Optimization method of energy transmission efficiency in electromagnetic induction wireless energy transmission system

Abstract

The present invention belongs to the technical field of medical implant devices, and is specifically a method for optimizing the energy transmission efficiency in an electromagnetic induction wireless energy transmission system for a cardiac pacemaker. In the electromagnetic induction wireless energy transmission system of the present invention, the transmitting coil adopts a planar spiral coil structure, the receiving coil adopts a spiral tube structure, and the receiving coil is wound on the side of the cardiac pacemaker; the present invention finds the various parameters of the wireless energy transmission system when the transmitting coil and the receiving coil are aligned through theoretical calculation of the energy transmission efficiency in the system and simulation based on the three-dimensional simulation software HFSS: the geometric shape of the transmitting coil, the distance between the transmitting coil and the surface of the human tissue, analyzes the influence of these parameters on the energy transmission efficiency, and verifies the simulation results through experiments; the method of the present invention can conveniently and quickly obtain the key parameter values ​​of the transmitting and receiving coils to maximize the energy transmission efficiency; it can provide a reference for the design of wireless energy transmission systems for such medical implant devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of medical implant devices, and in particular relates to a method for optimizing energy transmission efficiency in an electromagnetic induction wireless energy transmission system for a cardiac pacemaker. Background Art

[0002] In recent years, wireless energy transmission technology has been a hot topic of research for scholars at home and abroad. Its research results can be widely used in household appliances, electric vehicles and human implant devices, especially in the application of human implant devices. When the power of current pacemakers is exhausted, the original pacemaker is replaced with a new one through a secondary operation, which brings double pain and burden to the patient both physiologically and economically. In order to solve the battery power problem, the present invention proposes a design and implementation method of electromagnetic induction wireless energy transmission to charge the battery in the pacemaker, thereby extending the service life of the device. Summary of the invention

[0003] The purpose of the present invention is to provide a method for optimizing the energy transmission efficiency in an electromagnetic induction wireless energy transmission system for a medical implant device (cardiac pacemaker).

[0004] In the electromagnetic induction wireless energy transmission system of the present invention, the transmitting coil adopts a planar spiral coil structure (such as a mosquito coil shape), the receiving coil adopts a spiral tube structure, the receiving coil is wound around the side of the pacemaker, the geometric shape and placement position of the pacemaker are determined, the coil radius of the receiving coil, and the distance between the receiving coil and the human body surface are also determined accordingly. This is more conducive to conveniently and quickly designing and optimizing the wireless energy transmission system.

[0005] The present invention summarizes an optimization scheme for improving transmission efficiency through theoretical analysis and simulation based on three-dimensional simulation software HFSS. Specifically, by using theoretical calculation of energy transmission efficiency in electromagnetic induction wireless energy transmission system and simulation with three-dimensional simulation software HFSS, various parameters of the wireless energy transmission system are found when the transmitting coil and the receiving coil are aligned; these parameters include: the geometric shape of the transmitting coil, the distance between the transmitting coil and the surface of human tissue, etc., and the influence of these parameters on the energy transmission efficiency is analyzed, and the simulation results are verified by experiments.

[0006] The present invention provides a method for optimizing transmission efficiency in a wireless energy transmission system for medical implant devices, the process of which is as follows: Figure 2 As shown, the specific steps are:

[0007] (1) Establishing the initial values ​​of the wireless energy transmission model: including the initial values ​​of the receiving coil geometry: coil radius R2, coil turns n2 and wire radius r2, as well as the distance d2 between the receiving coil and the surface of human tissue;

[0008] (2) Based on the transfer efficiency and energy transmission efficiency, the parameters of the wireless energy transmission model are optimized. These parameters include the inner diameter R of the transmitting coil. in , outer diameter R out , and the number of turns of the transmitting coil n1, the wire radius r1, and the distance d1 between the transmitting coil and the surface of the human tissue; the method for optimizing the parameters of the wireless energy transmission model is:

