Omni-Directional Ultrasonic Powering via Platonic Solid Receiver for mm-Scale Implantable Devices

Abstract

Despitethe recent advancements in implantable microdevices, providingsufficient electrical power to deeply seated microsystems has remainedchallenging due to the small dimension of the system, limiting thetotal storable energy. Ultrasound powering, where a portion of theexternally induced ultrasonic wave is converted to electrical powerby a small receiver, has been explored as an attractive source ofpower, especially for deeply seated implantable microdevices. Whileall other components have been advanced and miniaturized, the ultrasonicreceiver is still a slab of bulk piezoelectric materials, e.g., dicedPZT (lead zirconate titanate). Such a rectangular or disc shape isnot an ideal form factor for wireless ultrasonic power transfer dueto many challenges, particularly angular sensitivity with respectto an incoming ultrasonic wave. In this paper, we present the firstdemonstration of omnidirectional ultrasonic powering enabled by thehigh geometrical symmetry of three-dimensional polyhedral shapes.Based on our 3D printing technique of lead-free piezoelectric bariumtitanate ceramic, we designed highly symmetric, miniaturized, regularpolyhedra, known as Platonic solids (i.e., cube, octahedron, dodecahedron),as well as a sphere. For each geometry, we investigate the effectof axial and radial piezoelectric poling, output power levels, efficiency,and angular sensitivity while the surface areas are the same. Acrossall the geometric shapes, radially poled Platonic solid receiversproduce at least 1 order of magnitude larger electrical power densitycompared to diced PZT. Further, we observed that the higher the orderof Platonic solid, the more excellent power transfer efficiency andomnidirectionality. The 3D printability of the Platonic solid alsoallows for customizable packaging, which we implemented as an implantablelight source. Overall, the proposed ultrasonic powering scheme warrantsa revolutionary solution for implantable biomedical devices.