure the radiation of the transmitted beam and measure the p-polarization transmittance of samples of all thicknesses, which is recorded as γ[γ1,γ2,γ3…,γ N ]; where p is h or v, indicating horizontal polarization or vertical polarization, respectively; The processor is used to fit the output loss index factor Q, the Fresnel reflectivity T according to the following formula p ; Lian Li T p and Q to solve for the complex refractive index: The complex dielectric constant is obtained, which is expressed as: e r =e r '-je r " e r '=n' 2 -n” 2 ε r ”2n'n” where λ is the free space wavelength, n' and n" are the real and imaginary parts of the complex refractive index, respectively.

8. The measuring device according to claim 7, characterized in that The first radiation source and the second radiation source are used to switch the radiation intensity for irradiating the wave-transparent material to be tested.

9. The measuring device according to claim 8, characterized in that The first radiation source is a wave absorbing material, and the second radiation source is a metal plate.

10. The measuring device according to claim 7, characterized in that The surface roughness s of the wave-transmitting material to be tested satisfies: Where λ is the free space wavelength.

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