Volume 13, Number 2, 2005
John Xiao and Shridhar Yarlagadda spend much of their time working with so-called “left-handed materials,” but the UD researchers aren’t designing scissors and baseball gloves for southpaws.
Instead, they’re working with a type of material so unusual that its properties are the reverse of those found in nature. Left-handed materials weren’t even imagined until the 1960s and weren’t able to be manufactured until about five years ago.
Xiao, associate professor of physics and astronomy, and Yarlagadda, research associate in the College of Engineering’s Center for Composite Materials, conduct their research through the composite materials center.
Left-handed materials, which Xiao and Yarlagadda prefer to call “negative-index materials,” are defined by a unique property. Both their magnetic permeability, a number that describes how they respond to a magnetic field, and their electric permittivity, which describes their response to an electric field, are negative numbers. With right-handed materials—including all known materials found in nature, as well as common man-made materials such as plastics—at least one of those numbers is positive.
The result is that left-handed materials have unexpected properties. Light passing through them, for example, bends in the opposite way than is normally seen. Other electromagnetic waves, such as microwaves and radio waves, also exhibit different behavior when traveling through left-handed materials.
The counterintuitive properties of these materials were first described in a paper published in 1968 by Russian theorist Victor Veselago.
“At that time, the technology didn’t exist to fabricate such materials, so Veselago’s idea was interesting, but it died out because it was entirely theoretical,” Xiao says. “Today, we can make a fully engineered material, from the ground up, that has these kinds of fantastic properties.”
Left-handed materials were first manufactured by University of California-San Diego researchers Sheldon Schultz and David R. Smith, who announced their discovery in 2000. For the next few years, physicists and engineers debated whether the materials actually existed, but by the 2003 national meeting of the American Physical Society, most scientists agreed that left-handed materials are real. Now, researchers are trying to determine how useful, or even potentially revolutionary, their applications will be.
Possible uses are in the fields of optics, telecommunications, medical technology and computer chip design.
“An example in optics is a lens, which normally must be either concave or convex. A normal lens also has a limit to its resolution, so that past a certain point, you can no longer see the image,” Xiao says. “But, using a left-handed material with negative imaging, you could create a flat lens that doesn’t lose any resolution. It would be a perfect lens.”
More work is needed, he notes, before such applications move from theory to reality.
“Optics could be the field where these materials have the most uses, although those applications are probably not going to happen soon,” Yarlagadda says. “But, there are other potential uses that could change radar and telecommunications technology, and those could have a big impact on those industries.”
Some scientists envision using left-handed materials’ ability to focus light in a new way to improve magnetic resonance imaging (MRI) for medical diagnosis. In telecommunications, cellular phones, which work at microwave wavelengths, might use left-handed materials to improve their reception.
The University of California researchers produced their original left-handed materials from an array of thin copper rings and wire, using an electronic circuit to create two-dimensional results. Xiao and Yarlagadda are attempting to make three-dimensional materials, with Xiao focusing on nanotechnology and Yarlagadda on bulk materials in quantities that would be suitable for experimentation.
“There might be cases where you could use the nanoscale materials, but in other cases, you’ll need them on a larger scale,” Yarlagadda says. “The challenge is to keep those unique properties of the nanoscale materials, but fabricate them in bulk.”
The researchers use a machine with a high-vacuum chamber to make nanoparticles that are free from impurities. They place a chunk of magnetic metal, such as nickel, in the chamber and bounce ions off it to free up its atoms, which then are deposited in an extremely thin film on glass or some other type of surface. The film, which Yarlagadda describes as a type of plating, is generally less than 20 nanometers thick. A nanometer is one-billionth of a meter.
“You can also create a composite film with multiple layers of different materials, one on top of the other,” Yarlagadda says. “The combination of materials and the scale you select give you some very interesting properties.”
—Ann Manser, AS ’73, CHEP ’73