Novel concepts for the detection of threat objects in shoes by millimeter-wave radar imaging

• Applicant: Dr.-Ing. Ingrid Ullmann
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 546339340

Millimeter-wave imaging radars are state of the art in many security-related applications. Personnel screening as part of airport security checks is a well-known example. While millimeter-wave based personnel security screening has been an established technique for some years, screening shoes with millimeter-wave radar has not yet found its way into practical application. At airports, shoe screening is commonly performed by means of X-ray, for which passengers have to take off their shoes. Millimeter-wave based shoe screening, included into the personnel screening procedure, could significantly enhance efficiency and comfort in security checks. However, for various technical reasons, screening shoes with radar is not trivial and many problems have not been solved yet. Therefore, this research project aims at investigating novel approaches for a reliable, highly precise detection of threat objects in shoes by means of millimeter-wave radar imaging. We propose to use a multimodal imaging system consisting of a multiple-input-multiple-output (MIMO) radar operating at millimeter-wave frequencies and an optical time-of-flight camera. The camera is used as an assisting sensor modality within the radar imaging system. It is able to capture the shoe sole’s profile with high accuracy. This information forms the basis for a customized radar image reconstruction of the shoe’s interior which takes into account wave propagation effects such as refraction caused by the sole. It is expected that with this technique the shoe’s interior will be depicted much more accurately than it has been possible before. Additionally, it is possible to simulate the radar echo caused by the sole based on the data captured by the camera. This simulated echo can be numerically subtracted from the actually measured radar signal. The resulting, modified radar signal only contains echoes from inner structures, e.g. threat objects hidden inside the shoe. Reconstructing this modified signal yields an image which clearly displays the inner structures - also those which without compensation would be masked by the sole’s reflection. With these novel approaches, we expect an improvement with respect to resolution and visibility compared to the state of the art. To verify the elaborated concepts, several measurement campaigns will be performed as part of the project.

• DFG Programme: Research Grants