An activation circuit for battery-powered biomedical implantable systems

Biomedical implantable devices in real-time telemetry applications offer many advantages to study and monitor physiologic parameters in human and animal bodies. As in power-constrained implantable devices, batteries and wires are two key issues that usually compromise their application. Inductive coupling is a well-established technology because it replaces simultaneously the wired connection and avoids the use of batteries. In stand-alone applications that requires total freedom of movements, this technology may present some constrains. On the other hand, very-low power electronics, advanced energy harvesting techniques and smaller implantable rechargeable batteries makes now possible the conception of fully autonomous implantable devices. This paper describes an activation circuit used to completely turn-off battery-powered implantable devices. In addition, it allows the reception of embedded commands, suitable for calibration and sensor selection purposes. Results from an experimental device to be used in a smart hip prosthesis telemetry system for loosening detection shows the usefulness of the proposed activation concept.