A portable dual-frequency microwave imaging darkroom

Abstract

The present application relates to a kind of portable dual-frequency microwave imaging darkroom, including hard cylindrical shell, hard cylindrical shell is installed on support, the geometric center of hard cylindrical shell is provided object to be measured, object to be measured is placed on two-dimensional rotating platform, double-frequency electromagnetic wave absorption unit is attached on the inner wall of hard cylindrical shell, double-frequency electromagnetic wave absorption unit, transmitting antenna and multiple receiving antennas are integrally formed, the transmitting antenna and receiving antenna are all using microstrip patch antenna, and radio frequency switch network controls the opening and shutdown of multiple receiving antennas.The present application uses ultrathin double-frequency electromagnetic wave absorption unit, can simultaneously realize near perfect absorption effect to electromagnetic wave from normal incidence direction and oblique incidence direction, and further constructs portable dual-frequency microwave imaging darkroom;With the help of the dual-frequency microwave imaging darkroom constructed, microwave imaging experiment based on inverse scattering principle can be measured on site, and is expected to be widely used in practical engineering application scenarios.

Description

Technical Field

[0001] This invention relates to the field of microwave imaging experimental systems, and in particular to a portable dual-frequency microwave imaging anechoic chamber. Background Technology

[0002] Microwave backscattering imaging technology has the advantages of being fast, non-contact, and non-destructive to the object being tested, and therefore has broad application prospects in military, civilian, and biomedical fields.

[0003] In computational electromagnetics, microwave backscattering imaging theory is derived in an ideal, infinitely large free space or a space with no-scattering boundary conditions. In practical microwave engineering, a no-scattering space environment can be achieved through an ideal open area. However, with the increasing complexity of the electromagnetic environment in space, ideal open areas are difficult to find. To simulate open areas, microwave imaging technology relying on electrically large-scale microwave anechoic chambers has emerged. However, traditional microwave anechoic chambers have a scale of hundreds or thousands of wavelengths, are expensive, have long construction periods, and are inconvenient to move. At the same time, the equipment used for microwave imaging experiments is complex to configure. Therefore, the large size, high cost, and inconvenience of microwave anechoic chambers are the main factors limiting the application of microwave backscattering imaging experiments in practical engineering environments.

[0004] In recent years, small microwave anechoic chambers have been extensively studied, providing a portable, scatter-free spatial environment for microwave imaging technology based on inverse scattering theory. However, how to construct a miniature microwave imaging anechoic chamber for practical engineering applications and achieve a high degree of integration of microwave imaging experimental systems remains an urgent problem to be solved. Summary of the Invention

[0005] To address the problems of traditional microwave anechoic chambers being expensive, large in size, and immobile once built, the present invention aims to provide a portable dual-frequency microwave imaging anechoic chamber that can simultaneously achieve near-perfect absorption of electromagnetic waves from both normal and oblique incident directions, enabling on-site measurements of microwave imaging experiments based on the principle of backscattering.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a portable dual-frequency microwave imaging anechoic chamber, comprising a rigid cylindrical shell, the rigid cylindrical shell being mounted on a support, an object to be tested being placed at the geometric center of the rigid cylindrical shell, the object to be tested being placed on a two-dimensional rotating platform, a dual-frequency electromagnetic wave absorbing unit, a transmitting antenna, and multiple receiving antennas being attached to the inner wall of the rigid cylindrical shell, the dual-frequency electromagnetic wave absorbing unit, the transmitting antenna, and the multiple receiving antennas being integrally formed, the transmitting antenna and the receiving antennas both being microstrip patch antennas, and an RF switch network controlling the opening and closing of the multiple receiving antennas.

[0007] The dual-frequency electromagnetic wave absorption unit consists of a metal ground plane, an intermediate dielectric layer, and an upper metal pattern. The transmitting antenna, receiving antenna, and dual-frequency electromagnetic wave absorption unit share a metal ground plane and an intermediate dielectric layer.

[0008] The plurality of receiving antennas are evenly arranged on the surface of the dual-frequency electromagnetic wave absorbing unit, with a spacing of more than half a wavelength at the operating frequency between two adjacent receiving antennas.

[0009] The thickness of the dual-frequency electromagnetic wave absorbing unit is 0.636 mm.

[0010] The diameter of the rigid cylindrical outer shell is 412 mm.

[0011] The upper metal pattern consists of two structurally identical parts, each including an upper I-shape and a lower I-shape, with the upper I-shape folded inward and the lower I-shape folded upward.

