Remember Harry’s invisibility cloak from the Harry Potter series? Metamaterials may hold the key to partial versions of cloaking devices and other seemingly impossible technologies.
Metamaterials are engineered materials with properties that are not normally found in nature. In the real world, they play roles in technologies such as wireless devices, medical imaging, and noise control.
Structure instead of composition
Metamaterials are engineered to manipulate electromagnetic waves, such as light, or in other cases sound waves. Unlike natural materials whose properties are often determined by their chemistry, metamaterials’ properties are defined mainly by their structure.
They are composed of tiny, carefully designed structures, often at scales much smaller than the wavelength of whatever they interact with. These building blocks are also known as “meta-atoms.” Because the meta-atoms are smaller than the wavelength, waves can move through the material in unusual ways, such as bending in unexpected directions.
The small size of the meta-atoms also allows for “homogenization.” This means that a wave perceives the collection of tiny structures as one continuous, homogeneous material.
Bending light the “wrong” way
Some metamaterials exhibit a negative refractive index. Unlike ordinary materials with a positive refractive index, these structures can cause light to bend the “wrong way.” In the diagram below, the glass on the left shows a normal glass of water with a positive refractive index. The glass on the right demonstrates what the straw could look like if the water had a negative refractive index.
Effective properties and applications
Metamaterials are often described using effective properties, which represent the behavior of the material as a whole. These properties help researchers determine how a wave will move through a metamaterial without tracking its interaction with billions of individual meta-atoms. Examples include effective permittivity, which describes how the material responds to an electric field, and effective permeability, which describes its response to a magnetic field.
Their ability to control electromagnetic waves can improve wireless communication through smaller antennas and better signal direction. In optics, metamaterials can also be used to create “superlenses” that capture details smaller than the wavelength of light.
Metamaterials demonstrate that carefully designing structure instead of composition can give us precise control over waves, opening the door to extraordinary possibilities.