Method and system for testing terahertz wave band dielectric constant of small-size hazardous article

Abstract

The invention relates to the technical field of hazardous article detection, and provides a small-size hazardous article terahertz wave band dielectric constant testing method and system, and the method comprises the steps: placing a to-be-tested material between two convex lenses, controlling a horn antenna of a spread spectrum module to emit an electromagnetic wave, and in any radiation angle, viewing the electromagnetic wave as a plane wave, acquiring an S parameter measured by the vector network analyzer, and performing conversion; obtaining the thickness of the to-be-measured material, and converting the thickness into equivalent thickness; obtaining an inversion dielectric constant through an inversion model; acquiring a radiation angle, an image distance and an object distance, converting an incident angle, and determining a conversion dielectric constant on the basis that the refraction angle and the incident angle meet the Snell law; the refraction angle enabling the difference between the inversion dielectric constant and the conversion dielectric constant to be minimum is searched, the dielectric constant under the corresponding radiation angle is obtained, the average dielectric constant is obtained through integration, and the method adapts to measurement of non-uniform samples and size-limited samples.

Description

Technical Field

[0001] The present invention belongs to the technical field of dangerous goods detection, and particularly relates to a method and system for measuring the dielectric constant of small-sized dangerous goods in the terahertz band. Background Technique

[0002] The statements in this part only provide background technical information related to the present invention and do not necessarily constitute prior art.

[0003] Some flammable solids and oxidants can be pressed into flat plates, such as red phosphorus. In scenarios where they are not allowed to be carried, how to quickly and accurately detect these small-sized dangerous goods has become a key issue. The dielectric constant, as a physical quantity reflecting the ability of a substance to store charge, represents the ratio of the charge storage ability in a medium to that in a vacuum under the same electric field strength. The larger the dielectric constant, the greater the attenuation of the electric field strength by the material, and the stronger the ability of the material to shield the electric field. Moreover, the dielectric constant of a material may be different at different frequencies, because different microscopic changes occur inside the material when it responds to electromagnetic waves of different frequencies, that is, different polarization effects are generated. Therefore, characterizing the dielectric constant of a frequency band can be an important basis for identifying the material of an object. Terahertz waves have low energy and natural safety, and the dielectric constant detection based on terahertz waves has the non-contact feature, and there is no extrusion on the object to be measured during measurement. Considering these characteristics, for small-sized flammable solids, oxidants and other dangerous goods that can be made into flat plates, it is possible to characterize their categories by measuring the dielectric constant in the terahertz band, so as to achieve their rapid and safe detection.

[0004] Common dielectric constant measurement methods include the parallel plate method, the coaxial line method, the resonant cavity method, the free space method, etc. They are suitable for measuring different categories of substances and also have differences in measurement frequency and measurement accuracy. Among them, the free space method takes the vector network analyzer as the core instrument. Electromagnetic waves propagate in free space and interact with the object to be measured, showing absorption (inside the substance), reflection (at the interface between the object to be measured and air), and transmission (at the interface between the object to be measured and air) phenomena. Since the scattering parameters ( S parameters) measured by the vector network analyzer are related to the reflection coefficient, transmission coefficient, and propagation constant, and these parameters are in turn related to the dielectric constant, therefore, based on a specific physical model, the dielectric constant inversion calculation can be realized by measuring S parameters. The free space method is characterized by being suitable for large-sized flat materials, and the sample can be heated during the measurement process to characterize the dielectric constant of the flat material at a specific temperature. The free space method regards the material as a two-port network and directly measures S parameters ( S 11 , S 12 , S 21 ,S 22 ), which relies on a specific inversion algorithm to calculate the dielectric constant. Different inversion algorithms will produce different results even if the measured scattering parameters are the same.

