Efficient bioelectronic wireless transmission system and design method thereof

Abstract

The invention relates to an efficient bioelectronic wireless transmission system and a design method thereof. The system comprises a transmitting antenna, an implantable receiving antenna and a cascade metasurface, wherein the cascade metasurface is matched with air-human body wave impedance and converts linearly polarized waves into circularly polarized waves at the same time. The method is used for optimizing a channel and reducing air-human body reflection loss and polarization mismatch loss between a transmitting antenna and an implanted receiving antenna, and comprises the following steps: firstly, analyzing impedance values on two sides of a metasurface, and considering local Phipointt vector conservation and polarization conversion to obtain a scattering matrix; and solving the obtained scattering matrix and the electromagnetic response of each layer of the metasurface through a wave matrix to obtain an ideal electromagnetic response surface current value required by each layer of the metasurface. And designing a metasurface physical structure to realize theoretical parameters, and finally combining the three layers of metasurface structures into a metasurface unit. Compared with the prior art, the device has the advantages that high-efficiency bioelectronic wireless transmission is realized, and power loss caused by air-human body reflection and polarization isolation is reduced.

Description

Technical Field

[0001] The present invention relates to the field of wireless transmission technology, and in particular to a high-efficiency bioelectronic wireless transmission system and a design method thereof. Background Art

[0002] With the widespread application of bioelectronic devices such as implantable pacemakers, bladder pressure monitors, and cochlear implants, the establishment of an efficient bioelectronic wireless transmission system has become a very important topic in bioelectromagnetics. By solving the air-human wave impedance matching and polarization matching problems in the bioelectronic device wireless transmission system, efficient bioelectronic wireless transmission can be achieved. The two main factors that restrict the transmission efficiency of the bioelectronic device wireless transmission system are: the huge reflection caused by the huge impedance mismatch between the human body and the air at the air-skin interface; and the polarization mismatch caused by the uncertainty of the position and direction of the implantable bioelectronic device inside the human body and the uncertainty of the polarization direction of the incident linearly polarized electromagnetic wave.

[0003] In addition to selecting higher gain antennas or using higher input power, research on how to improve the efficiency of wireless transmission systems of bioelectronic devices has gone through three stages: by attaching the antenna directly to the human body, the near-field coupling of the electromagnetic field can efficiently transmit electromagnetic waves into the human body, but the mobility is poor, and the heating problem of the antenna will also affect the user experience; immersing the human body in a dielectric with a suitable dielectric constant can also improve the transmission efficiency of electromagnetic waves to the human body, but the user needs to remain still and the mobility is poor; by designing a metasurface structure that can produce specific electromagnetic responses, electromagnetic waves can be efficiently transmitted into the human body while maintaining mobility, which has better practicality.

[0004] As for solving the polarization mismatch problem, circularly polarized implantable antennas are now mostly used to solve it. However, for linearly polarized incident electromagnetic waves, circularly polarized implantable antennas can only receive half of the power. The above problem can be solved by optimizing the entire wireless transmission system of bioelectronic devices to convert the incident linearly polarized waves into circularly polarized waves, but research on this work is rare.

[0005] Currently, metasurface solutions are mostly used to optimize the wireless transmission systems of bioelectronic devices. The design methods include: analyzing the impedance difference between air and human body by using the Smith chart, and realizing the impedance matching layer between air and human body by constructing a quarter-wavelength impedance matching layer, so as to reduce the power loss caused by the huge reflection at the air-skin interface. However, the metasurface designed by this method is very thick and the effect of reducing reflection is general; modeling and analyzing the air, metasurface, and human body through the transmission line model, calculating using the wave matrix, obtaining the electromagnetic response of each layer and designing the metasurface based on this. This analysis method allows the metasurface to adopt a cascaded structure of three or more layers, which can more efficiently reduce the power loss caused by reflection, but the incident electromagnetic waves are mostly linearly polarized and cannot solve the polarization mismatch problem at the same time. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a high-efficiency bioelectronic wireless transmission system and a design method thereof.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] According to one aspect of the present invention, there is provided a highly efficient bioelectronic wireless transmission system, the system comprising a transmitting antenna, an implantable receiving antenna and a cascaded metasurface;

[0009] Furthermore, the cascaded metasurface is composed of N layers of metasurfaces, which are used to optimize the channel to reduce the reflection loss between air and human body and the polarization mismatch loss. The electromagnetic field components of the N layers of metasurfaces in the x and y directions have equal amplitudes and a phase difference of 90°, where N ≥ 2;

[0010] Furthermore, the metasurface includes a metal layer and a substrate layer, adopts an impedance matching cascade metasurface and integrates the function of wired-circular polarization conversion.

