Environmental material dielectric property perception inversion method based on terahertz channel

Abstract

The invention discloses an environmental material dielectric property perception inversion method based on a terahertz channel. A terahertz frequency band continuous wave signal is generated by using a signal generator and a frequency multiplication module. The signal is transmitted to a material to be tested through an accurate horn antenna, and a reflection signal is received through a matching antenna. In an experiment, the emitter is fixed, the receiver and a measured material are all mounted on an independent turntable, and multi-group measurement is performed by changing an incident angle, so that data that the reflectivity changes along with the incident angle is obtained. Theoretical calculation is carried out by combining a Fresnel equation, and a corresponding reflectivity curve is obtained. And the accuracy of the inversion dielectric constant is verified by comparing and analyzing the reflectivity data with reflectivity data measured by an experiment. The measurement scheme has the characteristics of simplicity and convenience in operation, high time efficiency, low requirement on sample preparation and the like, can be widely applied to the fields of material science, electronic engineering, photoelectric technology and the like, and promotes deep development of research on electromagnetic properties of materials. The whole method provides an effective solution for high-precision dielectric constant measurement in an unknown environment.

Description

Technical Field

[0001] The present invention belongs to the field of material science and physics, and specifically relates to a method for sensing and inverting dielectric properties of environmental materials based on a terahertz channel. Background Art

[0002] From the perspective of electromagnetism, the dielectric constants of different media are different, so measuring the dielectric constant can analyze the interaction between electromagnetic waves and media, as well as the field changes of electromagnetic waves and media. The dielectric constant is an important physical property of materials, and the study of the dielectric constant has important theoretical and application significance. Electromagnetic compatibility issues, terahertz communications, and electronic technology all utilize the electromagnetic properties of materials, especially in the field of terahertz communications. It is necessary to accurately measure the dielectric constant of materials at terahertz frequencies in order to study the reflection and scattering characteristics of the materials, which puts forward requirements for the measurement of the dielectric constant.

[0003] There are many methods for measuring dielectric constant. Typical existing methods for measuring dielectric constant of materials include measuring dielectric constant of materials by vector network analyzer (VNA) or terahertz time domain spectrometer (THz Time Domain Spectroscopy, THz-TDS). VNA obtains the transmittance and reflectivity of materials by measuring S parameters, thereby calculating the dielectric constant. This method requires sophisticated sample preparation and calibration, and the instrument is expensive. THz-TDS uses ultrashort pulse laser to generate and detect terahertz waves, and calculates the transmittance, reflectivity and dielectric constant of materials by measuring the time domain response of samples to terahertz pulses. The system is relatively complex and costly, and has high requirements for environmental stability. In addition, there is a resonant cavity method, which is to calculate the dielectric constant of materials by measuring the resonant frequency and quality factor changes after the material is inserted into the resonant cavity. This method has high measurement accuracy and is suitable for materials with high Q values, but the sample size and shape are limited, and the measurement is relatively complicated. The waveguide method measures the transmission characteristics of the material sample in the waveguide and calculates its electromagnetic characteristics through S parameters. This method is suitable for solid materials and has high measurement accuracy, but the sample preparation requirements are high and the system is relatively complex. Most importantly, the above four typical measurement methods may not be feasible in unknown environments. Summary of the invention

[0004] In order to solve the technical problems existing in the background technology, the present invention aims to provide a method for sensing and inverting the dielectric properties of environmental materials based on a terahertz channel. By measuring the reflectivity of the material when the incident angle changes, the change in the reflectivity value is theoretically calculated through the Fresnel formula, and error analysis is performed to verify the accuracy of the inverted dielectric constant.

[0005] In order to solve the technical problem, the technical solution of the present invention is:

[0006] A method for sensing and inverting dielectric properties of environmental materials based on a terahertz channel, the method comprising:

[0007] The transmitter is fixed, and the receiver and the material to be tested are installed on independent turntables. The reflectivity of the two materials at 140 GHz and 240 GHz is measured respectively. Multiple groups of measurements are performed by changing the incident angle to obtain the change of reflectivity with the reflection angle, which is used as the measurement data.

