Physical properties never before produced in nature Negative-index metamaterial

1 physical properties never before produced in nature

1.1 composite material
1.2 simultaneous negative permittivity , permeability
1.3 composite material passband
1.4 describing left-handed material

physical properties never before produced in nature

theoretical articles published in 1996 , 1999 showed synthetic materials constructed purposely exhibit negative permittivity , permeability.

these papers, along veselago s 1967 theoretical analysis of properties of negative-index materials, provided background fabricate metamaterial negative effective permittivity , permeability. see below.

a metamaterial developed exhibit negative-index behavior typically formed individual components. each component responds differently , independently radiated electromagnetic wave travels through material. since these components smaller radiated wavelength understood macroscopic view includes effective value both permittivity , permeability.

composite material

in year 2000, david r. smith s team of ucsd researchers produced new class of composite materials depositing structure onto circuit-board substrate consisting of series of thin copper split-rings , ordinary wire segments strung parallel rings. material exhibited unusual physical properties had never been observed in nature. these materials obey laws of physics, behave differently normal materials. in essence these negative-index metamaterials noted having ability reverse many of physical properties govern behavior of ordinary optical materials. 1 of unusual properties ability reverse, first time, snell s law of refraction. until demonstration of negative refractive index microwaves ucsd team, material had been unavailable. advances during 1990s in fabrication , computation abilities allowed these first metamaterials constructed. thus, new metamaterial tested effects described victor veselago 30 years earlier. studies of experiment, followed shortly thereafter, announced other effects had occurred.

with antiferromagnets , types of insulating ferromagnets, effective negative magnetic permeability achievable when polariton resonance exists. achieve negative index of refraction, however, permittivity negative values must occur within same frequency range. artificially fabricated split-ring resonator design accomplishes this, along promise of dampening high losses. first introduction of metamaterial, appears losses incurred smaller antiferromagnetic, or ferromagnetic materials.

when first demonstrated in 2000, composite material (nim) limited transmitting microwave radiation @ frequencies of 4 7 gigahertz (4.28–7.49 cm wavelengths). range between frequency of household microwave ovens (~2.45 ghz, 12.23 cm) , military radars (~10 ghz, 3 cm). @ demonstrated frequencies, pulses of electromagnetic radiation moving through material in 1 direction composed of constituent waves moving in opposite direction.

the metamaterial constructed periodic array of copper split ring , wire conducting elements deposited onto circuit-board substrate. design such cells, , lattice spacing between cells, smaller radiated electromagnetic wavelength. hence, behaves effective medium. material has become notable because range of (effective) permittivity εeff , permeability μeff values have exceeded found in ordinary material. furthermore, characteristic of negative (effective) permeability evinced medium particularly notable, because has not been found in ordinary materials. in addition, negative values magnetic component directly related left-handed nomenclature, , properties (discussed in section below). split-ring resonator (srr), based on prior 1999 theoretical article, tool employed achieve negative permeability. first composite metamaterial composed of split-ring resonators , electrical conducting posts.

initially, these materials demonstrated @ wavelengths longer in visible spectrum. in addition, nims fabricated opaque materials , made of non-magnetic constituents. illustration, however, if these materials constructed @ visible frequencies, , flashlight shone onto resulting nim slab, material should focus light @ point on other side. not possible sheet of ordinary opaque material. in 2007, nist in collaboration atwater lab @ caltech created first nim active @ optical frequencies. more (as of 2008), layered fishnet nim materials made of silicon , silver wires have been integrated optical fibers create active optical elements.

simultaneous negative permittivity , permeability

negative permittivity εeff < 0 had been discovered , realized in metals frequencies way plasma frequency, before first metamaterial. there 2 requirements achieve negative value refraction. first, fabricate material can produce negative permeability μeff < 0. second, negative values both permittivity , permeability must occur simultaneously on common range of frequencies.

therefore, first metamaterial, nuts , bolts 1 split-ring resonator electromagnetically combined 1 (electric) conducting post. these designed resonate @ designated frequencies achieve desired values. looking @ make-up of split ring, associated magnetic field pattern srr dipolar. dipolar behavior notable because means mimics nature s atom, on larger scale, such in case @ 2.5 millimeters. atoms exist on scale of picometers.

the splits in rings create dynamic srr unit cell can made resonant @ radiated wavelengths larger diameter of rings. if rings closed, half wavelength boundary electromagnetically imposed requirement resonance.

the split in second ring oriented opposite split in first ring. there generate large capacitance, occurs in small gap. capacitance substantially decreases resonant frequency while concentrating electric field. individual srr depicted on right had resonant frequency of 4.845 ghz, , resonance curve, inset in graph, shown. radiative losses absorption , reflection noted small, because unit dimensions smaller free space, radiated wavelength.

when these units or cells combined periodic arrangement, magnetic coupling between resonators strengthened, , strong magnetic coupling occurs. properties unique in comparison ordinary or conventional materials begin emerge. 1 thing, periodic strong coupling creates material, has effective magnetic permeability μeff in response radiated-incident magnetic field.

composite material passband

graphing general dispersion curve, region of propagation occurs 0 lower band edge, followed gap, , upper passband. presence of 400 mhz gap between 4.2 ghz , 4.6 ghz implies band of frequencies μeff < 0 occurs.

(please see image in previous section)

furthermore, when wires added symmetrically between split rings, passband occurs within forbidden band of split ring dispersion curves. passband occurs within forbidden region indicates negative εeff region has combined negative μeff allow propagation, fits theoretical predictions. mathematically, dispersion relation leads band negative group velocity everywhere, , bandwidth independent of plasma frequency, within stated conditions.

mathematical modeling , experiment have both shown periodically arrayed conducting elements (non-magnetic nature) respond predominantly magnetic component of incident electromagnetic fields. result effective medium , negative μeff on band of frequencies. permeability verified region of forbidden band, gap in propagation occurred – finite section of material. combined negative permittivity material, εeff < 0, form “left-handed” medium, formed propagation band negative group velocity there attenuation. validated predictions. in addition, later work determined first metamaterial had range of frequencies on refractive index predicted negative 1 direction of propagation (see ref #). other predicted electrodynamic effects investigated in other research.

describing left-handed material

a comparison of refraction in negative-index metamaterial in conventional material having same, positive refractive index. incident beam θ enters air , refracts in normal (θ ) or metamaterial (-θ ).

from conclusions in above section left-handed material (lhm) can defined. material exhibits simultaneous negative values permittivity, ε, , permeability, μ, in overlapping frequency region. since values derived effects of composite medium system whole, these defined effective permittivity, εeff, , effective permeability, μeff. real values derived denote value of negative index of refraction, , wave vectors. means in practice losses occur given medium used transmit electromagnetic radiation such microwave, or infrared frequencies, or visible light – example. in instance, real values describe either amplitude or intensity of transmitted wave relative incident wave, while ignoring negligible loss values.

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