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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| History of metamaterials | 4/5 | https://en.wikipedia.org/wiki/History_of_metamaterials | reference | science, encyclopedia | 2026-05-05T03:39:47.132262+00:00 | kb-cron |
=== Invention of the metamaterial === Historically, and conventionally, the function or behavior of materials can be altered through their chemistry. This has long been known. For example, adding lead changes the color or hardness of glass. However, at the end of the 20th century this description was expanded by John Pendry, a physicist from Imperial College in London. In the 1990s he was consulting for a British company, Marconi Materials Technology, as a condensed matter physics expert. The company manufactured a stealth technology made of a radiation-absorbing carbon that was for naval vessels. However, the company did not understand the physics of the material. The company asked Pendry if he could understand how the material worked. Pendry discovered that the radiation absorption property did not come from the molecular or chemical structure of the material, i.e. the carbon per se. This property came from the long and thin, physical shape of the carbon fibers. He realized rather than conventionally altering a material through its chemistry, as lead does with glass, the behavior of a material can be altered by changing a material's internal structure on a very fine scale. The very fine scale was less than the wavelength of the electromagnetic radiation that is applied. The theory applies across the electromagnetic spectrum that is in use by today's technologies. The radiations of interest are from radio waves, and microwaves, through infrared to the visible wavelengths. Scientists view this material as "beyond" conventional materials. Hence, the Greek word "meta" was attached, and these are called metamaterials. After successfully deducing and realizing the carbon fiber structure, Pendry further proposed that he try to change the magnetic properties of a non-magnetic material, also by altering its physical structure. The material would not be intrinsically magnetic, nor inherently susceptible to being magnetized. Copper wire is such a non-magnetic material. He envisioned fabricating a non-magnetic composite material, which could mimic the movements of electrons orbiting atoms. However, the structures are fabricated on a scale that is magnitudes larger than the atom, yet smaller than the radiated wavelength. He envisioned and hypothesized miniature loops of copper wire set in a fiberglass substrate could mimic the action of electrons but on a larger scale. Furthermore, this composite material could act like a slab of iron. In addition, he deduced that a current run through the loops of wire results in a magnetic response. This metamaterial idea resulted in variations. Cutting the loops results in a magnetic resonator, which acts like a switch. The switch, in turn, would allow Pendry to determine or alter the magnetic properties of the material simply by choice. At the time, Pendry didn't realize the significance of the two materials he had engineered. By combining the electrical properties of Marconi's radar-absorbing material with his new man-made magnetic material he had unwittingly placed in his hands a new way to manipulate electromagnetic radiation. In 1999, Pendry published his new conception of artificially produced magnetic materials in a notable physics journal. This was read by scientists all over the world, and it "stoked their imagination".
=== Negative refractive index === In 1967, Victor Veselago produced an often cited, seminal work on a theoretical material that could produce extraordinary effects that are difficult or impossible to produce in nature. At that time he proposed that a reversal of Snell's law, an extraordinary lens, and other exceptional phenomena can occur within the laws of physics. This theory lay dormant for a few decades. There were no materials available in nature, or otherwise, that could physically realize Veselago's analysis. Not until thirty-three years later did the properties of this material, a metamaterial, became a subdiscipline of physics and engineering. However, there were certain observations, demonstrations, and implementations that closely preceded this work. Permittivity of metals, with values that could be stretched from the positive to the negative domain, had been studied extensively. In other words, negative permittivity was a known phenomenon by the time the first metamaterial was produced. Contemporaries of Kock were involved in this type of research. The concentrated effort was led by the US government for researching interactions between the ionosphere and the re-entry of NASA space vehicles. In the 1990s, Pendry et al. developed sequentially repeating thin wire structures, analogous to crystal structures. These extended the range of material permittivity. However, a more revolutionary structure developed by Pendry et al. was a structure that could control magnetic interactions (permeability) of the radiated light, albeit only at microwave frequencies. This sequentially repeating, split ring structure, extended material magnetic parameters into the negative. This lattice or periodic, "magnetic" structure was constructed from non-magnetic components. Hence, in electromagnetic domain, a negative value for permittivity and permeability occurring simultaneously was a requirement to produce the first metamaterials. These were beginning steps for proof of principle regarding Veselago's original 1967 proposal. In 2000, a team of UCSD researchers produced and demonstrated metamaterials, which exhibited unusual physical properties that were never before produced in nature. These materials obey the laws of physics, but behave differently from normal materials. In essence these negative index metamaterials were noted for having the ability to reverse many of the physical properties that govern the behavior of ordinary optical materials. One of those unusual properties is the capability to reverse, for the first time, the Snell's law of refraction. Until this May 2000 demonstration by the UCSD team, the material was unavailable. Advances during the 1990s in fabrication and computation capabilities allowed these first metamaterials to be constructed. Thus, testing the "new" metamaterial began for the effects described by Victor Veselago 30 years earlier, but only at first in the microwave frequency domain. Reversal of group velocity was explicitly announced in the related published paper. First demonstration of a negative index of refraction in the optical range was done by Vladimir M. Shalaev et al.