[0008] The reflection coefficient is described by the Fresnel equation, which is as follows:

[0009]

[0010] In formula (1), θ1, θ2 and θ3 represent the incident angles of media 1, 2 and 3 respectively, λ2 is the wavelength of the terahertz wave in medium 2, and d is the thickness of the medium; the reflection coefficient ρ at the interface between medium 1 and medium 2 is 12 and the reflection coefficient ρ at the interface between medium 2 and medium 3 23 It can be expressed by the Fresnel equation:

[0011]

[0012]

[0013] Where ε1, ε2 and ε3 represent the dielectric constants of medium 1 (air), medium 2 (material surface) and medium 3 (air), respectively;

[0014] The theoretical reflectivity of the material calculated based on the above formula was compared with the measurement results to verify the accuracy of the inverted material dielectric constant.

[0015] Furthermore, the medium 1 is air, the medium 2 is a material surface, and the medium 3 is air.

[0016] Furthermore, the two materials are plastic products of two different materials.

[0017] Further, the measurement process through the experimental equipment includes:

[0018] Signal generation: Use a signal generator to generate baseband signals with a frequency range of 100KHz to 20GHz;

[0019] Frequency multiplication: The baseband signal is up-converted through the frequency multiplication module to achieve ×12 frequency multiplication, generating the required terahertz frequency range of 110-170GHz; for higher frequency bands (220-325GHz), other types of frequency multipliers are used to achieve ×18 frequency multiplication;

[0020] Signal transmission and reception: The continuous wave (CW) signal is transmitted through the horn antenna; the receiving end is also equipped with a matching horn antenna to receive the signal reflected from the material sample;

[0021] Power detection: The received signal is directly detected by a power sensor to obtain the power information of the reflected signal;

[0022] Beam steering: In the 220-325 GHz measurement, a horn antenna and a Teflon lens (focal length 10 cm) are configured to steer the signal beam;

[0023] Data acquisition and control: Use computer to set up control and data acquisition, manage signal generators and power meters, and ensure real-time data acquisition;

[0024] Sample placement: Place the material sample to be tested in the center of the experimental table, and place the transmitter and receiver on both sides of the material sample respectively; the entire experimental device is located 40 cm above the experimental platform to eliminate the first Fresnel zone;

[0025] Incident angle adjustment: by changing the incident angle between the transmitter and the material sample, multiple sets of measurements are performed to obtain reflectivity data at different angles;

[0026] Data processing and curve drawing:

[0027] Process the received power data, calculate the reflectivity corresponding to each incident angle and draw a reflectivity curve; apply the above Fresnel formula to perform theoretical calculations and generate a curve showing the change of theoretical reflectivity value with incident angle;

[0028] Result comparison and analysis: Compare the measured data at 140 GHz and 240 GHz with the theoretical calculation data, evaluate the quality of the fit between the two, and verify the correctness of the inverted dielectric constant.

[0029] Compared with the prior art, the advantages of the present invention are:

[0030] The present invention utilizes the inherent sensing characteristics of the terahertz channel and obtains the dielectric constant of the material by analyzing the reflection characteristics of the material, thereby solving the problem that VNA or THz-TDS cannot measure the dielectric constant of the material in an unknown environment, and at the same time, the measurement accuracy can achieve an ideal effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 , Reflection schematic diagram of the present invention:

[0032] Figure 2 , measurement experimental device diagram;

[0033] Figure 3 , Comparison of measurement results and theoretical calculations at 140GHz;

[0034] Figure 4 , comparison of measurement results and theoretical calculations at 240GHz;

[0035] Figure 5 , the application of the method of inverting the dielectric constant of materials in indoor scenes;

[0036] Figure 6 , and the application of the method of inverting material dielectric constants in outdoor scenes. DETAILED DESCRIPTION

[0037] The specific implementation mode of the present invention is described below in conjunction with embodiments:

[0038] It should be noted that the structures, proportions, sizes, etc. shown in this specification are only used to match the contents disclosed in the specification so that people familiar with this technology can understand and read them, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the effects and purposes that can be achieved by the present invention.

