Patent GB-1239310-A (GB)
IPC: H03H9/02
Filed: 1968-10-30
Abstract: 1,239,310. Acoustic impedances. WESTERN ELECTRIC CO. Inc. 30 Oct., 1968 [30 Oct., 1967 (2)], No. 51395/68. Heading H3U. An elastic waveguide structure comprises a body of elastic wave supporting medium and means for defining a localized acoustic wave path extending along or through said body from input coupling means to output coupling means with said body extending beyond at least two opposite sides of said path, said body having uniform elastic properties in a direction transverse to said path and said path having different elastic properties to said body such that the effective acoustic wave phase velocity is reduced in said path and/or the effective wave attenuation is increased in said path whereby spreading is restricted of an elastic wave travelling along said path. In one embodiment, 1A, a gold path 2 extends through a fused medium 4 between input and output transducers 1, 3. In another embodiment, Fig. 1B, the path between surface wave transducers 9, 17 is formed by a gold strip 12 formed on the polished upper surface 11 of a quartz substrate 10. The strip 12 is formed by electroplating or photo-masking techniques. In a further embodiment, Fig. 3, the path 32 is defined by a slot in an aluminium layer 31 on a glass substrate 30, the surface wave phase velocity of the layer being greater than that of the substrate. In another embodiment, Fig. 4, a strip 42 of relatively lossy material is provided on a relatively low-loss substrate 40. The strip 42 may be formed by irradiating a strip of a piezo-electric photo-conducting substrate with light. A delay line may be constructed by making the path in the form of a spiral (Fig. 5A, not shown) or meander (Fig. 5B, not shown). These delay lines are. formed by photo-resist techniques and these techniques may be used to form other surface wave devices. Fig. 6 shows such a device in the form of a power divider for dividing energy in a strip or slot 62 into branch strips or slots 63, 64. Fig. 7 shows a coupling arrangement for coupling energy in a strip or slot 72 to a strip or slot 71. Fig. 8A shows a resonant coupler for coupling a strip or slot 81 to a strip or slot 83 via a strip or slot 82 in the form of a closed loop. The loop 82 is resonant when its circumference is equal to an integral number of wavelengths. Fig. 9A shows a bandfilter formed by an interrupted strip 92, the transmission being minimum at frequency U/2D and maximum at frequency U/4D, where U is the wave velocity. Fig. 9B shows an alternative filter construction in which the strip or slot 92 has an increased loading at intervals. A combined filter and coupler is described with reference to Fig. 9C (not shown). Logic "OR" or " AND " gates may be constructed by using three coupled strips or slots (Fig. 10, not shown). Fig. 11 shows an amplifier formed by a strip 111 of semi-conductor material interposed in the acoustic path formed by the strip or slot 112, the principle of operation being as described in Specification 1,005,218. A circulator involving a directional coupler is described with reference to Fig. 12 (not shown). A switching device, Fig. 13, for switching an input from branch 132 to branch 134 or 135 comprises a Y-shaped semi-conductor strip 130, the switching being performed by reverse biasing from a source 136.