Sound in flight: measurement of sound fields by use of TV holography

Løkberg, Ole J.

doi:10.1364/ao.33.002574

Cited by 47 publications

(23 citation statements)

References 5 publications

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“…Optical techniques are both nonintrusive and easily scalable, which make them the preferred choice in many applications. Lökberg 12 and Lökberg et al 13 developed and used phase-modulated TV holography, 14 electro-optic holography, for measurements of sound fields in air radiating from harmonically vibrating objects. Schedin et al [15][16][17] used pulsed holographic interferometry and pulsed TV holography to measure transient sound fields outside impacted plates and beams.…”

Section: Introductionmentioning

confidence: 99%

Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction

2006

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Multifrequency digital holographic reconstructions of primary sound sources embedded in scattering media are demonstrated. The sound field is measured with a scanning laser Doppler vibrometer ͑LDV͒ and broadening of the spectral content of the sound source is achieved by tuning the primary ultrasound ͑US͒ transducer around its resonance frequency. The results show that combining the complex amplitudes from the different frequency reconstructions results in a reduced susceptibility to multiple scattered sound and makes possible a quite thorough localization of the primary sound source. The depth resolution obtained is 11 US frequencies. This depth sensitivity is improved even further to only 2.8 wavelengths by applying a filter determined from the standard deviation over the phases.

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Section: Introductionmentioning

confidence: 99%

Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction

2006

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“…It may be possible to solve the problems cited above if estimates can be made of the sound fields by noncontact methods, that is, without introducing a physical probe. Optical sensing [6][7][8][9][10][11][12] is typical of such noncontact methods, in that the noncontact step in obtaining the estimate is to target the sound fields. In 1994, Løkberg used a technique called television holography to estimate the realtime oscillations and phase characteristics of sound fields in air [6].…”

Section: Introductionmentioning

confidence: 99%

“…Optical sensing [6][7][8][9][10][11][12] is typical of such noncontact methods, in that the noncontact step in obtaining the estimate is to target the sound fields. In 1994, Løkberg used a technique called television holography to estimate the realtime oscillations and phase characteristics of sound fields in air [6]. In 1995, Neighbors and colleagues estimated the absolute sound pressure of 0.37-MHz focused sound fields in water by the Schlieren method using CCDs [7].…”

Section: Introductionmentioning

confidence: 99%

“…This possibility gives rise to problems when the methods described above are applied to computerized tomography (CT). On the other hand, the methods based on interference proposed above [6,9,10,12] can exploit the fact that only the sound field information can affect the measured intensities obtained for light that passes straight through the ensonified region, that is, is undiffracted, even when the width of the sound beam is large. This gives these methods an advantage that no currently used method based on the Schlieren method has.…”

Section: Introductionmentioning

confidence: 99%

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Optical measurement of sound fields estimated from multiple interference images using Mach‐Zehnder interferometer

Ezure

Mizutani

Masuyama

2004

Electron Comm Jpn Pt II

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SUMMARYIn this paper we discuss the acquisition of sound field information from optical interference patterns detected by a CCD camera. Although noncontact measurements of wide-beamwidth sound fields based on diffraction techniques such as the Schlieren method yield projected images with high SN ratios, the problem is that sound field information is not projected correctly. In this work, the measurements were made using a Mach-Zehnder interferometer. Because interference measurements measure light that has passed through a real focus generated by the sound fields, these measurements have a clear advantage over methods like the Schlieren method, in that they create no points at which there is a mismatch between the received light and the diffraction spots. By using CCDs as two-dimensional time averaging detectors, wide-range sound fields can be acquired at high speeds. In these experiments, we estimated the optical phase excursion caused by the sound field over an interval along the sound axis from 0 to 25 mm using an ultrasonic wave transducer 8.0 mm in diameter, operating at 1.4 MHz, with a beamwidth of 7 mm. Because there were bands along the sound axis within which our computational algorithm was unable to provide estimated values for the phase deviation, we augmented our primary data set with three other data sets obtained by shifting the phase of the reference light used to generate the interference pattern in the primary measurement by +0.20 π, +0.48 π, +0.94 π (rad), and combining the resulting data sets to interpolate through the gaps in the primary data set, thereby realizing a continuous estimate along the whole sound axis. In this continuous estimate, the data we used to interpolate the primary data set came mostly from the interference pattern whose phase relative to the first measured pattern was in the neighborhood of π/2 rad. By averaging the four estimate results together, we were able to decrease the percentage of no-data sectors over the entire range 2%. The estimated phase deviation was a gradually decreasing function with distance, starting with a value of about 0.7π rad.

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“…Having extensively studied refractive index changes induced by airborne acoustic fields emanating from vibrating objects such as loudspeakers using ESPI, 20,21 the Applied Optics Group at the Norwegian University of Science and Technology successfully implemented the observation of underwater acoustic fields using the same technology. 22 In a more specific study, Rustad demonstrated the suitability of ESPI for studying the acoustic field generated by a 3.25 MHz continuous wave medical ultrasound probe, with a spatial resolution of better than 100 m. 23 This technique is, however, limited by the spatial resolution and fixed aspect ratio of the TV camera used to acquire the images and the fact that the sensitivity of the ESPI system is a complex function of the spherical spreading of the optical wave front and target shape and position.…”

Section: Introductionmentioning

confidence: 99%

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

Harland¹,

Petzing²,

Tyrer³

2003

The Journal of the Acoustical Society of America

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Localized changes in the density of water induced by the presence of an acoustic field cause perturbations in the localized refractive index. This relationship has given rise to a number of nonperturbing optical metrology techniques for recording measurement parameters from underwater acoustic fields. A method that has been recently developed involves the use of a Laser Doppler Vibrometer ͑LDV͒ targeted at a fixed, nonvibrating, plate through an underwater acoustic field. Measurements of the rate of change of optical pathlength along a line section enable the identification of the temporal and frequency characteristics of the acoustic wave front. This approach has been extended through the use of a scanning LDV, which facilitates the measurement of a range of spatially distributed parameters. A mathematical model is presented that relates the distribution of pressure amplitude and phase in a planar wave front with the rate of change of optical pathlength measured by the LDV along a specifically orientated laser line section. Measurements of a 1 MHz acoustic tone burst generated by a focused transducer are described and the results presented. Graphical depictions of the acoustic power and phase distribution recorded by the LDV are shown, together with images representing time history during the acoustic wave propagation.

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Sound in flight: measurement of sound fields by use of TV holography

Cited by 47 publications

References 5 publications

Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction

Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction

Optical measurement of sound fields estimated from multiple interference images using Mach‐Zehnder interferometer

Nonperturbing measurements of spatially distributed underwater acoustic fields using a scanning laser Doppler vibrometer

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