Research cooperation for radar camouflage materials at WIWeB

Radar camouflage can only be retrofitted to existing aircraft at great expense. It should therefore be taken into account directly during development. For example, the shape of the aircraft and the engine integration must be designed in such a way that the aircraft has the smallest possible radar cross-section and low infrared and acoustic signatures. Radar-absorbing materials play a key role in this.

The camouflage materials currently used in combat aircraft require a great deal of maintenance and are sensitive to environmental influences. Particularly with regard to joint European armament projects, expertise and production technologies for camouflage materials with a corresponding supply chain are to be established in Germany and Europe.

The Wehrwissenschaftliches Institut für Werk- und Betriebsstoffe (WIWeB) in Erding has been researching suitable materials for years to make aircraft lighter, more stable and more functional. Together with the German Aerospace Center (DLR), the AIRBUS company and the Institute for Lightweight Engineering at the University of the German Armed Forces (UniBw M) in Munich, a joint technical center for camouflage materials was opened in Erding at the beginning of December 2022, where the cooperation partners intend to jointly research and develop a new generation of camouflage materials. The research project is being worked on in close collaboration among several doctoral students at the various locations.

The main focus of the project at WIWeB is the conception and development of new manufacturing processes for the production of suitable fiber or fiber-matrix semi-finished products for use in radar-absorbing or radar-camouflaged structures. The aim is to understand the basic mechanisms of action in the new materials and to be able to influence them in a targeted manner.

In a first step, suitable manufacturing concepts and material combinations are systematically explored to introduce the desired properties. For this purpose, it is already necessary to characterize the raw materials accordingly. In order to be able to assess potential material compositions in advance, existing solutions are to be examined with regard to their effectiveness and optimizability. Subsequently, the technical solution spaces for the further processing of the raw materials, for example in the form of suspensions, will be defined.

In the further course, manufacturing competencies for the production of absorbent fiber composite semi-finished products are to be established. One focus here is on the systematic understanding of process parameters in order to be able to achieve an optimum effect and adjustability of the desired material effects. In the course of setting up the pilot plant, all the materials produced are to be characterized electro-magnetically.

Research, selection and characterization of raw materials

• Development of a compilation of radar-absorbing fillers
• Determination of relevant characteristic values for evaluating material suitability
• Determination of material parameters such as particle size distributions and shape

Development of a processing strategy and production plant on a laboratory scale

• Development and evaluation of filler suspensions for further processing in downstream processes
• Optimization of a method to introduce radar absorbing materials into fiber composites
• Design and implementation of a facility for the production of filled fiber-matrix systems, or semi-finished products
• Identification and validation of a reproducible measurement methodology for filler determination in the manufactured fiber composite components
• Evaluation and potential integration of an in-situ process monitoring system

Characterization and measurement of materials

• Optical analysis of cross sections, e.g. micrographs, using microscopy and SEM
• Mechanical qualification using standardized methods, e.g. tensile tests, DMA, impact
• Electromagnetic measurement and comparison with simulation results, as well as assessment of suitability for use as a material for radar absorbers
• Correlation of the influence of fillers on mechanical and electromagnetic material properties

Simulation

• Composition of a single- or multilayer structure from the filled materials
• Optimization of the composition with respect to the absorption properties and the achievable bandwidth
• Electromagnetic simulation of the resulting design with a numerical method (e.g. FEM) and comparison with measurements
• Investigation of the absorption properties for oblique angles of incidence or curved surfaces

Radar absorbers can be used in many different forms on aircraft. Since available solutions are very maintenance-intensive and thus cost-intensive in terms of flight time, future developments will increasingly focus on robust absorber systems. The new development of a radar absorbing material (RAM) based on fiber composites is therefore promising.

By adding electrical or magnetic materials to the composite, it is hoped that absorbent properties can be integrated into robust components for a variety of uses on aircraft. Initial material demonstrations appear promising.

The knowledge gained from the research project will be used to expand competencies in Low Observability (LO) nationally. All project partners are committed to advancing camouflage technology Made in Germany.