Flexible MNG-MNZ metamaterial array design method for wireless energy supply system of implantable device

Abstract

The invention discloses a flexible MNG-MNZ metamaterial array design method for an implantable device wireless energy supply system, a flexible metamaterial array takes polyimide as a substrate and is composed of n * n metamaterial elements, an MNZ element is arranged on the outer side, an MNG element is arranged on the inner side, the MNG element has negative magnetic conductivity, and the MNZ element has zero magnetic conductivity. The method comprises the following steps: firstly, determining the size of a metamaterial array and the number of elements through the position of an implantable device, and further adjusting the line width, turn spacing, turn number, coil gap and other parameters of a metal spiral, so that the quality factor of each element in the working frequency is optimal; and finally, the external capacitor of the element is adjusted to enable the element to present the required magnetic conductivity, and the flexible MNG-MNZ metamaterial array is formed. By adopting the method, the flexible MNG-MNZ metamaterial array for the wireless power transmission system of the implantable device is designed, and the energy transmission efficiency and the electromagnetic safety of the system are obviously improved while the flexible MNG-MNZ metamaterial array is attached to the human body.

Description

Technical Field

[0001] The present invention relates to the field of wireless power transmission for implantable devices, and particularly to a design method for a flexible MNG-MNZ metamaterial array for a wireless power supply system of implantable devices. Technical Background

[0002] With the progress of modern medical standards, implantable devices such as implantable brain pacemakers and implantable cardiac pacemakers have become important medical means for treating some major diseases and maintaining the normal vital signs of patients, which can reduce the risk of patient death. Most existing treatment plans choose permanent implantation of medical devices. However, the built-in battery of implantable devices has a limited working life, and a second operation is required when replacing the battery, bringing additional intraoperative infection risks and complications to patients. Using wireless power transfer (WPT) technology to supply energy to implantable devices from outside the body has become an important means to ensure the long-term stable operation of implantable devices, avoid second operations on patients, and reduce medical costs. Due to certain limitations of WPT technology, such as low energy transfer efficiency, high sensitivity to external disturbances, and electromagnetic radiation to the human body. How to quickly, efficiently, and safely charge implantable devices from outside the body has become an urgent problem to be solved.

[0003] Chinese invention patent CN202410183166.5 discloses a flexible metamaterial for improving low-frequency wireless charging efficiency, its preparation method and application. The flexible metamaterial described in this patent is composed of a square spiral coil in series with a lumped capacitor and has a negative magnetic permeability. However, it fails to consider the negative impact of electromagnetic radiation on the human body while improving the charging efficiency. Chinese invention patent CN202210807796.6 discloses a metamaterial array structure for enhancing the signal-to-noise ratio of 0.1T ultra-low-field MRI. The main purpose of the metamaterial array described in this patent is to enhance the imaging signal-to-noise ratio and obtain a clearer MRI image, but it has no obvious effect on improving the charging efficiency of the wireless power transmission system. Chinese invention patent CN202210225527.9 discloses an implantable cardiac pacemaker wireless power supply device based on electromagnetic metamaterials. The metamaterial array in the device described in this patent improves the energy transfer efficiency of the system to a certain extent, but its metamaterial array cannot conform to the human body and has certain limitations. Based on the above problems, the present invention starts from improving the degree of conformity of the metamaterial to the human body, enhancing the wireless power transmission efficiency of implantable devices, and reducing electromagnetic radiation, and proposes a design and optimization method for a flexible MNG-MNZ metamaterial array. Summary of the Invention

[0004] The object of the present invention is to provide a design method for a flexible MNG-MNZ metamaterial array for a wireless power supply system of an implantable device. The inner array of the metamaterial is composed of negative magnetic permeability (MNG) elements, and the outer side is composed of zero magnetic permeability (MNZ) elements. The structural parameters of the two types of elements are exactly the same. The metal spiral is connected to an external capacitor through a via hole, and the flexible substrate enables the metamaterial array to better conform to the human body. By adjusting the external capacitor of the metamaterial element, each element exhibits a corresponding magnetic permeability within the operating frequency, achieving the purpose of improving the system transmission efficiency and reducing electromagnetic radiation.

