A Dual-Polarized Ultra-Wideband Conformal Slot Antenna for Microwave Brain Imaging

Abstract

The present invention discloses a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, which relates to the technical field of slot antennas. The antenna includes a metal radiation patch, a dielectric substrate, and a metal microstrip line. The dielectric substrate is disposed above the metal microstrip line, and the metal radiation patch is disposed above the dielectric substrate. The metal radiation patch is composed of a floor with an etched rounded square slot, a circular patch, and a cross-shaped elliptical patch. The circular patch is disposed at the center of the floor of the etched rounded square slot, and the cross-shaped elliptical patch is disposed at the center of the circular patch. The metal microstrip line is composed of a 50Ω microstrip line, an impedance converter, and a circular patch. The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention has many advantages such as dual polarization, ultra-wideband, extremely low profile, and directional beam, and can be effectively applied to a microwave brain imaging system.

Description

Technical Field

[0001] The present invention relates to the technical field of slot antennas, and in particular to a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging. Background Art

[0002] Stroke, as a common neurological disease, has a rapid onset and a fatal risk. Therefore, rapid and accurate diagnosis is particularly crucial. Compared with traditional medical diagnostic methods such as magnetic resonance imaging, the brain imaging system based on the microwave band exhibits significant advantages, including low cost, fast diagnostic speed, and convenient portability of the device. This technology even has the potential to become an important equipment on ambulances and holds great application potential and research value in the field of new-generation medical electronics.

[0003] The imaging principle of this technology is based on the differences in the propagation characteristics of microwaves in media with different electromagnetic properties: when abnormal tissues or lesions appear in the body, their electromagnetic property parameters (mainly dielectric constant and conductivity) will change. By detecting the microwave signals reflected or scattered by the body, obtaining information such as the frequency, amplitude, and phase changes of the signals, and then performing inverse imaging based on this information, an image of the characteristics of the measured tissue can be obtained, thereby achieving the diagnosis of the patient.

[0004] In a microwave brain imaging system, the antenna, as a key device for signal transmission and reception, is the core component connecting the object under test and the backend processing system, and its performance largely determines the overall quality of imaging. However, due to the unique electromagnetic properties of the human head, antenna design faces many challenges. The human head is a lossy medium with a high dielectric constant (the dielectric constant of the head skin is about 40). Microwaves with higher frequencies are difficult to penetrate the brain to obtain effective information, while low-frequency antennas are too large in size and do not meet the requirements for portability in actual use. Therefore, a balance needs to be sought between penetrability and portability. Generally speaking, the microwave frequency band suitable for human brain imaging ranges from 0.5 to 4 GHz.

[0005] Currently, the antennas used for brain imaging are mainly divided into in vitro antennas and body-mounted matching antennas. In vitro antennas are antennas matched in a free space environment, and there is a large air gap between them and the human brain. Given the characteristics of the high dielectric constant of the human brain (the dielectric constant of the head skin is about 40), when the electromagnetic waves radiated by in vitro antennas pass through the air-scalp layer, strong reflections will occur, resulting in a decline in matching performance and radiation efficiency. The body-mounted matching antenna is an antenna optimized for the human body environment. It fits closely to the human brain and is matched through a matching medium or directly with the human brain. Although this method increases the complexity of the design to a certain extent, it can significantly reduce the electromagnetic waves reflected by the air-scalp layer, thus maintaining good matching effects and high radiation performance. However, antennas matched with the human brain through a matching medium or matching liquid usually have a relatively high profile, which is not conducive to conformal bending and portable use. Generally speaking, the antenna that directly fits and matches the human head is the best choice for microwave brain imaging systems.

[0006] In addition, increasing the polarization mode of the antenna helps to detect more abundant brain information, thereby achieving a more accurate imaging effect. However, there has been no relevant report on dual-polarized antennas for microwave brain imaging systems. Summary of the Invention

[0007] The object of the present invention is to propose a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, which has the characteristics of dual polarization, ultra-wideband, extremely low profile, and directional beam, helps to comprehensively detect brain information, achieve high-resolution imaging and conformal bending, and can be effectively applied to microwave brain imaging systems.

[0008] To achieve the above object, the present invention proposes a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, including a metal radiation patch, a dielectric substrate, and a metal microstrip line. The dielectric substrate is arranged above the metal microstrip line, and the metal radiation patch is arranged above the dielectric substrate.

