RF Attenuation Measurements Using Quantum Interference in Superconductors

A unique portable system has been developed for measuring RF attenuation over a dynamic range of 62 dB at 30 MHz. A superconducting quantum interference device (SQUID) is the basis of the system. A SQUID is a loop of superconducting metal closed by a weak point contact called a Josephson junction, operating in liquid helium. It converts variations in magnetic flux to periodic variations in impedance which are sensed at microwave frequencies. This provides a convenient natural means of measuring electrical quantities such as voltage, current, power, and attenuation.