In-plane backward and zero group velocity guided modes in rigid and soft strips.

Area of Science:

• Solid Mechanics
• Acoustics
• Materials Science

Background:

• Elastic wave propagation in waveguides exhibits complex dispersion phenomena.
• Understanding in-plane modes in rectangular bars is crucial for wave manipulation.
• Coupling between shear horizontal (SH0) and symmetrical Lamb (S0) modes influences low-frequency behavior.

Purpose of the Study:

• To investigate in-plane elastic wave modes in thin, isotropic rectangular waveguides at low frequencies.
• To analyze the dispersion curves, backward modes, and zero group velocity (ZGV) resonances.
• To compare experimental and numerical findings with theoretical models.

Main Methods:

• Experimental measurements using noncontact laser ultrasonic techniques on a metal tape.
• Numerical simulations of in-plane modes in a soft ribbon (Poisson's ratio ν≈0.5).
• Comparison with theoretical dispersion curves calculated using established methods.

Main Results:

• Observed complex dispersion curves for in-plane modes in rectangular waveguides.
• Measured backward modes and ZGV resonances in a metal tape.
• Numerical simulations showed that soft materials exhibit backward waves and ZGV modes at much lower frequencies than metal tapes.

Conclusions:

• The coupling of SH0 and S0 modes significantly impacts low-frequency elastic wave behavior in rectangular waveguides.
• ZGV resonances occur at substantially lower frequencies in soft materials due to their low shear velocity.
• The findings provide insights into wave propagation and resonance phenomena in structured materials.