Improved power transfer to wearable systems through stretchable magnetic composites

Abstract

The use of wireless power transfer is common in stretchable electronics since physical wiring can be easily destroyed as the system is stretched. This work presents the first demonstration of improved inductive power coupling to a stretchable system through the addition of a thin layer of ferroelastomeric material. A ferroelastomer, an elastomeric polymer loaded with magnetic particulates, has a permeability greater than one while retaining the ability to survive significant mechanical strains. A recently developed ferroelastomer composite based on sendust platelets within a soft silicone elastomer was incorporated into liquid metal stretchable inductors based on the liquid metal galinstan in fluidic channels. For a single-turn inductor, the maximum power transfer efficiency rises from 71 % with no backplane, to 81 % for a rigid ferrite backplane on the transmitter side alone, to 86 % with a ferroelastomer backplane on the receiver side as well. The coupling between a commercial wireless power transmitter coil with ferrite backplane to a five-turn liquid metal inductor was also investigated, finding an improvement in power transfer efficiency from 81 % with only a rigid backplane to 90 % with the addition of the ferroelastomer backplane. Both the single and multi-turn inductors were demonstrated surviving up to 50 % uniaxial applied strain.