Non-dimensional analysis of depth, orientation, and alignment in acoustic power transfer systems

Abstract

Acoustic power transfer systems are typically comprised of an electrical source, acoustic transmitter (TX), medium through which the acoustic waves propagate, acoustic receiver (RX) and an electrical load. The voltage generated across and power delivered to the load from the TX is a function of RX position (depth, orientation, and alignment relative to the TX), frequency, TX and RX diameter, and source and load impedance. In applications where the RX position is not fixed, such as in implantable medical devices, slight disturbances in RX position can result in a severe reduction in load voltage and power. Therefore, the sensitivity of voltage and power as a function of RX position is crucial to system design. This paper presents an analysis of the load voltage and power as a function of RX depth, orientation, alignment, frequency, RX and TX diameter, and load impedance. Design graphs are developed and presented as a means of visualizing the sensitivity of voltage and power to system parameters. Non-dimensional design graphs are then generated to broaden the applicability of simulation results.

Ultrasound‐Induced Wireless Energy Harvesting for Potential Retinal Electrical Stimulation Application

“…Figure a shows the schematic profile of the working principle. A primary design goal for an ultrasonically powered implant is to minimize power losses, mainly including beam divergence, pressure wave reflection, tissue absorption, and piezoelectric coupling . First, a focused ultrasonic transmitter which can improve the energy utilization by concentrating the acoustic beam to a smaller area was adopted in this study.…”

Ultrasound‐Powered Implants: A Critical Review of Piezoelectric Material Selection and Applications

“…When operation is performed in the d 33 mode, the strain and the polarization are in the same direction—resulting in a high coupling coefficient; whereas, in the d 31 mode the strain and polarization are perpendicular, causing a lowered coupling coefficient. [ 117 ] Figure 2D shows examples of the two operation modes with indicated directions of force application and poling axis. As such, UPI architecture, such as electrode design, should take the ideal operational mode into account, For example, operational modes were theoretically and experimentally compared for cantilever devices by Kim et al.…”

“…They are operated in d 33 mode and the face is in contact with tissue or an acoustic matching layer. [ 117 ] Plate devices are somewhat limited in the achievable minimum size by the inherent increase in resonant frequency of piezoelectric crystals as thickness is reduced. [ 119 ] Increasing the thickness of a plate structure decreases the resonant frequency causing less attenuation in tissue, and increases voltage harvesting during operation.…”

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics

“…The wavelength of ultrasound is critical to ensure both the resolution and penetration depth. The ultrasonic energy harvester is based on vibration, or sound waves, which can operate through either capacitance mode or piezoelectric mode . The ultrasonic energy harvesters generally utilize piezoelectric transducers to convert mechanical vibrations induced by acoustic waves into electrical power, in order to achieve a desirable power level for in vivo applications.…”

“…Conventional bioimplanted piezoelectric ultrasonic energy harvesters focus on the plate architecture because of its high theoretical acoustic power output. Diaphragm architecture has also been proposed to ensure conformal contact with the nonplanar surfaces of tissues and organs, generating more power than the plate architecture and lowered sensitivity to changes in implantation depth and absorption power losses for sub‐millimeter size devices …”