Design of a Multi-layered On-chip Wireless Power Transfer (WPT) System Design for Brain Neuromodulation Applications

Chronic pain is a common disease and as a negative consequence can cause paralysis to an individual in the long run. Noninvasive brain stimulation is an effective method to reduce pain in the short term. However, for long-term treatment, neural data analysis along with the stimulation is highly desirable. In this work, a unique multilayer spiral coil with a total dimension of 500 μm×500 μm is designed in a 0.5 μm CMOS process to make it suitable for a fully implantable system. The electrical modeling of the coil is also analyzed and simulated using Keysight's Advanced Design System (ADS) software to compare the theoretical modeling results with the simulation results. The electromagnetic (EM) simulation to characterize the on-chip coil in-terms of scattering parameters (S-parameters), Q-factor, power transfer efficiency (PTE) is performed using the Ansys High-Frequency Structure Simulator (HFSS) software. The operating frequency of the WPT system is chosen to be within 402-405 MHz which is the Medical Implant Communication System (MICS) band. The simulated Q-factor of the proposed on-chip coil is approximately 15 at 402 MHz. The on-chip coil is integrated with an on-chip seven-stage rectifier and some commercial off-the-shelf (COTS) components such as a DC-DC converter and a μ LED to design the complete optogenetic neuro-stimulation system. A minimum power transfer efficiency (PTE) of 0.4% is achieved through a 16 mm thick tissue media using the proposed WPT system. With that efficiency, the proposed system is able to provide constant power to light up a μ LED and proves to be a good candidate for neuromodulation applications.