Near-field focusing microwave thermal therapy device and method based on Huygens metasurface

Abstract

The invention discloses a near-field focusing microwave thermal therapy device and method based on a Huygens metasurface. The device comprises a feed source antenna, a Huygens metasurface array and a biological tissue model. The feed source antenna is a 5.8 GHz double-ridge horn antenna and is used for transmitting x-polarized electromagnetic waves; the Huygens metasurface array is formed by periodically arranging double-layer through-hole-free Huygens units, anti-symmetric E-shaped metal patterns are symmetrically arranged on the upper surface and the lower surface of the single-layer PCB substrate, and phase regulation and efficient transmission are achieved by adjusting unit structure parameters; the biological tissue model is of a two-layer structure attached to the Huygens metasurface array, electromagnetic waves emitted by the feed source antenna are subjected to phase compensation regulation and control through the Huygens metasurface array, and then near-field focusing is achieved on the surface layer of the biological tissue, so that the electric field intensity, the SAR value and the temperature of a target area reach design threshold values respectively, and the target area is obtained. And local precise heating of electromagnetic resonance and phase regulation is formed. According to the invention, an efficient, stable and easy-to-implement technology is provided for local precise heating in microwave hyperthermia.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave hyperthermia, and in particular to a near-field focusing microwave hyperthermia device and method based on a Huygens metasurface. Background Art

[0002] Tumor hyperthermia therapy is an interdisciplinary field that integrates knowledge from biology, physics, engineering, and clinical medicine, with research at the forefront of these disciplines. This therapy aims to treat tumors through heating. Using physical energies such as microwaves, radiofrequency, and ultrasound, it generates a thermal effect within human tissue, raising the temperature of tissue cells to above 41.5°C for a sustained period of time. This accelerates the death of cancer cells while minimizing damage to normal cells. Among the many hyperthermia treatment techniques, microwave hyperthermia therapy has attracted considerable attention due to its ability to more precisely control heat distribution and penetrate deeper into tissues, opening up new avenues for the treatment of superficial cancers.

[0003] Microwave hyperthermia is primarily categorized into two types: invasive and non-invasive. Interventional microwave hyperthermia involves inserting a microwave antenna into the body and has demonstrated application value in treating superficial tumors in specific locations. For example, in the localized treatment of liver tumors, researchers have continuously improved the structure and performance of microwave antennas, enabling them to more precisely focus microwave energy on the tumor area, enhancing the local thermal effect and effectively killing cancer cells. However, the disadvantages of invasive treatments include complex procedures, requiring high technical skills from medical personnel, and the potential for damage to normal tissue, increasing the risk and risk of complications. Non-invasive microwave hyperthermia, by placing an antenna outside the body to irradiate specific locations, offers the advantages of simple operation and non-invasiveness, making it a significant advantage in treating superficial tumors such as breast cancer and skin cancer. In the development of non-invasive microwave hyperthermia technology, traditional non-invasive hyperthermia antennas, such as waveguide antennas and microstrip antennas, have been a focus of research. Waveguide antennas have attracted attention for their high radiation power and rapid heating, but their bulk and weight limit their portability and maneuverability in clinical practice. Although microstrip antennas are compact and lightweight, their energy focusing accuracy and power carrying capacity are limited, resulting in a limited amount of heat generated. In recent years, the emergence of innovative technologies such as multi-antenna arrays has effectively improved the focusing accuracy of microwave energy by dynamically adjusting array layout and parameters, reducing damage to normal tissue and improving the therapeutic effects of non-invasive microwave hyperthermia.

[0004] Despite progress in non-invasive microwave hyperthermia, numerous challenges remain regarding focusing accuracy, equipment cost, and portability. Against this backdrop, electromagnetic metasurface technology, with its powerful wavefront manipulation capabilities and lightweight, thin structure, offers new opportunities for the development of microwave hyperthermia. Metamaterials and metasurfaces have recently demonstrated significant potential in electromagnetic wave absorption, thermal management, and wireless communications. Their application in microwave hyperthermia has garnered significant attention and become a research hotspot. Research has demonstrated that metasurfaces can effectively achieve wavefront manipulation and near-field focusing, promising the ability to precisely focus electromagnetic waves and generate heat within small biological tissue regions, thereby enabling precise thermal ablation of tumor tissue. However, conventional transmissive metasurfaces typically employ multilayer structures to achieve efficient transmission and a 360° transmission phase. While effective, this design also increases manufacturing complexity. The Huygens metasurface, a typical transmissive metasurface, achieves efficient electromagnetic wave transmission by constructing electric and magnetic resonant devices, offering new insights into the research of transmissive metasurfaces. However, the current application of metasurface technology in microwave hyperthermia is still in the exploratory stage. For example, the adaptability problem in complex biological tissue environments has not been effectively solved, and the performance change law under the coupling of multiple physical fields still needs to be further studied. Summary of the Invention

[0005] Based on the above technical problems, the present application discloses a near-field focusing microwave hyperthermia device based on Huygens metasurface, including a feed antenna, a Huygens metasurface array and a biological tissue model; the feed antenna is a 5.8GHz double-ridged horn antenna, and its phase center is 85-90mm away from the center of the Huygens metasurface array along the z-axis direction, and is used to emit x-polarized electromagnetic waves; the Huygens metasurface array is composed of a double-layer periodic arrangement of Huygens units without through holes, and an antisymmetric E-shaped metal pattern is symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate, and nearly 360° phase control and efficient transmission in the 5.8GHz frequency band are achieved by adjusting the unit structure parameters; the biological tissue model is a two-layer structure that fits the Huygens metasurface array, and the electromagnetic parameters match the characteristics of the biological tissue; the electromagnetic waves emitted by the feed antenna are phase-compensated and controlled by the Huygens metasurface array, and near-field focusing is achieved on the surface of the biological tissue, so that the electric field strength, SAR value and temperature of the target area reach the design thresholds, respectively, forming local precise heating with electromagnetic resonance and phase control.

[0006] Preferably, the feed antenna is a 5.8GHz double-ridged horn antenna, which is connected to a signal generator and a power amplifier. The double-ridged horn antenna can radiate the calibrated power electromagnetic wave in the form of a spherical wave to the Huygens metasurface array. Its polarization direction matches the induced current direction of the Huygens metasurface array unit, exciting the electric resonance and magnetic resonance effects of the unit structure, ensuring that the electromagnetic wave is controlled by the Huygens metasurface array to achieve near-field focusing on the surface of the biological tissue model. The radiation characteristics work synergistically with the phase compensation design of the Huygens metasurface array to ensure efficient convergence of microwave energy in the target area and local heating effect.

[0007] Preferably, the Huygens metasurface array is composed of a single-layer F4B dielectric substrate and a double-layer antisymmetric E-shaped metal pattern symmetrically distributed on the upper and lower surfaces of the substrate, and the substrate thickness is 1-2 mm; the metal layer of each Huygens unit is made of copper-clad material, and the upper and lower surface metal patterns achieve all-round transmission phase control and transmission amplitude by adjusting the vertical short arm length, horizontal short arm length and arm width; the Huygens units are arranged in a periodic matrix to form a transmission array, which ensures efficient focusing and energy deposition of electromagnetic waves on the tissue surface by matching the electromagnetic properties of biological tissue.

[0008] Preferably, the biological tissue model is a multi-layer structure attached to the back of the Huygens metasurface array, which is used to simulate the electromagnetic response characteristics of the human body's superficial tissue; the biological tissue model is composed of skin layers and fat layers superimposed in sequence, wherein the skin layer is close to the Huygens metasurface array, and the fat layer is located below the skin layer. The two layers of tissue are tightly attached to form a planar structure, and the overall size is adapted to the Huygens metasurface array.

[0009] A near-field focused microwave hyperthermia method based on a Huygens metasurface, comprising:

[0010] S1. By using a double-layer, through-hole-free Huygens metasurface unit, antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate. By adjusting the unit structure parameters, the unit can achieve nearly 360° phase control and a transmission amplitude greater than -2dB in the 5.8GHz frequency band, constructing a Huygens unit library with full phase coverage capability.

