SQUID detection of electronic circuits

The author reports on the use of a SQUID (superconducting quantum interference device) magnetometer to detect audio-frequency timing signals from electronic and electromechanical clock circuits. Narrowband spectrum analysis was used to determine the quality factor (Q) in one case. Magnetic field maps indicated that the source of the magnetic fields could be localized to better than 1 mm. X-rays showed the presence of circuit elements in the region of the magnetic field maxima. Interpretation of the field sources as magnetic dipoles yielded m₂ values ranging from 10^-6 Am² to 10^-8 Am². The implication of this work is that SQUID magnetometers have potential use in noncontact detection of timing signals of timing circuits and microprocessors