[0009] Preferably, the metal microstrip line is composed of a 50Ω microstrip line, an impedance converter, and a circular patch. The 50Ω microstrip line is connected to the impedance converter, and the impedance converter is connected to the circular patch.

[0010] Preferably, there are 4 metal microstrip lines, which are orthogonal to each other in pairs and arranged on the four sides at the bottom of the dielectric substrate; two of the orthogonally placed metal microstrip lines are welded with SMA interfaces and connected to a 50Ω coaxial line.

[0011] Preferably, the metal radiation patch is composed of a floor with an etched rounded square slot, a circular ring patch, and a cross-shaped elliptical patch. The circular ring patch is arranged at the center of the floor with the etched rounded square slot, and the cross-shaped elliptical patch is arranged at the center of the circular ring patch.

[0012] Preferably, the floor with etched rounded square gaps connects the vertical and horizontal sides of the square with four rounded corners and is etched on the copper-clad surface.

[0013] Preferably, the antenna is placed in free space, and its metal radiation patch closely adheres to the human brain medium for operation.

[0014] Preferably, the antenna is conformalized, and cylinders with different radii are used to simulate human heads of different sizes.

[0015] Therefore, the present invention proposes a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, and its beneficial effects are as follows:

[0016] (1) The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention adopts a dual-linear polarization design, which can detect more abundant detailed information of the human brain. Through two mutually orthogonal polarization directions, bleeding points of different shapes in the brain can be captured, providing more detailed data support for comprehensively understanding the brain bleeding condition.

[0017] (2) The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention has ultra-wideband characteristics, which is convenient for realizing high-resolution human brain imaging and assisting doctors in accurate diagnosis.

[0018] (3) The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention has an extremely low profile design, which is beneficial for the antenna to be conformal with the human head and greatly improves the portability in actual use.

[0019] (4) The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention can direct the electromagnetic wave to radiate towards the human brain, effectively coping with the attenuation problem of the electromagnetic wave during its propagation inside the human brain, ensuring concentrated energy transmission, enabling the signal to stably reach the target area in the complex brain environment, and guaranteeing the imaging quality.

[0020] (5) The dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging proposed by the present invention has a certain robustness to different conformal bending degrees. That is, when acting on the heads of patients with different sizes, the antenna can still work normally without significant performance deterioration. Thus, ensuring the universality of its application.

[0021] The technical solution of the present invention will be further described in detail below through the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a side view of a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention;

[0023] Figure 2 The bottom view of a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention;

[0024] Figure 3 The top view of a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention;

[0025] Figure 4 The schematic diagram of the structural parameters of a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention; wherein, Figure 4 In (a) is the schematic diagram of the structural parameters of the metal radiation patch; Figure 4 In (b) is the schematic diagram of the structural parameters of the metal microstrip line;

[0026] Figure 5 The structural evolution diagram of the antenna according to the present invention; wherein, Figure 5 In (a) is antenna Ant.1; Figure 5 In (b) is antenna Ant.2; Figure 5 In (c) is antenna Ant.3;

[0027] Figure 6 The S-parameter curve corresponding to the evolved structure of the antenna according to the present invention;

[0028] Figure 7 The normalized near-field pattern in the yz plane at 1.33 GHz of the evolved structure of the antenna according to the present invention;

[0029] Figure 8 The surface current distribution at different frequencies according to the present invention; wherein, Figure 8 In (a) is the surface current distribution at 0.48 GHz; Figure 8 In (b) is the surface current distribution at 1.33 GHz; Figure 8 In (c) is the surface current distribution at 2.19 GHz;

[0030] Figure 9 The conformal model diagram according to the present invention; wherein, Figure 9 In (a) is the schematic diagram of the conformal working scenario; Figure 9 In (b) is the schematic diagram of the conformal bent antenna;

[0031] Figure 10 The S-parameter curves at different conformal cylinder radii according to the present invention;

[0032] Figure 11 The normalized near-field patterns at different frequencies and different planes according to the present invention; wherein, Figure 11 In (a) is the normalized near-field pattern in the yz plane at 0.48 GHz; Figure 11Among them, (b) is the normalized near-field pattern in the yz plane at 1.33 GHz; Figure 11 Among them, (c) is the normalized near-field pattern in the yz plane at 2.19 GHz; Figure 11 Among them, (d) is the normalized near-field pattern in the xz plane at 0.48 GHz; Figure 11 Among them, (e) is the normalized near-field pattern in the xz plane at 1.33 GHz; Figure 11 Among them, (f) is the normalized near-field pattern in the xz plane at 2.19 GHz.

