A KNN composite-based piezoelectric helix for ultrasonic transcutaneous energy harvesting

Abstract

Ultrasonic energy harvesting has been developed as a promising power solution for implantable medical devices (IMDs) to perform tasks such as diagnosis, therapy, and monitoring. However, most current ultrasonic electronics use toxic lead-based piezoelectric materials (e.g., lead zirconate titanate) as core components and feature bulk or flat structures, representing common barriers to the development of future IMDs that should be eco-friendly and long-term fixation in the implanted position. Here, we present a KNN composite-based lead-free piezoelectric helix for ultrasonic transcutaneous energy harvesting. The device contains multilayer components (a matching layer, lead-free composites, a copper foil, and a Parylene-C film) to form a final self-supporting helix harvester, which can adapt to cylindrical objects (e.g., blood vessels) to maintain fixation. Nanodomain-induced high-performance (d33 ∼ 465 pC N−1) KNN ceramic was fabricated and further processed into 1–3 composites to enhance electromechanical coupling properties and mechanical flexibility. The developed prototype can be excited ultrasonically to generate adjustable power output up to ∼22.97 mW cm−2. The generated electricity was stored in capacitors and used to operate light-emitting diodes. Further ex vivo tests showed that the device is still sufficient to support wireless energy transfer through porcine tissues, demonstrating the great potential of the lead-free piezoelectric helix for IMDs.