Experimental characterization of polaroid ultrasonic sensors in single and phased array configuration

Many mobile robots use Polaroid ultrasonic sensors for obstacle avoidance. This paper describes the experimental characterization of these sensors using a unique, fully automated testbed system. Using this testbed, we gathered large data sets of 5,000-16,000 data points in every experiment for characterization purposes; in a repeatably fashion and without human supervision. In the experimental characterization reported in this paper we focused on a comparison of the "beamwidth" of a single sonar with that of a dual sonar phased array. For the single sonar we found that flat walls trigger echo signals up to an angle of +/-42degrees, which is well beyond the traditional assumed beamwidth of +/-15degrees. We determined that these echoes result from the secondary and tertiary lobe of the well known multi-lobed propagation patterns of Polaroid ultrasonic sensors. In contrast, with the dual sonar phased array echo signals were triggered only up to beamwidths of +/-18degrees. By implementing a power-reducing modification in the sonar circuits, we achieved narrow beamwidths of 4-6degrees. The results in this paper were obtained for two test targets: a specular surface and a cylindrical object.