[0033] Reference numerals

[0034] 1. Metal radiation patch; 2. Dielectric substrate; 3. Metal microstrip line; 4. 50Ω microstrip line; 5. Impedance converter; 6. Circular patch; 7. Floor with etched rounded square slot; 8. Ring patch; 9. Cross-shaped elliptical patch. Detailed implementation manners

[0035] To make the technical solutions, advantages and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of this application.

[0036] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the art to which the present invention belongs.

[0037] As Figures 1 - 3 shown, the present invention provides a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, including a metal radiation patch 1, a dielectric substrate 2 and a metal microstrip line 3. The dielectric substrate 2 is arranged above the metal microstrip line 3, and the metal radiation patch 1 is arranged above the dielectric substrate 2. The metal radiation patch 1 is composed of a floor 7 with an etched rounded square slot, a ring patch 8 and a cross-shaped elliptical patch 9. The ring patch 8 is arranged at the center of the floor 7 with an etched rounded square slot, and the cross-shaped elliptical patch 9 is arranged at the center of the ring patch 8; the floor 7 with an etched rounded square slot connects the vertical and horizontal sides of the square with four rounded corners and is etched on the copper-clad surface; the dielectric substrate 2 uses Rogers 5880 with a thickness of 0.254 mm, which has the advantages of low dielectric loss , low dielectric constant and high stability.

[0038] The metal microstrip line 3 is composed of a 50 Ω microstrip line 4, an impedance converter 5, and a circular patch 6. The 50 Ω microstrip line 4 is connected to the impedance converter 5, and the impedance converter 5 is connected to the circular patch 6. There are 4 metal microstrip lines 3, which are pairwise orthogonal and arranged on the four sides at the bottom of the dielectric substrate 2. Two of the orthogonally placed metal microstrip lines 3 are welded with SMA interfaces and connected to a 50 Ω coaxial line for the transmission of electrical signals. The circular patch 6 is used to achieve feed tuning within a wide bandwidth, and the impedance converter 5 is used to connect the two to achieve impedance transformation, so that the input impedance of the overall antenna is near 50 Ω within the operating bandwidth, reducing reflection loss.

[0039] As Figures 5 - 7 shown, it demonstrates the evolution process of the antenna, mainly including structural evolution and corresponding performance improvement. As Figure 5 shown in (a) of Figure 5 , Ant.1 is the initial design of a dual-polarized wide-slot antenna, connecting the vertical and horizontal edges of the square slot with rounded corners to reduce the cross-polarization component at low frequencies. However, it has a relatively narrow bandwidth range, from 1.16 GHz to 1.9 GHz. As Figure 5 shown in (b) of Figure 4 , to expand the bandwidth, a circular patch and crossed elliptical patches are added at the center of the slot. The added center patch extends the current path and introduces an additional low-frequency resonance point, thus expanding the bandwidth to 0.48 - 2.19 GHz. As

[0040] Table 1 Antenna Structure Parameters

[0041] ;

[0042] To further analyze the operating modes of the proposed antenna structure, Figure 8 the surface current distributions of the antenna at different frequencies (lower sideband, center frequency, upper sideband) at T / 2 are shown, where T represents the period duration of the current distribution. As Figure 8 shown in (a) of Figure 8 , at 0.48 GHz, the surface current is mainly distributed around the slots and the central circular patch, corresponding to the full-wavelength mode. The circular patch effectively extends the current path, thus introducing a new low-frequency resonance point. As

[0043] shown in (b) and (c) of Figure 9 , at 1.33 GHz and 2.19 GHz, the current distribution around the slots no longer shows the full-wavelength mode. The antenna mainly radiates through the circular patch and the cross-shaped elliptical patch. The proposed antenna has different current modes in different frequency bands, thus realizing its ultra-wideband characteristic.

