Thermally Drawn Piezoelectric Fiber Enables Fabric for Acoustic Healthcare Monitoring

Thermally drawn piezoelectric fibers woven into clothing can continually monitor heartrate and breathing rate. In thermal drawing, viscoelastic materials flow in a laminar regime, maintaining the cross-sectional geometry of the macroscopic preform. In the fiber device, the piezoelectric composite of P(VDF-TrFE) and barium titanate (BTO) nanoparticles is flanked by carbon-loaded polycarbonate electrodes and encapsulated in an elastomer cladding. The d₃₁ piezoelectric coefficient is 46 pC/N, more than double previously reported values. Evidently, neither the thermal drawing nor the incorporation of BTO alone explains the enhanced d₃₁. During the draw, cavities form between the polymer and the particle on either side of the particle in the direction of the draw. It is hypothesized that the piezoelectric domain thus functions as a novel ferroelectret material. The sensitivity of the fiber woven into fabric is comparable to handheld microphones, and fibers reliably detect heartbeat and breathing. Arrays of fibers are used to determine the direction of a sound source with 1-degree accuracy. In everyday clothing, fibers can continuously capture acoustic signals that provide the wearer with insight into their health, making healthcare more accessible outside clinical settings.