[0005] Common dielectric constant inversion algorithms currently include the NRW algorithm, the NIST algorithm, and the SCL algorithm. Most of these models assume that the electromagnetic wave is incident on the interface as a plane wave. Therefore, the actual free-space optical path must adhere to this assumption as much as possible; otherwise, the calculated results will deviate significantly from the actual situation. For example, if a horn antenna connected to a vector network analyzer is placed at the focus of a convex lens, with the horn antenna axis coinciding with the lens's optical axis, the electromagnetic wave can be converged by the lens to produce a near-plane wave near the sample. However, due to the lens size, focal length, and radiation direction of the horn antenna, the optical path is not suitable for measuring small targets. In actual measurement tasks, some materials have limited size and cannot meet the requirements of conventional free-space optical paths. First, the dielectric constant of the material can vary significantly at different locations, making the average dielectric constant over a large area meaningless. Second, due to processing technology, some materials cannot be made larger in cross-sectional dimensions (for example, some thin films are grown on substrates; oversized substrates are fragile and cannot accommodate processing equipment). Therefore, the free-space method has certain requirements for the actual measurement sample size, limiting its application to dielectric constant characterization of small materials. Summary of the Invention

[0006] In order to solve the technical problems existing in the above-mentioned background technology, the present invention provides a terahertz-band dielectric constant testing method and system for small-sized dangerous goods. By building a focused optical path, it is suitable for the measurement of non-uniform samples and samples with limited size, and finds the refraction angle that minimizes the difference between the inverted dielectric constant and the converted dielectric constant to obtain the dielectric constant at the corresponding radiation angle. The integration method is used within the focused beam range to realize the inversion of the average dielectric constant of the measurement area, thereby realizing the dielectric constant test under the focused optical path.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: A first aspect of the present invention provides a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band, comprising: The material to be tested is placed between two convex lenses, and the two convex lenses, the vector network analyzer and the two spectrum spreading modules form a symmetrical focusing optical path; The horn antenna of the spectrum spread module is simulated to obtain the ratio of the output voltage wave to the entire horn within a narrow beam at any radiation angle, as well as the ratio of the received voltage wave to the output, as simulation results. Control the horn antenna of a spectrum spreading module to transmit electromagnetic waves. Within any radiation angle, the electromagnetic waves are regarded as plane waves, and the vector network analyzer is used to measure the electromagnetic waves. SThe parameters are converted based on the simulation results for S the parameters; the thickness of the material to be measured is obtained and converted into an equivalent thickness; based on the equivalent thickness and the converted S parameters, the inverse dielectric constant is obtained through an inversion model; the radiation angle, image distance, and object distance are obtained, and the incident angle is converted. Based on the Snell's law being satisfied by the refraction angle and the incident angle, the converted dielectric constant is determined; the refraction angle that minimizes the difference between the inverse dielectric constant and the converted dielectric constant is found, and the inverse dielectric constant corresponding to this refraction angle is the dielectric constant at the corresponding radiation angle; Based on the dielectric constants at all radiation angles, the average dielectric constant is obtained through integration.

[0008] Furthermore, the symmetric focusing optical path is set as: The horn antenna of the first frequency spreading module, the first convex lens, the material to be measured, the second convex lens, and the horn antenna of the second frequency spreading module are arranged in a straight line in sequence, and the end face of the material to be measured is perpendicular to the straight line; The distance from the horn antenna of the first frequency spreading module to the first convex lens is equal to the distance from the horn antenna of the second frequency spreading module to the second convex lens, and the distance from the second convex lens to the material to be measured is equal to the distance from the first convex lens to the material to be measured; The vector network analyzer is connected to each frequency spreading module through coaxial cables.

[0009] Furthermore, the converted S parameters include: S 11 ( θ ) = S 11 · R 2 / R 1; S 21 ( θ ) = S 21 · R 2 · R 2 / R 1; where S 11 and S 21 are the S parameters measured by the vector network analyzer, R 1 is the ratio of the output voltage wave within a narrow beam with a radiation angle of θ and a width of d θ to the overall horn, R 2 is the ratio of the received voltage wave to the output.

[0010] Furthermore, the inverse dielectric constant is: NRW( S 11 (θ ), S 21 ( θ ), d / cos(β)), where d / cos(β) is the equivalent thickness, d is the thickness of the material to be measured, β is the refraction angle, S 11 ( θ )and S 21 ( θ ) is the converted S parameter.

[0011] Furthermore, the incident angle satisfies: u tan( θ )= v tan( α );in, v represents the image distance, α represents the angle of incidence, θ represents the radiation angle, u Indicates object distance.

[0012] Furthermore, the converted dielectric constant is: ;in, is the refractive index of the material to be tested, n 1 is the refractive index of air, α represents the angle of incidence, β is the refraction angle.

