Bandgap tunability and programmability of four-leaf clover shaped elastic metastructures

This paper studies the propagation of elastic waves in a four-leaf clover shaped elastic metastructure (EM), which consists of periodically distributed solid blocks connected by slender beams. The bandgap structure and vibrational transmittance of four-leaf clover shaped EM plates were examined using two-dimensional (2D) and threedimensional (3D) solid elements. The comparison of elastic wave propagation experiments and numerical transmittance attenuation analysis shows excellent consistency and efficient wave regulation. Based on the experimentally validated model, the effect of structural parameters on the bandgap distribution is explored. It is found that the bandgap frequency can be lowered by up to 50 % and widened by 22 % by adjusting structural parameters, providing useful guidance for parameter settings to lower or widen the low-frequency bandgap. Finally, a programmable EM plate capable of guiding elastic wave propagation is proposed, which has the advantages of convenient adjustment and reliable structure, altering the bandgap from "on" to "off" by adjusting the distribution of the local resonators in the unit cell. Numerical demonstrations and experimental verifications are further carried out, illustrating that the proposed EM plate is capable of highly tuning elastic wave propagation. The results of the study indicate that the four-leaf clover shaped EM has a lower and wider bandgap adjustment range, which can realize waveguide control in a broadband range. The current findings provide important insights for the design of alternative devices such as vibration isolators, beams, and plates.