Bent flow arm circular patch antenna for microwave thermal therapy

Abstract

The invention discloses a meandering arm circular patch antenna for microwave thermal therapy, and belongs to the field of medical equipment. According to the meandering arm circular patch antenna, three key factors of robustness, miniaturization and current distribution uniformity are considered; in the aspect of robustness, a mode of loading an annular arm on the periphery of a circular patch is adopted, and a new characteristic mode is excited by utilizing a strong electromagnetic coupling effect between the circular patch and the annular arm, so that the antenna keeps stable performance when facing electromagnetic characteristic difference of human tissues; in the aspect of miniaturization, an annular arm resonance circuit is combined with a meandering flow technology, so that a current path is effectively expanded, and low-frequency resonance is excited; in the aspect of current distribution uniformity, a highly symmetrical annular meandering arm design is adopted, so that the current distribution uniformity is ensured, and the irregularity of energy radiation and a focusing area is avoided; the design has extremely high practical value for the microwave hyperthermia antenna working under complex electromagnetic characteristics.

Description

Technical Field

[0001] The invention relates to the field of medical equipment, and in particular to a meander arm circular patch antenna for microwave thermal therapy. Background Art

[0002] Prior art: A Chinese invention patent with publication number CN107715309B discloses a wearable microwave thermal therapy array antenna (Patent 1); the above technology uses a simple circular patch as an antenna unit, which faces robustness issues.

[0003] The robustness problem is as follows: When the patch is close to the human body, its stability will be affected by a variety of related factors. These factors include differences in the electromagnetic properties of human tissue (such as skin thickness, fat content and water content) and changes in the patient's posture. Changes in these factors will cause changes in the target effective wavelength, which in turn causes a shift in the resonant frequency. In addition, in the actual array deployment process, the electromagnetic environment between the array elements at different positions and the human body is significantly different, which increases the difficulty of array deployment.

[0004] like Figure 1 The figure shows the structure diagram of the wearable microwave hyperthermia array antenna provided by Patent 1. Figure 2 This is the return loss (S11) diagram of the array elements at different positions in Patent 1. Figure 2 It can be seen that in the actual array process, the return loss (S11) of the array elements at different positions shows obvious instability and deviation. This inconsistency highlights the challenges faced by existing technologies in practical applications, and also highlights the need to develop more robust antenna designs. Summary of the invention

[0005] The object of the present invention is to provide a meander arm circular patch antenna for microwave thermal therapy, which at least solves the robustness problem in the background technology.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The present invention provides a meander arm circular patch antenna for microwave hyperthermia, wherein the meander arm circular patch antenna is a circular patch with a radius of 7 mm as a whole, wherein the center of the circular patch is a circular portion with a radius r of 5 mm, and four 1 / 4 circular ring-shaped annular arms are arranged around the periphery of the circular portion and are concentric with the center of the circle; the width d1 of the annular arm is 1.8 mm, and four identical arc-shaped first slits are formed between the four annular arms and the circular portion, and the width d2 of the four first slits is 0.2 mm, and the four first slits are equiangular. The first slits are distributed at the edge of the circular portion, and the four first slits are concentric with the circular portion; the angle between adjacent first slits is α, and α is 7.5°; a second slit with an angle β is formed between adjacent annular arms, and β is 2°; the starting end of each first slit is connected to a second slit; in the counterclockwise direction, the first end point of the first slit is the starting end; a third slit and a fourth slit in opposite directions are formed on each annular arm; the third slit and the fourth slit are arc-shaped and concentric with the circular portion; wherein the third slit is located at The third slit is located outside the first slit, the width d3 of the third slit is 0.2 mm, and the distance D1 between the third slit and the first slit is 0.5 mm; the third slit extends clockwise, the starting end of the third slit is connected to a second slit, and the third slit extends clockwise to the adjacent second slit; the angle between the end point of the third slit and the adjacent second slit is λ, and λ is 7.5°; the fourth slit is located outside the third slit, the width d4 of the fourth slit is 0.2 mm, and the distance D1 between the fourth slit and the third slit is 0.5 mm. The distance D2 is 0.5 mm; the fourth slit extends counterclockwise, the starting end of the fourth slit is connected to a second slit, and the fourth slit extends counterclockwise toward the adjacent second slit; the angle between the end point of the fourth slit and the adjacent second slit is ρ, and ρ is 7.5°; a curved three-winding structure is formed between the first slit, the third slit, and the fourth slit; the meander arm circular patch antenna is printed on a FR4 dielectric substrate with a thickness of 0.8 mm, a dielectric constant of 4.5, and a loss tangent of 0.02.

