A New Multiscale Bioinspired Compliant Sensor

Abstract

A challenge in fabricating compliant electrical sensors for various applications, such as wearable electronics, has been the lack of compatible connection concepts that are reliable and can support large levels of force without failure. Recently, we have developed compliant, carbon-based strain and thermal sensors using nanosized exfoliated graphite (EG) dispersed in latex that are highly deformable (>50 % strain) and piezoresistive. They undergo large changes in electrical resistance, resulting in highly sensitive strain (1 × 10⁻³/μstrain) and thermal (1 × 10⁻³/K) measurement sensors. Such compliant sensors are typically attached to external wiring using conductive silver epoxies or paints. However, the silver epoxy and the metal wires are rigid, and they detach from the compliant sensor at low load levels. By using micron-sized braided carbon fibers instead of metal, and a carbon-based composite instead of silver epoxy, a mechano-electrical interface to the sensor is created that has a significantly higher load bearing capacity than achieved with metal wires, with an inherent electrical resistivity of only 1.7 × 10⁻³ Ω−cm. The resulting sensor is similar to a sensory nerve receptor where the percolated network of nanosized EG act as “receptors,” while the micro-sized carbon fiber acts as the sensory ganglion attaching to the central nervous system. The resulting “biologically inspired” multi-scale strain and temperature sensor has advantages in addition to durability, including amenability to additive manufacturing processes, ease of fabrication, and scalability. We also demonstrate the ability to use the new sensing material to make “sensing gloves” that could potentially be used in applications such as recording signals during manual tasks by human hands or for providing sensing capability to robotic hands.