Patent ID: 8076822
Filing Date: 2011-12-13
Classification: F04B,H01L,H02N

Abstract:
1. A method for controlling a frequency of a drive signal for driving a piezoelectric element included in a resonant circuit so that the drive-signal frequency substantially matches a resonant frequency of the resonant circuit, the method comprising the steps of: changing the drive-signal frequency in a predetermined frequency range multiple times; detecting an impedance change in the piezoelectric element each time the drive-signal frequency is changed; determining the resonant frequency on a basis of a transition of values of the detection; and determining the drive-signal frequency so that the determined resonant frequency is obtained, wherein, in the resonant-frequency determining step, a difference between a maximum value and a minimum value of the detection values is determined and is compared with a predetermined reference value, and when the comparison shows that the difference is larger than or equal to the predetermined reference value, the resonant frequency of the piezoelectric element is determined on the basis of the transition of the detection values, and when the comparison shows that the difference is smaller than the predetermined reference value, the detection values are invalidated.