[0008] Furthermore, the meander arm circular patch antenna is arranged on a hemispherical conformal structure, which is a hemispherical shell composed of a nylon inner shell and a nylon outer shell, and a hemispherical shell-shaped water bag is formed between the nylon inner shell and the nylon outer shell; the water bag is filled with deionized water, and a water inlet and a water outlet are provided on the water bag; the meander arm circular patch antenna is arranged in the water bag, and the meander arm circular patch antenna is connected to the coaxial input line; the coaxial input line passes through the nylon outer shell; the coaxial input line consists of an SMA connector inner conductor, an SMA connector filling medium, and an SMA connector outer conductor; the SMA connector outer conductor is filled with an SMA connector filling medium; the SMA connector inner conductor is arranged in the SMA connector outer conductor, the SMA connector inner conductor passes through the SMA connector outer conductor and is connected to the meander arm circular patch antenna; the inner surface of the nylon outer shell is covered with a copper layer, which serves as a hemispherical ground plane shared by all array elements.

[0009] Furthermore, the nylon inner shell and the nylon outer shell are made of PA12 material.

[0010] Furthermore, the distance H1 from the meander arm circular patch antenna to the skin is 3 mm.

[0011] Furthermore, a distance H2 between the meander arm circular patch antenna and the hemispherical ground plane is 2 mm.

[0012] Furthermore, the width S1 of the connection of the outer peripheral curved arms of the curved arm circular patch antenna is 7.5 degrees.

[0013] Furthermore, 40 curved arm circular patch antennas are arranged on the hemispherical conformal structure, and the 40 curved arm circular patch antennas are arranged in a honeycomb shape.

[0014] Furthermore, the nylon shell is composed of a hemispherical shell with a radius of 59 mm and a thickness of 6 mm and an eave edge with a width of 10 mm and a thickness of 2 mm.

[0015] Furthermore, the nylon inner shell is composed of a hemispherical shell with a radius of 49.5 mm and a thickness of 1.5 mm and a flange with a width of 10 mm and a thickness of 2 mm.

[0016] The beneficial effect of the present invention is that the present invention provides a meander arm circular patch antenna for microwave hyperthermia, which takes into account three key factors: robustness, miniaturization, and uniformity of current distribution. First, by adopting the method of loading annular arms on the periphery of the circular patch, the strong electromagnetic coupling between the circular patch and the peripherally loaded annular arms is utilized to excite new characteristic modes, so that the antenna can maintain stable performance even when there are certain differences in the electromagnetic characteristics of human tissue. Secondly, in terms of miniaturization, by loading the annular arm as a resonant circuit, the newly excited characteristic mode is successfully resonated at a low frequency. Furthermore, by the strategy of loading the meander technology on the annular arm resonant circuit, the current path is effectively expanded, and the miniaturization of the antenna is further realized. Finally, the design of the antenna also takes into account the symmetry of the structure and the uniformity of the current distribution. By loading multiple highly symmetrical annular meander arms, the uniformity of the current distribution is successfully achieved. The symmetry of the structure helps to reduce the asymmetry of the radiation pattern, while the uniformity of the current distribution avoids the unevenness of the energy radiation of the microwave hyperthermia antenna and the irregularity of the focusing area. This provides strong support for the flexibility and scalability of subsequent antenna array design. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Shown is a schematic diagram of the structure of the wearable microwave hyperthermia therapy array antenna provided by Patent 1.

[0018] Figure 2 This is the return loss (S11) diagram of array elements at different positions in Patent 1.

[0019] Figure 3 The above is a schematic diagram of the hemispherical conformal structure, antenna array element and human breast model of the present invention.

[0020] FIG. 4( a ) shows a diagram of the process of gradually evolving from a simple circular patch antenna (step # 1 ) to the curved arm circular patch antenna of the present invention.

[0021] Figure 4(b) shows the current distribution on the patch surface at five antenna evolution stages at 915 MHz.

[0022] Figure 5 The return loss (S11) graphs at five evolutionary stages are shown.

[0023] Figure 6(a) shows the S11 graph of the antenna at different distances from the patch to the skin (H1).

[0024] Figure 6(b) shows the S11 graph of the antenna at different distances (H2) between the patch and the hemispherical ground plane.

[0025] Figure 6(c) shows the S11 diagram of the antenna under different widths of the connection between the circular patch and the peripheral meander arm (S1).

[0026] Figure 7 Shown is a schematic diagram of the array element structure of the curved arm circular patch antenna of the present invention.

[0027] Figure 8 It is a simulated return loss diagram of the meander arm circular patch antenna of the present invention.

[0028] FIG. 9( a ) is a side view of the meander arm patch antenna array applicator of the present invention.

[0029] FIG. 9( b ) is a top view of the meander arm patch antenna array applicator of the present invention.

[0030] Figure 10(a) is the S11 diagram of each array element simulated by HFSS.

[0031] FIG10( b ) is a schematic diagram of the array element coupling coefficient (Sn1) simulated by HFSS.

[0032] Fig.11 This is a schematic diagram of a manufacturing sample of the meander arm circular patch antenna array of the present invention before actual assembly.

