The literature review on Metamaterials and its future applications.

1. Metamaterials and Applications
Sudeep Kumar Giri1
, Vimal Kishore Yadav2
, Aman Gupta3
Department of Electronics and Communication, Amity School of Engineering and Technology
Amity University Madhya Pradesh
1
sudeep197ono@gmail.com
3
guptaaman15031994@gmail.com
Abstract-Metamaterials are general artificial materials which possess properties that don’t occur in nature. These properties are
observed due to the structure of a certain metamaterial rather than the composition. They are observed to have Negative Refractive
Index, frequency tuning and many other optical properties.
All the materials that are classifiedunderMetamaterials are considered to have repetition of individual elements that form the basis
of regular materials like metals, plastic, etc. This regularity in patterns, size, orientation and arrangement are microscopic in level
and have the ability to render changes to light and sound waves that are not possible in any other naturally occurring materi al.
Natural materials have the tendency to affect electromagnetic waves, generally the electric component of it. But metamaterials have
shown a tendency to affect the magnetic component as well and thus opening a vast area of research which can lead to various
hypothetical and fictional events possible. The idea of these materials is generated by arranging different elements in certain shapes
and patterns thus combining their properties, giving them the ability to affect electromagnetic waves which can lead to future
applications like Invisible Cloaking, Ultra-Fast Data Processing and many more.
Keywords- Negative Refractive Index, Optical, Cloaking, Electromagnetic Properties.
I. INTRODUCTION
Metamaterials are human engineered materials which consist
of properties that are hardly found in the nature. These
materials are made in such a way that they consist of
periodically arranged metallic elements and atoms at
microscopic levels.
This repetition of the elements impart some special properties
in these materials, these properties are generally based on its’
capability to manipulate the electric as well as the magnetic
components of the light, which is apparently an EM wave.
These properties include Negative Refraction, Frequency
Tuning, Resolution of Sound and light waves and others.
These properties are observed in the metamaterials due to the
geometric arrangement of its components rather than the
generally observed composition of the material.
These materials include some changes and inputs that is
brought into the general metallic component, and these inputs
or changes bring a total deviation into the behaviour of these
materials towards the electric and magnetic components.
Designing a metamaterial solely depends on these slight
changes and arrangement of some inclusions into the main
frame; but after defining certain parameters like the size,
shape, quantity, type and placement of the other elements.
II. FABRICATION
The idea of metamaterials dates long back to the medieval
times when there were materials that could impart some of
these properties too. The Ruby Glass is one of these materials
with small gold droplets, the size being few nanometres the
materials made out of it give out different colours to that of its
original. Lycurgus Cup is one of the best example of things
made out of these materials as shown in Fig 1.
Fig. 1 The Lycurgus Cup

2. The main contribution however goes to the idea that was
proposed by Victor Veselago in 1968; he proposed that there
could be materials having negative permittivity as well as
permeability. These materials were termed as Left Handed
Materials due to their left handed sets of Electric, magnetic
and wave vectors instead of the usual right hand set. However,
this was just an idea of how a materials as such could be there.
The main contribution in fabricating a metamaterial goes to
D.R. Smith and his team (in 2000) who designed a basic yet
complicated structure of split rings (SRRs) and metallic wires
which could give out magnetically active properties rather
being all metallic in nature. The main idea behind this was to
arrange the elements in a manner to affect the Electromagnetic
vectors galling on the surface of the structure. The level on
which these materials are fabricated has reached its peak
where they are sized in nanometres and arranged in quantities
never thought of.
The various techniques that are used in the fabrication process
include:
i) Lithography Patterning: This process is one of the most
basic fabrication which involves both etching and metal
deposition methods.
Fig 2. Lithography Patterning
The first model of Resist and Substrate is taken in layers with
the resist layer being on top. An electron beam is focused on
the resist and hence a part of the resist is removed. The
removed resist give out a pattern which is either etched out
give the same pattern on the substrate or a specific metal is
deposited through these removed resist portions to give a layer
of metallic pattern. This forms the primary layer of
metamaterial.
ii) Focused Ion Beam Technique: In this technique a focused
beam of ions (generally Gallium) is used for designing or
creating a certain pattern. The main layer of the substance is
taken and the Ion Beam is focused to remove the thin layer of
the material. The Ga+ ion beams hit the surface to leave some
i+ or i- ions on the surface. This is what makes the etch marks.
Fig. 3 Focused Ion Beam Technique
iii) Photolithography: Firstly, a deposited formof substrate is
taken on which there is a film of material. On this film a
further layer of Photoresist is applied, after which light is
focused to hit the surface along with the mask that is needed
to save the portion that is not to be etched. This leads to the
creation of etchings or patterns of the desired material. The
photoresist is removed and the final metamaterial portion is
obtained.
iv) Polymer Moulding: One of the primary methods used for
the fabrication is called Polymer Moulding.
Fig. 4 Polymer Moulding Technique

