The letter deals with theoretical analysis on Lamb waves propagating in a composite membrane of ZnO and SiO2. Calculation was done for the lowest pseudo symmetric (S0) and antisymmetric (A0) modes. It was shown that, for example, when the thickness of each film is of the order of 0.1 wavelengths or less, S0 mode has a large electromechanical coupling coefficient of about 6% and a velocity of more than 5,000 m/s. A0 mode, as may be expected, has a quite small velocity of less than 1,500 m/s with an electromechanical coupling coefficient of about 3%. The result suggests that it may be possible to realise various monolithic acoustic wave devices based on Lamb waves propagating in the ZnO/SiO2 composite membrane.

This letter deals with a horn for radiating focused surface acoustic waves launched from circular arc interdigital electrodes into a narrow waveguide. A simple method of designing a horn using geometric optics was given and some experiments using a v/v waveguide were performed.

Linear array antennas weighted by selective withdrawal of elements have been optimized for sidelobe reduction. The optimization was carried out for antennas with total elements up to 41 by modifying implicit enumeration algorithm for 0-1 type integer optimization. Results obtained, for example, show that the sidelobe level optimized decreases almost monotonically with an increase in the total number of elements, and that the sidelobe level of about 19.0 dB is obtainable for the antenna with total elements of 41.