[0033] FIG. 12( a ) is a graph showing the measured results of S11 of 40 array elements of the meander arm circular patch antenna array applicator of the present invention.

[0034] FIG. 12( b ) is a diagram showing the coupling coefficient S1n between array element No. 1 and all other array elements in the array according to the present invention. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0037] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] Patent 1 in the background technology discloses a wearable microwave hyperthermia array antenna, the array antenna includes multiple microstrip patch antenna units placed in deionized water, and multiple coaxial input lines respectively connected to the multiple microstrip patch antenna units; wherein the multiple microstrip patch antenna units have a common ground plane, and the deionized water is placed in a water bag close to the skin; the water bag is in the shape of a hemispherical shell; and multiple microstrip patch antenna units are distributed around the water bag. The antenna unit includes: an internal circular structure and an external annular structure; the center of the circular structure and the annular structure is the same; wherein the radius of the circular structure is 4mm, and its thickness is 0.5mm; the outer circle radius of the annular structure is 12mm, and its inner circle radius is 7mm. The distance from the antenna unit to the skin is 10mm, and the distance from the antenna unit to the common ground plane is 12mm. The number of antenna units is 9.

[0040] In the technical solution disclosed in Patent 1, the return loss (S11) of array elements at different positions shows obvious instability and deviation. This inconsistency highlights the challenges faced by existing technologies in practical applications, and also highlights the necessity of developing more robust antenna designs.

[0041] An embodiment of the present application provides a curved arm circular patch antenna for microwave thermal therapy. The main structure in the present application is the same as the main structure in Patent 1, and a patch antenna with a different structure from that in Patent 1 is used. Figure 7 Shown is a schematic diagram of the array element structure of the curved arm circular patch antenna of the present invention. Figure 7 In the figure, a circular portion 11.1, an annular arm 11.2, a first slit 11.3, a second slit 11.4, a third slit 11.5, and a fourth slit 11.6.

[0042] like Figure 7 As shown in , the meander arm circular patch antenna of the present invention is a circular patch with a radius of 7 mm as a whole, and the center of the circular patch is a circular portion with a radius r of 5 mm, and four 1 / 4 circular ring-shaped annular arms are arranged around the periphery of the circular portion with the same center; the width d1 of the annular arm is 1.8 mm, and four identical arc-shaped first slits are formed between the four annular arms and the circular portion, and the width d2 of the four first slits is 0.2 mm. The four first slits are distributed at equal angles on the edge of the circular portion, and the four first slits are concentric with the circular portion; the angle between adjacent first slits is α, and α is 7.5°; a second slit with an angle β is formed between adjacent annular arms, and β is 2°; the starting end of each first slit is connected to a second slit; as shown in Figure 7 As shown in the figure, in the counterclockwise direction, the first end point of the first slit is the starting end; a third slit and a fourth slit in opposite directions are formed on each annular arm; the third slit and the fourth slit are arc-shaped and are concentric with the circular portion; wherein the third slit is located outside the first slit, the width d3 of the third slit is 0.2 mm, and the distance D1 between the third slit and the first slit is 0.5 mm; the third slit extends clockwise, the starting end of the third slit is connected to a second slit, and the third slit extends clockwise to the adjacent second slit; the angle between the end point of the third slit and the adjacent second slit is λ, and λ is 7.5°; The slit is located outside the third slit, the width d4 of the fourth slit is 0.2 mm, and the distance D2 between the fourth slit and the third slit is 0.5 mm; the fourth slit extends counterclockwise, the starting end of the fourth slit is connected to a second slit, and the fourth slit extends counterclockwise to the adjacent second slit; the angle between the end point of the fourth slit and the adjacent second slit is ρ, and ρ is 7.5°; a curved three-winding structure is formed between the first slit, the third slit, and the fourth slit; the meander arm circular patch antenna is printed on an FR4 dielectric substrate with a thickness of 0.8 mm, a dielectric constant of 4.5, and a loss tangent of 0.02.

[0043] like Figure 3 The above is a schematic diagram of the hemispherical conformal structure, antenna array element and human breast model of the present invention. Figure 3 In the figure, tumor 1, breast tissue 2, skin 3, fat 4, muscle 5, nylon inner shell 6, nylon outer shell 7, deionized water 8, water injection port 9, water outlet 10, meander arm circular patch antenna 11, SMA connector inner conductor 12, SMA connector filling medium 13, SMA connector outer conductor 14.

