Spoof surface plasmon

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Spoof surface plasmons, also known as spoof surface plasmon polaritons and designer surface plasmons, [1] are surface electromagnetic waves in microwave and terahertz regimes that propagate along planar interfaces with sign-changing permittivities. Spoof surface plasmons are a type of surface plasmon polariton, which ordinarily propagate along metal and dielectric interfaces in infrared and visible frequencies. Since surface plasmon polaritons cannot exist naturally in microwave and terahertz frequencies due to dispersion properties of metals, spoof surface plasmons necessitate the use of artificially-engineered metamaterials.

Contents

Spoof surface plasmons share the natural properties of surface plasmon polaritons, such as dispersion characteristics and subwavelength field confinement. They were first theorized by John Pendry et al. [2]

Theory

SPP oscillation in between a metal-dielectric interface Electron density wave - plasmon excitations.png
SPP oscillation in between a metal-dielectric interface

Surface plasmon polaritons (SPP) result from the coupling of delocalized electron oscillations ("surface plasmon") to electromagnetic waves ("polariton"). SPPs propagate along the interface between a positive- and a negative-permittivity material. These waves decay perpendicularly from the interface ("evanescent field"). For a plasmonic medium that is stratified along the z-direction in Cartesian coordinates, dispersion relation for SPPs can be obtained from solving Maxwell's equations: [3]

where

Per this relation, SPPs have shorter wavelengths than light in free space for a frequency band below surface plasmon frequency; this property, as well as subwavelength confinement, enables new applications in subwavelength optics and systems beyond the diffraction-limit. [3] Nevertheless, for lower frequency bands such as microwave and terahertz, surface plasmon polariton modes are not supported; metals function approximately as perfect electrical conductors with imaginary dielectric functions in this regime. [4] Per the effective medium approach, metal surfaces with subwavelength structural elements can mimic the plasma behaviour, resulting in artificial surface plasmon polariton excitations with similar dispersion behaviour. [4] [5] [6]

For the canonical case of a metamaterial medium that is formed by thin metallic wires on a periodic square lattice, the effective relative permittivity can be represented by the Drude model formula: [4]

where

Methods and applications

Simulation of spoof surface plasmon propagation through a backward-wave metamaterial in the microwave regime [7]

The use of subwavelength structures to induce low-frequency plasmonic excitations was first theorized by John Pendry et al. in 1996; Pendry proposed that a periodic lattice of thin metallic wires with a radius of 1 μm could be used to support surface-bound modes, with a plasma cut-off frequency of 8.2 GHz. [4] In 2004, Pendry et al. extended the approach to metal surfaces that are perforated by holes, terming the artificial SPP excitations as "spoof surface plasmons." [5] [6]

In 2006, terahertz pulse propagation in planar metallic structures with holes were shown via FDTD simulations. [8] Martin-Cano et al. has realized the spatial and temporal modulation of guided terahertz modes via metallic parallelepiped structures, which they termed as "domino plasmons." [9] Designer spoof plasmonic structures were also tailored to improve the performance of terahertz quantum cascade lasers in 2010. [10]

Spoof surface plasmons were proposed as a possible solution for decreasing the crosstalk in microwave integrated circuits, transmission lines and waveguides. [2] In 2013, Ma et al. demonstrated a matched conversion from coplanar waveguide with a characteristic impedance of 50Ω to a spoof-plasmonic structure. [11] In 2014, integration of commercial low-noise amplifier with spoof plasmonic structures was realized; the system reportedly worked from 6 to 20 GHz with a gain around 20 dB. [12] Kianinejad et al. also reported the design of a slow-wave spoof-plasmonic transmission line; conversion from quasi-TEM microstrip modes to TM spoof plasmon modes were also demonstrated. [13]

Khanikaev et al. reported nonreciprocal spoof surface plasmon modes in structured conductor embedded in an asymmetric magneto-optical medium, which results in one-way transmission. [14] Pan et al. observed the rejection of certain spoof plasmon modes with an introduction of electrically resonant metamaterial particles to the spoof plasmonic strip. [15] Localized spoof surface plasmons were also demonstrated for metallic disks in microwave frequencies. [16] [17]

