A review of acoustic power transfer for bio-medical implants

Abstract

Bio-implantable devices have been used to perform therapeutic functions such as drug delivery or diagnostic monitoring of physiological parameters. Proper operation of these devices depends on the continuous reliable supply of power. A battery, which is the conventional method to supply energy, is problematic in many of these devices as it limits the lifetime of the implant or dominates the size. In order to power implantable devices, power transfer techniques have been implemented as an attractive alternative to batteries and have received significant research interest in recent years. Acoustic waves are increasingly being investigated as a method for delivering power through human skin and the human body. Acoustic power transfer (APT) has some advantages over other powering techniques such as inductive power transfer and mid range RF power transmission. These advantages include lower absorption in tissue, shorter wavelength enabling smaller transducers, and higher power intensity threshold for safe operation. This paper will cover the basic physics and modeling of APT and will review the current state of acoustic (or ultrasonic) power transfer for biomedical implants. As the sensing and computational elements for biomedical implants are becoming very small, we devote particular attention to the scaling of acoustic and alternative power transfer techniques. Finally, we present current issues and challenges related to the implementation of this technique for powering implantable devices.

Zero-Power Defense Done Right: Shielding IMDs from Battery-Depletion Attacks

“…3 [22,29]. State-of-the-art IMD-specific WPT techniques can be broadly categorized into three types 2…”

“…We now analyze the effect of the EM-noise attack, in which the attacker's aim is to cause IMD retransmissions due to high error rates at the IMD transceiver. Based on the analysis from Gelenbe et al [13] of battery-DoS attacks on sensor nodes, the IMD current consumption under an EM-noise attack can be represented by (2).…”

Design of Ceramic Packages for Acoustically Coupled Implantable Medical Devices

“…≠ ) has been shown to be negligible [37], so we will ignore mutualimpedance and only focus on self-impedance: = (16) Given that = . Plugging (16) into (14) and rearranging for yields:…”

“…As devices get smaller, the amount of available space for energy harvesting decreases, reducing the overall amount of energy harvested by the device. With this in mind, traditional wireless power transfer modalities such as RF or inductive coupling are less effective than ultrasonic power transfer at millimeter scales, due to the improved efficiency of acoustic propagation in tissue over electromagnetic propagation [15][16][17]. In the past decade, acoustic power transfer has been gaining popularity as a method for powering medical devices; the number of papers discussing acoustic power transfer for IMDs has increased from roughly 6 published papers between the years 2000-2009 to almost 300 published papers between 2010-2018 ( Fig.…”

Performance Enhancement of an Ultrasonic Power Transfer System Through a Tightly Coupled Solid Media Using a KLM Model

“…As shown in Figure 1, the transducers were mechanically pressed to the metal wall using Neoprene rubber with low specific acoustic impedance on the backside to minimize the emission losses. For the approach illustrated in Figure 1, the energy transmission depends heavily on the properties of the piezoceramic material [10], the acoustic impedance of the media [11], and the media attenuation [12], as well as the transmission frequency [13] and the attached electric loads [14]. In [14], the zero reflection and power maximization condition for a similar power link were compared to each other with water as the transmission medium.…”