[0012] As can be seen from the above technical solution, the beneficial effects of the present invention are as follows: First, the present invention uses an ultra-thin dual-frequency electromagnetic wave absorption unit, which can simultaneously achieve near-perfect absorption of electromagnetic waves from both the normal incident direction and the oblique incident direction, and further constructs a portable dual-frequency microwave imaging anechoic chamber; Second, with the help of the constructed dual-frequency microwave imaging anechoic chamber, microwave imaging experiments based on the principle of backscattering can be performed on-site, and are expected to be widely used in practical engineering application scenarios. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the present invention;

[0014] Figure 2 This is a schematic diagram of oblique and normal incidence of the transmitting antenna in this invention;

[0015] Figure 3 This is a schematic diagram of the structure of the dual-frequency electromagnetic wave absorption unit in this invention;

[0016] Figure 4 This is a schematic diagram of the structure of the dual-frequency electromagnetic wave absorption unit, transmitting antenna, and receiving antenna in this invention;

[0017] Figure 5 This is a schematic diagram of the simulation results of the reflection parameters of the dual-frequency electromagnetic wave absorption unit operating at 0° and 10°.

[0018] Figure 6 This is a schematic diagram of the simulation results of the reflection parameters of the dual-frequency electromagnetic wave absorption unit operating at 0° and 40°.

[0019] Figure 7 This is a schematic diagram of the full-wave simulation results of the present invention using COMSOL under the conditions of normal and oblique electromagnetic wave incidence at an operating frequency of 5.12GHz.

[0020] Figure 8 This is a schematic diagram of the full-wave simulation results of the present invention using COMSOL under the conditions of normal and oblique incident electromagnetic waves at an operating frequency of 8.97GHz. Detailed Implementation

[0021] like Figure 1 As shown, a portable dual-frequency microwave imaging anechoic chamber includes a rigid cylindrical shell 1, which is mounted on a support. The support serves to fix the rigid cylindrical shell 1, and its specific structure is not limited. An object to be tested 2 is placed at the geometric center of the rigid cylindrical shell 1 and is placed on a two-dimensional rotating platform 3. The bottom surface of the support and the bottom surface of the two-dimensional rotating platform 3 are on the same horizontal plane. In this application, both the bottom surface of the support and the bottom surface of the two-dimensional rotating platform 3 are located on the ground. A dual-frequency electromagnetic wave absorbing unit 4, a transmitting antenna 5, and multiple receiving antennas 6 are attached to the inner wall of the rigid cylindrical shell 1. The dual-frequency electromagnetic wave absorbing unit 4, the transmitting antenna 5, and the multiple receiving antennas 6 are integrally formed. The transmitting antenna 5 and the receiving antennas 6 are both microstrip patch antennas. An RF switch network controls the on and off of the multiple receiving antennas 6. The thickness of the dual-frequency electromagnetic wave absorbing unit 4 is 0.636 mm. The diameter of the rigid cylindrical shell 1 is 412 mm. The two-dimensional rotating platform 3 is used to rotate the object to be tested 2 at a fixed angle. The receiving antenna 6 is controlled by a radio frequency switch network, which sequentially selects the receiving antennas to collect electromagnetic field information. Figure 1 For ease of demonstration, transmitting antenna 5 and receiving antenna 6 are represented by symbols only; their actual structures are as follows: Figure 4 As shown.

[0022] like Figure 3 , 4As shown, the dual-frequency electromagnetic wave absorbing unit 4 consists of a metal ground plane 7, an intermediate dielectric layer 8, and an upper metal pattern 9. The upper metal pattern 9 is divided into two roughly I-shaped parts. One part, along with its corresponding metal ground plane 7 and intermediate dielectric layer 8, forms a sub-unit, and the other part, along with its corresponding metal ground plane 7 and intermediate dielectric layer 8, forms another sub-unit. One sub-unit is mainly used to absorb electromagnetic waves from the normal incident direction, and the other sub-unit is mainly used to absorb electromagnetic waves from the oblique incident direction. The transmitting antenna 5, receiving antenna 6, and dual-frequency electromagnetic wave absorbing unit 4 share a metal ground plane 7 and an intermediate dielectric layer 8. The multiple receiving antennas 6 are evenly arranged on the absorbing surface formed by the dual-frequency electromagnetic wave absorbing unit 4. To reduce the potential mutual coupling problem between antennas, the distance between two adjacent receiving antennas 6 is more than half a wavelength of the operating frequency. The upper metal pattern 9 consists of two structurally identical parts, each including an upper I-shape 9a and a lower I-shape 9b. The upper I-shape 9a is folded inward, and the lower I-shape 9b is folded upward.