[0044] As Figure 10 shown, the S-parameters of the proposed antenna under different conformal radii R are presented. For the planar antenna , due to the symmetric structure of the antenna, the echo impedance curves (|S 11 | and |S 22 |) when feeding ports 1 and 2 are exactly the same. Taking the frequency band corresponding to the echo impedance below -10 dB as the antenna bandwidth, its bandwidth is from 0.48 GHz to 2.19 GHz. Within the bandwidth range, the port isolation |S 21All are below -10 dB, indicating that the proposed antenna has good port isolation, and at least 90% of the energy does not flow out through port 2. Compared with the planar antenna, the trends of the return loss and port isolation curves of the conformal antenna are roughly the same, indicating that the antenna can be bent to a certain extent without serious performance deterioration. At the same time, it is observed that the conformal bending mainly affects the resonance points at medium and high frequencies, while the resonance points at low frequencies remain basically stable because the wavelength at low frequencies is longer and can cope with the changes of conformal bending. In addition, compared with port 1, the return loss curve of port 2 is more sensitive to the conformal radius because when port 2 is fed, the cylindrical conformal bending has a greater impact on its current path and thus has a more obvious impact on its impedance matching.

[0045] To verify the directivity of the proposed antenna, it is necessary to simulate its near-field radiation pattern under operating conditions. Considering that the head circumference of an adult is generally between 54 cm and 62 cm, corresponding to a radius of about 8 cm, the radiation pattern simulation is carried out on the spherical surface 8 cm away from the center of the antenna. As Figure 11 shown, the normalized near-field electric field radiation patterns of the proposed antenna structure at different frequencies (lower side frequency, center frequency, and upper side frequency) are presented. It can be observed that without a reflector, the main lobe of the proposed antenna points to the human brain, and the front-to-back ratio at different frequencies is above 11 dB. This phenomenon is due to the fact that the antenna design utilizes the loading effect of the human brain. That is, for an omnidirectional antenna operating in free space (radiating in both the upper and lower half-spaces), after increasing the dielectric constant of a certain space medium, the high dielectric constant difference between the upper and lower half-spaces will cause the antenna to radiate towards the space medium with a high dielectric constant, that is, the loading of the high dielectric constant medium will change the radiation pattern of the antenna from omnidirectional to directional. And the human brain, as a high dielectric constant medium, when loaded onto the omnidirectional slot antenna, will also change the antenna beam and make it point to the human brain. By utilizing the loading effect of the human brain, it is possible to achieve a high front-to-back ratio within the bandwidth while maintaining an extremely low profile of 0.254 mm. In addition, the cross polarization of the antenna is less than -10 dB and -20 dB in the yz-plane and xz-plane respectively. The low cross polarization indicates that the proposed dual-polarized antenna has a high polarization purity and the dual-polarization mode can work well.

[0046] Therefore, the present invention provides a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, which has the advantages of dual polarization, ultra-wideband, extremely low profile, directional beam, and conformal. It can detect richer brain detail information, achieve ultra-high resolution imaging, and while being portable, it can fit the heads of patients with different sizes and can be effectively applied to the microwave brain imaging system.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements do not enable the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging, characterized in that: It comprises a metal radiation patch, a dielectric substrate and a metal microstrip line, wherein the dielectric substrate is arranged above the metal microstrip line, and the metal radiation patch is arranged above the dielectric substrate; The metal microstrip line is composed of a 50Ω microstrip line, an impedance converter and a circular patch, the 50Ω microstrip line is connected to the impedance converter, and the impedance converter is connected to the circular patch; There are four metal microstrip lines, which are orthogonal to each other and are arranged on four sides of the bottom of the dielectric substrate; The metal radiation patch is composed of a floor with rounded square gaps etched on it, a circular patch and a cross-shaped elliptical patch; The circular ring patch is arranged at the center of the etched rounded square gap floor, and the cross-shaped elliptical patch is arranged at the center of the circular ring patch.

2. A dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: Two of the orthogonally placed metal microstrip lines are welded with SMA interfaces and connected to a 50Ω coaxial line for power feeding.

3. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: The floor with rounded square gaps is etched with four rounded corners to connect the vertical sides and horizontal sides of the square, and etching is performed on the copper-clad surface.

4. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: The antenna is placed in free space, and its metal radiation patch works in close contact with the human brain medium.

5. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: The antenna is conformally processed, and cylinders with different radii are used to simulate human heads of different sizes.

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