[0009] (2.1) The optimization parameter is the geometry of the transmitting coil, and the constraint condition is the geometry and size of the receiving coil;

[0010] (2.2) The optimization parameter is the distance d1 between the transmitting coil and the surface of the human tissue, and the constraint condition is the geometric shape and size of the transmitting coil and the receiving coil;

[0011] (3) The wireless energy transmission model results obtained by using simulation software optimization are verified by theoretical calculation or experimental results; specifically, a vector network analyzer is used to measure the scattering parameters (S parameters) to obtain the impedance parameters (Z parameters), and the resistance (real part of Z) and inductance (imaginary part of Z) of the coil are obtained from the Z parameters.

[0012] In step (2.1) of the present invention, the specific steps of optimizing the geometric shape of the transmitting coil are: aligning the transmitting coil with the receiving coil, fixing the position and geometric shape of the receiving coil, setting the inner diameter R of the transmitting coil in =5mm, outer diameter R out =25mm; AWG21 (0.362mm), AWG22 (0.321mm), AWG23 (0.287mm) are used to design the transmitting coil. The number of turns of the transmitting coil is 3, 4, and 5 respectively. There are 9 types of transmitting coils in total. By comparing the HFSS simulation, the receiving coil geometry with maximum energy transmission efficiency is obtained.

[0013] In step (2.2) of the present invention, the specific steps of optimizing the distance d1 between the transmitting coil and the surface of human tissue are: simulating the distance d1 = 2 mm, 3 mm, and 5 mm from the transmitting coil to the surface of human tissue respectively, and comparing the HFSS simulation results to obtain d1 at the maximum energy transmission efficiency.

[0014] In the present invention, the theoretical calculation of energy transmission efficiency in the electromagnetic induction wireless energy transmission system is derived as follows:

[0015] The circuit model and equivalent T-type diagram of the electromagnetic induction wireless energy transmission system are as follows: Figure 2 As shown in (a) and (b) in .

[0016] Assume that the inductance of the transmitting coil and the receiving coil are L1 and L2 respectively, which are connected to the power supply and the load respectively. L C1 and C 2e They are external capacitors used to generate resonance in the transmitting and receiving circuits, and C 2e Parallel C 2p is the load parasitic capacitance, M is the mutual inductance between L1 and L2, I1 and I2 are the currents in the transmitting coil and the receiving coil respectively.

[0017] According to the circuit diagram, the theoretical calculation formula for energy transmission efficiency can be obtained as follows:

[0018]

[0019] Under the condition of biological safety of wireless energy transmission (specific absorption rate limit), the theoretical calculation formula of the maximum energy released to the load is:

[0020]

[0021] in: ω is the angular frequency during operation; in the embodiment, R is set L =1kΩ.

[0022] In step (3) of the present invention, the wireless energy transmission model result obtained by optimizing the simulation software, and optimizing the simulation program, is verified by theoretical calculation or experimental results, specifically, using a vector network analyzer, by measuring the scattering parameters (S parameters) to obtain the impedance parameters (Z parameters), and the resistance (real part of Z) and inductance (imaginary part of Z) of the coil are obtained from the Z parameters. By constructing a system circuit, using a signal generator to provide power, measuring the power at both ends of the load, solving the energy transmission efficiency of the circuit system, and lighting up the light-emitting diode.

[0023] The specific steps are as follows: the coil is connected to the vector network analyzer through a pair of threaded pinhole connectors (SMA), and the de-embedding calibration method is used to reduce the influence of the magnetic interference generated by the SMA connector on the experimental results (reference: H.Choand D.Burk, "A three-step method for the de-embedding of high-frequency S-parameter measurements," IEEE Trans.Electron Devices, vol.38, no.6, pp.1371–1375, Jun.1991); this method subtracts the parasitic parameters generated by the measurement fixture from the measurement of the original device under test; the original S parameter measured is represented by S dut , which can be converted into the admittance parameter Ydut , the relationship is as follows:

