Laser-assisted Vibroacoustic Holography


Establishing the root cause of noise in vibrating structures is critical in reducing or eliminating the noise. To date, numerous methods, both measurement- and reconstruction-based techniques, have been developed to aid noise reduction in vibrating structures. The notable difference between measurement and reconstruction methods is that the former only offers absolute values of certain physical quantities at specific locations. The measured data are typically isolated, insufficient, and uncorrelated. As a result, it is difficult to establish an effective noise reduction strategy. In contrast, the latter provides comprehensive and correlated vibroacoustic quantities both on source surfaces and in 3D space, but only under certain conditions. Over the past decades, significant efforts have been made to improve the feasibility and robustness of the existing noise reduction methods.

Particularly, the reconstruction technique based on Fourier transform-based near-field acoustic holography (NAH) has drawn attention owing to its ability to reconstruct vibroacoustic quantities. Unfortunately, this approach suffers from many shortcomings such as the requirement that source surface be planar, spherical, or cylindrical, etc. which severely limits its practical applications. Efforts to overcome these challenges have taken shape in recent years. For instance, the development of statistically optimized NAH (SONAH) has successfully removed some of the restrictions. However, its reconstruction is limited to acoustic quantities, not structural vibrations. Moreover, SONAH requires a source-free environment that is non-existent in practice. The boundary element method (BEM)-based NAH enables one to tackle an arbitrarily shaped object, but requires a significant amount of measurements and computations in the mid-to-high frequency regimes, making it impractical for engineering applications.

Recently, laser-assisted vibroacoustic holography has been developed. The underlying principle of this technology is Helmholtz equation least squares (HELS)-based HAH. This new technology is a promising tool to reconstruct all vibroacoustic quantities with higher computation efficiency based on limited measurements on the surface a complex structure and in 3D space. Specifically, it enables one to see operational deflection shapes of a vibrating structure, structural resonances, where sound sources are located, how sound waves are emitting from vibrating structures and how they transmit through a structural surface, etc. With this comprehensive knowledge, engineers will be able to establish the optimal noise and vibration mitigation strategies in an easy-to-understand manner.

Antonio Figueroa (PhD candidate), Mr. Michael Telenko Jr. from Shiloh Industries together with Dr. Lingguang Chen and led by Dr. Sean F. Wu (University Distinguished Professor at Wayne State University) have published the theory and applications of laser-assisted vibroacoustic holography in the research journals, Journal of Theoretical and Computational Acoustics1 and Journal of Sound and Vibration.2

In this approach, the input data comprised both acoustic pressures measured by a small microphone array in the field and normal surface velocities measured by a laser vibrometer at discrete points on the source surface. The modified HELS method was used to reconstruct the distribution of the normal surface velocity on the entire source surface and the results are compared to the benchmark data. The acoustic power was also reconstructed, and results compared to those of measurements. In addition, a semi-empirical formula was derived to depict the dimensionless structural damping ratio, and reconstructed results were interrogated and validated experimentally.

The results demonstrated that the dimensionless structural damping ratio for metals such as steel is not constant but rather frequency dependent. The proposed semi-empirical formula enabled one to predict a dimensionless damping ratio spectrum over the frequency range of 0 – 10,000 Hz. The reconstructed normal velocity and acoustic pressure distributions were smooth and more accurate than those produced by the existing methods. Furthermore, it allows one to utilize non-uniform measurement approaches; higher-density measurements on surfaces accessible to accelerometers and laser vibrometers, and lower density measurements on surfaces inaccessible to measurement instruments. This provides a high flexibility in measurements for engineering applications.

In summary, laser-assisted vibroacoustic holography enables one to determine all vibroacoustic quantities including dimensionless structural damping ratio spectrum. The method is feasible and convenient for analyzing vibroacoustic responses of arbitrarily shaped vibrating structures. The results demonstrated the advantages of using input data comprising both field acoustic pressure and normal surface velocity, making this technology much superior to all previous versions. In a statement to Advances in Engineering, University distinguished Professor Sean F. Wu said that laser-assisted vibroacoustic holography is suitable and applicable to most structure-borne sound radiation and transmission, and provides a direct and easy-to-understand way to analyze structural vibration and sound radiation, leading to the most cost-effective noise and vibration mitigation strategies.

