Fabrication and characterization of wearable sensing system using mechanical micromachining process.

Abstract

The present work reports a flexible and stretchable wearable sensing system based on a piezoresistive method inspired by human skin mechanoreceptors and strain gauges. The tactile sensor consists of Polydimethylsiloxane (PDMS) as a flexible and stretchable body and liquid metal Eutectic Gallium Indium (EGaIn) as the sensing material. Microchannel fabrication on a PDMS elastomer is an essential step, and we are achieving this by preparing the mold of stainless steel using mechanical micromachining and casting out the PDMS. Microchannel fabrication using a micromachining facility on stretchable and flexible material is a green and economical alternative to commonly known chemical itch and photolithography techniques. In addition, it has advantages over 3D printing techniques in terms of the size limitation fabricating the smallest feature and surface finish. This work focuses on fabricating microchannels using a multipurpose micromachining setup, which can prepare microchannel patterns of different shapes like serpentine and coil and sizes such as 200x200μm2 cross-section. The overall size of the sensor is just 15mm x15mm x1mm with a sensing area of 10mm x 10 mm, which is suitable to wear on human fingers. With this pattern, we have cast out the outer layer of elastomer for the development of the sensor. A strain sensor design has been developed to fabricate these sensors to sense directional forces and bending. Most importantly, creating microchannels on the PDMS is the point of focus where a micromachining facility is being used. Up to 25% strain, we have achieved a gauge factor of 0.98. It has many applications, such as healthcare, human motion detection, virtual reality gaming, human-robot interaction, etc.