A wireless ultrasound energy harvester based on flexible relaxor ferroelectric crystal composite arrays for implanted bio-electronics

Implanted bio-electronic (IBE) devices such as pacemakers and neurostimulators have become increasingly important for therapeutic and diagnostic medical purposes. The life span of the IBE batteries ranges from several months to 10 years, resulting in high costs and non-negligible risks to patients undergoing replacement surgery. Recently, implanted ultrasound energy harvesting based on the piezoelectric effect has emerged as a promising technology for wirelessly powering the IBEs. However, it is still challenging to transfer sufficient output electric power for the implanted piezoelectric ultrasonic energy harvesters (PUEHs), due to the difficulty in achieving both high piezoelectricity and flexibility in piezoelectric components. Herein, inspired by the climbing habit and the flexible distribution of green leaves along with the stems of twisted plants, we proposed a flexible helix-like PUEH by connecting high-performance Nd-doped Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) crystal based composites with stretchable electrodes to simultaneously achieve high piezoelectricity and flexibility. Owing to the ultrahigh piezoelectric performance of Nd-doped PMN-PT ferroelectric crystal based 1-3 composites, the as-developed PUEH (abbreviated as Nd-PUEH) exhibited a high output power density of 0.27 mW mm⁻³ under an input acoustic intensity of 0.3 W cm⁻², which is much higher than that of previously reported PUEHs (∼0.1 mW mm⁻²). Notably, the output voltage of the Nd-PUEH reached up to 24 V_pp, approximately 4 times higher than that of the piezoelectric ceramic composite based PUEH. In addition, experiments on transferring energy under tissue and wirelessly powering the light emitting diodes (LEDs) of the Nd-PUEH were conducted, showing outstanding powering capability and potential for implanted energy harvesters. This work may benefit the development of multifunctional and advanced implanted bio-electronics.