[0011] S2. Establish a phase compensation model in a multilayer medium and use MATLAB to calculate the ideal phase distribution of the transmission array so that the electromagnetic waves emitted by the feed antenna are focused at a specified focal length on the surface of the biological tissue after being regulated by the array.

[0012] S3. Map the calculated ideal phase distribution to the Huygens cell library, select cells with corresponding structural parameters to form a Huygens metasurface array, and optimize the cell layout through CST simulation to ensure that the error between the actual transmission phase and the theoretical value is ≤7°, thus achieving the ability to precisely control the electromagnetic wave front;

[0013] S4. Use a 5.8 GHz double-ridged horn antenna as the feed source, set the distance between the phase center and the center of the Huygens metasurface array, align the antenna polarization direction with the direction of the induced current of the Huygens metasurface unit to stimulate the electromagnetic resonance effect of the unit, and connect the antenna to the signal generator and power amplifier to form an electromagnetic wave transmission link;

[0014] S5. Fit the Huygens metasurface array tightly to the biological tissue model, match the thickness and electromagnetic parameters of the biological tissue model to the superficial tumor treatment scenario, turn on the signal source, and radiate x-polarized electromagnetic waves to the Huygens metasurface array at a power of 1W;

[0015] S6. After the phase of the Huygens metasurface array is controlled, the electromagnetic waves are focused on the surface of the biological tissue, so that the temperature of the target area rises to the therapeutic range, achieving localized and precise heating of microwave energy.

[0016] Preferably, a Huygens cell library with full phase coverage capability is constructed in S1, specifically: antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer F4B dielectric substrate, and the metal layer is made of copper-clad material. By changing the vertical short arm length h, the horizontal short arm length l and the arm width b, the transmission phase and transmission amplitude under different parameter combinations are simulated using CST Microwave Studio; four representative sampling points and more discrete parameter points are selected to ensure that the transmission phase covers 0°-360° at a frequency of 5.8 GHz, and the transmission amplitude of each unit is higher than -2 dB, and the parameter combinations b, h, l that meet the conditions and their corresponding phase and amplitude values ​​are organized into a cell library to construct a Huygens cell library with full phase coverage capability.

[0017] Preferably, the phase compensation model in the multilayer medium is established in S2, specifically: determining the propagation speed formula of electromagnetic waves in free space and multilayer medium, where the free space speed is The velocity in the medium is Combined wavelength The relationship between phase difference and optical path difference is derived, ε0 and μ0 are the dielectric constant and magnetic permeability in vacuum, ε r is the relative dielectric constant, μ r is the relative magnetic permeability; for the biological tissue model, the electromagnetic wave passes through the air, Huygens metasurface array, skin layer and fat layer in sequence, and the optical path difference of each layer is defined as the difference between the unit to the focus distance and the focal length. According to the generalized sheet transition condition and the quasi-optical path theorem, the relative dielectric constant ε of each layer of the medium is r and relative magnetic permeability μ r Substitute into the phase compensation formula and accumulate the phase contribution of each layer Where λ0 is the free space wavelength, d iBased on the optical path difference of each layer, a two-layer medium phase compensation model suitable for the skin layer and fat layer is established. The phase compensation value required for each position of the unit array is calculated through the phase compensation model to ensure that the electromagnetic wave is focused at the target focal length after being controlled by the metasurface.

[0018] Preferably, the calculated ideal phase distribution is mapped to the Huygens unit library and the unit layout is optimized through CST simulation in S3, specifically: using MATLAB to calculate the ideal transmission phase distribution of each position of the unit array according to the multilayer dielectric phase compensation model to form a continuous phase matrix covering 0°-360°; each phase value in the matrix is ​​corresponded to the discrete unit with the closest phase in the Huygens unit library, and the structural parameters b, h, and l of the unit at each position are preliminarily determined, and a full-wave simulation model including a feed antenna, a Huygens metasurface array, and a biological tissue model is established in CSTMicrowave Studio, the distance and focal length from the phase center of the horn antenna to the center of the array are set, the structural parameters of each unit are imported, and periodic boundary conditions are applied; by scanning the reference phase of the units in the center and edge areas of the array, the unit layout is adjusted, and the unit parameters are iteratively optimized until the error between the actual transmission phase and the ideal value is controlled within 7°, thereby forming a precise control capability of the electromagnetic wave front.

[0019] Preferably, in S4, the antenna is connected to the signal generator and the power amplifier to form an electromagnetic wave transmission link, specifically: the output end of the signal generator is connected to the input end of the power amplifier through a coaxial cable, and the frequency of the signal generator is set to 5.8 GHz to generate a continuous wave signal; the output end of the power amplifier is connected to the feeding port of the 5.8 GHz double-ridged horn antenna through a low-loss coaxial cable, and the power amplifier is adjusted to stabilize the output power at 1 W; the feed antenna (double-ridged horn antenna) is fixed on the bracket so that the distance between its phase center and the center of the Huygens metasurface array along the z-axis direction is 85-90 mm, and the polarization direction of the antenna is consistent with the induced current direction of the Huygens metasurface unit, the signal generator and the power amplifier are turned on, and the x-polarized electromagnetic wave generated by the signal generator is amplified by the power amplifier, and then radiated to the Huygens metasurface array in the form of a spherical wave by the double-ridged horn antenna, forming an electromagnetic wave transmission link.

[0020] Preferably, the electromagnetic wave in S6 is focused on the surface of the biological tissue after being phase-controlled by the Huygens metasurface array, so that the temperature of the target area rises to the treatment range. Specifically, the x-polarized electromagnetic wave of 5.8 GHz is emitted by the feed antenna and is phase-compensated by the Huygens unit of the Huygens metasurface array. The x-polarized electromagnetic wavefront is corrected to a spherical wave that converges at a specified focal length on the surface of the biological tissue, forming a high electric field intensity area at the interface between the skin layer and the fat layer; according to the electromagnetic properties of the biological tissue, the higher dielectric constant and conductivity of the skin layer make it absorb the electromagnetic wave more strongly, and the electric field energy is converted into heat energy. Through the Pennes bioheat equation Calculations show that the central area of ​​the skin layer heats up rapidly due to the high SAR value under 1W input power, where ρ is tissue density, C is tissue specific heat capacity, k is tissue thermal conductivity, A0 is tissue metabolic heat production, B is heat exchange caused by capillary blood perfusion, and T B is the constant blood temperature, T is the temperature of the tissue, Q r The thermal power density generated by electromagnetic waves in biological tissues is limited by the near-field focusing characteristics of the Huygens metasurface array to limit the diffusion of energy to deep layers. The fat layer absorbs less energy due to its low electrical conductivity, and the temperature gradually decreases with increasing depth. Through theoretical calculations, CST thermal simulation and experimental tests, it is verified that the temperature of the superficial skin layer and fat layer rises to the treatment range of 40-42°C, and the temperature of the non-target area is lower than 39°C, realizing the precise deposition and local heating of microwave energy in the superficial tumor area.

[0021] Compared with the prior art, the technical solution of this application has the following technical effects:

[0022] This invention achieves efficient, focused heating of superficial tissue areas through precise control of the electromagnetic wave transmission phase and energy distribution. The Huygens metasurface unit, through its electromagnetic resonance design with a double-layer metal structure, achieves near-ideal full-phase coverage within the 5.8 GHz frequency band, and can flexibly adjust the wavefront morphology based on the characteristics of biological tissue. This characteristic enables electromagnetic waves, after being modulated by the metasurface array, to converge into high-intensity energy in superficial areas such as the skin layer, avoiding the energy dispersion issues of traditional non-invasive hyperthermia and providing a precise energy control method for localized tumor heating.

[0023] The metasurface array successfully focuses microwave energy on the surface, raising the target temperature to the required range for clinical hyperthermia therapy while exhibiting excellent spatial selectivity. The energy is primarily concentrated in the superficial layers of the skin and fat, with significant energy attenuation with increasing tissue depth. This characteristic effectively reduces the risk of thermal damage to deeper normal tissues, demonstrating the safety and feasibility of non-invasive treatment.

