Eddy-current Testing with Gmr Magnetic Sensor Arrays

The advent of GMR magnetic sensors and GMR sensor arrays with frequencyindependent sensitivity offers improvements in speed, depth, and resolution in eddy-current testing. Arrays of GMR magnetic sensors allow rapid scanning of an area for defects in a single pass. The small size and low power consumption of these solid-state magnetic sensors enable the fabrication of compact arrays of sensors on circuit boards and even on-chip sensor arrays. Arrays have been fabricated with sensor spacing as small as 5 micrometers when fine resolution is required. GMR sensor elements can be deposited on active silicon substrates facilitating on-chip signal processing and multiplexing. This integration simplifies the sensor/signal-processing interface, minimizes the number of leads, and can reduce the effect of noise. This paper will discuss the technology of fabricating arrays on GMR sensors, especially on-chip arrays. Integrated sensor arrays with on-chip signal processing and multiplexing will be described. Finally, some applications of arrays to crack and corrosion detection will be discussed.