Proximity detector circuits: an alternative to tunnel diode oscillators for contactless measurements in pulsed magnetic field environments.

A radio frequency oscillator circuit based on a proximity detector integrated circuit is described as an alternative for the traditional tunnel diode oscillator used for pulsed magnetic field measurements at low temperatures. The proximity detector circuit design, although less sensitive than tunnel diode oscillator circuits, has a number of essential advantages for measurements in the extreme environments of pulsed magnetic fields. These include the insensitivity of operation to voltages induced in the inductor coil, the elimination of a diode bias circuit and tuning, and a broad dynamic range of resonant frequency variation. The circuit has been successfully applied to measure the superconducting upper critical field in Ba(0.55)K(0.45)Fe2As2 single crystals up to 60 T.