Measurement of air velocity and shape in underground space by ultra sonic

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The following experiments were executed to know characteristics of the recognition of a shape using an ultra sonic distance meter. The frequency of the ultra sonic used in the experiments was 40 kHz.1. The length between a cube whose size is from one to five centimeters and the ultra sonic sensor was measured to know the minimum size which can be detected. The ultra sonic sensor detected to two centimeters cube.2. The accuracy of the measurement of length was studied between a one meter cube laid near a corner of a room and the ultra sonic sensor. The length could be detected fairly accurately when the direction of the measurement is near perpendicular to the surface of the cube. The length could not be detected when the measurement direction comes to parallel to the surface. It was impossible to detect an opening between the cube and a wall of the room.3. The strength of a signal reflected at a surface in various angle from 0 to 35 degree was measured to get basic date of the ultra sonic sensor. The strength was highest when the angle was almost 0 and was not detected when the angle was larger than some degree. This might be the reason why the length could not be detected in experiment 2.