Measuring and testing – Vibration – By mechanical waves
Patent
1983-08-08
1985-06-18
Ciarlante, Anthony V.
Measuring and testing
Vibration
By mechanical waves
73583, G01N 2904
Patent
active
045234736
ABSTRACT:
A dark-field magneto-elastic non-destructive testing technique for detection of defects in a conductive material by inducing eddy currents or applying an electric current to the material along a path in such manner that the current will be diverted from the path in the vicinity of any material defect, causing the generation of acoustic waves locally from the interaction of the diverted current with a local magnetic field. The resulting acoustic waves are detected as an indication of the presence and location of a material defect. In typical application, a current is induced in the conductive material by the generation of eddy currents in the material along a substantially linear path by coupling from a current excited wire insulated from and applied near the surface of the material. The eddy current will tend to follow substantially the direction opposite of the current excited wire. This current will be diverted from the path by any material surface defect, creating a normal component which interacts with a magnetic field component substantially parallel to the path, providing for the generation of an acoustic wave within the material which are detected by an acoustic sensor applied along an edge or face of the material. Typically the acoustic waves are generated as the relative electromagnetic fields of the applied current and the local magnetic fields are varied with respect to each other. By pulsing or varying the applied current or applied magnetic field, the time between the generation of the acoustic pulse, which is relatively instantaneous at any location in the material, and the reception of the acoustic pulse at the detector provides an indication of the distance from the defect to the detector. An array of detectors may be used to triangulate the defect. The elastic waves are generated only in the presence of a defect by the defect giving three dimensional location information about the defect location, as well as other characteristics, in contrast to conventional ultrasonic NDE techniques, where the defect is used as a scatterer of incident ultrasonic waves.
REFERENCES:
patent: 4348903 (1982-09-01), Sato et al.
patent: 4395913 (1983-08-01), Peterson
patent: 4434663 (1984-03-01), Peterson et al.
"Non-contact Ultrasonics", by Parkinson et al., Jul. 77.
Ciarlante Anthony V.
The Charles Stark Draper Laboratory Inc.
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