[0024] The present invention provides a flexible and adjustable solution for microwave hyperthermia technology, expanding its clinical applicability. The device and method of the present application can be specifically applied to microwave hyperthermia, tumor treatment, microwave weight loss and other fields. By adjusting parameters to adapt to the needs of different tissues, it shows a broad application prospect. By adjusting the structural parameters of the metasurface unit (such as arm length, arm width), array phase distribution and operating frequency, the frequency of the electromagnetic wave can be flexibly adjusted to other frequency bands (such as 2.45GHz, 915MHz, etc. commonly used in medical treatment) according to actual needs. At the same time, the geometric structure of the Huygens metasurface unit (such as the arm length, arm width, and substrate thickness of the E-shaped metal pattern) and the overall size of the array will be re-optimized through electromagnetic simulation to match the wavelength and electromagnetic characteristics of the target frequency band, ensuring full phase coverage and efficient energy transmission in the new frequency band; at the same time, it can adapt to the electromagnetic response characteristics of different human tissues. According to the differences in tissue thickness and dielectric constant of tumors in different parts, the unit resonance characteristics and phase compensation mechanism can be redesigned to achieve personalized focusing solutions. This adjustability not only improves the universality of the technology, but also lays the foundation for optimizing treatment parameters by combining multi-physics field coupling analysis (such as temperature-electromagnetic joint simulation) in the future, and promotes the widespread application of metasurface technology in the biomedical field.

[0025] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application so that it can be implemented in accordance with the contents of the specification, and to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following is a detailed description of the preferred embodiment of the present application in conjunction with the accompanying drawings.

[0026] Based on the detailed description of the specific embodiments of the present application in conjunction with the accompanying drawings below, those skilled in the art will become more aware of the above and other objects, advantages and features of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without inventive work. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0028] Figure 1 This is a diagram of the Huygens metasurface unit structure of the present invention;

[0029] Figure 2 (a) is the top surface current, (b) is the bottom surface current, and (c) is the unit magnetic field distribution diagram at 5.8 GHz;

[0030] Figure 3 (a) is the unit transmission amplitude, (b) is the imaginary part of the unit normalized surface magnetic surface impedance Zms and surface electrical admittance Yes when the parameters are b = 0.1 mm, h = 13.2 mm, l = 16.3 mm;

[0031] Figure 4 (a) is the transmission phase of the unit at points P1, P2, P3, and P4, and (b) is the transmission amplitude of the unit at points P1, P2, P3, and P4;

[0032] Figure 5 is the geometric structure diagram of the HMS array;

[0033] Figure 6 Schematic diagram of electromagnetic wave propagation through HMS array in different media;

[0034] Figure 7 This is a three-layer model diagram of pork tissue structure;

[0035] Figure 8 (a) is the ideal unit transmission phase distribution, (b) is the difference between the ideal unit transmission phase and the actual unit;

[0036] Figure 9 (a) is a top view of the HMS array, and (b) is a simulation model of the HMS array and pork tissue;

[0037] Figure 10 (a) is the electric field distribution diagram of the yoz cross section at different depths; (b) is the yoz plane energy loss diagram (normalized electric field intensity change curve along the z-axis direction when y = 0);

[0038] Figure 11 Figure 2 shows the SAR distribution in pork tissue. (a) shows the SAR distribution of the yoz section and the xoy section at depths of z = 1 mm, 3 mm, and 5 mm, respectively; (b) shows the maximum SAR value distribution along the penetration depth; (c) shows the normalized SAR distribution of the x section at depths of z = 1 mm, 3 mm, and 5 mm.

[0039] Figure 12 Figure 2 shows the temperature distribution in pork tissue. (a) shows the temperature distribution of the yoz section and the xoy section at depths of z = 1 mm, 3 mm, and 5 mm, respectively. (b) shows the temperature variation with penetration depth. (c) shows the temperature distribution of the x section at depths of z = 1 mm, 3 mm, and 5 mm.

[0040] Figure 13 (a) shows a 15×15 metasurface array sample; (b) shows the experimental test platform; (c) shows the temperature of pork tissue measured at z = 1 mm, 3 mm, and 5 mm using a multi-channel temperature detector.

[0041] Figure 14 This is the display screen of the multi-channel temperature detector: CH01, CH02, and CH03 are the temperature readings of pork tissue at z = 1mm, 3mm, and 5mm. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. In the following description, specific details such as specific configurations and components are provided only to help fully understand the embodiments of the present application. Therefore, it should be clear to those skilled in the art that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of the present application. In addition, for clarity and brevity, the description of known functions and structures has been omitted in the embodiments.

[0043] It should be understood that references throughout this specification to "one embodiment" or "this embodiment" mean that a particular feature, structure, or characteristic associated with the embodiment is included in at least one embodiment of the present application. Therefore, the appearance of "one embodiment" or "this embodiment" throughout this specification does not necessarily refer to the same embodiment. Furthermore, these particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0044] In addition, the present application may repeat reference numerals and / or letters in different examples. This repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed.

[0045] The term "and / or" in this article is only a description of the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, B exists alone, and A and B exist at the same time. The term " / and" in this article describes another type of association object relationship, indicating that two relationships can exist. For example, A / and B can mean: A exists alone, and A and B exist alone. In addition, the character " / " in this article generally indicates that the previous and subsequent associated objects are in an "or" relationship.

[0046] The term "at least one" in this article is merely a description of the association relationship between associated objects, indicating that three relationships may exist. For example, at least one of A and B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0047] It should also be noted that, in this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include," "comprises," or any other variations thereof are intended to cover non-exclusive inclusion.

[0048] Example 1

[0049] This embodiment mainly describes a near-field focusing microwave hyperthermia device based on a Huygens metasurface, specifically:

[0050] A near-field focusing microwave hyperthermia device based on a Huygens metasurface comprises a feed antenna, a Huygens metasurface array and a biological tissue model; the feed antenna is a 5.8GHz double-ridged horn antenna, the phase center of which is 85-90mm away from the center of the Huygens metasurface array along the z-axis, and is used to emit x-polarized electromagnetic waves; the Huygens metasurface array is composed of a double-layer periodic arrangement of Huygens units without through holes, and antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate, and nearly 360° phase control and efficient transmission in the 5.8GHz frequency band are achieved by adjusting the unit structure parameters; the biological tissue model is a two-layer structure that fits the Huygens metasurface array, and the electromagnetic parameters match the characteristics of the biological tissue; the electromagnetic waves emitted by the feed antenna are phase-compensated and controlled by the Huygens metasurface array, and near-field focusing is achieved on the surface of the biological tissue, so that the electric field strength, SAR value and temperature of the target area reach the design thresholds, respectively, forming local precise heating with electromagnetic resonance and phase control.

[0051] Furthermore, the feed antenna is a 5.8GHz double-ridged horn antenna, which is connected to a signal generator and a power amplifier. It can radiate the calibrated power electromagnetic wave in the form of a spherical wave to the Huygens metasurface array. Its polarization direction matches the induced current direction of the Huygens metasurface array unit, stimulating the electric resonance and magnetic resonance effects of the unit structure, ensuring that the electromagnetic wave is near-field focused on the surface of the biological tissue model after being controlled by the Huygens metasurface array. The radiation characteristics work synergistically with the phase compensation design of the Huygens metasurface array to ensure the efficient convergence of microwave energy in the target area and the local heating effect.

[0052] Furthermore, the Huygens metasurface array is composed of a single-layer F4B dielectric substrate and a double-layer antisymmetric E-shaped metal pattern symmetrically distributed on the upper and lower surfaces of the substrate. The substrate thickness is 1-2 mm. The metal layer of each Huygens unit is made of copper-clad material, and the metal patterns on the upper and lower surfaces achieve all-round transmission phase control and transmission amplitude by adjusting the vertical short arm length, horizontal short arm length and arm width. The Huygens units are arranged in a periodic matrix to form a transmission array, which ensures efficient focusing and energy deposition of electromagnetic waves on the tissue surface by matching the electromagnetic properties of biological tissue.

[0053] Furthermore, the biological tissue model is a multi-layer structure attached to the back of the Huygens metasurface array, which is used to simulate the electromagnetic response characteristics of the human body's superficial tissue; the biological tissue model is composed of skin layers and fat layers superimposed in sequence, wherein the skin layer is close to the Huygens metasurface array, and the fat layer is located below the skin layer. The two layers of tissue are tightly attached to form a planar structure, and the overall size is adapted to the Huygens metasurface array.

