Patent ID: 7456544

Claim:
A boundary acoustic wave device comprising: a first medium; a second medium laminated on the first medium; and an interdigital transducer disposed between the first medium and the second medium, the interdigital transducer including a plurality of laminated conductive layers, wherein a boundary plane separates the interdigital transducer into two equal parts in a thickness direction such that El/E 2 >El′/E 2 ′, wherein El represents a first energy level of boundary acoustic waves at a first medium side of the boundary plane, E 2 represents a second energy level of the boundary acoustic waves at a second medium side of the boundary plane, El′ represents a third energy level of the boundary acoustic waves at the first medium side of the boundary plane when the interdigital transducer is configured so that a first sound velocity of the boundary acoustic waves when the interdigital transducer includes the plurality of conductive layers is equal to a second sound velocity of the boundary acoustic waves when the interdigital transducer includes only a conductive layer having a highest density among the plurality of conductive layers, and E 2 ′ represents a fourth energy level of the boundary acoustic waves at the second medium side of the boundary plane when the interdigital transducer is configured so that the first sound velocity of the boundary acoustic waves when the interdigital transducer includes the plurality of conductive layers is equal to the second sound velocity of the boundary acoustic waves when the interdigital transducer includes only the conductive layer having the highest density among the plurality of conductive layers.