A comparison of near-field beamforming and acoustical holography for sound source visualization

2009 ◽  
Vol 223 (4) ◽  
pp. 819-834 ◽  
Author(s):  
Yong Thung Cho ◽  
M J Roan ◽  
J S Bolton
Keyword(s):  
Near Field ◽  
Random Noise ◽  
Sound Intensity ◽  
Field Measurements ◽  
Absolute Intensity ◽  
Visualization Technique ◽  
High Frequencies ◽  
Measurement Surface ◽  
Acoustical Holography ◽  
Source Geometry

Acoustical holography procedures make high-resolution visualization possible via estimation of the sound intensity on surfaces closer to the sources than the near-field measurement surface. Another source localization technique, beamforming, has been used to estimate the direction of arrival of sound from sources that typically lie in the far-field. However, little work has been done using beamforming as a visualization technique based on near-field measurements. As a result, the performance of beamforming and acoustical holography in terms of source resolution capabilities has not been directly compared when using near-field measurements. In this work, point source beamforming was used to visualize sources based on near-field measurements. Acoustic intensity estimated from beamformed pressure measurements was compared with the absolute intensity estimated using acoustical holography techniques. In addition to noise-free, anechoic simulations, cases of measurement pressure with random noise were generated and used to compare source resolution accuracy of acoustical holography and beamforming techniques in the presence of measurement noise. It was found that intensity estimated using acoustical holography provided the clearest image of sources when the measurement surface was conformal with the source geometry. However, sources can be resolved more accurately using near-field beamforming than acoustical holography at high frequencies when the sources are not located perfectly on a surface conformal with the measurement geometry.

Simulation and experimental investigations for the patch near-field acoustical holography

2008 ◽  
Vol 222 (6) ◽  
pp. 945-953 ◽  
Author(s):  
C Yang ◽  
J Chen ◽  
J Q Li ◽  
W F Xue
Keyword(s):  
Fourier Transform ◽  
Sound Pressure ◽  
Near Field ◽  
Sound Field ◽  
Experimental Investigations ◽  
Regularization Methods ◽  
Aperture Size ◽  
Measurement Surface ◽  
Physical Necessity ◽  
Acoustical Holography

In order to reconstruct the sound field, the fast Fourier transform (FFT)-based near-field acoustical holography (NAH) demands that the measurement surface must extend to a region where the sound pressure decreases to a low level. This method is unfit for reconstructing the partial sound field in which the measurement aperture size is limited either by physical necessity or as a way of reducing the measurement cost. Statistically optimal NAH (SONAH) performs plane-to-plane calculations directly in the spatial domain, avoids all errors occurred in the FFT-based NAH and significantly increases the accuracy of the reconstruction of the partial sound field. In the present work, combined with the different regularization methods, SONAH is performed for reconstructing the partial sound field. The errors over the central and the peripheral sections of the reconstruction area are researched separately. Simulations and experiments show that SONAH is successful in reconstructing the partial sound field and the errors over the central sections are smaller than that over the peripheral sections. Experiments demonstrate that Tikhonov regularization in conjunction with Engl's criterion is suitable for the reconstruction of the practical sound field.

On study of antenna-radome system near-field measurements with a spherical scanner

2020 ◽  
Vol 49 (9) ◽  
pp. 14-21
Author(s):  
A. V. Kirpanev ◽  
N. A. Kirpanev ◽  
V. V. Shubnikov
Keyword(s):  
Plane Wave ◽  
Transmission Coefficient ◽  
Near Field ◽  
Wave Spectrum ◽  
Spherical Wave ◽  
Field Measurements ◽  
Radiation Fields ◽  
Vector Characteristic ◽  
Measurement Surface ◽  
The Relationship

The paper presents a research technique for studying an antenna-radome system based on nearfield measurements with a most common «roll over azimuth» spherical scanner. It is based on the relationship between the components of the plane wave spectrum and the spherical wave coefficients, in terms of which the radiation fields of the tested antenna and the antenna-radome system are represented. Expressions for the plane wave spectrum components at the pole of the spherical measurement surface are given. To assess the effect of the radome on the antenna characteristics, it is proposed to use the spectral vector characteristic of the radome passage. Methods for estimating the dielectric constant of the radome by determining the transmission coefficient of its wall at various points on the surface are proposed. It is shown that the use of a weakly directional antenna in the study of the radome characteristics simplifies the task, since the transmission coefficient is determined using the components of the electric field strengths in spherical coordinates.

