Biomimicry & NVH:
improve noise and vibration mitigation technologies
This is a technical problem that we find in many industries: to improve the comfort of product user, it is essential to reduce the noise pollution and vibrations that it generates and emits.
We need to be able to think of intelligent, absorbent structures, review coverings and conduits, rethink shock absorbers, joints, articulations or fixings of a product or component. A major challenge, especially since it often has very direct repercussions on the reliability of a technology, and therefore its security.
An expert in discretion, nature has extensive know-how in this area.
Prey and predators, to hunt or defend themselves, must be as stealthy as possible. The strategies for avoiding detection are numerous and intelligent. Animals are experts at controlling noise and vibration. To guarantee their survival, their structures and shapes must optimise “NVH performance” as much as possible.
An expert in the resistance of materials, nature also has extensive know-how in the absorption of shocks and vibrations. Any system must be multi-functional and optimised at the same time, between robustness and lightness, acoustics, and sometimes even thermo-regulation and aerodynamics.
Specialist in the field, Bioxegy explains to you why and how biomimicry allows you to find skillful and effective approaches in matters and NVH. We provide you with a selection of particularly evocative examples.
Feline pads: the necessary search for stealth
In the wild, felines occupy the top of the food chain. They are formidable predators. Even a large tiger can walk silently and stealthily thanks to the anatomy of its pads.
Very large in size compared to those of canines (dogs, wolves, foxes, etc.), these pads are extremely elastic and absorb the slightest vibration or shock. Their structure is particularly interesting to study and opens up numerous potential for innovation through biomimicry.
Felines are digitigrades: they move on the tips of their fingers. This makes them more discreet and agile, like masters of the hunt.
Their pads are essential for this. Soft and velvety, they feel the slightest vibrations of the ground, conceal their presence when moving, and are also extremely sensitive because they allow felines to identify the texture of their prey. Despite this, they are strong enough to support the entire weight of the body.
What is the secret of these mysterious pads?
They are made up of numerous elastic fibers caught in adipose tissue, that is to say containing fat cells, tight and dense. The thick outer surface, the epidermis, is made up of several layers including the stratum corneum composed of numerous layers of keratin cells, the same proteins as our nails. Below, the more flexible dermis is rich in sensory receptors, then the subcutaneous tissue (adipose tissue) plays the role of shock absorber and thermal insulator thanks to the juxtaposition of multiple fat cells.
This multilayer structure can inspire vibration damping systems in many industrial parts and components, from aeronautics to automobiles, household appliances and railways.
Crédits images : ©Chris Hubbard, Virginia Naples, Erin Ross, Burcu Carlon
The spiderweb: an expert in vibration absorption.
Spider silk is renowned for its unusual combination of lightness and extreme strength, which sometimes exceeds that of steel. Because of these properties, researchers have developped materials inspired by spider silk that are both strong and lightweight.
Until now, the acoustic properties of spider webs have not yet been explored. However, it has been discovered that the canvases have remarkable acoustic advantages. The architecture of the web, consisting of concentric circles or "rings", combined with the variable elastic properties of the radial and circumferential silk, is capable of attenuating and absorbing vibrations in wide frequency ranges, despite its lightness.
Based on this complex natural architecture, a team of researchers from Italy, France and the United Kingdom published their research on a bio-inspired acoustic metamaterial in 2016. It is a material with a specific periodic architecture which gives it remarkable properties such as blocking sound waves and mechanical vibrations.
This bio-inspired metamaterial is formed from square meshes containing resonant rings and supporting ligaments that radiate from the center of the rings outwards. According to the digital modeling carried out, this new concept inhibits low frequency sounds more effectively than other existing metamaterials.
This therefore opens the door to completely new applications through biomimicry, in particular for the construction of bridges or anti-seismic structures in architecture or in the design of innovative light vehicles with vibration-damping and shock-absorbing structures.
Crédits images : ©Marco Miniaci, Anastasiia Krushynska, Alexander B. Movchan, Federico Bosia', Nicola M. Pugno'
Grapefruit: porosity to neutralise vibrations.
Grapefruit is a very heavy fruit: its mass can reach 6 kg. Once ripe, it falls from its tree and falls ten to fifteen meters, without cracking on impact.
Its skin has a remarkable capacity to absorb shock and neutralise vibrations. Experimental results show that up to 90% of the energy on impact is dissipated during its free fall.
The outer layer of its structure, called the exocarp, is dense and rigid. Conversely, the part between the skin and the quarters, called the mesocarp, is not very dense and porous. It is loaded with intercellular air and acts like a compressible foam.
The density of pores gradually increases between the mesocarp and the exocarp, which makes these two parts difficult to distinguish. There is therefore no abrupt change in structural properties between tissues that could cause them to separate.
The PROSE (Product Synthesis Engineering) laboratory at Texas A&M University has developped a finite element model based on the non-uniform porosity of grapefruit skin. The model simulated aluminum foam with 66% of pores dispersed within 0.6 cm of the top and bottom faces of the foam.
To test the effectiveness of the porosity distribution, the team simulated the foam falling onto its upper side from a height of 1.5 meters, then measured the stress distribution. The shock caused by the impact was mainly absorbed by the upper side and did not fully propagate into the lower side, which demonstrated shock absorption properties similar to those of grapefruit.
This foam design is a remarkable illustration of biomimicry. It could be useful in applications involving significant shock or vibration. For example, in the automotive field: improve the damping of a vehicle and reduce vibrations in the transmission, internal mechanics, engine or wheels.
Crédits images : ©Ortiz J, Zhang G, DA McAdams
Other promising prospects for biomimicry in industrial sectors
