General expressions and physical origin of the coupling coefficient of arbitrary tuned coupled electromagnetic resonators

Elnaggar, Sameh Y.; Tervo, R.; Mattar, Saba M.

doi:10.1063/1.4935634

Cited by 26 publications

(18 citation statements)

References 31 publications

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“…Agreeing with (11), higher values of κ correspond to more absorbed load power (lower Q max w ). Moreover, the value of η max increases with κ; a manifestation of (12). Even lower Q max w values can be achieved by increasing Q 2 .…”

Section: Transfer Efficiencymentioning

confidence: 95%

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An electromagnetic induced transparency-like scheme for wireless power transfer using dielectric resonators

Elnaggar

2017

Journal of Applied Physics

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Similar to the hybridization of three atoms, three coupled resonators interact to form bonding, anti-bonding and non-bonding modes. The non-bonding mode enables an electromagnetic induced transparency like transfer of energy. Here the non-bonding mode, resulting from the strong electric coupling of two dielectric resonators and an enclosure, is exploited to show that it is feasible to transfer power over a distance comparable to the operating wavelength. In this scheme, the enclosure acts as a mediator. The strong coupling permits the excitation of the non-bonding mode with high purity. This approach is different from resonant inductive coupling which works in the sub-wavelength regime. Optimal loads and the corresponding maximum efficiency are determined using two independent methods: Coupled Mode Theory and Circuit modelling. It is shown that, unlike resonant inductive coupling, the figure of merit depends on the enclosure quality and not on the load, which emphasizes the role of the enclosure as a mediator. Briefly after the input excitation is turned on, the energy in the receiver builds up via all coupled and spurious modes. As time elapses, all modes except the non-bonding cease to sustain. Due to the strong coupling between the dielectrics and the enclosure, such systems have unique properties such as high and uniform efficiency over large distances; and minimal fringing fields. These properties suggest that electromagnetic induced transparency like schemes which rely on the use of dielectric resonators can be used to power autonomous systems inside an enclosure or find applications when exposure to the fields needs to be minimal. Finite Element computations are used to verify the theoretical predictions by determining the transfer efficiency, fields profile and coupling coefficients for two different systems. It is shown that the three resonators must be present for efficient power transfer; if one or more are removed, the transfer efficiency reduces significantly.

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Section: Transfer Efficiencymentioning

confidence: 95%

“…The coupling between centre '1' ('3') and '2' is quantified by the coupling coefficient κ. 12 For simplicity, the coupling coefficient between the pairs ('1','2') and ('2','3') are taken to be equal. Unlike the capacitively loaded coils (Fig.1b), the coupling between the DRs and enclosure modes in Fig.1c is electric.…”

Section: Figures 1(b)mentioning

confidence: 99%

An electromagnetic induced transparency-like scheme for wireless power transfer using dielectric resonators

Elnaggar

2017

Journal of Applied Physics

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“…Circuit models have also been developed to qualitatively and quantitatively analyse SRRs and their coupling 34,38 . Moreover, based on a coupled mode formalism, general expressions for the coupling coefficient κ T valid for both conducting and dielectric resonators have been derived that make it possible to estimate the frequencies and fields of the coupled modes for arbitrarily oriented and spaced resonators [39][40][41] . These approaches enable the calculation of the characteristic parameters of a coupled system; in principle, they could be used to tailor the coupling and quality factor Q of the two SRR elements forming a meta-dimer to realize the array excitation prescribed for superdirectivity, given that these latter requirements can be translated into equivalent conditions on T κ and Q, as anticipated in 20,22 and discussed in detail in 28 .…”

Section: Discussionmentioning

confidence: 99%

Superdirective dimers of coupled self-resonant split ring resonators: Analytical modelling and numerical and experimental validation

