Learing Basics of MEMS & Metamaterials 1

8/13/2019 Learing Basics of MEMS & Metamaterials 1

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OUTLINES

• EM spectrum

• Why Metamaterials?

• Introduction to Metamaterials

•

Properties of Metamaterials

• Why MEMS?

• How to actuate the MEMS structure?

• Principles of electrothermal actuation of MEMS

•

Design of MEMS structure for tunablemetamaterials

• How to Design Metamaterials?

• Split Ring Resonators (SRR)

• Tunable Metamaterials

•Applications of Metamaterials



EM spectrum

•

All EM waves except the EM waves in the range of THz respond to naturalmaterials.



Why Metamaterials?

• The band of frequency in EM spectrum betweenradio waves and IR light is THz gap. Its is defined as0.1 to 10THz.

• EM waves in this range does not respond to naturalmaterials.

• Thus we have to develop metamaterials, which canshow unusual natural material properties, so that itcan respond to the THz range of EM waves.



Introduction to Metamaterials

What’s in a name?

- “Meta-” means “altered, changed” or “higher, beyond”

Why are they called Metamaterials?

- Existing materials only exhibit a small subset of

electromagnetic properties theoretically available

- Metamaterials can have their electromagnetic properties

altered to something beyond what can be found in nature.

- Can achieve negative index of refraction, zero index of

refraction, magnetism at optical frequencies, etc.






•

Metamaterial is a periodic material that derives its properties fromits structure rather than its components

• Depending on the structure , metamaterials may have refractiveindex less than 1 and even negative

• They are assemblies of multiple individual elements fashioned from

conventional microscopic materials such as metals or plastics, butthe materials are usually arranged in periodic patterns

• Their precise shape, geometry, size, orientation and arrangementcan affect the waves of light or sound in an unconventional manner,creating material properties which are unachievable withconventional materials



• In negative index metamaterials (NIM), both

permittivity and permeability are negative resulting ina negative index of refraction.

• When a negative index of refraction occurs,

propagation of the electromagnetic wave is reversed.

• Resolution below the diffraction limit becomes

possible. This is known as Sub wavelength imaging.


Negative index of refraction, Backwardwaves and Sub-wavelength imaging





Left Handed Materials (LHMs)if E is along the positive x direction and H along the positive y direction,

the wave will propagate along the negative z direction in a LHM

Conventional materials Left Handed materials




How to Design Metamaterials?

• Designing each unit cell using MEMS structure

• Periodic arrangement of the unit cell structure leadto the pattern for metamaterial



a

a

p

p

schematics of the elementary cell.

d

•Mostly the open ring resonator canbe considered as an LC circuit

•The incident wavelength, λi > 1m

•From the figure,

P→ pitch of the cell

a→ metamaterials dimension

Unit Cell Size



Split Ring Resonators (SRR)

• one of the most common elements used tofabricate metamaterials

• designed to mimic the magnetic response of atoms and tohave a stronger magnetic coupling than is found in nature

• Each unit can be designed to have its own magnetic

response and the overall effect reduces power requirements



• A metamaterial with a variable response to anincident electromagnetic wave.

• The response includes the capability to determine

whether the EM wave is transmitted, reflected, orabsorbed

• Allow arbitrary adjustments to frequency changes inthe refractive index.

•the lattice structure of the tunable metamaterial isadjustable in real time, making it possible toreconfigure a metamaterial device during operation

Tunable metamaterials



Applications of Metamaterials

•

There'd be plenty of applications in the civilian world aswell, even for rudimentary cloaking devices.

• For example, to create receptacles to shield sensitivemedical devices from disruption by MRI scanners, or buildcloaks to route cellphone signals around obstacles.

• Potential applications of metamaterials are diverse:

• remote aerospace applications,

• sensor detection and infrastructure monitoring,

• smart solar power management,

• public safety, high-frequency battlefield communication .

• lenses for high-gain antennas, improving ultrasonic sensors,and even shielding structures from earthquakes.



LIGHT

SOURCE

OBJECT

METAMATERIAL

LIGHT

RAYS

A 3D Possibility

Invisibility using metamaterials



WhyMEMS?•

To control the transmission and reflectionproperties of metamaterials

• More drastic change of THz transmissionperformance by geometrically changing the

metamaterial unit cells

How to actuate the MEMSstructure?•

Electrostatics• Electrothermal

• Electromagnetic

• Piezoelectric



Principles of electrothermalactuation of MEMS

Material A

Material B

• Coefficient of Thermal Expansion (CTE) measures the

fractional change in length per degree change in temperature

at a constant pressure of a solid substance.

• Due to CTE) of the material, substrate will bend towards the

opposite direction of the expanded material

• If both the materials are thermally expanded, depending on

the CTE, the material will bend to the side of material with

less CTE.

For example: refer to figure 1CTE of Material A = 27nm/K

CTE of Material B = 0.1nm/K

The cantilever tends to bend downwards since

the CTE of Material A is more than Material B.Figure 1



Design of MEMS structure fortunable metamaterials

• A cantilever structure is to be designed and fabricated to act

as an actuator

• The structure will be tuned with an AC input and it will beactuated.

• This cantilever actuated MEMS structure will be the unit cell

for the metamaterials

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Learing Basics of MEMS & Metamaterials 1