Radiometer-based method and apparatus for measuring complex permittivity of a wave-transparent material

Abstract

The application discloses a method and device for measuring complex permittivity of wave-transparent material based on radiometer, and belongs to the field of passive microwave / millimeter wave remote sensing and detection technology. The method comprises the following steps: preparing N (N>=3) material samples with different thicknesses, and recording the thicknesses as d [d1, d2, d3…, d N ]; the thickness of each sample should be smaller than the skin depth of the material to ensure that electromagnetic waves can effectively penetrate the sample; measuring linear polarization transmittance of the material samples with all the thicknesses at an incident angle θ, and recording the transmittance as γ [γ1, γ2, γ3…, γ N ]; using a fitting algorithm to fit the output loss index factor Q (ε r , θ) and the Fresnel reflectivity T p (ε r , θ) according to the calculation formula of the transmittance of the wave-transparent material; and calculating the complex permittivity ε r using the Q (ε p , θ) and the T r (ε r ). The application can obtain a unique solution of the complex permittivity of the wave-transparent material, and realize accurate measurement of the complex permittivity of the wave-transparent material.

Description

Technical Field

[0001] This invention belongs to the field of passive microwave / millimeter-wave remote sensing and detection technology, and more specifically, relates to a method and apparatus for measuring the complex permittivity of transparent materials based on a radiometer. Background Technology

[0002] In nature, all matter with a physical temperature above absolute zero radiates energy outward in the form of electromagnetic waves, with a frequency range covering almost the entire wavelength band. Different substances have different radiation spectra. Millimeter-wave radiation detection technology has advantages such as all-weather and 24 / 7 operation, stealth, and good penetration, and has important applications in remote sensing, target detection, and human security checks.

[0003] Electromagnetic parameters (including complex relative permittivity and complex relative permeability) are core parameters describing 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 reflecting the difference in material composition. Targets of different materials exhibit different millimeter-wave radiation characteristics due to their different complex permittivity. Accurate complex permittivity enables better target classification and even identification, and helps promote the application of millimeter-wave radiation measurement in fields such as human security inspection, ground object monitoring, and military target detection, providing theoretical and methodological support for obtaining target information in these areas.

[0004] Currently, commonly used methods for measuring complex permittivity include the resonance method and the free-space method. The resonance method compares the resonant frequency and quality factor of the resonant cavity before and after the target is placed, and obtains the complex permittivity of the target by inverting the difference between the two. However, the resonance method is not suitable for measuring dielectric materials with high losses and cannot perform broadband frequency sweep measurements. The free-space method uses a vector network analyzer to measure the reflection coefficient of the sample in free space and then inverts the complex permittivity. However, because the S-parameters of the free-space method are complex, phase ambiguity occurs during the inversion process, and the inversion result has multiple values. Moreover, high-frequency vector network analyzers, such as those in the W-band, are expensive, costing over a million. Therefore, it is extremely urgent to propose a method for measuring the complex permittivity of transparent materials that can obtain a unique and definite solution and is applicable to different levels of loss, as well as a simple and relatively inexpensive measuring device. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method and apparatus for measuring the complex permittivity of transparent materials based on a radiometer. The invention proposes a method for measuring the complex permittivity of transparent materials that can obtain a unique solution, as well as a measuring apparatus that is simple in structure and low in cost.

[0006] To achieve the above objectives, the present invention provides a method for measuring the complex permittivity of transparent materials 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 denot the thicknesses as d[d1,d2,d3…,d…]. N The sample thickness is less than the skin depth of the wave-transparent material being tested; where N is an integer greater than or equal to 3;

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

[0009] (3) Fit the output loss exponent factor Q and Fresnel reflectance T according to the following formula. p ;

[0010]

[0011] (4) Combined T p Solve for the complex refractive index using Q:

[0012]

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

[0014]

[0015] Thus, the complex permittivity is obtained, 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, and n' and n” are the real and imaginary parts of the complex refractive index, respectively.

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

[0021] (21) Align the radiometer with the center of the transparent material to be tested, and make the angle between the center of the radiometer and the normal of the transparent material equal to θ; place the first radiation source behind the transparent material to be tested as the background radiation source, measure for a duration of T, and record the horizontal polarization output voltage V of the radiometer during this duration. 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 transparent material to be tested to the same position as in (21), remove the first radiation source and replace it with the second radiation source, using the second radiation source as the background radiation source, and record the horizontal polarization output voltage of the radiometer during time T, denoted 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 middle M data points of each 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 sample (1≤i≤N), j is the j-th data point (1≤j≤M), and γ is an M×N matrix.