3. In this process a Silicate stamp of the pattern or arrangement
of the material is taken and is allowed to compress the resist,
which is to be used as the main material. This stamp is
directly imparted onto the main resist to get the pattern. The
resist hardens to give out the final product.
III. CLASSIFICATION OF METAMATERIALS
As mentioned earlier, to design a certain metamaterial the
parameters should be followed. These parameters define the
whole properties of a material but in addition to themthe main
elements used in the designing also possess some properties,
involving their response to the Electromagnetic waves. All
these properties that are associated with the EM wave directly
corresponds to the values of Permeability and Permittivity of
the substance. The classification is thus divided into various
parts depending upon the values seen above:
i) Negative Refractive Index: Light is an Electromagnetic
Wave, it consists of both the Electric as well as the Magnetic
Properties and shows behaviour in accordance to them. Light
plays a very important role in framing the world that we see
these days; this is mainly due to its two main properties-
‘Reflection’ and ‘Refraction’. These properties make us see
what surrounds us, help us build what is good for us and
hence help us build the world we live in. We are able to see
the things around us due to the reflection ad refraction and
some other properties of light. Even the materials surrounding
us respond to these properties by ‘absorption’ and ‘emission’.
This is possible due to the Laws of Reflection and Refractive
Index respectively. The materials’ surface absorb the light
rays and hence emit them to make them visible to the naked
eye. However, if there is any change in the atomic structure
and composition of the material, it might show some new
properties, thus not abiding by the general laws of reflection
or refraction, here comes the idea of metamaterials.
Fig. 5 Metamaterials Classification
Mostly all the materials in nature, from wood to paper and
from glass to rocks, everything has a certain value for ε
(permittivity) and μ (permeability), and these values are
generally greater than zero. This makes these naturally
occurring materials transparent. However, if any of these
values get a negative value they change their property and
become opaque. And going far ahead of this, if we make both
ε < 0 and μ < 0. The whole scenario changes and the product
‘n=εμ’ (where ‘n’ relates to the Refractive Index of a specific
material) gets totally changed.
Fig. 6 A microscopic view of metamaterials
These materials possessing such different valued units and
parameters come under the category of Negative Refractive
Index Metamaterials.These materials are further divided into
types depending upon the value of the permittivity and
permeability. If a material is supposed to have ε < 0 or μ < 0,
it is said to be a Single Negative Metamaterial. If both the
values of ε and μ are less than zero, the material is referred to
as a Double Negative Metamaterial. There are other classes of
metamaterials depending upon the EM wave classification
like Double Positive, Chiral Metamaterials, Bi-Isotropic and
Anisotropic Metamaterials etc.
ii) Photonic Metamaterials: Apart from the electric and
magnetic components, frequency also has a major role in
transforming the regular world and the photons that consist of
small energy packets have certain frequencies in which they
act. There are certain materials that are engineered to interact
with the photons of energy and its optical frequencies, thus
imparting or changing the refractive index linked to them.
These photonic metamaterials, are seen to manipulate the light
from the very low to very high frequency. This leads to a
different aspect of these materials, which show their ability to
effect and bring new scope to the field of Optics. These MMs
can be used in the fast transfer of data, storage of the data and
in defence.
iii) Terahertz Metamaterials: The name itself suggests the
property of the materials to interact at the frequencies ranging
terahertz i.e. from 0.1 to 10 THz.