[0024] Y dut =(G0-S dut )(Z0·S dut +Z0) -1 ; (3)

[0025] Among them, G0 is the unit matrix, Z0 is the characteristic impedance matrix of each port, expressed as 50G0;

[0026] Similarly, the S obtained by opening and shorting the coil short and S open Convert to Y short and Y open ; After removing parasitic capacitance coupling and self-capacitance, the system's admittance parameter Y parameter is expressed as:

[0027] Y=[(Y dut -Y open ) -1 -(Y short -Y open ) -1 ] -1 , (4)

[0028] Convert the obtained Y parameter to Z parameter (Z = Y -1 ).

[0029] Through the Z parameter, we can get the physical quantities such as the resistance and inductance of the coil, and the mutual inductance coefficient M. In this way, all the physical quantities in equations (1) and (2) can be obtained, so that the energy transmission efficiency and the maximum energy released to the load can be calculated.

[0030] The method of the present invention can conveniently and quickly obtain the key parameter values ​​of the sending and receiving coils, thereby maximizing the transmission efficiency.

[0031] The present invention provides an efficient and convenient design scheme for wireless energy transmission of medical implant devices, and provides a useful reference for the design of wireless energy transmission systems of such medical implant devices.

[0032] As an application example, an energy transmission system with a spacing of 2 mm between the transmitting coil and the surface of human tissue is optimized (in most cases, the spacing between the transmitting and receiving coils of medical implants is about 20 mm. In the present invention, the distance between the transmitting coil and the surface of human tissue is 2 mm, and the distance between the receiving coil and the surface of human tissue is 10 mm. The receiving coil is wound around a pacemaker with a thickness of 8 mm in a spiral tube structure. The spacing between the transmitting coil and the receiving coil is similar to the common spacing), and key parameters such as the transmitting coil geometry that produces the maximum energy transfer efficiency value and the spacing between the transmitting coil and human tissue are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A side view of the wireless energy transfer system in HFSS and a bird's-eye view of the transmitter and receiver coils.

[0034] Figure 2 The circuit model and equivalent T-type diagram of the electromagnetic induction wireless energy transmission system. Among them, (a) is the circuit model, and (b) is the equivalent T-type diagram.

[0035] Figure 3 Design an optimized flow chart for wireless energy transfer system.

[0036] Figure 4 It is the energy transfer efficiency of the wireless energy transfer system under different geometric shapes of the transmitting coil.

[0037] Figure 5 It is the energy transfer efficiency at different distances between the transmitting coil and the surface of human tissue after determining the geometric shapes of the receiving coil and the transmitting coil.

[0038] Figure 6 is the SAR size on the surface of human tissue.

[0039] Figure 7 It is the temperature rise of human tissue around the receiving coil.

[0040] Figure 8 The LED is successfully lit. DETAILED DESCRIPTION

[0041] For the implantable wireless energy transmission system, the present invention uses HFSS simulation software or theoretical calculation formulas to obtain the energy transmission efficiency under different conditions.

[0042] Figure 3 Design an optimized flow chart for wireless energy transfer system.

[0043] The specific steps are:

[0044] (1) First, since the design flexibility of the receiving coil is relatively low, the present invention adopts the method of winding the coil around the side of the pacemaker for design, so the geometric parameters of the receiving coil are greatly affected by the pacemaker. The pacemakers on the market are mainly Medtronic, and Medtronic pacemakers represent the highest level of the entire industry. The length of Medtronic pacemakers is within 42.9-52.3mm, the width is generally 40.2-45.4mm, and the height is about 8mm. The present invention uses a cylindrical shell of titanium material with a radius of 20mm and a height of 8mm to replace the pacemaker for simulation and experiment. The titanium shell is placed 10mm below the skin surface to simulate the pacemaker placed in human tissue, so the radius of the receiving coil is the radius of the titanium shell, 20mm;

[0045] The receiving coil is wound with AWG23 (0.287mm) copper wire, and the copper wire is wound with 5 turns at equal intervals on the side of the titanium shell to form a solenoid structure as the receiving coil. The placement position of the receiving coil is determined according to the placement position of the pacemaker in the human body, that is, the distance d2 between the receiving coil and the surface of the human tissue is 10mm. In order to avoid direct contact between the copper wire and the human tissue, the present invention uses an epoxy resin material with good biocompatibility to wrap the copper wire, which not only blocks the direct contact between the receiving coil and the titanium shell, but also avoids the direct contact between the receiving coil and the human tissue.

