GB882127A - Improvements in or relating to electrical apparatus and circuit arrangements incorporating such apparatus - Google Patents

Abstract

882,127. Transformers. LIGNES TELEGRAPHIQUES & TELEPHIQUES. April 29, 1959 [May 16, 1958], No. 14627/59. Class 38 (2). [Also in Group XL (b)] A four-terminal non-reciprocal device comprises two magnetic core members extending in mutually perpendicular planes, one of the cores carrying a pair of windings arranged to have negligible mutual inductance and the other core being subject to a magnetic field of magnitude sufficient to cause gyromagnetic resonance within the material of the cores at the operating frequency of the device. As shown, an elongated core 3 extends through a disc-like core 4 with negligible clearance. The disc is apertured to accommodate two mutually perpendicular windings 5, 6 having terminals 10, 11 and 12, 13 which constitute the input and output terminals of the device. The elongated core 3 is arranged within the gap of a magnet 14 carrying a D.C. winding 15. In an alternative construction (Fig. 3, not shown), the core 4 is in the form of a four-spoked wheel with the windings around the spokes. In a further modification (Fig. 4, not shown), the coils 5, 6 are wound around four square-section members each extending at right angles from a face of the core 3. These members have pointed outer extremities to avoid demagnetization effects. The material of the cores must have high initial permeability and low conductivity, nickel-zinc ferrite or a compressed ferromagnetic alloy powder being suitable. Thin insulated magnetic tapes or wires may also be used. The core 3 may consist of a central portion made of ferrite and end portions made of soft iron. Under conditions of gyromagnetic resonance coupling between the two windings is produced, this coupling being non-reciprocal in the sense denoted by the following equations: where I 1 , I 2 and V 1 , V 2 respectively denote input and output currents and voltages. Z 1 and Z 2 denote input and output impedances under open-circuited conditions and S (which has a negative sign in the second equation) denotes the gyromagnetic transfer impedance between the windings. When the device is connected in an unbalanced transmission line the terminals 10, 12 are connected to each other as shown. In order to obtain transmission characteristics which are prescribed functions of frequency, an impedance 18 of value Z 3 is connected between the terminals 11, 13. It can be shown that the value m of the difference between the transfer exponents for the two directions of transmission is given by: where Z 1 =Z 2 =Z (i.e. identical windings are used). Since m is a given function and S, Z are experimentally determinable functions of frequency, the functional form of Z 3 may be determined and its physical structure approximately defined. For low attenuators in one direction and infinite attenuation in the other, tanh m/2 must be equal to unity, giving Z 3 =S+Z<SP>2</SP>/S. In this case the impedance 18 may comprise a capacitor in series with a parallel LC circuit, the inductor of which comprises a coil wound upon a nickel-zinc ferrite core. The Specification gives the dimensions of a suitable core and the values of the other circuit elements. Suitable corresponding dimensions and materials for the cores 3 and 4 are also given. If the device is used in a balanced transmission line, impedances of value Z3/2 are connected between terminals 10, 12 and 11, 13. The conditions for Z 3 when the windings have an unequal number of turns are discussed.