[0054] This embodiment describes in detail a near-field focused microwave hyperthermia device based on a Huygens metasurface. The device achieves nearly 360° phase control and efficient energy transmission in the 5.8 GHz frequency band through a 15×15 transmission array composed of a double-layer Huygens unit without through holes, precisely focusing microwave energy on the surface of biological tissue. The device can raise the temperature of the target area to a therapeutic range of 40-42°C. At the same time, due to the characteristic of rapid energy attenuation with depth, thermal damage to deep normal tissues is reduced. The device has the advantages of high focusing accuracy, good spatial selectivity, and a thin and adjustable structure, providing a safe and efficient solution for non-invasive precision hyperthermia treatment of superficial tumors.

[0055] Example 2

[0056] This embodiment mainly describes a near-field focused microwave hyperthermia method based on a Huygens metasurface, specifically:

[0057] S1. By using a double-layer, through-hole-free Huygens metasurface unit, antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate. By adjusting the unit structure parameters, the unit can achieve nearly 360° phase control and a transmission amplitude greater than -2dB in the 5.8GHz frequency band, constructing a Huygens unit library with full phase coverage capability.

[0058] S2. Establish a phase compensation model in a multilayer medium and use MATLAB to calculate the ideal phase distribution of the transmission array so that the electromagnetic waves emitted by the feed antenna are focused at a specified focal length on the surface of the biological tissue after being regulated by the array.

[0059] S3. Map the calculated ideal phase distribution to the Huygens cell library, select cells with corresponding structural parameters to form a Huygens metasurface array, and optimize the cell layout through CST simulation to ensure that the error between the actual transmission phase and the theoretical value is ≤7°, thus achieving the ability to precisely control the electromagnetic wave front;

[0060] S4. Use a 5.8 GHz double-ridged horn antenna as the feed source, set the distance between the phase center and the center of the Huygens metasurface array, align the antenna polarization direction with the direction of the induced current of the Huygens metasurface unit to stimulate the electromagnetic resonance effect of the unit, and connect the antenna to the signal generator and power amplifier to form an electromagnetic wave transmission link;

[0061] S5. Fit the Huygens metasurface array tightly to the biological tissue model, match the thickness and electromagnetic parameters of the biological tissue model to the superficial tumor treatment scenario, turn on the signal source, and radiate x-polarized electromagnetic waves to the Huygens metasurface array at a power of 1W;

[0062] S6. After the phase of the Huygens metasurface array is controlled, the electromagnetic waves are focused on the surface of the biological tissue, so that the temperature of the target area rises to the therapeutic range, achieving localized and precise heating of microwave energy.

[0063] Furthermore, a Huygens cell library with full phase coverage capability is constructed in S1, specifically: antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer F4B dielectric substrate, and the metal layer is made of copper-clad material. By changing the vertical short arm length h, the horizontal short arm length l and the arm width b, the transmission phase and transmission amplitude under different parameter combinations are simulated using CST Microwave Studio; four representative sampling points and more discrete parameter points are selected to ensure that the transmission phase covers 0°-360° at a frequency of 5.8 GHz, and the transmission amplitude of each unit is higher than -2 dB. The parameter combinations b, h, l that meet the conditions and their corresponding phase and amplitude values ​​are organized into a cell library to construct a Huygens cell library with full phase coverage capability.

[0064] Furthermore, the phase compensation model in the multilayer medium is established in S2, specifically: determining the propagation velocity formula of electromagnetic waves in free space and multilayer medium, where the free space velocity is The velocity in the medium is Combined wavelength The relationship between phase difference and optical path difference is derived, ε0 and μ0 are the dielectric constant and magnetic permeability in vacuum, ε r is the relative dielectric constant, μ r is the relative magnetic permeability; for the biological tissue model, the electromagnetic wave passes through the air, Huygens metasurface array, skin layer and fat layer in sequence, and the optical path difference of each layer is defined as the difference between the unit to the focus distance and the focal length. According to the generalized sheet transition condition and the quasi-optical path theorem, the relative dielectric constant ε of each layer of the medium is r and relative magnetic permeability μ r Substitute into the phase compensation formula and accumulate the phase contribution of each layer Where λ0 is the free space wavelength, d i Based on the optical path difference of each layer, a two-layer medium phase compensation model suitable for the skin layer and fat layer is established. The phase compensation value required for each position of the unit array is calculated through the phase compensation model to ensure that the electromagnetic wave is focused at the target focal length after being controlled by the metasurface.

[0065] Furthermore, in S3, the calculated ideal phase distribution is mapped to the Huygens unit library and the unit layout is optimized through CST simulation, specifically: MATLAB is used to calculate the ideal transmission phase distribution of each position of the unit array according to the multilayer dielectric phase compensation model to form a continuous phase matrix covering 0°-360°; each phase value in the matrix is ​​corresponded to the discrete unit with the closest phase in the Huygens unit library, and the structural parameters b, h, and l of the unit at each position are preliminarily determined. A full-wave simulation model including the feed antenna, Huygens metasurface array, and biological tissue model is established in CSTMicrowave Studio, the distance from the phase center of the horn antenna to the center of the array and the focal length are set, the structural parameters of each unit are imported, and periodic boundary conditions are applied; by scanning the reference phase of the units in the center and edge areas of the array, the unit layout is adjusted, and the unit parameters are iteratively optimized until the error between the actual transmission phase and the ideal value is controlled within 7°, thereby forming the ability to accurately control the electromagnetic wave front.

[0066] Furthermore, in S4, the antenna is connected to the signal generator and the power amplifier to form an electromagnetic wave transmission link, specifically: the output end of the signal generator is connected to the input end of the power amplifier through a coaxial cable, and the frequency of the signal generator is set to 5.8 GHz to generate a continuous wave signal; the output end of the power amplifier is connected to the feeding port of the 5.8 GHz double-ridged horn antenna through a low-loss coaxial cable, and the power amplifier is adjusted to stabilize the output power at 1 W; the feed antenna (double-ridged horn antenna) is fixed on the bracket so that the distance between its phase center and the center of the Huygens metasurface array along the z-axis direction is 85-90 mm, and the polarization direction of the antenna is consistent with the induced current direction of the Huygens metasurface unit, the signal generator and the power amplifier are turned on, and the x-polarized electromagnetic wave generated by the signal generator is amplified by the power amplifier, and then radiated to the Huygens metasurface array in the form of a spherical wave by the double-ridged horn antenna, forming an electromagnetic wave transmission link.

[0067] Furthermore, the electromagnetic waves in S6 are focused on the surface of biological tissue after being phase-controlled by the Huygens metasurface array, so that the temperature of the target area rises to the treatment range. Specifically, the x-polarized electromagnetic wave of 5.8 GHz is emitted by the feed antenna and is phase-compensated and controlled by the Huygens unit of the Huygens metasurface array. The x-polarized electromagnetic wavefront is corrected into a spherical wave that converges at a specified focal length on the surface of the biological tissue, forming a high electric field intensity area at the interface between the skin layer and the fat layer; according to the electromagnetic properties of biological tissue, the higher dielectric constant and conductivity of the skin layer make it absorb electromagnetic waves more strongly, and the electric field energy is converted into heat energy. Through the Pennes bioheat equation Calculations show that the central area of ​​the skin layer heats up rapidly due to the high SAR value under 1W input power, where ρ is tissue density, C is tissue specific heat capacity, k is tissue thermal conductivity, A0 is tissue metabolic heat production, B is heat exchange caused by capillary blood perfusion, and TB is the constant blood temperature, T is the temperature of the tissue, Q r The thermal power density generated by electromagnetic waves in biological tissues is limited by the near-field focusing characteristics of the Huygens metasurface array to limit the diffusion of energy to deep layers. The fat layer absorbs less energy due to its low electrical conductivity, and the temperature gradually decreases with increasing depth. Through theoretical calculations, CST thermal simulation and experimental tests, it is verified that the temperature of the superficial skin layer and fat layer rises to the treatment range of 40-42°C, and the temperature of the non-target area is lower than 39°C, realizing the precise deposition and local heating of microwave energy in the superficial tumor area.

