Magnetoactive Acoustic Metamaterials

Abstract

Acoustic metamaterials with negative constitutive parameters (modulus and/or mass density) have shown great potential in diverse applications ranging from sonic cloaking, abnormal refraction and superlensing, to noise canceling. In conventional acoustic metamaterials, the negative constitutive parameters are engineered via tailored structures with fixed geometries; therefore, the relationships between constitutive parameters and acoustic frequencies are typically fixed to form a 2D phase space once the structures are fabricated. Here, by means of a model system of magnetoactive lattice structures, stimuli-responsive acoustic metamaterials are demonstrated to be able to extend the 2D phase space to 3D through rapidly and repeatedly switching signs of constitutive parameters with remote magnetic fields. It is shown for the first time that effective modulus can be reversibly switched between positive and negative within controlled frequency regimes through lattice buckling modulated by theoretically predicted magnetic fields. The magnetically triggered negative-modulus and cavity-induced negative density are integrated to achieve flexible switching between single-negative and double-negative. This strategy opens promising avenues for remote, rapid, and reversible modulation of acoustic transportation, refraction, imaging, and focusing in subwavelength regimes.

Mechanical Metamaterials and Their Engineering Applications

“…Other potential applications of mechanical metamaterials which makes use of its topological flexibility, size effects, and material constituents includes the creation of architected thermal heat exchangers and insulators, photonic crystals with unique optical properties, phononic crystals with tailorable bandgaps for acoustic cloaking, battery electrodes with optimized topology for electron transport, electrochemical and mechanical properties, and bio‐scaffolds or meta‐biomaterials, which involves the rational design of an optimized combination of mechanical, mass transport and biological properties to enhance tissue regeneration . Recently, microlattices for tunable electromagnetic shielding has also been reported …”

“…A cellular metamaterial with both negative Poisson's ratio and tunable acoustic band gap has been developed recently by Chen et al via tailoring its geometric parameters such as length of unit cell, porosity and aspect ratio of the individual pores . Yu et al have also developed a stimuli‐responsive acoustic metamaterial based on an octet‐truss topology made of ferromagnetic nanoparticle‐filled elastomer . The effective modulus of the synthesized magnetoactive acoustic lattice could be reversibly switched between positive and negative through elastic buckling which occurs as the applied magnetic field is varied.…”

Healable, memorizable, and transformable lattice structures made of stiff polymers

“…A promising direction in the field is designing transformable lattice structures whose configurations can be reversibly switched to enable tunable properties 10,11 . Existing transformation mechanisms primarily rely on nonfracture deformation such as origami [12][13][14] , instability [15][16][17] , shape memory [18][19][20] , and liquid crystallinity 21 . Fractures have rarely been harnessed to transform lattice structures, because fractures have long been considered a failure mode that compromises the structural integrity and properties; furthermore, healing fractures is also typically challenging for three-dimensional (3D)-architected lattice structures.…”

Planar Mechanical Metamaterials with Embedded Permanent Magnets

“…Embedding dielectric or piezoelectric elements and magnetorheological elastomers seems to be a feasible strategy to enable control over the performance of these mechanical metamaterials. Application of an external magnetic or electric field can almost immediately trigger the deformation and reconfiguration of the internal architecture, which directly affects the properties and overall performance of the metamaterial [31,32]. However, the current generation of dielectric elastomers/magnetorheological elastomers demonstrates a rather weak coupling between the electromagnetic field and the mechanical deformation [33,34].…”