Power transfer via magnetic resonant coupling for implantable mice telemetry device

Implantable biomedical devices play an important role in research for use as stimulators, sensors and biomimetic prosthesis. The use of implantable devices is desired since long-term operation or monitoring is possible, without need for replacement of embedded batteries. This work presents a wireless power transfer (WPT) system that is designed to deliver power efficiently from a stationary primary source to a moving implantable device (secondary circuit) via magnetic resonant coupling. Power is induced in the moving secondary circuit while it translates and rotates within the magnetic field generated by the stationary primary coil cage. In a typical application, a mouse with such a device implanted would move freely inside the cage while continuous power is supplied to the implantable telemetry device. Two different secondary coil configurations are proposed in this work, which are described as the air core and the ferrite core configurations. Finite element analysis (FEA) is done to assist in performance prediction for these configurations. Experimental measurements show that the air core configuration loses magnetic coupling with the primary coil, when the implantable device becomes oriented at 60° or more with respect to the primary field flux direction. For achieving improved coupling for a freely moving mouse within the primary cage, a wrapped ferrite rod could be used in the secondary implant prototype (SIP). This wrapped ferrite rod (WFR) coil provides the coupling required when the SIP moves beyond the 60° and 90° orientations. These two coils are attached to their own tank capacitors and to a separate rectifier. The maximum received power is 60 mW. It is delivered by applying a sinusoidal current through the primary coil of 2.5 A (peak-to-peak). The resonant frequency of the mouse implant device (MID) used in our experiments is 2.135 MHz.