Abstract
Wireless power transfer (WPT) systems have become increasingly suitable solutions for the electrical powering of advanced multifunctional micro-electronic devices such as those found in current biomedical implants. The design and implementation of high power transfer efficiency WPT systems are, however, challenging. The size of the WPT system, the separation distance between the outside environment and location of the implanted medical device inside the body, the operating frequency and tissue safety due to power dissipation are key parameters to consider in the design of WPT systems. This article provides a systematic review of the wide range of WPT systems that have been investigated over the last two decades to improve overall system performance. The various strategies implemented to transfer wireless power in implantable medical devices (IMDs) were reviewed, which includes capacitive coupling, inductive coupling, magnetic resonance coupling and, more recently, acoustic and optical powering methods. The strengths and limitations of all these techniques are benchmarked against each other and particular emphasis is placed on comparing the implanted receiver size, the WPT distance, power transfer efficiency and tissue safety presented by the resulting systems. Necessary improvements and trends of each WPT techniques are also indicated per specific IMD.
Highlights
Wireless power transfer (WPT) can be defined as a technology capable of transmitting energy across a medium, from a power source to an electrical load, without the use of electrical wires connecting this power source to the load [1,2]
(2) To satisfy the safety regulations set by the Food and Drug Administration (FDA) and Federal Communications Commission (FCC) for far-field based WPT systems, the radiated TX power and received power at the implant side are small compared to the Non-radiative inductive coupling (NRIC) and Non-radiative magnetic resonance coupling (NRMRC) WPT systems
The following safety regulations are recommended with respect to static magnetic field strength, Radio frequency (RF) heating and time varying magnetic fields [35]: (1) Typical exposure to static magnetic field must not exceed
Summary
Wireless power transfer (WPT) can be defined as a technology capable of transmitting energy across a medium, from a power source to an electrical load, without the use of electrical wires connecting this power source to the load [1,2]. The former includes electric, magnetic and optical coupling systems, which can be further classified as non-radiative transfer or as near-field systems, i.e., less than 100 mm distance between transmitter and IMD [12], and radiative transfer systems. The article overlooks the possibility of optical power transfer for MIDs. a complete guide of different WPT techniques and their potential MID applications implemented by different research groups is absent in the literature. Power transfer efficiency values for a specific WPT link (i.e., the efficiency of the system without the electronic circuit) are included whenever it is available in the literature This is followed by a presentation of the range of applications using this WPT technique. The value of SAR must be lower than the IEEE standard of 2 W/kg for 10 g of tissue [60]
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