| 摘要 |
PURPOSE:To reduce insertion loss and to obtain an effective frequency characteristic by installing reflecting lattices for reflecting acoustic waves having irregular repeating cycles to the surface of a piezoelectric substrate provided with comb-shaped encoding electrodes for input and output. CONSTITUTION:A comb-shaped electrode 10 for input, another comb-shaped electrode 11 for output, and repellers 4 and 5 are installed to the surface of a piezoelectric substrate 1. The electrodes 10 and 11 are encoding electrodes and the largest output appears when a pulse train corresponding to the electrode 10 is excited from the phase-encoded input electrode 10 and its propageting pusle train is completely superposed on that of the same phase-encoded output elecctrode 11. Reflecting lattices 4 and 5 are obliquely installed against the propagating direction with an angle of 45 deg. and their pitches are gradually changed. Therefore, an acoustic wave radiated from the electrode 10 is propagated inside the lattice 4 and, where the wavelength of the acoustic wave coincides with the double of the lattice interval of the reflecting lattice 4, the acoustic wave is reflected by the lattice 4 in a direction normal to the propagating direction. The acoustic wave reflected by the lattice 4 is again reflected by the other lattice 5 in the normal direction, and then, reaches the electrode 11. |
