Flexible and active self-powered pressure, shear sensors based on freeze casting ceramic–polymer composites

Self-powered flexible electronics are of particular interest and important for next generation electronics due to their light weight, flexible and self-sustainable properties. Many self-powered sensors made from piezoelectric composite materials are either inflexible or possess low piezoelectricity. In this work, we demonstrate self-powered flexible and highly active pressure and shear sensors based on freeze casting ceramic–polymer structures. A lamellar lead zirconate titanate (PZT) structure is initially developed via freeze-casting and the piezoelectric composites are formed by impregnating a polydimethylsiloxane (PDMS) matrix into the aligned pore channels. The structured PZT–PDMS composites exhibited a high effective longitudinal piezoelectric coefficient (d33*) of 750 pC N−1, which is higher than that of the monolithic ceramic due to the combination of bending and flexural effects. The use of freeze casting enables the manufacture of complex and arbitrary shaped 3D piezoelectric architectures, along with the unique advantages of low-cost and ease of fabrication. A 14 × 14 mm2 PZT–PDMS pressure sensor was able to bend to a small radius of 8 mm and maintain a high d33. Furthermore, the manufactured self-powered sensors are demonstrated in a range of applications, such as acceleration, strain and touch sensors that use the d33, d31 and d15 coefficients to detect longitudinal, transverse and shear loads. This work expands on the potential applications of freeze casting and provides new opportunities for the manufacture of future electronic sensors.