| 摘要 |
<P>PROBLEM TO BE SOLVED: To make a vibrational amplitude large with a compact dust-screening member. Ž<P>SOLUTION: A piezoelectric element 120a is driven so as to produce vibration Z(x, y) expressed as follows: Z(x, y)=Wmn(x, y)×cos(γ)+Wnm(x, y)×sin(γ) (where Wmn(x, y)=sin(nπ×x+π/2)×sin(mπ×y+π/2), Wnm(x, y )=sin(mπ×x+π/2)×sin(nπ×y+π/2), and λ=+π/4 or λ=-π/8 to -π/4) where Z(x, y) is vibration at a given point P(x, y) on the dust-screening filter, and (m) and (n) are positive integers including 0, indicating the order of natural vibration corresponding to a vibrational mode. Further, LP/LF is 0.5 or more and less than 1, where LP is the length of a side where a virtual rectangular piezoelectric element having the same area as the dust-screening member and having sides including the one side which the dust-screening member has is arranged, and LP is a length which is parallel to the side and in the length direction of the piezoelectric element. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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