Coupling and maintaining link efficiency ultrasonics in transcutaneous energy transfer systems

Abstract

We present on the development of a 12.8 mm diameter ultrasonic transcutaneous energy transfer system for powering implanted hearing devices. The system was based on two custom 8mm diameter PMN-PT 1-3 composite transducers operating at 1.25MHz and featured three significant innovations. First, to ensure long-term biocompatibility and reliability of the implanted portion of the link and to ensure robust attachment to bone, the implanted transducer was designed into a 12.8 mm diameter, 3.5 mm thick hermetically sealed titanium package in an easy-to-implant form factor. The transducer was designed to deliver sound efficiently through the casing walls using a mass-spring acoustic matching technique. Second, for the external unit a “dry” acoustic coupling system based on a silicone pressure sensitive adhesive was designed that combined efficient acoustic coupling, robust adhesion to skin and that was comfortable to wear. The external unit was aligned with the internal unit using a magnetic alignment system. Third, we developed and demonstrated an efficient Class E transmit amplifier and receive electronics that incorporated compensation for changes in acoustic separation between the transducer to maintain robust, high efficiency power transmission. The system achieved 33% DC-to-DC electrical conversion efficiency through 5mm of water and 19% DC-to-DC efficiency through 5mm of porcine tissue.