[0013] Furthermore, the integral is expressed as: ;in, is the radiation angle θ The dielectric constant calculated below is, represents the maximum radiation angle, D p ( θ ) is the angle-dependent normalized power density function.

[0014] A second aspect of the present invention provides a terahertz-band dielectric constant testing system for small-sized dangerous goods, comprising: An optical path setting module is configured to: place the material to be tested between two convex lenses, and the two convex lenses, the vector network analyzer and the two spectrum spreading modules form a symmetrical focusing optical path; a simulation module configured to simulate the horn antenna of the spectrum spreading module and obtain, as simulation results, a ratio of an output voltage wave within a narrow beam at any radiation angle relative to the entire horn and a ratio of a received voltage wave relative to the output; The unit area dielectric constant calculation module is configured to: control the horn antenna of a spread spectrum module to emit electromagnetic waves, regard the electromagnetic waves as plane waves within any radiation angle, and obtain the S parameters, based on the simulation results, perform conversion on the S parameters; obtain the thickness of the material to be measured and convert it into an equivalent thickness; based on the equivalent thickness and the converted S parameters, through an inversion model, obtain the inverted dielectric constant; obtain the radiation angle, image distance, and object distance, convert them into the incident angle, and based on the refraction angle and the incident angle satisfying Snell's law, determine the converted dielectric constant; find the refraction angle that minimizes the difference between the inverted dielectric constant and the converted dielectric constant, and the inverted dielectric constant corresponding to this refraction angle is the dielectric constant at the corresponding radiation angle; The integration module is configured to: based on the dielectric constants at all radiation angles, obtain the average dielectric constant through integration.

[0015] The third aspect of the present invention provides a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, it implements the steps in a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band as described above.

[0016] The fourth aspect of the present invention provides a computer device, including a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor. When the processor executes the program, it implements the steps in a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band as described above.

[0017] Compared with the prior art, the beneficial effects of the present invention are: By building a focusing optical path, the present invention reduces the interaction area between millimeter waves and terahertz waves and the material to be measured, minimizes the limitation of the free space method on the lateral cross-sectional size of the material, adapts to the measurement of uneven samples and samples with limited sizes, and thus expands the types of materials that can be measured and reduces the requirements for building the optical path.

[0018] The present invention finds the refraction angle that minimizes the difference between the inverted dielectric constant and the converted dielectric constant to obtain the dielectric constant at the corresponding radiation angle, and uses the method of integrating according to the power density within the focused beam range to realize the inversion of the average dielectric constant in the measurement area, thus realizing the measurement of the dielectric constant under the focusing optical path. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0020] Figure 1This is an optical path diagram for measuring the dielectric constant of a small-sized sample according to the first embodiment of the present invention; Figure 2 1 is a schematic diagram of thickness conversion according to the first embodiment of the present invention; Figure 3 Schematic diagram of an equivalent optical path of the first embodiment of the present invention; Figure 4 It is a structural diagram of a computer device according to the fourth embodiment of the present invention. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0022] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0023] Example 1 This embodiment provides a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band.

[0024] This embodiment provides a terahertz-band dielectric constant testing method for small-sized dangerous goods, which can be used for dangerous goods detection.

[0025] To resolve the inherent contradictions in the optical path, model, and material when measuring dielectric constants using the free-space method in the terahertz band, for example, when measuring the dielectric constant of 75-110GHz indium phosphide materials using the free-space method, since large-sized indium phosphide is difficult to process, it is necessary to measure small-sized materials under a special optical path. This embodiment provides a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band. By building a focusing optical path to reduce the interaction area between millimeter waves, terahertz waves, and the material being measured, the limitation of the free-space method on the transverse cross-sectional size of the material is minimized, and the measurement of non-uniform samples and samples with limited size is adapted. Therefore, the types of measurable materials are expanded and the requirements for building the optical path are reduced. The free-space optical path can be flexibly constructed based on the existing lenses at the measurement site, reducing the demand for high-priced horn lens antennas for measurement.

