For as long as human beings have been writing about fantasy, myth, and science fiction, the dream of invisibility has always been a top priority. There would be so much you could do or accomplish, under a stealthy guise, if only you didn’t have to worry about being seen. While _Star Trek_ brought the idea of a cloaking device into the popular consciousness, and _Harry Potter_ brought with it the widespread idea of an actual invisibility cloak, there haven’t been many useful applications of invisibility-based technology on a large scale.
In fact, the closest we’ve come to achieving actual invisibility has been through the development of stealth technology, which only bestows a rudimentary invisibility at far longer wavelengths than human eyes can perceive by making the your target effectively smaller than the device itself. The invisibility to radar, which is microwave-to-radio wavelength electromagnetic radiation, might have been the first step, but recent developments in metamaterials have extended this even further, bending light around an object and rendering it truly undetectable. Perhaps the critical advance that could finally bring an invisibility cloak to reality occurred in 2018, in a novel material called abroadband achromatic metalens.
For the first time, it rendered an object undetectable across the entire visible light spectrum. The fusion of this technology with metamaterial cloaking — another recent nanotechnology advance — could finally enable the first visible-light cloaking device. Here’s the scientific story behind what’s actually under development in today’s reality.
The B-2 Spirit stealth bomber, shown here, It is a low-observable aircraft, meaning that its cross-section for being spotted by radar devices is far smaller than its actual, physical size. A combination of reduced signatures to visual, infrared, radar, thermal, and acoustic measurements makes it a low-observable aircraft. Its wing design, composite materials, and (classified) special coatings all serve to reduce its observability, making it one of the most stealthy and difficult-to-detect aircraft on planet Earth today.
The concept of stealth technology is the closest thing we have, at present, to an implementation of the idea of invisibility. Although these craft are not invisible in any sense, they are optimized to greatly reduce their sensitivity to being detected by conventional means, including: A wide combination of interventions are used to make a craft or vehicle as invisible to these conventional means of detection as possible. The craft is shaped in such a way that it produces a minimal cross-section towards whatever territory it’s approaching, reducing its signature in the direction that it would be most threatened by.
The materials that it’s made out of and coated in are designed to convert any absorbed, long-wavelength light into heat, which ensures that signals (such as radar signals) aren’t reflected back towards a detector that’s looking for them. Then the emitted heat and noise signatures are masked through a variety of special coatings. Stealth technology goes way beyond old-fashioned ideas of camouflage, but is still, even in its optimized, modern incarnation, extraordinarily different from the notion of “cloaking,” or true invisibility.
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