  Multifunctional capability, flexible design, rugged lightweight construction,
and self-powered operation are desired attributes for electronics that directly
interface with the human body or with advanced robotic systems. For these and
related applications, piezoelectric materials, in forms that offer the ability
to bend and stretch, are attractive for pressure/force sensors and mechanical
energy harvesters. In this paper we introduce a large area, flexible
piezoelectric material that consists of sheets of electrospun fibers of the
polymer poly[(vinylidenefluoride-co-trifluoroethylene]. The flow and mechanical
conditions associated with the spinning process yield free-standing,
three-dimensional architectures of aligned arrangements of such fibers, in
which the polymer chains adopt strongly preferential orientations. The
resulting material offers exceptional piezoelectric characteristics, to enable,
as an example, ultra-high sensitivity for measuring pressure, even at
exceptionally small values (0.1 Pa). Quantitative analysis provides detailed
insights into the pressure sensing mechanisms, and engineering design rules.
Applications range from self-powered micro-mechanical elements, to
self-balancing robots and sensitive impact detectors.
