Pendry discovered that the electrical properties allowing the material to absorb radiation came not from the carbon per se but from the shape of its long, thin fibers.
John Pendry of Imperial College London
Imperial College London, Mike Finn-Kelcey
Scientists had long known that they could change the behavior of a material by altering its chemistry. For instance, you can alter the color and hardness of glass by adding lead. But now Pendry saw that he could also alter function by changing a material’s internal structure on a very fine scale, less than a wavelength of whatever he was manipulating. (A wave of visible light, just about the size of a virus, has a length of a few hundred nanometers.)
These new, structurally altered materials would soon become known as metamaterials, based on the Greek meta, meaning “beyond.” “We knew we were onto something,” Pendry says.
Marconi was so pleased with Pendry’s insight into the carbon fibers that the company wanted to know whether he might have any new tricks up his sleeve. Pendry proposed trying to change the magnetic properties of a material. He wondered: Could he take a material that wasn’t intrinsically magnetic and magnetize it by altering its physical structure alone?
Ordinarily, either a material has the innate ability to be magnetized—generating forces from electrons moving inside them—or it does not. To invest this quality where it does not naturally appear, Pendry envisioned a theoretical metamaterial: a precisely crafted composite material that could selectively mimic properties of a conventional magnetic substance like iron. “Magnetism involves charge going around in a circle,” Pendry says. “If electrons in atoms could do this, then we could do it on a larger scale.”
This kind of metamaterial, he hypothesized, could be manufactured from minuscule loops of copper wire (copper is not naturally magnetic) embedded in a material like fiberglass. Pendry predicted that when current flowed through those loops, a magnetic response would occur.
There were many nuances to this scheme. If you cut the loops you could make a magnetic resonator, which would act like a switch. The switch would allow Pendry to change the magnetic properties of the fabricated material on command.
Pendry knew he was in uncharted territory, but at first he didn’t comprehend the magnitude of his idea: By combining the electrical properties of Marconi’s radar-absorbing material with the magnetism imparted by the copper wire, he had unknowingly figured out how to manipulate electromagnetic radiation, including visible light—making wild applications like Harry Potter’s invisibility cloak suddenly within reach.
Pendry’s incredible conception, published in a respected physics journal in 1999, stoked the imagination of scientists worldwide. One of the first to be drawn in was an experimental physicist at the University of California at San Diego named David Smith, who heard Pendry speak shortly before his landmark paper was published. Pendry’s results were startling, especially to a physicist, because magnetism is one of the core properties of matter. For any given element, this property or its absence was carved into atoms since the time of creation. The idea of being able to switch magnetism on and off was counterintuitive, to say the least. After the lecture, Smith returned to his lab and excitedly described to a colleague, Willie Padilla, what he had just heard. Padilla was just as captivated.
A prototype
invisibility device created by David Smith's
team at Duke. When microwaves
shine through the meshlike metamaterial
onto the copper-colored bump at the center, the
waves reflect back as if the bump were not there.
Duke Photography
Smith and Padilla were the perfect sorts of scientists to hear Pendry’s claim. Most of the physics one reads about in the popular press concerns big-picture concepts like string theory and black holes and alternate universes. Such matters are important, of course, but the profession has a lower-profile side as well: developing the skills and tools required to actually measure the behaviors of the physical world. The researchers who do this are called experimental physicists, and their guiding principle is that while the world is full of bright ideas, the only way to know if you have something real is if you can build it and then measure what you have built. Smith and Padilla belonged to this group.
Being who they were, they set to work immediately to build a real version of Pendry’s device and measure its behavior. The magnetism switch built by Smith and Padilla was faithful, in concept, to the machine Pendry had conceived. Made of tiny structures, arrays of very small coils, it could “tune in” to a magnetic field the same way a radio antenna receives and concentrates signals of a given radio frequency. When illuminated by a source of radiation, the material behaved as though it were naturally magnetic.
By the time the pair’s work was published, in May 2000, it was obvious that the ideas in play were far bigger than just artificial magnetism. A whole new branch of physics was coming up over the horizon. “We realized it was like finding a new state of matter no one had achieved before,” Padilla recalls, still marveling. He, too, was beginning to think it might be possible to create a new class of materials, comprising substances whose physical properties came not from their position in the periodic table of elements but from design decisions made by human beings.
In a stroke of great luck, Padilla and Smith made their discoveries just as physicist Valerie Browning, a new DARPA program manager, was launching an initiative of her own. Better software, massive computational resources, and increasingly precise microfabrication techniques were making it possible to fabricate materials out of minuscule building blocks specifically engineered to exploit the different sorts of physics that emerge on very small scales. (To give one example, surface-to-volume ratios, which are critical to many physical behaviors, change radically with scale. To give another example, the rules of quantum physics—the physics that dominates inside the atom—give particles capabilities amazingly different from those we see in the macro world, from tunneling through solids to instant communication between particles that are located far apart.)
At first Browning called these hypothesized materials engineered composites. Later she called them metamaterials, the term Pendry and Smith used for their devices that interacted with waves. No matter what the name, the important thing was that, like Zhang, Browning envisioned the transformative power of this brave new material world. Even before Pendry published his breakthrough paper and before Zhang fathomed invisibility cloaks or computers of light, Browning was struggling to convince the military to fund a program based on her ideas about metamaterials. In 2000, with Pendry’s paper vindicating her argument, she finally convinced DARPA to pony up $40 million for an advanced materials program. The agency was ready and waiting with an open checkbook when Smith and Padilla and Zhang, racing to build the new materials, sent proposals her way. With the money and motivation coming together, innovation soon followed.
By the fall of 2000, Pendry had laid the groundwork for a supermicroscope capable of seeing to a scale never before achieved. The inability to see the extremely small is becoming more of a problem all the time, since the objects our scientists and engineers think about are steadily shrinking (metamaterials are themselves an example). Each year scientists lose more direct access to their work; more of their landscape goes black. Tools for working around this problem have been invented, like the electron microscope and X-ray diffraction, but these are like canes for blind people: no substitute for direct observation. (To look at something with an electron microscope, for instance, you often have to coat the object being observed with metal and place it in a vacuum. Since this kills living things outright, it imposes serious limits on biological studies.) We have had no way to see living viruses infect cells, or to observe the interactions of proteins, or to watch DNA make a transcript of its biomolecular assembly instructions.
