Patent GB-814098-A (GB)
Title: Gyromagnetic resonance apparatus
Inventor: MALLING LEONARD REGINALD
IPC: G01R33/36
Filed: 1956-04-23
Abstract: 814,098. Electric tests. VARIAN ASSOCIATES. April 23, 1956, No. 12402/56. Class 37. A probe for use in a gyromagnetic resonance system comprises a body of non-magnetic material having a hollow member of dielectric material fixedly mounted within a cavity therein, a first coil carried by the member, a second coil mounted within the cavity with its axis perpendicular to that of the first coil, and an electrostatic shield fixed mounted within the cavity between the two coils. As shown, the main body of the probe comprises a block of metal containing sweep coils 7 embedded in recesses 5 in opposite faces of the block where they are retained in position by a thermosetting plastic. A large cylindrical bore 13 extends at right angles to the axis of the sweep coils and houses the sub-assembly shown in Fig. 4 which comprises transmitting and receiving coils. The sub-assembly comprises a pair of tubes 17, 18 of glass or plastic, tube 17 being fitted inside tube 18 and projecting from the ends. Sandwiched between the tubes are a number of insulated shielding wires 19 which run side by side between the two tubes and are held in position by a thermoplastic film. One end of each wire is left unconnected while the other ends are connected together by three contact bands 24 and an encircling band of wire. Small tags 26 connect bands 24 to mounting ring 25. On the outer surface of tube 18 is the transmitter coil 29 which is made in two sections. The receiver coil 34 is wound on the inside of tube 17. Both coils are held in position by a'thermosetting plastic. Coarse balancing members 41, 42 are positioned adjacent the transmitter and receiver coils 29, 24 by means of plastic screws 43, 45. Member 41 consists of a plastic cylindrical block having a discshaped copper end piece 45 while 42 is of carbon. A hollow cylindrical support tube and handle 48 is threaded to one end of block 1 and is closed by an end cap 49. Extending through this cap are screwed rods 54, 55 which are threaded to bars 52, 53 and which push intermediate rods 56, 57 carrying fine balancing members 58, 59 one of which carries a disc of copper and the other of which is of carbon. L-shaped spring members 62, 63 return the fine balancing members when the screwed rods 54 and 55 are withdrawn. A pair of trimmer condensers 66 and a pair of inductance coils 67 are mounted in a recess 32 in the block 1 and are connected in circuit with a transmitter coil and with a twin lead connector 122 (see also Fig. 9). A third trimmer condenser 71 and inductance 72 are mounted within a further recess 39 and are connected to the receiver coil 34 and coaxial connector 721. A two-wire cord 73 extends through a small opening into support tube 48 and eventually connects to sweep coil 78. In a further arrangement (Fig. 11) the transmitter coil is in two parts 162, 163 carried on coil formers 155, 156. The formers are themselves slidable in blocks 144, 145 which are adjustable vertically by screws 153, 154 while further screws 157, 161 permit the adjustment of the coil formers toward the specimen. In the centre of block 131 is a cylindrical tube 133 which tapers to a smaller hollow cylindrical portion 134. This tube is covered with shielding wires 135. Inside tube 133 is a receiver coil former 137 having a receiver coil 138 secured on its outside surface. Eccentric adjusting rings 139, 141 enable the coil form 137 to be moved in a conical path. The various adjustments enable coupling between the transmitter and receiver coils to be eliminated. A still further arrangement is described (Fig. 14, not shown) in which the sections of the transmitting coils are each mounted on two screws which may be independently adjusted and fine tuners of the type described with reference to Fig. 1 are included. Operation and circuits.-A specimen in a test tube may be inserted in the receiving coil or a continuous flow of material under test through the centre of the coil may be arranged. As shown in Fig. 8, the specimen is placed in tube 76 and the block is arranged between the poles of a magnet 75. Sweep generator 77 feeds an audio-frequency voltage to the sweep coils which modulate the polarizing field. Oscillator 79, which is capable of producing any frequency from 2 to 16 megacycles feeds the transmitter coil through amplifier 81 and attenuator 82 to vary the field intensity. The output of the receiver coil is fed through R.F. amplifier 83, which may include a pre-amplifier mounted on the probe, a detector 84, which removes the R.F. signal, and an audio amplifier 86 the output of which is indicated on oscilloscope 78. The timebase sweep of the oscilloscope is controlled by the sweep generator 77 which modulates the polarizing field. Fig. 9 shows an arrangement for controlling the strength of the R.F. oscillation. Oscillator 79 feeds class " C " amplifier 87 and, through attenuator arrangements consisting of resistors 108, 115 and 116, the transmitter coils 29. In the first position switch 109 short-circuits resistor 108, in the second, it removes the short-circuit on the resistor, and in the third and fourth it introduces shunting resistors. This acts as a coarse control. A fine control is obtained by controlling the screen potential of amplifier 87 by means of potentiometer 102. Specification 753,495 is referred to.