Metamaterials (Main Paper)

Metamaterials (Main Paper)

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  Metamaterials and Applications SudeepKumar 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
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  The main contributionhowever 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
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  In this processa 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.
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  This frequency gapliesbetween 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.
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  V. CONCLUSION The engineeringmaterials 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