System for wireless power transfer to rotating objects with stable power transmission based on parity-time symmetry

We propose a system for wireless power transfer to a rotating object using solenoid coils based on parity-time symmetry (PTS). Solenoid coils are ideal for wireless power transfer in confined spaces (e.g., they can be attached to the mechanical joints of robotic arms). Under PTS, the theorical transmission power and efficiency remain constant even when the magnetic coupling coefficient (km) changes. However, to preserve PTS, km values must be above the critical magnetic coupling coefficient (kmc) value. We conducted simulations and experiments to analyze the relationship between the rotation angle and km. Based on the results, we identified a coil arrangement for which km does not fall below kmc at any rotation angle. We maintained a transmission power of 20 W and a transmission efficiency of 80% during fast rotation with an angular velocity of 2.6 rad/s using a pair of small solenoid coils arranged with a gap of 33 mm between them.