Soft Shear and Compressive Contact Stresses Sensor With Conductive Microfluidic Channels Fabricated by Additive Manufacturing

A fully soft and conformable sensor that can simultaneously measure contact stresses on two-axis (shear and compressive stresses) designed using finite element analysis (FEA) and fabricated through direct ink writing (DIW), an additive manufacturing process, is presented. The sensor consists of a silicone receptor and two parallel microfluidic channels filled with liquid metal. The electrical resistance of the liquid metal within the microfluidic channels changes depending on the shear and compressive stresses on the receptor. The cross-section of the microfluidic channels is designed to have a unique solution between the measured electrical resistances and shear and compressive stresses, which was predicted through FEA. The DIW of silicone enables the flexibility to fabricate this one-piece soft sensor with the desired microfluidic channel shape. This study validates the FEA and DIW approach and demonstrates the contact sensor can measure the shear and compressive stresses up to 60 kPa and 396 kPa, respectively. Results of this study can be utilized to design and fabricate the fully soft, conformable, and custom contact sensor for wearable devices.