We’re getting closer to an invisibility cloak
Star Trek‘s Romulans and Harry Potter better watch out — we are getting closer to an invisibility cloak, a physics team reports.
Built of a natural calcite crystal, the cloak that the Nature Communications journal team led by Shuang Zhang of the United Kingdom’s University of Birmingham, reports (an“invisibility cloak” device ) can hide millimeter-sized objects and maybe much more.
“The cloak can be readily scaled up to hide larger objects, depending on how large a calcite crystal we can find in nature,” Zhang says, by email. “The cloaks might have military applications, for instance, to hide something (such as submarine) on the sea floor, or applications in cosmetics, to hide moles or blemishes on human skin.”
In the last decade, physicists have made advancements in”invisibility cloak” devices, typically engineered “metamaterials” that can conceal objects from microwaves at microscopic sizes.
Zhang and colleagues beat having to make their cloaking device by letting Nature do the work, in the form of a calcite crystal:
In this article, we report the first demonstration of a macroscopic volumetric cloaking device operating at visible frequencies, which can conceal objects of sizes of at least 3 orders of magnitude larger than the wavelength of light in all three dimensions, and works for a specific polarization of the incident light. The cloaking design uses birefringence in a natural crystal calcite, thus eliminating the necessity of time-consuming nanofabrication processes and enabling the realization of cloaking at macroscopic scales. Th e cloaking eff ect was directly observed for red and green laser beams and incoherent white light without resorting to use of a microscope. The demonstration of a macroscopic invisibility-cloak paves the way for future applications of invisibility cloaking.
Calcite is a natural “anisotropic” material that bends light in the way that engineered metamaterials have to be carefully crafted to cause. The crystal, “transforms a deformed mirror into a flat one from all viewing angles,” says the study. “The cloak is capable of hiding three-dimensional objects three to four orders of magnitudes larger than optical wavelengths, and therefore, it satisfies a layman ‘ s definition of an invisibility cloak: namely, the cloaking eff ect can be directly observed without the help of microscopes.”
Say Zhang, by email: “In terms of the time scale, I think there are still years to come to see them being commercialized. The major issue is very large size of the cloak relative to the object to be concealed (about 20 times larger). In reality, cloaks of much more compact size (relative to the objects to be hidden) are highly desired, which requires materials with much larger birefringent effect than calcite. Such materials have yet to be synthesized by materials scientists.”