Non-invasive sensing of the electrical energy harvested by medical implants powered by an ultrasonic transcutaneous energy transfer link

Ultrasonic transcutaneous energy transfer is an effective tool for powering medical implanted devices non-invasively. The power harvested by the implanted receiver is sensitive to the distance between the transmitting and receiving transducers, and to the orientation of one with respect to the other. This work describes an inductive link as a means for the contactless measurement of the voltage generated by the ultrasonically powered implanted transducer. A closed form analytic expression of the proposed sensor is presented. The sensor was successfully simulated for an implantation depth of up to 50 mm, achieving a voltage measurement accuracy of +/- 5%. The simulation is performed by exciting an external coil attached on the skin (50 mm diameter) by an AC current source (0.01 A). The excitation frequency is swept in the range of 2-6 MHz, the peak voltage across the current-source is then measured, and the resonance frequency is correlated to the equivalent inductive link impedance.