| 摘要 |
<p>PURPOSE:To improve the ability of an ultrasonic sensor to detect a nearby object by setting the time and gain of wave reception according to the Q value(Q value) of an ultrasonic vibrator. CONSTITUTION:An amplifying portion 8 amplifies a signal sampled from a wave transmitting portion 2. The output of the signal is detected by a detecting portion 9 and the level of the envelope of the signal is detected. Next a first comparing portion 10 the level of the signal to a first threshold and a second comparing portion 11 similarly compares the level to a second threshold. The outputs of the results of the comparison are input to a period detecting portion 12. The detecting portion 12 detects the period of time required for the signal level to fall from the first to second threshold value. A Q-value detecting portion 72 detects a Q value according to the period of time. A reception time setting portion 73 sets the time of reception according to the Q value. When the Q value is great a reception gain setting portion 6 sets a smaller reception gain in accordance with an increase in output sound pressure. The time and gain of reception are thus controlled whereby it is possible to start receiving action just after reverberation is finished.</p> |
