Helmholtz Coils Based WPT Coupling Analysis of Temporal Interference Electrical Stimulation System

Abstract

Electrical nerve stimulation (ENS) is clinically important in treating neurological diseases. This paper proposes a novel temporally interfering wireless power transfer (WPT) system, based on Helmholtz coils, to address energy depletion and the miniaturization of wireless power transfer systems for implantable devices. Compared to conventional WPT systems, this paper uses Helmholtz coils with a centrosymmetric structure as the transmitting coils. A more uniform and stable magnetic field was obtained through structural improvements. It also improves the problem that changes in the receiving coil’s position affect the transmission power’s stability. Based on the principle of temporal interference (TI), two transmitting coils with a slight frequency difference generate a superposition of magnetic fields on the receiving coil and then induce a low-frequency electrical signal on it. The electrical stimulation system applies stimulation parameters of a specific intensity and frequency directly to the target nerve with electrodes connected to it. This eliminates the need for the conventional high-frequency signal to low-frequency signal processing circuitry and reduces the device’s size. In this paper, numerical calculations and an experimental verification of the proposed system are carried out. The magnetic field distribution and the receiving coil current waveform of the system were tested to verify the effectiveness and stability of the proposed design. The experimental results showed that the proposed wireless power transfer system can generate electrical signals of the desired waveform in the receiving coil. Its frequency of 10 Hz and amplitude of 42.4 mA meet the requirements for the electrical stimulation of the sciatic nerve.