| 摘要 |
PURPOSE:To increase the reliability of detection with a simple circuit by a method wherein a stationary wave is composed of emitting and reflecting waves of ultrasonic waves to change the impedance of a microphone when an object to be detected has reached a certain level against an ultrasonic microphone. CONSTITUTION:If ultrasonic waves are continuously emitted to an object 5 to be detected from an ultrasonic microphone 1, when the object 5 to be detected is too much away from the microphone 1, an oscillating circuit using the microphone 1 oscillates stably because no stationary wave is developed, and ultrasonic waves are emitted on a constant level from the microphone 1. When the object 5 to be detected approaches the microphone 1 within the specified level 1, the stationary wave is produced and oscillation is suspended since the impedance of the microphone 1 changes. Therefore, the detection of the size of oscillating voltage at that time makes it possible to perform highly reliable level detection with the use of only a single ultrasonic microphone. |