4. This frequency gap liesbetween the Infrared and Microwave
Frequencies in the Electromagnetic Spectrum. The specific
arrangement of some MEMS (Microelectromechanical
systems) cantilevers results in the change in the properties of
the material thus enabling it to tune and resonate with
different frequency levels. This particular work is carried on
SRRs (Split Ring Resonators), also known as Double
Negative Metamaterials (due to the values of ε and μ being
negative).
Fig. 7 Microstrip Structure of SRRs
These SRRs are a pair of concentric rings with gaps or slits at
opposite ends. These rings are generally made up of copper
and when a magnetic field is just perpendicular to the ring, a
small current is induced into it and we get a small LC
oscillator working as such. These and many such arranged in a
certain pattern lead to various alterations in the way they
respond to the EM wave.
iv) Non-LinearMetamaterials: In nature we rarely find
materials having the same properties to that of a metamaterial.
This is due to their behaviour towards the electromagnetic and
other related waves. In this category falls yet another
metamaterial called Non-linear Metamaterial. These materials
are fabricated in a way that they have non-linear media as
such for the main content which gives them the general
property of responding to the electromagnetic field. But
instead of giving a weak response as such, these unique
metamaterial possess the ability to respond with a huge
amount to even an average field. These materials have a great
use in Non-Linear Optics and Laser Optics.
IV. APPLICATIONS
The most impressive and useful contribution of the
metamaterials is their applications in the near future. The
metamaterials possess properties that are not easily obtained
in the nature so this lets the materials to go par the scientific
theories that we have considered near to impossible. The
properties like negative refractive index opens up a whole new
dimension towards the study of optics and the branches like
electric and magnetic research fields. The most important and
possible applications are:
i) Cloaking: The negative refractive index gives the
metamaterial a unique capability to develop a device that
could cloak any substance in touch with it or being draped by
it. Cloaking refers to ‘hiding’ or ‘disappearing’. This device
is capable of bending the light waves around the object to the
extent that it makes the whole object disappear and lets the
observer see the background.
The cloaking devices can be used in modern warfare
strategies, where there is a need to hide a whole aircraft so as
to make is both out-of-sight of the naked eyes as well as the
radar. The invisible tanks and other vehicles can also prove to
be an asset in defence and other related areas.
ii) Antennas: The most important use in this regard will be the
construction of Metamaterial Antennas or Smart Antennas.
The substances in these materials have the ability to enhance,
improve and increase the performance of the normal antennas.
They possess the ability to tune the frequency to the apt
amount, enhance the radiated power of these antennas and the
biggest benefit is to go beyond the bandwidth limitation for
the general antennas.The antennas constructed these days are
limited due to their size and efficiency to radiate power, but
these metamaterial based antennas have the tendency to go
beyond themand perform.
iii) Superlens: The diffraction limit is one of the biggest issues
faced by the photographers and other imaging field experts.
This is generally due to the Diffraction Limit, which creates a
limit for the resolution of the image. Whereas for the lenses
that are made up of metamaterials are capable of going
beyond this limit and get the images with resolution better
than any other lens ever made; basically due to the property to
react differently to the light wave.
iv) Absorbers: An absorber in the literal language means a
substance that takes something in and doesn’t let it out. In the
terms of optics and other scientific terms, it is a substance that
neither reflects nor transmits the incident radiation. The
metamaterial absorbers unlike the traditional absorbers have
an upper hand in being compact, effective and capabilities that
make them absorb the Electromagnetic waves. The
applications of absorbers are- emitters, photovoltaics and
sensors etc.
v) Acoustic Devices: Just like the optics devices, there are
certain acoustic metamaterial devices as well that have the
ability to effect the sound waves according to the fabrication
of the elements into the main structure. These devices can be
used to get a better quality sound transmission, ultrasonic and
sonic wave’s manipulation and can be imparted into cloaking
by making the objects undetectable by any acoustic means.

5. V. CONCLUSION
The engineering materials are undergoing a drastic change
throughout. Many new materials are being discovered,
invented and drafted into this world. Metamaterials are one of
these and can help frame the future world. With properties
that are still not available in nature these materials can help
develop devices that have capabilities to effect and manipulate
the Electromagnetic Wave.
These materials have applications including cloaking,
frequency tuning, Superlens, super-antennas, absorbers and
other smart devices are the future. The path leading their
development from the medieval times to the present scenario
is a less travelled one, but it has the most significant role to
play in the world we are stepping into. The materials require a
process that is extensive and wide.
Many such materials are being developed and tested in many
labs around the world. These researches are bringing out
results that are world changing, like impacting the optical
science, the magnetic vector science and the science of new
materials. In this paper we have seen the general overview of
metamaterials, their properties, which are totally arbitrary but
have been proved to be practical. The classification of
metamaterials that are totally based on the properties and
values of the different scientific factors like permeability and
permittivity. This classification lies down the basic ground for
the materials that are to be developed depending on their
properties. The next topic was the fabrication methods used to
build these metamaterials, including the EBL (Electron Beam
Lithography), Photolithography and Polymer Moulding etc.
The metamaterials are a part of future and this is the high time
that researches should be undertaken for them.
REFERENCES
[1] Tao Chen, Suyan Li andHui San “Metamaterials in Sensing”,
Mechanical & Power EngineeringCollege, HarbinUniversity of Scienceand
Technology, Harbin 150080, China, 29February2012.
[2] Shridhar E. MendheandYogeshwar PrasadKosta
“MetamaterialProperties andApplications”, International Journal of
InformationTechnology andKnowledge Management January-June 2011.
[3] RichardW. Ziolkowski “Design, Fabrication andTestingof Double
Negative Elements”.
[4] Arvin Reza “The Optical Properties of Metamaterial Waveguide
Structures”, Department ofPhysics, EngineeringPhysics, andAstronomy,
October, 2008.
[5] JB Pendry “Metamaterials andthe Control ofElectromagnetic Fields”,
Optical Societyof America, 2007
[6] Metamaterials andPlasmonics- http://users.ece.utexas.edu/~aalu/
[7] Metamaterials andApplication-
http://science.howstuffworks.com/invisible-tank1.htm
[8] Link forimages- www.google.co.in