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

[0029] Furthermore, after obtaining M values ​​of the real and imaginary parts of the complex permittivity, we take the average:

[0030]

[0031]

[0032] The average result ε r As the final inversion result of the real part of the complex permittivity, ε r "This is the final inversion result of the imaginary part of the complex permittivity."

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

[0034]

[0035] Where λ is the wavelength in free space.

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

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

[0038] Furthermore, there are no requirements regarding the incident angle. However, at large incident angles, when measuring thicker samples, it's important to note that the radiometer's main beam may be projected onto the edges, which are also within the observation field of view. This results in inconsistent radiation characteristics on the thicker surface compared to the front surface of the transmissive material being measured. In such cases, an absorbing material can be used to construct a "measurement window." This "measurement window" utilizes the absorbing material to enclose and cover the edge of the object being measured while fixing the effective radiation area, thus controlling the effective radiation area. Alternatively, the sample size can be appropriately increased to avoid this error.

[0039] Furthermore, the beneficial effect of this invention is that it 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 permittivity measuring device based on a radiometer, comprising a sample clamp, a radiometer, and a processor;

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

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

[0043] The processor is used to fit and output the loss exponent factor Q and Fresnel reflectance T according to the following formula. p ;

[0044]

[0045] Lianli T p Solve for the complex refractive index using Q:

[0046]

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

[0048]

[0049] Thus, the complex permittivity is obtained, 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, and n' and n” are the real and imaginary parts of the complex refractive index, respectively.

[0054] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0055] 1. The method and apparatus for measuring the complex permittivity of transparent materials based on radiometer provided by the present invention fits the transmittance data of samples with multiple thicknesses, and then calculates the complex permittivity of the sample to be tested based on the fitting output parameters. The fitting of multi-dimensional measurement data makes the measurement results more accurate, and the inversion method provided by the present invention can uniquely determine the solution.

[0056] 2. The radiometer-based method for measuring the complex permittivity of transparent materials provided by this 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.

[0057] 3. The measurement tool for the method of measuring the complex permittivity of transparent materials based on radiometer provided by the present invention is a radiometer. Radiometers are inexpensive, and this method only requires measuring the transmittance, incident angle and sample thickness of the sample to be tested. The measurement steps are simple and save time and effort. Attached Figure Description

[0058] Figure 1 The diagram shows a three-layer radiation model provided by this invention.

[0059] Figure 2 The diagram shows the three-layer radiation equivalent structure provided by this invention.

[0060] Figure 3(a) is a schematic diagram of radiation measurement when the "edge problem" occurs, provided by the present invention.

[0061] Figure 3(b) is a schematic diagram of the "measuring window" provided by the present invention.

[0062] Figure 3(c) is a schematic diagram of the "measuring window" provided by the present invention to solve the "edge problem" in radiation measurement.

[0063] Figure 4 This is a scene diagram of the experimental measurement of the complex permittivity of transparent materials based on a radiometer, provided by the present invention. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this 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 a wave-transparent material can be approximated by a three-layer radiation model. This model 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 theory of reflection and transmission of electromagnetic waves in a single-layer medium, combined with the principle of multiple reflections, it is applied to a three-layer medium. The radiation transmission contribution of each layer is analyzed, and the expressions for the upward or downward radiation brightness temperature of each layer are obtained. The final radiation brightness temperature of the air layer is obtained by summing these expressions.

[0067] like Figure 1 As shown, the radiation source in the three-layer radiation model mainly consists of three parts: upward and downward radiation from the second layer of medium, and upward radiation from the third layer. The temperatures of the second and third layers of medium are T2 and T3, respectively, which can be directly measured by temperature sensors. Each layer of medium is isotropic. Let the loss factor of the second layer of medium be L2, and the reflectivity of the interface between the first and second layers of medium, and the incoherent reflectivity of the interface between the second and third layers of medium, be T1 and T2, respectively. Therefore, the final radiation brightness temperature entering the first layer of medium, calculated using radiation transfer theory, is:

[0068]

[0069] Where T 2U and T 2D T represents the contribution of the second-layer medium's self-upward and downward radiation to the final brightness temperature. 3U Let θ be the contribution of the self-upward radiation of the third medium to the final brightness temperature, θ be the corresponding observation angle, and p be the polarization mode. The final radiation brightness temperature of the first medium is calculated as follows:

[0070]

[0071] According to the Fresnel reflectance calculation formula, 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 within the transparent material. If P i If the incident power is the power at the first boundary, then the steady-state reflected and transmitted power are:

[0073]

