| 摘要 |
PURPOSE:To obviate the production of receiving signal despite receiving of reverberation and generate reflected wave receiving signal when reflected wave is received while the reverberation exists by providing a charge and discharge circuit whieh is charged by the output of a preamplifier only at the transmission of ultrasonic waves. CONSTITUTION:A variable amplifier 3 is connected between a preamplifier 2 which amplifies the output of an ultrasonic wave transmitting-receiving head 1 and a rectifying and smoothing circuit 4, and a charge and dicharge circuit 6 which is charged only at the transmission of ultrasonic waves and keeps discharging thereafter is connected to the preamplifier 2. The output voltage of the charge and discharge circuit 6 is highest at the ultrasonic wave transmission and keeps decreasing from the time when transmission ends. If the amplification factor of a variable amplifier 3 is so controlled as to be inversely proportional to the output voltage level of the charge and discharge circuit 6, the amplification factor assumes a minimum value close to zero at the transmission, thus decreasing the amplification factor in the period where the reverberation exists. On the other hand, when the reflected waves from the object arrive within the reverberation period, the signal which have received the reflected wave by a certain degree of output may be obtained. |
