Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring

TLDR

Flexible pressure sensors, especially liquid‑metal‑based ones, promise high strain tolerance but currently cannot resolve the few‑kPa pressure changes needed for heart‑rate monitoring. This work presents a microfluidic tactile diaphragm pressure sensor with embedded Galinstan microchannels that can detect pressure changes below 50 Pa, has a detection limit under 100 Pa, and responds within 90 ms. An embedded equivalent Wheatstone bridge exploits tangential and radial strain fields to achieve a sensitivity of 0.0835 kPa⁻¹ and provides temperature self‑compensation across 20–50 °C. The sensor was integrated into a PDMS wristband for real‑time pulse monitoring and into a PDMS glove with multiple sensors to deliver comprehensive tactile feedback when the hand touches or holds objects.

Abstract

Flexible pressure sensors have many potential applications in wearable electronics, robotics, health monitoring, and more. In particular, liquid-metal-based sensors are especially promising as they can undergo strains of over 200% without failure. However, current liquid-metal-based strain sensors are incapable of resolving small pressure changes in the few kPa range, making them unsuitable for applications such as heart-rate monitoring, which require a much lower pressure detection resolution. In this paper, a microfluidic tactile diaphragm pressure sensor based on embedded Galinstan microchannels (70 µm width × 70 µm height) capable of resolving sub-50 Pa changes in pressure with sub-100 Pa detection limits and a response time of 90 ms is demonstrated. An embedded equivalent Wheatstone bridge circuit makes the most of tangential and radial strain fields, leading to high sensitivities of a 0.0835 kPa-1 change in output voltage. The Wheatstone bridge also provides temperature self-compensation, allowing for operation in the range of 20-50 °C. As examples of potential applications, a polydimethylsiloxane (PDMS) wristband with an embedded microfluidic diaphragm pressure sensor capable of real-time pulse monitoring and a PDMS glove with multiple embedded sensors to provide comprehensive tactile feedback of a human hand when touching or holding objects are demonstrated.