[0044] In the present invention, the meander arm circular patch antenna is arranged on a hemispherical conformal structure, and the hemispherical conformal structure is a hemispherical shell composed of a nylon inner shell and a nylon outer shell, and the nylon inner shell and the nylon outer shell are preferably made of PA12 material. A water bag in the shape of a hemispherical shell is formed between the nylon inner shell and the nylon outer shell; the water bag is filled with deionized water; a water inlet and a water outlet are provided on the water bag; the water inlet is used to inject deionized water into the water bag; the water outlet is used for the deionized water in the water bag to flow out. A meander arm circular patch antenna array element is arranged in the water bag, and the meander arm circular patch antenna is connected to a coaxial input line; the coaxial input line passes through the nylon shell. The coaxial input line consists of an SMA connector inner conductor, an SMA connector filling medium, and an SMA connector outer conductor. The SMA connector outer conductor is filled with an SMA connector filling medium; the SMA connector inner conductor is arranged in the SMA connector outer conductor, the SMA connector inner conductor passes through the SMA connector outer conductor and is connected to the meander arm circular patch antenna.

[0045] In Patent 1, the patch antenna is made on an FR4 dielectric substrate with a thickness of 0.8 mm, a dielectric constant of 4.5, and a loss tangent of 0.02. The antenna patch structure consists of a microstrip circular patch, and the central circular patch is connected to the inner conductor of the 50Ω SMA connector by backfeeding. The main structure of the patch antenna is placed between the inner and outer nylon shells, and a copper layer is covered on the inner surface of the hemispherical shell as a hemispherical ground plane shared by all array elements. Due to the high dielectric and high loss characteristics of the human body, electromagnetic waves will absorb a large amount of electromagnetic waves and heat up rapidly when penetrating the surface of the breast, hindering the formation of hot spots required for deep tumor treatment. In order to solve this problem, a circulating deionized water method is used in the closed space of the nylon inner and outer hemispherical shells to reduce the surface temperature of the breast. In addition, deionized water is used as a dielectric coupling agent between the antenna and the tissue, achieving complete conformality between the antenna and the breast, ensuring efficient and stable transmission of energy. In addition, microwaves will form a "slow wave structure" when transmitted in deionized water, a high dielectric constant material, which significantly reduces the size of the antenna.

[0046] The design process of the curved arm circular patch antenna array element of the present invention is described in detail below.

[0047] FIG4(a) shows a process diagram of the gradual evolution from a simple circular patch antenna (step #1) to the curved arm circular patch antenna of the present invention. In the figure, a circular arm with a full circle is loaded on the periphery of the circular patch (step #2); two symmetrical semicircular arms are loaded on the periphery of the circular patch (step #3); four 1 / 4 circular arms are loaded on the periphery of the circular patch (step #4); finally, in step #5, a transverse three-winding structure is loaded on the four 1 / 4 circular arms in step #4. FIG4(b) is a diagram of the current distribution on the patch surface at 915MHz in the five antenna evolution stages. Figure 5 The return loss (S11) graphs at five evolutionary stages are shown.

[0048] The initial configuration of the antenna (step #1) is a circular patch antenna with a radius of 5mm. As shown in Figure 4(b), it generates a linear current density on the patch and propagates a tangential electric field into the tissue. When the circular patch antenna is placed near the human body, it actually forms a "cavity" composed of the human body and the antenna. The resonant frequency and mode of this cavity depend on the electromagnetic properties of the human body, including parameters such as dielectric constant and conductivity. When the ratio between the size of the patch antenna and the response of human tissue to electromagnetic waves of a specific frequency approaches a certain value, the resonant mode of the cavity may be excited, causing the antenna to resonate at a specific frequency. This phenomenon is usually called "cavity mode coupling."

[0049] However, due to the significant individual differences in the electromagnetic properties of human tissue, such as skin thickness, fat content, and water content, these factors will significantly affect the electromagnetic environment of the cavity, thereby causing the resonant frequency to shift. In addition, in the subsequent array deployment process, considering that the cavity electromagnetic environment between the array elements at different positions and the human body may be different, this also increases the complexity of the array. In order to reduce power loss in deionized water, the patch antenna should be as close to the skin as possible. However, when the antenna is close to the skin, the electromagnetic properties of the human body will affect the propagation of electromagnetic waves, resulting in enhanced reflected signals, increased return loss, and a direct impact on the radiation efficiency of the antenna. At the same time, when the antenna is close to the skin, the size of the "cavity" will be compressed, and the wavelength of the resonance will also be shortened, causing the resonance to move to a high frequency.

[0050] like Figure 5As shown in the figure, when the distance between the antenna and the skin is compressed to 3mm, the resonant frequency remains at 3296MHz despite the use of a slow-wave structure loaded with deionized water. At this time, the only way to adjust the resonant frequency to 915MHz is to enlarge the size of the circular patch antenna. However, due to the limited size of the breast, increasing the size of the circular patch is not a feasible solution. Small-sized array elements can arrange more array elements on the conformal hemispherical structure, thereby improving the focusing accuracy and steering ability of the array antenna, achieving more precise treatment, and reducing thermal damage to healthy tissue. In addition, the miniaturization of the array elements can also increase the spacing between the array elements, reduce the coupling effect (<-20dB), and further reduce unnecessary hot spots in healthy tissue.

