1. Introduction

Poly(vinylidene fluoride) (PVDF) is a chemically stable piezoelectric polymer with high piezo-, pyroand ferroelectric properties [1, 2]. PVDF film under poling is most widely used in transducers and sensors for its extraordinary properties, it is particularly functional in harsh and biological environments [3, 4]. In addition, it is inexpensive, and exceptionally sensitive. For example, sensors based on PVDF film have been applied even in erosive media to detect pressure [5–10], in biological environments to aid minimally invasive surgery [11], test and characterize fabrics [12], and monitor human health [13–16]. However, the application of PVDF film, especially for force sensors, is very limited due to its rigidity and air permeability. The requirement for mechanical treatment and poling also prevents it from being used for extended applications.

Recently, by electrospinning technology, PVDF fabrics have been made for application as biomedical materials,

3 Author to whom any correspondence should be addressed. http://www.hfnl. ustc.edu.cn/2010/0819/954.html.

polymer electrolytes and filtration membranes [17–19]. Various studies have been carried out on electrospinning conditions and nanofiber structures [20–23], as PVDF fabrics can be produced by electrospinning while simultaneously controlling the ferroelectric and piezoelectric β-phase of PVDF, thus combining solution casting and electric field poling into one step [22, 23]. The achievement of making sensors based on PVDF fabrics is attributed to Kim et al [24]; in his method the fabrics were embedded with inorganic salts to increase their piezoelectric sensitivity. However an additional step of removing the salts was needed in the application. To the best of our knowledge, there is very little reliable information about PVDF-fabric-based force sensors.

This research focuses on developing a suitable material and a proper methodology for fabricating flexible and breathable force sensors. To better understand the PVDF fabrics and sensors, we fabricated and compared force sensors based on the fabrics. In this study, two sets of samples were prepared at multiple applied voltages and flow rates. Their crystalline structures were also analyzed with FTIR and x- ray diffraction. Finally, the piezoelectric properties of the fabricated sensors were evaluated on a self-made system.