A novel phase-difference transcranial alternating current stimulation system enables precise dual-site...

Precise modulation of large-scale brain networks requires neuromodulation technologies capable of delivering frequency-locked stimulation with accurate and stable inter-regional phase control. However, conventional transcranial alternating current stimulation (tACS) systems generally lack robust dual-channel phase regulation and are rarely validated under realistic biological impedance conditions. Here, we present a novel phase-difference tACS system (PD-stim) designed to deliver programmable, high-precision phase offsets between stimulation targets. We performed a comprehensive engineering and in vivo validation of PD-stim, assessing biological impedance stability, waveform fidelity, amplitude stability, and phase-delivery accuracy. Impedance measurements obtained from the medial prefrontal cortex and hippocampus of rats demonstrated stable frequency-dependent profiles during stimulation. Benchmark comparisons against a clinically approved tACS device revealed comparable waveform fidelity and amplitude stability under both a standardised resistive load and in vivo recording conditions. Using simultaneous dual-channel oscilloscope recordings, PD-stim consistently generated stable sinusoidal waveforms with high phase-delivery accuracy across theta (8 Hz), beta (20 Hz), and gamma (40 Hz) frequency bands, under both biological and resistive conditions. Together, these results establish PD-stim as a precise, stable, and biologically robust dual-site neuromodulation platform that overcomes key technical limitations of existing tACS systems. This work provides a rigorously validated engineering framework for future mechanistic investigations of phase-specific modulation in distributed brain networks, while not addressing functional or therapeutic outcomes.