[0005] The technical solution of the present invention is as follows: 1. Determine a suitable flexible metamaterial area based on the differences in the organs around the implantation position of the implantable device and the local specific absorption rate (SAR) values of the human head and torso, and set the substrate material of the flexible metamaterial array to polyimide; 2. Divide the flexible metamaterial array into n equal parts, and determine the shape, side length, thickness of the metamaterial substrate, and outer diameter of the spiral coil of a single flexible metamaterial element; 3. Calculate the AC impedance, equivalent capacitance, and coil inductance of the spiral coil. According to the principle of optimal quality factor, determine the number of turns, gap, width of the coil, and calculate the inner diameter of the coil; 4. Calculate the external capacitor required for different elements based on the resonance frequency at which the flexible metamaterial operates and the equivalent magnetic permeability of the element; 5. Arrange the elements in an n×n flexible metamaterial array with MNG elements on the inner side and MNZ elements on the outer side; 6. Establish a model to analyze the optimization effect of the flexible metamaterial array on the wireless power transmission system at different bending angles, ensuring that while the metamaterial array improves the system efficiency, it reduces the adverse effects of electromagnetic radiation on the human body.

[0006] The beneficial effect of the present invention is that a flexible MNG-MNZ metamaterial array for a wireless power transmission system of an implantable device is designed, which significantly improves the energy transmission efficiency and electromagnetic safety of the system while conforming to the human body. Description of the Drawings

[0007] Figure 1 It is a flowchart of the optimization process; Figure 2 It is a schematic diagram of a 4×4 flexible MNG-MNZ metamaterial array formed by taking a square spiral coil as an example; Figure 3 It is an equivalent magnetic permeability curve that the MNG and MNZ elements should satisfy, taking a square coil with an operating frequency of 6.78 MHz, a substrate thickness of 0.2 mm, an outer coil diameter of 13 mm, a turn pitch of 0.45 mm, a coil width of 0.55 mm, and 5 turns as an example; Figure 4 It is a corresponding relationship diagram of the quality factor of the metamaterial varying with the line width of the spiral coil; Figure 5 Taking the square spiral coil as an example, it is a simulation model of adding a flexible metamaterial array to the wireless power transmission system; Figure 6 It is a comparison diagram of the performance improvement effect of the system after adding the flexible metamaterial array. Specific implementation method The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The selected embodiment of the present invention is: the implantation position of the cardiac pacemaker is subcutaneous in the left chest cavity. The length of the flexible metamaterial array is set to 60 mm, the substrate thickness is 0.2 mm, the inner 2×2 array is composed of MNG elements, and the outer side is MNZ elements. Their arrangement is as Figure 2 shown. The side length of each element is 15 mm, and the outer diameter of the spiral coil is 13 mm. The AC impedance R S 、equivalent inductance L, and coil capacitance C of the spiral coil can be calculated by the following formulas: L = 1 . 2 7 μ 0 n 2 d a v g 2 [ l n ( 2 . 0 7 φ ) + 0 . 1 8 φ + 0 . 1 3 φ 2 ] ρ c represents the conductivity of the copper wire, φ represents the filling factor of the metal spiral coil, d avg is the average diameter of the metal spiral coil, ε rc 、ε rs are the relative dielectric constants, t is the thickness of the metal spiral coil, and l is the gap length of the metal spiral coil. The flexible metamaterial element is preset as a square spiral coil, and the number of turns and turn spacing of the coil are adjusted so that the line width and the quality factor Q satisfy the change trend of the curve as Figure 3 shown. Furthermore, the number of turns of the metal spiral coil is determined to be 5, the outer diameter d out is 13 mm, the turn spacing s is 0.45 mm, and the coil width w is 0.55 mm. Thus, the area ratio of the metal spiral coil in the element is F. At the system resonance frequency f, the external lumped capacitance C0 of the element is changed so that the element exhibits different equivalent permeabilities μ eff :