[0039] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" cited in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0040] Embodiment 1:

[0041] The materials used in the present invention are two different plastic products, recorded as material 1 and material 2, and the reflection characteristics of the two materials are measured to invert their dielectric constants. The transmitter is fixed, and the receiver and the material to be measured are installed on independent turntables. The reflectivity of the two materials at frequencies of 140 GHz and 240 GHz are measured respectively. The incident angle is changed to perform multiple groups of measurements, and the change of reflectivity with reflection angle is obtained, and the data is used as measurement data. The reflection coefficient can be described by the Fresnel equation in theoretical calculation, and the formula is as follows:

[0042]

[0043] In formula (1), θ1, θ2 and θ3 represent the incident angles of media 1, 2 and 3 respectively. λ2 is the wavelength of the terahertz wave in medium 2, and d is the thickness of the medium. The reflection coefficient ρ at the interface between medium 1 and medium 2 is 12 and the reflection coefficient ρ at the interface between medium 2 and medium 3 23 It can be expressed by the Fresnel equation:

[0044]

[0045]

[0046] Where ε1, ε2 and ε3 represent the dielectric constants of medium 1 (air), medium 2 (material surface) and medium 3 (air) respectively. Figure 1 shown.

[0047] The theoretical reflectivity of the material calculated based on the above formula was compared with the measurement results, which verified the accuracy of our inverted material dielectric constant.

[0048] Embodiment 2:

[0049] The laboratory equipment measurement process is as follows:

[0050] The signal generator generates baseband signals in the spectrum range of 100KHz to 20GHz, which are up-converted to the required terahertz frequency range (110-170GHz) through a frequency doubling module to achieve ×12 frequency multiplication. The generated continuous wave (CW) signal is transmitted through a horn antenna, while the receiving end is equipped with a matching horn antenna to forward the incoming signal to the power sensor for direct detection. For measurements in the higher frequency domain (220-325GHz), the configuration includes a frequency multiplier to multiply the signal by ×18, with a horn antenna and a polytetrafluoroethylene lens (angst 10cm) to guide the beam. At the same time, a laptop is used to set up control and data acquisition, manage the signal generator and power meter. Therefore, the material sample is placed in the center of the experimental table, and the transmitter and receiver are placed on both sides of the material sample. Multiple measurements are performed by changing the incident angle, such as Figure 2 The measurement experimental device is shown in FIG. 1 . The received power data obtained by processing is used to obtain the reflectivity curve that changes with the incident angle. The theoretical calculation is performed using the above formula to obtain the curve of the theoretical reflectivity value changing with the incident angle. The result is shown in FIG. Figure 3 and 4 As shown in the figure, the comparison results of the measured data at 140 GHz and the theoretical calculation data and the comparison results of the measured data at 240 GHz and the theoretical calculation data respectively, it can be seen that the theoretical calculation data and the measured data fit well, which verifies the correctness of the inverted dielectric constant. This measurement scheme can achieve high measurement accuracy while saving time and labor, has no requirements for the preparation of material samples, and is easy to operate. Figure 5 As shown in FIG. 1 , in an indoor scene, a sample of the material to be tested is fixed, and the dielectric constant of the material at terahertz frequency is measured using this method. Figure 6 As shown, in outdoor scenes, the dielectric constant of the building surface material is unknown, so this method can be used to measure the dielectric properties of various materials on the building surface.

[0051] Embodiment 3:

[0052] In the described experimental process, the hardware equipment used mainly includes the following categories:

[0053] Signal generator: used to generate baseband signals with a frequency range of 100KHz to 20GHz.

[0054] Frequency doubling module:

[0055] Frequency multiplier (×12): Up-converts the baseband signal to the required terahertz frequency range (110-170 GHz).

[0056] Frequency multiplier (×18): Up-converts the baseband signal to the required terahertz frequency range (220-325 GHz).

[0057] antenna:

[0058] Horn antenna (110-170GHz): used to transmit the generated continuous wave (CW) signal.

[0059] Horn antenna (220-325GHz): used for higher frequency measurements, with PTFE lens.

[0060] Polytetrafluoroethylene lens (focal length 10 cm): used to guide and focus the terahertz signal beam.

[0061] Power sensor: used to directly detect the received signal power.

[0062] Data acquisition and control equipment:

[0063] Laptop: Used to set up and control the signal generator and power meter, and to collect data.

