Patent GB-1161166-A (GB)
Title: Gyromagnetic Resonance Apparatus.
IPC: G01R33/389
Filed: 1967-04-21
Abstract: 1,161,166. Nuclear magnetic resonance spectrometer. NIHON DENSHI K. K. April 21, 1967 [April 23, 1966] No. 18598/67. Heading G1N. In a nuclear magnetic resonance spectrometer utilizing the side band technique in which the sample under investigation is subjected to a D.C. polarizing field and an audio-modulated r.f. field, both an internal reference sample (i.e. one associated with the sample under investigation) and an external (separate) reference sample are alternatively used for the control of the polarizing field, the internal reference sample being used during measurements and the external reference sample while the sample is being replaced. The internal reference sample and the sample itself are situated in a probe 1, Fig. 1, including an r.f. coil 7 energized by an r.f. transmitter 5 and the external sample is situated in a probe 2 including an r.f. coil 16 energized from the same transmitter. Both probes are immersed both in the D.C. polarizing field of an electromagnet, of which one pole 18a is shown, and in an a.f. field composed of two frequencies, a fixed frequency Wmo generated by oscillator 11 and a variable frequency Wmv generated by oscillator 12. The polarizing field in which the probe 1 is immersed is scanned using coil 22 energized either by a sawtooth generator 23 during sample replacement or by a sweep unit 35 during measurement; the audio frequency of oscillator 12 is also synchronously swept. At the start of the operations, with switches 24, 27, 29, 36 as indicated in full lines, the output signals from bridge detection circuits 6,15 of the internal and external reference samples are demodulated at 9 and 17 and supplied to phase detectors 26, 31, to which reference signals from oscillators 12,11 respectively are also fed. The output from phase detector 31 is supplied via a flux stabilizer unit 32 to control coil 21 for the control of the polarizing field to keep the Wmo side band signal of the external sample at resonance and the output from the phase detector 26 is supplied to the y axis of CRO 25 to whose x axis a signal from oscillator 23 is fed and on which the Wmv side band of the resonance spectrum of the internal reference sample is observed. The magnitude of the D. C. field, which is under the control of the external reference sample, is then adjusted to bring the internal reference sample into resonance by adjusting the local D. C. field at the external reference sample using a biasing coil 33 energized from an adjustable source 34. Thus the Wmo side band signal of the external reference sample and the Wmo side band signal of the internal reference sample are brought into resonance simultaneously. For measurement the switches 24, 27, 29, 36 are reversed so that the output from the detector 9 is fed to both phase detectors 26, 31, also supplied with reference signals by oscillators 11, 12 respectively, so that the Wmv side band signal from the internal reference sample, previously observed on the CRO 25, is used for the control of the D.C. field and that from the sample itself is fed to a recorder 28. At the end of the measurement switches 24, 27, 29, 36 are reversed before the probe 1 is removed to ensure that the D. C. field is maintained at the level at which both internal and external samples are at resonance. In a modification, Fig. 6 (not shown), the circuitry 15, 17, 30 associated with the external reference sample is omitted, the signals from both samples being fed to the bridge circuit 6, detector 9 and then to two phase detectors 26, 31 to which signals from oscillators 11,12 respectively are fed. By changing the r.f. level, using an attenuator (37), so as to saturate either the resonance signal of the internal reference sample or that of the external reference sample, only one sample reached the optimum condition, thus whichever one has reached this condition is used to control the D.C. field. During sample replacement, the attenuator (37) is adjusted to supply a strong r.f. level which is at an optimum condition for the external reference sample. The resonance signal from this sample is much stronger than that from the internal reference sample and is therefore used to control the D. C. field. During measurement, the r.f. level is lowered until it is at an optimum condition for the internal reference sample which is then used to control the D.C. field.