1,975 research outputs found
Transversal-rotational and zero group velocity modes in tunable magneto-granular phononic crystals
We report on the design and operation of a 1D magneto-granular phononic
crystal composed of a chain of steel spherical beads on top of permanent
magnets. The magnetic field of the permanent magnets induces forces in the
granular structure. By changing its strength, we can tune the dynamic response
of the granular structure. We present experimental results with evidence of
coupled transversal-rotational modes, and zero group velocities modes. These
observations are well supported by a proposed model taking into account the
mechanical coupling between the beads and the magnets by linear stiffnesses and
including all degrees of freedom in translations and rotations
Nonlinear Hysteretic Torsional Waves
We theoretically study and experimentally report the propagation of nonlinear
hysteretic torsional pulses in a vertical granular chain made of cm-scale,
self-hanged magnetic beads. As predicted by contact mechanics, the torsional
coupling between two beads is found nonlinear hysteretic. This results in a
nonlinear pulse distortion essentially different from the distortion predicted
by classical nonlinearities, and in a complex dynamic response depending on the
history of the wave particle angular velocity. Both are consistent with the
predictions of purely hysteretic nonlinear elasticity and the
Preisach-Mayergoyz hysteresis model, providing the opportunity to study the
phenomenon of nonlinear dynamic hysteresis in the absence of other type of
material nonlinearities. The proposed configuration reveals a plethora of
interesting phenomena including giant amplitude-dependent attenuation, short
term memory as well as dispersive properties. Thus, it could find interesting
applications in nonlinear wave control devices such as strong
amplitude-dependent filters
Waveguiding by a locally resonant metasurface
Dispersion relations for acoustic and electromagnetic waves guided by resonant inclusions located at the surface of an elastic solid or an interface between two media are analyzed theoretically within the effective medium approximation. Oscillators on the surface of an elastic half-space are shown to give rise to a Love-type surface acoustic wave only existing below the oscillator frequency. A simple dispersion relation governing this system is shown to also hold for electromagnetic waves guided by Lorentz oscillators at an interface between two media with equal dielectric constants. Different kinds of behavior of the dispersion of the resonantly guided mode are identified, depending on whether the bulk wave in the absence of oscillators can propagate along the surface or interface.National Science Foundation (U.S.) (Grant CHE-1111557
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