[0023] For a semi-enclosed cylindrical microwave imaging anechoic chamber, when the transmitting antenna 5 at a fixed position radiates electromagnetic waves onto the inner wall of the anechoic chamber (i.e., the inner wall of the rigid cylindrical shell 1), two incident electromagnetic waves will simultaneously exist at any position on the inner wall: one is the obliquely incident electromagnetic wave directly radiated by the transmitting antenna 5 onto the inner wall of the anechoic chamber, and the other is the normally incident electromagnetic wave scattered by the transmitting antenna 5 through the geometric center of the anechoic chamber (i.e., the object under test 2). Figure 2 As shown. To avoid scattering or even multiple scattering of electric field energy not received by the receiving antenna 6 on the inner wall of the anechoic chamber, which would cause inaccuracies in the electric field received by the receiving antenna 6, a dual-frequency electromagnetic wave absorbing unit 4 is attached to the inner wall of the anechoic chamber. The dual-frequency electromagnetic wave absorbing unit 4 needs to have the characteristic of achieving near-perfect absorption of electromagnetic waves from two incident angles simultaneously. Based on the oblique incident angle relationship between the transmitting antenna 5 and the inner wall of the anechoic chamber, the dual-frequency electromagnetic wave absorbing unit 4 can be used to complete the configuration of the microwave imaging anechoic chamber.

[0024] The dual-frequency electromagnetic wave absorption unit 4 can simultaneously absorb electromagnetic waves radiated by the transmitting antenna 5 in the oblique incident direction and electromagnetic waves scattered by the object under test 2 in the normal incident direction.

[0025] The object under test 2 is placed at the geometric center of the dark room. When the incident electromagnetic wave radiated by the transmitting antenna 5 is incident on the object under test 2, the electromagnetic wave scattered by the object under test 2 will be incident on the inner wall of the dark room in the positive incident direction.

[0026] The dual-frequency electromagnetic wave absorption unit 4 is mainly composed of two I-shaped structures. To reduce the operating frequency without increasing the unit size, a folded structure is further introduced during the unit design process. The dual-frequency electromagnetic wave absorption unit 4 can operate at two separate frequencies simultaneously, improving the stability and accuracy of microwave imaging experimental measurement results based on the inverse scattering principle.

[0027] The receiving antenna 6 uses a radio frequency switch network for selection, sequentially acquiring electromagnetic field information. The specific experimental measurement process is detailed below: The dual-frequency measurement method combines the stability of low frequencies with the high resolution of high frequencies, overcoming the limitations of single-frequency algorithms in terms of stability and resolution. First, at a certain operating frequency, a two-dimensional rotating platform 3 located at the geometric center of the imaging anechoic chamber drives the object under test 2 to rotate at a fixed angle. Each rotation acquires one revolution of electromagnetic field information. Subtracting the incident field information obtained when the object under test 2 is absent from the total field information obtained when it is present yields the scattered field information introduced solely by the object under test 2. Second, by changing the operating frequency and repeating the above steps, the scattered field information at another operating frequency can be obtained. Using this scattered field information, after appropriate calibration and imaging algorithms—specifically, based on an incident field calibration scheme and microwave backscattering imaging algorithms such as TSOM—the object under test 2 can be reconstructed.

[0028] Based on the actual size of the object to be tested 2, the size of the dual-frequency microwave imaging anechoic chamber can be customized. The size of the anechoic chamber can be as small as the wavelength, making it portable.

[0029] Simulation results of the reflection parameters of dual-frequency electromagnetic wave absorbing unit 4 operating at 0° and 10° and dual-frequency electromagnetic wave absorbing unit 4 operating at 0° and 40° are as follows: Figure 5 , 6 As shown, the "dual frequency" in the dual-frequency electromagnetic wave absorption unit 4 includes two frequencies of 5.12 GHz and 8.97 GHz, respectively.

