Wireles Energy

Annals of Physics 324 (2009) 1783–1795

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Annals of Physics
journal homepage: www.elsevier.com/locate/aop

Efficient weakly-radiative wireless energy transfer: An EIT-like approach
ˇ ´ Rafif E. Hamam *, Aristeidis Karalis, J.D. Joannopoulos, Marin Soljacic
Center for Materials Science and Engineering and Research Laboratory of Electronics,Massachusetts Institute of Technology, Cambridge, MA 02139, USA

a r t i c l e

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a b s t r a c t
Inspired by a quantum interference phenomenon known in the atomic physics community as electromagnetically induced transparency (EIT), we propose an efficient weakly radiative wireless energy transfer scheme between two identical classical resonant objects, strongly coupled to an intermediateclassical resonant object of substantially different properties, but with the same resonance frequency. The transfer mechanism essentially makes use of the adiabatic evolution of an instantaneous (so called ‘‘dark”) eigenstate of the coupled 3-object system. Our analysis is based on temporal coupled mode theory (CMT), and is general enough to be valid for various possible sorts of coupling, includingthe resonant inductive coupling on which witricity-type wireless energy transfer is based. We show that in certain parameter regimes of interest, this scheme can be more efficient, and/or less radiative than other, more conventional approaches. A concrete example of wireless energy transfer between capacitively-loaded metallic loops is illustrated at the beginning, as a motivation for the moregeneral case. We also explore the performance of the currently proposed EIT-like scheme, in terms of improving efficiency and reducing radiation, as the relevant parameters of the system are varied. Ó 2009 Elsevier Inc. All rights reserved.

Article history: Received 5 December 2008 Accepted 15 May 2009 Available online 27 May 2009 Keywords: Wireless energy transfer Coupling Electromagneticallyinduced transparency (EIT) Stimulated Raman Adiabatic Passage (STIRAP) Adiabatic following Coupled mode theory Resonance

1. Introduction The decade has witnessed a considerable interest in energy issues, such as safe generation of renewable energy, energy storage and management, etc. In particular, there is a substantial recent interest [1–5] in enabling efficient and safe wireless energy transfer,motivated by the increased
* Corresponding author. E-mail address: rafif@mit.edu (R.E. Hamam). 0003-4916/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.aop.2009.05.005

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R.E. Hamam et al. / Annals of Physics 324 (2009) 1783–1795

involvement of autonomous electronic devices (e.g. laptops, cell phones, household robots) in almost all aspects of our everydaylives, and the need to charge those devices repeatedly. In this respect, wireless nonradiative energy transfer schemes have been recently proposed [6,7] based on strong coupling between electromagnetic resonances. In this work, we explore a somewhat different scheme of efficient energy transfer between resonant objects coupled in some general way. Instead of transferring energy directly between thetwo resonant objects, an intermediate resonant object will be used to mediate the transfer. The intermediate object is chosen such as to couple very strongly to each of the objects involved in the energy transfer (i.e. much more strongly than the other two objects couple to each other). In practice, enabling such strong coupling will usually come with a price; in typical situations, the mediatingobject will often be substantially radiative. Yet, surprisingly enough, the proposed ‘‘indirect” energy transfer scheme will be shown to be efficient and weakly-radiative by merely introducing a meticulously chosen time variation of the coupling rates. The inspiration as to why the particular time variation had to work so well comes from a quantum interference phenomenon, known in the atomic...