Engineers at the University of Texas at Austin have discovered fundamental limitations that prevent the creation of devices that make large objects completely invisible. The larger the body, the more difficult it is to hide it from light, which consists of waves of different lengths. You can get around this obstacle with additional power supplies, according to an article published in Optica magazine.
Scientists have established the bandwidth limits of electromagnetic raincoats for objects of various sizes and compositions, and also determined the optimal performance of cloaking devices. Cloaks are made of metamaterials - composite materials, whose properties are determined not by the characteristics of their constituent substances, but by the periodic structure. As a result, raincoats in a special way control the propagation of electromagnetic waves incident on them, making the object invisible or transparent. Researchers have studied the performance limits of passive metamaterials that do not have an external power source.
Estimating the throughput and the effect of the size of the cloaked object on it should help assess the potential of electromagnetic raincoats for communications antennas, biomedical devices and military radars, scientists say. The results of the study showed that the performance of invisibility devices is determined by the ratio of the size of the object and the wavelength of the light incident on it. It is more difficult for electromagnetic raincoats to mask a large object from short wavelengths.
This means that passive metamaterials cannot make a tank, plane or person invisible to the human eye. However, scientists believe that a similar effect can be achieved using active camouflage, that is, by connecting electromagnetic raincoats to an external source of energy.