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The description of acoustical waves can be achieved using an expansion over basic functions with weighting coefficients which may be called beam shape coefficients (BSCs). There is a strong analogy between the scalar formalism of acoustical waves and the vectorial electromagnetic formalism, known as generalized Lorenz–Mie theory (GLMT), describing the interaction between a homogeneous sphere and an arbitrary illuminating beam. In particular, BSCs have been introduced as well in GLMT and the mathematical arsenal to evaluate them, developed since several decades, can be used mutatis mutandis to evaluate BSCs in acoustics. In particular, the present paper introduces a method named localized approximation to the evaluation of the acoustical BSCs, similar to the localized approximation used to evaluate electromagnetic BSCs, in the case of Bessel beams. Such a formalism akin to the electromagnetic GLMT may be viewed as an acoustical GLMT and should allow a renewal of the calculation of various properties of acoustical wave scattering, in particular to the design of acoustical tweezers similar to optical tweezers.

With the model of generalized Lorenz-Mie theory (GLMT) and the extended boundary condition method, describing the interaction between electromagnetic (EM) waves (more specifically laser beams) and particles, an acoustical GLMT-like framework can be used to deal with acoustical wave scattering. The incident acoustical wave may then be encoded in a set of beam shape coefficients (BSCs) similar to the ones used in EM scattering. Following a paper devoted to the evaluation of acoustical BSCs using a localized approximation in the case of on-axis Gaussian acoustical beams, the present paper deals with the evaluation of acoustical BSCs in the case of off-axis Gaussian acoustical beams. [ABSTRACT FROM AUTHOR]

Electromagnetic Gaussian beams may be described by using a Davis scheme of approximations. It is demonstrated that this scheme also may be used, with minor changes, to manage the description of acoustical waves. The acoustical version of the Davis scheme afterward allows one to establish an efficient and accurate localized approximation to evaluate beam shape coefficients, which encode the structures of acoustical waves, similar to the localized approximation, which has been made famous when dealing with electromagnetic waves. The present paper is restricted to the case of on-axis beams. [ABSTRACT FROM AUTHOR]

Generalized Lorenz–Mie theory (GLMT) describes the interaction between electromagnetic waves (more specifically, laser beams) and homogeneous spherical particles. An acoustical GLMT-like framework can be used to deal with acoustical wave scattering. The incident acoustical wave may then be encoded in a set of beam shape coefficients (BSCs) similar to the ones used in electromagnetic scattering. One method to evaluate the acoustical BSCs is the localized approximation which takes the form of a variant of a localized approximation used to evaluate the electromagnetic BSCs. These acoustical BSCs are discussed and rigorously justified in the case of on-axis Gaussian beams. Examples of field reconstruction and remodeling using the localized approximation are presented which reinforce the robustness of such a method for very small confinement parameters. We expect that the results presented here will encourage a wider use of localized approximation schemes in acoustic scattering problems. [ABSTRACT FROM AUTHOR]