[0064] Experimental table: used to place material samples and fix the transmitter and receiver. The entire experimental device is located 40cm above the experimental platform to eliminate the first Fresnel zone.

[0065] Turntable: A separate turntable device used to adjust the angle of incidence between the emitter and the material sample.

[0066] Embodiment 4:

[0067] Compared with using VNA or THz-TDS to measure the dielectric constant of a material, the present invention has no requirements for the preparation of material samples. It only needs to measure and process the change of reflectivity within a certain reflection angle range. The operation time is short and the efficiency is improved. The comparison between the measurement results of the present invention and the THz-TDS measurement results is shown in Table 1. It can be seen that the error is less than 6% compared with the measurement using THz-TDS, and better accuracy can be achieved.

[0068] Table 1. Refractive index comparison

[0069]

[0070] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

[0071] Many other changes and modifications may be made without departing from the concept and scope of the present invention.It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for sensing and inverting dielectric properties of environmental materials based on terahertz channels, characterized in that: The method comprises: Fix the transmitter, install the receiver and the material to be tested on independent turntables, measure the reflectivity of the two materials at 140GHz and 240GHz respectively, change the incident angle to perform multiple groups of measurements, and obtain the change of reflectivity with reflection angle, which is used as the measurement data; The reflection coefficient is described by the Fresnel equation, which is as follows: In formula (1), θ1, θ2 and θ3 represent the incident angles of media 1, 2 and 3 respectively, λ2 is the wavelength of the terahertz wave in medium 2, and d is the thickness of the medium; the reflection coefficient ρ at the interface between medium 1 and medium 2 is 12 and the reflection coefficient ρ at the interface between medium 2 and medium 3 23 Using the Fresnel equation, it can be expressed as: Where ε1, ε2 and ε3 represent the dielectric constants of medium 1, medium 2 and medium 3 respectively; The theoretical reflectivity of the material calculated based on the above formula was compared with the measurement results to verify the accuracy of the inverted material dielectric constant.

2. The method for sensing dielectric properties of environmental materials based on terahertz channels according to claim 1, characterized in that: The medium 1 is air, the medium 2 is a material surface, and the medium 3 is air.

3. The method for sensing dielectric properties of environmental materials based on terahertz channels according to claim 1, characterized in that: The two materials are plastic products made of two different materials.

4. The method for sensing dielectric properties of environmental materials based on terahertz channels according to claim 1, characterized in that: The measurement process through the experimental equipment includes: Signal generation: Use a signal generator to generate baseband signals with a frequency range of 100KHz to 20GHz; Frequency multiplication: The baseband signal is up-converted through the frequency multiplication module to achieve ×12 frequency multiplication, generating the required terahertz frequency range of 110-170GHz; for higher frequency bands, i.e. 220-325GHz, other types of frequency multipliers are used to achieve ×18 frequency multiplication; Signal transmission and reception: The continuous wave CW signal is generated by transmitting through the horn antenna; the receiving end is also equipped with a matching horn antenna to receive the signal reflected from the material sample; Power detection: The received signal is directly detected by a power sensor to obtain the power information of the reflected signal; Beam steering: In the 220-325 GHz measurement, a horn antenna and a Teflon lens (focal length 10 cm) are configured to steer the signal beam; Data acquisition and control: Use computer to set up control and data acquisition, manage signal generator and microwave power meter, and ensure the real-time data acquisition; Sample placement: Place the material sample to be tested in the center of the experimental table and fix it on the turntable. The transmitter and receiver are placed on both sides of the material sample respectively. The entire experimental device is located 40 cm above the experimental platform to eliminate the first Fresnel zone. Incident angle adjustment: by changing the incident angle between the transmitter and the material sample, multiple sets of measurements are performed to obtain reflectivity data at different angles; Data processing and curve drawing: Process the received power data, calculate the reflectivity corresponding to each incident angle and draw a reflectivity curve; apply the above Fresnel formula to perform theoretical calculations and generate a curve showing the change of theoretical reflectivity value with incident angle; Result comparison and analysis: Compare the measured data at 140 GHz and 240 GHz with the theoretical calculation data, evaluate the quality of the fit between the two, and verify the correctness of the inverted dielectric constant.

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