A New Measurement Method of Thickness of a Thin Film

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Sound generated from a speaker through a signal generator travels to a thin film which in spread on a rigid container with an air-layer. Resonant sound generates in an air-layer of the container. Resonant frequency of sound depends on the thickness of the thin film and air-layer. Resonant sound in introduced to the FFT though the microphone, and resonant frequency is analyzed. A new measuring method of the thickness of a thin film by using the sound frequency is presented. Experimental equipment was set up to measure the thickness of the thin film. Experiments were conducted for polyethylene and vinyl chloride films. Following conclusion were obtained.(1) Good correspondence between the resonant frequency and thickness of the film was obtained. It was made clear that thickness of the film can be measured from the resonant frequency.(2) The measurement frequency increases with the decrease of the distance between the speaker and film, thickness of air-layer and thickness of the film.(3) The variation of the resonant frequency caused by the variation of thin film is big in case that the height of the speaker and thickness of the air-layer are small.(4) Relationship between the thickness of the film and the resonant. frequency describes a curved line with the decrease of the height of the speaker and thickness of the air-layer.