IEEE Spectrum – new antennas based on metamaterials, though, may soon rescue Web-addicted travelers from expensive connections in the air and elsewhere, and a group at the patent-licensing firm Intellectual Ventures (IV) thinks that it can implement the new technology by 2014.
While IV has researched exotic applications of metamaterials like cloaking devices that could make an object invisible, our current focus is on more practical applications of the technology:
* Satellite user terminals to connect boats, planes, cars and other vehicles to broadband service
* Dynamic cellular base station antennas to expand cell phone service
* Dynamic antennas for home and office wireless routers
* Collision avoidance radar systems for vehicles
* Advanced medical devices for focused surgical procedures
* Imaging systems for non-destructive testing of composite materials
Metamaterial Surface Antenna Technology
Unlike today’s large, heavy and hand-built mechanical and phased array user terminals, MSA-T’s antenna structure is similar to printed circuit boards and can be fabricated using established lithography and mass-production techniques. MSA-T allows for lower-cost user terminals as thin as 2-3 cm that weigh only a few kilograms. MSA-T transmit and receive modules can be tiled as needed to meet customer bandwidth requirements. Variants of MSA-T offer the potential for curved antenna products that conform to a mounting surface, such as the fuselage of an aircraft.
Image: Intellectual Ventures Radio Row: Individual metamaterial elements, like those shown here, can be tuned to dynamically redirect radio waves.
Airlines would be able to direct dynamic antennas straight up at satellites, which is possible in one of two ways: mechanically, with a gimbal that points a dish antenna to the right part of the sky, or with a phased array, a complicated setup that electronically directs a beam by pulsing individual elements of an array in precise patterns. But mechanical gimbals are not exactly aerodynamic—one example is that massive protuberance on the nose of Predator drones. And the many phase shifters needed for phased arrays make them extremely expensive—about US $1 million a pop.
With options like these, companies like Boeing are itching for a low-cost, low-power, electronically scanned array, a technology that IV’s metamaterials researcher Nathan Kundtz calls “the holy grail of antenna design.”
The group at IV has developed a thin, lightweight antenna that takes advantage of metamaterials—synthetic substances that are being researched for use with invisibility cloaks, among other things. While natural substances derive their electromagnetic properties from their atomic composition, metamaterials gain theirs from fine, deliberately designed internal structures, which, though larger than atoms, exist on a smaller scale than the wavelengths of light they manipulate.
“Using metasurfaces for antennas is very similar to the concept used in cloaking,” says IEEE Fellow Stefano Maci, a professor of electromagnetics at the University of Siena, in Italy, who was not involved in the IV product but is working on a similar metamaterials-based antenna for the European Space Agency. The subwavelength features of metamaterials produce electromagnetic properties not found in nature, bending optical and radio waves in ways once thought to be impossible. Metamaterial cloaking devices work by refracting light around an object, and the same wave-bending concepts can be used to steer beams from antennas.
Today the real problem isn’t constructing those antennas—that’s been done many times over. “The most difficult step is to reconfigure and maintain a good shape of the beam over the bandwidth,” says Maci. That’s important on a bucking plane—or train or automobile—that needs to keep in constant contact with a satellite. In order to fluidly redirect a beam, the frequency and direction of each individual element on the antenna needs to be controlled on the fly.
There are a number of different ways that the metamaterial elements’ properties can be changed, says Kundtz. “In the nascent stages of the project, we outlined about 10 different ways we could change a cell’s properties,” he says, including ferroelectric materials, MEMS devices, and liquid crystals. IV won’t disclose what it has settled on yet. “We found a very inexpensive way of tuning each one of those elements,” says Russell Hannigan, director of business development at IV. “By applying a voltage across [an element], you can scatter energy whatever way you want to across the surface.”
Antenna researchers express some disbelief at IV’s claims: In just two years, the company professes to have achieved a degree of reconfigurability that others have struggled with for much longer. Maci says that he’s skeptical of the group’s work without further evidence of their methods. “In principle, it is possible to achieve what they claim; I’m working on it myself,” he says. “But it’s extremely difficult to do.”
Before the IV researchers came up with their technique, a group at HRL Laboratories led by IEEE Fellow Daniel Sievenpiper, now at the University of California, San Diego, developed an antenna whose metamaterial elements were controlled by “varactors”—diodes with variable capacitance—at nodes between them. “While more research and development is needed to achieve the performance of today’s phased-array technology for electronic beam steering, our initial data provides an indication of what could be possible,” writes Joe Colburn, director of antenna research at HRL, in an e-mail.
IV’s metamaterials antenna isn’t yet ready for production. The researchers first demonstrated two-dimensional steering only this June, and they’re aiming to have something commercially available by late 2014. Before then, they’ll have to improve the efficiency of their antenna. “Historically, efficiency is one of the banes of metamaterials,” says Kundtz. “They tend to suck up a lot of energy.”
But that should be a surmountable obstacle. Says Maci: “I believe this will be the future of reconfigurable antennas.”
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