Ray tracing simulation tool for portal-based millimeter-wave security systems using the NVIDIA® OptiX™ ray tracing engine

Summary form only given. Person-borne weapons and explosives present major security threats at civil infrastructures such as airports. Millimeter-wave whole body imaging systems are used to identify anomalous objects hidden underneath people´s clothing. Improvements to these systems can be investigated using electromagnetic computational models. Such forward models allow prediction of scattering from objects and give insight into the most effective sensor configurations and imaging techniques. Conventional full-wave simulation methods such as Finite Difference Frequency Domain and the Method of Moments provide extremely accurate solutions but are usually slow, ranging from minutes to hours in 3D depending on the domain size and frequency range. Less accurate but faster methods include physical optics and the Modified Equivalent Current Approximation (MECA). Simulating a portal-based scanning system involves evaluating the scattered field from the human body at multiple frequencies and at multiple receiver points, which is computationally expensive when using these methods. This work presents a fast forward ray tracing simulation tool. Rays are launched in the direction of a simulated tessellated human body and traced until reaching simulated system receivers. The scattered field at these receivers is computed by using the pathlength phase of each ray and adding ray fields within finite size receiver elements. Although the algorithm presented in this work excludes the modeling of phenomena such as refraction and diffraction, the path distance information encoded in reflected rays gives acceptable accuracy in scattered field amplitude and phase data and for images processed with SAR methods. The figure shows reflectivity magnitude of 2D SAR of a human body, using field data generated from ray tracing (left) and a 2D Method of Moments (right). The green contour is the true transverse body profile with torso and arms.