Modulated inductance magnetometers

2014 The principles of operation of a modulated inductance magnetometer and the problems that have been encountered in an attempt to realize the expected sensitivity are discussed. A magnetometer for which inductance modulation is effected by a superconducting plane vibrating near a long inductance element is described. The suitability of this magnetometer to the measurement of small magnetic fields is considered in conjunction with the most recent experimental results. REVUE DE PHYSIQUE APPLIQUÉE TOME 5, FÉVRIER 1970, PAGE For superconductors in a state where a complete Meissner effect is exhibited the fluxoid [1] : remains essentially constant in time; in this expression the line integral is taken around a path in the superconducting loop; J is the current density, 03BB, the London penetration depth and (D, the magnetic flux threading the loop. When the path of integration can be chosen to lie several penetration depths inside the superconductor, the fluxoid is nearly equal to the magnetic flux. In a modulated inductance magnetometer it is this conservation that is used to measure the magnetic flux externally applied to a superconducting loop. In this paper the principles of operation of such a modulated inductance magnetometer are described, and theoretical and practical limits to the sensitivity are discussed. A method to realize inductance modulation is then considered. Following this is a brief description of the results of the preliminary experiments and of the useful properties expected of such a magnetometer. Figure 1 shows some of the important features of the magnetometer.