In the development of jet noise reduction devices, high efficiency and low cost can be achieved by using 1% scale nozzles and low-density gas as an alternative to full scale devices and hot gas. However, very high frequency noise is generated from the nozzle, and the upper limit frequency of a normal condenser microphone is insufficient. Therefore, a high frequency optical microphone based on the Schlieren method was developed, which measures the density gradient caused by the sound wave. The frequency response of the optical microphone was numerically calculated and corrected, and the frequency response was investigated using the characteristics of jet noise. Additionally, the noise reduction performance of the ejector nozzle was investigated using the optical microphone.
