Drones have become a crucial element in modern security and defence. The ability to manipulate the signals reflected from drones – so that, for example, it is possible to fly close to a radar without being detected – is therefore not only exciting science, but also of commercial and security interest.
Efforts to achieve this are underway at DTU, among other places, where researchers have been working for many years to develop advanced electromagnetic materials. Most recently, this has taken place in a project in collaboration with Aarhus University, the Danish Technological Institute and several companies, including TICRA and Arctic Unmanned.
"The project is being carried out along two parallel tracks. One track is based on the Physical Vapour Deposition (PVD) method, which is used to design very thin coatings that can alter a material's radar signature, making the reflections stronger or weaker – and thus helping to create confusion," explains Samel Arslanagic, Associate Professor and Head of Electromagnetic Systems at DTU and project leader.
The signals have been significantly attenuated
The PVD method involves bombarding the surface of a material with atoms.
"Initial tests with PVD-coated materials have shown that it is possible to achieve significant attenuation of the reflected signals. This has been achieved on objects with very simple shapes, such as rectangular plates and a cylinder. It is precisely these simple shapes that have enabled us to gain a theoretical understanding of the physics behind the wave-matter interactions and attenuation achieved," explains Samel Arslanagic, continuing:
"The next step will now be to apply the method to the far more advanced shape that a drone represents. This will require a fair amount of adaptation, as it is a complex geometry to work with."
Tests in the laboratory and in realistic environments
In connection with the first successful radar signature tests at DTU's Electromagnetic Test Centre, the researchers have characterized the electromagnetic properties of the material used for the drone to which the coatings were applied. These characteristics have been used as the basis for developing computer-based models that calculate how the structure can be optimized as the geometry becomes more realistic.
"The next task is to carry out the somewhat more complex calculations involved in the geometry of a drone, and the effect of the coatings must be tested in realistic environments to see how the coated drone is detected by radar. Several Danish companies with expertise in areas such as drones, radar systems and electromagnetic modeling are participating in the project and will contribute to these calculations, measurements and tests," says Samel Arslanagic. In the near future, the researchers will also investigate whether it is necessary to coat the entire surface of the drone, or if it suffices to coat only a part of it.
The coatings must be suitable for use in drone production
A key requirement of the project is that the coatings must be robust, not increasing the drone's overall weight, and be suitable for inclusion in future industrial production. The aim is to apply a coating as early as possible in the drone's manufacturing stage.
Once the final calculations and tests have been completed, the project will be one step closer to industrial production.
Artificial materials can manipulate electromagnetic waves
At the same time, the researchers will move ahead with the project's second track: the development of so-called metasurfaces. These are artificial materials composed of periodic arrangements of very small elements made of electrically insulating materials or metal, which together can control electromagnetic waves.
The work focuses on creating metasurfaces and individual elements that can manipulate the electromagnetic energy scattered from an object, and thus the way in which it is detected by radar.
"There is great potential in pursuing the development of metasurfaces with the right properties for use in manipulating the radar signatures of, for example, drones. Not least because it will presumably be cheaper both to manufacture and use metasurfaces than to treat the drone's surface using the PVD method," says Samel Arslanagic.
