GB1484859A - Dispersive delay lines - Google Patents

Abstract

1484859 Dispersive surface wave delay lines MARCONI CO Ltd 12 Sept 1974 [6 Nov 1973] 51562/73 Heading H3U In a dispersive surface wave delay line of the kind which, as shown in Fig. 1, has a reflective array of fingers 10, 11, 12, on a piezo-electric surface, the spacing between the fingers being graded so that waves of different wavelengths are reflected by different portions of the array, the amplitude of the reflected waves of selected frequencies is reduced by displacing some of the fingers from the nominal positions shown in Fig. 1, the amount of the reduction being determined by the amount of the offsetting. As shown in Fig. 2 alternate fingers are displaced so that the fingers form pairs 10a-10c, 12a-12c, the distance between fingers of a pair being less than, and the distance between adjacent pairs being more than the nominal finger spacing, i.e. #/2 for a wavelength of #. The fingers may be in the form of grooves etched in the piezo-electric substrate, e.g. lithium niobate, or deposited insulating or conductive material e.g. silicon oxide, aluminium or titanium. The two Rayleigh surface wave components in quadrature are changed by variations in the depth of the groove or the amount of deposited insulating material, one of the components being changed proportionally, the other in proportion to the square of the depth or thickness of deposit. When the fingers consist of electrically conductive material, they may be electrically isolated, or interconnected at one or both ends and preferably also between their ends. In another embodiment (Fig. 3, not shown) the launching transducer sends acoustic waves from one end of the piezo-electric bcdy which are reflected through 90 degrees by a first set of graded fingers disposed at 45 degrees, and reflected through a further 90 degrees by a second set of angled fingers. The reflected waves are received by a transducer adjacent the launcher. Selected fingers of one or both sets of fingers may be displaced to suppress predetermined frequencies as before. This embodiment may be used for pulse compression.