[0068] This embodiment describes in detail how to achieve efficient near-field focusing of microwave energy on the surface of biological tissue by designing a double-layer Huygens metasurface (HMS) array without through holes. This technology uses unit structure parameter control in the 5.8GHz frequency band to achieve nearly 360° phase coverage and high transmittance, and combines the phase compensation model to adapt to the electromagnetic characteristics of the tissue, so that the temperature of the target area (skin layer and shallow fat layer) at 1W power rises to the treatment range of 40-42°C. At the same time, the energy decays rapidly with depth, and has good spatial selectivity. The technical solution has a light and thin structure and strong adjustability, providing a stable and efficient solution for non-invasive precision thermal therapy of superficial tumors.

[0069] Based on the above-mentioned Example 1 and Example 2, this embodiment describes the design and analysis of the Huygens cell in detail, specifically:

[0070] Huygens metasurface (HMS) is a typical transmissive metasurface whose working principle combines electric resonance and magnetic resonance. By designing the dipole structure of the metasurface unit, the intensity of the electromagnetic resonance can be adjusted to achieve effective control of the transmittance, phase and polarization of the incident electromagnetic wave. According to the surface equivalence principle, HMS can be regarded as a two-dimensional metamaterial that can interact with the incident field on a microscopic scale. Its macroscopic performance is similar to that of a homogeneous medium. The surface impedance Zms and surface admittance Yes of HMS are determined by the generalized sheet transition conditions (GSTCs). Only the case of single-polarized incident waves is considered, so the surface impedance and admittance are regarded as scalars, and the formula is: Where η is the free space wave impedance, and the reflection coefficient R and transmission amplitude T of the unit can be obtained through full-wave simulation. According to the above formula, when the imaginary parts of the normalized surface electrical admittance and magnetic impedance are equal and are pure imaginary numbers, Y es η=Z ms / η, the transmission amplitude is 1, achieving ideal transmission characteristics.

[0071] like Figure 1As shown in the figure, the Huygens metasurface unit structure of this application is shown. The unit consists of a dielectric substrate and an antisymmetric E-shaped metal pattern symmetrically located on the upper and lower surfaces of the substrate; the metal layer is made of copper-clad material with a thickness of 0.018mm, the substrate material is F4B, and the dielectric constant ε r =2.55, loss tangent tanδ = 0.002, thickness d = 1mm, and unit period p = 19mm. By adjusting the unit's structural parameters (such as length h, l, and width b), nearly 360° phase control was achieved near the 5.8GHz frequency band, while maintaining a transmission amplitude above -2dB.

[0072] In the commercial electromagnetic simulation software CST Microwave Studio, when using the frequency domain solver to simulate the unit structure, periodic boundary conditions are used to simulate the situation where the unit structure is irradiated by x-polarized electromagnetic waves at a frequency of 5.8 GHz. At this time, the upper and lower metal patterns show the surface current and magnetic field distribution under Huygens resonance, as shown in the figure below. Figure 2 As shown in (a) and (b), the short arms of the top and bottom layers exhibit similar induced current distributions, resulting in equivalent electrical responses. In the x-direction, the top current J is induced by the two horizontal short arms at the top and bottom, respectively. top and bottom current J bot , the two directions are opposite, forming a closed current loop, thereby generating a magnetic field orthogonal to the electric field. When the resonant frequency of the induced electric field and the induced magnetic field is the same as the incident electromagnetic wave, the electromagnetic wave can efficiently pass through the metasurface unit. At the same time, the induced currents of the vertical short arms (y direction) in the left and right directions cancel each other out, so the overall contribution can be ignored. Figure 2 As shown in (c), the distribution of the induced magnetic fields excited by the top and bottom metal patterns on the dielectric substrate is clearly visible. These induced magnetic fields not only balance the surface current but also further enhance the Huygens resonance effect.

[0073] In order to deeply analyze the Huygens resonance mechanism of the designed unit, this application further studies the transmission characteristics of a single element and analyzes the surface electrical admittance Y es and surface impedance Z ms The relationship between the imaginary part of and the frequency. Figure 3 As shown in Figure 1, the electric resonance frequency is located at about 7.6 GHz, while the magnetic resonance frequencies are located at around 5.7 GHz and 7.0 GHz respectively. The superposition of the two forms a typical Huygens resonance effect. In addition, due to the Y es and Z ms The difference in the imaginary part within the resonant frequency band is small, resulting in a broadband flat transmission passband with high transmission amplitude (>-2dB) in the frequency range of 5.7 to 7.6 GHz.

[0074] In order to achieve effective control of the transmission phase of the Huygens cell and ensure high transmission amplitude at the 5.8 GHz frequency point, this application fine-tunes the cell structure parameters h, l, and b. Four representative sampling points (labeled as P1, P2, P3, and P4) were selected to study the transmission phase and transmission amplitude of the cell at these points. Figure 4 As shown in (a), these Huygens cells can achieve a wide range of transmission phase changes at a frequency of 5.8 GHz. Figure 4 (b) shows that the transmission amplitudes of these units are all higher than -2dB, indicating that the designed unit structure can achieve high transmission performance while achieving phase control. It can be seen that the proposed Huygens unit structure has excellent phase control performance and can effectively adjust the electromagnetic wave front passing through the HMS, thereby realizing near-field focusing function. Table 1 further summarizes the specific unit structure parameters for achieving 360° omnidirectional transmission phase control, which details the transmission phase, transmission amplitude and corresponding structural dimensions (b, h and l) of each unit, which can be used to construct Huygens metasurfaces with different functions.

[0075] Table 1 Unit structure parameters for achieving 360° high transmission phase control

[0076]

[0077] This embodiment describes in detail the design and analysis of the Huygens unit, which achieves efficient control of the electromagnetic wave transmission characteristics through an innovative double-layer non-through-hole structure. The designed unit is based on the principle of electric resonance and magnetic resonance coupling. By precisely adjusting structural parameters such as the length and width of the metal arm, it constructs nearly 360° full phase coverage within the 5.8GHz frequency band, ensuring phase modulation of the wavefront of the incident electromagnetic wave at any angle. The unit structure is optimized to achieve high transmission performance and significantly reduce energy loss, laying the foundation for the near-field focusing function and simplifying the multi-layer structural complexity of traditional transmission-type metasurfaces. The effectiveness of the Huygens resonance mechanism is also verified through simulations of surface current and magnetic field distribution, proving that the unit can efficiently transmit energy and achieve phase control through electromagnetic coupling, providing a reliable unit library and theoretical support for the phase compensation required for precise focusing in subsequent array design, and solving the problems of complex structure and insufficient control accuracy of traditional metasurfaces in biomedical applications.

[0078] Based on the above-mentioned embodiment 1 and embodiment 2, this embodiment describes the Huygens array design in detail, specifically:

[0079] Based on the designed HMS unit, a near-field focusing HMS array for microwave hyperthermia was further designed. The schematic diagram of the designed array is shown in Figure 5As shown in the figure, the phase center on the left represents the equivalent position of the wave source, and the middle is the designed HMS array. The incident electromagnetic wave is controlled by the array and converges at the focus. In the design process of the HMS array, it is first necessary to determine the phase compensation value required for different unit positions to achieve beam focusing. Through reasonable phase distribution design, the electromagnetic waves emitted by the feed antenna can be converged at the specified focal position. The transmission phase of each unit It can be calculated by the following formula: Where f is the operating frequency, c is the speed of light in free space, (x, y) is the coordinate of the unit relative to the center of the array, d is the distance from the phase center of the wave source to the center of the array, and z is the distance from the center of the array to the focus. is a constant phase, which is applicable to the propagation of electromagnetic waves in the air. In order to accurately describe the phase propagation characteristics of electromagnetic waves when they pass through the HMS array and enter biological tissues, the formula needs to be further modified. The propagation speed of electromagnetic waves in free space is: μ0 is the dielectric constant and magnetic permeability of vacuum, and the relative dielectric constant is ε r and the relative permeability of the medium μ r The propagation speed is: The wavelength λ, frequency f and propagation speed v of the electromagnetic wave satisfy v = fλ. Related to the optical path difference d and the wavelength λ, in free space, the phase difference of electromagnetic waves is: In the medium it becomes: When an electromagnetic wave passes through multiple layers of media in sequence, the phase contribution of each layer of media needs to be accumulated. Assume that the electromagnetic wave passes through n+1 layers of media in sequence, and the optical path difference of the wave in each layer of media is d i , where the optical path difference is defined as the difference between the distance from the unit on the metasurface to the focus and the focal length. The relative dielectric constant is ε ri , the relative magnetic permeability is μ ri (i=1,2,…,n+1). Phase change of the first layer of medium for: For the second layer of medium, the phase change for: In a multilayer medium, the total phase difference is the sum of the phase contributions of each layer of medium: The physical meaning can be expressed through Figure 6 The propagation path of the electromagnetic wave is intuitively explained as follows: From the wave source (phase center) to the metasurface, the optical path difference d1 that the wavefront needs to compensate is: After being regulated by the HMS array, different dielectric layers (rectangular layers represented by different colors in the schematic diagram, each layer has a specific relative dielectric constant ε) are used. ri and relative magnetic permeability μ ri ), the optical path difference d that needs to be compensated for each layeri for: Where F is the preset focal length. After a series of phase compensation superpositions, the electromagnetic waves are finally converged and focused at the target position.

