Flexible lead-free cruciform piezo-arrays for implantable wireless energy harvesting on complex surfaces

Abstract

With the advancement of implantable medical electronics, higher demands have been placed on their power supply, as well as their safety and flexibility. Ultrasonic wireless transmission based on piezoelectric materials holds great potential in bioelectronics, but current materials engineering and device structure design remain deficient. Here, we develop a flexible lead-free piezoelectric array for ultrasonic wireless energy harvesting on nonplanar complex surfaces. Environmentally friendly 1–3 composite piezoelectric materials were employed as the core piezoelectric elements, which were developed by finely tuning the ratio of (K,Na)NbO₃-based ceramic phase to the second polymer phase in the composite structure of 1–3 to obtain the optimal piezoelectric voltage constant g₃₃ (40.6 × 10⁻³ V m N⁻¹) and harvesting figure of merit d₃₃ × g₃₃ (16 065 × 10⁻¹⁵ m² N⁻¹), and thus to improve the harvesting efficiency. The flexible lead-free piezoelectric arrays adopt a cruciform structure with soft, serpentine-shaped electrodes capable of harvesting energy over complex curved surfaces. We demonstrate the energy harvesting capability of the cruciform device across varying angles and thicknesses of pork tissue ex vivo, with ultrasound-induced adjustable outputs up to 22.75 Vpp and an average charging rate of 57.1 μW, providing an alternative for wirelessly powering of next-generation implantable bioelectronics.