See also

Related Research Articles

<span class="mw-page-title-main">Plasmon</span> Quasiparticle of charge oscillations in condensed matter

In physics, a plasmon is a quantum of plasma oscillation. Just as light consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantization of plasma oscillations, just like phonons are quantizations of mechanical vibrations. Thus, plasmons are collective oscillations of the free electron gas density. For example, at optical frequencies, plasmons can couple with a photon to create another quasiparticle called a plasmon polariton.

Plasma oscillations, also known as Langmuir waves, are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability in the dielectric function of a free electron gas. The frequency depends only weakly on the wavelength of the oscillation. The quasiparticle resulting from the quantization of these oscillations is the plasmon.

<span class="mw-page-title-main">Metamaterial</span> Materials engineered to have properties that have not yet been found in nature

A metamaterial is any material engineered to have a property that is not found in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. These materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.

<span class="mw-page-title-main">Surface plasmon resonance</span> Physical phenomenon of electron resonance

Surface plasmon resonance (SPR) is a phenomenon that occurs where electrons in a thin metal sheet become excited by light that is directed to the sheet with a particular angle of incidence, and then travel parallel to the sheet. Assuming a constant light source wavelength and that the metal sheet is thin, the angle of incidence that triggers SPR is related to the refractive index of the material and even a small change in the refractive index will cause SPR to not be observed. This makes SPR a possible technique for detecting particular substances (analytes) and SPR biosensors have been developed to detect various important biomarkers

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<span class="mw-page-title-main">Extraordinary optical transmission</span>

Extraordinary optical transmission (EOT) is the phenomenon of greatly enhanced transmission of light through a subwavelength aperture in an otherwise opaque metallic film which has been patterned with a regularly repeating periodic structure. Generally when light of a certain wavelength falls on a subwavelength aperture, it is diffracted isotropically in all directions evenly, with minimal far-field transmission. This is the understanding from classical aperture theory as described by Bethe. In EOT however, the regularly repeating structure enables much higher transmission efficiency to occur, up to several orders of magnitude greater than that predicted by classical aperture theory. It was first described in 1998.

<span class="mw-page-title-main">Split-ring resonator</span>

A split-ring resonator (SRR) is an artificially produced structure common to metamaterials. Its purpose is to produce the desired magnetic susceptibility in various types of metamaterials up to 200 terahertz.

Plasmonic nanolithography is a nanolithographic process that utilizes surface plasmon excitations such as surface plasmon polaritons (SPPs) to fabricate nanoscale structures. SPPs, which are surface waves that propagate in between planar dielectric-metal layers in the optical regime, can bypass the diffraction limit on the optical resolution that acts as a bottleneck for conventional photolithography.

<span class="mw-page-title-main">Negative-index metamaterial</span> Material with a negative refractive index

Negative-index metamaterial or negative-index material (NIM) is a metamaterial whose refractive index for an electromagnetic wave has a negative value over some frequency range.

<span class="mw-page-title-main">Terahertz metamaterial</span>

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

<span class="mw-page-title-main">Photonic metamaterial</span> Type of electromagnetic metamaterial

A photonic metamaterial (PM), also known as an optical metamaterial, is a type of electromagnetic metamaterial, that interacts with light, covering terahertz (THz), infrared (IR) or visible wavelengths. The materials employ a periodic, cellular structure.

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Surface plasmon polaritons (SPPs) are electromagnetic waves that travel along a metal–dielectric or metal–air interface, practically in the infrared or visible-frequency. The term "surface plasmon polariton" explains that the wave involves both charge motion in the metal and electromagnetic waves in the air or dielectric ("polariton").

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<span class="mw-page-title-main">Plasmonic nanoparticles</span>

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<span class="mw-page-title-main">Plasmonics</span>

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<span class="mw-page-title-main">Electromagnetic metasurface</span>

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References

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Further reading