Pulsed Eddy-Current Measurements of Corrosion-Induced Metal Loss: Theory and Experiment

Response Function of an Electromagnetic Microscope

“…::.<I>p = ;p J ! ::.Ad · ~ diJ, (2) expresses magnetic flux, ! ::.<I>p, threading a pickup circuit from a current dipole, where 1;, is current density in a filamentary pickup circuit carrying current Ip and !…”

“…An ELECTROMAGNETIC MICROSCOPE uses a superconductive quantum interference device (SQUID) to achieve high resolution l at low frequencies (.$ 100 Hz), for deep, eddy current evaluation of airframes [1][2][3]. The probe is a reflection type, with a superconductive source coil and a superconductive pickup loop that couples inductively to a remote SQUID.…”

“…The probe is a reflection type, with a superconductive source coil and a superconductive pickup loop that couples inductively to a remote SQUID. The SQUID measures change in mutual inductance 2 between the source and pickup coils, measured in picohenries (PH). A description of the change in mutual inductance follows from vector potentials of the source and pickup coils.…”

Electromagnetic Microscope for Low Frequency, Pulsed, Eddy Current Evaluation of Airframes

“…An ELECTROMAGNETIC MICROSCOPE uses a superconductive quantum interference device (SQUID) to achieve high resolution) at low frequencies (;:5 100 Hz), for deep, pulsed, eddy current evaluation of airframes [1][2][3]. A test bed instrument, operating at ",5 Kelvin, uses a reflection type probe with a superconductive source coil and a superconductive pickup coil that couples inductively to a remote SQUID.…”

Electromagnetic Microscope for Deep, Pulsed, Eddy Current Inspections

“…Their high sensitivity at low frequency 1 enables penetration of 15 mm or so of aluminum, through multiple layers, to identify millimeter fatigue cracks and material loss of a few percent from corrosion in underlayers [1] [2]. Pulsed eddy currents [3] provide a three dimensional view of defects in sublayers and enable tomographic sectioning of multilayer structures. Together with SQUIDs, they would give an ELECTROMAGNETIC MICROSCOPE for examining fatigue darnage and corrosion in underlayers of structures.…”