One-way sound propagation via spatio-temporal modulation of magnetorheological fluid

Abstract

This manuscript details the possibility of achieving one-way sound propagation using a smart fluid such as magnetorheological fluid (MRF) by subjecting it to a spatio-temporally varying magnetic field. The local speed of sound in MRF is dependent on applied magnetic field as demonstrated in several experimental works and this property of MRF has been leveraged, in this work, to induce one-way bandgaps. Initially, a general wave equation pertaining to fluid with space-and-time-varying material properties was derived. Assuming plane wave propagation in one dimension, an approximate Floquet solution was imposed and the dispersion relationship was obtained. A comprehensive finite element analysis was conducted and good agreement was noted between the numerical and theoretical dispersion relations. It was concluded that space-time periodic modulation of fluid density and local sound speed is necessary to induce asymmetry in the band diagram around the ω axis. The feasibility of real-world implementation using MRF has been discussed. A parametric study detailing the effect of viscosity on the one-way bandgaps has been undertaken. It was found that one-way bandgaps formed at relatively lower frequencies are more robust to viscous corruption. A real-world implementation may be feasible if the viscosity of MRF is less than 3000 Pa-s.

Magnetorheology: a review

“…In a later publication by the same authors, they observed significant differences in the propagation depending on the orientation and mode of application of the magnetic field. 227 Nanda and Karami 228 detailed the possibility of achieving one-way sound propagation using MRFs by subjecting them to a time-space varying magnetic field.…”

Active Willis metamaterials for ultracompact nonreciprocal linear acoustic devices

“…Topological insulators have been shown to break sound propagation reciprocity 20,21 but these techniques provide narrow band solutions which are not applicable to three-dimensional waves. Materials with time modulated properties support non-reciprocal broadband sound, however, the modulation must occur on a significant length scale, therefore these materials necessarily occupy a large volume which becomes an issue especially at low frequencies [22][23][24] .…”

Conjugate unscented transformation–based uncertainty analysis of energy harvesters

“…The repulsive force between the magnets reduces the natural frequency of the beam and makes the vibration system nonlinear and, therefore, less sensitive to the frequency of excitation. Using magnetic forces for tuning and manipulation of mechanical dynamical systems (Nanda and Karami, 2018;Nanda, 2018, Nanda et al, 2016 has a long and storied history. A schematic diagram of a nonlinear harvester is shown in Figure 1(b).…”