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

[0075] e + ρ + γ = 1 (1.4)

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

[0077]

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

[0079]

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

[0081] χ is the real transmission angle, k e2 k a2 and k s2 Let a0 be the extinction coefficient, absorption coefficient, and scattering coefficient of the second layer medium, respectively. Here, we assume the single-scattering albedo a2 = k s2 / k e2 It is quite small; diffuse reflection is negligible. 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. Its specific expression is:

[0082]

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

[0084] Therefore, L2 can be represented as:

[0085]

[0086] The sample thickness d is peeled off, and the loss exponent factor Q is defined:

[0087]

[0088] The process of solving for 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 wavenumber of air, and k1 is the wavenumber of the first layer of medium.

[0096] Simplifying equations (1.11) and (1.12) together, we get:

[0097]

[0098] in

[0099]

[0100] The reflectivities T1 and T2 at the boundaries are Fresnel reflectivities. The horizontally polarized Fresnel reflectivities and the vertically polarized Fresnel reflectivities can be expressed as follows:

[0101]

[0102] Based on the above principles, this invention proposes a method for measuring the complex permittivity of transparent materials using a radiometer:

[0103] The linear polarization transmittance γ is expressed as a function of the loss exponent Q(ε). e θ), Fresnel reflectivity T p (ε e The forms in which θ and sample thickness d are expressed are:

[0104]

[0105] p is h or v, Q(ε) e ,θ) and T(ε e ,θ) are expressed by equations (1.10) and (1.15) respectively, and it is easy to see that Q(ε)e ,θ) and T p (ε e ,θ) is only related to the complex permittivity ε r The transmittance is related to the incident angle θ, but not to 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 considered as a constant, satisfying the nonlinear least squares fitting condition. The Levenberg-Marquardt (LM) algorithm is used in the fitting process, with the transmittance measurement data vector γ[γ1,γ2,γ3…,γ…]. N ] and sample thickness vector d[d1,d2,d3…,d N ] is the input, where N is the number of discrete data points, and Q(ε) is the input. e ,θ) and T p (ε e ,θ) are the fitted output parameters, with the ranges set to [0,10000] and [0,1] respectively, and the initial values ​​set to [37,0.5]. Finally, based on the output Q(ε) e ,θ) and T p (ε e Substitute θ into equations (1.10) and (1.15) to solve for the complex permittivity.

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

[0107] (1) A target to be measured has a complex permittivity of ε. r (ε r =ε r '-jε r First, prepare N (N≥3) material samples of different thicknesses, denoted as d[d1,d2,d3…,d…]. N The sample thickness should be less than the skin depth of the target to ensure that electromagnetic waves can effectively penetrate the sample.

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

[0109] (3) Using the Levenberg-Marquardt (LM) algorithm, input d and γ according to the following formula, and fit the output loss exponent factor Q and surface reflectivity T. h The ranges of the fitted output parameters were set to [0, 10000] and [0, 1], respectively, and the initial values ​​were set to [37, 0.5].

[0110]

[0111] (4) Solve the following equation using numerical methods:

[0112]

[0113] We obtain two real solutions, denoted as n. e1 and n e2 n e1 Less than n e2 , will n e2 Substituting into the following formula, we get A0:

[0114]

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

[0116] a6A + 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 using wavelength λ and loss exponent Q as follows:

[0127]

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

[0129] (6) A + *Substitute In the middle, we get A - *, then A + * and A - *Substitute:

[0130] A + A - =n'n”

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

[0132] The real part n' and imaginary part n” of the complex refractive index are obtained;

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

[0134] ε r '=n' 2 -n”2

[0135] ε r =2n'n";

[0136] More specifically, step (2) is implemented as follows:

[0137] (21) Adjust the height-adjustable bracket and the adjustable-angle sample clamp so that the radiometer is aligned with the center of the transparent material to be tested, and the angle between the center of the radiometer and the normal of the transparent material to be tested is equal to θ. Place the absorbing material behind the transparent material to be tested as a background radiation source. The measurement time is equal to T, and record the horizontal polarization output voltage V of the radiometer during this time. object_black ;

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

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

[0140] (24) Keep the metal plate stationary, 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 points and calculate the transmittance at the incident angle θ according to the following formula.

