Abstract
The use of resonant structures to control scattering strength and directionality is of importance in various electromagnetic systems. Here we propose and demonstrate sub-wavelength unidirectional scattering by two nearby spoof localized surface plasmon resonators for microwave. The principle is that metal surfaces corrugated by grooves can support magnetic dipolar modes, as well as electric dipolar modes. The resonance is essentially dictated by the geometric parameter of the structure, enabling extremely high degrees of freedom for tuning the scattering properties of the resonator. Particularly, by adjusting the thickness of the resonators, we can make the magnetic dipole mode of one resonator have nearly the same resonant frequency with that of the electric dipole mode of the other resonator. We show that nearly zero backscattering happens when the distance between the two resonators is subwavelenght but larger than a certain value, otherwise strong vertical coupling and mode splitting occur. The results can be extended to other frequency bands and might find application in unique resonant devices as a radio frequency (RF) antenna, filter and metasurface.
Highlights
Kerker et al.[13] have noted that, by overlapping electric and magnetic dipolar resonances of the same strength in the same spectrum window, the scattered field of a Mie scatter can have constructive interferences in the forward direction
1 r py where r is the length of the radius-vector from the dipole location to the observation point, k =ω/c is the wave vector in the vacuum, η = μ0/ε0 denotes the free space impedance; and θ and φ are the angles with respect to the z –and x-axes, respectively
By adjusting the thickness tI and tII of the two spoof localized surface plasmon (SLSP) resonators, we found that the magnetic dipole (MD) of resonator Πoverlapped well with the electric dipole (ED) of resonator Ιat f = 3.583 GHz in the spectrum [see the inset of Fig. 2(b), notice that the purple line corresponding to sub-resonator Ιand the pink line corresponding to sub-resonator Π], when the thickness of the resonator Ιis tI = 0.8 mm and that of resonator Πis tΠ = 1.2 mm
Summary
Spoof Localized Surface Plasmon received: 15 April 2016 accepted: 23 June 2016 Published: 13 July 2016. We propose and demonstrate sub-wavelength unidirectional scattering by two nearby spoof localized surface plasmon resonators for microwave. The uni-directionality derives from a configuration of locally driven feed elements coupled with several parasitic director elements in the far field Such array antennas are complex to design and have a relatively large spatial footprint in the RF and terahertz region. Kerker et al.[13] have noted that, by overlapping electric and magnetic dipolar resonances of the same strength in the same spectrum window, the scattered field of a Mie scatter can have constructive (destructive) interferences in the forward (backward) direction. It was shown that both electric dipole (ED) and magnetic dipole (MD) resonances can be supported and engineered to be of comparable strength[18] They can be used as sub-wavelength RF antenna and have prominent potential in building integrated microwave device. The design is fundamentally based on the Kerker condition, and zero backscattering is shown for a particular geometrical configuration that would be realized in experiment
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