Design and Characterization of an Integrally‐Soft Piezoresistive Sensor Combining an Elastomeric Nanocomposite and a Liquid Metal

The present study focuses on the innovative design of a multimaterial pressure sensor with a soft sensing core and soft electrodes. In the first part of the work, nanocomposites based on low-stiffness poly(dimethylsiloxane) (PDMS) and different fractions of single-walled carbon nanotubes (CNTs, from 0.15 to 0.5 wt.%) are electromechanically tested to assess piezoresistivity and stiffness. In the second part, the design of the sensor is described. It features an innovative architecture with liquid-metal electrodes placed on the sides of the sensing nanomaterial. This alignment enhances sensitivity and induces monotonicity by constructively coupling the geometric and resistivity components of the piezoresistive response. Fabrication by stepwise molding is demonstrated using two outer shells with different stiffnesses. Various pressure sensors are then produced using the best-performing sensing nanomaterials, characterized, and compared. The innovative characteristics of the proposed sensors are highlighted in terms of electrode material, architecture and positioning, simple design and fabrication, integral softness and low stiffness (< 1 MPa), appreciable linearity up to 0.0105 (Ω/Ω)/kPa, mid-to-high working stresses in the 0–210 kPa range, and recoverable compressive strains up to 43%. The reduced bandwidth of the sensor suggests applicability in the detection of pressure changes rather than in the measurement of absolute pressure values.