What are metamaterials, and what are they used for?

Metamaterials are artificially engineered materials that are designed to have properties that are rarely observed in nature. These materials gain their properties from their internal microstructure rather than from their composition. Metamaterials are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. The materials are usually arranged in repeating patterns at scales that are smaller than the wavelengths of the phenomena they influence. This unique arrangement allows the metamaterials to exhibit unusual properties, like negative refractive index, cloaking, superlensing, etc.

In the RF & Microwave universe, Metamaterials are used to enhance the performance of the antenna systems, electromagnetic characteristics, absorb electromagnetic radiation and modification of elastic properties of materials.

Classification of metamaterials 

Metamaterials are classified into several distinct classes, based upon modified properties of the materials they are thermal, acoustic/transport, electromagnetic and mechanical.

Acoustic Metamaterials

Acoustic Metamaterials are developed by combining two or more than two materials with distinct density and bulk modulus. They can have negative density, negative emastic modulus and anisotropic mass. These metamaterials can be further divided into three distinct categories: Phonic crystals, resonant structure and space coiling.

Phonic crystals generally contain resonating sites as well as regular arrays of acoustic scattering withing the material and provide  periodicity in their structure. The Resonant structures are the type of metamaterial that are utilized for sound control and acoustic filtering. The Space coiling metamaterial provide Fabry-Perot resonances and are used in conditions where the waves can be guided without cut-off.

Electromagnetic metamaterials 

Electromagnetic metamaterials are a type of metamaterial developed by arranging homogeneous metal structures. They are used to sense humidity, pressure, biological molecules that are present in the environments and are characterized based on their permeability and electrical permittivity. They affect the electromagnetic waves that interact with their surface features, which are smaller than the wavelength of electromagnetic radiation.

Mechanical Metamaterials 

Mechanical metamaterials consist of negative elastic modulus, zero Shear modulus, and negative Poisson’s ratio. Materials with negative Poisson’s ratio have property to stiffer when the value of load increases. Also, they provide good sound and vibration absorption due to which they’re used extensively in defense and aerospace applications.

Applications of Metamaterials

Metamaterials are used as antennas in the medical sector to increase the radiated power as well as matching the characteristics and efficiency bandwidth performance of an antenna system. Also, it minimizes the mutual coupling between the antenna parts. They’re used in automotive sector to operate the motors using electricity and to ensure electromagnetic compatibility. Now-a-days, bio sensing method based on metamaterials are preferred due to their less cost and label-free biomolecule detection. Based on the frequency of sensing biomolecule the sensors are characterized as plasmatic biosensor, microwave biosensor, and terahertz biosensor. In addition, metamaterials find application in MEMS, spectroscopy, light and sound filtering, etc.