Vallecchi

Radkovskaya

et al. 2020

Sci Rep

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Superdirective antennas developed over the last century have received renewed interest in recent years from the development of metamaterials. these arrays of electromagnetic resonators (or meta-atoms) carrying short wavelength electro-and/or magneto-inductive waves support current distributions with very high spatial frequency as required by the classical conditions for superdirectivity. As meta-atoms can have both electric and magnetic dipole characteristics (and hence radiation properties), developing antennas exploiting these distributions can challenge conventional intuitions regarding the optimal configurations required. In this work we are reporting the development of a genuinely superdirective array using split ring resonators (SRRs). We provide a comprehensive analytical model characterizing the radiation from SRR dimers in which excitation of only one split ring leads to superdirective radiation via mutually coupled modes. our model exploits simple circuit descriptions of coupled resonant circuits, combined with standard radiation formulae for curvilinear current distributions. Using this simple model we are able to map directivity against possible SRR locations and orientations in two dimensions and identify the unique optimal configuration which meets the requirements for superdirective emission. We validate the theoretical findings by comparison to both full wave simulations and experiments showing that our SRR dimer achieves endfire directivity very close to the maximum theoretical value. Directional and smart antennas are one of the approaches that could be used to increase the capacity and flexibility of wireless systems in future integrated gigabit communications (5G and beyond). The advantages of a steerable antenna system include the possibility of tracking a terminal signal and mitigating interference between network nodes, thus improving network capacity. Directional antennas can also improve power efficiency 1. The most common technique to realize a directive antenna consists in assembling a multiple-antenna array in which the radiation pattern can be reinforced in a particular direction and suppressed in undesired directions. By individually controlling each array element in phase and amplitude, the direction of radiation can be electronically steered (phased arrays) 2. Multi-element arrays are by now widely used in based stations of cellular networks, but simple implementation for mobile devices is severely constrained by the need for small antennas, the conventional phased array techniques for enhancing the directivity leading to a significant increase of the antenna size and requiring a separate RF chain for each antenna element. On the other hand, antenna miniaturization is usually achieved at the expense of efficiency, bandwidth, directivity and gain, but especially miniaturized antennas tends to present a practically omnidirectional radiation pattern. However, future regulations might require the use of adaptive directional antennas also for mobile terminals, due to the invaluable role...

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“…In terms of circuit elements, κ is directly proportional to the mutual coupling M between the different resonators. For a general electromagnetic resonators, it is the net overlap of electromagnetic fields of resonant modes 3 . To reduce unnecessary intrinsic losses, it is desirable to maximize the source and receiver intrinsic Q factors.…”

Section: Introductionmentioning

confidence: 99%

Wireless power transfer via dielectric loaded multi-moded split cavity resonator

Elnaggar

Saha

Antar

2019

Journal of Applied Physics

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Wireless power transfer via a dielectric loaded multi-moded split cavity resonator (SCR) is proposed in this article. Unlike conventional inductive resonant coupling, the scheme enables the control of both the real and imaginary parts of the transfer impedance. It is demonstrated through measurements, analytical models and extensive full-wave simulation that the inclusion of dielectric resonators (DRs) tuned to the SCR T E 012 mode, significantly enhances the system figure of merit, optimal efficiency and maximum power transferred to the load. The effect of the DRs is shown to be related to the resonant coupling of the DRs T E 01δ and SCR modes, resulting in an electromagnetic induced transparency-like window. An efficiency of 70% is achieved when the transfer distance is 7 cm, or half wavelength. Additionally, it was shown that the efficiency is above 40% over a relatively wide bandwidth and a wide range of optimum load impedance. A circuit model is developed that enables the decomposition of the two port network parameters into their modal contributions. Hence it allows the comparison with conventional inductive resonant coupling systems on the fundamental level. Additionally, a Vector Fitting based method is proposed to calculate the circuit parameters from the measured scattering parameters.

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General expressions and physical origin of the coupling coefficient of arbitrary tuned coupled electromagnetic resonators

Cited by 26 publications

References 31 publications

An electromagnetic induced transparency-like scheme for wireless power transfer using dielectric resonators

An electromagnetic induced transparency-like scheme for wireless power transfer using dielectric resonators

Superdirective dimers of coupled self-resonant split ring resonators: Analytical modelling and numerical and experimental validation

Wireless power transfer via dielectric loaded multi-moded split cavity resonator

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