OMNIDIRECTIONAL POLYHEDRAL ULTRASOUND TRANSDUCER FOR POWERING IMPLANTABLE MICRODEVICES

Ultrasonic powering is an emerging power source for implantable microdevices due to its superior efficiency in energy transfer at millimeter-scale, long operation distance, and near omnidirectionality. In this paper, we investigate a novel polyhedral ultrasound transducer with emphasis on angular alignment between piezoelectric poling vector and incident waves. Three different polyhedrons (i.e., sphere, octahedron, and dodecahedron) are fabricated via 3D printing lead-free barium titanate ceramic. The maximum output voltage for a unit area occurred at 0° when the poling and waves direction aligned, which were measured to be
$0.677\pm 0.071,1.058\pm 0.049$
, and
$0.709\pm 0.092\ \mathrm{V}$
, respectively. At the extreme angular misalignment at 90° (poling and waves perpendicular to each other), only the dodecahedron could sustain the voltage output with 21% reduction, whereas sphere and octahedron dropped by 46%. The results imply that the geometry factor may overcome the poling vector, enabling omnidirectional ultrasonic powering for implantable microdevices.