Experimental Comparison of the Low-Frequency Noise of Small-Size Magnetic Sensors

Small-size ac magnetic-field sensors are used for nondestructive testing (NDT), magnetic particle detection, and other applications, which require high spatial resolution. Up to now, inductive coils dominated this area, as their sensitivity at kHz frequencies, is superior to other magnetic sensors. However, some applications, such as magnetic imaging through conducting sheath, require lower working frequencies, in extreme case units of Hz. We successfully replaced inductive coils by an AMR sensor in NDT application and for distance measurement. In this paper, we compare designs of miniature ac magnetic field sensors, their achievable frequency characteristics, dynamic range, and noise parameters.