| 摘要 |
PROBLEM TO BE SOLVED: To suppress reverberation vibration of a vibrator of an ultrasonic sensor in spite of temperature variation of the vibrator and individual differences, and further to lower the manufacturing cost.SOLUTION: An ultrasonic sensor 1 includes a reverberation suppression circuit 4, which includes a transformer 41 boosting and outputting voltage, input to a primary side, from a secondary side to a vibrator 2, and a variable capacitance circuit 42 connected to the primary side of the transformer 41 in parallel. Even if the vibrator 2 varies in natural frequency owing to temperature variation or has variance in natural frequency due to individual differences, the resonance frequency of the reverberation suppression circuit 4 can be adjusted substantially to the natural frequency of the vibrator 2 by varying the electrostatic capacitance of the variable capacitance circuit 42. Reverberation vibration by the vibrator 2 can, therefore, be suppressed by utilizing a resonance phenomenon. Further, the variable capacitance circuit 42 is provided on the primary side of the transformer 41 which is lower in voltage than the secondary side, and a low-breakdown-voltage capacitor is thereby usable for the variable capacitance circuit 42. |
