Protecting the TIPPSI infrastructure with millimeter waves

Simulated image reconstruction of TAARDIS system with 4 x 3 array configuration.
© Photo Fraunhofer FHR

Simulated image reconstruction of TAARDIS system with 4 x 3 array configuration.

The EDA project TIPPSI aims to demonstrate the future of imaging millimeter wave systems in a simulation as well as in practice. The most promising approaches, namely radiometry, radar and MIMO, are compared within the framework of a project.

Wide-range surveillance

Since 2010, measures implemented to enhance the security of civil aviation in Europe include the utilization of radar-based body scanners. These active systems can detect suspicious objects concealed under clothing and make them visible to the security personnel. Similar systems are recently also being used to protect the critical infrastructure of the German Armed Forces. The conditions here, however, are identical to those of a close-range scanner: the persons who have to be scanned have to approach the scanner one-by-one and stand within a distance of just a few centimeters. This also allows the detection of very small suspicious objects, even if the person throughput is relatively low.

Up to now, there is no solution for extended environmental surveillance. The objects that have to be detected obscure a substantial portion of the body and, for this reason, detection has to take place at much greater distances.

EDA project TIPPSI

Active and passive millimeter wave systems can be used for detection over greater distances, but the efficiency of the systems and the signal processing need to be significantly increased. Under the project management of Fraunhofer IAF, four nations are now collaborating within the framework of the EDA project TIPPSI (THz Imaging Phenomenology Platforms for Stand-off IED Detection) to face this challenge.

Three possible approaches are being investigated: a passive scanner, an active scanner and an active MIMO scanner. The active scanners at 240 GHz are being developed in Sweden at FOI, Linköping, based on the chip design of the Chalmers University of Technology. The reflector optics are being developed by the partners at the Technical University of Delft, while the MIMO signal processing is being supplied by TNO in the Netherlands.

The core element of the passive scanner is currently being researched at Fraunhofer IAF in Freiburg: a multi-channel 300 GHz receiver provides enhanced spatial resolution. Fraunhofer FHR is designing the imager optics and the signal processing, so that a complete system can be produced.

Simulation and material testing

An important aspect of the TIPPSI project is the creation of a simulation environment in which the detection capacity of all systems can be predicted. To this end, FOI in Sweden is working on a simulation capability that uses animated, three-dimensional scenarios as a basis. In addition to models of people and objects, multi-layered clothing models and their dynamics are also being considered. These models are combined with material measurements that are individually created in line with the requirements, such as those created at the Wojskowa Akademia Techniczna (WAT) in Warsaw. The characteristics of the actual systems that are to be produced, e.g. noise and antenna patterns, are included in a post-processing phase. In this way, the simulations can be compared with the measurements and the limits of what is technically feasible can be defined.

TAARDIS – fast 300 GHz scanner with high resolution

To meet the high imaging capacity requirements, the scanner system TAARDIS is being designed at Fraunhofer FHR on the basis of a confocal Gregorian reflector system – an approach that has already proved successful in satellite technology. Thanks to the optics, several receivers can either operate parallel in the focal place or the array can be configured for electronic beam steering. In the present case, all passive receivers are sampled simultaneously. The rotation of a single mechanical component is sufficient to measure an image section with a high image repetition rate. The largest possible aperture must be produced to achieve optimal spatial resolution. Given that the system was designed as part of a building or a vehicle right from the start, experiments are currently being carried out with diameters of more than 60 cm for the primary reflector. The construction of an operable scanner with front-end and signal acquisition is planned for 2015. Joint measurements and a comparison with the simulation are planned for the end of the project in 2016.