Design and Optimization of Planar Spiral Coils for Powering Implantable Neural Recording Microsystem

Abstract

This paper presents a design and optimization method utilizing inductive coupling coils for wireless power transfer in implantable neural recording microsystems, aiming at maximizing power transfer efficiency, which is essential for reducing externally transmitted power and ensuring biological tissue safety. The modeling of inductive coupling is simplified by combining semi-empirical formulations with theoretical models. By introducing the optimal resonant load transformation, the coil optimization is decoupled from an actual load impedance. The complete design optimization process of the coil parameters is given, which takes the maximum theoretical power transfer efficiency as the objective function. When the actual load changes, only the load transformation network needs to be updated instead of rerunning the entire optimization process. Planar spiral coils are designed to power neural recording implants given the challenges of limited implantable space, stringent low-profile restrictions, high-power transmission requirements and biocompatibility. The modeling calculation, electromagnetic simulation and measurement results are compared. The operating frequency of the designed inductive coupling is 13.56 MHz, the outer diameter of the implanted coil is 10 mm and the working distance between the external coil and the implanted coil is 10 mm. The measured power transfer efficiency is 70%, which is close to the maximum theoretical transfer efficiency of 71.9%, confirming the effectiveness of this method.

Loss-Optimized Design of Magnetic Devices

“…The planar helical coils of implantable neural recording microsystems comprise PCB and copper foil magnetic devices, and the extended theory can optimize their design effectively. Its AC resistance model can be incorporated into the proposed optimization method, and the model is presented below [ 11 , 44 ]: …”

“…In the realm of power electronics, devices like transformers and inductors facilitate the conversion of electrical energy [ 1 ] and provide electrical isolation, which is integral to power supply systems [ 2 , 3 , 4 ], micro-electro-mechanical systems [ 5 , 6 ], and electric vehicles [ 7 , 8 ]. Additionally, magnetic devices form the core of sensors [ 9 , 10 ] and implantable neural recording microsystems [ 11 ].…”