[0011] Optionally, the transmitting antenna adopts a high-gain antenna, and the implantable receiving antenna includes a high-gain linearly polarized omnidirectional antenna or a high-gain circularly polarized omnidirectional antenna.

[0012] Optionally, the metal layer structure of each layer of the metasurface includes a cross structure, a Jerusalem cross structure, a resonant ring structure or a flower structure.

[0013] According to another aspect of the present invention, a method for designing an efficient bioelectronic wireless transmission system is provided. The method is applied to the above-mentioned efficient bioelectronic wireless transmission system. The specific steps of the design method include:

[0014] S1. Use the transmission line model to perform an equivalent analysis on the air-metasurface-human body model. By analyzing the wave impedance values ​​of the air and human body on both sides of the metasurface, combined with the local Poynting vector conservation and linear-circular polarization conversion, the scattering matrix required to achieve impedance matching and linear-circular polarization conversion functions is obtained;

[0015] S2. Determine the parameters of the metasurface, establish a wave matrix, use the scattering matrix obtained in S1, obtain the ideal electromagnetic response required for each layer of the metasurface through the wave matrix, and express the ideal electromagnetic response as an ideal admittance value;

[0016] S3, establish an ideal model of air-metasurface-human body, input the parameters of the metasurface set in S2 into the model to observe whether the output admittance value is consistent with the ideal admittance value, if not, return to step S2, adjust the parameters of the metasurface, and recalculate the ideal admittance value; if consistent, record the parameters of the metasurface and the ideal admittance value;

[0017] S4, analyzing the ideal admittance value recorded in S3, and designing the structure of each metasurface metal layer according to the analysis result, and parameterizing it, specifically setting the size parameters in the designed structure;

[0018] S5, establishing a model for extracting the electromagnetic response of each layer of the metasurface separately, extracting the actual admittance value of each layer from the metasurface structure in S4 by the model, and comparing it with the ideal admittance value recorded in S3; if they are inconsistent, returning to step S4, iterating the parameters of the metasurface structure designed in S4, and if they are consistent, proceeding to step S6;

[0019] S6. By putting the current layers of metasurface structures together, we can obtain a highly efficient bioelectronic wireless transmission system.

[0020] As a preferred technical solution, the process of obtaining the scattering matrix required to realize impedance matching and linear-circular polarization conversion function in S1 is: first define the area where the electromagnetic wave enters the metasurface as area 1, and the area where the electromagnetic wave exits the metasurface as area 2, and then calculate it by the following formula:

[0021]

[0022] in, is the electric field propagating along the +z axis in region 1; is the electric field propagating along the -z axis in region 1; is the electric field propagating along the +z axis in region 2; is the electric field propagating along the -z axis in region 2; S ij is the 2×2 scattering tensor in the form of Jones matrix of electromagnetic waves transmitted from air to human body, is the scattering matrix, S11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient.

[0023] Furthermore, the reflection coefficient S 11 and S 22 Need to meet:

[0024] S 11 =S 22 =0;

[0025] To match the wave impedance difference between air and human body, the reflection-free transmission of electromagnetic waves is realized; and the transmission coefficient S 12 and S 21 Need to meet:

[0026]

[0027] To ensure the conservation of local power flux, where η1 is the wave impedance of air, η2 is the wave impedance of human tissue, and Φ is the transmission phase generated by the metasurface.

[0028] Furthermore, the parameters of the super surface in S2 include operating frequency, plate parameters, and interlayer thickness.