[0080] By adopting a three-layer biological tissue model, the model is suitable for simulating pork tissue characteristics at a working frequency of 5.8 GHz, such as Figure 7 As shown in Figure 2, the established biological tissue structure is demonstrated. The model size is 300 mm × 300 mm. The structure consists of a 1.5 mm thick skin layer, a 10 mm thick fat layer, and a 20 mm thick muscle layer in sequence. Table 2 lists the electromagnetic parameter values ​​of different tissue types.

[0081] Table 2 Electromagnetic parameters of pork tissue

[0082]

[0083] Since the penetration depth of 5.8GHz electromagnetic waves into the skin is relatively shallow, usually between 0.2 and 0.5mm. In the fat layer, due to its weak absorption of electromagnetic waves, the penetration depth is slightly deeper than the skin, but generally does not exceed 1cm. In view of the actual needs of the penetration depth of electromagnetic waves and the application of microwave hyperthermia, the simulation model only considers two layers of tissue: the skin layer and the fat layer. The operating frequency of the designed HMS array is 5.8GHz. For the horn feed used, the closer to the center of the array, the higher the radiation energy. Using the units designed in this application, a metasurface array with an area of ​​285mm×285mm (15×15 units) was constructed. The -10dB half-power angle of the horn antenna used as the feed source is 59.0°, so the distance from the phase center of the horn antenna to the center of the metasurface is set to 85.6mm, and the focal length of the electromagnetic wave focusing is set to 10mm. The electromagnetic parameters and thickness physical quantities of the biological tissue are substituted into the revised phase compensation formula, and the phase compensation value required for the metasurface array is calculated.

[0084] The ideal phase transmission distribution of the metasurface array calculated using MATLAB is shown in the figure below: Figure 8 As shown in (a), the actual transmission phase of each unit is then designed to compensate for the corresponding phase delay. The designed unit can meet the 360° omnidirectional transmission phase requirement. The difference between the ideal unit transmission phase and the actual selected unit transmission phase is shown in Figure 8 As shown in (b), the error between the transmission phase of the actual unit and the ideal value is within 7°, indicating that the designed discrete unit basically meets the theoretical requirements.

[0085] Corresponding programs were written in MATLAB to describe the structure and material properties of units at different locations. By combining MATLAB with CST simulation software, the optimization design process was achieved by adjusting the reference phase. Units with high transmission amplitude and broadband characteristics were arranged in the center area of ​​the array to improve the overall performance. Subsequently, a complete near-field focusing HMS array with 15×15 units was established in CST, as shown in the figure below. Figure 9 shown. Figure 9 (a) is the top view of the HMS array. Figure 9 (b) shows the structure of two layers of pork tissue model (skin layer and fat layer) tightly fitted with the HMS array, which is used to simulate the situation where electromagnetic waves directly enter biological tissue through the metasurface.

[0086] This example describes in detail how a Huygens array design achieves precise focusing of microwave energy in superficial areas by constructing a phase compensation model adapted to the electromagnetic properties of biological tissue. A 15×15 element transmission array designed based on multilayer dielectric propagation theory uses MATLAB to calculate the ideal phase distribution and optimizes the element layout through CST simulation. This solves the phase mismatch problem of electromagnetic waves at the air-tissue interface, correcting the wavefront to a converging spherical wave. The design not only provides adjustable focusing distance and phase distribution schemes, but also enhances adaptability to different tissue types through parametric modeling. This provides a flexible and efficient technical path for personalized clinical treatment of non-invasive microwave hyperthermia, overcoming the bottlenecks of traditional arrays, which suffer from uncontrollable focusing depth and poor tissue adaptability.

[0087] Based on the above-mentioned Example 1 and Example 2, this embodiment describes the simulation effect of the present application in detail, specifically:

[0088] Using CST simulation software, a detailed simulation of the electromagnetic field and temperature distribution within biological tissue was conducted at a frequency of 5.8 GHz. In the simulation model, the horn antenna and HMS array were positioned along the z-axis, with their centers on the x-axis and the antenna polarization parallel to the y-axis. The horn antenna was 85.6 mm from the HMS array. The biological tissue model was closely aligned with the metasurface array to simulate the propagation of electromagnetic waves within the tissue after passing through the array. The metasurface array was positioned on the xoy plane, with the array center coinciding with the coordinate origin.

[0089] like Figure 10 As shown, the electric field distribution and energy loss results of the HMS and pork tissue simulation model are displayed. Figure 10(a) shows the electric field distribution in pork tissue at z-axis distances of 1 mm, 3 mm, and 5 mm, respectively. The image depicts the distribution of electric field intensity through a gradual color shift from the center to the periphery. The results demonstrate that electromagnetic waves are effectively focused after passing through the metasurface array, transmitting a large amount of electromagnetic energy into the body, resulting in significant accumulation of electromagnetic energy in the pork tissue. The electromagnetic energy concentration is highest in the skin layer (z = 1 mm). As the electromagnetic wave propagates through the tissue, the attenuation effect of the pork tissue gradually becomes apparent, with the energy density gradually decreasing in the middle (z = 3 mm) and end (z = 5 mm) of the fat layer.

[0090] from Figure 10 (a) It can be clearly seen that when the electromagnetic wave penetrates into the tissue to a depth of about 6mm, the energy is almost dissipated. Due to the focusing effect of the HMS array, the energy attenuation in the focal area is significantly less than that in the surrounding area. To further demonstrate the focusing effect of the electromagnetic wave, Figure 10 (b) shows the normalized electric field intensity distribution of tissue sections at different depths. At the fat-end section (z = 5 mm), the electric field intensity is highest in the central region and gradually decreases with increasing distance from the center. At the middle of the fat (z = 3 mm), the electric field intensity has decayed to approximately 77.1% of its initial value, while at the fat-end (z = 5 mm), the electric field intensity is approximately 52.1% of the initial incident value. Compared to the incident surface (z = 1 mm), the normalized electric field intensity at the fat-end section is approximately 40% lower, indicating that electromagnetic wave energy decays rapidly within tissue with increasing penetration depth.

[0091] To evaluate the energy deposition effect of the focusing system in pork tissue, a simulation study based on the SAR indicator was conducted. The SAR value in biological tissue is proportional to the square of the electric field strength within the tissue, as expressed as follows: Where σ(r) is the conductivity of the medium and ρ(r) is the density of the medium; is the electric field strength;

[0092] like Figure 11 As shown in the figure, the SAR distribution of 1W input power on the yoz section and the SAR distribution at different depths of the xoy section in the non-uniform mode obtained by simulation calculation are shown. Figure 11 As shown in (a), the SAR distribution is concentrated in the central tissue region. The SAR value in the skin layer (z = 1 mm) is approximately 1.8 to 2.0 W / kg, while the SAR value in the middle of the fat layer (z = 3 mm) drops to approximately 0.8 to 1.2 W / kg. The SAR value at the distal end of the fat layer (z = 5 mm) further decreases to less than 1 W / kg. The areas with higher SAR values ​​are primarily located in the skin and the fat layer immediately adjacent to the skin. The maximum SAR value occurs in the skin layer closest to the antenna. This is because the skin layer is closest to the radiation source and has the highest electric field strength.

