Wireless power transfer with bidirectional telemetry for active implantable medical devices

Avan, Onur
This thesis presents a wireless power transfer (WPT) system for powering implantable medical devices (IMDs).In order to make IMDs smaller and longer life devices primary batteries are replaced with rechargeable ones for the last two decades. Consequently, WPT systems are implemented for IMD’s. Electromagnetic induction is the most preferred and safety proven method among existing WPT methods. However, loose coupling inherent in these systems limits the implant depth and increases the battery recharge time. A multi-coil approach (Strongly Coupled Magnetic Resonance) using Litz wire is implemented in this work to increase the power transfer efficiency and to alter problems defined in the traditional methods. 1 MHz operation frequency is selected by analyzing AC resistance of Litz wire types to achieve high quality factor coils and also by analyzing dielectric and conductivity losses in tissue. To take control over WPT and communicate with the device, a half-duplex bidirectional telemetry system is designed. In the design procedure, first, WPT system is modeled analytically and then optimized in MATLAB platform. The results are verified numerically in COMSOL Multiphysics program. A frequency control method is demonstrated by using a switch capacitor array at the power amplifier side to adapt the system to different implant depths. In the telemetry part, ASK modulation is used for both forward and backward communication with low modulation depth without disturbing the received power at the implant side. Modulator and demodulator circuit designs are simulated using LT Spice software. PCB design for the hardware of both implantable device and the external charger device is performed in Altium CAD platform. 58 % (DC/DC) power transfer efficiency is achieved to transfer 485 mW power at 4 cm implant depth. A Manchester encoded half-duplex bidirectional telemetry system with 19200 baud rate is also established.
Citation Formats
O. Avan, “Wireless power transfer with bidirectional telemetry for active implantable medical devices,” M.S. - Master of Science, Middle East Technical University, 2017.