Abstract: An acoustic surface wave device using an interdigital electrode array 2, 3 to launch and receive surface waves overcomes problems of diffraction by making the arrays approximately 3.lambda..sub.c wide between the outer boundaries of the bus bars. As a result, the arrays can each only propagate and transduce a single acoustic surface waveguide mode which is symmetrical about the axis of the array.

Abstract: An acoustic surface wave device comprising a piezoelectric substrate provided with an input transducer (2), an output transducer (4) and a compact reflective multistrip coupler (6) in which the strips of each pair of comparatively widely spaced strips (7 or 8) in one array of mutually parallel strips are connected to respective strips of a pair of comparatively narrowly spaced strips (8 or 7) in the other array. The wide and narrow spacings alternate along each array. The improvement provides further electrodes 9 located in the relatively wide spaces in each array and electrically interconnected so as to effect a transfer of signal currents along each array and from one array to the other. The device improves efficiency, reduces insertion loss and improves the shape of the pass band.

Abstract: A surface acoustic wave device includes apodized interdigital electrode arrays 2,3 coupled by a multistrip coupler 5. In a device in which the apodization 8 comprises a main lobe flanked by a succession of minor lobes, the effects of diffraction relating to short electrode pair overlaps are reduced by dividing at least the far end of the array into two or more series connected array portions 21, 22. Difficulties arising from unbalanced electrode edge overlaps at transitions 20 between different members of electrode pairs connected in series are reduced by locating such transitions in the region of nulls in the apodization pattern.

Abstract: An acoustic surface wave device using apodized interdigital transducers 32, 33, of the kind disclosed in DE 28 54 072 in which the ungrounded bus-bar 44 is inclined towards the transducer axis and a velocity compensation section 36 is provided formed by grounded dummy electrodes 37 arranged parallel to the array electrodes.The improvement comprises locating a grounded bus-bar portion 38 adjacent the inwardly inclined bus-bar portion 44' so that the facing boundary edges are uniformly spaced in the axial direction, the inclination being such that either a minimum or a side-lobe of substantially reduced magnitude of the sin x/x response is directed axially.

Abstract: A surface acoustic wave bandpass electrical filter has double electrode input and output transducers (IP and OP) whose combined amplitude-frequency response has a fundamental passband centered on a frequency f.sub.o and a corresponding third harmonic passband. An interposed multistrip coupler (MSA2) has strips (ST) with a mark-to-space ratio of one-to-one and a center-to-center spacing .lambda..sub.S2 /2 chosen such that f.sub.o /f.sub.S2 is in the range 0.80 to 1.14 but excluding substantially 1.0, whereby a stopband in the amplitude-frequency response of the coupler (MSA2) between 2f.sub.S2 and 4f.sub.S2 suppresses the amplitude-frequency response of the input and output transducers (IP and OP) over a range of frequencies including 3f.sub.o .+-.0.5f.sub.o.

Abstract: A surface acoustic wave bandpass electrical filter consists of input and output interdigital transducers (IP, OP) with an interposed track changing multistrip array (MSA). A conventional broadband array (MSA) is divided into three sub-groups of strips with respect to a center of symmetry (C) separated by different distances along the input track (T1) and the output track (T2) such that the amplitude-frequency response of the array (MSA) has a stopband centered on a predetermined frequency. If the input and output transducers (IP, OP) both have a double electrode configuration, electrode separation .lambda.o/4, providing a fundamental passband at a corresponding frequency f.sub.o and an equal amplitude passband at the third harmonic 3f.sub.o, then a separation difference of .lambda.o/6 between the sub-groups of the array (MSA) in the two tracks (T1, T2) can suppress the third harmonic passband in the filter output.

Abstract: Carboxylic acids and/or esters are prepared by converting the ##STR1## moiety in a 1-substituted 2,2-trihaloethanol, or derivative wherein X represents halogen and R is hydrogen or an acyl group to an organic acid and/or ester grouping of the formula ##STR2## wherein R' is hydrogen or alkyl of 1 to 6 carbon atoms, in the process which comprises reacting the 1-substituted 2,2,2-trihaloethanol or acylated derivative with molecular oxygen in the presence of a catalyst comprising a complex of a transition metal having an atomic number from 21-30, 39-48 or 57-80 and at least one molecule of a ligand containing trivalent nitrogen, phosphorus, arsenic or antimony. This reaction is carried out in a reaction medium comprising an alcohol or aqueous alcohol having 1 to 6 carbon atoms optionally containing an alkali metal, said alcoholic solvent also serving as a reactant source when carboxylic acid esters are formed.

Abstract: A process for the preparation of 2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane by reacting isobutylene with diphenylolpropane in the presence of a substantially anhydrous aromatic sulfonic acid.