Patent ID: 8482184

Claim:
A plate wave element comprising: a piezoelectric body; a comb-shaped electrode disposed on an upper surface of the piezoelectric body, the comb-shaped electrode exciting a Lamb wave as a main wave; a first medium layer disposed on the upper surface of the piezoelectric body so as to cover the comb-shaped electrode; and a second medium layer that is disposed on a lower surface of the piezoelectric body wherein the first medium layer is made of silicon oxide, the piezoelectric is made of lithium niobate, a thickness H 1 of the piezoelectric body, a wavelength λ of the Lamb wave, and a thickness H 2 of the first medium layer satisfy a condition that, when a ratio H 1 /λ is not less than 0.075 less than 0.125, a ratio H 2 /λ is 0.048 to 0.080, when the ratio H 1 /λ is not less than 0.125 less than 0.175, the ratio H 2 /λ is 0.067 to 0.108, when the ratio H 1 /λ is not less than 0.175 less than 0.225, the ratio H 2 /λ is 0.084 to 0.136, and when ratio H 1 /λ is not less than 0.225 less than 0.275, ratio H 2 /λ is set at 0.103 to 0.175.