Imaging radar systems for non-destructive material testing. An overview of the state of the art, the limitations and the opportunities of radar technology

Radar systems have been used for over 100 years to measure distances and angular positions accurately. Radar systems benefit from relatively long wavelengths, which means that most absorption and scattering mechanisms do not have a relevant influence on the propagation conditions of the emitted electromagnetic waves. As a result, radar systems were and are used primarily for measurements under poor environmental conditions. Today, we usually find applications that work with waves in the meter to millimeter wave range. Especially in the millimeter wave range, the influence of the atmosphere can no longer be neglected. Communication systems, in particular, with their need for large bandwidths, are driving the development of components in the millimeter wave range, thus opening up further fields of application. In this context, imaging radar systems are increasingly important in various application areas. This paper will look at the possible applications in industrial process monitoring. The monitoring of production processes benefits from the phenomenon’s importance that many non-conductive materials are partially transparent to an electromagnetic wave. Radar systems thus allow a view below the surface and can therefore measure the material thickness of, e.g. plastics in extruders. This paper will investigate the advantages and disadvantages of radar technologies and procedures and their suitability for use in production lines.