This document provides an overview of metamaterials and their applications in radar and optics. It defines metamaterials as artificially constructed materials designed to exhibit properties not found in nature, such as a negative index of refraction. Metamaterials are constructed by introducing periodic structures that are electrically small. While microwave metamaterials have been successfully implemented, realizing optical metamaterials faces challenges of smaller wavelengths requiring nanoscale fabrication and increased losses at higher frequencies. The document outlines examples of microwave metamaterial applications and the current theoretical state of optical metamaterials research.

1. Overview of Metamaterials
and their
Radar and Optical Applications
Jay B Bargeron

2. Overview
- Personal Background in Metamaterials
- Introduction to Metamaterials
- Definition of Metamaterial
- How Metamaterials work
- Microwave Metamaterials
- Optical Metamaterials
- Conclusions

3. Personal Background

4. Introduction to Metamaterials

5. Introduction to Metamaterials
Electromagnetic waves
- Not much difference between 1kHz (λ=300km) and 1THz
(λ=0.3mm)
Why can’t optical light (Terahertz frequency) go through walls like
microwaves?
- Material response varies at different frequencies
- Determined by atomic structure and arrangement (10-10 m).
How can we alter a material’s electromagnetic properties?
- 1 method is to introduce periodic features that are electrically
small over a given frequency range, that appear “atomic” at those
frequencies

6. 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.

7. Definition of Metamaterial
- “Metamaterial” coined in the late 1990’s
- According to David R. Smith, any material composed of periodic,
macroscopic structures so as to achieve a desired electromagnetic
response can be referred to as a Metamaterial
-(very broad definition)
-Others prefer to restrict the term Metamatetial to materials with
electromagnetic properties not found in nature
- Still some ambiguity as the exact definition
- Almost all agree the Metamaterials do NOT rely on chemical/atomic
alterations.

8. How Metamaterials Work
Example: How to achieve negative index of refraction
-
- negative refraction can be achieved when both µr and εr are
negative
- negative µr and εr occur in nature, but not simultaneously
-silver, gold, and aluminum display negative εr at optical
frequencies
-resonant ferromagnetic systems display negative µr at
resonance
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9. How Metamaterials Work
Example: How to achieve negative index of refraction
― What if the structures that cause this frequency variance of µr and εr at
an atomic scale could be replicated on a larger scale?
― To appear homogeneous, the structures would have to be electrically
small and spaced electrically close
― The concept of metamaterials was first proven in the microwave
spectrum.

10. Microwave Metamaterials
― Early metamaterials relied on a combination of Split-ring resonators
(SSRs) and conducting wires/posts
― SSRs used to generate desired µr
for a resonant band of frequencies.
― Conducting posts are polarized by
the electric field, generating the
desired εr for all frequencies below
a certain cutoff frequency.

11. Microwave Metamaterials
― Other approaches for fabricating microwave metamaterials have also
been developed
- Transmission line models using shunt inductors for affecting εr
and series capacitors for affecting µr. This method, however, is
restrained to 1D or 2D fabrication

12. Microwave Metamaterials
― Conducting wires/posts can be replaced with loops that mimic an LC
resonating response. SRRs are still required to affect µr.

13. Microwave Metamaterials
Proven areas of Microwave Metamaterials:
― Microwave cloaking by
bending EM rays using
graded indices of refraction
― Currently limited to relatively
narrow bandwidths and
specific polarizations
― Limited by resonant frequency
response

14. Microwave Metamaterials
Proven areas of Microwave Metamaterials:
― Sub-wavelength antennas
- n = 0 in metamaterial
- capable of directionality
- same antenna can be used for
multiple frequency bands
- currently used in Netgear
wireless router (feat. right) and
the LG Chocolate BL40

15. Microwave Metamaterials
Tuneable metamaterials:
― Consider a 2-D metamaterial, with series capacitance to affect its EM
response
- This capacitance can be tuned via ferroelectric varactors,
affecting the index of refraction of the material
― The size of the split in SRR’s can
also be adjusted, from fully closed
to fully “open” (see Fig. right)
― Capable of achieving phase
modulation of up to 60 degrees
― Applications in phased-arrays,
beam forming, and beam scanning

16. Microwave Metamaterials
Planar microwave focusing lens
―Researchers at University of Colorado have achieved a planar array
for focusing microwave radar
-Though not touted as metamaterial, meets the requirements
under the broad definition of metamaterials.
The Perfect Lens
―J.B. Pendry theoretically described how a rectangular lens with n = -1
could make a “perfect lens” capable of resolving sub-wavelength
features.
-Researchers in China, using a planar Transmission Line type of
metamaterial to focus a point source (480 MHz) , managed to
achieve sub-diffraction focusing down to 0.08λ)

17. Faster than light transmission lines?
Could this be possible?
- recall that v = c / n, where v is the phase velocity.
- if then phase velocity will be greater than c!
Reality: Law of Causilty
- We cannot see into the future OR even the present
- While phase velocity can exceed c, group velocity cannot
- Any change in energy/frequency will propagate through the
metamaterial slower than c.
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18. Optical Metamaterials
Fabrication/Design Challenges for optical metamaterials:
― Smaller wavelength = smaller features
- Coupling between elements becomes more serious
― Metal’s response to electromagnetic waves changes at higher
frequencies.
- Metal no longer behaves as perfect electrical conductors
(dielectric losses need to be taken into account)
- A frequency is eventually reached where the energy of the oscillating,
excited electrons becomes comparable to the electric field. When this
occurs, the metal’s response is known as plasmonic
- Resistive and dielectric losses become much more significant

19. Optical Metamaterials
― Most research on optical metamaterials has been at the theoretical
stage
- Mathematically characterizing nanoscale plasmonice effects.
- Computer simulations of proposed designs.
― Relatively little work has been done with physically realized optical
metamaterials

20. Optical Metamaterials
― Rare example of 3D optical metamaterial. Gold nanostructures with
70nm spacing between layers.

21. Optical Metamaterials
―Experimental measurements of the previous optical metamaterial
parallel polarized waves perpendicular polarized waves

22. Conclusions
― Introduction of metamaterials in 1990’s opened new possibilities in
electromagnetics.
― Successful implementation of metamaterial technology in the
microwave spectrum.
― Inherent difficulties exist in fabricating optical metamaterials
― Most work to date related to modeling proposed designs
― Little work, so far, on successful application of optical metamaterials

23. Fin
Questions???