Compact, Autonomous Robotic Detection and Identification (CARD) Sensor System
Automation has been a key factor since the Industrial Revolution in reducing the cost of goods and services. Clearing land mines is slow and dangerous work. The casualty rate for de-mining personnel ranges from 1 per 100 to 1 per 1000 land mines cleared. Crude land mine clearing efforts frequently involve just an individual with a simple metal detector and a long stick. More sophisticated approaches like heavily armored tanks dragging chains and low flying helicopters are very expensive. To decrease the danger many complex and expensive robotic devices have also been proposed. Recent high-technology proposals for detecting, classifying and assessing underground mines include the use of ground penetrating radar, ultrasonic sonar, passive infrared and microwave sensing. These techniques do not address the portability requirements or the low cost requirements for civilian de-mining applications.
The Johns Hopkins University Applied Physics Laboratory has developed and patented a metal detection system that includes a chassis for supporting electromagnetic sensor components above a medium such as soil or water. A transmitter coil is attached to the chassis and induces an electromagnetic field in the medium beneath the chassis. The electromagnetic field creates eddy currents in the metal objects in the medium. As the eddy currents decay, a first receiver coil is attached to one position of the chassis for receiving electromagnetic signals form the objects in the medium. A second receiver coil attached to the other position of the chassis also receives electromagnetic signals from the object in the medium. A propulsion system is attached to the chassis between or adjacent to the first and second receiver coils. The location of the propulsion system causes electromagnetic interference signals emanating from the propulsion system to be received at a nominally equal magnitude by each receiver coil finally, signal processing components add or subtract the outputs of the receiver coils, whereby interfering signals emanating from the propulsion system and received by the receiver coils are nulled.
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