Abstract
Nowadays, with the development of wearable devices, stretchable pressure sensors have been widely adopted in all kinds of areas. Most of the sensors aim to detect small pressure, such as fingertip tactile sensing, but only a few are focused on high-pressure sensing, such as foot pressure sensing during men’s walking. In this work, a liquid metal-based stretchable sensor for large-pressure measurement is investigated. This sensor is fully stretchable because it is made of soft materials. However, when the soft sensor is subjected to high pressure, the liquid metal easily leaks from microchannels because it maintains the liquid state at room temperature. We therefore propose to fabricate liquid metal-based leakage-free electrodes to handle the liquid-metal leak. Parametric studies are conducted to compare this sensor with liquid-metal-only electrodes and leakage-free electrodes. The leakage-free electrodes increase the measurement ranges from 0.18, 0.18, and 0.15 MPa to 0.44 MPa, with higher linearity and precision. The improvement in the liquid-metal electrode enables the sensors to work stably within 0.44 MPa pressure and 20% strain. In addition, we integrate two capacitors, namely, a working capacitor and a reference capacitor, into one sensor to reduce the influence of parasitic capacitance brought about by external interference. This stretchable capacitive sensor capable of working under a wide range of pressure with good repeatability, sensitivity, and linearity, exhibits great potential use for wearable electronics. Finally, the method for fabricating leakage-free electrodes shows great value for hyperelastic electronics manufacturing and micromachine technology.
Highlights
With development in soft wearable devices, stretchable sensors have been widely studied in recent years [1,2]
The stretchable sensor consists of two identical capacitors, i.e., a working capacitor (WC) and a reference capacitor (RC), to reduce parasitic capacitance brought about by external interference
The sandwich-structured sensor consists of PDMS substrates, a pair of liquid metal-based electrodes, a PDMS membrane, and silver plated copper wires
Summary
With development in soft wearable devices, stretchable sensors have been widely studied in recent years [1,2]. Yeo et al [28] developed a liquid metal-based resistive sensor that could sense various levels of pressure, such as foot stomping, chair rolling, and car rolling; this sensor did not have a linear output within the whole sensing range, and the fabrication of the screen-printed silver electrode of the sensor was costly and complicated as screen printing technology requires multiple procedures [31]. For a liquid electrode-based stretchable sensor, a wide working range necessitates good packaging because liquid electrodes will leak once the applied pressure exceeds a certain value This leak will change the effective facing area of capacitive sensors or the original resistance of resistive sensors, thereby limiting the working range and lowering the repeatablity. This work presents a simple method to fabricate a stretchable pressure sensor with leakage-free electrodes that measures large pressure, reduces parasitic capacitance, and has a relatively high sensitivity
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