[0026] A method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band provided by this embodiment simulates the ratio of the output voltage wave of a narrow beam in any direction to the overall horn, and the ratio of the received voltage wave to the output; a free-space symmetric focusing optical path is composed of a vector network analyzer, a frequency spreading module, and a pair of convex lenses with a known focal length; under the condition of normal incidence of plane waves, an existing free-space dielectric constant inversion model is established or used for calculation, and then the equivalent thickness considering the incident angle is converted to obtain the dielectric constant per unit area related to the angle; based on the calculation results of the above steps, the average dielectric constant of the measurement area is inverted by the method of integrating according to the power density within the focused beam range, realizing the measurement of the dielectric constant of small-sized samples under the focusing optical path.

[0027] A method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band provided by this embodiment, as Figure 1 shown, includes the following steps: S1. Simulate the ratio of the output voltage wave of a narrow beam in any direction to the overall horn, and the ratio of the received voltage wave to the output.

[0028] Specifically, according to the shape, size, and working frequency band of the horn antenna, any commercial electromagnetic simulation software or self-written program is used for simulation. The narrower the beam, the closer the simulation is to the actual situation, and the better the calculation result.

[0029] In step S1, it includes simulating and calculating the power spatial distribution of the horn antenna of the frequency spreading module, meeting the following settings: (1) Regarding the horn antenna as a point source, after calculating the normalized phase delay and amplitude attenuation in each direction near the horn aperture using electromagnetic simulation software, calculate the ratio of the output voltage wave of a narrow beam in any direction near the horn aperture to the overall horn, and the ratio of the received voltage wave to the output; among them, the normalization method is the electromagnetic wave of a unit angle in any direction compared to the electromagnetic wave of a unit angle on the horn center line. (2) The simulation angle range should be large enough to cover the radiation aperture range of the horn antenna. Assuming that the radiation aperture of the horn antenna is 1 steradian, the simulation range must include a solid angle of 1 steradian centered on the horn axis.

[0030] S2. A symmetric focusing optical path is composed of a vector network analyzer, a frequency spreading module, and a pair of convex lenses with a known focal length.

[0031] The 1-port and 2-port of the vector network analyzer are respectively connected to a pair of frequency spreading modules with the same performance, which can shift the operating frequency of the electromagnetic wave output by the vector network analyzer to the millimeter wave and terahertz bands, and set indicators such as the frequency multiplication coefficient and power inside the vector network analyzer or in the control host computer to ensure the normal operation of the frequency spreading module.

[0032] The spread spectrum module includes a pair (2) of components with the same structure, specifications, and performance. Electromagnetic waves are transmitted or received through horn antennas. One spread spectrum module is a pair of transmitters / receivers, with a single horn antenna.

[0033] Two sets of test ports of the vector network analyzer are respectively connected to a spread spectrum module through coaxial cables. When the vector network analyzer serves as a signal source, it can transmit electromagnetic wave signals to spread spectrum module 1 and spread spectrum module 2, and at the same time, control of spread spectrum module 1 and spread spectrum module 2 is achieved through software; when the vector network analyzer serves as a load, it can receive electromagnetic wave signals from spread spectrum module 1 and spread spectrum module 2. The vector network analyzer itself and other objects in the measurement environment do not obstruct the propagation of electromagnetic waves in free space.

[0034] Among them, connecting one spread spectrum module to the vector network analyzer requires more than 1 connecting line, including local oscillator input (LO: local oscillation, data from the vector network analyzer to the spread spectrum module), reference input (reference input, data from the vector network analyzer to the spread spectrum module), measurement output (measurement output, data from the spread spectrum module to the vector network analyzer)), and reference output (reference output, data from the spread spectrum module to the vector network analyzer).

[0035] As Figure 1 shown, the horn antenna 1 of spread spectrum module 1, convex lens 1, sample, convex lens 2, and horn antenna 2 of spread spectrum module 2 are arranged in a straight line in sequence (referred to as the axis). The two horn antennas are placed face to face so that one side can receive the electromagnetic waves emitted by the other side, that is: the divergent electromagnetic waves emitted by spread spectrum module 1 are converged at the center of the sample through convex lens 1. The electromagnetic waves passing through the sample are divergent, and then are converged by convex lens 2 and received by spread spectrum module 2.

