Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring

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.

Herein, a flexible microfluidic diaphragm pressure sensor using liquid-metal microchannels is presented. The sensor is capable of detecting sub-100 Pa pressures with sub-50 Pa resolution. As a proof of concept, both heart-rate monitoring and tactile pressure mapping of a glove with multiple embedded sensors are demonstrated.

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