[0046] (2) After determining the shape and position of the receiving coil, the transmitting coil is designed. The size and position of the transmitting coil are relatively flexible and can be designed to a larger size. The transmitting coil adopts a spiral structure with equal spacing. The outer radius of the transmitting coil is 25mm and the inner radius is 5mm. Three sizes of copper wire, AWG21 (0.362mm), AWG22 (0.321mm), and AWG23 (0.287mm), are used to design the transmitting coil. The number of turns of the transmitting coil is 3, 4, and 5 respectively. There are a total of 9 types of transmitting coils. The HFSS optimization simulation obtains the performance comparison of the transmitting coil under 9 conditions, thereby determining the geometric shape of the receiving coil. Figure 4 It is found that when n1=5 and r1=0.362 mm, the energy transmission efficiency is always the highest. Therefore, the present invention selects n1=5 and r1=0.362 mm as the transmitting coil parameters, and the geometric shape of the transmitting coil is determined.

[0047] (3) After the outer diameter, inner diameter, number of turns and copper wire radius of the transmitting coil are determined, the present invention also simulates and optimizes the position of the transmitting coil. The position of the receiving coil under the skin is limited by the pacemaker. In the present invention, the distance between the receiving coil and the surface of human tissue is fixed at 10 mm, and the simulated pacemaker is installed 10 mm below the surface of the human body, d2 = 10 mm. The distance from the transmitting coil to the skin has a high degree of flexibility. The central axes of the transmitting coil and the receiving coil coincide, so the distance from the transmitting coil to the surface of human skin can be adjusted to optimize the simulation. The present invention simulates the distance from the transmitting coil to the surface of human tissue d1 = 2 mm, 3 mm, and 5 mm, respectively. Figure 5It is found that when d1=2mm, the wireless charging system always has the highest transmission efficiency and energy transmission efficiency in the simulations of the three distances. At the same time, the simulation can show the general trend of the change in the transmission efficiency of wireless energy transmission. The closer the distance between the transmitting coil and the skin surface, the higher the transmission efficiency. Considering that in practical applications, a certain distance needs to be maintained between the transmitting coil and human tissue, the present invention selects d1=2mm as the distance from the transmitting coil to the skin surface. Therefore, the shape, size and position of the transmitting coil can be determined. The transmitting coil is a spiral structure with an inner radius of 5mm and an outer radius of 25mm. The 5 turns of the coil are equally spaced. The center of the transmitting coil is aligned with the center of the titanium shell and is placed parallel to the skin surface. The transmitting coil is placed in the air at d1=2mm from the skin surface.

[0048] (4) Safety verification: Taking 20MHz as an example, simulations were performed in HFSS and icepak to obtain the SAR of the human skin surface and the temperature of the human tissue around the receiving coil. Figure 6 As shown in the figure, the highest SAR value on the human body surface is 2.84W / kg, which is always lower than the safe value of 2.89W / kg. Figure 7 As shown, at 20MHz, the human body base temperature is set to 36.5°C, and the 1.09A current simulation of the transmitting coil finally obtains the highest temperature around the transmitting coil of 38.71°C, which is within the safe range that the human body can bear. Therefore, the design of the present invention meets the safety standards.

[0049] (5) Scientific verification: The comparison between simulation results and experimental results is based on the same calculation formula. Table 1 compares the differences between simulation results and experimental results by using the Z parameter. The four sets of data are all obtained at 20MHz, including simulation data and experimental data in air environment and simulation data and experimental data in muscle environment. After comparison, the simulation data and experimental data are basically consistent.