[0142]

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

[0144] In this embodiment, the materials to be tested are low-loss PP and general-loss soda-limeglass. The PP sample thicknesses are 2mm, 10mm, 30mm, and 50mm, and the glass sample thicknesses are 2mm, 3mm, 4mm, and 5mm. The radiometer integration time t is 2ms, the total measurement time T is 2s, and M equals 100. The complex permittivity is measured using a 3mm radiometer at a 50° incident angle. The measurement results are as follows:

[0145] ε PP =2.0735-0.0018j

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

[0147] Reference value:

[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. With a large incident angle, when measuring a thicker sample, it is necessary to be aware that the main beam of the radiometer may be projected onto the edge, and the edge is also within the field of view. The radiation characteristics of the thick surface are inconsistent with the front surface of the transparent material to be measured. At this time, a "measurement window" can be constructed using absorbing material. The "measurement window" is to use absorbing material to enclose and cover the edge of the measured object and fix the effective radiation area, thereby controlling the effective radiation area. Alternatively, the size of the sample can be appropriately increased to avoid this error. Figures 3(a)-3(c) A schematic diagram illustrating how to solve the "edge problem" for measurement windows.

[0151] The present invention also provides a device for measuring the complex permittivity of transparent materials based on a radiometer, such as... Figure 4 As shown, it includes a height-adjustable support, an adjustable-angle sample fixture, a radiometer, a microwave-absorbing material, and a metal plate. The microwave-absorbing material and the metal plate are used to switch the radiation intensity of the microwave-transparent material to be tested. The main beam after transmission propagates to the radiometer fixed on the turntable. The radiometer is used to perform radiation measurement on the microwave-transparent material to be tested. The complex permittivity of the microwave-transparent material to be tested is obtained based on the radiation voltage measured by the radiometer.

[0152] Those skilled in the art will readily understand that the above description is merely 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 within the scope of protection of the present invention.

Claims

1. A method for measuring the complex permittivity of transparent materials based on a radiometer, characterized in that, Includes the following steps: (1) Take N samples of the wave-transmitting material to be tested with different thicknesses, and denot the thicknesses as d[d1,d2,d3…,d…]. N The sample thickness is less than the skin depth of the wave-transparent material being tested; where N is an integer greater than or equal to 3; (2) At the incident angle θ, measure the p-polarized transmittance of samples of all thicknesses, denoted as γ[γ1,γ2,γ3…,γ…]. N ]; where p is h or v, representing horizontal polarization or vertical polarization, respectively; (3) Fit the output loss exponent factor Q and Fresnel reflectance T according to the following formula. p ; (4) Combined T p Solve for the complex refractive index using Q: A + 2 =A - 2 +n' 2 -n” 2 -sin 2 i Thus, the complex permittivity is obtained, 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, and n' and n” are the real and imaginary parts of the complex refractive index, respectively.

2. The measurement method according to claim 1, characterized in that, Step (2) specifically includes: (21) Align the radiometer with the center of the transparent material to be tested, and make the angle between the center of the radiometer and the normal of the transparent material equal to θ; place the first radiation source behind the transparent material to be tested as the background radiation source, measure for a duration of T, and record the horizontal polarization output voltage V of the radiometer during this duration. 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 transparent material to be tested to the same position as in (21), remove the first radiation source and replace it with the second radiation source, using the second radiation source as the background radiation source, and record the horizontal polarization output voltage of the radiometer during time T, denoted 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 middle M data points of each 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 sample (1≤i≤N), j is the j-th data point (1≤j≤M), and γ is an M×N matrix.

3. The measurement 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 measurement method according to claim 2, characterized in that, After obtaining M values ​​of the real and imaginary parts of the complex permittivity, take the average: The average result ε r As the final inversion result of the real part of the complex permittivity, ε r "This is the final inversion result of the imaginary part of the complex permittivity." 5. The measurement 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 wavelength in free space.

6. The measurement 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 permittivity of transparent materials based on a radiometer, characterized in that, Includes sample fixtures, radiometers, and processors; The sample fixture is used to allow the incident beam to be incident on the sample at an incident angle θ, wherein the sample consists of N pieces of wave-transmitting material of different thicknesses, denoted as d[d1, d2, d3…, d…]. N The sample thickness is less than the skin depth of the wave-transparent material being tested; N is an integer greater than or equal to 3; The radiometer is used to measure the radiation of the transmitted beam, measuring the p-polarized transmittance of samples of all thicknesses, denoted as γ[γ1, γ2, γ3…, γ…]. N ]; where p is h or v, representing horizontal polarization or vertical polarization, respectively; The processor is used to fit and output the loss exponent factor Q and Fresnel reflectance T according to the following formula. p ; Lianli T p Solve for the complex refractive index using Q: Thus, the complex permittivity is obtained, 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, and 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, It also includes a first radiation source and a second radiation source, which are used to switch the radiation intensity of the 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 wavelength in free space.

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