Search Results (10)

This article explores the propagation behaviors of electromagnetic waves within a metamaterial structure composed of three distinct layers, nano, micro, and macro, arranged from the outermost to the innermost section. The outermost layer, which serves as the focus of this investigation, consists of carbon nanotubes. The second layer, positioned just behind the outermost coating, exhibits micro properties and features a graded structure in terms of nonlocal characteristics and material property parameters. Therefore, the analyses conducted in this micro layer are grounded in nonlocal theory. The nonlocal constant is set at values of $\eta$: 0.7, $\eta$: 0.5, and $\eta$: 0.25, with investigations carried out using a nano-graded approach. Additionally, this micro layer is configured in a material-graded manner concerning its property parameters, defined as $D$: 0.1, $D$: 0.3, and $D$: 0.7, respectively. In the micro layer, a nano-graded approach achieves the highest frequencies of electromagnetic wave propagation when the material property parameter $D$ is set at 0.5 and the nonlocal constant $\eta$ is 0.25. In contrast, the lowest frequencies of electromagnetic wave propagation are observed when the material property parameter $D$ is 0.1, and the nonlocal constant $\eta$ is 0.5. The innermost layer of the metamaterial structure is characterized by macro properties. Notably, unlike many other studies, this research specifically examines the behavior of backward electromagnetic waves, rather than traveling waves, within the context of the aforementioned metamaterial properties. The amplitude values of the reflected waves, particularly those corresponding to the backward electromagnetic waves delineated in this study, exhibit a reduction as they propagate through the metamaterial components. Full article

Functionally Graded Metamaterials (FGMMs) constitute an innovative class of materials within the realm of additive manufacturing (AM), attracting substantial attention from material science and research communities. These materials, characterized by unique designs and gradient properties, are not commonly found in nature but are deliberately engineered through the arrangement of subwavelength structures. The distinct attributes of such materials have propelled them into significant prominence across various industries, including automotive, aerospace, medical, electronics, and agriculture. This review paper aims to present a comprehensive overview of a range of techniques applied in the fabrication, design, theoretical models, and simulation methods related to these materials. It delves into the assessment of such material’s performance, specifically focusing on mechanical, thermal, and electromagnetic properties. Moreover, this review addresses advancements, challenges, and potential solutions in the field. Ultimately, it delivers valuable insights to researchers, practitioners, and stakeholders, enhancing their understanding of FGMMs and their significance in the broader context. Full article

Metamaterials exhibit unique ultrasonic properties that are not always achievable with traditional materials. However, the structures and geometries needed to achieve such properties are often complex and difficult to obtain using common fabrication techniques. In the present research work, we report a novel metamaterial acoustic delay line with built-in impedance matching that is fabricated using a common 3D printer. Delay lines are commonly used in ultrasonic inspection when signals need to be separated in time for improved sensitivity. However, if the impedance of the delay line is not perfectly matched with those of both the sensor and the target medium, a strong standing wave develops in the delay line, leading to a lower energy transmission. The presented metamaterial delay line was designed to match the acoustic impedance at both the sensor and target medium interfaces. This was achieved by introducing graded engineered voids with different densities at both ends of the delay line. The measured impedances of the designed metamaterial samples show a good match with the theoretical predictions. The experimental test results with concrete samples show that the acoustic energy transmission is increased by 120% and the standing wave in the delay line is reduced by over a factor of 2 compared to a commercial delay line. Full article

This paper thoroughly examines the advancements and challenges in the field of additively manufactured Functionally Graded Materials (FGMs). It delves into conceptual approaches for FGM design, various manufacturing techniques, and the materials employed in their fabrication using additive manufacturing (AM) technologies. This paper explores the applications of FGMs in diverse fields, including structural engineering, automotive, biomedical engineering, soft robotics, electronics, 4D printing, and metamaterials. Critical issues and challenges associated with FGMs are meticulously analyzed, addressing concerns related to production and performance. Moreover, this paper forecasts future trends in FGM development, highlighting potential impacts on diverse industries. The concluding section summarizes key findings, emphasizing the significance of FGMs in the context of AM technologies. This review provides valuable insights to researchers, practitioners, and stakeholders, enhancing their understanding of FGMs and their role in the evolving landscape of AM. Full article

In this review, we discuss a nonequilibrium thermodynamic theory for heat transport in superlattices, graded systems, and thermal metamaterials with defects. The aim is to provide researchers in nonequilibrium thermodynamics as well as material scientists with a framework to consider in a systematic way several nonequilibrium questions about current developments, which are fostering new aims in heat transport, and the techniques for achieving them, for instance, defect engineering, dislocation engineering, stress engineering, phonon engineering, and nanoengineering. We also suggest some new applications in the particular case of mobile defects. Full article

In this paper, three large curved waveguides based on Sunflower Graded photonic crystal are designed. Numerical simulations of electromagnetic beam bending in Sunflower Graded photonic crystals have shown that homogenization based on the Maxwell–Garnett theory gives very good results for steering the electromagnetic field. In contrast to the progressive bending waveguide structures based on periodic photonic crystal designs reported in the literature, this structure is not only simple in design, but also the optical wave trends in the progressive bending waveguide structures are more smooth. Sunflower structures, due to their high circular symmetry, have a great advantage in making arbitrary curved waveguides. The results have some theoretical implications for the design of optical integrated circuits and the selection of optically thin communication devices. It is also useful for the selection of meta-materials. Full article