[0050] Table 1

[0051]

[0052] According to the measured Z parameter, the above calculation method is used to calculate and compare the important parameters, as shown in Table 2. The experimental results are basically consistent with the simulation results. Under the condition of 20MHz, the transmission efficiency in the air environment in the simulation and experiment is 36.77% and 35.20% respectively, and the transmission efficiency in the muscle environment in the simulation and experiment is 33.92% and 32.90% respectively. In particular, considering the SAR safety and temperature safety, the input current of 1.09A is selected in the muscle environment, and the final power obtained in the experiment is 263.58mW, which is close to 313.31mW in the simulation.

[0053] Table 2

[0054]

[0055] In order to further verify the scientific nature of the wireless energy transmission system, the present invention constructs a circuit system, which mainly includes a signal generator, a compensation circuit, a wireless energy transmission structure, and a receiving end load. The signal generator provides power to solve the energy transmission efficiency of the wireless energy transmission system. The maximum frequency of the selected signal generator is 10MHz, so the circuit experiment is carried out at 10MHz. A bridge rectifier circuit is added to the receiving circuit, and a 1000Ω load is connected in series. Then, the following formula is used to solve the transmission efficiency. The energy transmission efficiency is finally obtained in the experiment. The energy transmission efficiency is 18.70%, which is close to the simulated transmission efficiency of 16.99%. The scientific nature of the wireless energy transmission system can be proved, see Table 3. The 1000 ohm load is changed to a light-emitting diode, and it is finally successfully lit up, see Figure 8 .

[0056]

[0057]

[0058]

[0059] Table 3

[0060] simulation experiment <![CDATA[R1]]> 0.2654Ω 0.2489Ω <![CDATA[R ref ]]> 0.5515Ω 0.6204Ω <![CDATA[R' L ]]> 0.7991Ω 0.8034Ω η 16.99％ 18.70％

