Abstract
Conventional flexible piezoresistive strain sensors that use conductive particles polymer composites exhibit thick structures with a low sensitivity to external tension. This paper presents a cost-effective method to fabricate ultra-thin and highly sensitive piezoresistive strain sensors. In our fabrication steps, carbon ink that is mainly composed of carbon black particles is solidified with a drying process to form a “paperlike,” flexible conductive film. Without any surface modification techniques, the carbon ink film is directly placed onto liquid-state PDMS and then bonded after the drying process. Following the rapid prototyping, different performance metrics of the fabricated sensors, including piezoresistivity, gauge factor, temperature dependency, elastic modulus, and repeatability are measured. Specifically, sensors fabricated with this method show a significantly improved gauge factor (~26) compared to similar flexible sensors fabricated by more complicated micro-fabrication methods. The proposed method of fabrication and the corresponding ultra-thin (~45 μm) sensor prototype may benefit the design and mass production of future wearable biomedical and healthcare sensors.
Highlights
Flexible and lightweight strain sensors are critical components for applications such as human motion detection [1, 2], touch panels [3, 4], soft robotics [5], electronic skin [6, 7], wearable electronics [8], health monitoring [9, 10]
The sensitivity of the capacitive strain sensor, is low when the effective compression applied to the dielectric layer is weak
In contrast to piezoelectric and capacitive sensors, piezoresistive sensors react to external tension with resistance changes
Summary
Flexible and lightweight strain sensors are critical components for applications such as human motion detection [1, 2], touch panels [3, 4], soft robotics [5], electronic skin [6, 7], wearable electronics [8], health monitoring [9, 10]. A strain sensor exhibits piezoelectric [11, 12], capacitive [13, 14], or piezoresistive [15,16,17] transduction to external forces While piezoelectric materials, such as P(VDF-TrFE), produce electrical charges when mechanical stress is applied [11], the materials are usually stiff [18] and only able to function in conditions of dynamic tension [11], which greatly limits their applications. In contrast to piezoelectric and capacitive sensors, piezoresistive sensors react to external tension with resistance changes They can be designed using simple structures and are compatible with many read-out approaches [8]. Various materials, including copper nanowire [20], silver nanowire [21], gold nanowire [2], carbon nanotube (CNT) [22, 23], polymer nano-fibers [24, 25], metal particles [26, 27], graphene [28, 29], and carbon black [30, 31] can be used to fabricate piezoresistive sensors
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