Electromagnetic sensor element and methods and apparatus for making and using same.

摘要

A novel sensor element (30) having low magnetic coercivity and an asymmetric hysteresis characteristic is formed by heating a strip of cobalt alloy (32)in an oxidizing atmosphere to form an oxide coating (34) thereon and then the strip is cooled in the presence of a magnetic field of about 0.3 oersteds along its length. The strip is detected by subjecting it to an alternating magnetic interrogation field and passing the resulting magnetic disturbances through signal processing circuits which select pulses produced only once in each interrogation field cycle. The element is deactivated by subjecting it to a magnetic field which eliminates its asymentry.