GB901829A - Improvements relating to nuclear magnetic resonance apparatus - Google Patents

Abstract

901,829. Nuclear resonance-testing apparatus. FAIREY CO. Ltd. Oct. 14, 1958 [June 30, 1958], No. 20902/58. Class 37. A nuclear magnetic resonance detector comprises a test coil in a transverse magnetic field and adapted to receive a test specimen the test coil being coupled to a radio frequency generator and forming part of a tuned circuit in a feed-back loop which increase the effective Q of the tuned circuit. In Fig. 1, a specimen 11 is inserted in a coil 10 located in the field of a magnet 12 and coupled to a R.F. generator circuit 13. The coil being tuned by capacitors 18 and 19 and coupled to a detector circuit 20, 40, 41, 42, 43. The magnetizing current of the magnet 12 is varied in saw-tooth fashion by means of a generator 16 so that the nuclear resonance frequency is varied through a range which includes the frequency of an R.F. generator. When the two frequencies are the same, energy is absorbed from the R.F. generator 13 and a corresponding indication is obtained in the meter 43 or a cathode-ray tube circuit connected in its place. The tuned circuit 10, 18, 19 is connected to the valve 20, in Colpitts fashion so as to provide positive feed-back and so increase the effective Q of the circuit and the sensitivity of the apparatus. A negative feed-back resistor 24 is provided to stabilize the circuit and this is adjustable to enable the gain to be set to a value just below that which causes the circuit to oscillate. In an alternative circuit (Fig. 3, not shown), the adjustment is effected by varying the screen potential of valve 20. The Specification also describes a circuit as disclosed in Specification 901,827 in which a different method of detecting nuclear resonance is used, the detector coil being connected in a circuit similar to Fig. 1 (Fig. 2, not shown). The radiofrequency generator may be crystal-controlled and may provide a harmonic series of frequencies so that a single crystal may be used to cover a wide frequency range, interpolation between the harmonics being effected by a magnetic shunt, as described in. Specification 901,828.