| 摘要 |
PURPOSE:To detect the adhesion of water drops, by attaching a transmitter and a receiver on a platelike medium and transmitting ultrasonic waves under a condition to make the transmissivity of ultrasonic waves maximum, and detecting the difference between signal levels in dry and water drops adhering states. CONSTITUTION:A sensor section 20 of a water drop detecting device 10 consists of a non-corrosive platelike medium such as glass and a transmitter 22 and a receiver 23 provided on corners of the medium respectively. If the thickness of the platelike medium 20 is denoted with d, and the wavelength of signal ultrasonic waves with lambda1, the transmissivity of ultrasonic waves becomes maximum when the incident angle theta1, of the signal ultrasonic waves to the platelike medium 21 satisfies the following formula. 2d.costheta1=mlambda1 where, m=0, 1, 2,... The attaching angle of the transmitter 22 is specified so as to be able to transmit ultrasonic waves at an incident angle theta1. A signal processing section 34 compares a signal level of transmitted signals from the transmitter 22 with a signal level of received signals feed backed from the receiver 23, and outputs signals indicating that water drops lie on the medium 21, from the reduction of the received signal level caused by leakage of the ultrasonic waves to water drops on the surface of the medium 21. |
