Abstract
Measurements of physiological parameters such as pulse rate, voice, and motion for precise health care monitoring requires highly sensitive sensors. Flexible strain gauges are useful sensors that can be used in human health care devices. In this study, we propose a crack-based strain gauge fabricated by fused deposition modeling (FDM)-based three-dimensional (3D)-printing. The strain gauge combined a 3D-printed thermoplastic polyurethane layer and a platinum layer as the flexible substrate and conductive layer, respectively. Through a layer-by-layer deposition process, self-aligned crack arrays were easily formed along the groove patterns resulting from stress concentration during stretching motions. Strain gauges with a 200-µm printing thickness exhibited the most sensitive performance (~442% increase in gauge factor compared with that of a flat sensor) and the fastest recovery time (~99% decrease in recovery time compared with that of a flat sensor). In addition, 500 cycling tests were conducted to demonstrate the reliability of the sensor. Finally, various applications of the strain gauge as wearable devices used to monitor human health and motion were demonstrated. These results support the facile fabrication of sensitive strain gauges for the development of smart devices by additive manufacturing.
Highlights
As the importance of smart industrial fields has increased in recent times, several state-of-the-art systems have been studied extensively to enhance their efficiency
A high gauge factor (GF) (~2000) in a small strain range was achieved through advanced prestretching[3], it was noteworthy that the crack-based strain gauges developed in this study exhibited sufficiently high GFs with faster recovery times compared to other devices[1,5,16], supporting real-time monitoring applications
Simple 3D printing-based fabrication of highly sensitive strain gauges with small strains (0–1.67%) was demonstrated using fused deposition modeling (FDM)-type additive manufacturing with a sputtered metal layer
Summary
As the importance of smart industrial fields (e.g., human monitoring, the Internet of Things, and soft robotics) has increased in recent times, several state-of-the-art systems have been studied extensively to enhance their efficiency. After the entire fabrication, a prestretching process using 2% strain (i.e., 0.6 mm stretching considering the effective 30 mm length of the Pt coating, as shown in Fig. 1) was performed to generate highly aligned crack arrays in advance between each pattern (i.e., valleys of groove patterns).
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