Observation of nonreciprocal propagation for guided Lamb modes in piezoelectric phononic crystalsa).

Piezoelectric phononic-crystal plates, structured on their surface with metallic strips introducing electric-circuit loads, exhibit a tunable frequency-dispersion behaviour, nondestructively controlled in real time. Under an appropriate choice of boundary conditions through these loads, obeying a space-time propagation rule, it is demonstrated experimentally that these systems support nonreciprocal propagation of Lamb-like guided modes in their interior. The observations combined with numerical calculations confirm a broadband translation of the dispersion curves in the frequency-wavenumber space depending on the modulation speed.

Shear wave modes in an equilateral triangular prismatic bar.

Shear wave excitation of an equilateral triangular solid bar shows the existence of horizontally polarized (SH) and vertically polarized (SV) shear waves. The SH wave modes are Lamé solutions of the Neumann problem for displacement and Dirichlet problem for stress in the equilateral triangle. It is shown that Lamé's solutions are obtained from superposition of three equal plane waves and their reflections.

Underwater metamaterial absorber with impedance-matched composite.

By using a structured tungsten-polyurethane composite that is impedance matched to water while simultaneously having a much slower longitudinal sound speed, we have theoretically designed and experimentally realized an underwater acoustic absorber exhibiting high absorption from 4 to 20 kHz, measured in a 5.6 m by 3.6 m water pool with the time-domain approach.

Proof of concept of a frequency-preserving and time-invariant metamaterial-based nonlinear acoustic diode.

Acoustic filters and metamaterials have become essential components for elastic wave control in applications ranging from ultrasonics to noise abatement. Other devices have been designed in this field, emulating their electromagnetic counterparts. One such case is an acoustic diode or rectifier, which enables one-way wave transmission by breaking the wave equation-related reciprocity.