[0030] A two-dimensional cylindrical microwave imaging anechoic chamber was constructed using the commercial electromagnetic simulation software COMSOL. The chamber diameter is 412 mm, which, in wavelength terms, equals 7 wavelengths (calculated based on 5.1 GHz). Using a line current source as the transmitting antenna, full-wave simulations were performed at two operating frequencies to simulate normal and oblique incident electromagnetic waves. The simulation results are shown below. Figure 7 , 8 As shown, Figure 7 The left image shows normal incidence, and the right image shows oblique incidence. Figure 8 The left image shows normal incidence, while the right image shows oblique incidence.

[0031] As can be seen from the above embodiments, this invention discloses a portable dual-frequency microwave imaging anechoic chamber. This invention can design a dual-frequency electromagnetic wave absorption unit 4 for a given dual-frequency, and can construct a portable microwave imaging anechoic chamber that meets imaging requirements for different sizes of the objects under test 2.

[0032] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A portable dual-frequency microwave imaging anechoic chamber, characterized in that: The device includes a rigid cylindrical shell (1), which is mounted on a support. The object to be tested (2) is placed at the geometric center of the rigid cylindrical shell (1). The object to be tested (2) is placed on a two-dimensional rotating platform (3). A dual-frequency electromagnetic wave absorption unit (4), a transmitting antenna (5), and multiple receiving antennas (6) are attached to the inner wall of the rigid cylindrical shell (1). The dual-frequency electromagnetic wave absorption unit (4), the transmitting antenna (5), and the multiple receiving antennas (6) are integrally formed. The transmitting antenna (5) and the receiving antennas (6) are both microstrip patch antennas. The radio frequency switch network controls the opening and closing of the multiple receiving antennas (6). The dual-frequency electromagnetic wave absorption unit (4) is composed of a metal ground plane (7), an intermediate dielectric layer (8) and an upper metal pattern (9). The transmitting antenna (5), the receiving antenna (6) and the dual-frequency electromagnetic wave absorption unit (4) share a metal ground plane (7) and an intermediate dielectric layer (8). The plurality of receiving antennas (6) are evenly arranged on the surface of the dual-frequency electromagnetic wave absorbing unit (4), and the interval between two adjacent receiving antennas (6) is more than half a wavelength at the working frequency. The thickness of the dual-frequency electromagnetic wave absorbing unit (4) is 0.636 mm; The diameter of the rigid cylindrical shell (1) is 412 mm; The upper metal graphic (9) consists of two identical parts, each including an upper I-shape (9a) and a lower I-shape (9b), with the upper I-shape (9a) folded inward and the lower I-shape (9b) folded upward. For a semi-enclosed cylindrical microwave imaging anechoic chamber, when the transmitting antenna (5) at a fixed position radiates electromagnetic waves to the inner wall of the anechoic chamber, i.e. the inner wall of the rigid cylindrical shell (1), there will be electromagnetic waves with two incident directions at any position on the inner wall of the anechoic chamber: one is the obliquely incident electromagnetic wave directly radiated by the transmitting antenna (5) to the inner wall of the anechoic chamber, and the other is the electromagnetic wave with the positive incident direction scattered by the electromagnetic wave emitted by the transmitting antenna (5) through the geometric center of the anechoic chamber, i.e. the object under test (2). The dual-frequency electromagnetic wave absorption unit (4) can simultaneously achieve matched absorption of the electromagnetic waves radiated by the transmitting antenna (5) in the oblique incident direction and the electromagnetic waves in the normal incident direction scattered by the object under test (2). The object to be tested (2) is placed at the geometric center of the dark room. When the incident electromagnetic wave radiated by the transmitting antenna (5) is incident on the object to be tested (2), the electromagnetic wave scattered by the object to be tested (2) will be incident on the inner wall of the dark room in the positive incident direction. The receiving antenna (6) is selected by a radio frequency switch network and electromagnetic field information is collected in sequence. The specific experimental measurement process is detailed as follows: First, at a certain working frequency, the two-dimensional rotating platform (3) located at the geometric center of the imaging darkroom is used to drive the object to be measured (2) to rotate at a certain fixed angle. Each rotation collects one circle of electromagnetic field information. Subtracting the incident field information obtained when the object under test (2) is absent from the total field information obtained by measuring the total field information obtained when the object under test (2) is present, we can obtain the scattered field information introduced only by the object under test (2); secondly, by changing the working frequency and repeating the above steps, we can obtain the scattered field information at another working frequency; using this scattered field information, after corresponding calibration and imaging algorithms, specifically, based on the calibration scheme of the incident field and the microwave backscattering imaging algorithm, we can realize the reconstruction of the object under test (2).

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