A wireless, smartphone-aided magnetic strain sensor for biomedical applications

This paper reports an implantable wireless strain sensor comprising laser-machined polymeric magnetic stripes embedded in a dual-silicone stretchable matrix. Each magnetic stripe is encapsulated in a stiffer PDMS package which is then embedded in a softer Ecoflex
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band. This unique dual-silicone structure takes advantage of the elastic modulus mismatch between PDMS and Ecoflex
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, significantly reducing the dislocation of magnetic stripes which may occur due to poor bonding while keeping the band stretchable. Strains within a physiological relevant range (e.g., cardiac cycle of 60-100 bpm, 40%-60% strain) can be picked up wirelessly by the magnetic sensor of a smartphone at 2.5 cm away, a distance practical for cardiovascular and pulmonary applications.