Acoustic radiation force and torque exerted on a small viscoelastic particle in an ideal fluid

Abstract

We provide a detailed analysis on the acoustic radiation force and torque exerted on a homogeneous viscoelastic particle in the long-wave limit (i.e. the particle radius is much smaller than the incident wavelength) by an arbitrary wave. We assume that the particle behaves as a linear viscoelastic solid, which obeys the fractional Kelvin-Voigt model. Simple analytical expressions for the radiation force and torque are obtained. The developed theory is used to describe the interaction of acoustic waves (traveling and standing plane waves, and zero- and first-order Bessel beams) in the MHz-range with polymeric particles, namely lexan, low-density (LDPE) and high-density (HDPE) polyethylene. We found that particle absorption is chiefly the cause of the radiation force due to a traveling plane wave and zero-order Bessel beam when the frequency is smaller than 5MHz (HDPE), 3.9MHz (LDPE), and 0.9MHz (lexan). Whereas in a standing wave field, the radiation force is mildly changed due to dispersion inside the particle. We also show that the radiation torque caused by a first-order Bessel beam varies nearly quadratic with frequency. These findings may enable new possibilities of particle handling in acoustophoretic techniques.

Orbital Angular Momentum Transfer to Stably Trapped Elastic Particles in Acoustical Vortex Beams

“…We note that the existence of a stable trapping potential for clusters of these dimensions is unexpected from single particle theories of acoustic radiation forces. Accordingly, theses observations call for a deeper understanding of the interaction of AVs with various particles involving multiple scattering processes and secondary forces and torques [42,43].…”

Acoustic spin transfer to a subwavelength spheroidal particle

“…Our choice relies on the fact that the acoustic FOBB possesses spin, which corresponds to the local expectation value of a spin-1 operator [4]. This beam not only may produce a radiation torque on the particle but also a time-averaged force, known as the acoustic force [19][20][21]. Besides, some symmetry considerations have motivated the choice for a prolate spheroidal particle.…”

Physical constraints on the non-dimensional absorption coefficients of compressional and shear waves for viscoelastic cylinders

“…For such materials, absorption varies linearly with frequency, thus, the attenuation of compressional and shear-waves inside the material core can be modeled by introducing complex wavenumbers [6] into the acoustic scattering theory, such that the expressions for the complex wavenumbers corresponding to the compressional and shear-waves contain normalized absorption coefficients independent of frequency [7,8], which account for the attenuation of acoustical waves within the material of the scattering object. This linear VE model assuming a hysteresis-type of absorption in plastic polymers has been utilized in various investigations dealing with numerical computations for the acoustic scattering [9][10][11][12], and radiation forces on a sphere or cylinder [13][14][15][16][17][18] in the development of improved acoustical tweezers devices [19][20][21][22][23][24], that can be coated by a layer of a VE material [25][26][27][28][29] in a non-viscous fluid. Moreover, the acoustic radiation force and torque experienced by a VE polymer sphere or spherical shell filled with water or air in the field of a Bessel (vortex) beam has been evaluated, based on this VE model [30][31][32].…”