11

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

22

Double Negative Media (DNG)

0

0

D E

B H

0

0

0

0

0

0

0

0

DPSDPS MNGMNGENGENG DNGDNG

SNGSNGpropagationpropagation

evanescenceevanescence

propagationpropagation

Isotropic and homogeneous

33

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

44

Negative Refraction

, 0 , 0

ki

kt

kri

t

r

air

ki

kt

kri

t

r

air

DPS DNG

Regular refractionRegular refraction Negative refractionNegative refraction

55

Negative Refraction Index (NRI)

Snell’s LawSnell’s Law

1 1 2 2sin | | sinn n

2 0n

V. G. VeselagoV. G. Veselago

66

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

77

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

0

2 2

2 20

p

p

m m

m mi

:pe

0:e:

pm

0:m

Negative permittivity (effect of wires)

Negative permeability (effect of rings)

88

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.

99

The Split Ring Resonator (SRR)The Split Ring Resonator (SRR)

1010

Waveguide Waveguide ExperimentsExperiments

220k a

Metallic rectangular waveguide: TEMetallic rectangular waveguide: TE0101 mode mode

Waveguide miniaturizationWaveguide miniaturization

SWR

Gunn

bb

1111

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 p

1212

Double Negative MediaDouble Negative Media

D. R. Smith and S. Schultz, UCSD

1313

DNG WaveguidesDNG Waveguides

DNG

DPS

DPS

P1

P2

P2

DNG slab waveguide

DNG

DPS

DNG/DPS directional coupler

P1

P2

Back propagationBack propagation

1414

ApplicationsApplications

DNG

• Cloaking devices

• Metamaterial antennas: increased performance and miniaturization