[0036] The sample to be measured is a parallel thin plate, and the end face of the sample is perpendicular to the straight line where the foregoing components are arranged. Here, "thin" means that the thickness is less than the wavelength of electromagnetic waves in vacuum.

[0037] The entire optical path is symmetric with respect to the sample: the distance from horn antenna 1 of spread spectrum module 1 to convex lens 1 is equal to the distance from the horn antenna of spread spectrum module 2 to convex lens 2; the distance from convex lens 1 to the sample is equal to the distance from convex lens 2 to the sample.

[0038] When the electromagnetic wave beam propagates from the horn antenna of spread spectrum module 1 to the horn antenna of spread spectrum module 2, the beam width changes successively (from horn antenna 1 to convex lens 1), becomes narrower (from convex lens 1 to the sample to be measured), becomes wider (after passing through the sample and being converged by convex lens 2), and becomes narrower (after passing through convex lens 2 to horn antenna 2). Convex lens 1 focuses the electromagnetic waves emitted by horn antenna 1 of spread spectrum module 1 on the surface of the sample.

[0039] To ensure that the electromagnetic waves accurately converge to the center of the sample, the object distance and image distance on both sides of the convex lens need to satisfy the Gaussian formula, that is, in formula (1), half of the aperture (diameter) of the horn antenna of the spread spectrum module is regarded as the object size; the size of the image is calculated according to optical knowledge, and the magnification M satisfies formula (2): (1) (2) In the formula, u represents the object distance, v represents the image distance, f represents the focal length of the lens. To ensure a real image, the object distance must be greater than 1 times the focal length. To ensure that the converging electromagnetic waves irradiate on the center of the sample without diffraction, it is necessary to ensure that the imaging size is less than half of the sample size.

[0040] Preferably, the convex lens 1 and the convex lens 2 are double convex lenses or plano-convex lenses of the same material and the same specification.

[0041] In the embodiment, the convex lens material is selected as TPX (poly-4-methylpentene-1) with good transparency in the millimeter wave and terahertz bands.

[0042] To facilitate the optical path debugging, the spread spectrum module 1 is fixed on the lifting platform that can be adjusted up and down, and the horn antenna 1 of the spread spectrum module 1 always points horizontally; the spread spectrum module 2 is fixed on the platform where the pitch angle and roll angle can be adjusted; the convex lens 1 and the convex lens 2 are fixed on the mirror frame with fine-tunable direction, and the mirror frame is fixed on the base with adjustable height. The convex lens base, the lifting platform, the platform where the spread spectrum module 1 and the spread spectrum module 2 are located are all fixed on the same linear guide rail.

[0043] S3. Under the condition of normal incidence of plane waves, establish or use the original free space permittivity inversion model for calculation, and then consider the equivalent thickness of the incident angle for conversion to obtain the permittivity of the unit direction related to the angle.

[0044] In this embodiment, the NRW (Nicholson Ross Weir) model is selected for the free space permittivity inversion model in this test. This model requires that the electromagnetic waves are normally incident on the sample surface in the form of plane waves, and measure S 11 、 S 21 two scattering parameters ( S parameters) and the sample thickness d , substitute them into the relevant formula to calculate the permittivity, and require that the sample surface is a plane wave with normal incidence.

[0045] Since the free-space optical path established in step S2 is a focused optical path (the sample surface is not a plane wave), which does not meet the requirements of the NRW model, it is necessary to perform conversion based on the S parameters ( S 11 and S 21 ) measured by the vector network analyzer at this time and the simulation results to obtain the θ parameters with S as the independent variable, which are respectively denoted as S 11 ( θ ), S 21 ( θ ). Specifically: Through the simulation in step S1, it can be obtained that the ratio of the output voltage wave in the narrow beam with a radiation angle of θ and a width of d θ to the overall horn is R 1 (related to the structure of the horn), and the ratio of the received voltage wave to the output is R 2 (the modulus is less than 1, which is a complex number and related to the attenuation and phase delay caused by the lens). Then S 11 ( θ ) = S 11 · R 2 / R 1, S 21 ( θ ) = S 21 · R 2 · R 2 / R 1. Here, "·" represents multiplication and " / " represents division.

