There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Additive manufacturing of metallic components – Process, structure and properties

Freedom of design, mass customisation, waste minimisation and the ability to manufacture complex structures, as well as fast prototyping, are the main benefits of additive manufacturing (AM) or 3D printing. A comprehensive review of the main 3D printing methods, materials and their development in trending applications was carried out. In particular, the revolutionary applications of AM in biomedical, aerospace, buildings and protective structures were discussed. The current state of materials development, including metal alloys, polymer composites, ceramics and concrete, was presented. In addition, this paper discussed the main processing challenges with void formation, anisotropic behaviour, the limitation of computer design and layer-by-layer appearance. Overall, this paper gives an overview of 3D printing, including a survey on its benefits and drawbacks as a benchmark for future research and development.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

This paper reviews the state-of-the-art of an important, rapidly emerging, manufacturing technology that is alternatively called additive manufacturing (AM), direct digital manufacturing, free form fabrication, or 3D printing, etc. A broad contextual overview of metallic AM is provided. AM has the potential to revolutionize the global parts manufacturing and logistics landscape. It enables distributed manufacturing and the productions of parts-on-demand while offering the potential to reduce cost, energy consumption, and carbon footprint. This paper explores the material science, processes, and business consideration associated with achieving these performance gains. It is concluded that a paradigm shift is required in order to fully exploit AM potential.

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Metal Additive Manufacturing: A Review

Natural structural materials are built at ambient temperature from a fairly limited selection of components. They usually comprise hard and soft phases arranged in complex hierarchical architectures, with characteristic dimensions spanning from the nanoscale to the macroscale. The resulting materials are lightweight and often display unique combinations of strength and toughness, but have proven difficult to mimic synthetically. Here, we review the common design motifs of a range of natural structural materials, and discuss the difficulties associated with the design and fabrication of synthetic structures that mimic the structural and mechanical characteristics of their natural counterparts.

Bioinspired structural materials

Periodic printed metallodielectric structures have been used for a long time to control the transmission, absorption and polarization of electromagnetic waves from the RF / microwave domains up to the optical range. During the last two decades, the modeling of these structures has become a popular research topic due several incentives. Such incentives are both of technical (frequency selective surfaces, reflectarrays, planar lenses, etc.) and scientific (extraordinary transmission, exotic diffraction effects, etc.) nature. In this contribution we present some recent advances carried out by our research group along two directions: (i) approximate analytical circuit-like models, and (ii) highly efficient computational methods. The goal is to develop fast and accurate tools to be used in conjunction with optimizers to design antennas, filters and other devices. These techniques also provide simple models to explain the exotic behavior of some periodic structures.

Analytical and highly efficient numerical modeling of electromagnetic periodic structures

In this paper, we report on the analysis of transmissivity of electromagnetic waves through a stack of dielectric slabs loaded with atomically thin graphene sheets at low-terahertz frequencies. It is observed that the structure supports a series of bandpass regions separated by bandgap regions, similar to the case of stacked metallic meshes separated by dielectric slabs at microwave/THz frequencies or metal-dielectric stack at optical frequencies. The transmission resonances in the bandpass region are identified as coupled Fabry-Perot resonances associated with the individual dielectric slabs loaded with graphene sheets. The study is carried out using a simple circuit theory model, with the results verified against the numerical simulations.

Low-terahertz transmissivity with a graphene-dielectric micro-structure

This work reports on a modified version of λ/2 open stubs bandpass filters (λ/2-OSBPFs) and λ/4 open stubs bandstop filters (λ/4-OSBSFs) for wide/narrow bandwidth operation. When wide bandwidths (for λ/2-OSBPF) or narrow bandwidths (for λ/4-OSBSF) are required, conventional microstrip implementation of this kind of filters is not possible owing to unattainable high stub characteristic impedance values, which lead to extremely narrow strips. To overcome this drawback, we propose the introduction of slots under the stubs along the grounded backside of the substrate. This provides additional flexibility for the width of the strips printed on the upper side of the substrate, which can be much wider than without the slots. To avoid undesired resonances of the slot mode and radiation problems, printed narrow strip short circuits are distributed along the slotted regions. It is shown that the presence of these strips does not meaningfully affect the filter performance while suppresses the undesired slot mode effects. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:1242–1246, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26792

Bandpass and bandstop filters based on open stubs with ground plane slots

This chapter introduces two types of balanced filters with dual operation bands utilizing the potential substrate integrated waveguide (SIW) technology. For the first type of dual‐band balanced bandpass filters (BPF), it is constructed by utilizing the TE
101
 and TE
102
 modes, where the common‐mode (CM) signals are effectively suppressed by the balanced sections resonating at the TE
102
 mode. As for the second type of dual‐band balanced BPF, it is designed by the adoption of TE
101
, TE
102
, TE201, and TE
202
 modes, where the CM signals are effectively suppressed by the balanced sections resonating at the TE
102
 and TE
202
 modes. The chapter shows a typical SIW cavity configuration. It deals with a new dual‐band balanced filter using high‐order resonant modes in SIW cavities. Specifically, in the differential‐mode (DM) response, the first passband is derived by the dominant modes, while the second passband is obtained by employing the higher‐order modes in the SIW cavities.

Dual‐band balanced filters implemented in substrate integrated waveguide (siw) technology

In this Letter, the mixed potential integral equation (MPIE) method is used in conjunction with the complex images technique to carry out a full-wave analysis of a multiconductor coplanar waveguide (CPW) embedded in a layered substrate. Special attention is paid to the correct application of the method so as to maintain high accuracy and stability of the numerical results. It is shown that the procedure only provides a robust and accurate approach when the complex images expansion variable is properly chosen and the singularities of the Green's functions are properly handled. Numerical problems arise in any other case. In particular, it is demonstrated that the two-level sampling scheme used by some authors is not enough to overcome the numerical problems. However, the two-level sampling method is shown to be essential to deal with the presence of extremely thin substrate layers such as those found in multichip-module-deposition (MCM-D) technologies. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 198–203, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10416

Francisco Medina

Papers

Analytical and highly efficient numerical modeling of electromagnetic periodic structures

Low-terahertz transmissivity with a graphene-dielectric micro-structure

Bandpass and bandstop filters based on open stubs with ground plane slots

Dual‐band balanced filters implemented in substrate integrated waveguide (siw) technology

Robust application of the complex images technique to the full-wave analysis of slot-like transmission lines