Spoof Plasmonics: From Metamaterial Concept to Topological Description

Abstract

Advances in metamaterials have offered the opportunity of engineering electromagnetic properties beyond the limits of natural materials. A typical example is "spoof" surface plasmon polaritons (SPPs), which mimic features of SPPs without penetrating into metal, but only with periodic corrugations on metal surfaces. They hold considerable promise in device applications from microwaves to the far infrared, where real SPP modes do not exist. The original spoof SPP concept is derived from the description of corrugated surfaces by a metamaterial that hosts an effective plasma frequency. Later, studies have attempted to describe spoof SPP modes with the band structure by strictly solving Maxwell's equations, which can possess band gaps from polaritonic anticrossing principle or Bragg interference. More recently, as inspired by the development of topological framework in condensed matter physics, the topological description of spoof SPPs is used to propose topologically protected waveguiding phenomena. Here, the developments of spoof SPPs from both practical and fundamental perspectives are reviewed.

Variable‐Temperature Electron Transport and Dipole Polarization Turning Flexible Multifunctional Microsensor beyond Electrical and Optical Energy

“…The reflected and transmitted wave decreases sharply, with greatly enhanced absorption. [20] Figure 4c shows that the frequency of absorption peak is shifted over 1.2 GHz, just by raising temperature from 323 to 473 K. As the temperature rises, more electrons are thermally activated and break loose to participate in collective oscillation, leading to increased electronic concentration (n) www.advmat.de www.advancedsciencenews.com and thus enlarged ω p (Equation (S8), Supporting Information). Actually, plasma resonance is composed of two parts, i.e., absorption (PRA) and scattering (PRS).…”

“…At that time, the energy of EM wave is strongly harvested and transformed to the energy of collective electron oscillation. The reflected and transmitted wave decreases sharply, with greatly enhanced absorption …”

Exploiting Localized Surface Plasmon Resonances in Subwavelength Spiral Disks for THz Thin Film Sensing

“…Using the investigation results for similar structures in the microwave region [22] and taking into account our technological limitations, we rescaled spiral disk parameters to the range of 0.2-0.5 THz compatible with our instrumentation capabilities: the inner radius r = 18 µ m, the outer radius R = 192 µ m, the spiral arm line width w = 8 µ m, the number of arms N = 12. We considered two types of arrays differed in the lateral periodicity p of single spirals in the X-and Y-directions: 1) p = 768 µm, distantly spaced disks; 2) p = 408 µm, closely spaced disks with a "hybridization effect" (excitation of hybridized plasmon modes).…”

“…An azimuthally grooved disk supports the resonances up to the asymptotic frequency fa, which depends on the groove width h and the refractive index n in the groove as fa = с/(4hn), where c is the light speed [22]. Increase in the width h shifts the asymptote frequency (and the resonance spectrum) towards lower frequencies and, consequently, enhances confinement of LSPR modes.…”

“…Thus, a spiral disk design is expected to be very promising for sensing applications at THz, whereat this kind of structures is still understudied. It is worth mentioning that numerical calculations, theoretical analysis, and experimental tests of spiral grooves were reported in literature mainly for the microwave region [22], and we know only one paper on experimental implementation of a simple design of spiral disks in the THz range [24]. In this paper, we present the results of numerical simulations and experimental testing of spiral metal disks patterned on a dielectric substrate to excite electric and magnetic multipole LSPRs in the spectral region of 0.2-0.5 THz.…”