MRC-Based Double Figure-of-Eight Coil Sensor System With Triple-Mode Operation Capability for Biomedical Applications

Efficient wireless power transmission to a designated location can reduce the size of implantable device and save source energy, but the receiver coil and rectifier circuit still occupy a large area. This paper proposes a novel magnetic resonant coupling (MRC)-based double figure-of-eight coil sensor system to induce and monitor heat. Implantable devices could obtain energy from the surrounding electric field or heating effect. The fundamental of generating the heating effect by the proposed coil-based sensor system is derived, and conceptual system architecture is built. Then the radiating coil is analyzed in terms of Litz-wire coil optimization, lumped parameter extraction, impedance-matching network, equivalent circuit model, and coupling coefficient. Considering the current ratio, operating frequency, and designated location, the triple-mode operation mechanism is analyzed for the first time to adjust superposed electromagnetic fields at the designated location. At the odd-mode resonance, the electric field intensity in the middle between two figure-of-eight coils is significantly improved. Finally, the physical prototype of proposed coil-based sensor system is built up and experiments are conducted to test the currents in both figure-of-eight coils as well as the induced voltage and temperature change in the in-vitro sample by using the electrode sensor and thermocouple sensor. Measurements validate the feasibility of the proposed coil-sensor system. It also provides essential guidance on designing sensors for deep-tissue stimulation and hyperthermia treatment.