[0046] Regarding the electromagnetic wave as a plane wave in the narrow beam with a radiation angle of θ and a width of d θ meets the requirements of the NRW model. As shown in Figure 2 and Figure 3 , above the hollow arrow is the actual focused optical path, and below is the equivalent parallel optical path. The width of the equivalent parallel optical path is , and the thickness of the equivalent plane mirror L 等效 = L ( u tan( θ ))), and the equivalent thickness of the sample d 等效 = d / cos(β), where u represents the object distance, that is, the distance from the object (horn antenna) to the convex lens, which is read from the scale indication of the guide rail;L (x) is the thickness function of the convex lens, x= u tan( θ ) is the distance from the parallel light to the central axis, L 等效 It is used in the simulation of step S1, so it can be used S 11 ( θ ), S 21 ( θ ) replaces the NRW model S 11 、 S 21 , using equivalent thickness d 等效 = d / cos(β) replaces the material thickness in the NRW model d . Assume that the NRW algorithm is denoted as function NRW( S 11 , S 21 , d ), which is equivalent to the inversion dielectric constant NRW( S 11 ( θ ), S 21 ( θ ), d / cos(β)).

[0047] Refraction angle β and the angle of incidence α Satisfies Snell's law n 1sin( α )= n 2sin( β ), then the converted dielectric constant expressed by the refraction angle is , where the incident angle α and radiation angle θ Related, satisfying u tan( θ )= v tan( α ), v Indicates the image distance, that is, the distance from the convex lens to the image point (measurement spot), which is read by the scale on the guide rail; n 2 is the refractive index of the material to be tested, n 1=1 (the refractive index of air is 1).

[0048] Find the inverse dielectric constant NRW( S 11 ( θ ),S 21 ( θ ), d / The conversion dielectric constant represented by cos(β)) and the refraction angle with the smallest difference β is the true refraction angle. At this time, the inversion dielectric constant corresponding to the smallest refraction angle obtained is the dielectric constant calculated at this radiation angle θ .

[0049] S4. Based on the antenna pattern and the calculation results of the foregoing steps, the average dielectric constant inversion of the measurement area is realized by using the method of integrating according to the power density within the focused beam range.

[0050] Specifically, calculate to obtain the dielectric constant of the sample at the electromagnetic wave spot. In the formula, represents the maximum radiation angle, D p (θ) is the angle-dependent normalized power density function, satisfying = 1. By integrating, all angles are taken into account, reflecting the comprehensive result of the measurement of the conical focused beam illuminating the spot.

[0051] In summary, the electromagnetic wave under the unit aperture angle is regarded as a plane wave. The electromagnetic wave of a unit angle emitted by the horn antenna at port 1 can be received by the convex lens 1, and after being reflected by the sample, it can be completely received by the convex lens 1 and then received by the horn antenna 1 through the focusing effect of the lens; the electromagnetic wave of a unit angle emitted by the horn antenna at port 2 can be received by the convex lens 2, and after being reflected by the sample, it can be completely received by the convex lens 2 and then received by the horn antenna 2 through the focusing effect of the lens. The reception described here and below refers to the area where the lens covers the electromagnetic wave, and does not mean that the lens absorbs all the electromagnetic waves in this area (attenuates to infinitesimal).

[0052] According to the optical path symmetry, the electromagnetic wave of a unit angle emitted by the horn antenna 1 passes through the lens 1 and the measured target successively, and can be completely received by the lens 2 on the other side and then received by the horn antenna 2 through the focusing effect. Similarly, the electromagnetic wave of a unit angle emitted by the horn antenna 2 passes through the lens 2 and the measured target successively, and can be completely received by the lens 1 on the other side and then received by the horn antenna 1 through the focusing effect.

[0053] Determine the S parameters of the electromagnetic wave of a unit angle according to the radiation power and phase of the electromagnetic wave of a unit angle, and regard it as S ( θ ), and substitute S ( θ ) into the free space dielectric constant inversion model in step S3 for calculation to obtain the dielectric constant of a unit angle ε ​( θ ); Integrate with ε ( θ ) as the integrand variable within the radiation angle range of the horn antenna to obtain the dielectric constant of the measured area ε .

