Location

La Jolla, CA

Start Date

1-1-1993 12:00 PM

Description

Although superconducting quantum interference devices (SQUIDs) provide an exquisitively sensitive means for measuring magnetic fields, their usage in the past has been limited chiefly to biomagnetic research. However, over the past few years interest in applying SQUID techniques to the field of nondestructive evaluation (NDE) has blossomed [1]. Many experiments have exploited the sensitivity of SQUIDs for diverse NDE applications, especially those requiring large separation distances between the sensor and the item to be inspected. Our work instead has focused on the potential to detect very small defects with SQUIDs, specifically in thin-walled tubes. In this paper, we discuss three different methods for creating magnetic fields in tubes. The methods comprise (a) directly injecting a current through the tube, (b) using a separate induction coil to create induced currents in the tube, and (c) utilizing a ferromagnetic tracer technique. To illustrate the capabilities of each method, we present two-dimensional maps of the spatial distribution of the magnetic field as measured by a SQUID magnetometer — that is, SQUID images. The images will also be used to compare the sensing methods with respect to such practical considerations as relative sensitivity and signal-to-noise ratio.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

12A

Chapter

Chapter 2: Emerging Inspection Technologies

Section

Electromagnetic Techniques

Pages

633-640

DOI

10.1007/978-1-4615-2848-7_80

Language

en

File Format

application/pdf

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Jan 1st, 12:00 PM

A comparison of SQUID imaging techniques for small defects in nonmagnetic tubes

La Jolla, CA

Although superconducting quantum interference devices (SQUIDs) provide an exquisitively sensitive means for measuring magnetic fields, their usage in the past has been limited chiefly to biomagnetic research. However, over the past few years interest in applying SQUID techniques to the field of nondestructive evaluation (NDE) has blossomed [1]. Many experiments have exploited the sensitivity of SQUIDs for diverse NDE applications, especially those requiring large separation distances between the sensor and the item to be inspected. Our work instead has focused on the potential to detect very small defects with SQUIDs, specifically in thin-walled tubes. In this paper, we discuss three different methods for creating magnetic fields in tubes. The methods comprise (a) directly injecting a current through the tube, (b) using a separate induction coil to create induced currents in the tube, and (c) utilizing a ferromagnetic tracer technique. To illustrate the capabilities of each method, we present two-dimensional maps of the spatial distribution of the magnetic field as measured by a SQUID magnetometer — that is, SQUID images. The images will also be used to compare the sensing methods with respect to such practical considerations as relative sensitivity and signal-to-noise ratio.