[0029] As a preferred technical solution, the formula for establishing the wave matrix in S2 is:

[0030]

[0031] in, is the wave matrix, I is the second-order identity matrix, S 11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient, is the wave matrix of the ith metasurface, and the area where the electromagnetic wave enters the metasurface is defined as area 1, and the area where the electromagnetic wave exits the metasurface is defined as area 2. is the electric field propagating along the +z axis in region 1; is the electric field propagating along the -z axis in region 1; is the electric field propagating along the +z axis in region 2; is the electric field propagating along the -z axis in region 2.

[0032] As a preferred technical solution, the specific expression of the ideal electromagnetic response required to be achieved by each layer of the metasurface is obtained by wave matrix in S2:

[0033]

[0034] in, is the wave matrix of the ith metasurface, Y i is the 2×2 admittance value representing the ideal electromagnetic response of the metasurface T i is the 2×2 transmission matrix of the material interface r and t are the Fresnel reflection and transmission coefficients, η i is the incident wave impedance on the patterned metal metasurface, is the phase delay caused by passing through the dielectric substrate, is the tensor product symbol.

[0035] As a preferred technical solution, the model expression for extracting the electromagnetic response of each layer of the metasurface separately in S5 is:

[0036]

[0037] Among them, Y i is the admittance value representing the electromagnetic response of the single-layer metasurface; S 11 is the extracted reflection coefficient of the single-layer metasurface, I is the second-order unit matrix, η in is the wave impedance at the incident end of the electromagnetic wave, η tr is the wave impedance at the output end of the electromagnetic wave.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. In the present invention, the transmission line model is used to perform an equivalent analysis on the air-metasurface-human body model. By analyzing the wave impedance values ​​on both sides of the metasurface, namely the air and the human body, combined with the local Poynting vector conservation and linear-circular polarization conversion, the required scattering matrix is ​​obtained, impedance matching and linear-circular polarization conversion functions are realized, and the electromagnetic wave transmission efficiency from the outside to the implantable bioelectronic device is improved.

[0040] 2. The present invention uses three or more layers of cascaded metasurfaces to achieve impedance matching between air and human body, which has better performance than the same type of impedance matching layer. In addition, the present invention sets the reflection coefficient S when determining the scattering matrix. 11 and S 22 is zero, that is, the reflection coefficient S is ignored 11 and S 22 , thereby matching the wave impedance between air and human body and realizing reflection-free transmission of electromagnetic waves.

[0041] 3. In the present invention, the electromagnetic field components in the x and y directions are equal in amplitude and 90° in phase on the supersurface. When determining the scattering matrix, the transmission coefficient S is set. 12 and S 21 satisfy:

[0042]

[0043] This ensures the conservation of local power flux, thereby converting the linearly polarized electromagnetic waves incident on the human body into circularly polarized electromagnetic waves, solving the problem of polarization mismatch and reducing the power loss caused by polarization isolation due to the uncertainty of the position of the implantable bioelectronic device. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a schematic diagram of a highly efficient bioelectronic wireless transmission system of the present invention;

[0045] Figure 2 This is a flow chart of a highly efficient bioelectronic wireless transmission method of the present invention;

[0046] Figure 3 Schematic diagram of the split structure of the super surface periodic unit structure in the present invention;

[0047] Figure 4 Schematic diagram of the overall structure of the super surface periodic unit structure in the present invention

[0048] Figure 5 Schematic diagram of a single-layer structure of the super surface in the present invention;

[0049] Figure 6 A schematic diagram of transmission efficiency in an embodiment of the present invention;

[0050] Figure 7 A phase diagram in an embodiment of the present invention;

[0051] Figure 8 Schematic diagram of the efficiency and axial ratio of the transmission from the metasurface to the human body in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0053] Currently, metasurface solutions are mostly used to optimize the wireless transmission systems of bioelectronic devices. The design methods include: analyzing the impedance difference between air and human body by using the Smith chart, and realizing the impedance matching layer between air and human body by constructing a quarter-wavelength impedance matching layer, so as to reduce the power loss caused by the huge reflection at the air-skin interface. However, the metasurface designed by this method is very thick and the effect of reducing reflection is general; modeling and analyzing the air, metasurface, and human body through the transmission line model, calculating using the wave matrix, obtaining the electromagnetic response of each layer and designing the metasurface based on this. This analysis method allows the metasurface to adopt a cascaded structure of three or more layers, which can more efficiently reduce the power loss caused by reflection, but the incident electromagnetic waves are mostly linearly polarized and cannot solve the polarization mismatch problem at the same time.

