A new study published by scientists from the University of Texas set up a list of arguments towards the impossibility of human invisibility.
Invisibility cloaking devices are real. However, they are not perfect. They remain undetectable to certain electromagnetic waves, such as light, infrared or microwaves.
The cloak can only be used to hide something in a different wavelength. However, the researchers say that the mission becomes more challenging when the object has a large size.
The author of the study created a framework of the boundaries related to invisibility in different sizes and compositions.
The study aims to aid engineers to calculate the likely performance of their invisibility devices.
“The question is, can we make a passive cloak that makes human-scale objects invisible? It turns out that there are stringent constraints in coating an object with a passive material and making it look as if the object were not there, for an arbitrary incoming wave and observation point,” said Andrea Alu, the leading author of the study.
The cloaks are made from metamaterials with a property that enables the control over the incoming waves. The research focuses on materials that do not need an external power source. The key conditions for creating an invisible cloth are estimations on the bandwidth and size the limitations of the cloaking.
The author of the study explains that the discovery is important in the field of communication antennas, military radars, and biomedical devices. The performance of a passive cloak is determined by the size of the object and the length of the incoming wave.
The researchers mention the fact that it would be impossible to hide large objects, like a human body or a tank. However, smaller objects like a radio-wave antenna can be easily obscured from the view.
The current study shows the limits of metamaterials and their relation with their respective wavelengths. Scientists do not see in the results of research a fatalistic limit of technical capabilities. They said they would try to find new ways to improve the performance of the materials.
Some of the new techniques explore nonlinear approaches to cloaking technologies. In this new field, the invisibility limits do not apply.
Regarding camouflage, the scientists will also study phase delays methods, camouflage techniques, and optical tricks. These new approaches will give the impression of transparency, and they will avoid reducing the light scattering.
Another option would be to use metamaterials with an external energy source, which would probably show more performance in achieving transparency.
The ultimate limit on invisibility is Einstein’s theory of relativity. However, nonlinear metamaterials could help scientists invent the invisibility cloak.
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