ITMO researchers used the radio-frequency anechoic chamber for the experiment​ on makings objects invisible. (ITMO)

Obejcts Can Be Made Invisible Without Metamaterial Coating, Show ITMO Researchers

Physicists are able to make cylindrical objects completely invisible in the microwave range, without using any metamaterial coating layers, ushering in new era of electromagnetic wave scattering.

The scientists from ITMO University, Ioffe Institute and Australian National University achieved the unique result based on light scattering from a glass cylinder filled with water, representing a two-dimensional analog of a classical scattering from a homogenous sphere (Mie scattering).

Using ordinary water whose refractive index can be regulated by reducing temperature, they applied two scattering methods —
resonant and non-resonant scattering. Resonant scattering is related to localization of light inside the cylinder and in non-resonant it is reflected by smooth dependence on the wave frequency, they explained. And interaction between the two
mechanisms is called Fano resonances.


ITMO researchers used the radio-frequency anechoic chamber for the experiment​ on makings objects invisible. (ITMO)

In their experiment, the researchers discovered that at certain frequencies waves scattered via both mechanisms in opposite
phases and are mutually destroyed, making the object invisible. By the cancellation of scattering, they were able to develop a new technique to switch from visibility to invisibility at the same freequency of 1.9GHz by reducing the temperature of water in a cylinder from 90°C to 50°C.

“Our theoretical calculations were successfully tested in microwave experiments. What matters is that the invisibility idea we implemented in our work can be applied to other electromagnetic wave ranges, including to the visible range,” said Mikhail Rybin, lead author of the paper at the Metamaterials Laboratory in ITMO University.

The discovery can help develop nanoantennas, wherein invisible rods could be used as supports for a miniature antenna complex connecting two optical chips. Since the new discovery of invisibility phenomenon in a homogenous object and not an object covered with additional coating layers makes it deviate from conventional ideas of invisibility.

Nevertheless, coating layers based on metamaterials are extremely hard to fabricate and are not compatible with many other invisibility ideas. The new method based on scattering processes leaves behind the existing mechanisms both in simplicity and cost-effectiveness, they said.

Wearing an invisibility cloak is every fantasy-lovers dream. It has caught the attention of physicists for centuries and even films like ‘Mr India’ with an invisibility watch had an exciting viewership, while epics are aplenty about the examples of ancient sages going invisible or making objects invisible.

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