[0054] The scheme of using metasurfaces to convert linear polarization into circularly polarized electromagnetic waves is currently used in applications such as satellite communications to reduce power losses caused by polarization mismatch, but there is no relevant research in the field of improving the electromagnetic wave reception efficiency of implantable bioelectronic devices.

[0055] By proposing an efficient bioelectronic wireless transmission system and its design method, the impedance mismatch problem between air and human body and the polarization mismatch problem between implantable bioelectronic devices can be solved at the same time. This can greatly improve the electromagnetic wave transmission efficiency of the entire bioelectronic wireless transmission system. It is expected to play a big role in the fields of wireless charging, wireless communication and even wireless detection and imaging of vital signs of bioelectronic devices, which is of great significance to the future development of bioelectronic devices.

[0056] Example

[0057] In this embodiment, a highly efficient bioelectronic wireless transmission system is applied, the system comprising a transmitting antenna, an implantable receiving antenna and a cascaded metasurface;

[0058] The cascaded metasurface is composed of N layers of metasurfaces, which are used to optimize the channel to reduce the reflection loss between air and human body and the polarization mismatch loss. The electromagnetic field components of the N layers of metasurfaces in the x and y directions have equal amplitudes and a phase difference of 90°, where N ≥ 2;

[0059] The metasurface includes a metal layer and a substrate layer. It adopts an impedance matching cascade metasurface and integrates the function of wired-circular polarization conversion. It can be used in bioelectronic devices to realize polarization conversion.

[0060] In this embodiment, N=3, i.e., a three-layer impedance matching cascaded metasurface is selected as an example.

[0061] The scheme in this embodiment is as follows Figure 1As shown, by designing artificial electromagnetic structures (such as metasurfaces and impedance matching layers) to simultaneously achieve the functions of air-to-human impedance matching and linear-to-circular polarization conversion, the bioelectronic wireless transmission system can achieve almost reflection-free transmission at the air-to-human interface, while ensuring that the electromagnetic waves transmitted in the body are circularly polarized to avoid the problem of polarization mismatch, thereby greatly improving the transmission efficiency of the bioelectronic wireless transmission system.

[0062] In this embodiment, a method for designing an efficient bioelectronic wireless transmission system is used for design, that is, a design method for impedance matching cascade that can realize polarization conversion in bioelectronic devices is used to design the above-mentioned efficient bioelectronic wireless transmission system. The specific process of the method is as follows: Figure 2 This method first uses a transmission line model to equate the air-metasurface-human body model, and then further considers the local Poynting vector conservation and polarization conversion by analyzing the impedance values ​​on both sides of the metasurface, and obtains the scattering matrix that can simultaneously achieve impedance matching and polarization conversion functions.

[0063] Then, the wave matrix method is used for calculation, and the scattering matrix obtained above and the electromagnetic response of each layer of the metasurface structure are respectively linked to the wave matrix, and further solved to obtain the ideal electromagnetic response value that each layer of the metasurface structure needs to achieve and express it with admittance.

[0064] Afterwards, a formula for extracting the admittance value of each layer of the metasurface structure was given. The approximate structure of the metasurface was obtained by analyzing the ideal electromagnetic response value and equivalent circuit methods. The actual electromagnetic response value was extracted and compared and iterated with the ideal value, and then the metasurface structure of each layer was obtained.

[0065] Finally, three or more layers of metasurface structures are put together and full-wave simulation software is used to verify their feasibility.

[0066] The specific steps of the method are as follows:

[0067] S1. Use the transmission line model to perform an equivalent analysis on the air-metasurface-human model. By analyzing the wave impedance values ​​of the air and human body on both sides of the metasurface, combined with the local Poynting vector conservation and linear-circular polarization conversion, the scattering matrix required to achieve impedance matching and linear-circular polarization conversion functions is obtained, such as Figure 2 As shown in 401.

[0068] Generally speaking, the human body impedance value is obtained by using water to approximate the human body impedance value and establishing a three-layer model of skin-fat-muscle for equivalent analysis. The impedance values ​​of different parts of the human body are different.

