Piezoelectric sensor device and a method for detecting change in electric constants using the device

A method for detecting change in electric constants, comprising:

• using a piezoelectric sensor device comprising:
• a piezoelectric body vibrator consisting of a piezoelectric body sandwiched by a pair of electrodes;
• a power source which applies a voltage to said piezoelectric body vibrator so as to get excited for vibration, means for monitoring electric constants to detect changes in electric constants accompanied by vibration of the piezoelectric body, the change in electric constants in the piezoelectric body being detected as a change in frequency for vibration of the piezoelectric body corresponding to an electric constant under the determined conditions;
• and means for obtaining the frequency value from frequencies at not less than two points giving a determined electric constant, and
• obtaining the frequency value as their average value of two points, which gives a same electric constant, closest to and putting therebetween the frequency where a change in the electric constants gives its extreme value.

A method for detecting change in electric constants, comprising:

• using a piezoelectric sensor device comprising:
• a piezoelectric body vibrator consisting of a piezoelectric body sandwiched by a pair of electrodes;
• a power source which applies a voltage to said piezoelectric body vibrator so as to get excited for vibration, means for monitoring electric constants to detect changes in electric constants accompanied by vibration of the piezoelectric body, the change in electric constants in the piezoelectric body being detected as a change in frequency for vibration of the piezoelectric body corresponding to an electric constant under the determined conditions;
• and means for obtaining the frequency value from frequencies at not less than two points giving a determined electric constant, and
• performing measurement of the frequency applying an electric field surpassing the coercive field of the piezoelectric body.

A method for detecting change in electric constants, comprising:

• using a piezoelectric sensor device comprising:
• a piezoelectric body vibrator consisting of a piezoelectric body sandwiched by a pair of electrodes;
• a power source which applies a voltage to said piezoelectric body vibrator so as to get excited for vibration, means for monitoring electric constants to detect changes in electric constants accompanied by vibration of the piezoelectric body, the change in electric constants in the piezoelectric body being detected as a change in frequency for vibration of the piezoelectric body corresponding to an electric constant under the determined conditions, means for obtaining the frequency value from frequencies at not less than two points giving a determined electric constant, means for keeping the polarization state of the piezoelectric body vibrator constant, and a power source making polarization processing take place on the piezoelectric body vibrator, as means for keeping the polarization state of the piezoelectric body vibrator constant, and
• proceeding with polarization processing with the power source making polarization processing take place on the piezoelectric body vibrator whenever frequency is being measured.

A method to detect change in electric constants, comprising:

• using a piezoelectric sensor device comprising:
• a piezoelectric body vibrator consisting of a piezoelectric body sandwiched by a pair of electrodes;
• a power source which applies a voltage to said piezoelectric body vibrator so as to get excited for vibration, means for monitoring electric constants to detect changes in electric constants accompanied by vibration of the piezoelectric body, the change in electric constants in the piezoelectric body being detected as a change in frequency for vibration of the piezoelectric body corresponding to an electric constant under the determined conditions;
• means for obtaining the frequency value from frequencies at not less than two points given a determined electric constant, means for keeping the polarization state of the piezoelectric body vibrator constant, a power source making polarization processing take place on the piezoelectric body vibrator, as means for keeping the polarization state of the piezoelectric body vibrator constant, and means for discharging the electric charge stored in the piezoelectric body after the polarization processing, and
• discharging the electric charge stored in the piezoelectric body after the polarization processing is performed by means for discharging the electric charge stored in the piezoelectric body after the polarization processing.