Patent ID: 7937056

Claim:
A variable capacitance device, comprising: a piezoelectric driving part which has a piezoelectric film, an upper electrode disposed on a top surface of the piezoelectric film, a lower electrode disposed on an undersurface of the piezoelectric film and electrode slits which separate the upper electrode and the lower electrode into two, respectively; a movable electrode provided via the electrode slits at one end of the piezoelectric driving part; a fixed electrode disposed opposite to the movable electrode via a gap; a dielectric film which is disposed opposite to the movable electrode via the gap and provided on the fixed electrode; and a driving control unit which adjusts a distance between the movable electrode and the fixed electrode to reduce a fluctuation of a predetermined capacitance of a variable capacitor formed between the variable electrode and the fixed electrode., wherein the driving control part includes: a capacitance change detector which detects a change in the capacitance of the variable capacitor per unit time; and a control voltage adjusting part which adjusts a control voltage to be applied to the upper electrode and the lower electrode of the piezoelectric driving part to cancel out the change detected by the capacitance change detector, or which adjusts a control voltage to be applied to the upper electrode and the lower electrode of the piezoelectric driving part to prevent the movable electrode from contacting the dielectric film when the change detected by the capacitance change detector exceeds a predetermined value.