Visualization of sound field by means of Schlieren method with spatio-temporal filtering

Chitanont, Nachanant; Yaginuma, Keita; Yatabe, Kohei; Oikawa, Yasuhiro

doi:10.1109/icassp.2015.7178021

Cited by 16 publications

(5 citation statements)

References 11 publications

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“…One potential avenue of processing is the use of digital filters, which can be designed to reduce noise in the image without diminishing the signal, applied to either the temporal or spatial frequencies of intensity variation in the video. Chitanont et al have implemented this kind of approach for the schlieren visualization of sound fields [12] [13] [14]. The blunt approach of designing a bandpass filter around the expected sound field frequency component can produce attractive images, but is not advisable for two reasons.…”

Section: Previous Attempts At Schlieren Imaging Of Acoustic Wavesmentioning

confidence: 99%

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Harvey

Smithson

Siviour

2018

Optics and Lasers in Engineering

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We present a high-speed single-mirror double-pass coincident schlieren system and corresponding algorithms for the visualization of acoustic waves and recovery of their associated audio signals. Schlieren systems are extensively used to visualize strong shockwaves, such as those from supersonic motion or explosions. Recently, they have also been used to visualize lower amplitude non-linear acoustic phenomena, such as the weak shockwaves arising from impact events including hand claps, belt snaps, and towel cracks. Time-invariant sounds produced by loudspeakers have also been imaged, in one case leading to frequency analysis, although these have been limited to high-frequency signals at very high sound pressure levels. The research presented here shifts the focus from sound-field visualization towards audio signal recovery. A comprehensive exploration of several parameters for imaging sound sources, including frequency, wave form, and amplitude, is presented. In addition, we address for the first time the recovery of phase information, which would be essential for speech intelligibility, and the more general case of non-contact sound field reconstruction. Through image and signal processing, it is shown that audio signals can be recovered from high-speed schlieren video whose acoustic waves appear to be below the limit of visibility, and were previously deemed unrecoverable by virtue of their frequency and sound pressure level. This includes sounds at frequencies and loudnesses relevant for human hearing, producing the first 'schlieren microphone'.

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Section: Previous Attempts At Schlieren Imaging Of Acoustic Wavesmentioning

confidence: 99%

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Harvey

Smithson

Siviour

2018

Optics and Lasers in Engineering

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“…A band-pass finite impulse response (FIR) filter was used [14] to enhance the visualization of the audible sound field in real time using the Schlieren technique, such that the noise was reduced by removing unwanted frequency components. The sinusoidal sound fields of frequency 10 kHz and 15 kHz were obtained using a band-pass filter with the order parameter equal to 200 (for a Nth order FIR filter, there will be N + 1 coefficients [15]).…”

Section: Introductionmentioning

confidence: 99%

Comparison of Three Linear Digital Filters Applied to Improve the Quality of the Measured Acoustic Field

Rodrigues,

Santos,

Buiochi

2023

Eng

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The measurement of acoustic fields generated by ultrasonic transducers is important for determining the focal length, lateral resolution, and amplitudes of the lateral and grating lobes. The acoustic field is commonly characterized by a set of scans using a needle hydrophone. The output of the hydrophone can be connected to an analog filter to enhance the signal. However, the analog filter might not be sufficient to avoid the noises that distort the signals. Alternatively, linear digital filters can be advantageous to improving the acoustic-field characterization. In this work, three filters were investigated: moving average (MA), band-pass Hamming window (HW), and band-pass Blackman window (BW). The filters were implemented and evaluated in terms of the root-mean-square error (RMSE) of the measured sound field, which was filtered, in relation to the simulated acoustic field (gold standard). As a compromise between effective filtering and signal non-distortion, a method to model the MA kernel length was proposed. All the filters reduced the noise of the measured acoustic field. The HW and the BW filters were more effective (RMSE = 4.01%) than the MA filter (RMSE = 4.28%). In spite of the small quantitative difference, acoustic field comparisons showed qualitative improvements.

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“…By combining with a stroboscopic timing scheme, transient surface acoustic waves have been dynamically visualized with photorefractive interferometry [14] and white-light interferometry [15]. Also, Schlieren photography has been utilized to image the dynamic sound pressure in the air [16,17]. A sensitive optical interferometer based on diffractive optics has been reported to image thermoelastic strain of non-transparent materials quantitatively [18].…”

Section: Introductionmentioning

confidence: 99%

Visualization of ultrasonic wave field by stroboscopic polarization selective imaging

Liu¹,

Xiong²,

Cao³

et al. 2020

Opt. Express

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A stroboscopic method based on polarization selective imaging is proposed for dynamic visualization of ultrasonic waves propagating in a transparent medium. Multiple independent polarization parametric images were obtained, which enabled quantitative evaluation of the distribution of the ultrasonic pressure in quartz. In addition to the detection of optical phase differences δ in conventional photo-elastic techniques, the azimuthal angle ϕ and the Stokes parameter S 2 of the polarized light are found to be highly sensitive to the wave-induced refraction index distribution, opening a new window on ultrasonic field visualization.

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Visualization of sound field by means of Schlieren method with spatio-temporal filtering

Cited by 16 publications

References 11 publications

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone

Comparison of Three Linear Digital Filters Applied to Improve the Quality of the Measured Acoustic Field

Visualization of ultrasonic wave field by stroboscopic polarization selective imaging

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