Flux focusing eddy current probe

US5617024A · kind A · utility

Assignee

• The United States of America as represented by the United States National Aeronautics and Space Administration · US

Inventors

• John W. Simpson · Madison, US
• C. Gerald Clendenin · Williamsburg, US
• James P. Fulton · Hampton, US
• Russell A. Wincheski · Williamsburg, US
• Ronald G. Todhunter · Grafton, US
• Min Namkung · Yorktown, US
• Shridhar Champaknath Nath · Gaithersburg, US

Key dates

• Filing date: May 8, 1996
• Grant date: Apr 1, 1997
• Expiry date: May 8, 2016

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N27/902
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A flux-focusing electromagnetic sensor which uses a ferromagnetic flux-focusing lens simplifies inspections and increases detectability of fatigue cracks and material loss in high conductivity material. The unique feature of the device is the ferrous shield isolating a high-turn pick-up coil from an excitation coil. The use of the magnetic shield is shown to produce a null voltage output across the receiving coil in the presence of an unflawed sample. A redistribution of the current flow in the sample caused by the presence of flaws, however, eliminates the shielding condition and a large output voltage is produced, yielding a clear unambiguous flaw signal. The maximum sensor output is obtained when positioned symmetrically above the crack. Hence, by obtaining the position of the maximum sensor output, it is possible to track the fault and locate the area surrounding its tip. The accuracy of tip location is enhanced by two unique features of the sensor; a very high signal-to-noise ratio of the probe's output which results in an extremely smooth signal peak across the fault, and a rapidly decaying sensor output outside a small area surrounding the crack tip which enables the region …