Ultra-low frequency vibration isolation of a novel click-beetle-inspired structure with large quasi-zero stiffness region

Inspired by the three postures of a click beetle, a novel passive click-beetle-inspired structure (CBIS) with variable asymmetric stiffness characteristics is proposed and systematically investi-gated for stiffness tunning and low-frequency vibration isolation. The main structure of CBIS is consisted of three rods and two springs but the geometrical nonlinearity and stiffness properties are abundant. Based on the Lagrange principle, the stiffness properties of CBIS is analyzed comprehensively for the unbending posture, down-bending posture and up-bending posture, respectively. The corresponding displacement transmissibility derived with the harmonic balance method. The hardening and softening stiffness phenomenon may occur by tuning geometric pa-rameters. The stiffness can be tuned easily among negative, quasi-zero, zero, small positive by the initial assembly angle, length ratio and linear stiffness ratio. The zero stiffness (ZS) or quasi-zero stiffness (QZS) region can be extremely huge under some special parameters, which can broaden the working range of CBIS and benefit to large-deflection vibration isolation. The peak trans-missibility can be reduced to 7 dB or even 0 dB and the resonant frequency can be smaller than 2 Hz, which is conductive to ultra-low frequency vibration isolation. The proposed CBIS opens a new route towards tunning asymmetric stiffness for low frequency vibration isolation.