[0069] In this embodiment, the impedance value of water is used to approximate the impedance value of the human body.

[0070] In this embodiment, the area where the electromagnetic wave enters the metasurface is defined as area 1, and the area where the electromagnetic wave exits is defined as area 2. Figure 1 As shown, the electric field in region 1 propagates in the positive direction along the +z axis. The electric field propagating in the negative direction along the -z axis in region 1 The electric field in region 2 propagates in the positive direction along the +z axis and the electric field in region 2 propagating in the negative direction along the -z axis The relationship can be analyzed by the scattering parameters:

[0071]

[0072] in, is the electric field propagating in the positive direction along the +z axis, is the electric field propagating in the negative direction along the +z axis (i=1, 2); S ij is the 2×2 scattering tensor (i=1, 2; j=1, 2) of electromagnetic waves transmitted from air to the human body in the form of Jones matrix, where S 11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient;

[0073] In this embodiment, in order to match the wave impedance difference between air and human body to achieve non-reflection transmission of electromagnetic waves, the emission coefficient S 11 and S 22 Need to be ignored, that is, S 11 =S 22 =0.

[0074] In this embodiment, the local power flux conservation must be ensured. In addition, considering the function of linear circular polarization conversion, the transmission coefficient S 21 and S 12 Must meet:

[0075]

[0076] Among them, η1 is the wave impedance of air, η2 is the wave impedance of human tissue, and Φ is the transmission phase generated by the metasurface.

[0077] S2. Determine the parameters of the metasurface, establish a wave matrix, and use the scattering matrix obtained in S1 to obtain the ideal electromagnetic response required for each layer of the metasurface through the wave matrix. The ideal electromagnetic response is expressed as an ideal admittance value, such as Figure 2 As shown in 402.

[0078] In this embodiment, the scattering matrix obtained in step S1 and the ideal electromagnetic response of each layer of the metasurface structure are respectively linked to the wave matrix for solution, and the ideal electromagnetic response required to be achieved by each layer of the metasurface structure is respectively obtained;

[0079] For electromagnetic response, admittance value or impedance value is generally used to represent it. A positive admittance value indicates that the electromagnetic response is similar to that of a capacitor, and a negative admittance value indicates that the electromagnetic response is similar to that of an inductor.

[0080] In this embodiment, the electromagnetic response is represented by an admittance value.

[0081] Specifically, the process of calculating the electromagnetic response of each metasurface required to achieve the desired effect through the wave matrix and expressing it in admittance value includes:

[0082] The scattering matrix and the wave matrix are deduced theoretically. Establish contact as follows:

[0083]

[0084] in, is the wave matrix, S 11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient; the wave matrix directly relates the incident and transmitted electric field components of one port to those of the other port;

[0085] In this embodiment, the scattering matrix obtained in S1 is substituted into the scattering matrix and wave matrix In the formula for establishing the connection, the following two formulas are then combined to obtain the admittance value of each layer of the three-layer metasurface;

[0086] Specifically, the wave matrix Decomposing it, we can get the product of the wave matrices of the n-layer metasurface:

[0087]

[0088] in, is a wave matrix of the i-th metasurface, including a patterned metal metasurface structure and a dielectric substrate; is the electric field propagating in the positive direction along the +z axis, It is the electric field propagating in the negative direction along the +z axis (i=1, 2).

[0089] Specifically, the wave matrix of the i-th metasurface is linked to the electromagnetic response of the actual physical structure of the metasurface. The ideal electromagnetic response is represented by the admittance value Y i Indicates as follows:

[0090]

[0091] Among them, Y iis the 2×2 admittance value representing the ideal electromagnetic response of the metasurface T i is the 2×2 transmission matrix of the material interface where r and t are the Fresnel reflection and transmission coefficients, η i is the incident wave impedance on the patterned metal metasurface, is the phase delay caused by passing through the dielectric substrate, I is the second-order unit matrix, is the tensor product symbol.

