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

In this paper, experimental results are presented for microstrip symmetrical-gap discontinuities. The experimental technique is based on the measurement of the resonant frequencies of several gap-coupled rectangular microstrip resonators. In particular, gap discontinuities on anisotropic dielectric and two-layer composite substrates have been investigated. Reasonably good agreement has been found in most cases between theoretical data [obtained by means of the excess charge technique in the spectral domain (EC-SDA)] and experimental data, even though the theoretical results have been obtained by using a quasi-static approach.

Comparison between theoretical and measured microstrip gap parameters involving anisotropic substrates

This chapter discusses several kinds of balanced‐to‐balanced power divider/ combiner. As the key component in a balanced RF transceiver, the concept of balanced‐to‐balanced power divider/combiner is proposed, which divides the input differential‐mode power into several ways with good port isolation and common‐mode suppression. To extend the applications of balanced‐to‐balanced power dividers, the chapter designs a dual‐band balanced‐to‐balanced power divider. It introduces balanced‐to‐balanced Wilkinson power dividers implemented using microstrip technology. The desired performance of the balanced‐to‐balanced Gysel power divider has been implemented with the half‐mode substrate integrated waveguides (SIWs) ring structure, and a high power handling capability can be expected. The balanced‐to‐balanced power dividers are designed in Wilkinson and Gysel topologies and realized in microstrip line and half‐mode SIW. They are also designed with arbitrary power division ratio, bandpass filtering response, and dual‐band operation.

Balanced power dividers/combiners

Subwavelength imaging of the near field of a magnetic line-source excitation is studied for several wire-medium (WM) lens topologies using complex-plane analysis of the radiation integral. Nonlocal homogenization is used for the wire medium, resulting in an analytical expression for the transfer function of the lens. It is shown that by evaluating the Sommerfeld integral of the transmitted field in terms of the discrete and continuous spectra provides a general framework for better understanding of electromagnetic phenomena involved with subwavelength imaging. Results are obtained for a WM slab, and for a wire medium loaded with graphene monolayers and periodic arrays of graphene patches, demonstrating the interplay of the discrete and continuous spectral components in different operating regimes of the lenses. The imaging with a stack of silver slabs is also considered for comparison purposes.

Excitation of Discrete and Continuous Spectrum in Subdiffraction Wire-Medium Type Lenses

Developing Processing Parameters for Nickel-base Superalloys for the Electron Beam Melting Additive Manufacturing Process

In this work a double annular aperture frequency selective surface is analyzed from an equivalent circuit perspective. A comparison between full wave numerical solution and the proposed equivalent circuit results is provided for different examples. A very good agreement is obtained endowing the equivalent circuit with great potential as a very powerful and efficient design tool for advanced space filters.

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Francisco Medina

Papers

Comparison between theoretical and measured microstrip gap parameters involving anisotropic substrates

Balanced power dividers/combiners

Excitation of Discrete and Continuous Spectrum in Subdiffraction Wire-Medium Type Lenses

Developing Processing Parameters for Nickel-base Superalloys for the Electron Beam Melting Additive Manufacturing Process

Equivalent circuit for double annular aperture frequency selective surfaces