Research on auxetic metamaterials is important due to their high performance against impact loadings and their usefulness in actuators, among other applications. These metamaterials offer a negative Poisson’s ratio at the macro level. However, usual auxetic metamaterials face challenges in (1) grading the effect, (2) coupling and combining auxetic metamaterials with non-auxetic materials due to boundary compatibility, (3) obtaining the same auxetic behavior in all directions in the transverse plane, and (4) adapting the regular geometry to the component design boundary and shape. The goal of this paper is to present a novel, recently patented tunable 3D metamaterial created to reproduce a wide spectrum of 3D auxetic and non-auxetic Poisson’s ratios and Young’s moduli. This wide range is obtained using the same basic unit cell geometry and boundary connections with neighboring cells, facilitating designs using functionally graded metamaterials as only the connectivity and position of the cell’s internal nodes are modified. Based on simple spatial triangularization, the metamaterial is easily scalable and better accommodates spatial curvatures or boundaries by changing the locations of nodes and lengths of bars. Full article

Lenses are used for multiple applications, including communications, surveillance and security, and medical instruments. In homogeneous lenses, the contour is used to control the electromagnetic propagation. Differently, graded-index lenses make use of inhomogeneous materials, which is an extra degree of freedom. This extra degree of freedom enables the design of devices with a high performance. For instance, rotationally symmetric lenses without spherical aberrations, e.g., the Luneburg lens, can be designed. However, the manufacturing of such lenses is more complex. One possible approach to implement these lenses is using metamaterials, which are able to produce equivalent refractive indices. Here, we propose a new type of three-dimensional metamaterial formed with two independent sets of wires. The double-mesh twin-wire structure permits the propagation of a first mode without cut-off frequency and with low dispersion and high isotropy. These properties are similar to periodic structures with higher symmetries, such as glide symmetry. The variations of the equivalent refractive index are achieved with the dimension of the meandered wires. The potential of this new metamaterial is demonstrated with simulated results of a Luneburg meta-lens. Full article

This paper discusses the surface-engineered nanomaterials (adaptive nano-structured physical vapor deposition (PVD) thin-film coatings) that can effectively perform under severely non-equilibrium tribological conditions. The typical features of these nanomaterials are: (a) Dynamically interacting elements present in sufficient amounts to account for its compositional/structural complexity; (b) an initial non-equilibrium state; (c) optimized micro-mechanical characteristics, and (d) intensive adaptation to the external stimuli. These could be considered as functionally graded nanomaterials that consist of two major layers: an underlying (2–3 microns) thin-film PVD coating, the surface on which an outer nanoscale layer of dynamically re-generating tribo-films is produced as a result of self-organization during friction. This tribo-film nanolayer (dissipative structures) was discovered to represent complex matter, which exhibits characteristic properties and functions common to naturally occurring systems. These include adaptive interaction with a severely non-equilibrium environment; formation of compounds such as sapphire, mullite, and garnet, similar to those that arise during metamorphism; ability to evolve with time; as well as complexity and multifunctional, synergistic behavior. Due to several nanoscale effects, this nanolayer is capable of protecting the surface with unprecedented efficiency, enabling extensive control over the performance of the entire surface-engineered system. These surface-engineered nanomaterials can achieve a range (speed and level) of adaptability to the changing environment that is not found in naturally occurring materials. Therefore, these materials could be classified as metamaterials. The second major characteristic of these materials is the structure and properties of the coating layer, which mostly functions as a catalytic medium for tribo-film generation and replenishment. A functioning example of this type of material is represented by an adaptive hard thin-film TiAlCrSiYN/TiAlCrN nano-multilayer PVD coating, which can efficiently work in an extreme environment, typical for the dry machining of hard-to-cut materials. Full article

The Laser Beam Melting (LBM) Additive Manufacturing technology for metal processing is based on the local application of an intense laser beam, causing a characteristic microstructure, which can achieve higher mechanical properties than conventionally manufactured equivalents. The material is created incrementally in sections that are processed with different manufacturing parameters. This paper proposes the creation of Designed Materials by varying the manufacturing parameters and exposure strategy in order to induce a gradient or a local change of properties by designing the microstructure. Such materials could also be created by changing the material topology on a micro-, meso-, or macro-scale, or on multiple scales at once. This enables systematic creation of material types like Functionally Graded Materials (FGMs), Metamaterials, or other Designed Materials, in which characteristics can be varied locally in order to create a customized material. To produce such materials by LBM, it is necessary to gain a detailed understanding about the influence of the manufacturing parameters. Experimental studies have been carried out to investigate the melt pool geometry and microstructure resulting from the exposure parameters. Based on the results, parameter sheets have been derived, which support the process of finding optimized parameter sets for a specific purpose. General methods and their ability to influence the material structure and properties were tested and evaluated. Furthermore, the resulting change of the microstructure was analyzed and a first Graded Material was generated and analyzed to show the potential and possibilities for Designed Materials on multiple scales by Laser Beam Melting. Full article