Recent advances in transducers for through-tissue ultrasonic power transfer

Ultrasonic power transfer (UPT) is gaining traction for wireless energy delivery to implants and wearables because it combines centimeter-scale penetration with compact receivers. This review takes a transducer-centric view of UPT and organizes the field across bulk piezoelectrics (including lead-free options), piezoelectric micromachined ultrasonic transducers, capacitive micromachined ultrasonic transducers, flexible polymer platforms and magnetostrictive transducers. We connect working mechanisms and structural configurations to practical performance-operating frequency ranges, bandwidth, link efficiency and output power, and miniaturization trade-offs-and summarize representative demonstrations in biomedical systems. System-level considerations for integration (acoustic/electrical matching and rectification) and bidirectional links (including backscatter and active telemetry) are highlighted to show how a single acoustic carrier can deliver power and data through tissue. We conclude with challenges (attenuation and misalignment, materials reliability and packaging, and scaling to millimeter/sub-millimeter form factors) and opportunities that draw on materials innovations (metamaterials, lead-free ceramics, flexible polymers) and machine-learning-assisted co-design for robust, efficient through-tissue operation. Together, this transducer-focused synthesis provides a practical map from device physics and fabrication choices to system performance and emerging applications.