| Description |
Implantable medical devices (IMDs) are small devices that can be implanted into biological tissue to perform a diagnostic or therapeutic function. In this work, acoustic power transfer (APT) is investigated to wirelessly power IMDs. Acoustic power transfer systems (APTS) are typically comprised of an electrical source, acoustic transmitter (TX), medium through which the acoustic waves propagate, acoustic receiver (RX), and electrical load. The source powers the TX that emit acoustic waves through the medium to power the RX. The electrical load is attached to the RX and represents the IMD sensing or actuation system with associated electronics. In this work, the bulk-mode piezoelectric plate and flexure-mode piezoelectric diaphragm are considered for the acoustic TX and RX. A comparative study of power transfer potential (PTP) of the plate and diaphragm as a function of size and depth found that the diaphragm has higher PTP at submillimeter device sizes, the plate and diaphragm have comparable PTP at low-millimeter sizes, and the plate has higher PTP at larger sizes. Current modeling techniques for APTS include use of basic equations, circuit equivalent models, Huygens principle, two-dimensional (2D) axisymmetric finite-element analysis (FEA), and three-dimensional (3D) FEA. These techniques are used to model the PTP of the APTS in terms of electrical load, frequency, depth, and transducer diameter. Although researchers acknowledge that the orientation and alignment of the RX relative to the TX play a significant role in power transfer, none of the modeling techniques employed, except 3D FEA, are able to model these effects and 3D FEA is generally not employed because of its steep computational cost. This research develops a modeling technique that is capable of modeling Depth, Orientation, and Alignment via Ray Tracing (DOART) and is one to two orders of magnitude faster than 3D FEA. DOART is used to explore PTP sensitivity to disturbances in RX depth, orientation, and alignment. Four types of design graphs are developed to aid designers in the selection of APTS parameters such as TX and RX diameter, frequency, and depth. These design graphs are generated using nondimensional parameters to broaden their applicability and provide insight into scaling. |
