UWB radar target sensing and imaging for granular materials research applications

Granular materials research involves the study of dynamic movement of objects with granular shape and characteristics. Researchers in this field of study rely on accurate experiments to validate theoretical models or solve problems empirically. Current experiments are either expensive (e.g., MRI or X-ray technologies), limited in scope (e.g., High-Speed High-Resolution Photography which is limited to 2D experiments due to granular material opacity) or extremely tedious and time-consuming. In this paper, we investigate a first-generation prototype of a radar system that will provide a minimally invasive fully automated measurement of individual and bulk particle movement in a 3D volume. The radar system [1] comprises inexpensive tracer particles as targets, a test signal generation and measurement unit, and a post-processing unit for imaging. The proposed target is a square retroreflector, which is made up of three orthogonal square metal plates (see Figure 1). An array of wideband antennas surrounding the testbed is operated in monostatic mode using swept-frequency VNA measurements that are processed to mimic an ultrawideband (UWB) bandpass pulse. In our first-generation prototype, we synthesize a linear array by moving the testbed relative to a single antenna. The testbed contains one or more targets deployed in a free-space (rather than granular material) volume. We perform delay-and-sum beamforming to reconstruct an image of the testbed. Images are generated for the retroreflector at two distinct orientations - (normal and oblique) relative to the array.