Seahorse exoskeleton-inspired structure with linear-to-torsion transition property for low-frequency vibration isolation

Low-frequency vibrations are a persistent challenge in fields ranging from aerospace and precision instrumentation to naval engineering. With frequencies typically below 5 Hz, such vibrations can disrupt sensitive equipment, introduce measurement errors, degrade performance, and even cause structural damage.

Conventional isolators often either achieve vibration suppression at the cost of load-bearing capacity or support heavy loads while failing to isolate low-frequency disturbances. Although quasi-zero-stiffness (QZS) designs have offered improvements, they usually demand delicate tuning and remain highly sensitive to operating conditions. Hence, there is a need to develop new structures that can simultaneously provide strong support and effective ultra-low-frequency isolation.

In a recent study published in the KeAi journal Fundamental Research, a team of researchers led by Professor Bo Yan at the School of Mechanical Engineering, Zhejiang Sci-Tech University, drew inspiration from nature to design a novel bio-inspired isolator.

The researchers observed that the square exoskeleton of seahorse twists under force to dissipate impact. Translating this principle into engineering, they developed a structure capable of converting linear motion into torsional motion. Through the integration of a rotating disc and springs, the system generates advantageous nonlinear effects, broadening the isolation bandwidth while maintaining load-bearing performance.

The study highlights two key innovations:

1. Linear-to-torsion transition: The combination of oblique rods and a rotating disc introduces torsional inertia and an anti-resonance effect, effectively lowering the resonant frequency to achieve low-frequency isolation.

1. Nonlinear force design: Using geometric modeling and Lagrange equation together with the harmonic balance method, the team established quantitative relationships between parameters such as spring placement, disc radius, and hinge damping and the QZS region, providing systematic theoretical guidance for engineering design.

“In subsequent tests, a prototype built on a vibration exciter produced results consistent with simulations,” shares Yan, “Under typical conditions, the system achieved a peak transmissibility of about 1.7 at 2 Hz, but by increasing the initial disc angle or adjusting the rod length ratio, the peak transmissibility was reduced to 1.2, while the resonant frequency shifted to 1.5 Hz.”

These findings demonstrate that the structure provides excellent low-frequency isolation performance, Further, the team found that seahorse-exoskeleton-inspired structures achieved a minimum resonant frequency of 1.5 Hz, enabled by the combined effects of torsional inertia and anti-resonance.

“This confirms the effectiveness of the bio-inspired transition mechanism in the critical low-frequency range,” adds Yan. “Spring placement and angle can be adjusted to switch between positive and negative stiffness and expand the isolation range; hinge damping can effectively suppress resonance peaks; and nonlinear damping increases with vibration amplitude, ensuring strong performance even under severe disturbances.

The team hopes that this breakthrough can move beyond the laboratory and be applied to real-world needs in precision instruments, aerospace systems, and marine equipment.  “Nature has provided us with inspiration, while engineering modeling and experimental validation have ensured feasibility,” says Yan.

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Contact the author: Hongye Ma, School of Mechanical Engineering, Zhejiang Sci-Tech University, Hangzhou 310018, China. mahongye@zstu.edu.cn

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