A robotic apparatus equipped with ultrasonic probes and other instrumentation has been proposed to reduce the danger and cost and increase the speed of searching for land mines. The apparatus would implement modified versions of the proven techniques used by human searchers (delicately probing for, and excavating around, suspected objects) aided by dogs trained to sniff out explosives.

The instrumentation would be mounted on a robotic vehicle (see figure). The ultrasonic probes would include 30-cm-long prods that would be inserted gently in the ground at an angle of about 30°, as in manual demining. Piezoelectric actuators at the upper ends of each probe would vibrate the prod at a frequency of about 20 kHz. The probes would be placed 5 cm apart in a comb-like structure, and the vehicle would move in 5-cm steps. Thus, the search pattern would be a square array of points at intervals of 5 cm.

Ultrasonically Vibrating Prods would be inserted in the ground, in a manner similar to that of a manual search for mines. The robotic vehicle could also be equipped with an arm for digging up and removing mines.

Although all the probes would be operated simultaneously, each would be pushed into the ground under separate control to search for hard objects. The insertion mechanism for each probe would be instrumented to measure the position, speed, and force of insertion. Contact between a probe tip and a buried mine, rock, or other hard object would be indicated by a sharp increase in the force and a corresponding sharp decrease in the speed of insertion. Once an object suspected of being a mine had been detected, probes could be inserted at various positions and angles to determine the size, shape, and location of the object. The force applied by the insertion mechanism would be limited to a level (preferably <10 N) below the force that could detonate a mine. The speed of insertion would also be limited to prevent accidental impact and detonation.

The prods would be in the form of hollow tubes, through which dust kicked up by the vibrations could be collected and analyzed. In particular, the vibrating tip of a prod could scratch the surface of a suspected object and the resulting dust could be analyzed by use of a miniature onboard mass spectrometer to determine whether the surface is a plastic, metal, wood, or other material of a suspected mine case. The effect of a suspected object on the acoustic impedance of the ultrasonic transducer in each probe would be examined to obtain additional information about a suspected object. Other sensors and actuators could also be used; for example, an eddy-current sensor could be used to detect a metallic surface, and localized heat could be applied to melt or decompose a small amount of surface material for analysis. Information acquired through multiple sensors could be processed by a sensor-fusion algorithm in an effort to confirm that a suspected object is a mine and, if possible, identify the type of mine. The algorithm would incorporate expert-system and other artificial-intelligence software.

This work was done by Yoseph Bar-Cohen of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Machinery/Automation category.


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Ultrasonic Detector and Identifier of Land Mines

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This article first appeared in the October, 2001 issue of NASA Tech Briefs Magazine.

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