| 摘要 |
PURPOSE:To detect objects at a high speed with good reliability with relatively simple constitution by providing a transmitter and a receiver for ultrasonic waves by facing a passage for the objects. CONSTITUTION:A transmitter 2 and a receiver 3 for ultrasonic waves 3 are provided so as to face each other by way of a passage 11 for paper 10 of a copying device. With each of the transmitter and receiver 2, 3, a surface sensitive plate 21 such as auminum disc is adhered via an elastic layer 22 in the opening at the front face of a resin case 20, a piezoelectric element 23 is adhered to the rear surface thereof and the respective electrodes thereof are connected to pin electrodes 24A, B penetrating through the bottom part of the case 20. The resonance frequency of the transmitter 2 is set between the resonance frequency and antiresonance frequency of the receiver 3. The signal of the receiver 3 is amplified and detected with amplifier circuits 4, 5 and an amplitude detecting circuit 6, and an output is produced according to the presence or absence of the paper 10 from a DC amplifier circuit 7 and the output terminal 30 of an output circuit 8. |
