Automatic inductance compensation for class E driven flexible coils

When driving an inductive link with a class E inverter, only little variation can be tolerated on the inductance value of the transmitting coil. Flexible or deformable coils are hence not compatible with a classic open-loop class E design. To tackle this limitation, a transductor—having an electrically controllable inductance value—is placed in series with the deformable coil. A control loop steers the transductor to the appropriate inductance value while the transmitting coil is being deformed. Based on this principle, a class E driver for deformable coils was realised that works at a frequency of 132 kHz and has an output magnetomotive force of 125 ampere-turns. Class E regime and a fixed output current are maintained for inductance variations up to 27%. The principal advantage of transductor compensation compared to earlier reported techniques, is that the operation frequency remains untouched.