GB1134293A - Delay line - Google Patents

Abstract

1,134,293. Electromechanical delay lines. MULLARD Ltd. 29 March, 1967, No. 14224/67. Heading H3U. [Also in Division H1] A single-port delay line comprises a single crystal of ferrimagnetic material which forms the dielectric of a coaxial transmission line and, at the same time, functions as a transducer and propagation medium for elastic waves. The crystal 3 may be of yttrium iron garnet (YIG) and is arranged to fill the space between the conductors of a coaxial line which is terminated in a resistive or reactive matched load 5. A further section of the line is occupied by an element 4 made of polycrystalline YIG, the total length of the YIG elements 3, 4 being L. A constant and spatially uniform external magnetic field Hext is applied to the YIG elements in the longitudinal direction of the line. Fig. 2 shows the non-uniform intensity of the resultant internal field which rises to a maximum at the central point of the elements 3, 4 and falls to a minimum value at either end (the graph shows the left-hand half only). The YIG elements 3, 4 are matched to the input section 6 and to the termination 5 respectively by dielectric members 7, 8 which may be tapered in the usual manner. An electromagnetic (e-m.) wave from the input section 6 propagates from left to right in the single crystal 3 and is transformed into a spin wave at the transverse plane where the internal field reaches a value Ht known as the turning value. The spin wave propagates from right to left and is converted to an elastic wave at the plane where the internal field has dropped to a value He known as the crossover value. The elastic wave continues to propagate to the left and is reflected by the polished end-face 9 of the crystal 3. The reverse transformations take place and a delayed e-m. wave appears at the section 6 which thus forms both input and output port. The delay may be altered by adjustment of the field to shift the planes defined by Ht and Hc. The delay path may be increased by providing a further elastic-wave propagation element to the left of the crystal 3. This must be made of a non-magnetic material of low acoustic loss, e.g. lithium niobate or sapphire. A square, instead of circular, section crystal 3 may be used.