An ultrasound technique for wireless power transmission through tissue to implanted medical devices

Abstract

An ultrasound electrical recharging system (USERTM) is developed and tested, which wirelessly transmits significant amount of energy through animal tissue to charge implantable devices, batteries, or capacitors. The goal of this approach is wireless power transmission to active human implant devices. Experiments with transducers with resonant frequencies between 0.5 and 3.5 MHz led us to adopt 0.75 to 1.25 MHz as the range of optimum efficiency. In vitro experiments demonstrated significant charging of 4.1 V medically qualified Li-ion batteries across tissue depths of up to 5 cm. Charging currents close to 300 mA were achieved in vitro. Several in vivo tests confirmed the power delivery in a porcine model. In an in vivo survival test, tissue was exposed to 1 MHz ultrasound at an average intensity of 0.4 W/cm2 for 11.5 h. Histology of the exposed tissue showed tissue changes primarily attributable only to surgical implantation of the prototype device. Many traditional and developing implanted medical devices are targets for the introduction of this method of power delivery, to reduce the number of battery replacement operations, and improve performance compared to the existing electromagnetic method of wireless power delivery. [Work supported by the NIH/NIBIB R44EB007421.]