Magnetic tunnel junction based eddy current testing probe for detection of surface defects

Abstract

In recent years, magnetoresistive sensors have been applied to a large spectrum of applications from biomedical devices to industrial devices. Their high sensitivity and high spatial resolution are of special interest for eddy current based non-destructive testing. In this particular application, giant magnetoresistive sensors have been recently used for detecting surface and buried defects. Nevertheless, although very promising, magnetic tunnel junctions (MTJs) are still barely used in this application. In this work, two sensors with 6 and 10 MTJs in series were successfully fabricated, characterized, and tested on an aluminum mock-up including defects 100 μm wide and with a depth ranging from 0.2 to 1 mm. The sensors including 6 MTJ in series showed sensitivities of 50.8 mV/mT, while the sensor with 10 MTJ in series showed a sensitivity of 84.5 mV/mT. Due to its high sensitivity the latter was able to detect the smallest defect with a signal to noise ratio of 50, which seems promising for more challenging applications.