Microwave Superdirectivity with Dimers of Helical Elements

Petrov, P.; Hibbins, Alastair P.; Sambles, J. R.

doi:10.1103/physrevapplied.13.044012

Cited by 2 publications

(3 citation statements)

References 14 publications

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“…As may be expected both electric and magnetic couplings weaken with The coupling dependence on the distance between elements, while being helpful in the design of metamaterial arrays, may be particularly useful for the metamaterial inspired applications such as miniature superdirective antennas, where both the spacing and the coupling strength have to be tuned in order to obtain close to theoretical maximum antenna performance. The general approach to the design and characterisation of such structures is found in [20].…”

Section: Magnetic and Electric Coupling Dependence On The Distance Be...mentioning

confidence: 99%

“…The coupling coefficients between helices can be adjusted for the particular applications depending on the performance requirements. For instance superdirective antennas can benefit from elements with low quality factor [20]; a small number of turns is necessary for artificial magnetic conductor structures [21]; while large negative values of coupling provided by capped helices allows one to design broadband surfaces with negative mode index [22].…”

Section: Capped Helicesmentioning

confidence: 99%

“…Because of this, helices have been optimised and used to control the effective properties of metamaterials such as the dielectric, magnetic, and chiral susceptibilities [12,13] the reflectivity, transmissivity, and absorption of metamaterial layers [14][15][16][17][18], operational bandwidth [15] as well as circular polarization conversion [19]. Moreover helical elements have been also used for superdirective antenna applications [20], to construct artificial magnetic conductors [21], and to design metasurfaces with broadband negative mode index [22].…”

Section: Introductionmentioning

confidence: 99%

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Near-field electromagnetic coupling between helices

Petrov

Hibbins

Sambles

2021

J. Phys. D: Appl. Phys.

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A fresh approach to the design of metamaterials formed from closely spaced helices is developed based on the retrieved values of electric and magnetic coupling coefficients between adjacent helices. A coupling retrieval method has been implemented to obtain numerical and experimental values for both electric-and magnetic-coupling coefficients between helical elements. Couplings between both right-and left-handed helices in side-by-side and axial arrangements are evaluated providing both positive and negative electric-, as well as magnetic-coupling components. The dependence of coupling strength on separation distance, relative axial rotation, helical pitch and the geometrical arrangement of the helices has been quantified both numerically and experimentally and a geometry giving zero net-coupling between very close helices is illustrated.

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Section: Magnetic and Electric Coupling Dependence On The Distance Be...mentioning

confidence: 99%

Section: Capped Helicesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Near-field electromagnetic coupling between helices

Petrov

Hibbins

Sambles

2021

J. Phys. D: Appl. Phys.

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Multiband superbackscattering via mode superposition in a single dielectric particle

Powell

Hibbins

Sambles

2021

Applied Physics Letters

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The superposition of resonances in a subwavelength particle can be used to achieve powerful scattering beyond the single channel limit, and can also determine the directionality of scattered radiation. It has been proposed that by overlapping only modes with equivalent polarity in the far-field, a 'superbackscattering' condition, where the total backscattered power is maximised, can be achieved. This effect can be observed through the simple geometry of a high permittivity, subwavelength sphere with a hollow core, and we demonstrate this experimentally by comparing the radar cross section (RCS) of such structures, attaining a doubling of the RCS compared to a solid particle. Furthermore we show that several sets of modes can be overlapped at once, leading to a multi-band, superbackscattering effect.Control over the magnitude and directionality of electromagnetic scattering by an object is fundamental to applications as diverse as novel antenna design[1], energy harvesting[2] and radar detection [3]. Subwavelength particles are of particular interest as their strong resonant response enables them to provide a much larger scattering cross section than their physical dimensions [4]-[6]. Although the scattering spectra from a subwavelength object is determined by the well-established Mie theory -where each resonance has a defined order, magnitude and radiation pattern [7], it can be shown that by manipulating the particle structure one can excite modes at significantly different frequencies than might be expected, opening the door to a much wider range of behaviours.

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Microwave Superdirectivity with Dimers of Helical Elements

Cited by 2 publications

References 14 publications

Near-field electromagnetic coupling between helices

Near-field electromagnetic coupling between helices

Multiband superbackscattering via mode superposition in a single dielectric particle

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