A NEW MEASURING METHOD FOR UNDERWATER DISPLACEMENT UTILIZING SOUND SIGNAL - (EXPERIMENTAL RELATIONSHIP BETWEEN SOUND FREQUENCY AND DISPLACEMENT)

This paper deals with a newly developed underwater displacement sensor utilizing the acoustic resonant frequency of water in a submerged pip e. Both ends of the pipe are closed. A speaker to generate sound is fi xed on the end of the pipe with the reflector at the other end. A piez oelectric ceramic is used as a speaker. Sweeping signal is radiated fr om the speaker to the water column in the pipe. The sound pressure tak es the largest value at the resonant frequency. The displacement of th e reflector which is inserted from the other end of the pipe by the pl unger, corresponds to the length of the water column. The displacement of the reflector has good correspondence to the resonant frequency of the water column. It is found from the experiment that it is possible to measure accurately underwater displacement using this sensor.