When a beam of light travels from one medium to another-from air to glass, say-its speed changes, causing the beam to bend, or “refract.” The difference in index of refraction between the two materials defines the angle of that bending. Smith of Duke University, the late Sheldon Schultz of the University of California, San Diego, and their colleagues created an engineered material unlike any seen before-a material with a negative index of refraction. The modern era of metamaterials can be traced back to 2000, when physicists David R. Bose's twisted jute showed that it was possible to engineer an artificial material to control light in unprecedented ways. By manually twisting jute fibers and arranging them in regular arrays, he demonstrated that linearly polarized electromagnetic waves-light whose electric and magnetic fields oscillate along straight lines-rotate their polarization as they propagate through and interact with the jute structures. In the late 19th century, a few years after James Clerk Maxwell's discovery of the equations of electromagnetism, Jagadish Chandra Bose built the first examples of what we could call a metamaterial. Although humans cannot distinguish one polarization from another with our eyes, several animal species have polarization sensitivity, allowing them to see more, better orient themselves in their surroundings and signal to other creatures. A third important property of light is its polarization, which describes the trajectory that light's electromagnetic fields trace in space over time. Human eyes are excellent at detecting two fundamental properties of light: its intensity (brightness) and its wavelength-that is, its color. In the 17th century Isaac Newton and Robert Hooke recognized that the hue and iridescence of some animals are created by nanoscale patterns on the surface of their body parts-another example of how nanostructured materials can create surprising optical effects. The tiny metal nanoparticles dispersed in the glass absorb specific wavelengths and let others through, creating bright colors in masterpieces that we still admire today. An early success in this quest was the invention of stained glass: ancient Romans and Egyptians learned how to melt metallic salts into glass to tint it. Bending and Twisting Lightįor centuries scientists have strived to control the properties of light and sound as they interact with our sensory systems. With modern nanofabrication tools and a better understanding of how light and matter interact, we can now structure metasurfaces to produce any pattern, color and optical feature we can think of. Other metamaterials allow light to travel one way but not the opposite-a valuable tool for communication and detection of objects-and to break symmetries of geometry and time. Although these inventions have limitations-they aren't quite the Harry Potter–style invisibility cloaks that many people imagine-they nonetheless interact with light in a way that seems like magic.Ĭloaks are just one example of metamaterial technology. Several research teams around the world, including mine, have designed and produced metamaterial coatings that can redirect light waves that hit them, effectively preventing light from bouncing off the object and reaching our eyes and even from leaving shadows. The marquee example of this new style of materials is the “invisibility cloak”-a metamaterial coating that can hide an object in plain sight. The Greek prefix meta means “beyond.” These engineered materials let us move beyond the traditional ways in which waves and matter interact, creating technologies where light and sound appear to disobey conventional rules. And recently there has been a revolution in our ability to control these waves using materials, engineered at the nanoscale, known as metamaterials. Remarkably, all these different waves are governed largely by the same fundamental physical principles. Electromagnetic waves bring radio, television and endless streaming content to our devices. Light waves stimulate the retinas of our eyes. tiny vibrational waves transport sound to our ears.
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