[0051] In view of the above-mentioned robustness and miniaturization problems, the present invention proposes a method of loading a meander arm around the periphery of a circular patch, thereby extending the current path and exciting new characteristic modes, ultimately achieving the purpose of stable resonance at 915 MHz.

[0052] As shown in Figure 4(a), a full-circle ring arm is loaded on the periphery of the circular patch as a resonant circuit to achieve low-frequency resonance (step #2). By analyzing the surface current distribution of the patch (Figure 4(b)), it can be seen that the current is mainly concentrated in the gap between the circular patch and the ring arm, which indicates that the newly excited radiation at the low resonant frequency is mainly generated by the strong electromagnetic coupling between the circular patch and the ring arm loaded on the periphery. However, according to Figure 5 The antenna return loss (S11) curve shown in Figure 2 shows that although step #2 successfully introduces a new resonant frequency in the low frequency band compared to step #1, the center of the new resonant frequency is located at 360MHz. This is because the effective length of the electromagnetic coupling path of the full-circle ring arm is too long, resulting in a low resonant frequency. The size of the ring arm can be further adjusted to change the length of the equivalent current path, thereby achieving a shift in the center frequency of the newly excited resonance.

[0053] In the design of step #3, two symmetrical half-circle ring arms loaded on the periphery of the circular patch replace the full-circle ring arms in step #2 (Figure 4(a)). Figure 5From the antenna S11 curve shown in , the center frequency of the patch antenna has been adjusted to 732MHz. As expected, this improvement significantly shortens the effective length of the electromagnetic coupling path, thereby increasing the resonant frequency of the patch antenna. In-depth analysis of the surface current distribution of the patch, as shown in Figure 4(b), similarly, the current is mainly concentrated in the gap between the circular patch and the arm, especially at the connection position between the patch and the arm, where the current distribution is more dense. This uneven current distribution directly affects the radiation effect of the patch. When the current flows mainly along the joint edge of the circular patch and the arm, a strong electric field is formed in this area, causing the energy radiated by the antenna to the human tissue to show an uneven distribution characteristic, which poses a challenge to the subsequent antenna array design and layout.

[0054] In the design of step #4, in order to further optimize the antenna performance, four 1 / 4 ring arms are loaded on the periphery of the circular patch. This measure not only further shortens the effective length of the electromagnetic coupling path, but also achieves a more uniform current distribution by increasing the number of ring arms. By analyzing the surface current distribution diagram of Figure 4(b), it can be observed that the current is more evenly distributed between the patch and the ring arms, especially at the connection between the patch and the ring arms, the current density becomes more uniform. This uniform current distribution helps to improve the radiation pattern of the antenna and reduce the non-uniformity of energy radiation and the irregularity of the focusing area. In addition, the configuration of four 1 / 4 rings increases the symmetry of the antenna structure, which is conducive to reducing the asymmetry of the radiation pattern and improving the flexibility of the antenna array design. However, according to Figure 5 The S11 curve shows that the center frequency of the antenna is 1392MHz, which is lower than the expected 915MHz. This indicates that the effective length of the electromagnetic coupling path in the current design is too short and needs further adjustment and optimization.

[0055] In order to reduce the resonant frequency of the antenna to 915MHz, in the design of step #5, a transverse three-winding structure is loaded on the ring arms of the four 1 / 4 rings in step #4, as shown in Figure 4(a). This design utilizes the principle of loading meander technology on the ring arm resonant circuit to effectively expand the current path. By precisely controlling the size, shape and position of the slot, the center frequency of the final designed "meander arm circular patch antenna" is adjusted to 915MHz, achieving the expected frequency matching. It is worth mentioning that the design of step #5 not only solves the problem of frequency mismatch, but also cleverly retains the advantages of antenna structure symmetry and uniform current distribution in the design of step #4 ( Figure 5 ).

[0056] After the design and evolution from step #1 to step #5, the final design of the "meandering arm circular patch antenna" takes into account the three key factors of robustness, miniaturization and current distribution uniformity. First, the robustness of the antenna is significantly improved by adopting the method of loading the meandering arm on the periphery of the circular patch. This design not only extends the current path, but also excites new characteristic modes, so that the antenna can maintain stable performance even when there are certain differences in the electromagnetic characteristics of human tissue. This design has extremely high practical value for microwave thermal therapy antennas working under complex electromagnetic characteristics. Secondly, in terms of miniaturization, by loading the ring arm as a resonant circuit and utilizing the strong electromagnetic coupling between the circular patch and the arm loaded on the periphery, the excitation of the low resonant frequency is successfully achieved. Furthermore, by applying the strategy of loading the meandering technology on the ring arm resonant circuit, the current path is effectively extended, thereby realizing the miniaturization of the antenna. Finally, the design of the antenna also takes into account the symmetry of the structure and the uniformity of the current distribution. By loading multiple highly symmetrical ring-shaped meandering arms, the uniformity of the current distribution is successfully achieved. The symmetry of the structure helps to reduce the asymmetry of the radiation pattern, while the uniformity of the current distribution avoids the non-uniformity of the energy radiation of the microwave thermal therapy antenna and the irregularity of the focusing area. This provides strong support for the flexibility and scalability of the subsequent antenna array design.

