Metamaterials are set to migrate out of the laboratory and into the marketplace

Metamaterial applications such as cheaper satellite communications, thinner smartphones and ultrafast optical data processing are where metamaterials are poised to make a huge impact within a year or so.

Kymeta of Redmond, Washington, a spin-off from Intellectual Ventures, hopes to market a compact antenna that would be one of the first consumer-oriented products based on metamaterials. The relatively inexpensive device would carry broadband satellite communications to and from planes, trains, ships, cars and any other platform required to function in remote locations far from mobile networks.

At the heart of the antenna — the details of which are confidential — is a flat circuit board containing thousands of electronic metamaterial elements, each of which can have its properties changed in an instant by the device’s internal software. This allows the antenna to track a satellite across the sky without having to maintain a specific orientation towards it, the way a standard dish antenna does. Instead, the antenna remains still while the software constantly adjusts the electrical properties of each individual metamaterial element. When this is done correctly, waves emitted from the elements will reinforce one another and propagate skywards only in the direction of the satellite; waves emitted in any other direction will cancel one another out and go nowhere. At the same time — and for much the same reason — the array will most readily pick up signals if they are coming from the satellite.

This technology is more compact than alternatives such as dish antennas. It offers “significant savings in terms of cost, weight and power draw”. Kymeta has already performed demonstrations of this technology for investors and potential development partners. But Smith cautions that the company has yet to set a price for the antenna and that it must still work to bring production costs down while maintaining the strict performance standards that regulatory agencies demand for any device communicating with satellites. Kymeta’s antenna will first by used on private jets and passenger planes. If buyers respond well, the company hopes to incorporate the technology into other product lines, such as portable, energy-efficient satellite-communication units for rescue workers or researchers in the field.

Metamaterial camera can create compressed microwave images without a lens or any moving parts. One important application of the device might be to reduce the cost and complexity of airport security scanners.

In their current form, these scanners have to physically sweep a microwave sensor over and around the subject. This produces an unwieldy amount of data that has to be stored before it is processed into an image. The Duke group’s device requires very little data storage. It takes numerous snapshots by sending beams of microwaves of multiple wavelengths across the target at about ten times per second. When the microwaves are reflected back by the subject, they fall on a thin strip of square copper metamaterial elements, each of which can be tuned to block or let through reflected radiation. The resulting pattern of opaque and transparent elements can be varied very rapidly, with each configuration transmitting a simplified snapshot of a scanned object into a single sensor. The sensor measures the total intensity of radiation from each snapshot, then outputs a stream of numbers that can be digitally processed to reconstruct a highly compressed image of the subject.

This is admittedly just a first step: demonstrations carried out so far have been crude affairs restricted to two-dimensional images of simple metallic objects. Expanding it to three-dimensional images of complex objects remains a challenge. But if that challenge can be overcome, says Driscoll, airports could retire the bulky, expensive, slow booths that currently constitute security checkpoints, and instead use a larger number of thin, inexpensive metamaterial cameras hooked up to computers. Such a shift, Driscoll says, could extend security scanning to rooms, hallways, and corridors throughout airports and other sensitive facilities.

Metamaterials for optical light are more difficult and an area of research

Metamaterials for optical light become much more useful for applications such as fibre-optic communications or consumer-oriented cameras and displays.

“It won’t be easy,” cautions Stephane Larouche, a member of Smith’s research team at Duke. For any given type of radiation, he explains, metamaterials can wield their exotic powers only if the elements are smaller and more closely spaced than the wavelength of that radiation. “So the shorter and shorter the wavelength we wish to use, the smaller each metamaterial element must be,” says Larouche.

In the microwave and radio regions of the spectrum, this is relatively easy: wavelengths are measured in centimetres to metres. But an optical metamaterial’s elements would have to measure considerably less than a micrometre. That is not impossible: today’s high-performance microchips contain features only a few tens of nanometres across. But unlike those essentially static features, says Larouche, the metamaterial elements in many applications would need to incorporate ways for software to change their properties dynamically as needed.

Workable designs for optical metamaterials have begun to emerge. One was published in March by a group working under Nikolay Zheludev, a physicist at the University of Southampton, UK, who directs a research centre focused on metamaterials at Nanyang Technological University in Singapore. The team’s device can greatly alter its ability to transmit or reflect optical wavelengths by means of nanometre-scale, electrically controlled metamaterial elements etched from gold film; it could one day serve as a switch in high-speed fibre-optic communications networks.

Commercial applications of flat metamaterial lenses with 60 nanometer or smaller elements are probably still a decade away. This is partly because silicon is a rigid and fragile substrate for etching the elements; researchers are looking at more robust and flexible alternatives that would be easier to handle on the production line. They are also looking for better ways to control the carving of the nanoscale elements, which has to be done very precisely.

A smartphone incorporating a flat metamaterial camera lens could potentially be made “as thin as a credit card”. The flat lens also avoids aberrations that plague glass lenses, such as the coloured ‘fringes’ created by the inability to focus all wavelengths to the same point. This means that Capasso’s flat lens could also be used to make better, aberration-free microscopes.

Nature Nanotechnology – An electromechanically reconfigurable plasmonic metamaterial operating in the near-infrared

Current efforts in metamaterials research focus on attaining dynamic functionalities such as tunability, switching and modulation of electromagnetic waves. To this end, various approaches have emerged, including embedded varactors, phase-change media the use of liquid crystal electrical modulation with graphene and superconductors, and carrier injection or depletion in semiconductor substrates. However, tuning, switching and modulating metamaterial properties in the visible and near-infrared range remain major technological challenges: indeed, the existing microelectromechanical solutions used for the sub-terahertz and terahertz regimes cannot be shrunk by two to three orders of magnitude to enter the optical spectral range. Here, we develop a new type of metamaterial operating in the optical part of the spectrum that is three orders of magnitude faster than previously reported electrically reconfigurable metamaterials. The metamaterial is actuated by electrostatic forces arising from the application of only a few volts to its nanoscale building blocks—the plasmonic metamolecules—that are supported by pairs of parallel strings cut from a flexible silicon nitride membrane of nanoscale thickness. These strings, of picogram mass, can be driven synchronously to megahertz frequencies to electromechanically reconfigure the metamolecules and dramatically change the transmission and reflection spectra of the metamaterial. The metamaterial’s colossal electro-optical response (on the order of 10^−5–10^−6 m V−1) allows for either fast continuous tuning of its optical properties (up to 8% optical signal modulation at up to megahertz rates) or high-contrast irreversible switching in a device only 100 nm thick, without the need for external polarizers and analysers.

Science – Metamaterial Apertures for Computational Imaging

By leveraging metamaterials and compressive imaging, a low-profile aperture capable of microwave imaging without lenses, moving parts, or phase shifters is demonstrated. This designer aperture allows image compression to be performed on the physical hardware layer rather than in the postprocessing stage, thus averting the detector, storage, and transmission costs associated with full diffraction-limited sampling of a scene. A guided-wave metamaterial aperture is used to perform compressive image reconstruction at 10 frames per second of two-dimensional (range and angle) sparse still and video scenes at K-band (18 to 26 gigahertz) frequencies, using frequency diversity to avoid mechanical scanning. Image acquisition is accomplished with a 40:1 compression ratio.

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