Engineering as a field of innovation and creation, engineers are looking for composing new material that has new structure; having response functions that are recognized physically and have properties that are not found directly in nature. Metamaterial is one of the material that has raised recently especially the last decades. Metamaterial in general is composed of artificial material that has unit cells arranged periodically. In addition to the periodicity of cells, it is structured in a macroscopic level, and that is what provides the material with the special electromagnetic response as desired. By including some artificial fabrications and embedding them in the material, parameters and characteristics can be modified and changed for the material. Metamaterial also is known to have a negative refractive index, and are also called left-handed material. Metamaterial as an application is used in few products such as absorbers, sensors, and antennas. Since metamaterial has a negative refractive index, not only is light bent in an unusual way when it goes through it, but also light goes out in the same way it came in. Moreover, it is expected that metamaterial may have some unseen cloak application within time.
Regarding the history of Metamaterial, Victor Veselago was the first person to propose a theoretical principle of new material that has reversed physical features and has a negative refractive index. The material he proposed also had the feature of having both negative permittivity and permeability. That was all at 1967, but the first actual Metamaterial was manufactured at 2000 by a person known as Doctor Smith in the University of California. The material is manufactured by several elements including metals and plastic materials, which provides the material with its features, based on the structure of the material, not on the components themselves.
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The main aim behind metamaterial is to have negative permeability and negative permittivity, and also having a negative refractive index, where all of these mentioned features are not found in any natural material that is not synthesized. According to Snell law, in the third quadrant, the refractive index is supposed to have a negative sign. However in metamaterial, the light is refreacted in an opposite way of how it is in the normal refractive material. N. Engheta in 2006 stated that a ray has a negative refraction when it bends on the surface, but when it goes through the material the refraction is considered to be positive as shown in the below figure.
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It is known that there are three different types of metamaterial that have been proposed, are they are known as, electromagnetic, acoustic, and mechanical metamaterials. First of all, regarding the electromagnetic metamaterial, they are composed of particles that are conductive and also traces inside a dielectric matrix. Those material are known to either no or negative permeability, permittivity. They also always have a negative refractive index. Duke University and the Imperial University of London are known to be the current highest contributors of this category of metamaterias. This category of metamaterials is used in the application of microwave and optics. They can be used for steering the beams, radomes for antennas, modulators, and as couplers for microwaves. Electromagnetic metamaterial affects the electromagnetic waves due to having less wave length than usual electromagnetic wave length radiation. There are three sub-types of electromagnetic metamaterials knowns as, single negative, double negative, and photonic electromagnetics. (As if only, From the second page). Single negative ones are the ones that have either permeability or permittivity to be negative, but not both of them. Double negative ones are the ones that have negative permeability and permittivity, and also have a negative refraction index, and they are also called backward wave media. The third type is known as photonic metamaterials, and they are manufactured in a way to have interaction with the material of optics, and they are also known to be called as the optical metamaterial. This type of electromagnetic metamaterial has a zero value regarding the refraction index, and this type is the one that is related to the field of optics and which the optical research is concerned about.
The second main type of metamaterials is known to be acoustic metamaterials. In general the acoustic metamaterials include two materials at least, each with a distinct bulk modulus and mass density. This type of metamaterials has a negative effect on the bulk modulus and the mass density, or on one of them only. The current most contributors regarding this type of metamaterials are University of Liverpool and Hong Kong University of Science and Technology, and both universities are trying to apply what they have had their researches around such as transfer of wireless power, damping of vibration, anti-sonar, and seismic protection. Acoustic metamaterial is made for the purpose of controlling and modifying and directing the sound waves in all states of material. All types of waves of sound can be contolled just by changing the parameters the acoustic metamaterial is made from, as manipulating the value of bulk modulus and mass density.
After that, the third type of the metamaterial is called the mechanical metamaterial. The main feature about the mechanical metamaterial is that it consists of different material that have different mechanical properties. And this type of metamaterial has a negative value for all the parameters as ratio of Piosson, elastic modulus, and the properties of friction. It also has a zero value for the Shear modulus. Mechanical metamaterials are mainly made of secondary material included or by having pored structure inside them.
In this following paragraph, we will mention some of the application where metamaterials have been used and implemented. First of all, antennas are designed using metamaterials, and in this application the purpose of using metamaterials is to have better system efficiency. Also the metamaterial can be used to coat so that they can increase the radiation but with an associated increase in the power consumed. Since the metamaterials have a negative permeability, this provides some features in the systems for antennas. Having a refraction index with a zero value helps