Location

Brunswick, ME

Start Date

1-1-1997 12:00 AM

Description

Of the electromagnetic sensors currently under investigation for nondestructive evaluation (NDE), the superconducting quantum interference device (SQUID) arguably has the greatest potential. The characteristics [1] which make it suitable for eddy current NDE are: high sensitivity even in large ambient fields (detection of sub-nT signals); operation from very low frequencies (a few Hz or less) to very high frequencies (potentially MHz) permitting detection of surface and subsurface flaws; and high spatial resolution. Spatial resolution is related to the physical size of the device, which is often less than 1 mm square, even when the need to maintain its other properties is taken into account. This often allows the SQUID to be treated theoretically and practically as an ideal point sensor. However, it must be operated in a cryogenic environment: low temperature superconductor (LTS) SQUIDs need liquid helium and liquid nitrogen (LN2) is needed even for high temperature superconductor (HTS) SQUIDs. This makes it difficult to reduce the specimen-to-sensor stand-off below approximately 1 mm.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

16A

Chapter

Chapter 4: NDE Sensors

Section

Electromagnetic Probes

Pages

1075-1081

DOI

10.1007/978-1-4615-5947-4_140

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Advances in the Use of LTS and HTS SQUIDS in Electromagnetic NDE

Brunswick, ME

Of the electromagnetic sensors currently under investigation for nondestructive evaluation (NDE), the superconducting quantum interference device (SQUID) arguably has the greatest potential. The characteristics [1] which make it suitable for eddy current NDE are: high sensitivity even in large ambient fields (detection of sub-nT signals); operation from very low frequencies (a few Hz or less) to very high frequencies (potentially MHz) permitting detection of surface and subsurface flaws; and high spatial resolution. Spatial resolution is related to the physical size of the device, which is often less than 1 mm square, even when the need to maintain its other properties is taken into account. This often allows the SQUID to be treated theoretically and practically as an ideal point sensor. However, it must be operated in a cryogenic environment: low temperature superconductor (LTS) SQUIDs need liquid helium and liquid nitrogen (LN2) is needed even for high temperature superconductor (HTS) SQUIDs. This makes it difficult to reduce the specimen-to-sensor stand-off below approximately 1 mm.