Laser-assisted vibroacoustic holography has been successfully used to analyze and reduce noise emission and sound transmission through the front dash panel of a full-size F-150 Pick-Up Truck.1 In fact, it is suited for diagnosis, analysis, and reduction of noise emission from any complex vibrating structure.

About the author

Sean F. Wu received his BSME from Zhejiang University (China); MSME and Ph.D. from Georgia Institute of Technology, U.S.A. Dr. Wu joined the Department of Mechanical Engineering at Wayne State University (WSU) as an Assistant Professor for Research in 1988; became a tenure-track Assistant Professor in 1990; Associate Professor in 1995, and a Professor in 1999. He was awarded the title of Charles DeVlieg Professor of Mechanical Engineering in 2002 – 2005; and was appointed by the Board of Governors to the rank of University Distinguished Professor every year since 2005.

Dr. Wu holds the rank of Fellow in the Acoustical Society of America (ASA) and the American Society of Mechanical Engineers (ASME), and is a member of the Society for Automotive Engineering (SAE). Currently, Dr. Wu serves as an Associate Editor for the Journal of the Acoustical Society of America, Managing Editor and Co-Editor-in-Chief for the Journal of Theoretical and Computational Acoustics. In 2018, Dr. Wu received Per Bruel Gold Medal, ASME, 2018 (the highest award in acoustics and noise control and the first Asian to receive this prestigious award issued by the ASME since its inception in 1987).

About the author

Antonio Figueroa holds a bachelor’s degree in electronics and communications engineering from the University of Guadalajara, Guadalajara, Mexico; obtained his master’s degree in mechanical engineering from Wayne State University, Detroit, USA; and is currently working on getting his PhD in mechanical engineering from Wayne State University, Detroit, USA. Mr. Figueroa has worked for automotive industry as a process engineer, product development engineering, technical specialist, and principal engineer in the areas of manufacturing engineering and acoustics and vibrations for over 20 years for a car maker and several tier 1 suppliers.

Mr. Figueroa has author and co-author technical papers featuring vibroacoustic reconstruction technologies based on the Helmholtz least-squared methodology and its application to noise control.

About the author

Lingguang Chen received a M.S. degree in vehicle engineering from Zhejiang University, China, in 2013 and a Ph.D. degree in mechanical engineering from Wayne State University, US, in 2017. He is currently a product R&D manager at Signal-Wise LLC.

Dr. Chen’s research activities are focused on vibration and noise control and machine health monitoring issues. He developed a vibration-acoustic analysis system which could solve the problems of noise source localization and suppression of structure-borne sounds. He also developed the X-tractor system which is ideal for online and end-of-line Quality Control (QC) Testing and Nondestructive Testing (NDT) or NDT related Machinery Health Monitoring (MHM).

About the author

Director of Laboratory Services and Core Engineering

Michael has spent 40 plus years in the automotive supply sector. He is currently the Director of Laboratory Services and Core Engineering at Shiloh Industries. Focusing on the development of laser welded blanks from steel and aluminum. Most notably aluminum laser welding, which was recognized by the 2021 Altair Enlighten Award for achievement in the future of light weighting.

Michael started his career in 1976 with Firestone/Bridgestone before moving on to Uniroyal and Masland Industries, with increasing greater levels of engineering and management responsibilities.

Michael’s career has spanned truck tire manufacturing, rubber mixing, coated fabrics, foams, automotive soft trim, sheet metal stampings and vibro-acoustic material. With experience in tooling, design and release engineering, CAD management and Research and Development.

Michael holds 30 granted US and Foreign Patents. With numerous patent applications pending approval.


S. F. Wu, L. Chen, A. Figueroa, and M. Telenko, Jr., Laser-assisted reconstruction of vibro-acoustic behaviors of an arbitrarily shaped vibrating structure. Journal of Theoretical and Computational Acoustics, Vol. 28, No. 3, 1950011 – 1950023 (2020).

Go To Journal of Theoretical and Computational Acoustics

Figueroa, A., Telenko, M., Chen, L., & Wu, S. (2021). Determining structural damping and vibroacoustic characteristics of a non-symmetrical vibrating plate in free boundary conditions using the modified Helmholtz equation least squares method.

Go To Determining structural damping and vibroacoustic characteristics

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