Optical measurement of
nonlinear ultrasound loudspeaker
Optical measurement of
nonlinear ultrasound loudspeaker
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nonlinear ultrasound loudspeaker
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K. Ishikawa et al. ``Spurious-sound-free measurement of parametric acoustic array using optical interferometry,'' JASA Express Letters vol.1, 112801 (2021). [Paper]
When measuring a parametric acoustic array (PAA) with a microphone, the sound often suffers from so-called spurious sound, the noise generated by the nonlinearity of the microphone. This paper proposes a spurious-sound-free measurement method for a PAA using optical interferometry and Gaussian beam expansion. Comparison between the proposed method and numerical simulation by the finite element method confirmed that the proposed method measures the demodulated audio sound without any effect from spurious sound.
Parametric acoustic array
Parametric acoustic array
A parametric acoustic array (PAA) is a nonlinear acoustic phenomenon that generates secondary sounds due to the nonlinear propagation of large-amplitude ultrasound beams. Owing to its ability to generate narrow audio beams or audio spots, parametric array loudspeakers using PAA have been used for various applications, including audio guides in public spaces, spatial audio productions, active noise control, and material characterizations.
Spurious sound caused by microphone
Spurious sound caused by microphone
Despite years of research so far, measuring a PAA is still a challenging issue. Measuring it with a microphone often causes the sound to suffer from so-called spurious sound, the noise caused by the distortion in the receiving system exposed to primary waves. The spurious sound makes the measurement of PAA in a near-field very challenging. Here, we proposed the optical measurement method for PAA. Since the optical method does not rely on the mechanical vibration of a diagram, we realized a spurious-sound-free measurement of PAA for the first time.
Optical measurement of PAA
Optical measurement of PAA
We compared our proposed method with numerical simulations (without spurious sound) and microphone measurements. We confirmed that the proposed method did not suffer from the spurious sound and agreed well with the simulation, while microphone results were contaminated by the spurious sound.
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