Fraunhofer Institute for High Frequency Physics and Radar Techniques FHR
Material Characterization Across a Broad Frequency Range
Accurate knowledge of electromagnetic material properties is essential for the research and development of radomes, sensor covers, antennas, and radar-absorbing and low-observable materials. Fraunhofer FHR offers a range of measurement techniques for determining these properties over a broad frequency range from 0.5 to 90 GHz. With additional measurement effort, this range can be extended to frequencies of up to 170 GHz.
Precise Determination of Material Properties
Different measurement techniques and sample fixtures are used depending on the frequency range, the material, and the characteristics of the sample. Material characterization involves measuring the transmission and reflection characteristics of electromagnetic waves interacting with a material sample. Depending on the measurement technique, the complex permittivity and complex permeability of the material can be determined from the measured scattering parameters. Multilayer structures with very thin individual layers, such as paints and coatings, can also be characterized.
Material parameters describe how electromagnetic fields and waves interact with a material. Within a material, electromagnetic properties affect the phase velocity and attenuation of electromagnetic waves, while impedance discontinuities at interfaces between different materials can cause reflections. These effects must be taken into account in the development of RF and microwave components.
Basis for Simulation and Component Development
Radomes and sensor covers are designed to minimize their effect on the propagation of electromagnetic waves. For radar absorbers and low-observable materials, by contrast, the objective is to reduce reflections and absorb incident electromagnetic energy within the material.
In the development of such components, the material properties are incorporated into electromagnetic simulation models, which are used to optimize the material structure and component geometry. Reliable material parameter values are essential for this purpose. However, manufacturer datasheets often do not provide the required accuracy or may not contain data for the relevant frequency range. Fraunhofer FHR can therefore determine the required material parameters experimentally using suitable measurement techniques.
Nondestructive Material Characterization
The measurement technique used depends, among other factors, on the frequency range. At lower frequencies, material samples generally have to be cut or machined to a size and geometry suitable for the respective measurement method. At frequencies above approximately 25 GHz, however, free-space measurement techniques are available that allow suitable samples to be characterized nondestructively without requiring such geometric modification.
The infrastructure enables the characterization of a wide range of materials and components. These include automotive body components, plastic covers and housings, electromagnetic shielding materials, absorbers, and substrate materials, as well as paints and coatings, low-observable materials, metamaterials, metasurfaces, wall construction elements, and adhesives. The resulting measurement data provide a reliable basis for the development and optimization of RF, microwave, and millimeter-wave components and systems.