Arbitrary Waveform Multi-Lead Temporal Interference Stimulation

Temporal interference stimulation (TIS) is used as a spatially selective tool for electrical deep brain stimulation in research applications. Despite its advantages over conventional stimulation methods, most of the current TIS systems are constrained by their reliance on only two leads and purely sinusoidal signals. Multi-lead and arbitrary waveform TIS may provide enhanced control over the stimulation location in a 2D plane or 3D space and the stimulation efficiency, respectively. This paper presents a novel therapeutic system for multi-lead arbitrary waveform TIS. The system uses a Direct Digital Synthesis (DDS) integrated circuit (IC) as a signal generator and a voltage-controlled constant current source, based on a Howland current pump, as an output stage to generate arbitrary signals. A frequency range from 100Hz to 1.5MHz (with a current gain of −3dB point at 1.5MHz into a 10kΩ load) and a current range from 0 to 80mA were achieved. This performance enables, for example, the generation of rectangular interference pulses with a duration of 10µs using five harmonics. This is a substantial increase over commonly used signal sources in TIS research, which typically operate at maximum frequencies between 20kHz and 400kHz. The system was evaluated in an in vitro experiment using a saline solution to characterize the interference patterns generated by three channels. The results obtained were in line with simulations and confirmed the system's capability to produce consistent and spatially precise temporal interference (TI) patterns in a 2D plane. Combined with the arbitrary waveform capacity, the system has high potential for advanced electrical therapies with TIS beyond deep brain stimulation, such as nerve, muscle, or cardiac stimulation.