Broad and Low Frequency Bandgap in Truss Core Sandwich Beam

The concept of phononic crystals is employed to improve vibroacoustic properties of truss core sandwich beams. A typical sandwich beam exhibits a flexural wave bandgap, as well as significant vibration attenuation, from 968 to 2132 Hz without adding any structure. Therefore it has big advantages of easy manufacturing and lightweight over sandwich beams with local resonators, which include complex structures and additional weight. In addition, through developing simplified model, the analytic expressions are obtained to determine bandgap edges. The results show bandgap structure can be engineered by adjusting the geometrical dimensions of the unit cell. The fundamental origin of the bandgap is Bragg scattering of the local flexural wave, which results from metastructure of the sandwich beam. Benefiting from the low stiffness face sheets and mechanism of Bragg scattering, the structure owns a bandgap with low frequency and broad width at the same time. Hence the truss core sandwich structure has great potential in engineering practice to reduce the sound and vibration transmission.