6. SQUID metrology applications

The SQUID is a natural magnetic field sensor with very high resolution. The constraints associated with its use (cryogenics, protection against environmental interference) make it ideal for detecting or amplifying signals dominated by the intrinsic noise of semiconductor-based systems. Over the past 30 years, considerable progress has been made in fine magnetometry (magnetoencephalography, non-destructive testing), and SQUID-based devices (magnetoencephalographic imaging, susceptometers) have been commercialized. In addition, many other experiments that can be grouped under the generic term of voltage measurement (picovoltmeters, selective or broadband preamplifiers) have been carried out in laboratories; the frequency...