A Portable Electrical Stimulation System with User Interface for Multiple tVNS Treatment

The importance of electrical stimulation has been growing recently given the progress of electrophysiology. The popularization of smart devices and the ability to minimize hospital instruments has led to the new generation of home healthcare. In this study, an onboard system of electrical modulation for transcranial direct current stimulation (tDCS) and transcutaneous vagus nerve stimulation (tVNS) treatment is proposed. The waveform patterns and parameters are designed to cover the major usage of state-of-the-art papers on and devices for tDCS and tVNS. Three modes of tDCS and monophasic/biphasic waveforms are realized for the treatment. Using Bluetooth, the stimulation device wirelessly communicates with the user interface application developed on iOS devices. The frequency of stimulation can be set from 0.1 Hz to 750 Hz with a 0.1 Hz scale. The current amplitude, tested on a $1 \mathrm{~K} \Omega$ with 1-ms stimulations, can range from 0 to 19 mA with a $5 \mu \mathrm{~A}$ step. The duration ranges from $50 \mu \mathrm{~s}$ to $5000 \mu \mathrm{~s}$ with a $10 \mu \mathrm{~s}$ scale. The safety issue is secured with a monitoring unit circuit and careful selection of electrodes. A transcutaneous auricular vagus nerve stimulation (taVNS) test is performed with a portable prototype of the proposed system to verify the stimulation function and demonstrate the scenario of a feasible product which can fit into an earpiece. The analysis of collected data shows an alignment with related research.