End-to-End Design of Efficient Ultrasonic Power Links for Scaling Towards Submillimeter Implantable Receivers

Abstract

We present an analytical framework for optimizing the efficiency of ultrasonic wireless power links for implantable devices scaled down to sub-mm dimensions. Key design insights and tradeoffs are considered for various parameters including the operating frequency, the transmission depth, the size of the transmitter, the impedance and the aperture efficiency of the miniaturized receiver, and the interface between the receiver and the power recovery chain on the implant. The performance of spherically focused transducers as ultrasonic transmitters is analyzed to study the limits and the tradeoffs. Two optimization methods are presented: "Focal Peak" sets the focus of transducers at target depths, and "Global Maximum" maximizes the efficiency globally with offfocus operation. The results are also compared to phased array implementations. To investigate the efficiency of implants, miniaturized receivers made from single crystalline piezoelectric material, PMN-PT, are used as they have resonances in the derived optimal carrier frequency range (~ l-2 MHz). A methodology to achieve an efficient interface to the power electronics is then provided using an optogenetic stimulator as an example platform. The analytical results are verified through both simulations and measurements. Finally, an example ultrasonic link using a spherical transmitter with a radius of 2 cm is demonstrated; link efficiencies of 1.93-0.23% are obtained at 6-10 cm depths with sub-mm receivers for the optogenetic application.

Miniaturised Wireless Power Transfer Systems for Neurostimulation: A Review

“…In this work, it is suggested that it would be possible to deliver at least half the power to the receiver by reducing the size of the piezoelectric to 0.5 mm 3 while keeping the same input power intensity. Later, the same research group developed an end-to-end design for a sub-mm implantable receiver with a high efficiency single crystalline piezoelectric material that resonate in the range of 1−2 M Hz [93]. They obtained a maximum efficiency of 1.93 − 0.23% for an implantation depth ranging from 6 to 10 cm and for a receiver width of 0.6 mm.…”

Optimizing Volumetric Efficiency and Modeling Backscatter Communication in Biosensing Ultrasonic Implants

“…Similar to the series resonant frequency, characterization of Γ at the parallel resonant frequency of the piezo is also of interest as described in Section II. Air is sometimes used as a backing layer of the implant piezo [24] to reduce mechanical losses and enhance the electro-acoustical efficiency of the implant piezo in exchange for a more complex implant assembly and larger implant volume. Therefore, here we provide closed-form expressions for Γ(Z E ) to include: 1) Γ's dependence on Z E at both the series and parallel resonant frequencies 2) the effect of low-Q mechanically damped piezo, and 3) the effect of air-backing.…”

Optimization of the Coupling Coefficient of the Inductive Link for Wireless Power Transfer to Biomedical Implants

“…ere are several techniques to realize WPT, such as ultrasound, optical, microwave radiation, electric field coupling, and inductive coupling [10][11][12][13][14][15][16][17][18]. Among these methods, inductive coupling is the most preferred for IMDs, where power is transmitted from one coil and received by the other (usually integrated with the IMD inside a human body) through electromagnetic induction.…”