Field Cancellation for Circuits Encircled by VHF Wireless Power Transfer Coils

Components and circuits encircled by wireless power transfer coils allow miniaturization but require field cancellation for components and circuits that are sensitive to the magnetic field. Very high frequency operation reduces the volume and number of components, which makes encirclement within WPT coils easier. A field cancellation method is investigated to minimize the magnetic field for the encircled circuits in WPT coils using a two-coil structure toward the best cancellation performance, practical construction, and minimum cost. The WPT and canceling coils are driven together by a single current-mode class D power converter with opposite-phase currents to optimize the field cancellation within the coils. Using this cancellation method, the magnetic field for the encircled circuits was reduced by 99% in hardware compared to that without cancellation.