Applied magnetic sensing: a long way

Our laboratory has more than 20 years of experience in LTS or HTS superconducting quantum interference devices (SQUID). For a few years, we have extended our field of investigation in the study and characterization of high sensitivity magnetic sensors (flux gate, anisotropic magnetoresistive sensor, giant magnetoresistive sensor, giant magneto inductance, /spl mu/-Hall...). One part of our researches is to study, implement and test high sensitivity magnetic sensors, improve their performances and compare, especially, the evolution of their intrinsic magnetic noise in a shielded to open environment. A good part of applications needs high sensitivity magnetic sensors, like magnetic anomaly detection, geomagnetism, space magnetometry, magnetocardiography, biomagnetism, NMR or low magnetic field MRI, metrological application, magnetic microscopy, nondestructive testing or evaluation... Meanwhile, the environmental magnetic noise often shades the ultimate noise level of high sensitivity magnetic sensors. Therefore, a theoretical and "real world" comparison of their performances seems necessary (equivalent magnetic noise spectrum, gradiometric rejection bandwidth, transfer, spatial resolution, figure of merit, dynamic and so one). In particular, some researches have pointed out that the proposed applications in open environment for some low temperature and high sensitivity magnetic sensors like SQUID magnetometer or gradiometer had to be defended using larger comparisons against high sensitivity room temperature magnetic sensors rather than, only, pointing to their intrinsic performances. So, the development and the necessity of very high sensitivity magnetometers are still in question for some applications.