[0092] In this embodiment, the central frequency of the metasurface is determined to be 28 GHz, and the dielectric plate is Rogers 5880 (ε rogers =3.2), the disassembly diagram of the super surface structure is as follows Figure 3 As shown, the dielectric thickness of the first substrate 412 and the second substrate 413 is 2 mm, and the dielectric thickness of the third substrate 414 is 1 mm. Then, the above parameters and the scattering matrix obtained in S1 are substituted into the formula, and the phase delay Φ after passing through the metasurface is preset to be 120°. By calculation, the admittance values ​​of the first metasurface in the x and y polarization directions are -0.0012 and -0.0058, respectively, the admittance values ​​of the second metasurface in the x and y polarization directions are -0.0119 and -0.0205, respectively, and the admittance values ​​of the third metasurface in the x and y polarization directions are -0.0018 and -0.0027, respectively;

[0093] S3, establish an ideal model of air-metasurface-human body, input the parameters set in S2 into the model to observe whether the output admittance value is consistent with the ideal admittance value, if not, return to step S2, adjust the parameters of the metasurface, and recalculate the ideal admittance value; if consistent, record the set parameters and the ideal admittance value, such as Figure 2 As shown in 403.

[0094] In this embodiment, the specific steps for verifying whether the parameters set in S2 meet the expected effect are: the electromagnetic response value obtained in S2 is simulated by full-wave simulation software, and the full-wave simulation structure is observed. The x and y direction components of the electromagnetic wave with 45° polarization and vertical incidence are equal in amplitude, and the phase difference is 90°. An ideal model is established by using an ohmic surface or setting the surface current of an ideal surface in the electromagnetic wave full-wave simulation software to simulate the admittance value of each layer, and verifying whether the admittance value obtained in S2 meets the expected effect. If it does, the set parameters and the ideal admittance value are recorded and step S4 is executed. If it does not, step S2 is re-executed to adjust the plate material and plate thickness.

[0095] In this embodiment, the characteristics of the process of establishing an ideal model in S3 to verify whether the admittance value of each layer of the metasurface obtained in S2 can achieve the expected effect are: simulating the ideal admittance value using the Ohmic surface in the full-wave simulation software or by setting the surface current on the ideal surface: the boundary conditions around the metasurface plane are set to periodic boundaries to simulate an infinitely large metasurface.

[0096] S4, analyze the ideal admittance value recorded in S3, and according to the analysis results, design the metasurface structure of each layer through equivalent circuit theory and perform parameterization, such as Figure 2 As shown in 404.

[0097] The metasurface structure of each layer is designed through theories such as equivalent circuits, including a cross structure, a Jerusalem cross structure, a resonant ring structure, and a flower-shaped structure.

[0098] In this example, a cross-shaped structure is used as the periodic unit structure, such as Figure 3 As shown, the unit structure has a length and a width of 4 mm, the first metal structure 409, the second metal structure 410, and the third metal structure 411 use copper as the metal material of the super surface, the first substrate 412, the second substrate 413, and the third substrate 414 use Rogers 5880 as the plate material, the first substrate 412 and the second substrate 413 are 2 mm thick, and the third substrate 414 is 1 mm thick. Figure 4 The overall schematic diagram of the supersurface unit structure is shown in Figure 2. The pattern of each layer of the supersurface is then parameterized. In this example, a cross-shaped structure is used, and the widths of the metal strips in the x and y directions are set to Wx and Wy, respectively, for subsequent optimization. Figure 5 As shown;

[0099] In this embodiment, parameterization is specifically to set the size parameters in the structure, so as to facilitate subsequent iterative changes. Taking the cross-shaped structure as an example, the widths of its two crosses are defined as Wx and Wy respectively, with the purpose of iterating it so that it meets the ideal admittance value. Other structures are also parameterized. For example, the circular open ring structure can parameterize the inner diameter, outer diameter, opening size, etc. of the ring.

[0100] In this embodiment, the formula for extracting the electromagnetic response of a single-layer metasurface is obtained as follows:

[0101]

[0102] Among them, Y i is the admittance value representing the electromagnetic response of the metasurface monolayer, S 11 is the extracted reflection coefficient of the single-layer metasurface, I is the second-order unit matrix, η in is the wave impedance at the incident end of the electromagnetic wave, η tris the wave impedance at the output end of the electromagnetic wave;

[0103] S5, establish a model for extracting the electromagnetic response of each layer of the metasurface separately, use this model to extract the actual admittance value of each layer of the metasurface structure in S4, and compare it with the ideal admittance value recorded in S3; repeat S4 and S5, iterate the parameters of the metasurface structure designed in S4, until the actual electromagnetic response meets the ideal admittance value recorded in S3, such as Figure 2 As shown in 405 and 406.

