Machine Design
Metamaterial cloaks can hide objects from bands of microwave radiation Image courtesy of David SchurigProceedings of the National Academy of Sciences

Metamaterial cloaks can hide objects from bands of microwave radiation. (Image courtesy of David Schurig/Proceedings of the National Academy of Sciences)

Metamaterials: Driving Performance in New Directions

Metamaterials get their amazing mechanical, electromagnetic, and acoustic properties from carefully controlled microstructures rather than from chemistry alone. They are increasingly the subject of media hype over their prospects and what miracles they may bring—invisibility and inaudibility cloaks, buildings immune to earthquakes, and ships without wakes. Developers are taking the underlying principle that says a material’s patterned structure affects its physical and pushing the properties achieved by patterning much further, using more complex structural patterns. In some cases, the properties achieved are not only different than typical bulk properties for that material, but unachievable by unpatterned materials.

In 1967, Russian V.G. Veselago published the first detailed theoretical analysis of how electromagnetic metamaterials would behave. Over the next several decades, theoretical papers occasionally advanced physicists’ fundamental understanding of what such materials could do, such as refracting light in the opposite direction as a normal material. However, until the 1990s no one knew how to make such materials or even if they were physically possible.

Since the late 1990s, each individual property and theoretical possibility that theorists predicted has been demonstrated in lab demonstrations of both electromagnetic and acoustic metamaterials. In many cases, these demonstrations have been narrow, producing metamaterials that only showed off their desired properties when interacting with electromagnetic radiation in a wavelength range as little as 5 nm wide or coming from a very specific direction. In addition, most metamaterials, particularly those that affected infrared and optical electromagnetic radiation, have relied on expensive nanofabrication methods like lithography, which are too expensive for commercial applications. Nevertheless, such demonstrations have encouraged continued development and highlight potential future applications.

Some metamaterials are based on textured surface patterning. Although these are more mature, in practice developers rarely refer to them as metamaterials. For example, companies like Hoowaki, nanoGriptech, and Sharklet Technologies are all developing patterned surfaces that impart functional properties such as high or low friction, adhesion, antimicrobial, and hydrophobic, but do not typically mention metamaterials when discussing their technologies.

These companies are among a handful of start-ups that have been founded to commercialize metamaterials. The majority of these start-ups, such as Rayspan (no longer operating), Kymeta, and Fractal Antenna Systems, focus on using radio and microwave frequency electromagnetic metamaterials as high-efficiency broadband antennas for communications – the low-hanging fruit in the metamaterials space. More recently, companies like Metamaterial Technologies have been focusing on optical metamaterials for more efficient solar panels and LEDs, while Evolv, a recent entrant, is working on more complex metamaterials for imaging. In the past 10 years, these companies have collectively raised more than $110 million in venture capital funding.

Governments and large corporations are also pursuing electromagnetic metamaterials for the long-term opportunity they represent. Communications, electronics, and defense corporations like MW, Harris Corp., Kyocera Wireless, Tyco Electronics, Alcatel-Lucent, Samsung Electronics, Murata Manufacturing, Hewlett Packard, Philips Electronics, NEC, Murata Manufacturing, Lockheed Martin, Raytheon, and Boeing hold more than 500 metamaterial patents, and China’s government-funded Kuang Chi Institute of Advanced Technology holds nearly an additional 1,000. Although significant development needs to done, this rapid pace of development points to large-scale adoption of such technologies beginning  eight to ten years from now. It is likely the new technologies will be used for more efficient wireless communications, high speed (THz frequency) electronics,  and lightweight, durable, and extremely quiet components for motors, engines, and other mechanical devices.

Over the past 15 years, researchers have taken the solid theoretical foundations behind metamaterials and made significant proof-of-concept lab demonstrations of a wide range of different Metamaterials. However, the only metamaterials that have been commercialized to date are antennas for wireless communication and textured surfaces that supplement or replace coatings. That’s because they are relatively easy to make produce using circuit board printing for the former and extrusion or molding for the latter.

Commercialization of other metamaterials is primarily a manufacturing problem. We simply lack effective tools to economically pattern large volumes of material. 3D printing is a natural candidate for addressing this problem. Today, no single 3D printer combines the necessary resolution and throughput to create large amounts of optical metamaterials. However, as 3D printing technology improves, it could become the tool of choice for most metamaterial manufacturing. Expect these two trends to feed into one another and support the general global trend toward smarter, more complex materials.

TAGS: Materials
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