HTS SQUID NDE of Curved Surfaces Using Background Field Cancellation Techniques

Single-layer high-temperature superconducting SQUID gradiometers are well established for measuring small localized magnetic fields in the presence of much larger background interference. Such sensors have proved extremely useful for eddy-current nondestructive evaluation (NDE) of aircraft and other metallic structures. Most applications to date have involved either the sensor remaining stationary or being moved in a straight line in an unshielded environment. However it is desirable for many field mapping applications for the sensor to be rotated or tilted in the Earth's field whilst retaining full device sensitivity. We report on the development and performance of a portable NDE scanning system which uses background field cancellation techniques to allow the device orientation to change whilst mapping the surface of a curved wing structure.