Ultrasonic Holography Techniques for Localizing and Imaging Solid Objects

Ultrasonic holographic imaging holds the potential for recognizing object contours in two-dimensional or three-dimensional space. The theory of both the monofrequency and multifrequency modes of the method, as suitable for the requirements of object recognition in robot assembly tasks, is described. The theory was implemented experimentally. Results obtained show that the monofrequency approach provides fairly good lateral but insufficient depth resolution. By contrast, with multifrequency holography, depth resolutions of better than 3 mm and lateral resolutions of about 10 mm are attainable. New ultrasonic transducers, combined with a special signal preprocessing procedure, are a prerequisite for resolutions of this order. Typical images as obtained from several test scenes are presented. Suitable applications and possible future research are briefly outlined.