Reluctance Modulation of Structured Magnetorheological Elastomers for Wireless Biomechanical Sensing

Inductive sensors are widely implemented in industry due to their noncontact measurement capabilities and inherent immunity to environmental factors such as humidity and electrostatic charges. The rigid construction, however, confines the applications of inductive sensors to heavy machinery and robotics, with few uses in detecting subtle mechanical signals in biology. Here, we cover planar coils with structured magnetorheological elastomers (MRE) to yield a flexible inductive sensor that matches the soft mechanical properties of biological tissues. Multilayer microcavities within the MRE enable structural deformation under tiny fluctuations of pressure and strain, thereby modulating the magnetic reluctance surrounding the coil. Demonstrations in wearable monitoring of pulse, motion, and so forth, as well as implantable measurement of intracranial pressure (ICP) in a rat model, validate the capabilities of the wireless, continuous sensing in vivo. The materials, device architecture, and sensing mechanism offer a promising solution for fundamental and clinical research in biomechanics.