An active mechanical Willis meta-layer with asymmetric polarizabilities

Area of Science:

• Acoustics and Mechanics
• Materials Science
• Metamaterials

Background:

• Willis materials demonstrate cross-coupling between mechanical properties but have limitations in practical applications due to intrinsically coupled coefficients.
• Existing designs hinder full implementation in structural dynamics, necessitating novel approaches for independent control.

Purpose of the Study:

• To overcome limitations of intrinsically coupled Willis coefficients.
• To introduce an active scatterer for independent control of elastic wave propagation.
• To demonstrate real-time adaptive control of wave transmission and reflection.

Main Methods:

• Introduction of an active scatterer within a mechanical meta-layer.
• Utilization of piezoelectric sensor-actuator pairs controlled by digital circuits.
• Experimental validation in beams and plates to analyze flexural wave propagation.

Main Results:

• Independent engineering of transmission and reflection coefficients for flexural waves in amplitude and phase.
• Demonstration of nonreciprocal wave propagations.
• Characterization of the meta-layer using a flexural wave polarizability tensor capturing higher-order couplings.

Conclusions:

• The active meta-layer provides unprecedented control over elastic waves.
• Programmability enables real-time, reconfigurable broadband operation.
• Potential applications include vibration protection, ultrasonic sensing, and structural evaluation.