[0054] Embodiment 2 This embodiment provides a small-sized dielectric constant test system for dangerous goods in the terahertz band, which specifically includes: An optical path setting module configured to place the material to be measured between two convex lenses, and the two convex lenses, a vector network analyzer, and two frequency spreading modules form a symmetric focusing optical path; A simulation module configured to simulate the horn antenna of the frequency spreading module to obtain the ratio of the output voltage wave within the narrow beam at any radiation angle to the overall horn and the ratio of the received voltage wave to the output as the simulation results; A unit area dielectric constant calculation module configured to control the horn antenna of one frequency spreading module to emit electromagnetic waves. Within any radiation angle, consider the electromagnetic waves as plane waves, and obtain the S parameters measured by the vector network analyzer. Based on the simulation results, convert the S parameters; obtain the thickness of the material to be measured and convert it to an equivalent thickness; based on the equivalent thickness and the converted S parameters, through an inversion model, obtain the inversion dielectric constant; obtain the radiation angle, image distance, and object distance, convert them into the incident angle, and based on the refractive angle and incident angle satisfying Snell's law, determine the converted dielectric constant; find the refractive angle that minimizes the difference between the inversion dielectric constant and the converted dielectric constant, and the inversion dielectric constant corresponding to this refractive angle is the dielectric constant at the corresponding radiation angle; An integration module configured to obtain the average dielectric constant through integration based on the dielectric constants at all radiation angles.

[0055] It should be noted here that each module in this embodiment corresponds one by one to each step in Embodiment 1, and the specific implementation process is the same, so it will not be repeated here.

[0056] Embodiment 3 This embodiment provides a computer-readable storage medium with a computer program stored thereon. When the program is executed by a processor, it implements the steps in a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band as described in Embodiment 1 above.

[0057] Embodiment 4 This embodiment provides a computer device, as Figure 4As shown, it includes a display device, an input device, a computer-readable storage medium (volatile memory and non-volatile storage medium), a processor, a communication interface (i.e., a network interface), and a computer program stored on the computer-readable storage medium and executable on the processor. Among them, the processor, the communication interface, and the computer-readable storage medium can be connected through a bus or other means. Among them, the communication interface is used to receive and send data, and when the processor executes the program, it implements the steps in a method for testing the dielectric constant of small-sized dangerous goods in the terahertz band as described in Embodiment 1 above.

[0058] Among them, any reference to a memory, storage, database, or other medium provided in this application and used in the embodiments may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or an external cache memory. By way of illustration and not limitation, RAM is available in various forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (SSRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and Rambus dynamic RAM (RDRAM), etc.

[0059] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to embodiments of the present invention. It should be understood that each flow and / or block in the flowchart and / or block diagram, and the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate a device for implementing the functions specified in Figure 1 one or more flows and / or blocks Figure 1 one or more blocks.

[0060] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including an instruction device that implements the functions in Figure 1 one or more flows and / or blocksFigure 1 The functions specified in one or more boxes.

[0061] These computer program instructions can also be loaded onto a computer or other programmable data processing device, so that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process. Thus, the instructions executed on the computer or other programmable device provide for implementing the steps of the functions specified in one or more processes and / or boxes Figure 1 One or more processes and / or boxes Figure 1 The steps of the functions specified in one or more boxes.

[0062] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band, characterized in that, Including: Placing the material to be measured between two convex lenses, and the two convex lenses, a vector network analyzer and two spread-spectrum modules form a symmetric focusing optical path; Simulating the horn antennas of the spread-spectrum modules to obtain the ratio of the output voltage wave in the narrow beam at any radiation angle to the overall horn and the ratio of the received voltage wave to the output as the simulation results; Control the horn antenna of a spread spectrum module to emit electromagnetic waves. Within any radiation angle, regard the electromagnetic waves as plane waves and obtain the S parameters measured by a vector network analyzer. Based on the simulation results, S parameters are converted; obtain the thickness of the material to be measured and convert it to an equivalent thickness; based on the equivalent thickness and the converted S parameters, through an inversion model, obtain the inverted dielectric constant; obtain the radiation angle, image distance, and object distance, convert them into the incident angle, and based on the fact that the refraction angle and the incident angle satisfy Snell's law, determine the converted dielectric constant; find the refraction angle that minimizes the difference between the inverted dielectric constant and the converted dielectric constant, and the inverted dielectric constant corresponding to this refraction angle is the dielectric constant at the corresponding radiation angle; Based on the dielectric constants at all radiation angles, obtaining the average dielectric constant through integration.

