Dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging

Abstract

The invention discloses a dual-polarized ultra-wideband conformal slot antenna for microwave brain imaging, and relates to the technical field of slot antennas. The antenna comprises 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; the metal radiation patch is composed of a floor etched with a round-corner square gap, a circular patch and a cross-shaped elliptical patch, the circular patch is arranged at the center of the floor etched with the round-corner square gap, and the cross-shaped elliptical patch is arranged at the center of the circular patch; the metal microstrip line is composed of a 50-ohm microstrip line, an impedance converter and a circular patch. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging provided by the invention has the advantages of dual polarization, ultra wideband, extremely low profile, directional beam and the like, 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-polarization ultra-wideband conformal slot antenna for microwave brain imaging. Background Art

[0002] Stroke, as a common neurological disease, develops rapidly and carries a risk of death, so rapid and accurate diagnosis is particularly critical. Compared with traditional medical diagnostic methods, such as magnetic resonance imaging, brain imaging systems based on microwave frequency bands have shown significant advantages, with low cost, fast diagnosis speed, and easy portability. This technology is even expected to become an important equipment on ambulances, and has great application potential and research value in the field of new generation medical electronic applications.

[0003] The imaging principle of this technology is based on the difference in microwave propagation characteristics in different electromagnetic media: when abnormal tissue or lesions appear in the body, its electromagnetic characteristic parameters (mainly dielectric constant and conductivity) will change. By detecting the microwave signal reflected or scattered by the organism, obtaining information such as the frequency, amplitude and phase change of the signal, and then performing inversion imaging based on this information, the characteristic image of the measured tissue can be obtained, thereby achieving diagnosis of the patient.

[0004] In microwave brain imaging systems, antennas are key devices for signal transmission and reception, and are the core components that connect the object being measured with the back-end processing system. Their 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). Higher-frequency microwaves have difficulty penetrating the brain to obtain effective information, while low-frequency antennas are too large and do not meet the requirements for portability in actual use. Therefore, it is necessary to find a balance between penetration and portability. Generally speaking, the microwave frequency band suitable for human brain imaging ranges from 0.5-4GHz.

[0005] At present, antennas used for brain imaging are mainly divided into off-body antennas and body-matched antennas. Off-body antennas are antennas that are matched in a free space environment, and there is a large air gap between them and the human brain. Given the high dielectric constant of the human brain (the dielectric constant of the head skin is about 40), the electromagnetic waves radiated by the off-body antenna will produce strong reflections when passing through the air-scalp layer, which will lead to a decrease in matching performance and radiation efficiency. On-body matching antennas are antennas that are optimized for matching in the human body environment. They fit closely to the human brain and are matched to the human brain through matching media or directly. Although this method increases the complexity of the design to a certain extent, it can greatly reduce the electromagnetic waves reflected by the air-scalp layer, thereby maintaining a good matching effect and efficient radiation performance. However, antennas that are matched to the human brain through matching media or matching liquids usually have a higher profile, which is not conducive to conformal bending and portable use. On the whole, antennas that are directly matched to the human head are the best choice for microwave brain imaging systems.

[0006] In addition, increasing the polarization mode of the antenna can help detect richer brain information, thereby achieving more accurate imaging. However, there are currently no reports on dual-polarized antennas for microwave brain imaging systems. Summary of the invention

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

[0008] To achieve the above objectives, the present invention proposes a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging, comprising 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.

[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 four metal microstrip lines, which are orthogonal to each other and are arranged at four sides of the bottom of the dielectric substrate; two of the orthogonally placed metal microstrip lines are welded to SMA interfaces and connected to a 50Ω coaxial line.

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

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

[0013] Preferably, the antenna is placed in free space, and its metal radiation patch works in close contact with the human brain medium.

[0014] Preferably, the antenna is conformally processed, using cylinders with different radii to simulate human heads of different sizes.

[0015] Therefore, the present invention proposes a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging, which has the following beneficial effects: (1) The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging proposed in the present invention adopts a dual-linear polarization design and can detect richer detailed information of the human brain. Through two mutually orthogonal polarization directions, it can capture bleeding points of different shapes in the brain, providing more detailed data support for a comprehensive understanding of the brain hemorrhage condition.

[0016] (2) The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging proposed in the present invention has ultra-wideband characteristics, which facilitates high-resolution human brain imaging and helps doctors make accurate diagnoses.

[0017] (3) The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging proposed in the present invention has an extremely low profile design, which is conducive to the conformality of the antenna to the human head and greatly improves the portability in actual use.

[0018] (4) The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging proposed in the present invention can radiate electromagnetic waves to the human brain in a direction, effectively addressing the attenuation problem of electromagnetic waves when propagating inside the human brain, ensuring concentrated energy transmission, and allowing the signal to stably reach the target area even in a complex brain environment, thereby ensuring imaging quality.

[0019] (5) The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging proposed in the present invention has certain robustness for different degrees of conformal bending. That is, when acting on the heads of patients with different sizes, the antenna can still work normally without significant performance degradation, thereby ensuring the universality of its application.

