Energy focusing flexible acoustic meta-structure for enhanced ultrasound power transfer

Ultrasound power transfer (UPT) is a rapidly advancing field with promising applications in charging medical implants, wearable electronics, IoT devices, and unmanned underwater vehicles. UPT systems typically use an ultrasound transducer to transmit acoustic energy and a piezoelectric ceramic (PZT) to harvest it by converting sound waves into electricity. While metamaterials have been explored to enhance energy harvesting efficiency, most reported designs are bulky, rigid, and heavy, which limits their use in applications that require flexible and lightweight devices for user comfort, such as medical implants and wearable devices. In this talk, we present a lightweight and flexible acoustic meta-structure that focuses acoustic energy to enhance the efficiency of UPT. The meta-structure is composed of air-filled inclusions that create a resonant cavity around the PZT. The resonant cavity transforms the incident ultrasound into lateral vibrations, thereby increasing lateral deformation of the PZT and improving energy conversion. The performance of the meta-structure is experimentally demonstrated by doubling the energy harvesting efficiency of a PZT in a reflectionless environment, without increasing the weight or reducing the flexibility of the energy harvester. Furthermore, the meta-structure demonstrated robustness to reflective environments and deformed configurations, underscoring its suitability for a wide range of UPT scenarios.