Physical mechanism of order between electric and magnetic dipoles in spoof plasmonic structures

Abstract

It has been recently shown that a solid-textured metal cylinder can support electric and magnetic dipolar resonances simultaneously [Phys. Rev. X4, 021003 (2014)PRXHAE2160-330810.1103/PhysRevX.4.021003] which are almost degenerate in a two-dimensional (2-D) structure and non-degenerate in a three-dimensional (3-D) structure, and with the magnetic dipole appearing at higher frequency. They are described as spoof localized plasmonic modes analogous to localized plasmonic resonances in optical frequencies. Here, we consider a hollow metal cylinder corrugated by periodic cut-through slits. Our results indicate that the magnetic dipole can be separated from the electric dipole in a 2-D structure, and magnetic dipolar resonance appears at lower frequency, rather than electric resonance in both 2-D and 3-D structures. In order to clarify the physical mechanism behind the abnormal phenomenon, we study the influence of the core material on the electric- and magnetic-dipole modes based on theoretical analysis and numerical simulation. It is discovered that there is a threshold of an imaginary part of permittivity for switching the order between electric and magnetic dipoles. These results may provide fundamental understanding and physical insight for spoof plasmonic modes supported in designer structures.

Tunable multiband directional electromagnetic scattering from spoof Mie resonant structure

“…It is well known that m = 0, m = 1, and m = 2 in Eq. ( 4 ) respectively correspond to magnetic dipole, electric dipole and electric quadrupole 29 , then three peaks in analytical SCS can be identified by calculating the SCS of individual resonance mode as shown in blue dash, green dash, and pink dash lines in Fig. 1(b) , respectively.…”

“…In fact, the spectral shift mainly depends on the shift of these resonant modes for changing the structure parameters. It is well known that the resonant frequencies of the electric dipole and quadrupole are increased with decreasing the depth of the metallic slits 29 or grooves 21 whether by decreasing the outside radius or increasing the inner radius of the hollow textured PEC cylinder. While the resonant frequency of magnetic dipolar mode mainly depends on the radius of displacement current circle excited by electric field.…”

“…Since then, extensive theoretical and experimental works have been performed to verify the existence of spoof LSPs in various textured metallic structures 22 – 28 . Recently, we also have demonstrated that a hollow metallic cylinder corrugated by periodic cut-through slits can supports the magnetic and electric dipole resonances similar to the Mie resonance in dielectric particles with a high-refractive index, as the spoof Mie resonant structure 29 . Different from the spoof LSPs supported on the solid textured metal cylinder 28 , our results indicate that the magnetic dipole can be separated from the electric dipole in a 2D structure, and magnetic dipolar resonance appears at lower frequency, rather than electric resonance in both 2D and 3D structures.…”

“…Since then, extensive theoretical and experimental works have been performed to verify the existence of spoof LSPs in various textured metallic structures [20][21][22][23][24]. In addition, we also have demonstrated that a hollow metallic cylinder corrugated by periodic cut-through slits can supports the magnetic and electric dipole resonances similar to the subwavelength dielectric nanoparticles with a high-refractive index at optical frequencies, as the spoof Mie resonant structure [25]. Certainly, the optical properties for the high-index nanoparticles in the near-infrared or visible regimes can be rescaled to big-size particles in low frequencies with similar radius to wavelength ratios.…”

Plasmonics for Biosensing

“…In the second mode, a loop-like current is generated and it can be treated as a magnetic dipolar moment. Currently, most of the research on magnetic dipole is mainly on standing nanostructures [83,84,85], and for modes coupling to generate Fano resonance to have narrow spectra features for RI sensing [86].…”