Evaluation of Coating Thickness Using Lift-Off Insensitivity of Eddy Current Sensor.

Defect detection in ferromagnetic substrates is often hampered by nonmagnetic coating thickness variation when using conventional eddy current testing technique. The lift-off distance between the sample and the sensor is one of the main obstacles for the thickness measurement of nonmagnetic coatings on ferromagnetic substrates when using the eddy current testing technique. Based on the eddy current thin-skin effect and the lift-off insensitive inductance (LII), a simplified iterative algorithm is proposed for reducing the lift-off variation effect using a multifrequency sensor.

Use of sputtered zinc oxide film on aluminium foil substrate to produce a flexible and low profile ultrasonic transducer.

A flexible and low profile ultrasonic transducer was fabricated for non-destructive testing (NDT) applications by DC sputtering of 3 μm thick, c-axis oriented, ZnO film on 50 μm aluminium foil. Due to the thin foil-based construction, the transducer can be applied to curved objects and used in sites of restricted accessibility. The device has been used to demonstrate detection of simulated defects in a 45 mm diameter steel pipe, and for thickness measurement on a 3.