[0009] In this embodiment, polyimide is used as the substrate material of the flexible metamaterial array. The equivalent magnetic permeability of the outer MNZ element is set to μ1 = 0, and the equivalent magnetic permeability of the inner MNG element is set to μ2 = -1. The equivalent magnetic permeability of the metamaterial at the operating frequency is as Figure 4 shown. The system resonance frequency is set to 6.78 MHz. An MCR-WPT system including a flexible metamaterial array is constructed in COMSOL as Figure 6 shown, and the following comparative analyses are carried out: 1. Analyze the change in the system energy transfer efficiency after adding a flexible MNG-MNZ metamaterial array compared with an MCR-WPT system without a metamaterial; 2. Analyze the influence of adding flexible MNG-MNZ metamaterial arrays with different bending angles on the system energy transfer efficiency and the change trend of the system energy transfer efficiency; 3. Analyze the effect of adding a flexible MNG-MNZ metamaterial array on reducing the system electromagnetic radiation compared with adding an MNG metamaterial array; 4. Analyze the effect of adding a flexible MNG-MNZ metamaterial array on improving the system stability compared with an MCR-WPT system without a metamaterial when the receiving coil and the transmitting coil of the system are offset; 5. Analyze whether the system temperature change and the SAR value change are within the safe range after adding a flexible MNG-MNZ metamaterial array; 6. Summarize the feasibility and safety of the flexible MNG-MNZ metamaterial array in improving the performance of the wireless power transfer system for implantable devices.

[0010] The above are only embodiments of the present application and are not used to limit the present application. The general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of the claims of the present application.

Claims

1. A design method for a flexible MNG-MNZ metamaterial array used in a wireless power supply system for implantable devices, characterized in that, The inner array of the metamaterial with a polyimide substrate is composed of negative magnetic permeability (MNG) elements, and the outer side is composed of zero magnetic permeability (MNZ) elements. The structural parameters of the two types of elements are exactly the same. By adjusting the external capacitance of the metamaterial elements, the resonance frequency of each element is made equal to the system resonance frequency, so as to achieve the purpose of improving the system transmission efficiency and reducing electromagnetic radiation.

2. The design method of the flexible MNG-MNZ metamaterial array according to claim 1, characterized in that According to the differences in the local specific absorption rate (SAR) values of the organs around the implantation position of the implantable device in the human head and torso, determine the appropriate flexible metamaterial area, number of elements, shape of the elements, and side length of the elements.

3. The metamaterial unit according to claim 2, wherein Calculate the AC impedance, equivalent capacitance, and coil inductance of the spiral coil, and determine the outer diameter, wire width, number of turns, and gap of the spiral coil based on the principle of optimal quality factor.

4. The metamaterial unit according to claim 3, characterized in that Calculate the external capacitance of different elements according to the operating frequency of the metamaterial and the equivalent magnetic permeability of the elements, so that the MNG elements achieve negative magnetic permeability within the operating frequency, and the MNZ elements achieve zero magnetic permeability within the operating frequency.

5. The metamaterial unit according to claim 4, wherein Arrange them into an n×n flexible metamaterial array with MNG elements on the inner side and MNZ elements on the outer side.

6. The flexible MNG-MNZ metamaterial array according to claim 5, wherein Analyze the optimization effect of the flexible metamaterial array with different bending angles on the wireless power transmission system, ensure that while the metamaterial array improves the system efficiency, it reduces the adverse effects of electromagnetic radiation on the human body; evaluate the improvement effect of the flexible metamaterial array on the anti-offset performance of the system when there is an offset between the receiving coil and the transmitting coil of the system.

Images