[0104] In this embodiment, the specific step of S5 is: the metasurface structure designed in S4 is subjected to the admittance value extraction model proposed in S5 to extract the admittance value of the structure designed in step S5, and compared with the ideal admittance value calculated in step S2 respectively. If they do not match, S4 and S5 are repeated to adjust the width of the metal strip in the x and y directions: Wx and Wy, until they match the ideal admittance value.

[0105] In this embodiment, a formula is established by theoretical derivation to extract the admittance value of each layer, and a model is established by full-wave simulation software. Each layer of the metasurface adopts the structure designed in S4. It is worth noting that the boundary condition should be a periodic boundary;

[0106] In this embodiment, the parameters that finally meet the requirements are: first layer: Wx=0.1mm, Wy=0.9mm; second layer: Wx=1.6mm, Wy=2.0mm; third layer: Wx=0.1mm, Wy=0.4mm.

[0107] S6. Putting together the three-layer metasurface structures iteratively obtained in S4 and S5, a highly efficient bioelectronic wireless transmission system is obtained, such as Figure 2 As shown in 407.

[0108] In this embodiment, when a 28 GHz 45° polarized electromagnetic wave is incident vertically on the human body, the metasurface has a transmission efficiency of nearly 96.4%, and the x-direction component and the y-direction component of the outgoing electromagnetic wave have a phase difference of nearly 90°, as shown in FIG. Figure 6 , Figure 7 As shown, the expected effect was met;

[0109] In this embodiment, the bioelectronic wireless transmission system can maintain an axial ratio below 3dB at 27.09-29.95GHz, while the efficiency is higher than -3dB, and has good broadband performance, such as Figure 8 As shown, it can be seen that the efficiency has been significantly improved compared with the incident light without the metasurface.

[0110] In summary, the bioelectronic wireless transmission system used in this embodiment significantly improves the efficiency of electromagnetic wave transmission from the outside to implantable bioelectronic devices; realizes reflection-free transmission of electromagnetic waves; solves the problem of polarization mismatch, and reduces the power loss caused by polarization isolation due to the uncertainty of the position of implantable bioelectronic devices.

[0111] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed by the present invention, and these modifications or replacements should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. An efficient bioelectronic wireless transmission system, It is characterized in that The system includes a transmitting antenna, an implantable receiving antenna, and a cascaded metasurface; The cascaded metasurface is composed of N layers of metasurfaces, which are used to optimize the channel and reduce the reflection loss between air and human body and the polarization mismatch loss. The electromagnetic field components of the N layers of metasurfaces in the x and y directions have equal amplitudes and a phase difference of 90°, where N≥2; The metasurface comprises a metal layer and a substrate layer, adopts an impedance matching cascade metasurface and integrates the function of wired-circular polarization conversion.

2. According to claim 1, a highly efficient bioelectronic wireless transmission system, It is characterized in that The transmitting antenna is a high-gain antenna, and the implantable receiving antenna includes a high-gain linear polarization omnidirectional antenna or a high-gain circular polarization omnidirectional antenna.

3. According to claim 1, a highly efficient bioelectronic wireless transmission system, It is characterized in that The metal layer structure of each layer of the super surface includes a cross structure, a Jerusalem cross structure, a resonant ring structure or a flower structure.

