Non-invasive absolute measurement methods based on optical methods are being considered to be potential new primary standard systems for airborne acoustics. These methods mainly based on methods to measure acoustic particle velocities, utilize photon correlation or interferometry. Recently, it has become necessary to observe the possibility of expanding these methods to airborne ultrasound, because of increasing number of applications related to airborne ultrasound range. In this study, the factors necessary to expand the range of primary system based on photon correlation method to the low ultrasonic frequency range were considered. The basic problems with the measurement system for this purpose are related to measurement system, sound source, and problems induced with the artifact (also referred to as device under test) setup. Regarding the measurement system, system design parameters to expand the lower bound of sound pressure were investigated, in addition to the suitability of the method to enhance the photon count signal by applying the phase resolved method. In addition, the feasibility of applying the synchronizing method to resonant and pulsar type sound sources to obtain sufficient sound pressure in the ultrasonic band was observed. In addition, signal processing procedures to remove the effect of specular reflection that occurs when calibrating a microphone were investigated. Work supported by the Korea Planning & Evaluation Institute of Industrial Technology (RS-2022-00154837).
Cho et al. (2025) studied this question.