Airborne ultrasound has been used for various purposes, including object detection and pest repellent systems. Recently, it has been used in haptic technology for virtual reality. The safety of exposure to airborne ultrasound has been studied as its use has increased. Although airborne ultrasound cannot be directly perceived by humans, some research has found that exposure to very high sound pressure levels can harm the human body. Thus, quantitative characterization of airborne ultrasound is essential. To contribute to the safe use of airborne ultrasound, this paper established the acoustic standards in Japan in terms of sound pressure from 20 to 100 kHz. This paper evaluates the measurement uncertainty in the free-field reciprocity calibration of quarter-inch condenser microphones, following the document “Guide to the Expression of Uncertainty in Measurement,” and describes a few significant uncertainty components, such as deviation from the plane sound field. As a result, it is realized that the expanded uncertainty of 0.3–0.7 dB in a frequency range from 20 to 100 kHz.

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See supplementary material at https://doi.org/10.1121/1.5063816 for audio. These audio files are examples of band-limited swept sine signals for 20, 25, 31.5, 40, 50, 63 and 80 kHz, and specially recorded and prepared for supplementary material. The sampling frequency is 200 kHz.
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