Lepidopteran insect wings or lepidopteran scales geometry solves a triple trade-off in flight materials

Harbin Institute of Technology

Modern aircraft, high-speed trains, and electric vehicles are engaged in a constant, frustrating tug-of-war with physics. To protect passengers in a crash, engineers need stiff, heavy structures that absorb brutal mechanical impacts. To shield sensitive onboard electronics and avoid radar detection, they need materials that trap electromagnetic radiation. And to make long flights tolerable, they must silence the relentless, low-pitched drone of engines.

Today, the only way to satisfy all three demands is an inefficient sandwich: a thick metal frame glued to radar-absorbing coatings and topped with bulky acoustic foams. This cumbersome stack hogs interior space, adds dead weight that burns excess fuel, and tends to peel apart over time as glue lines fatigue under flight stresses.

In the International Journal of Extreme Manufacturing, Prof. Longqiu Li at the Harbin Institute of Technology and his co-workers have eliminated the glue entirely, engineering an all-in-one printed metamaterial just 24 mm thick that carries immense weight, swallows microwave signals, and hushes low-frequency noise.

The achievement dismantles a stubborn physical bottleneck that has thwarted materials designers for decades. The dilemma comes down to air versus mass. Swallowing sound waves and matching electromagnetic impedance (the property that lets radar slip into a material instead of ricocheting right off its surface) demands high porosity and empty interior space. But the moment an engineer honeycombs a panel with holes to soak up noise, its load-bearing backbone collapses under pressure. Conversely, beefing up a material with solid walls creates a rigid shield that reflects incoming sound like a concrete wall and bounces radar like a mirror.

Nature resolved this exact dilemma millions of years ago in the delicate wings of butterflies and moths. To survive in a world of agile predators and bat sonar, lepidopteran insects evolved microscopic scale architectures that manage optical color, deaden high-frequency sound, and stay featherlight without snapping mid-flight.

Taking a cue from these intricate insect scales, Prof. Li's team designed a "hierarchical" architecture that nests two different geometries inside each other. They started with a classic hexagonal honeycomb frame, but instead of molding the internal walls out of solid plastic, they hollowed them out with a gyroid lattice - a continuous, curving 3D maze that resembles the porous channels of a sea sponge.

This nested layout operates like a multidisciplinary Swiss Army knife. Under sudden compression, ordinary honeycombs snap catastrophically at their sharp internal corners. In this bioinspired lattice, the smoothly arching gyroid pathways glide the force evenly across the entire surface, turning a brittle snap into an orderly, cushion-like crumple that absorbs 21.9 times more impact energy than a standard honeycomb of identical weight.

To trap electromagnetic waves, the team infused the interior gyroid sponge with a microscopic slurry of conductive carbon nanotubes and carbon black. Incoming radar waves enter the central cavity and plunge into the conductive maze, bouncing hundreds of times across internal surfaces until micro-currents convert the electromagnetic energy into harmless trace heat. Across a wide 2-40 GHz spectrum, the lattice swallows more than 90% of incoming wave power over 93.5% of that band.

To catch noise, Prof. Li capped each cell with a tiny perforated lid, transforming the chamber into an acoustic resonator. When sound waves strike the surface, vibrating air plunges down the neck and drags against the intricate gyroid matrix inside, exhausting its energy through thermoviscous friction. The result is an acoustic trap that captures 90% of sound energy in the persistent 600-900 Hz drone zone typical of commercial turboprop cabins.

The everyday scale of this trifunctional material is startling. In one bench test, a 74g sample was placed directly under the tire of a 1,750 kg family car, comfortably supporting a 438 kg corner load without cracking. In acoustic tests, it dropped an ear-piercing 88.5 dB screech down to a quiet 45.1 dB hum, dropping the loudness from that of an approaching diesel truck to a hushed library whisper. Crucially, the metamaterial performs the job of conventional multi-material stacks at just 36.9% of their traditional thickness, shaving away nearly two-thirds of the required bulk.

To help factory engineers tailor these panels to specific frequency ranges without waiting days for complex acoustic simulations, the authors designed a physics-based neural network based on Kolmogorov-Arnold representations. The model computes custom panel layouts in a fraction of a second while using 91% fewer parameters than standard artificial neural networks.

For manufactures, this single-piece design offers a direct pathway to ditching vulnerable glue lines and consolidating assembly lines into single-step additive manufacturing runs. Before passenger airliners or electric cars adopt the tiles, researchers must adapt the fabrication process from photosensitive resin printing to flight-grade carbon polymers and lightweight aluminum, while running fatigue tests to ensure the porous gyroid pores endure decades of non-stop flight vibrations.