Piezoelectric device and method for using same

A piezoelectric device operating by a piezoelectric effect and an inverse piezoelectric effect of a piezoelectric body film, the device comprising:

• a piezoelectric element unit;
• and
• a refresh voltage applying circuit, wherein
• bipolar polarization-electric field (Pr-E) hysteresis characteristics of a piezoelectric material are asymmetrically biased with respect to an axis of a zero electric field, and
• when a first coercive electric field having smaller absolute value is defined as Eel and a second coercive electric field having larger absolute value is defined as Ec2 of coercive electric fields in the piezoelectric material, and
• a bias ratio of the coercive electric field is defined as [(Ec2+Ec1)/(Ec2−Ec1)]×100[%],
• the piezoelectric element unit includes the piezoelectric body film whose bias ratio of the coercive electric field is equal to or more than 20%, and the piezoelectric element unit operates with an electric field intensity smaller than that of the first coercive electric field, and
• the refresh voltage applying circuit applies a voltage in order to restore a polarized state of the piezoelectric body film and maintain operation performance of the piezoelectric device, the voltage having an electric field intensity larger than the electric field intensity for the operating and being equal to or less than three times the absolute value |Ec1| of the first coercive electric field, wherein
• the piezoelectric element unit includes a piezoelectric element for drive configured to operate by an inverse piezoelectric effect, and a piezoelectric element for detection configured to operate by a piezoelectric effect,
• the piezoelectric device includes a drive circuit configured to supply a drive voltage to the piezoelectric element for drive, and a detection circuit configured to detect a voltage signal from the piezoelectric element for detection,
• the refresh voltage applying circuit is installed in at least one circuit of the drive circuit and the detection circuit, and
• the piezoelectric device further comprises a control unit configured to apply a voltage to the piezoelectric element unit from the refresh voltage applying circuit in a case where a detection voltage is lower than a reference value, the detection voltage being output from the piezoelectric element for detection when the piezoelectric element for drive is driven with a predetermined drive voltage.