[0020] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A side view of a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention; Figure 2A bottom view of a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention; Figure 3 A top view of a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention; Figure 4 The figure is a schematic diagram of the structural parameters of a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to the present invention; wherein: Figure 4 (a) is a schematic diagram of the structural parameters of the metal radiation patch; Figure 4 (b) is a schematic diagram of the structural parameters of the metal microstrip line; Figure 5 is a structural evolution diagram of the antenna of the present invention; wherein, Figure 5 (a) in the figure is antenna Ant.1; Figure 5 (b) in the figure is antenna Ant.2; Figure 5 (c) in the figure is antenna Ant.3; Figure 6 is the S parameter curve corresponding to the antenna evolution structure of the present invention; Figure 7 is the normalized near-field pattern of the antenna evolution structure of the present invention in the yz plane at 1.33 GHz; Figure 8 is the surface current distribution at different frequencies of the present invention; wherein, Figure 8 (a) is the surface current distribution at 0.48 GHz; Figure 8 (b) is the surface current distribution at 1.33 GHz; Figure 8 (c) is the surface current distribution at 2.19 GHz; Fig. 9 is a conformal model diagram of the present invention; wherein, Fig. 9 (a) is a schematic diagram of a conformal working scenario; Fig. 9 (b) is a schematic diagram of a conformal curved antenna; Fig.10 It is the S parameter curve of the present invention under different conformal cylinder radii; Fig.11 is the normalized near-field pattern of the present invention at different frequencies and different planes; wherein, Fig.11 (a) is the normalized near-field pattern in the yz plane at 0.48 GHz; Fig.11 (b) is the normalized near-field pattern in the yz plane at 1.33 GHz; Fig.11 (c) is the normalized near-field pattern on the yz plane at 2.19 GHz; Fig.11 (d) is the normalized near-field pattern on the xz plane at 0.48 GHz; Fig.11(e) is the normalized near-field pattern on the xz plane at 1.33 GHz; Fig.11 (f) in the figure is the normalized near-field pattern in the xz plane at 2.19 GHz.

[0022] Reference numerals 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 gaps; 8. Ring patch; 9. Cross-shaped elliptical patch. DETAILED DESCRIPTION

[0023] In order to make the technical solutions, advantages and purposes of the present invention clearer, the technical solutions of the embodiments of the present invention are clearly and completely described below. The described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of this application.

[0024] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0025] like Figure 1-3 As shown, the present invention provides a dual-polarization 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, wherein 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 a square slot etched with rounded corners, a ring patch 8 and a cross-shaped elliptical patch 9, wherein the ring patch 8 is arranged at the center of the floor 7 with a square slot etched with rounded corners, and the cross-shaped elliptical patch 9 is arranged at the center of the ring patch 8; the floor 7 with a square slot etched with rounded corners uses four rounded corners to connect the vertical and horizontal sides of the square, and is etched on the copper-clad surface; the dielectric substrate 2 adopts 0.254 mm thick Rogers 5880, which has low dielectric loss. , low dielectric constant And the advantages of high stability.

[0026] The metal microstrip line 3 is composed of a 50Ω microstrip line 4, an impedance converter 5 and a circular patch 6. The 50Ω microstrip line 4 is connected to the impedance converter 5, and the impedance converter 5 is connected to the circular patch 6. There are four metal microstrip lines 3, which are orthogonal to each other and are arranged on the four sides of the bottom of the dielectric substrate 2. Two of the orthogonally placed metal microstrip lines 3 are welded with SMA interfaces and connected to the 50Ω coaxial line for transmitting electrical signals. The circular patch 6 is used to realize feeding tuning within a broadband range, and the impedance converter 5 is used to connect the two to realize impedance transformation, so that the overall input impedance of the antenna is located near 50 Ω within the working bandwidth range to reduce reflection loss.

[0027] like Figure 5-7 As shown in Figure 2, the evolution of the antenna is shown, which mainly includes the structural evolution and the corresponding performance improvement. Figure 5 As shown in (a) in Figure 1, Ant.1 is the original design of the dual-polarized wide slot antenna, which uses rounded corners to connect the vertical and horizontal edges of the square slot to reduce the low-frequency cross-polarization components. However, it has a relatively narrow bandwidth range from 1.16 GHz to 1.9 GHz. Figure 5 As shown in (b), in order to expand the bandwidth, a circular patch and a crossed elliptical patch are added in the center of the gap. The additional central patch extends the current path and introduces an additional low-frequency resonance point, thereby widening the bandwidth to 0.48-2.19 GHz. Figure 5 As shown in (c), in order to further improve the impedance matching and cross-polarization, two matching microstrip lines are added to the antenna Ant.2 and placed at the symmetrical position of the two feeding microstrip lines to form the antenna Ant.3. The added microstrip lines make the input impedance curve of the antenna near the middle resonance point (0.85 GHz) flatter and closer to the ideal 50 Ω at 0.7-1 GHz, thereby improving the impedance matching in this bandwidth range. At the same time, the addition of microstrip lines increases the symmetry of the antenna structure, so that the orthogonal current components cancel each other out, thereby greatly improving the cross-polarization. The cross-polarization of antenna Ant.3 at 1.33 GHz is less than -10 dB, which is nearly 4 dB less than that of antenna Ant.2. Therefore, considering its good impedance matching and cross-polarization performance, Ant.3 is used as the antenna structure for brain imaging systems. The optimized antenna has a bandwidth range of 0.48-2.19 GHz and a compact size of 72 mm × 72 mm × 0.254 mm, as shown in Figure 2. Figure 4 The specific structural parameters of the antenna are shown in Table 1 (unit: mm): Table 1 Antenna structure parameters ;

