Material design and structural color inspired by biomimetic approach

Abstract

Generation of structural color is one of the essential functions realized by living organisms, and its industrial reproduction can result in numerous applications. From this viewpoint, the mechanisms, materials, analytical methods and fabrication technologies of the structural color are reviewed in this paper. In particular, the basic principles of natural photonic materials, the ideas developed from these principles, the directions of applications and practical industrial realizations are presented by summarizing the recent research results.     

A biomimetic accelerometer inspired by the cricket's clavate hair

Crickets use so-called clavate hairs to sense (gravitational) acceleration to obtain information on their orientation. Inspired by this clavate hair system, a one-axis biomimetic accelerometer has been developed and fabricated using surface micromachining and SU-8 lithography. An analytical model is presented for the design of the accelerometer, and guidelines are derived to reduce responsivity due to flow-induced contributions to the accelerometer''s output. Measurements show that this microelectromechanical systems (MEMS) hair-based accelerometer has a resonance frequency of 320 Hz, a detection threshold of 0.10 ms⁻² and a dynamic range of more than 35 dB. The accelerometer exhibits a clear directional response to external accelerations and a low responsivity to airflow. Further, the accelerometer''s physical limits with respect to noise levels are addressed and the possibility for short-term adaptation of the sensor to the environment is discussed.     

Reliability-based optimal structural design by the decoupling approach

A decoupling approach for solving optimal structural design problems involving reliability terms in the objective function, the constraint set or both is discussed and extended. The approach employs a reformulation of each problem, in which reliability terms are replaced by deterministic functions. The reformulated problems can be solved by existing semi-infinite optimization algorithms and computational reliability methods. It is shown that the reformulated problems produce solutions that are identical to those of the original problems when the limit-state functions defining the reliability problem are affine. For nonaffine limit-state functions, approximate solutions are obtained by solving series of reformulated problems. An important advantage of the approach is that the required reliability and optimization calculations are completely decoupled, thus allowing flexibility in the choice of the optimization algorithm and the reliability computation method.     

Axiomatic approach to structural design

As civil engineering enters the 21st century, the demands on the profession will move toward complex, interdisciplinary tasks such as infrastructure rehabilitation, environmental cleanup, and the delivery of high-technology facilities (e.g., hospitals, R&D laboratories, and advanced manufacturing plants). The current structural design paradigm is a top-down process that includes a nonhomogeneous approach to decision-making. There is an apparent lack of basic principles to formalize and evaluate conceptual design decisions while preliminary and detailed design decisions reflect increasing formalization and reliance on computational methods. This nonhomogeneous approach to decision-making limits how well the practicing engineer can meet the impending design challenges; particularly since conceptual design decisions determine a significant portion of a project's total cost. Axiomatic design is presented as a systematic framework for structural design because it aids the designer in satisfying multiple design objectives in a homogeneous manner throughout the design process. It is also an effective framework for formalizing and evaluating conceptual design decisions. The design of a structural frame for an innovative mechanical parking system is presented as an illustrative case study. This paper represents an initial effort to apply the principles of axiomatic design to the domain of civil engineering structures.     

Towards a biomimetic gyroscope inspired by the fly's haltere using microelectromechanical systems technology

Flies use so-called halteres to sense body rotation based on Coriolis forces for supporting equilibrium reflexes. Inspired by these halteres, a biomimetic gimbal-suspended gyroscope has been developed using microelectromechanical systems (MEMS) technology. Design rules for this type of gyroscope are derived, in which the haltere-inspired MEMS gyroscope is geared towards a large measurement bandwidth and a fast response, rather than towards a high responsivity. Measurements for the biomimetic gyroscope indicate a (drive mode) resonance frequency of about 550 Hz and a damping ratio of 0.9. Further, the theoretical performance of the fly''s gyroscopic system and the developed MEMS haltere-based gyroscope is assessed and the potential of this MEMS gyroscope is discussed.     

The toughening mechanism of nacre and structural materials inspired by nacre

Abstract

The structure and the toughening mechanism of nacre have been the subject of intensive research over the last 30 years. This interest originates from nacre’s excellent combination of strength, stiffness and toughness, despite its high, for a biological material, volume fraction of inorganic phase, typically 95%. Owing to the improvement of nanoscale measurement and observation techniques, significant progress has been made during the last decade in understanding the mechanical properties of nacre. The structure, microscopic deformation behavior and toughening mechanism on the order of nanometers have been investigated, and the importance of hierarchical structure in nacre has been recognized. This research has led to the fabrication of multilayer composites and films inspired by nacre with a layer thickness below 1 μm. Some of these materials reproduce the inorganic/organic interaction and hierarchical structure beyond mere morphology mimicking. In the first part of this review, we focus on the hierarchical architecture, macroscopic and microscopic deformation and fracture behavior, as well as toughening mechanisms in nacre. Then we summarize recent progress in the fabrication of materials inspired by nacre taking into consideration its mechanical properties.     

