Nüßler, D.D.NüßlerHeinen, S.S.HeinenSprenger, T.T.SprengerHübsch, D.D.HübschWürschmidt, T.T.Würschmidt2022-03-122022-03-122013https://publica.fraunhofer.de/handle/publica/38196910.1117/12.2029172Letter bombs are an increasing problem for public authorities, companies and public persons. Nowadays every big company uses in his headquarters inspection system to check the incoming correspondence. Generally x-ray systems are used to inspect complete baskets or bags of letters. This concept which works very fine in big company with a large postal center is not usable for small companies or private persons. For an office environment with a small number of letters x-ray systems are too expensive and oversized. X-ray systems visualize the wires and electric circuits inside the envelope. If a letter contains no metallic components but hazard materials or drugs, the dangerous content is invisible for the most low-cost x-ray systems. Millimeter wave imagining systems offer the potential to close this gap.en621conference paper