Patent GB-1001255-A (GB)
Title: Gyromagnetic resonance method and apparatus
IPC: H01J49/38
Filed: 1961-10-26
Abstract: 1,001,255. Gyromagnetic resonance apparatus. VARIAN ASSOCIATES. Oct. 26, 1961 [Nov. 23, 1960], No. 38401/61. Heading G1N. In a gyromagnetic resonance analysis apparatus and method in which the parameters are chosen so that the application of a modulation frequency W 1  to either the RF field or the magnet's field produces a fundamental frequency W and a range of sidebands W + n W 1 -W- n W 1 , and wherein detection produces a signal for example W 1  for comparison with the modulating signal, the modulating signal is produced by similar sideband techniques in a further sample of matter excited by gyromagnetic resonance in the same polarizing magnetic field which sample may serve as a standard. The arrangement is said to be field-frequency stabilized. Test sample 11, Fig. 1, is applied through a coil 14 with R.F. energization from a crystal controlled oscillator 15 at a frequency W and the unidirectional magnetic field is modulated at an audio or low frequency W 1  by a coil 17 supplied through a field modulator amplifier 34 from a self sustaining gyromagnetic sideband resonance apparatus in which a substance 12 is energized by the output from oscillator 15 through a coil 29, the frequency W 1  being detected, and amplified, and fed back to modulate the field to sample 12 at a frequency W 1 . The composite output from coil 14 due to resonance is amplified in 18, detected in a diode circuit 19 to produce a test signal at frequency W 1 , and applied to a recorder 23 through an audio mixer 22 supplied also with W 1  from amplifier 33 and thus acting as a phase detector. The unidirectional field is swept through resonance by a coil 26 energized by a saw tooth generator 25 and the recorder 23 is synchronized with the sweep. The relative field strengths through the two samples may be adjusted by a small bias current also applied to the sweep coil. The dispersion or absorption mode may be selected by adjustment of the phase of one of the signals of frequency W 1  applied to the audio mixer. The field modulator 34 may include a limiter or A.G.C. for stability and provision may be made for adjusting the phase of the oscillator feed back. The oscillator 15 may be provided with automatic frequency control, a variable reactor 38 being controlled by the output of a discriminator 37, or alternatively the discriminator may be applied to control the unidirectional field. A.G.C. may be provided for amplifiers 18 and 31. A switch 34<SP>1</SP> provides for converting the measuring channel to a self sustaining oscillator for calibration purposes which are described. Application of the apparatus to automatic control of the supply valves to a mixer is described with reference to Fig. 1a (not shown). As an alternative to the magnetic field modulation described the signal from oscillator 15 may be frequency modulated whilst the receiver and feed back path uses amplitude modulation or vice versa. F.M. A.M. and A.M. F.M. systems using cross coil type probes and bridge type probes respectively are described with reference to Figs. 4 and 5 (not shown). A further arrangement in which the audio modulation for both samples is applied by a single coil, and in which the sweep is applied to the oscillatorchannel is described with reference to Fig. 6 (not shown) a system wherein the two samples may be different, including a frequency synthesizer to establish the correct frequency difference is described with reference to Fig. 7 (not shown) and an arrangement including a small sweep generator of amplitude comparable to a line width and of about 3 cycles per second for calibration and field adjustment is described with reference to Fig. 8 (not shown). A still further system having separate pick up coils and a frequency controlled transmitter is described with reference to Fig. 9 (not shown).