LAUSR

We developed a sound wave phase meter (SWPM) and measured the amplitude and wavelength of sound waves in free space. The SWPM consists of two parallel metal plates, where the front plate was operated as a diaphragm. An aluminum perforated plate was additionally installed in front of the diaphragm, and the same signal as that applied to the sound source was applied to the perforated plate. The SWPM measures both the sound wave signal due to the diaphragm vibration and the induction signal due to the electric field of the aluminum perforated plate. Therefore, the two measurement signals interfere with each other due to the phase difference according to the distance between the sound source and the SWPM, and the amplitude of the composite signal that is output as a result is periodically changed. We obtained the wavelength of the sound wave from this periodic amplitude change measured in the free space and compared it with the theoretically calculated values.