2. The method for testing the dielectric constant of small-sized dangerous goods in the terahertz band according to claim 1, wherein, The symmetric focusing optical path is set as follows: The horn antenna of the first spread-spectrum module, the first convex lens, the material to be measured, the second convex lens and the horn antenna of the second spread-spectrum module are arranged in a straight line in sequence, and the end face of the material to be measured is perpendicular to the straight line; The distance from the horn antenna of the first spread-spectrum module to the first convex lens is equal to the distance from the horn antenna of the second spread-spectrum module to the second convex lens, and the distance from the second convex lens to the material to be measured is equal to the distance from the first convex lens to the material to be measured; The vector network analyzer is connected to each spread-spectrum module through a set of coaxial cables.

3. The method for testing the dielectric constant of small-sized dangerous goods in the terahertz band according to claim 1, wherein The converted S parameters include: S 11 ( θ ) = S 11 · R 2 / R 1; S 21 ( θ ) = S 21 · R 2 · R 2 / R 1; where S 11 and S 21 are parameters measured by a vector network analyzer, S parameter, R 1 is the ratio of the output voltage wave within a narrow beam with a radiation angle of θ and a width of d θ to the overall horn, R 2 is the ratio of the received voltage wave to the output.

4. The terahertz band dielectric constant testing method for small-sized dangerous goods according to claim 1, characterized in that, The inverted dielectric constant is: NRW( S 11 ( θ ), S 21 ( θ ), d / cos(β)), where d / cos(β) is the equivalent thickness, d is the thickness of the material to be measured, β is the refraction angle, S 11 ( θ ) and S 21 ( θ ) are the S parameters after conversion.

5. A method for testing the dielectric constant of small-sized dangerous goods in the terahertz band according to claim 1, characterized in that The incident angle satisfies: u tan( θ ) = v tan( α ); Among them, v represents the image distance, α represents the incident angle, θ represents the radiation angle, u represents the object distance.

6. The method for testing the dielectric constant of small-sized dangerous goods in the terahertz band according to claim 1, wherein The conversion dielectric constant: ; where is the refractive index of the material to be measured, n 1 is the refractive index of air, α represents the incident angle, β is the refraction angle.

7. A method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band according to claim 1, characterized in that The integral is expressed as: ; where is the dielectric constant calculated at the radiation angle θ , represents the maximum radiation angle D p ( θ ) is the angle-dependent normalized power density function.

8. A terahertz band dielectric constant test system for small-sized dangerous goods, characterized in that, Including: An optical path setting module configured to place the material to be measured between two convex lenses, and the two convex lenses, a vector network analyzer and two spread-spectrum modules form a symmetric focusing optical path; A simulation module configured to simulate the horn antennas of the spread-spectrum modules to obtain the ratio of the output voltage wave in the narrow beam at any radiation angle to the overall horn and the ratio of the received voltage wave to the output as the simulation results; The unit area permittivity calculation module is configured to: control a horn antenna of a spread spectrum module to emit electromagnetic waves, regard the electromagnetic waves as plane waves within any radiation angle, and obtain the S parameters, based on the simulation results, convert the S parameters; obtain the thickness of the material to be measured and convert it into an equivalent thickness; based on the equivalent thickness and the converted S parameters, obtain the inverted permittivity through an inversion model; obtain the radiation angle, image distance and object distance, convert them into the incident angle, and determine the converted permittivity based on the fact that the refraction angle and the incident angle satisfy Snell's law; find the refraction angle that minimizes the difference between the inverted permittivity and the converted permittivity, and the inverted permittivity corresponding to this refraction angle is the permittivity at the corresponding radiation angle; An integration module configured to obtain the average dielectric constant through integration based on the dielectric constants at all radiation angles.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by a processor, it implements the steps in a method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band as described in any one of claims 1-7.

10. A computer device, comprising a computer-readable storage medium, a processor, and a computer program stored on the computer-readable storage medium and executable on the processor, characterized in that, When the processor executes the program, it implements the steps in a method for measuring the dielectric constant of small-sized dangerous goods in the terahertz band as described in any one of claims 1-7.

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