Insect wings are an outstanding example of how a proper interplay of rigid and flexible materials enables an intricate flapping flight accompanied by sound. The understanding of the aerodynamics and acoustics of insect wings have enabled the development of man-made flying robotic vehicles and explained basic mechanisms of sound generation by natural flyers. This work proposes the concept of artificial wings with a periodic pattern, inspired by metamaterials, and explores how the pattern geometry can be used to control the aerodynamic and acoustic characteristics of the wing. For this, we analyzed bio-inspired wings with anisotropic honeycomb patterns flapping at a low frequency and developed a multi-parameter optimization procedure to tune the pattern design in order to increase lift and, simultaneously, manipulate the produced sound. Our analysis is based on the finite-element solution to a transient three-dimensional fluid-structure interactions problem. The two-way coupling is described by incompressible Navier-Stokes equations for viscous air and structural equations of motion for a wing undergoing large deformations. We manufactured three wing samples by means of 3D printing and validated their robustness and dynamics experimentally. Importantly, we showed that the proposed wings can sustain long-term resonance excitation that opens a possibility to implement resonance-type flights inherent to certain natural flyers. Our results confirm the feasibility of the metamaterial patterns to control the flapping flight dynamics and can open new perspectives for applications of 3D-printed patterned wings, e.g., in the design of drones with the target sound.
Excellent agreement with simulations No damage under long-term resonance exc. Design idea and analysis www.metamechanics.net Metamaterial pattern to control flight aerodynamics and acoustics Full-scale 3D modeling Explore possibilities of additive manufacturing and near-resonance flight conditions
Waveguiding is highly desirable for multiple applications but is challenging to achieve in wide continuous frequency ranges. In this work, we developed a three-dimensional phononic crystal with broadband waveguiding functionality. Waveguiding is achieved by combining two types of unit cells with different wave scattering features to create an arbitrary-curved defect path. The unit cell design is governed by contradictory requirements to induce narrow-and broad-band wave attenuation along the path and within the phononic medium, respectively. This is achieved by modulating structural parameters to activate Bragg's scattering, local resonances and inertial amplification mechanism and interplay between them. We demonstrated numerically and experimentally the waveguiding with strong wave localization and confinement in additively manufactured three-dimensional structures along straight, angle-and arbitrarycurved paths. This work opens new perspectives for the practical utilization of phononic crystals in ultrasonic sensors, medical devices, and acoustic energy harvesters.
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