Superconductive device including a supercooled first body heated by electromagnetic radiation at a first frequency and a supercooled second body heated at a second frequency greater than the the first for measuring a magnetic field

Device for measuring a magnetic field, of the type including a first body of superconducting material placed in the magnetic field to be measured, means for successively changing a temperature of said first body of superconducting material above and below its superconducting transition temperature, and therefore changing said first body, at a first frequency, from a first state in which said first body is permeable to field lines, when said first body is at a temperature greater than its superconducting transition temperature, to a second state in which said first body is impermeable to said field lines, when said first body is at a temperature less than its superconducting transition temperature, and vice versa, so as to generate magnetic field variations in the vicinity of said first body, and means for detecting said field variations and for determining a magnetic field from said field variations, and wherein the detection and determination means include a second body of superconducting material, placed in the magnetic field to be measured, in the vicinity of said first body, means suitable for changing a temperature of at least one portion of said second body of superconducting material, above and below its superconducting transition temperature, at a second frequency greater than said first frequency, in order to generate, in said second body, current variations proportional to the field variations induced by said first body, means for measuring said current variations in order to determine the corresponding field variations and means for determining the field from said current variations.