Optical fiber-based acoustic intensity microphone for high-intensity airborne ultrasound measurement

The increasing use of airborne ultrasonic waves in daily life, driven by advances in parametric and phased arrays, has led to innovative applications like highly directional speakers, non-contact tactile feedback, 3D acoustic levitation, and medical therapies. These advancements necessitate accurate measurement of high-intensity ultrasonic waves, exceeding the capability of traditional microphones limited to around 160 dB, and highlight the growing importance of measuring the sound field not merely as scalar (sound pressure) but as vector (acoustic intensity) to accommodate future technological developments. This paper introduces an acoustic intensity microphone using optical fibers as probes to overcome these limitations. The proposed method replaces the two ordinary microphones used in the traditional acoustic intensity measurement method with thin optical fibers, minimizing sound field disturbance. Experimental validation and the structure of a practical acoustic intensity microphone are discussed, building upon foundational work presented at USE2023 with added verification and insights.