GB985208A - Gyromagnetic resonance method and apparatus - Google Patents

Abstract

985,208. Gyromagnetic resonance apparatus. VARIAN ASSOCIATES. Sept. 22, 1961 [Sept. 22, 1960], No. 34083/61. Addition to 939,258. Heading H3B. A gyromagnetic resonance oscillator comprises a sideband resonance system in which the driving radio-frequency magnetic field or the polarizing magnetic field is modulated at a frequency lower than the driving radio frequency to produce side-band resonance, the arrangement being made self-sustaining by selecting one of the frequencies produced and applying it in its correct sense after amplification and detection to effect the said modulation. The transmitter coil 28, Fig. 4, of a crossed coil system is energized by a signal of frequency or from an R.F. oscillator 27 through an attenuator 29, and the R.F. output (# ; #+# 1 , #+2 #1 ) (where # 1 is the modulating frequency), from coil 32 is, after amplification, mixed with oscillations from oscillator 27 in a mixer 34, a filter 35 being provided to select the modulating frequency. The selected frequency is applied to field modulating coil 38 through an audioamplifier 36 and a circuit 37, including a limiter to prevent saturation, the circuit serving to hold constant the amplitude of the resonance signal. A phase shifting network may be included. A single coil system is described with reference to Fig. 5 (not shown.) In an alternative arrangement, Fig. 7, the R.F. driving field is frequency modulated in a unit 56 by the audio output from the resonance system, the audio output being detected by an amplitude detector 61 and being applied also via a discriminator 69 and coils 67 to compensate for field drift. The F.M. signal is limited in a limiter 58 before application to the sample. In a modification of the arrangement of Fig. 7 described with reference to Fig. 8 (not shown), the driving field is amplitude modulated and frequency variation in the gyromagnetic output is detected by a discriminator to produce the modulating frequency. These two systems are insensitive to changes in R.F. gain or to transmitter/receiver coil unbalance. In a further single coil system, Fig. 9 (not shown), wherein the polarizing field is modulated by the audio output, the audio output is used also to control the magnetizing power supply, a frequency discriminator being included in the control circuit, and the arrangement serving to compensate for drift. A sideband resonance electron-paramagnetic oscillator in which the field through a cavity resonator containing the substance is modulated by the detected audio output from a bridge including the cavity in one arm, and energized by a klystron is described with reference to Fig. 10 (not shown).