Pulse Density Modulation for Wireless Transfer of Power and Waveforms to Nanorectenna-based Closed-loop Neurostimulator

A non-linear model of a nanorectenna-based closed-loop neurostimulator employing pulse density (PD) modulation is proposed. Using an integrated design of the neurostimulator operating in the sub-Terahertz (sub-THz) band, radiative wireless power transfer from an external source is achieved while generating desired waveforms in the implant, simultaneously. The paper presents the steady-state bound on the rectenna’s harvested DC waveform which is used for either neuromonitoring or neuromodulation in a closed-loop neurostimulator when unmodulated or modulated PD sub-THz signal is transmitted, respectively. The theoretical design is validated with circuit simulations using a W-band nano-Schottky diode-based rectenna which demonstrates that a unipolar PD modulation is an effective signaling scheme to jointly implement the wireless transfer of constant power and desired waveform in both modes of operations in a closed-loop neurostimulator.