metamateriais proe
TRANSCRIPT
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METAMATERIALS
Metamaterials are artificial engineered composite structures that can be designed to exhibit specific electromagnetic properties not observed in the constituent materials and not commonly found in nature.
• What’s a double negative (DNG) medium and how does it work?
• Backward waves and negative refraction
• Applications
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Double Negative Media (DNG)
0
0
ε ε
µ µ
=
=
D E
B H
0
0
ε
µ
>
> 0
0ε
µ
>
< 0
0ε
µ
<
>
0
0
ε
µ
<
<
DPSDPS MNGMNGENGENG DNGDNG
SNGSNGpropagationpropagation
evanescenceevanescence
propagationpropagation
Isotropic and homogeneous
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Backward Propagation
E
H
Right-handed MediumRight-handed Medium
kk
E
kk
H
Left-handed MediumLeft-handed Medium
SS SS
= ×S E H
DPS medium DNG medium
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Negative Refraction
, 0ε µ > , 0ε µ <
ki
kt
krθi
θt
θr
air
ki
kt
krθi
θt
θr
air
DPS DNG
Regular refractionRegular refraction Negative refractionNegative refraction
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Negative Refraction Index (NRI)
Snell’s LawSnell’s Law
1 1 2 2sin | | sinn nθ θ= −
2 0n <
V. G. VeselagoV. G. Veselago
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Pendry Perfect Lens
AA BB
dd t-dt-dtt
1n = −
PendryPendry
The lens focuses all the “planes waves” radiated by a dipole source (even the evanescent waves), with no phase or amplitude distortion
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Material DispersionMaterial Dispersion
DNG metamaterials:DNG metamaterials: can be achieved by frequency resonancecan be achieved by frequency resonance of a mixture of of a mixture of metallic and/or dielectric particles in a host mediummetallic and/or dielectric particles in a host medium..
Electric plasma frequency
Electric resonance frequency
“Magnetic plasma frequency”
Magnetic resonance frequency.
0
2 2
2 20
p
p
e e
e ei
ω ωεε ω ω ωγ
−=
− −0
2 2
2 20
p
p
m m
m mi
ω ωµµ ω ω ωγ
−=
− −
:pe
ω
0:eω:
pmω
0:mω
Negative permittivity (effect of wires)
Negative permeability (effect of rings)
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The Split Ring Resonator (SRR)The Split Ring Resonator (SRR)
External magnetic field penetrates through the rings and currents are induced.
+−−+
Gap prevents currents from flowing around the ring, which considerably increases the resonance frequency of the structure.
Metamaterial, which response should be homogeneous on the scale of the wavelength.
SRR provides a resonant structure which is much smaller than the resonance wavelength.
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The Split Ring Resonator (SRR)The Split Ring Resonator (SRR)
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Waveguide ExperimentsWaveguide Experiments
220k a
πβ εµ = − ÷
Metallic rectangular waveguide: TEMetallic rectangular waveguide: TE0101 mode mode
Waveguide miniaturizationWaveguide miniaturization
SWR
Gunn
bb
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Array of Metallic WiresArray of Metallic Wires
For long wavelengths an array of metallic wires interacts with electromagnetic waves as a plasma, and thus exhibits a negative permittivity below the plasma frequency:
2
21 pω
εω
= −
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Double Negative MediaDouble Negative Media
D. R. Smith and S. Schultz, UCSD
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DNG WaveguidesDNG Waveguides
DNG
DPS
DPS
P1
P2
P2
DNG slab waveguide
DNG
DPS
DNG/DPS directional coupler
P1
P2
Back propagationBack propagation
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ApplicationsApplications
DNG
• Cloaking devices
• Metamaterial antennas: increased performance and miniaturization