| 摘要 |
PROBLEM TO BE SOLVED: To widen a band and to steepen an attenuation frequency by arranging plural IDTs and a grating between them on a piezoelectric substrate in the propagation direction of the surface waves, arranging reflectors on both sides, and specifying the ratio of the total number of electrode fingers of the IDTs to that of the grating and the thickness of an electrode film consisting of aluminum or the like. SOLUTION: The IDTs 2 and 3 and the grating 4 between them are arranged on the principal plane of the piezoelectric substrate 1 along the propagation direction of the surface waves and the reflectors 5a and 5b are disposed on both sides of the IDTs 2 and 3. In this case, the ratio of the total number L of electrode fingers L of the IDTs 2 and 3 constituted of a pair of comb-line electrodes to the total number M of electrode fingers of the grating 4 is defined as 0.25<M/L<0.80 and the thickness of the electrode film consisting of the aluminum or an aluminum alloy is defined as 3-12% of the wavelengthλof the surface waves to be excited. Then, vertical primary, secondary and third order resonance modes are forcibly excited so as to confine the surface waves excited by the IDTs 2 and 3 and the grating 4 between the reflectors 5a and 5b and to acoustically couple them.
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