A new technique for detecting invisibility cloaks

By | June 13, 2023

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Diagram of the difference between SCS and DT surveying techniques. a) The SCS is a scalar quantity related to the total power spread for a given incident direction. The sparse field phase is not taken into account. b) DT uses different illumination angles to obtain an RI map of the object from the space-dependent phase and amplitude of the diffuse field. Credit: Reviews on lasers and photonics (2022). DOI: 10.1002/lpor.202200237

A study developed by researchers at the Universitat Politcnica de Valncia (UPV), associated with the Nanophotonics Technology Center (NTC) and the company DAS Photonics, promises to revolutionize the design of the so-called invisibility cloaks. With their proposal, these cloaks will no longer be so invisible. And the key is simple: apply diffraction tomography techniques to detect these devices. Their work has been published in the magazine Reviews on lasers and photonics.

According to the Valencian researchers, invisibility cloaks have become one of the most important advances in the wide range of applications in the field of metamaterials. Until now, most efforts in invisibility science have been devoted to achieving practically feasible cloak designs and improving the efficiency of these devices.

“However, little attention has been paid to the opposite side of the technology: the development of more effective techniques for detecting such invisibility devices. This is the focus of our study, which will rethink the design of these cloaks, as it will significantly facilitate the their detection. And all thanks to diffraction tomography,” explains Carlos Garca Meca, research director at DAS Photonics.

As for the applications of the proposal that emerged from the NTC laboratories, the team of Valencian researchers emphasizes that it would cover multiple fields.

“One of these would be the ability to ensure proper use of the electromagnetic spectrum to allow detection of the presence of hostile agents, despite the use of countermeasures by the latter to avoid it. Consider, for example, a soldier using a cloak invisibility system to hide a small observation post and not be detected by standard detection methods. The technique we have developed would allow it to be identified,” explains Carlos Garca Meca.

Much more information thanks to tomography

So far, the performance rating of invisibility cloaks is based solely on the sum of all energy re-emitted by the cloak when it is illuminated. “What you do is estimate all that energy re-emitted in all possible directions, then the resulting value determines the performance of the cloak. If the number is low, the layer is considered very good; if you re-emit a lot, don’t make it invisible the object to hide,” explains Fran Daz, a researcher at the UPV’s Nanophotonic Technology Center.

The proposal presented in their study by the NTC-DAS team provides much more information about the layers. Tomography sheds light on the optical properties of the analyzed area. Using different angles of illumination, this technique intelligently processes previously ignored information (phase distribution and diffuse field), thus obtaining a map of the refractive index of the object.

“In this way, we drastically improve the detection sensitivity and we can even imagine invisibility cloaks, with their size and shape. This makes cloaks more easily detectable. Therefore, with this technique, invisibility cloaks are no longer so invisible,” says Fran Daz.

According to the Valencian researchers, this method could also be extended to detect acoustic invisibility cloaks. The work of the team of the Nanophotonics Technology Center of the Universitat Politcnica de Valncia and DAS Photonics has also been selected for the inside cover of Reviews on lasers and photonics.

Other applications in electronic warfare and biomedical imaging

Since diffraction tomography represents a much more challenging test for assessing the performance of invisibility cloaks, this new sensing technique could lay the groundwork for a unique design and characterization standard for such devices.

Furthermore, this new discovery opens up a number of potential benefits in various fields, from fundamental advances in the science of invisibility to technological applications in signal intelligence and electronic warfare, and even biomedical imaging. In this sense, the study by DAS Photonics and UPV researchers suggests that invisibility layers based on so-called ‘dispersion cancellation’ could be applied to improve the resolution of tomographic techniques when imaging clusters of small particles.

More information:
Francisco J. DazFernndez et al, Imaging of cloaked objects: Diffraction tomography of realistic stealth devices, Reviews on lasers and photonics (2022). DOI: 10.1002/lpor.202200237

Provided by Universitat Politcnica de Valncia

#technique #detecting #invisibility #cloaks

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