[0093] Figure 11 (b) shows the curve of maximum SAR changing with depth. Figure 11 (b) It can be seen that the SAR value is higher in the shallow layer (z<3mm) and drops rapidly to about 1.0W / kg at the fat end (z=5mm), reflecting the characteristic that microwave energy attenuates faster in the shallow layer of tissue. Figure 11 Figure (c) shows the variation of normalized SAR values ​​(SAR) with penetration depth. The shallow layer (z = 1 mm) has the highest SAR value, approaching 1.8, and then rapidly decreases with increasing depth, reaching only about 0.2 at z = 5 mm. These results further demonstrate that the near-field focusing HMS designed in this study achieves effective focusing while also exhibiting good safety performance, making it suitable for microwave hyperthermia treatment of superficial tumors.

[0094] In order to further study the effect of the designed system on the temperature of different locations of pork tissue, this application used CSTMulti-physicsStudio software to perform thermal simulation. The results of the thermal simulation are as follows: Figure 12 As shown; Figure 12 (a) shows the temperature distribution of the xoy section of pork tissue at three different depths: z = 1 mm, 3 mm, and 5 mm. As can be seen, the temperature is highest at the center of the skin layer (z = 1 mm), reaching approximately 41.8°C. The temperature gradually decreases from the center to the periphery, reaching approximately 39.4°C at the edge. The temperature in the middle of the fat layer (z = 3 mm) decreases to 41.2°C at the center and approximately 38.6°C at the edge. Finally, at the end of the fat layer (z = 5 mm), the center temperature drops further to 39.5°C, with the edge temperature approximately 38.0°C. Figure 12 (b) shows the temperature distribution of the tissue at different depths at x = 0, y = 0. Simulation results show that the proposed near-field focusing system, operating in the 5.8 GHz frequency band and with an input power of 1 W, can achieve a therapeutic temperature range of 40-42°C at the tissue surface (approximately 15 mm deep). Simultaneously, as the electromagnetic wave propagates through the tissue, the temperature gradually decreases, reflecting the energy dissipation within the tissue. Figure 12 (c) shows the temperature distribution of the x-section at z = 1mm, 3mm, and 5mm. The center temperatures of each section are 41.8℃, 41.2℃, and 39.5℃, respectively. The temperature drops rapidly after exceeding 5mm depth. The center temperature of the 40×40mm section is 40×40mm within 5mm depth. 2 In the area, the tissue temperature is mostly in the range of 40-41°C. The thermal simulation results verify the effectiveness and applicability of the proposed near-field focusing HMS array in hyperthermia therapy of superficial tumors.

[0095] Table 3 Medical thermal parameters used in the bioheat equation

[0096]

[0097] By making a 15×15 unit near-field focusing Huygens metasurface array sample, such as Figure 13 (a) shows the validation of the theoretical analysis and simulation results. The array consists of a single-layer PCB substrate and two upper and lower metal layers. The brown pattern represents the periodic metal resonant units, which are evenly distributed on the upper and lower surfaces of the gray dielectric substrate.

[0098] The experimental platform was built in a microwave darkroom. Figure 13 (b) The experimental setup includes a signal generator, a power amplifier, a 5.8GHz dual-ridged horn antenna, a focusing metasurface array, a pork tissue sample, and a multi-channel temperature probe. The test subjects were square pork samples with skin and fat layer thicknesses of 1.5mm and 8mm, respectively. At an ambient temperature of 22°C, the multi-channel temperature probe measured temperatures at three different depths: the skin layer, the middle of the fat layer, and the end of the fat layer. The experimental materials and structural parameters were consistent with the simulation model settings.

[0099] During the test, the centers of the dual-ridged horn antenna, the near-field focusing metasurface array, and the pork tissue were aligned at the same height. The pork tissue was placed against the back of the metasurface array, as shown in the figure. Figure 13 (c) As shown. The three channels (CH01, CH02, CH03) of the multi-channel temperature probe were used to access the skin layer (z = 1 mm), the middle of the fat layer (z = 3 mm), and the end of the fat layer (z = 5 mm). The calibration signal was transmitted to the double-ridged horn antenna after passing through the signal generator and 5.8 GHz power amplifier to radiate spherical electromagnetic waves. In the experiment, the horn antenna was radiated continuously for 15 minutes with a power of 1 W, and the maximum temperature at each depth was recorded, as shown in the figure. Figure 14 As shown in the figure, the experimental results show that the temperature of the skin layer (CH01 port) rose to 25.7°C, the middle of the fat layer (CH02 port) rose to 24.3°C, and the end of the fat layer (CH03 port) was 23.6°C, which were 3.7°C, 2.3°C, and 1.6°C higher than the room temperature, respectively. In addition, a slight temperature rise was observed at the port not connected to pork tissue, which is due to the influence of the antenna radiation energy on the ambient temperature. The experimental results are basically consistent with the simulation analysis, verifying that the proposed near-field focusing Huygens metasurface array can efficiently focus microwave energy to the target tissue area and achieve effective local heating.

[0100] This example details the validation of the Huygens array's focusing efficiency and safety through electric field, SAR, and temperature field simulations. The results demonstrate that the array can concentrate energy on the surface of tissue, creating a region of high electric field intensity, with energy rapidly decaying with depth. This ensures that the target area reaches the therapeutic temperature while minimizing thermal damage to deeper tissues, providing theoretical support for the device's practical application.

[0101] The above are only preferred embodiments of the present invention, which do not limit the scope of protection of the present invention. For those skilled in the art, the present invention can be modified and varied in various ways. Any changes, modifications, replacements, integrations and parameter changes to these embodiments through conventional substitutions or that can achieve the same functions without departing from the principles and spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A near-field focusing microwave hyperthermia device based on a Huygens metasurface, comprising a feed antenna, a Huygens metasurface array, and a biological tissue model; the feed antenna is a 5.8GHz double-ridged horn antenna, the phase center of which is 85-90mm away from the center of the Huygens metasurface array along the z-axis, and is used to emit x-polarized electromagnetic waves; the Huygens metasurface array is composed of a double-layer periodic arrangement of Huygens units without through holes, and an antisymmetric E-shaped metal pattern is symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate, and nearly 360° phase control and efficient transmission in the 5.8GHz frequency band are achieved by adjusting the unit structure parameters; the biological tissue model is a two-layer structure that fits the Huygens metasurface array, and the electromagnetic parameters match the characteristics of the biological tissue; the electromagnetic waves emitted by the feed antenna are phase-compensated and controlled by the Huygens metasurface array, and near-field focusing is achieved on the surface of the biological tissue, so that the electric field strength, SAR value, and temperature in the target area reach the design thresholds, respectively, forming local precision heating with electromagnetic resonance and phase control.

2. The near-field focusing microwave hyperthermia device based on a Huygens metasurface according to claim 1, characterized in that: The feed antenna is a 5.8GHz double-ridged horn antenna, which is connected to a signal generator and a power amplifier. It can radiate calibrated power electromagnetic waves in the form of spherical waves to the Huygens metasurface array. Its polarization direction matches the direction of the induced current of the Huygens metasurface array unit, stimulating the electric resonance and magnetic resonance effects of the unit structure, ensuring that the electromagnetic waves are controlled by the Huygens metasurface array to achieve near-field focusing on the surface of the biological tissue model. The radiation characteristics work synergistically with the phase compensation design of the Huygens metasurface array to ensure efficient convergence of microwave energy in the target area and local heating effect.

3. The near-field focusing microwave hyperthermia device based on a Huygens metasurface according to claim 1, characterized in that: The Huygens metasurface array consists of a single-layer F4B dielectric substrate and a double-layer antisymmetric E-shaped metal pattern symmetrically distributed on the upper and lower surfaces of the substrate. The substrate thickness is 1-2 mm. The metal layer of each Huygens unit is made of copper-clad material. The metal patterns on the upper and lower surfaces achieve all-round transmission phase control and transmission amplitude by adjusting the vertical short arm length, horizontal short arm length and arm width. The Huygens units are arranged in a periodic matrix to form a transmission array. By matching the electromagnetic properties of biological tissue, it ensures efficient focusing and energy deposition of electromagnetic waves on the tissue surface.