[0057] The scanning parameter analysis is as follows.

[0058] The impedance matching of the antenna (i.e., the return loss S11) is affected by the antenna structural parameters. The distance from the patch to the skin (H1), the distance from the patch to the hemispherical ground plane (H2), and the width of the connection between the circular patch and the peripheral meander arm (S1) are key parameters in the antenna design. Therefore, these parameters were swept and analyzed in HFSS to achieve the best impedance matching.

[0059] The changes in antenna S11 under simulations with different parameter values ​​are as follows. Figure 6(a) shows the effect of the distance from the patch to the skin (H1) on the antenna S11, by performing a parameter scan of H1 from 2mm to 5mm with a step of 0.5mm. The results show that as H1 decreases, the central resonant frequency of the antenna shifts toward high frequency. This is because when the antenna is close to the skin, the size of the "cavity" is compressed, resulting in a shortened wavelength of resonance, which in turn shifts the resonant frequency toward high frequency. In addition, the presence of the skin enhances the reflected signal, so as H1 decreases, the return loss of the antenna increases. In order to reduce power loss in deionized water, the patch antenna should be as close to the skin as possible, but at the same time, it is also necessary to avoid impedance mismatch and significant shift in resonant frequency caused by being too close. Taking all factors into consideration, H1 performs best at 3mm, at which time the antenna's S11 reaches -17.32dB.

[0060] Figure 6(b) shows the effect of the distance (H2) between the patch and the hemispherical ground plane on the antenna S11. By performing a parameter scan of H2 with a step of 0.2mm from 1.6mm to 2.4mm, the results show that H2 can achieve stable resonance below -10dB in the range of 1.6mm to 2.4mm, and when H2 = 2mm, the center frequency of the antenna is 915MHz.

[0061] Figure 6(c) shows the effect of the width (S1) of the connection between the circular patch and the peripheral meander arm on the antenna S11. By performing a parameter scan of S1 from 5.5deg to 15.5deg in steps of 1deg, the results show that as S1 increases, the center frequency of the antenna gradually moves toward high frequency. This is because the increase in S1 will reduce the equivalent current path, thereby gradually shifting the resonance point achieved by the meander technology toward high frequency. When S1 = 7.5deg, the center frequency of the antenna is 915MHz.

[0062] The final optimized element structure of the curved arm circular patch antenna is as follows: Figure 7 As shown. The antenna is printed on a FR4 dielectric substrate with a thickness of 0.8 mm, a dielectric constant of 4.5, and a loss tangent of 0.02. The overall dimensions of the antenna are a circular patch with a radius of 7 mm. At 915 MHz, the size of the antenna relative to the working wavelength is 0.042λ. Figure 8 This is a simulated return loss diagram of the meander arm circular patch antenna of the present invention. At an operating frequency of 915MHz, the S11 parameter of the meander arm circular patch antenna reaches -17.32dB, indicating that the antenna has good impedance matching performance at this frequency. In addition, the bandwidth of the antenna (S11<-10dB) is 30MHz, showing certain broadband characteristics and being able to maintain good performance over a wide frequency range.

[0063] The simulation results of the curved arm circular patch antenna array of the present invention are as follows.

[0064] In order to experimentally verify the performance of the designed array antenna, a 40-element meander arm circular patch antenna array is arranged on a hemispherical conformal structure. FIG9(a) is a side view of the meander arm patch antenna array applicator of the present invention, in which the array elements are arranged in a honeycomb pattern to achieve uniform distribution, thereby eliminating the blind spot in treatment and ensuring balanced energy transfer, thereby improving energy utilization. FIG9(b) is a top view of the meander arm patch antenna array applicator of the present invention, and the 40 array elements are numbered.

[0065] The meander arm circular patch antenna array was simulated in HFSS. As shown in Figure 10(a), when operating at a frequency of 915MHz, the S11 of the 40 elements in the applicator is less than -10dB. It is worth noting that the S11 parameters of all elements show a high degree of consistency, which strongly demonstrates the excellent robustness of the meander arm patch antenna design. Due to the high symmetry of the hemispherical structure, the parallel coupling characteristics between all elements in the entire array can be demonstrated by the coupling between a representative element (element 1) and other elements. Figure 10(b) shows the coupling coefficient S1n (n=2,...,40) between element 1 and all other elements in the array. Among these couplings, the coupling of elements 2, 6 and 7 adjacent to element 1 is relatively large, but they are also below -20dB. The coupling of the remaining elements with element 1 reaches below -40dB. As an array antenna radiator for microwave hyperthermia therapy of breast cancer, effective coupling isolation is achieved between the elements.

[0066] The actual processing and performance testing of the meander arm circular patch antenna array of the present invention are as follows.