Progress in discovery and structural design of color conversion phosphors for LEDs

Phosphor materials enable the optical frequency conversion to realize the full-color white emission light-emitting diodes (LEDs). So far much effort has been devoted to the design and discovery of novel LED phosphors for solid state lighting. In this review, firstly, we briefly describe several representative families of LED phosphors. Secondly, we propose the design methodology aimed at discovery of new phosphors with focus on the crystal structural considerations. Thirdly, we review the results of our work and other researchers on the recent advances in discovery and structural design of LED phosphors that exemplify the adopted strategies, including (1) design of the novel phosphors from the existed structural models, (2) discovery of novel phosphors from new crystal materials by doping and (3) structural modification of the known phosphors. The importance on the structure-property relations and recently reported methodologies involved in the crystal chemistry analysis for the discovery of LED phosphors, including mineral-inspired structural model design, exploratory crystal growth via single particle diagnostic approach, chemical unit cosubstitution, and so on, have been summarized in this review. We finally discuss the topics of structure-related active investigations and future opportunities for new and improved host materials for the color conversion applied in LEDs.     

A novel biomimetic approach to the design of high-performance ceramic–metal composites

The prospect of extending natural biological design to develop new synthetic ceramic–metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine-scale laminated ceramic–metal (bulk) composites that are inexpensive, lightweight and display exceptional damage-tolerance properties. Specifically, Al₂O₃/Al–Si laminates with ceramic contents up to approximately 40 vol% and with lamellae thicknesses down to 10 µm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa√m at a tensile strength of approximately 300 MPa. Salient toughening mechanisms are described together with further toughening strategies.     

Microstructures of chafer cuticle and biomimetic design

Insect cuticle has high strength and high fracture-toughness. The superior material properties are closely related to the various particular microstructures in the cuticle, which has passed through natural optimization for thousands of years. In this work, a scanning electron microscope (SEM) was used for observing the various microstructures in a chafer cuticle. The observation revealed that there are several special microstructures that include helicoidal layups, round-hole-fiber arrangements and branched fibers in the cuticle. These microstructures were analyzed in order to learn more about the strength and toughness mechanisms of these microstructures. Several biomimetic composites were then designed and fabricated with special processes and moulds. Obtained biomimetic composites were tested for investigating their strength and toughness and then compared with those of conventional man-made composites. It was shown that the mechanical properties of the biomimetic composites are remarkably better than those of the corresponding conventional man-made composites.     

Tunable structural color in organisms and photonic materials for design of bioinspired materials

Abstract

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.     

Tunable structural color in organisms and photonic materials for design of bioinspired materials

In this paper, the key topics of tunable structural color in biology and material science are overviewed. Color in biology is considered for selected groups of tropical fish, octopus, squid and beetle. It is caused by nanoplates in iridophores and varies with their spacing, tilting angle and refractive index. These examples may provide valuable hints for the bioinspired design of photonic materials. 1D multilayer films and 3D colloidal crystals with tunable structural color are overviewed from the viewpoint of advanced materials. The tunability of structural color by swelling and strain is demonstrated on an example of opal composites.     

A unified parametric design approach to structural shape optimization

This paper presents a general parametric design approach for 2-D shape optimization problems. This approach has been achieved by integrating practical design methodologies into numerical procedures. It is characterized by three features: (i) automatic selection of a minimum number of shape design variables based on the CAD geometric model; (ii) integration of sequential convex programming algorithms to solve equality constrained optimization problems; (iii) efficient sensitivity analysis by means of the improved semi-analytical method. It is shown that shape design variables can be either manually or systematically identified with the help of equality constraints describing the relationship between geometric entities. Numerical solutions are performed to demonstrate the applicability of the proposed approach. A discussion of the results is also given:     

A branched material based on biomimetic design: Synthesis and electrochemical properties

Based on the biomimetic route the metal material with tree-like fractal structure was prepared, which showed a rough surface observed by scanning electron microscopy. According to the electrochemical experiments, the formed material exhibited the strong catalytic capability as an electrode in hydrogen evolution reaction, comparing with other conventional structure materials under comparable scales. We suggested this promotion of property arose from the contribution of the great surface area and the excellent connectivity offered from the fractal structure.     

Permanent magnets for Faraday rotators inspired by the design of the magic sphere

Faraday polarization rotators are commonly used in laser experiments. Most Faraday materials have a nonnegligible absorption, which is a limiting factor for high power laser optical isolators or for intracavity optical diodes. By using a stronger magnetic field and a shorter length of Faraday material, one can obtain the same polarization rotation and a reduced absorption. In this paper, we describe two permanent magnet arrangements that are easy to build and produce magnetic fields up to 1.7 T, substantially more than commonly used. The field homogeneity is largely sufficient for a 30 dB isolation ratio. We finally discuss the prospects for producing even larger fields with permanent magnets.