Drones are playing an increasingly important role in security and defense. That is why the ability to control the signals reflected from a drone - for example, to approach a radar undetected - interests not only scientists but also commercial and security organizations. Work in this area is being carried out by the Technical University of Denmark (DTU) together with Aarhus University, the Danish Technological Institute and a number of companies.
The project is proceeding along two tracks. The first is the physical vapor deposition (PVD) method. This is the name for a technology in which the surface of a material is bombarded with atoms to create a very thin coating. It is capable of changing the radar signature - how an object reflects radio waves and appears to a radar. The coating can make reflections stronger or weaker, helping to confuse a radar. This is described by Samel Arslanagic, an associate professor and head of the electromagnetic systems area at DTU, who leads the project.
The first tests of materials treated by the PVD method showed that reflected signals can be significantly weakened. However, so far this concerns simple shapes - rectangular plates and a cylinder. It was on these that the researchers were able to theoretically understand the physics of the interaction of waves with the material and the attenuation achieved. The next step is to apply the method to a more complex shape, which is what a drone represents. This will require serious adaptation, since the geometry here is not simple.
After the first successful tests of the radar signature at DTU's Electromagnetic Test Center, the scientists described the electromagnetic properties of the material on which the coatings were applied. These data formed the basis of computer models calculating how to optimize the design in the transition to a more realistic geometry. Now more complex calculations must be performed for the drone's geometry, and the effect of the coatings must be checked under realistic conditions - to see how a treated drone is detected by radar. Several Danish companies specializing in drones, radar systems and electromagnetic modeling are taking part in the project; they will help with calculations, measurements and tests. In the near future, the researchers will also determine whether the entire surface of the drone needs to be coated or only part of it.
The key requirement is that the coatings must be durable, must not increase the drone's overall weight and must be suitable for future industrial production. They are planned to be applied as early as possible in the manufacturing stage. When the final calculations and tests are completed, the project will be one step closer to industrial production.
In parallel, the scientists will continue the second track - the development of so-called metasurfaces. These are artificial materials made of periodically arranged very small elements of insulating materials or metal that together can control electromagnetic waves. The task is to create metasurfaces and individual elements capable of changing the electromagnetic energy scattered by an object, and therefore how a radar detects it. According to Arslanagic, metasurfaces with the required properties have great potential, including because their production and use will probably cost less than treating a drone's surface by the PVD method.