Efficient wireless nonradiative midrange energy transfer
seminar surveyer Active In SP Posts: 3,541 Joined: Sep 2010 
12102010, 03:07 PM
Abstract We investigate whether, and to what extent, the physical phenomenon of longlifetime resonant electromagnetic states with localized slowlyevanescent field patterns can be used to transfer energy efficiently over nonnegligible distances, even in the presence of extraneous environmental objects. Via detailed theoretical and numerical analyses of typical realworld modelsituations and realistic material parameters, we establish that such a nonradiative scheme can lead to ‘‘strong coupling’’ between two mediumrange distant such states and thus could indeed be practical for efficient medium range wireless energy transfer. Introduction In the early days of electromagnetism, before the electricalwire grid was deployed, serious interest and effort was devoted (most notably by Nikola Tesla [1]) towards the development of schemes to transport energy over long distances without any carrier medium (e.g omnidirectional antennas (which work very well for information transfer) are not suitablefor such energy transfer, because a vast majority of energy is wasted into free space. Directed radiation modes, using lasers or highlydirectional antennas, can be efficiently used for energy transfer, even for long distances (transfer distance LTRANS ≫ LDEV, where LDEV is the characteristic size of the device), but require existence of an uninterruptible lineofsight and a complicated tracking system in the case of mobile objects. Rapid development of autonomous electronics of recent years (e.g. laptops, cellphones, household robots, that all typically rely on chemical energy storage) justifies revisiting investigation of this issue. Today, we face a different challenge than Tesla: since the existing electricalwire grid carries energy almost everywhere, even a mediumrange (LTRANS _ few*LDEV) wireless energy transfer would be quite useful for many applications. There are several currently used schemes, which rely on nonradiative modes (magnetic induction), but they are restricted to very closerange (LTRANS ≪ LDEV) or very lowpower (_mW) energy transfers. wirelessly). These efforts appear to have met with little success. For more details, please visit mit.edu/~soljacic/wirelesspower_AoP.pdf 


seminar flower Super Moderator Posts: 10,120 Joined: Apr 2012 
23082012, 02:53 PM
Efficient wireless nonradiative midrange energy transfer
1Efficient wireless.pdf (Size: 531.46 KB / Downloads: 17) Abstract We investigate whether, and to what extent, the physical phenomenon of longlifetime resonant electromagnetic states with localized slowlyevanescent field patterns can be used to transfer energy efficiently over nonnegligible distances, even in the presence of extraneous environmental objects. Via detailed theoretical and numerical analyses of typical realworld modelsituations and realistic material parameters, we establish that such a nonradiative scheme can lead to “strong coupling” between two mediumrange distant such states and thus could indeed be practical for efficient mediumrange wireless energy transfer. Introduction These efforts appear to have met with little success. Radiative modes of omnidirectional antennas (which work very well for information transfer) are not suitable for such energy transfer, because a vast majority of energy is wasted into free space. Directed radiation modes, using lasers or highlydirectional antennas, can be efficiently used for energy transfer, even for long distances (transfer distance LTRANS»LDEV, where LDEV is the characteristic size of the device), but require existence of an uninterruptible lineofsight and a complicated tracking system in the case of mobile objects. Rapid development of autonomous electronics of recent years (e.g. laptops, cellphones, household robots, that all typically rely on chemical energy storage) justifies revisiting investigation of this issue. Today, we face a different challenge than Tesla: since the existing electricalwire grid carries energy almost everywhere, even a mediumrange (LTRANS ≈ few∗LDEV) wireless energy transfer would be quite useful for many applications. There are several currently used schemes, which rely on nonradiative modes (magnetic induction), but they are restricted to very closerange (LTRANS«LDEV) or very lowpower (~mW) energy transfers [2,3,4,5,6]. Range and rate of coupling The range and rate of the proposed wireless energytransfer scheme are the first subjects of examination, without considering yet energy drainage from the system for use into work. An appropriate analytical framework for modeling this resonant energyexchange is that of the wellknown coupledmode theory (CMT) [8]. In this picture, the field of the system of two resonant objects 1 and 2 is approximated by F(r,t)≈ a1(t)F1®+a2(t)F2®, where F1,2® are the eigenmodes of 1 and 2 alone, and then the field amplitudes a1(t) and a2(t) can be shown [8] to satisfy, to lowest order. Capacitivelyloaded conductingwire loops Consider a loop of radius r of conducting wire with circular crosssection of radius a connected to a pair of conducting parallel plates of area A spaced by distance d via a dielectric of relative permittivity ε and everything surrounded by air (Figure 3). The wire has inductance L, the plates have capacitance C and then the system has a resonant mode, where the nature of the resonance lies in the periodic exchange of energy from the electric field inside the capacitor, due to the voltage across it, to the magnetic field in free space, due to the current in the wire. Losses in this resonant system consist of ohmic loss absR inside the wire and radiative loss radR into free space. Modesolving calculations for this type of RLCcircuit resonances were performed using again two independent methods: numerically, 3D finiteelement frequencydomain (FEFD) simulations (which solve Maxwell’s Equations in frequency domain exactly apart for spatial discretization) were conducted [15], in which the boundaries of the conductor were modeled using a complex impedance /2ccημω= boundary condition. Conclusion In conclusion, we present a scheme based on “stronglycoupled” resonances for midrange wireless nonradiative energy transfer. Although our consideration has been for a static geometry (namely κ and Γe were independent of time), all the results can be applied directly for the dynamic geometries of mobile objects, since the energytransfer time (1κ−μ−∼1100s for microwave applications) is much shorter than any timescale associated with motions of macroscopic objects. Analyses of very simple implementation geometries provide encouraging performance characteristics and further improvement is expected with serious design optimization. Thus the proposed mechanism is promising for many modern applications. For example, in the macroscopic world, this scheme could potentially be used to deliver power to robots and/or computers in a factory room, or electric buses on a highway (sourcecavity would in this case be a “pipe” running above the highway). In the microscopic world, where much smaller wavelengths would be used and smaller powers are needed, one could use it to implement optical interconnects for CMOS electronics, or to transfer energy to autonomous nanoobjects (e.g. MEMS or nanorobots) without worrying much about the relative alignment between the sources and the devices. 


