5,987 research outputs found
Pulse propagation in a linear and nonlinear diatomic periodic chain: effects of acoustic frequency band-gap
One-dimensional nonlinear phononic crystals have been assembled from periodic diatomic chains of stainless steel cylinders alternated with Polytetrafluoroethylene spheres. This system allows dramatic changes of behavior (from linear to strongly nonlinear) by application of compressive forces practically without changes of geometry of the system. The relevance of classical acoustic band-gap, characteristic for chain with linear interaction forces and derived from the dispersion relation of the linearized system, on the transformation of single and multiple pulses in linear, nonlinear and strongly nonlinear regimes are investigated with numerical calculations and experiments. The limiting frequencies of the acoustic band-gap for investigated system with given precompression force are within the audible frequency range (20–20,000 Hz) and can be tuned by varying the particle’s material properties, mass and initial compression. In the linear elastic chain the presence of the acoustic band-gap was apparent through fast transformation of incoming pulses within very short distances from the chain entrance. It is interesting that pulses with relatively large amplitude (nonlinear elastic chain) exhibit qualitatively similar behavior indicating relevance of the acoustic band gap also for transformation of nonlinear signals. The effects of an in situ band-gap created by a mean dynamic compression are observed in the strongly nonlinear wave regime
Anomalous wave reflection from the interface of two strongly nonlinear granular media
Granular materials exhibit a strongly nonlinear behaviour affecting the
propagation of information in the medium. Dynamically self-organized strongly
nonlinear solitary waves are the main information carriers in granular chains.
Here we report the first experimental observation of the dramatic change of
reflectivity from the interface of two granular media triggered by a noncontact
magnetically induced initial precompression. It may be appropriate to name this
phenomenon the "acoustic diode" effect. Based on numerical simulations, we
explain this effect by the high gradient of particle velocity near the
interface.Comment: 14 pages, 3 figure
Strongly nonlinear waves in a chain of Teflon beads
One dimensional "sonic vacuum" type phononic crystals were assembled from a
chain of Teflon spheres with different diameters in a Teflon holder. It was
demonstrated for the first time that this polymer-based "sonic vacuum", with
exceptionally low elastic modulus of particles, supports propagation of
strongly nonlinear solitary waves with a very low speed.Comment: 33 pages, 6 figure
Strongly Nonlinear Waves in Polymer Based Phononic Crystals
One dimensional "sonic vacuum"-type phononic crystals were assembled from chains of polytetrafluoroethylene (PTFE) beads and Parylene coated spheres with different diameters. It was demonstrated for the first time that these polymer-based granular system, with exceptionally low elastic modulus of particles, support the propagation of strongly nonlinear solitary waves with a very low speed. They can be described using classical nonlinear Hertz law despite the viscoelastic nature of the polymers and the high strain rate deformation of the contact area. Trains of strongly nonlinear solitary waves excited by an impact were investigated experimentally and were found to be in reasonable agreement with numerical calculations. Tunability of the signal shape and velocity was achieved through a non-contact magnetically induced precompression of the chains. This applied prestress allowed an increase of up to two times the solitary waves speed and significant delayed the signal splitting. Anomalous reflection at the interface of two "sonic vacua"-type systems was reported
Discrete breathers at the interface between a diatomic and monoatomic granular chain
In the present work, we develop a systematic examination of the existence,
stability and dynamical properties of a discrete breather at the interface
between a diatomic and a monoatomic granular chain. We remarkably find that
such an "interface breather" is more robust than its bulk diatomic counterpart
throughout the gap of the linear spectrum. The latter linear spectral gap needs
to exist for the breather state to arise and the relevant spectral conditions
are discussed. We illustrate the minimal excitation conditions under which such
an interface breather can be "nucleated" and analyze its apparently weak
interaction with regular highly nonlinear solitary waveforms.Comment: 11 pages, 10 figure
Nonlinear resonant wave interaction in vacuum
The basic equations governing propagation of electromagnetic and
gravitational waves in vacuum are nonlinear. As a consequence photon-photon
interaction as well as photon-graviton interaction can take place without a
medium. However, resonant interaction between less than four waves cannot occur
in vacuum, unless the interaction takes place in a bounded region, such as a
cavity or a waveguide. Recent results concerning resonant wave interaction in
bounded vacuum regions are reviewed and extended.Comment: 8 pages, 1 figure; Talk given at ITCPP03, Santorini, Greece (2003
- …