This article reviews acoustic microfiuidics: the use of acoustic fields, principally ultrasonics, for application in microfiuidics. Although acoustics is a classical field, its promising, and indeed perplexing, capabilities in powerfully manipulating both fluids and particles within those fluids on the microscale to nanoscale has revived interest in it. The bewildering state of the literature and ample jargon from decades of research is reorganized and presented in the context of models derived from first principles. This hopefully will make the area accessible for researchers with experience in materials science, fluid mechanics, or dynamics. The abundance of interesting phenomena arising from nonlinear interactions in ultrasound that easily appear at these small scales is considered, especially in surface acoustic wave devices that are simple to fabricate with planar lithography techniques common in microfluidics, along with the many applications in microfluidics and nanofluidics that appear through the literature.

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Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

A method employing holograms that conform with arbitrarily shaped sources has been developed for enhancing conventional near‐field acoustic holography, which has been limited to sources with simple geometries, e.g., planar or cylindrical surfaces. Four holography transformation algorithms have been developed, based on acoustic holography theory and the boundary element method (BEM). Singular value decomposition (SVD) has been incorporated into the algorithms in order to alleviate the ill‐posed nature frequently encountered in backward reconstruction of a field. A pulsating sphere, a cylinder with spherical endcaps, and a vibrating piston set in a rigid sphere have been adopted in a numerical simulation for verifying the algorithms. Satisfactory agreement has been achieved between the holographically transformed results and the analytical solutions.

/pdf/application-of-bem-boundary-element-method-based-acoustic-47vcspbht8.pdf

Application of BEM (boundary element method)‐based acoustic holography to radiation analysis of sound sources with arbitrarily shaped geometries

A method using spherical wave expansion theory to reconstruct acoustic pressure field from a vibrating object is developed. The radiated acoustic pressures are obtained by means of an expansion of independent functions generated by the Gram–Schmidt orthonormalization with respect to the particular solutions to the Helmholtz equation on the vibrating surface under consideration. The coefficients associated with these independent functions are determined by requiring the assumed form of solution to satisfy the pressure boundary condition at the measurement points. The errors incurred in this process are minimized by the least-squares method. Once these coefficients are specified, the acoustic pressure at any point, including the source surface, is completely determined. In this paper, this method is used to reconstruct the surface acoustic pressures based on the measured acoustic pressure signals in the field. It is shown that this method can be applied to both separable and nonseparable geometries, and the...

Helmholtz equation-least-squares method for reconstructing the acoustic pressure field

Estimation of acoustic source strength by inverse methods: part i, conditioning of the inverse problem

http://pure.tudelft.nl/ws/files/7747083/1_s2.0_S0888327015003647_main.pdf

General framework for transfer path analysis: History, theory and classification of techniques $

Because its underlying principles are so fundamental, holography has been studied and applied in many areas of science. Recently, a technique has been developed which takes the maximum advantage of the fundamental principles and extracts much more information from a hologram than is customarily associated with such a measurement. In this paper the fundamental principles of holography are reviewed, and a sound radiation measurement system, called nearfield acoustic holography (NAH), which fully exploits the fundamental principles, is described.

E. G. Williams

Papers

Nearfield acoustic holography: I. Theory of generalized holography and the development of NAH