Belmont Club

Now you see it, now you don't

Advances in materials now offer the promise of bending light rays around objects. “These structures can guide electromagnetic waves around an object, only to have them emerge on the other side as if they had passed through an empty volume of space.” In other words, they can create a kind of invisibility. At the heart of this technology is the ability to create structures which can manipulate light information.

The latest advance was made possible by the development of a new series of complex mathematical commands, known as algorithms, to guide the design and fabrication of exotic composite materials known as metamaterials. … Once the algorithm was developed, the latest cloaking device was completed from conception to fabrication in nine days, compared to the four months required to create the original, and more rudimentary, device. This powerful new algorithm will make it possible to custom-design unique metamaterials with specific cloaking characteristics, the researchers said. … Cloaking devices bend electromagnetic waves, such as light, in such a way that it appears as if the cloaked object is not there.

With appropriately fine-tuned metamaterials, electromagnetic radiation at frequencies ranging from visible light to radio could be redirected at will for virtually any application, Smith said. This approach could also lead to the development of metamaterials that focus light to provide more powerful lenses.

The newest cloak, which measures 20 inches by 4 inches and less than an inch high, is actually made up of more than 10,000 individual pieces arranged in parallel rows. Of those pieces, more than 6,000 are unique. Each piece is made of the same fiberglass material used in circuit boards and etched with copper.

The University of Rochester describes the mathematical foundation for cloaking.

Professor Allan Greenleaf first started working on the mathematics of invisibility in 2001. In 2003, with Professors Lassas and Uhlmann, he published two papers about the mathematics that could make objects with special properties invisible (“On Nonuniqueness for Calderon’s Inverse Problem,” Mathematical Research Letters 10, 685-693, 2003, and “Anisotropic Conductivities that cannot be Detected by EIT,” Physiological Measurement 24, 413-419, 2003).

These papers were concerned with the mathematics of electrical impedance tomography (EIT), a medical imaging technique that uses measurements of electric voltages and currents to obtain images of the interior of the body. It was previously known that, under certain assumptions, the measurements uniquely determine the electric conductivity function, which varies from point to point and whose behavior might indicate the presence of tumors. In the two papers of 2003, Greenleaf, Lassas, and Uhlmann showed that, if the conductivity function is allowed to be a tensor, which means that it can depend on direction as well as location, then there are recipes for mathematically constructing different conductivities that are indistinguishable from each other by EIT measurements. At the time, this seemed like something of a curiosity, since it was highly unlikely that the exact mathematical structures needed to produce this “invisibility” would occur in nature, for example, on the exterior of a tumor.

This same mathematics surfaced again in 2006 when Sir John Pendry of Imperial College, Dr. David Schurig and Professor David Smith of Duke University, and Professor Ulf Leonhardt of St. Andrew’s University, wrote papers theoretically proposing the construction of cloaking devices, rendering the objects inside them invisible from observation using electromagnetic (EM) waves. In October 2006, physicists and engineers led by the Duke University team built a device from man-made metamaterials that essentially cloaks a passive copper disk or rod. Based on a mathematical calculation very similar to one proposed in 2003, the metamaterials have special properties in the way that microwaves propagate through, or in this case, around them. The cloaking device bends microwaves around an object and does not cast a shadow. The copper disk or rod inside the cloaking device is invisible. It is as if absolutely nothing is there.

Nature’s full of surprises, isn’t it? But the burgeoning ability to manipulate information flows will not be confined to the visual spectrum. The public is already bombarded by digitally manipulated “fauxtographs” and managed news; it has already been told that the science behind Global Warming cannot be challenged. For a long time the public was told certain financial institutions were “too big to fail”. Pilate asked Jesus, “what is truth?” The modern answer is, “it depends.”