Claims

1. A method for optimizing energy transmission efficiency in an electromagnetic induction wireless energy transmission system for a cardiac pacemaker, characterized in that: In the electromagnetic induction wireless energy transmission system, the transmitting coil adopts a planar spiral coil structure, the receiving coil adopts a spiral tube structure, the receiving coil is wound around the side of the pacemaker, the geometric shape and placement position of the pacemaker are determined, and the coil radius R2 of the receiving coil and the distance between the receiving coil and the human body surface are also determined accordingly; this is conducive to convenient and quick design and optimization of the wireless energy transmission system; Through theoretical analysis and simulation based on 3D simulation software HFSS, an optimization solution to improve transmission efficiency is summarized; Specifically, the various parameters of the wireless energy transmission system when the transmitting coil and the receiving coil are aligned are found by using the theoretical calculation of the energy transmission efficiency in the electromagnetic induction wireless energy transmission system and the three-dimensional simulation software HFSS simulation; These parameters include: the geometric shape of the transmitting coil, the distance between the transmitting coil and the surface of human tissue, and the impact of these parameters on the energy transmission efficiency is analyzed, and the simulation results are verified through experiments; the specific steps are: (1) Establishing the initial values ​​of the wireless energy transmission model: including the initial values ​​of the receiving coil geometry: coil radius R2, coil turns n2 and wire radius r2, as well as the distance d2 between the receiving coil and the surface of human tissue; (2) Based on the transfer efficiency and energy transmission efficiency, the parameters of the wireless energy transmission model are optimized. These parameters include the inner diameter R of the transmitting coil. in , outer diameter R out , the number of turns of the transmitting coil n1, the wire radius r1, and the distance d1 between the transmitting coil and the surface of the human tissue; the method for optimizing the parameters of the wireless energy transmission model is: (2.1) The optimization parameter is the geometry of the transmitting coil, and the constraint condition is the geometry and size of the receiving coil; (2.2) The optimization parameter is the distance d1 between the transmitting coil and the surface of the human tissue, and the constraint condition is the geometric shape and size of the transmitting coil and the receiving coil; (3) Using simulation software to optimize the wireless energy transmission model results, and verifying the simulation software optimization results with theoretical calculations or experimental results. Specifically, using a vector network analyzer, the Z parameter is obtained by measuring the S parameter, and the resistance of the coil, i.e., the real part of Z, and the inductance, i.e., the imaginary part of Z, are obtained from the Z parameter. Here, the S parameter is a scattering parameter, and the Z parameter is an impedance parameter. The theoretical calculation formula of energy transmission efficiency in the electromagnetic induction wireless energy transmission system is as follows: Assume that the inductance of the transmitting coil and the receiving coil are L1 and L2, respectively, which are connected to the power supply and the load; R1, R2 and R L are the resistances of the transmitting coil, receiving coil and load respectively; C1 and C 2e They are external capacitors used to generate resonance in the transmitting and receiving circuits, and C 2e Parallel C 2p is the load parasitic capacitance, M is the mutual inductance between L1 and L2, I1 and I2 are the currents in the transmitting coil and the receiving coil respectively; the theoretical calculation formula for energy transfer efficiency is: In the case of biological safety of wireless energy transmission, the theoretical calculation formula for the maximum energy released to the load is: in: ω is the angular frequency during operation; In step (3), the simulation software is used to optimize the wireless energy transmission model result, and the optimization result of the simulation software is verified by theoretical calculation or experimental results; the vector network analyzer is used to measure the S parameter to obtain the Z parameter, and the resistance of the coil, i.e., the real part of Z, and the inductance, i.e., the imaginary part of Z, are obtained from the Z parameter; the specific steps are: the coil is connected to the vector network analyzer through a pair of threaded pinhole connectors, and the de-embedded calibration method is used to reduce the influence of the magnetic interference generated by the threaded pinhole connector on the experimental results; the parasitic parameters generated by the measuring fixture are subtracted from the measurement of the original device under test; the original S parameter obtained by measurement is represented as S dut , which can be converted into the admittance parameter Y dut , the relationship is as follows: Y dut =(G0-S dut )(Z0·S dut +Z0) -1 ; (3) Among them, G0 is the unit matrix, Z0 is the characteristic impedance matrix of each port, expressed as 50G0; Similarly, the S parameters S obtained by opening and shorting the coil are short and S open Converted into admittance parameter Y short and Y open ; After removing parasitic capacitance coupling and self-capacitance, the system's admittance parameter Y parameter is expressed as: And=[(And dut -AND open ) -1 -(AND short -AND open ) -1 ] -1 , (4) Convert the obtained Y parameter to Z parameter: Z = Y -1 ; Through the Z parameter, the resistance and inductance of the coil are obtained, and the mutual inductance coefficient M is obtained; therefore, the energy transmission efficiency and the maximum energy released to the load can be calculated through equations (1) and (2).

2. The method for optimizing energy transmission efficiency according to claim 1, characterized in that: In step (2.1), the specific steps of optimizing the geometric shape of the transmitting coil are: aligning the transmitting coil with the receiving coil, fixing the position and geometric shape of the receiving coil, and setting the inner diameter R of the transmitting coil in =5mm, outer diameter R out =25mm; AWG21, AWG22, and AWG23 copper wires are used to design the transmitting coils, and the number of turns of the transmitting coils are 3, 4, and 5 respectively. There are a total of 9 types of transmitting coils. By comparing the HFSS simulation, the receiving coil geometry with the maximum energy transmission efficiency is obtained.

3. The method for optimizing energy transmission efficiency according to claim 2, characterized in that: In step (2.2), the specific steps for optimizing the distance d1 between the transmitting coil and the surface of human tissue are: simulating the distance d1 = 2 mm, 3 mm, and 5 mm from the transmitting coil to the surface of human tissue respectively, and comparing the HFSS simulation results to obtain d1 at the maximum energy transmission efficiency.

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