[0067] Fig.11 This is a schematic diagram of the manufacturing sample of the curved arm circular patch antenna array of the present invention before the actual assembly, which is divided into two parts: a shell of a hemispherical conformal structure and an antenna array element. The hemispherical conformal structure shell is divided into a nylon outer shell for fixing and installing the antenna array element and a nylon inner shell for carrying a breast phantom. The nylon outer shell consists of a hemispherical shell with a radius of 59mm and a thickness of 6mm and an eaves with a width of 10mm and a thickness of 2mm. The hemispherical shell is provided with a square groove with a width of 13mm and a depth of 2mm, which is used to install the flange of the SMA connector of each array element. A circular hole with a radius of 2.06mm is provided in the center of the groove to allow the inner conductor and filling medium of the SMA head to pass through. In addition, a water inlet and outlet with a radius of 5mm are provided on both sides of the hemispherical shell. The nylon inner shell is provided with a hemispherical shell with a radius of 49.5mm and a thickness of 1.5mm and an eaves with a width of 10mm and a thickness of 2mm. The eaves of the inner and outer shells are both provided with holes so that the two can be fixed together by screws. Nylon PA12 material is used to 3D print the shell of the hemispherical conformal structure. Fig.11 (a) and (b) are top views of the inner and outer shells. The outer shell has an SMA connector with a square flange embedded in it, and each array element is numbered in the figure. Fig.11 (c) and (d) are top views of the inner and outer shells. A layer of copper foil is attached to the inner surface of the shell as the common ground plane for all array elements. In addition, 40 meandering arm circular patch antenna array elements are welded on the inner side of the shell. The meandering arm circular patch is printed on a circular FR4 dielectric substrate with a thickness of 0.8 mm and a radius of 7 mm. A circular hole with a radius of 0.64 mm is opened in the center of the circular patch. The inner conductor of the SMA connector passes through and is welded and fixed to serve as the feeding point of the array element.

[0068] The present invention uses a vector network analyzer of model E5071C manufactured by Keysight to detect the return loss and inter-element coupling characteristics of the array antenna. First, a nylon inner shell of a hemispherical conformal structure is fixed with screws, and a waterproof sealing treatment is performed using Kraft silicone sealant. In order to simulate the real electromagnetic environment of the human breast, a hemispherical phantom with the same electrical parameters as the human breast is prepared and placed in the inner shell hemisphere. At the same time, the shell is connected to a constant temperature circulating water bath through a rubber tube to continuously provide circulating deionized water for the meander arm circular patch antenna array applicator.

[0069] Figure 12(a) is a graph showing the measured results of S11 of 40 elements of the curved arm circular patch antenna array applicator of the present invention. At the operating frequency of 915MHz, the return loss of each element is less than -15dB and has a certain bandwidth. This shows that the curved arm circular patch antenna has excellent robustness and stable performance, meeting the needs of engineering applications. The present invention measures the coupling between element No. 1 and other elements. As shown in Figure 12(b), it is the coupling coefficient S1n (n=2,...,40) between element No. 1 of the present invention and all other elements in the array. The coupling between the elements is all below -20dB. It proves that the spacing between the elements of the array antenna processed in real objects is reasonable.

[0070] Miniaturized antenna array elements can not only be arranged more around the breast, improve focusing accuracy and steering ability, and achieve more accurate treatment. It also increases the spacing between array elements, thereby reducing the coupling effect. In addition, in order to reduce the loss of radiated power, the microstrip patch antenna should be as close to human tissue as possible. However, when the antenna is close to the skin, the resonant wavelength of the antenna will be compressed, causing the resonant frequency to shift to high frequency. In Patent 1, in order to ensure the miniaturization of the array element and stabilize the resonant frequency at 915MHz, the distance from the patch to the skin has to be increased. In Patent 1, the distance from the patch to the skin is 10mm, and the radius of the patch antenna is 12mm. Although the above approach achieves miniaturization and stable resonance at 915MHz, it will greatly reduce the thermal treatment efficiency and is not feasible in actual engineering applications. In contrast, the "meandering arm circular patch antenna" of the present invention has made a breakthrough in shortening the distance from the patch to the skin to only 3mm, while maintaining the patch radius of 7mm, successfully stabilizing the operating frequency of 915MHz while maintaining miniaturization. This innovative design not only overcomes the limitations of existing technologies, but also significantly improves the thermal therapy efficiency, providing a more practical and efficient solution for microwave thermal therapy of breast cancer.

[0071] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.

