Fraunhofer Institute for Industrial Mathematics ITWMModern vehicles contain highly sensitive instruments that must be protected against radiation. One question is particularly important here: What material should be used for the protective housing? In the mobility sector in particular, this usually involves classic radar and communication applications, such as distance sensors in cars, 4G or 5G mobile communication standards, and navigation instruments installed in aircraft noses, for example. This is why housings for these areas of application are referred to as »radomes. In most cases, glass fiber reinforced plastics (GFRP) are used as multi-layer composites. We have developed an ultra-wide, tunable photonic terahertz FMCW radar with a modulation bandwidth of up to 1.65 THz for testing these radomes.
Radars are essential for our navigation systems. They are protected from the weather by mechanical covers known as radomes. These must meet certain requirements in order not to impair the functionality of the radar.
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Material Characterization for RADAR Applications
Ultra-Wideband Terahertz (Frequency Modulated Continuous Wave Radar)
Non-destructive Testing of Multilayer Composites
As glass fiber composite materials are permeable to high-frequency radiation, they are used in particular where highly sensitive components need to be protected, but at the same time the influence of the housing materials on the radiation must be kept to a minimum. The use of terahertz technologies in industry for material characterization and volumetric testing is now in high demand due to their non-destructive and non-invasive nature. Terahertz FMCW imaging systems, which operate in the sub-terahertz range below 1 THz, are used for volumetric testing of materials for defects and anomalies. Compared to laser-based terahertz time-domain systems with bandwidths of several terahertz, FMCW radars typically operate with modulation bandwidths of less than 100 GHz.
Thanks to the high bandwidth of the photonic FMCW radar, individual composite layers can be distinguished in the submillimeter range and thickness variations of the individual layers can be resolved. This clearly illustrates the potential of our system for combined applications of non-destructive testing and layer thickness measurements.
Thanks to the high bandwidth of the photonic FMCW radar, individual composite layers can be distinguished with a resolution in the sub-millimeter range and thickness variations of the individual layers can be resolved with an accuracy of around 100 μm. This illustrates very well the potential of our system for a combined application of non-destructive testing and coating thickness measurements.
Radome Application Example
The Austrian company 4a manufacturing GmbH produces composite materials for radomes (CIMERA radomes), which are used in the 5G mmWave and satcom industries, among others. A team from our »Material Characterization and Testing« department is investigating their composites for high-frequency applications for the company – especially in the range between 4 and 40 GHz.
The exact structure of the complex multilayer composites is crucial for the functionality of the materials and the question: at which frequencies do the radomes appear as »electromagnetically transparent« as possible for the desired target application? To date, 4a manufacturing GmbH has provided the results of material simulations that allow statements to be made about this frequency behavior. In the collaboration, the simulations are now additionally validated by high-frequency measurements.
»Thanks to our shielded measuring chamber, we were able to get involved here as a service provider,« says project manager Dr. Maris Bauer. Transmission and reflection measurements on test radomes verify the simulation results. This provides additional certainty that the materials produced by 4a manufacturing GmbH are suitable for their specific applications. Our terahertz testing systems also allow us to examine the internal structure of finished radomes, for example to detect possible cracks or similar production defects at an early stage.
