Electrical Characterization and Modelling of an Ultrasound-Powered Triboeletric Generator for Implantable Applications

This paper reports on a method of exhaustive electrical characterization for biocompatible triboelectric nanogenerator (TENG) powered by ultrasound (US). The method is applied to a device made by stacking a $3 \times 3 \text{cm}^{2}$ copper electrode and a dielectric layer made of polyether ether ketone (PEEK). The device is submitted to 20 kHz US illumination, through a medium of medical US gel. Using a synchronous detection technique, the dynamic capacitance variation of the device is measured. The short-circuit current of the device is also measured in the same conditions. The impact of the gap variation between the probe and the dielectric layer on the electrical model is investigated. We use the results to fit an electrical dipole model of the US-driven TENG, which consists in the series connection of a variable capacitance $C_{\text{t}}$ with a DC voltage source $V_{\text{TE}}$. At a fixed 5 mm gap, the mean of $C_{t}$ was measured as 260.1 pF, and its amplitude as 9.8 pF. We also estimated $V_{\text{TE}}=82 \text{V}$ from these measurements. The power versus resistive loading is also measured, and is compatible with the electrical model which predicts an optimal loading of $23.8 \text{k} \Omega$. The corresponding power is measured as $0.83 \mu \text{W}$. The accurate electrical modeling method reported in this work will enable the design of battery-less implantable medical devices (IMDs) powered by US-driven TENG.