Wearable Microfluidic Diaphragm Pressure Sensor for Health and Tactile Touch Monitoring

Abstract

Flexible pressure sensors have many potential applications in wearable electronics, robotics, health monitoring, and more. In particular, liquid-metalbased 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.

Liquid Metal–Based Soft Microfluidics

“…Liquid metal can be loaded in the channels by positive (syringe injection) or negative pressure (vacuum injection), though also specialized methods, such as driving by electric field is possible . For example, Gao et al encapsulated Galinstan in an intricately designed microfluidic channel by injection with a syringe. The filled microfluidic channel formed an equivalent Wheatstone bridge circuit, as shown in Figure a, thereby yielding in a microfluidic tactile diaphragm pressure sensor, which is capable to resolve pressure changes smaller than 50 Pa at a detection limit of 100 Pa and a response time of 90 ms, while typical liquid metal pressure sensor cannot discern pressure changes as small as a few kPa.…”

“…a) Optical image and working principle illustration of microfluidic tactile pressure sensor. Reproduced with permission . Copyright 2017, John Wiley and Sons.…”

Untethered soft robotics

“…Because of the inherent compliance of these materials, liquid metal elastomer systems are ideal for sensing in fully soft applications 83,106 , such as gloves. These devices can be used for inertial sensing 83 or pressure sensing for tactile feedback and pulse monitoring 106 (Fig.…”

“…These devices can be used for inertial sensing 83 or pressure sensing for tactile feedback and pulse monitoring 106 (Fig. 4i), building on designs introduced by Majidi and Park et al 99 .…”

Advanced Wearable Microfluidic Sensors for Healthcare Monitoring

“…Precise control of fluid flows, excellent stretchability, and flexibility, and easy integration with sensory units enable microfluidic sensors to be an efficient platform for advanced sensor technologies. Currently, works on wearable microfluidic sensors mainly focus on sweat composition measurement to make an assessment of the physiological status …”