4. A design method for efficient bioelectronic wireless transmission system, It is characterized in that The following steps are involved: S1. Use the transmission line model to perform an equivalent analysis on the air-metasurface-human body model. By analyzing the wave impedance values ​​of the air and human body on both sides of the metasurface, combined with the local Poynting vector conservation and linear-circular polarization conversion, the scattering matrix required to achieve impedance matching and linear-circular polarization conversion functions is obtained; S2. Determine the parameters of the metasurface, establish a wave matrix, use the scattering matrix obtained in S1, obtain the ideal electromagnetic response required for each layer of the metasurface through the wave matrix, and express the ideal electromagnetic response as an ideal admittance value; S3, establish an ideal model of air-metasurface-human body, input the parameters of the metasurface set in S2 into the model to observe whether the output admittance value is consistent with the ideal admittance value, if not, return to step S2, adjust the parameters of the metasurface, and recalculate the ideal admittance value; if consistent, record the parameters of the metasurface and the ideal admittance value; S4, analyzing the ideal admittance value recorded in S3, and designing the structure of each metasurface metal layer according to the analysis result, and parameterizing it, specifically setting the size parameters in the designed structure; S5, establishing a model for extracting the electromagnetic response of each layer of the metasurface separately, using the model to extract the metasurface structure in S4 to obtain the actual admittance value of each layer, and comparing it with the ideal admittance value recorded in S3; If they are not consistent, then return to step S4 to iterate the parameters of the metasurface structure. If they are consistent, then execute step S6; S6. By putting the current layers of metasurface structures together, we can obtain a highly efficient bioelectronic wireless transmission system.

5. According to claim 4, a method for designing an efficient bioelectronic wireless transmission system, It is characterized in that The process of obtaining the scattering matrix required for realizing impedance matching and linear-circular polarization conversion function in S1 is as follows: first, define the area where the electromagnetic wave enters the metasurface as area 1, and the area where the electromagnetic wave exits the metasurface as area 2, and then calculate it by the following formula: in, is the electric field propagating along the +z axis in region 1; is the electric field propagating along the -z axis in region 1; is the electric field propagating along the +z axis in region 2; is the electric field propagating along the -z axis in region 2; S ij is the 2×2 scattering tensor in the form of Jones matrix of electromagnetic waves transmitted from air to human body, is the scattering matrix, S 11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient.

6. According to claim 5, a method for designing an efficient bioelectronic wireless transmission system, It is characterized in that The reflection coefficient S 11 and S 22 Need to meet: S 11 =S 22 =0; To match the wave impedance difference between air and human body, the reflection-free transmission of electromagnetic waves is realized; and the transmission coefficient S 12 and S 21 Need to meet: To ensure the conservation of local power flux, where η 1 is the wave impedance of air, η 2 is the wave impedance of human tissue, and Φ is the transmission phase generated by the metasurface.

7. According to claim 4, a method for designing an efficient bioelectronic wireless transmission system, It is characterized in that The parameters of the super surface in S2 include operating frequency, plate parameters, and interlayer thickness.

8. According to claim 4, a method for designing an efficient bioelectronic wireless transmission system, It is characterized in that The formula for establishing the wave matrix in S2 is: in, is the wave matrix, I is the second-order identity matrix, S 11 and S 22 is the reflection coefficient, S 12 and S 21 is the transmission coefficient, is the wave matrix of the ith metasurface, and the area where the electromagnetic wave enters the metasurface is defined as area 1, and the area where the electromagnetic wave exits the metasurface is defined as area 2. is the electric field propagating along the +z axis in region 1; is the electric field propagating along the -z axis in region 1; is the electric field propagating along the +z axis in region 2; is the electric field propagating along the -z axis in region 2.

9. According to claim 4, a method for designing an efficient bioelectronic wireless transmission system, It is characterized in that The specific expression of the ideal electromagnetic response required to achieve each layer of the metasurface is obtained by wave matrix in S2: in, is the wave matrix of the ith metasurface, Yi is the 2×2 admittance value representing the ideal electromagnetic response of the metasurface Ti is the 2×2 transmission matrix of the material interface r and t are the Fresnel reflection and transmission coefficients, η i is the incident wave impedance on the patterned metal metasurface, is the phase delay caused by passing through the dielectric substrate, is the tensor product symbol.

10. The method for designing an efficient bioelectronic wireless transmission system according to claim 4, It is characterized in that The model expression for extracting the electromagnetic response of each layer of the metasurface separately in S5 is: Among them, Yi is the admittance value representing the electromagnetic response of the single-layer metasurface; S 11 is the extracted reflection coefficient of the single-layer metasurface, I is the second-order unit matrix, η in is the wave impedance at the incident end of the electromagnetic wave, η tr is the wave impedance at the output end of the electromagnetic wave.

Images