Improvements in devices for measuring magnetic fields, even of low intensity, and, in particular, the earth magnetic field

摘要

929,022. Magnetic testing apparatus. COMMISSARIAT A L'ENERGIE ATOMIQUE. Jan. 25, 1960 [Jan. 30, 1959], No. 2663/60. Addition to 888,439. Class 37. In a magnetometer of the type described in the parent Specification comprising a solution of a paramagnetic substance placed in the unknown field, electronic resonance is induced in the substance by a rotating magnetic field perpendicular to the unknown magnetic field. Fig. 2 shows an organic glass vessel 1 containing one of the solutions specified in the parent Specification, within a weak unknown magnetic field Ho such as the earth's field. A rotating magnetic field at the electronic resonance frequency is provided by quadrature currents in coils 3a, 3b perpendicular to Ho and fed from a quartz oscillator 9. Coils 3a, 3b are respectively tuned by variable capacitors 6a, 6b above and below the frequency of oscillator 9 to provide the phase difference of 90 degrees. It is shown that the rotating field causes a strong emission of energy at the nuclear resonance frequency, e.g. 2 kc/s., which is proportional to the unknown field strength. The energy is received by a coil 4, screened by a shield 5 and tuned to resonance by a capacitor contained in a regenerative amplifier 14. The output of amplifier 14 is fed via a tuned amplifier 15 to a decade divider 16. The output of a 100 kc/s. quartz oscillator 18 is shaped by a circuit 19 and counted by a 6- decade divider 20 for a period determined by a trigger 17 operated after 10,000 cycles of the unknown frequency. A recorder 21 provides at least the last two digits of the time taken to count the 10,000 cycles of the unknown frequency and thus gives an indication dependent on the unknown field strength Ho. In Fig. 4, the 90 degrees phase difference is provided by coaxial lines 22a, 22b, differing in length by a quarter wavelength. Capacitors 25a, 25b match the coils 3a, 3b to the lines. Specification 914,751 also is referred to.