Abstract
HighlightsThe laser-engraved method was introduced to fabricate the electrode for the sensor.The sensor showed a wide linear working range, superior sensitivity, and fast response time and also exhibited excellent viability in a wet situation.Wireless integrated network sensors successfully monitored the health states.Developing flexible sensors with high working performance holds intense interest for diverse applications in leveraging the Internet-of-things (IoT) infrastructures. For flexible piezoresistive sensors, traditionally most efforts are focused on tailoring the sensing materials to enhance the contact resistance variation for improving the sensitivity and working range, and it, however, remains challenging to simultaneously achieve flexible sensor with a linear working range over a high-pressure region (> 100 kPa) and keep a reliable sensitivity. Herein, we devised a laser-engraved silver-coated fabric as “soft” sensor electrode material to markedly advance the flexible sensor’s linear working range to a level of 800 kPa with a high sensitivity of 6.4 kPa−1 yet a fast response time of only 4 ms as well as long-time durability, which was rarely reported before. The integrated sensor successfully routed the wireless signal of pulse rate to the portable smartphone, further demonstrating its potential as a reliable electronic. Along with the rationally building the electrode instead of merely focusing on sensing materials capable of significantly improving the sensor’s performance, we expect that this design concept and sensor system could potentially pave the way for developing more advanced wearable electronics in the future.
Highlights
200 400 600 800 Pressure engraved silver-coated fabric as “soft” sensor electrode material to mark‐ edly advance the flexible sensor’s linear working range to a level of 800 kPa with a high sensitivity of 6.4 kPa−1 yet a fast response time of only 4 ms as well as long-time durability, which was rarely reported before
Given that extensive reports have focused on the improvement of sensitivity, we primarily aimed at pushing the linear working range to a new horizon by using the soft silver-coated fabric (SF) as the integrated electrode for the first time in the flexible sensor (Fig. 1b), greatly expanding their applications of the flexible sensor compared to the traditional silicon-based micro-electro‐ mechanical systems (MEMS) device
A promisingly large-scale way using the laser-engraved stainless steel foil as the template for casting a waterproof PDMS micropillar film (MPF) grafted with carbon nanotube (CNT) (water contact angle (CA) is approaching 150o) was employed to further improve its viability in harsh environment such as the raining (Fig. 1a). Once these abilities are thoroughly evaluated, a Bluetooth served as a wireless signal device was successfully integrated to achieve the “communicateanalyze-interpret-decide” function to send the detected signal, i.e., pulse rate or applied pressure to the portable smartphone, thereby bringing the flexible sensor from laboratory to the real world
Summary
Prior to the preparation of the PDMS MPF, the PDMS solution was firstly prepared by mixing a base (Dow Corn‐ ing, Sylgard 184 A) with a curing agent (Dow Corning, Sylgard 184 B) with a weight mixing ratio of 10:1. The stainless steel mold with cylinder pores (200 μm in diam‐ eter) was initially manufactured carefully by the laser cut‐ ting machine. A certain amount of CNT solution (5 mg mL−1 in isopropyl alcohol (IPA)) was sprayed onto the above stainless steel foil with 1 mL cm−2. After the CNT solution was fully evaporated at 70 °C for 30 min, the prepared PDMS solution was poured into the mold and together put into the vacuum-drying oven to sufficiently remove the gas bubbles with the subsequence of heating at 70 °C for 1 h. The MPF covered with CNT was carefully peeled off from the substrate
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