A Flexible, Efficient, and Fully Lead‐Free Piezoelectric Ultrasound Wireless Energy Transfer System

Abstract Piezoelectric ultrasound energy transfer (PUET) is an emerging wireless technology and holds great promise in bioelectronics. However, current PUET systems primarily use toxic lead‐containing piezo‐materials and are bulky, compromising biocompatibility and portability. Despite advances in lead‐free transducers, PUET systems still face efficiency and stability challenges, necessitating optimization of corresponding material parameters and device structures. Herein, a flexible, high‐efficiency, fully lead‐free ultrasound wireless energy transfer system (f‐LPUET) for trans‐tissue energy transfer is presented. By combining material strategies of phase boundary engineering, defect dipole engineering, ferroelectric distortion, and local heterogeneity, two types of potassium sodium niobate‐based lead‐free ceramics are strategically endowed with hard (mechanical quality factor≈215, piezoelectric constant≈352 pC/N) and soft (piezoelectric constant ≈621 pC/N, planar‐mode electromechanical coupling factor ≈0.56) characteristics, respectively, to meet material requirements for efficient ultrasound transmitters and receivers. Considering wearability and implantability, the f‐LPUET is constructed with array architectures featuring exceptional flexibility (180° bending), enabling tunable and efficient transmitting acoustic pressure fields (adjustable focal depth from 25 to 30 mm, maximum pressure over 2 MPa) and trans‐tissue high electrical outputs (up to 40 Vpp, 0.22 mW, and 0.95 mW cm −2 ), superior to most PUET systems. Furthermore, this system is capable of long‐term stable power transmission with negligible thermal effects, while ensuring excellent biosafety.