Breathable Encapsulated Liquid Metal Foam-Based Soft Stress Sensor

Liquid metal (LM)-based soft and wearable sensors have great potential for applications in human motion monitoring and human-machine interfaces. To avoid smearing of exposed LM, it is necessary to encapsulate LM with elastomers, which decreases the breathability and results in discomfort and even skin irritation. To solve this problem, this work proposes a breathable encapsulated LM foam (BELMF)-based soft stress sensor. By using two polydimethylsiloxane foam layers, the BELMF-based sensor achieves non-smearing and breathability. Meanwhile, a three-dimensional electrode is designed to implement the electric connection without decreasing breathability. Appling stress to the BELMF-based sensor makes the LM foam collapse and forms new conductive paths, which reduces the resistance of the sensor. The sensitivity of the BELMF-based sensor can reach 1.4 Pa-1. The mechanisms of the breathable encapsulation and the sensor are investigated through experiments and simulations. In addition, the potential applications of the BELMF-based sensor for monitoring human motion are demonstrated.