A Lamb wave resonator utilizing an aluminum nitride (AlN) plate with biconvex edges to enhance the quality factor (Q) is demonstrated. The simulation results based on finite element analysis verify that the use of the biconvex edges, instead of the conventional flat edges, can efficiently confine mechanical energy in the AlN Lamb wave resonator. Specifically, the measured frequency response of a 491.8-MHz AlN Lamb wave resonator with biconvex edges yields a Q of 3280 which represents a 2.6× enhancement in Q over a 517.9-MHz Lamb wave resonator on the same AlN plate but with the suspended flat edges.
The unusual properties of a metamaterial come from special resonances supported by its resonating structure units. Guided by a previously developed effective medium theory, which links the resonances of the microstructures and the unusual properties, two types of elastic metamaterials in two dimensions were designed with different resonant structures in their building blocks that exhibit multiple negative dispersion bands with special characteristics. The first type possesses negative mass density and negative shear modulus simultaneously over a large frequency regime, which leads to a negative band for shear waves only. Mode conversion takes place at the interface of the metamaterial and the common solids. The second type is able to produce negative effective moduli in different frequency regimes within a large frequency regime of negative effective mass density. This results in a super anisotropic negative band and a negative band that only compressional is allowed. All of these unusual properties are demonstrated by simulations. This work was supported by Hong Kong RGC Grant No. 605008, HKUST604207 and KAUST start-up package.
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