In order to improve on existing solid-state soft pressure sensors that often suffer from limited stretchability, signal drifting, and long-term instability, the researchers decided to rely on so-called liquid-state electronics using liquid metal such as Galinstan, an eutectic metal alloy of gallium, indium, and tin.
To increase the soft pressure sensor’s compliance and sensitivity over prior-art designs, the research team used 3D-printing to integrate a rigid microbump array and the master mold for a liquid metal microchannel, reducing the complexity of the manufacturing process. The integration of the rigid microbump within the flexible elastomer encasing the microchannels drastically decreases the detection limit as the rigid microbumps act as mechanical pressure point amplifiers. What’s more, the new sensor design detailed in a paper titled “Wearable Sensors: Highly Sensitive and Wearable Liquid Metal‐Based Pressure Sensor for Health Monitoring Applications: Integration of a 3D‐Printed Microbump Array with the Microchannel“ and published in the journal of Advanced Healthcare Materials exhibits a negligible signal drift over 10,000 cycles of pressure, bending, and stretching and exhibited excellent stability when subjected to various environmental conditions.
These performance outcomes make it an excellent sensor for various health monitoring devices. As an application example, the researchers demonstrated a wearable wristband device that can continuously monitor one’s pulse during exercise and be employed in a noninvasive cuffless blood pressure monitoring system based on PTT calculations. Then, they introduced a wireless wearable heel pressure monitoring system that integrating three such sensors with a wireless communication module.
“It was possible to measure health indicators including pulse and blood pressure continuously as well as pressure of body parts using our proposed soft pressure sensor. We expect it to be used in health care applications, such as the prevention and the monitoring of the pressure-driven diseases such as pressure ulcers in the near future. There will be more opportunities for future research including a whole-body pressure monitoring system related to other physical parameters”, explained team leader Professor Inkyu Park from the Department of Mechanical Engineering at KAIST.