by Controlling Light and Sound in Metamaterials
Metamaterials hold tremendous promise for controlling electromagnetic waves like light and microwaves in unprecedented ways. These artificially engineered materials are designed to have properties that may not be readily available in natural materials. By precisely structuring materials at the microscopic level, properties like effective electrical permittivity and magnetic permeability can be manipulated. This enables metamaterials to interact with electromagnetic waves in unique ways.
Negative Refraction and Metamaterials
One intriguing application is achieving negative refraction of light. Certain metamaterials have been designed whose interaction with light causes it to refract negatively – that is, the light bends in the opposite direction than expected. This counterintuitive phenomenon arises due to the materials having a negative index of refraction. Negative refraction could enable the development of a true optical “invisibility cloak” – a Metamaterials covering that bends light around an object such that it appears optically invisible from certain viewing angles. While invisibility cloaks currently only work for microwaves, continued progress is being made to expand their capabilities to visible light frequencies.
Super resolution and Hyperlenses
Another exciting area is using metamaterials to achieve super resolution imaging and “hyperlenses”. Crafted metamaterials possessing a negative refractive index can squeeze light beams into subwavelength scale, beating the classical diffraction limit. Hyperlenses made of such metamaterials could enable microscopes with absolute resolutions far greater than permitted by conventional glass lenses. They promise to revolutionize high-resolution microscopy and lithography at the nanoscale. Successful hyperlenses have already been demonstrated able to image surface plasmon polaritons with up to three times more resolution than possible with ordinary lenses.
Acoustic Metamaterials
While most research thus far has focused on controlling light waves, the concepts of metamaterials have also been adapted to manipulate sound and acoustic waves. Metamaterials for sound, known as acoustic metamaterials, apply the same underlying principles but are constructed from materials with precise shapes tuned to affect mechanical vibrations rather than electromagnetic waves. They aim to provide capabilities like negative refraction, cloaking, and superlensing of sound. This could enable important applications in underwater acoustics, medical ultrasonics, and noise cancellation technology. One innovative acoustic metamaterial recently reported acts as an acoustic superlens able to image objects smaller than one-fifth the wavelength of sound.
Transforming Electronics and Sensing
Metamaterials also inspire new types of components for electronic and sensing devices. By tailoring material properties on the nanoscale, metamaterials allow new functionalities. For instance, artificial magnetism provided by magnetic metamaterials enables miniature inductors required for many RF devices. Tailored electric responses supply alternatives to capacitors. Novel plasmonic metamaterials are enabling ultrasensitive chemical and biological sensors utilizing powerful surface-enhanced spectroscopic techniques. They may one day lead to advanced diagnostic devices and Lab-on-a-Chip technologies for medical testing and environmental monitoring. Further innovation with metamaterials promises to revolutionize many technologies by unlocking unseen capabilities from specially engineered materials.
While metamaterials research has progressed dramatically, major challenges still lie ahead. Achieving optical properties like negative refraction over visible light frequencies is an active challenge that will require new material platforms and nanostructuring techniques. Losses from absorption also must be reduced, as many metamaterials strongly interact with and absorb the electromagnetic waves they aim to control.
Scale-up of metamaterials from narrow laboratory devices to practical, manufacturable components also presents obstacles. However, the field is overcoming such challenges at an impressive pace. With continued development, metamaterials may profoundly impact technologies in photonics, telecommunications, biomedicine, and more over the coming decades. Their capacity to manipulate waves in unprecedented ways based on artificial material designs still holds vast possibilities that remain to be discovered.