Claims

1. A meander arm circular patch antenna for microwave hyperthermia, characterized in that: The meander arm circular patch antenna is a circular patch with a radius of 7 mm as a whole. The center of the circular patch is a circular portion (11.1) with a radius r of 5 mm. Four 1 / 4 circular ring-shaped annular arms (11.2) are arranged around the periphery of the circular portion (11.1) and are concentric with the center of the circle. The width d1 of the annular arms (11.2) is 1.8 mm. Four identical arc-shaped first slits (11.3) are formed between the four annular arms (11.2) and the circular portion (11.1). The width d2 of the four first slits (11.3) is 0.2 mm. The four first slits (11.3) are distributed at equal angles on the circle. The edge of the circular portion (11.1), four first slits (11.3) are cocentric with the circular portion (11.1); the angle between adjacent first slits (11.3) is α, α is 7.5°; a second slit (11.4) with an angle β is formed between adjacent annular arms (11.2), β is 2°; the starting end of each first slit (11.3) is connected to a second slit (11.4); in the counterclockwise direction, the first end point of the first slit (11.3) is the starting end; each annular arm (11.2) is formed with a third slit (11.5) and a fourth slit (11.6) in opposite directions; The third slit (11.5) and the fourth slit (11.6) are arc-shaped and are concentric with the circular portion (11.1); the third slit (11.5) is located outside the first slit (11.3); the width d3 of the third slit (11.5) is 0.2 mm; the distance D1 between the third slit (11.5) and the first slit (11.3) is 0.5 mm; the third slit (11.5) extends clockwise, the starting end of the third slit (11.5) is connected to a second slit (11.4), and the third slit (11.5) extends clockwise toward the adjacent second slit (11.4); the angle between the end point of the third slit (11.5) and the adjacent second slit (11.4) is λ, and λ is 7.5°; the fourth slit (11.6) is located outside the third slit (11.5), the starting end of the third slit (11.5) is connected to a second slit (11.4), and the third slit (11.5) extends clockwise toward the adjacent second slit (11.4); the angle between the end point of the third slit (11.5) and the adjacent second slit (11.4) is λ, and λ is 7.5°. The width d4 of the four slits (11.6) is 0.2 mm, and the distance D2 between the fourth slit (11.6) and the third slit (11.5) is 0.5 mm; the fourth slit (11.6) extends counterclockwise, the starting end of the fourth slit (11.6) is connected to a second slit (11.4), and the fourth slit (11.6) extends counterclockwise toward the adjacent second slit (11.4); the angle between the end point of the fourth slit (11.6) and the adjacent second slit (11.4) is ρ, and ρ is 7.5°; a curved three-winding structure is formed between the first slit (11.3), the third slit (11.5), and the fourth slit (11.6); the meander arm circular patch antenna is printed on an FR4 dielectric substrate with a thickness of 0.8 mm, a dielectric constant of 4.5, and a loss tangent of 0.

02.

2. The meander arm circular patch antenna for microwave hyperthermia according to claim 1, characterized in that: The meander arm circular patch antenna is arranged on a hemispherical conformal structure, and the hemispherical conformal structure is a hemispherical shell composed of a nylon inner shell (6) and a nylon outer shell (7), and a hemispherical shell-shaped water bag is formed between the nylon inner shell (6) and the nylon outer shell (7); the water bag is filled with deionized water (8), and a water inlet (9) and a water outlet (10) are provided on the water bag; the meander arm circular patch antenna is arranged in the water bag, and the meander arm circular patch antenna is connected to a coaxial input line; the coaxial input line passes through the nylon outer shell (7); the coaxial input line is connected by SMA The invention is composed of an inner conductor (12), an SMA connector filling medium (13), and an SMA connector outer conductor (14); the SMA connector outer conductor (14) is filled with an SMA connector filling medium (13); the SMA connector inner conductor (12) is arranged in the SMA connector outer conductor (14), the SMA connector inner conductor (12) passes through the SMA connector outer conductor (14) and is connected to a meander arm circular patch antenna; the inner surface of the nylon shell (7) is covered with a copper layer, which serves as a hemispherical ground plane shared by all array elements.

3. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that: The nylon inner shell (6) and the nylon outer shell (7) are made of PA12 material.

4. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that: The distance H1 from the meander arm circular patch antenna to the skin is 3 mm.

5. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that The distance H2 between the meander arm circular patch antenna and the hemispherical ground plane is 2 mm.

6. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that The width S1 of the connection of the outer peripheral curved arms of the curved arm circular patch antenna is 7.5 degrees.

7. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that: 40 curved arm circular patch antennas are arranged on the hemispherical conformal structure, and the 40 curved arm circular patch antennas adopt a honeycomb layout.

8. The meander arm circular patch antenna for microwave hyperthermia therapy according to claim 2, characterized in that: The nylon shell (7) is composed of a hemispherical shell with a radius of 59 mm and a thickness of 6 mm and an eave edge with a width of 10 mm and a thickness of 2 mm.

9. The meander arm circular patch antenna for microwave hyperthermia according to claim 2, characterized in that: The nylon inner shell (6) is composed of a hemispherical shell with a radius of 49.5 mm and a thickness of 1.5 mm and an edge with a width of 10 mm and a thickness of 2 mm.

Images