SQUIDs "see" everything

Part of a sensor (7x7mm) Superconducting quantum interferometers – so–called SQUIDs (superconducting quantum interference devices) – are highly sensitive sensors to detect magnetic fields. The "sensing" proper is made possible by a superconducting ring interrupted in one or two points by a Josephson tunnel contact, which can record changes of the magnetic field. The SQUIDs were developed in the mid-sixties by the American scientist J. Zimmerman. At first the highly sensitive sensors were exclusively employed for technical measurements. But within some years first tests were carried out to depict the fine magnetic fields of the human body. The sensors work, however, only at very low temperatures. Only when the material is cooled to an appropriate value below the transition temperature Tc will the electrical resistance of the material vanish and the material become superconducting. Liquid helium surrounds the specifically arranged SQUIDs during the measuring procedure and cools them to a temperature just above the absolute zero point. The sturdy design of the measuring instrument which actually works with tiny sensors also accommodates the coolant. Instead of liquid helium for the so–called low Tc–SQUIDs liquid nitrogen may be used as well. This recent development reduces the operating costs for such measuring facilities considerably, for unlike helium, nitrogen need not be specifically recovered. The nitrogen-cooled, so–called high Tc–SQUIDs, too, can sense extremely weak magnetic fields.

For further information about the development of SQUIDs, visit us at our Working Group "Cryosensorics".