Three-dimensional selective imaging of sound sources

Olsson, Erik; Forsberg, Fredrik

doi:10.1117/1.3093609

Cited by 8 publications

(4 citation statements)

References 13 publications

(14 reference statements)

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“…In a simple adiabatic system a change in pressure results in a corresponding change in n. The resulting changes in propagation velocity, , can be measured using a laser Doppler vibrometer (LDV) [6,7,21]. The technique of refracto-vibrometry has primarily been used for acoustic pressure visualisation in air and water [13,[21][22][23][24]. The principle of the measurement technique is described by Nakamura et al [25] and is illustrated in Figure 1.…”

Section: Theory Of Refracto-vibrometrymentioning

confidence: 99%

A simple method for quantitative imaging of 2D acoustic fields using refracto-vibrometry

Malkin

Todd

Robert

2014

Journal of Sound and Vibration

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This paper presents a simple 2D method for rapid time resolved quantitative imaging of acoustic waves using refracto-vibrometry. We present the theoretical background, the experimental method and reconstructions of acoustic reflection and interference. We investigate the applicability of the method, in particular the effect of sound radiator geometry. Finite element and experimental reconstructions of the sound fields are analysed. The spatial limitations and accuracy of the method are presented and discussed.

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Section: Theory Of Refracto-vibrometrymentioning

confidence: 99%

A simple method for quantitative imaging of 2D acoustic fields using refracto-vibrometry

Malkin

Todd

Robert

2014

Journal of Sound and Vibration

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“…Therefore care needs to be taken to interpret any stress values calculated using the method. This 'line integration' issue is discussed in detail in [19], [20] and may be essentially eliminated when performing computer tomography, as shown by Olsson & Forsberg [14].…”

Section: Theoretical Backgroundmentioning

confidence: 99%

“…Most refracto-vibrometry is primarily based on using the method for either air or water pressure measurement [13][14][15][16][17], with some preliminary work conducted into stresses in solids by Zipser et. al.…”

Section: Theoretical Backgroundmentioning

confidence: 99%

High sensitivity non-contact method for dynamic quantification of elastic waves and strains in transparent media

Malkin¹,

Robert²

2014

Measurement

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This paper presents time resolved quantitative evaluation of elastic stress waves in solid media by utilising an adaptation of the well-established laser Doppler vibrometry method. We show that the introduction of elastic stress waves in a transparent medium gives rise to detectable and quantifiable changes in the refractive index, which is proportional to stress. The method is tested for mechanical excitation at frequencies from 10 to 25kHz in an acrylic bar. This refractometric quantification can measure internal strains as low as 1x10 -11 . Additionally, finite element analysis is conducted to gauge the validity of the results. In the presented work an acrylic bar is used, this method however should be applicable to any transparent solid. Theoretical backgroundThe refractive index, n, of a medium is defined as;With c 0 : velocity of light in a vacuum and v: the velocity of light in the medium. The refractive index of a medium is influenced by stress, density and temperature of the host medium [7][8]. If we consider a simple adiabatic (no change in system temperature), isochoric (no change in system volume) event in a solid domain where there is a change in stress, this will result in a corresponding change in n. Solids will exhibit either a positive or negative linear relationship between n and stress. Monitoring the change in n (refractometry) can therefore be used to monitor stresses within solids. Probing dynamic events with traditional refractometry where n changes at frequencies in the kHz range is, as yet, not possible. What can be probed however, using Laser Doppler interferometry, is the variation in velocity, v, of light in the medium and therefore allowing stress to be estimated. The principle of the measurement technique is elegantly described by Nakamura et al.[11] and is reported here in Figure 1. Monochromatic laser light is directed through a region of the medium, of length a, in which the stress fluctuates. The laser exits the region and if reflected from a rigid wall, back through the region and into the interferometer. This modulated path length, Δa, appears identical to a physical displacement of the reflective rigid wall.(2)The output signal from a laser Doppler vibrometer (LDV) is the velocity of the apparent displacement of the rigid wall, as shown in [12].Where f: frequency of stress fluctuation and, v LDV : velocity from LDV, which is integrated with respect to time to give the apparent displacement, Δa, as shown in Eq 2. Most refracto-vibrometry is primarily based on using the method for either air or water pressure measurement [13][14][15][16][17], with some preliminary work conducted into stresses in solids by Zipser et. al. [18]. The principle of measurement however holds for any medium, not just air. Therefore we developed an experimental procedure that enables the quantitative investigation of elastic waves propagating in a solid.An empirical relation between the longitudinal strain, ε, of a block of polymethyl methacrylate (PMMA), and n, from Nazarov et al [10], is show...

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“…Soon after, two-dimensional (2D) sound field imaging using scanning LDV was achieved [4][5][6][7][8][9][10]. Three-dimensional sound field reconstruction based on tomography has been well-researched [11][12][13][14], and optical wave microphones [15,16] and optical feedback interferometry [17] have been developed as scanning-based imaging methods. The application of scanning-based imaging is limited to reproducible field such as sounds generated by a loudspeaker because the 2D acoustical quantities are acquired by a number of measurements.…”

Section: Introductionmentioning

confidence: 99%

High-speed imaging of sound using parallel phase-shifting interferometry

et al. 2016

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Sound-field imaging, the visualization of spatial and temporal distribution of acoustical properties such as sound pressure, is useful for understanding acoustical phenomena. This study investigated the use of parallel phase-shifting interferometry (PPSI) with a high-speed polarization camera for imaging a sound field, particularly high-speed imaging of propagating sound waves. The experimental results showed that the instantaneous sound field, which was generated by ultrasonic transducers driven by a pure tone of 40 kHz, was quantitatively imaged. Hence, PPSI can be used in acoustical applications requiring spatial information of sound pressure.

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Three-dimensional selective imaging of sound sources

Cited by 8 publications

References 13 publications

A simple method for quantitative imaging of 2D acoustic fields using refracto-vibrometry

A simple method for quantitative imaging of 2D acoustic fields using refracto-vibrometry

High sensitivity non-contact method for dynamic quantification of elastic waves and strains in transparent media

High-speed imaging of sound using parallel phase-shifting interferometry

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