Analog Self-Synchronized Switching Technique for Stable High-Frequency Electromagnetic AC Stimulation in Neurorehabilitation

Electromagnetic alternating current (AC) stimulation, a key application of applied electromagnetics, is a non- invasive neuromodulation technique that delivers low-intensity oscillating electric fields to the brain via scalp electrodes. Conventional microcontroller (MCU)-based devices face computational loads that compromise stability at high frequencies. We propose an analog self-synchronized switching algorithm where the MCU only controls the DAC, while an analog circuit autonomously manages switching. A system based on an ATmega328p (50 samples/cycle, n=10) was implemented to compare both methods. The proposed algorithm improved the maximum frequency by 62% (to 1,250 Hz). In the 500Hz-1.25kHz high-frequency band, the proposed method showed statistically superior SNR (p < 0.002). Notably, at 1.1 kHz, the SNR with the proposed method was 9.67 dB higher. The proposed method's mean SNR in this band was higher and significantly more stable (33.069 ±1.201 dB vs 25.406 ±2.886 dB). Our algorithm improves high-frequency stability and reduces MCU burden, providing a robust foundation for multi-channel systems. It is believed that the developed tool will make a meaningful contribution to the advancement of rehabilitation medicine and neuromodulation research.