Dual surface beamforming and acoustical holography for sound field visualization in reverberant environments

2009 ◽  
Vol 224 (1) ◽  
pp. 55-70 ◽  
Author(s):  
Yong Thung Cho ◽  
M J Roan ◽  
J Stuart Bolton
Keyword(s):  
Near Field ◽  
Sound Field ◽  
Field Measurements ◽  
Sound Waves ◽  
Noise Sources ◽  
Reflected Waves ◽  
Reverberant Environments ◽  
Reverberant Environment ◽  
Reflecting Surface ◽  
Acoustical Holography

Near-field acoustical holography is a technique that has been widely used to visualize noise sources from pressure measurements in spaces that can be assumed to be anechoic or semi-anechoic. Previously, a dual surface acoustical holography procedure based on making measurements on two surfaces between the source and a reflecting surface was introduced to remove the effects of reverberation. Little work has been performed in which beamforming has been used to visualize sources based on dual surface, near-field measurements in a reverberant environment: such a procedure is described here. Because many practical measurement environments are not completely anechoic, the source resolution accuracy of dual surface acoustical holography and beamforming procedures in reverberant environments is compared here by using numerical simulations. It has been found that dual surface acoustical holography provides the clearest representation of the source location when sound waves radiating from the source and the reflected waves are propagating in the opposite directions and when the measurement surfaces are conformal with the source geometry. However, it has also been found that dual surface beamforming provides more consistent source resolution performance regardless of the relative direction of wave propagation of the source and reflected waves.

Effect on Measurement of the Radiated Acoustic Field of Underwater Structure Based on NAH with Swinging Measuring Surface

2012 ◽  
Vol 197 ◽  
pp. 778-781
Author(s):  
Lin Na Zhou ◽  
Shao Chun Ding ◽  
Ruo Yu Zhang ◽  
Jing Jun Lou ◽  
Shi Jian Zhu
Keyword(s):  
Sound Pressure ◽  
Power Level ◽  
Near Field ◽  
Sound Intensity ◽  
Sound Power ◽  
Mean Square ◽  
Sound Power Level ◽  
Measuring Surface ◽  
Underwater Structure ◽  
Acoustical Holography

This paper analyzes the effects of the swinging NAH(Near field Acoustical Holography) measuring array on measurement of the sound power level of underwater structure. We use the method of sound intensity integral, the method of mean square sound pressure and the method of NAH reversal pressure to calculate the sound power level under certain collection of frequency with measuring surface in different states. We also analyze the relative error of results acquired by those methods, which can help validating the reliability and the error estimate of the results calculated with NAH.

Sound field separation of multiple coherent sound sources with single measurement surface

2021 ◽  
pp. 107754632110201
Author(s):  
Jin Mao ◽  
Jinfu Du ◽  
Kai Liu ◽  
Jiang Liu ◽  
Yahui Cui
Keyword(s):  
Near Field ◽  
Sound Field ◽  
Single Measurement ◽  
Sound Sources ◽  
Equivalent Source ◽  
Coherent Sources ◽  
Measurement Surface ◽  
Acoustical Holography ◽  
Field Separation ◽  
Source Number

Sound field separation based on near-field acoustical holography has been developed worldwide, but with the increase in the number of sound sources, traditional measurement methods and calculation methods will generate more workload. To reduce the number of measuring points and save calculation time, the sound field separation of multiple coherent sources with a single measurement surface is proposed. On the basis of separating two coherent sources with this method, the separation formula of more sources based on an equivalent source method is given. Through numerical simulation, the effects of the number of holographic surface measuring points, measuring distance, array shape, and equivalent source number on the calculation accuracy of the sound field separation were compared at different frequencies. The correctness and effectiveness of the sound field separation method with a single surface are verified by actual experiments.

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