Enhanced sensitivity of compliant piezoresistive sensors with strain-modulated surface hole structures

Compliant sensors with enhanced sensitivity are of interest for a wide range of applications. However, it is still challenging to implement high-performance sensors at reduced fabrication costs. Herein, a new design of compliant sensors with enhanced sensitivity is investigated by jointly utilizing strain-dependent piezoresistive material properties and simple strain-modulated surface hole structures. The surface hole structure amplifies local piezoresistive responses at strain-concentrated regions, and enhances sensitivity globally. Multi-objective optimization is conducted to obtain maximal sensitivity at a minimal loss in mechanical strength due to the hole structure. Experimental validations are performed on sensors made of low-cost exfoliated graphite nanocomposites via a simple and scalable cut-and-spray technique. Results show that the single rectangular-hole structure maximizes sensitivity to ∼ 8.25 with a decrease in mechanical strength by 44 %, compared to sensors without surface structures. T-shape hole structures are shown to improve sensitivity (∼14.56) more effectively by a factor of 2.4 with a loss of mechanical strength by 21 %. The strain-modulated sensor also demonstrates long-term stability (∼ 500 cycles) in cyclic tests, and reliable performance in tracking the movement of a robotic finger. This work provides a promising way to achieve cost-competitive compliant sensors with enhanced sensitivity.