Vertically Printed Ferroelectret Microstructures

Using fused filament fabrication, ferroelectrets (i.e. polymer films with internal air-filled voids) can be manufactured from a variety of materials and with custom designed structures for optimum mechanical compliance and piezoelectric activity. In this study, we investigated a vertically oriented “double-wave” design, which results in structures with very low mechanical stiffness, and hence high piezoelectric
$d_{33}$
coefficients. The structures were designed in an open-source parametric modeler and 3D-printed from polylactic acid (PLA) and polypropylene (PP). The total thickness is approx.
$300 \mu\mathrm{m}$
and channel void heights are around
$100 \mu \mathrm{m}$
. When charged in direct contact, the ferroelectret samples exhibited a remanent polarization of
$0.25 \text{mC}/\mathrm{m}^{2}$
(PP) and
$0.12 \text{mC}/\mathrm{m}^{2}$
(PP), respectively. Piezoelectric
$d_{33}$
coefficients of up to
$800 \text{pC}/\mathrm{N}$
were observed, but showed a strong decrease when static bias forces in excess of 1 N were applied to the 16 mm diameter electrodes. This behavior is likely caused by a stiffening of the double-wave structure as more compressive stress is applied. FEM calculations showed a very low effective Young's modulus of 125 kPa.