4. The near-field focusing microwave hyperthermia device based on a Huygens metasurface according to claim 1, characterized in that: The biological tissue model is a multi-layer structure that fits the back of the Huygens metasurface array and is used to simulate the electromagnetic response characteristics of the human body's superficial tissue. The biological tissue model consists of skin layers and fat layers stacked in sequence, where the skin layer is close to the Huygens metasurface array and the fat layer is located below the skin layer. The two layers of tissue are tightly fitted to form a planar structure, and the overall size is adapted to the Huygens metasurface array.

5. A near-field focused microwave hyperthermia method based on a Huygens metasurface, characterized in that: include: S1. By using a double-layer, through-hole-free Huygens metasurface unit, antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer PCB substrate. By adjusting the unit structure parameters, the unit can achieve nearly 360° phase control and a transmission amplitude greater than -2dB in the 5.8GHz frequency band, constructing a Huygens unit library with full phase coverage capability. S2. Establish a phase compensation model in a multilayer medium and use MATLAB to calculate the ideal phase distribution of the transmission array so that the electromagnetic waves emitted by the feed antenna are focused at a specified focal length on the surface of the biological tissue after being regulated by the array. S3. Map the calculated ideal phase distribution to the Huygens cell library, select cells with corresponding structural parameters to form a Huygens metasurface array, and optimize the cell layout through CST simulation to ensure that the error between the actual transmission phase and the theoretical value is ≤7°, thus achieving the ability to precisely control the electromagnetic wave front; S4. Use a 5.8 GHz double-ridged horn antenna as the feed source, set the distance between the phase center and the center of the Huygens metasurface array, align the antenna polarization direction with the direction of the induced current of the Huygens metasurface unit to stimulate the electromagnetic resonance effect of the unit, and connect the antenna to the signal generator and power amplifier to form an electromagnetic wave transmission link; S5. Fit the Huygens metasurface array tightly to the biological tissue model, match the thickness and electromagnetic parameters of the biological tissue model to the superficial tumor treatment scenario, turn on the signal source, and radiate x-polarized electromagnetic waves to the Huygens metasurface array at a power of 1W; S6. After the phase of the Huygens metasurface array is controlled, the electromagnetic waves are focused on the surface of the biological tissue, so that the temperature of the target area rises to the therapeutic range, achieving localized and precise heating of microwave energy.

6. The near-field focused microwave hyperthermia method based on Huygens metasurface according to claim 5, characterized in that: In S1, a Huygens cell library with full phase coverage is constructed. Specifically, antisymmetric E-shaped metal patterns are symmetrically arranged on the upper and lower surfaces of a single-layer F4B dielectric substrate. The metal layer is made of copper-clad material. By changing the vertical short arm length h, the horizontal short arm length l, and the arm width b, the transmission phase and transmission amplitude under different parameter combinations are simulated using CST Microwave Studio. Four representative sampling points and more discrete parameter points are selected to ensure that the transmission phase covers 0°-360° at a frequency of 5.8 GHz, and that the transmission amplitude of each unit is higher than -2 dB. The parameter combinations b, h, l that meet the conditions and their corresponding phase and amplitude values ​​are organized into a unit library to construct a Huygens unit library with full phase coverage capability.

7. The near-field focused microwave hyperthermia method based on Huygens metasurface according to claim 5, characterized in that: The phase compensation model in the multilayer medium is established in S2, specifically: the propagation speed formula of the electromagnetic wave in free space and multilayer medium is determined, where the free space speed is The velocity in the medium is Combined wavelength The relationship between phase difference and optical path difference is derived, ε0 and μ0 are the dielectric constant and magnetic permeability in vacuum, ε r is the relative dielectric constant, μ r is the relative magnetic permeability; for the biological tissue model, the electromagnetic wave passes through the air, Huygens metasurface array, skin layer and fat layer in sequence, and the optical path difference of each layer is defined as the difference between the unit to the focus distance and the focal length. According to the generalized sheet transition condition and the quasi-optical path theorem, the relative dielectric constant ε of each layer of the medium is r and relative magnetic permeability μ r Substitute into the phase compensation formula and accumulate the phase contribution of each layer Where λ0 is the free space wavelength, d i Based on the optical path difference of each layer, a two-layer medium phase compensation model suitable for the skin layer and fat layer is established. The phase compensation value required for each position of the unit array is calculated through the phase compensation model to ensure that the electromagnetic wave is focused at the target focal length after being controlled by the metasurface.

8. The near-field focused microwave hyperthermia method based on Huygens metasurface according to claim 5 or 6, characterized in that: In the S3, the calculated ideal phase distribution is mapped to the Huygens unit library and the unit layout is optimized through CST simulation. Specifically, MATLAB is used to calculate the ideal transmission phase distribution at each position of the unit array based on the multilayer dielectric phase compensation model to form a continuous phase matrix covering 0°-360°; each phase value in the matrix is ​​mapped to the discrete unit with the closest phase in the Huygens unit library, and the structural parameters b, h, and l of the unit at each position are preliminarily determined. A full-wave simulation model including the feed antenna, Huygens metasurface array, and biological tissue model is established in CST MicrowaveStudio, the distance from the phase center of the horn antenna to the center of the array and the focal length are set, the structural parameters of each unit are imported, and periodic boundary conditions are applied; by scanning the reference phase of the units in the center and edge areas of the array, the unit layout is adjusted, and the unit parameters are iteratively optimized until the error between the actual transmission phase and the ideal value is controlled within 7°, thereby forming a precise control capability of the electromagnetic wave front.

9. The near-field focused microwave hyperthermia method based on Huygens metasurface according to claim 1, characterized in that: In the S4, the antenna is connected to the signal generator and the power amplifier to form an electromagnetic wave transmission link, specifically: the output end of the signal generator is connected to the input end of the power amplifier through a coaxial cable, and the frequency of the signal generator is set to 5.8GHz to generate a continuous wave signal; the output end of the power amplifier is connected to the feeding port of the 5.8GHz double-ridged horn antenna through a low-loss coaxial cable, and the power amplifier is adjusted to stabilize the output power at 1W; the feed antenna (double-ridged horn antenna) is fixed on the bracket so that the distance between its phase center and the center of the Huygens metasurface array along the z-axis direction is 85-90mm, and the polarization direction of the antenna is consistent with the induced current direction of the Huygens metasurface unit, the signal generator and the power amplifier are turned on, and the x-polarized electromagnetic wave generated by the signal generator is amplified by the power amplifier and radiated to the Huygens metasurface array in the form of a spherical wave by the double-ridged horn antenna, forming an electromagnetic wave transmission link.

10. The near-field focused microwave hyperthermia method based on Huygens metasurface according to claim 1, characterized in that: The electromagnetic waves in S6 are focused on the surface of biological tissue after being phase-controlled by the Huygens metasurface array, so that the temperature of the target area rises to the treatment range. Specifically, the x-polarized electromagnetic wave of 5.8 GHz is emitted by the feed antenna and is phase-compensated and controlled by the Huygens unit of the Huygens metasurface array. The x-polarized electromagnetic wavefront is corrected into a spherical wave that converges at a specified focal length on the surface of the biological tissue, forming a high electric field intensity area at the interface between the skin layer and the fat layer; according to the electromagnetic properties of biological tissue, the higher dielectric constant and conductivity of the skin layer make it absorb electromagnetic waves more strongly, and the electric field energy is converted into heat energy, and the Pennes bioheat equation is used. Calculations show that the central area of ​​the skin layer heats up rapidly due to the high SAR value under 1W input power, where ρ is tissue density, C is tissue specific heat capacity, k is tissue thermal conductivity, A0 is tissue metabolic heat production, B is heat exchange caused by capillary blood perfusion, and T B is the constant blood temperature, T is the temperature of the tissue, Q r The thermal power density generated by electromagnetic waves in biological tissues is limited by the near-field focusing characteristics of the Huygens metasurface array to limit the diffusion of energy to deep layers. The fat layer absorbs less energy due to its low electrical conductivity, and the temperature gradually decreases with increasing depth. Through theoretical calculations, CST thermal simulation and experimental tests, it is verified that the temperature of the superficial skin layer and fat layer rises to the treatment range of 40-42°C, and the temperature of the non-target area is lower than 39°C, realizing the precise deposition and local heating of microwave energy in the superficial tumor area.

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