Design considerations for ultrasonic power transmission to millimeter-sized implantable microelectronics devices

This paper presents the design considerations to improve the power transfer efficiency (PTE) of ultrasonic power transmission links for wireless powering of millimeter (mm)-sized implantable microelectronic devices (IMDs). We have shown by the ultrasound theory that the diameter of the transmitter (Tx) and receiver (Rx) ultrasonic transducers, operation frequency, and powering distance have significant effect on the sound beam profile and, therefore, PTE of the link. The proposed design guideline, which has been verified by measurement results, suggests that the Rx diameter should be maximized to the extent that the application allows, and then the Tx diameter and operation frequency should be carefully chosen such that the IMD locates inside the focal zone of the Tx transducer for a given powering distance. The PTEs of ultrasonic and optimized inductive links with 2 mm Rx have also been compared that suggests the use of ultrasound when the powering distance is larger than 45 mm.