Textile based ferroelectret for foot pressure sensor

Abstract

<p>Sensors based on piezoelectric materials like ZnO, lead zirconate titanate (PZT), MoS₂, poly (vinylidene fluoride) (PVDF) and its similar copolymer p(vdf-TrFE) have exhibit excellent through converting mechanical signal into electrical output [1-3]. For these conventional piezoelectric materials: PZT and PVDF, PZT possesses excellent dielectric and piezoelectric properties, but is a rigid ceramic with a very high Young's modulus (63 GPa). In contrast, PVDF is a soft polymer with low Young's modulus (2.9 GPa), but its piezoelectric charge coefficient d₃₃ is an order of magnitude lower than of PZT (20 pC/N), which are making they unsuitable for wearable application [4-5]. Therefore, there is the need to develop a piezoelectric material with high piezoelectric activity, low Young's modulus and the ability to stretch and conform for wearable sensing. Ferroelectret is a thin film of polymer foam that can generate electrical signal under mechanical force, which is similar to piezoelectric materials. The typical internal structure of a ferroelectret foam is randomly arranged cellular voids with positive and negative charges stored separately on each surface of the void. Due to the material of the polymer and its cellular structure, the elastic modulus of the ferroelectret is low. The ferroelectret is readily compressible and will undergo large deformation when under a compressive force, which results in a strong piezoelectric effect. Due to its advanced piezoelectric properties in comparison with other piezoelectric materials, numerous applications have been proposed, such as acoustic transducers, high frequency loudspeakers, ultrasonic transmitters and receivers, hydrophones and accelerometers [6]. The soft, flexible nature of the polymer ferroelectret makes it highly suitable for use in wearable sensing applications.</p>