| 摘要 |
<p>An ultrasonic sensor device having a circuit board (31), a piezoelectric vibrator (33), and a variable-gain means (70, 71, 110, 200, 210, 220, 230, 240, 250, 260). The piezoelectric vibrator (33) has a pair of detection electrodes (35, 36) disposed facing each other across the thickness direction of the circuit board (31) and a piezoelectric body (37) disposed between the electrodes (35, 36). The piezoelectric vibrator (33) is formed on one surface (31a) of the circuit board (31) and constitutes a membrane structure (34) that has lower rigidity than the other portions of the circuit board (31). An ultrasonic wave is transmitted from the piezoelectric vibrator (33), and a reflected wave thereof is received by the same piezoelectric vibrator (33). In the variable-gain means, the gain of the piezoelectric vibrator (33) during the period in which the piezoelectric vibrator (33) transmits the ultrasonic wave is greater than the gain of the piezoelectric vibrator (33) during the period in which the piezoelectric vibrator (33) receives the ultrasonic wave.</p> |