[0028] In order to further analyze the working mode of the proposed antenna structure, Figure 8The surface current distribution of the antenna at different frequencies (lower sideband, center frequency, upper sideband) at time T / 2 is shown, where T represents the periodic duration of the current distribution. Figure 8 As shown in (a) in Figure 1, at 0.48 GHz, the surface current is mainly distributed around the gap and the central ring patch, corresponding to the full-wavelength mode. The ring patch effectively extends the current path, thereby introducing a new low-frequency resonance point. Figure 8 As shown in (b) and (c), at 1.33 GHz and 2.19 GHz, the current distribution around the slot is no longer a full-wavelength pattern, and the antenna radiates mainly through the circular patch and the cross-shaped elliptical patch. The proposed antenna has different current patterns in different frequency bands, thus achieving its ultra-wideband characteristics.

[0029] In order to minimize the reflection of electromagnetic waves in the air-skin layer, the antenna needs to be close to the human head. However, the size of the human head is closely related to individual factors (such as age, gender, etc.), and different parts of the head have different curvatures. Therefore, the proposed antenna needs to work under different conformal curvature conditions to evaluate its robustness. Fig. 9 As shown in the figure, the structure of the conformal antenna is shown. The antenna works in free space, and its radiation structure fits the conformal carrier. The conformal carrier is a cylindrical human brain model. Considering that the relative dielectric constants of various parts of the human brain are approximately: skin: 43; gray matter: 52; white matter: 38 (at 0.9 GHz), the relative dielectric constant of the human brain model is set to 40 to simulate the electromagnetic characteristic of the high dielectric constant of the human brain in real scenes.

[0030] like Fig.10 As shown in the figure, the S parameters of the proposed antenna at different conformal radii R are shown. Due to the symmetrical structure of the antenna, the return impedance curve (|S 11 | and |S 22 |) is exactly the same, and the frequency band corresponding to the return impedance below -10 dB is used as the antenna bandwidth, then its bandwidth is 0.48 GHz to 2.19 GHz. Within the bandwidth range, the port isolation |S 21| are all lower than -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 echo impedance and port isolation curves of the conformal antenna have roughly the same trend, indicating that the antenna can be bent to a certain extent without serious performance degradation. At the same time, it is observed that conformal bending mainly affects the resonance points at the mid-frequency and high-frequency positions, while the position of the resonance point at the low frequency remains basically stable. This is because the wavelength of the low frequency is longer and can cope with the changes of conformal bending. In addition, compared with port 1, the echo impedance curve of port 2 is more sensitive to the conformal radius. This is because when port 2 is fed, the cylindrical conformal bending has a greater impact on its current path, which in turn has a more obvious impact on its impedance matching.

[0031] In order to verify the directivity of the proposed antenna, its near-field radiation pattern under working conditions needs to be simulated. Considering that the head circumference of an adult is generally between 54 cm and 62 cm, the corresponding radius is about 8 cm. Therefore, the radiation pattern simulation is performed on a spherical surface 8 cm away from the center of the antenna. Fig.11 As shown in the figure, the normalized near-field electric field pattern of the proposed antenna structure at different frequencies (lower sideband, center frequency and upper sideband) is shown. 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 working 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 toward the high dielectric constant medium space, that is, the loading of the high dielectric constant medium will change the antenna's radiation pattern from omnidirectional to directional. The human brain, as a high dielectric constant medium, will also change the antenna beam and point it to the human brain when it is loaded onto an omnidirectional slot antenna. By utilizing the loading effect of the human brain, it can 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 lower cross-polarization indicates that the proposed dual-polarized antenna has higher polarization purity and the dual-polarization mode can work well.

[0032] Therefore, the present invention provides a dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging, which has the advantages of dual polarization, ultra-wideband, extremely low profile, directional beam, conformal, etc. It can detect richer brain detail information and achieve ultra-high resolution imaging. It is portable and can fit the heads of patients of different sizes, and can be effectively used in microwave brain imaging systems.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging, characterized in that: The invention comprises 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.

2. A dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: The metal microstrip line consists 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.

3. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 2, characterized in that: 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.

4. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 3, 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.

5. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 1, characterized in that: The metal radiation patch is composed of a floor with rounded square gaps etched on it, a circular ring patch and a cross-shaped elliptical patch.

6. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 5, characterized in that: 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.

7. The dual-polarization ultra-wideband conformal slot antenna for microwave brain imaging according to claim 5, 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.

8. 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.

9. 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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