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.

/pdf/metal-additive-manufacturing-a-review-lwo0wxslqj.pdf

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

Extraordinary optical transmission (EOT) is a phenomenon which has received extraordinary attention since its discovery, twelve years ago. The phenomenon takes place at any frequency range — not only at the optical regime —, and it has been explained in terms of the excitation of surface waves along the periodically structured metal screens used in the experiments. EOT also takes place, however, through slit gratings for a polarization precluding the excitation of such surface waves. It can be also observed through electrically small diaphragms located inside hollow pipe waveguides. Along the last three years, some of the authors have developed models explaining the phenomenon in terms of simple concepts extracted from conventional waveguide theory. The models lead themselves to simple circuit equivalents which help the understanding of the underlying physics. This paper summarizes the main results obtained by the members of the group and some other collaborators concerning the capabilities of the proposed approach.

Advances on circuit modeling of extraordinary transmission

Transmission through stacked perforated metallic screens (2-D metallic meshes) printed on thin dielectric layers is studied at microwave frequencies using simple circuit models. The physical mechanisms of the transmission resonances are clearly explained and the most relevant parameters of the circuit are accurately determined. The results of the circuit model are tested by a proper comparison with previously obtained numerical and experimental results. The observed transmission peaks and lower/upper frequency band edges of the pass-band are explained in terms of the behaviour of a finite number of strongly coupled Fabry-Perot resonators using the circuit model.

http://ieeexplore.ieee.org/iel5/5497865/5504894/05505306.pdf

Analytical modelling and experimental verification of Fabry-Pérot resonances in multilayer sub-wavelength partially-reflecting surfaces

Two new compact balanced-to-balanced diplexers composed of two multiband balanced bandpass filters in a multilayer configuration are proposed in this letter to perform dual- and tri-band responses. The balanced bandpass filters are based on the use of magnetically coupled open-loop resonators. The magnetic coupling results in a strong inherent common-mode rejection, greater than 40 dB within all the dual-band diplexer passbands and greater than 30 dB for the tri-band diplexer passbands. All passbands in both diplexers are close to each other and well separated thanks to the presence of several transmission zeroes between them. Operating frequencies have been selected to be within the L band, used for many applications such as mobile services or satellite navigation. Specifically, the dual-band diplexer passbands are located at 1.08/1.58 GHz and 1.3/1.8 GHz with fractional bandwidths of 7/5.2 % and 7.4/5.5 %, while the tri-band diplexer passbands are located at 1.7/2.2/2.79 GHz and 1.97/2.37/2.95 GHz with fractional bandwidths of 4.1/4.6/3.5 % and 5.6/4.6/3.7 %. Measurements of two different prototypes are provided to validate the obtained simulation results, illustrating in this manner the usefulness of the proposed design methodology.

https://ieeexplore.ieee.org/ielx7/6287639/6514899/09966600.pdf

Compact Multilayered Balanced-to-Balanced Dual- and Tri-Band Diplexers Based on Magnetically Coupled Open-Loop Resonators

A critical discussion on the computation of the dispersion diagram in periodic one-dimensional guiding structures is carried out. In particular, an analysis is presented of the pros and cons of combined methods that make use of full-wave simulations done with commercial software packages with further analytical post-processing based on simplifications brought by an equivalent circuit model of the structure. Some of the most common methods reported in the literature are reviewed and their advantanges and limitations highlighted. Our discussion is complemented with several selected numerical examples in order to discuss the most relevant aspects that a potential user of these methods should be aware of. Special attention is paid to the relevant role played by the high-order coupling between the two halves of a symmetric unit cell of the periodic structure.

/pdf/on-the-computation-of-the-dispersion-diagram-of-symmetric-4096i1ddkl.pdf

On the Computation of the Dispersion Diagram of Symmetric Periodic One-dimensional Structures

A method is shown for the computation of the insertion loss of magnetostatic-surface wave transducers. In the first step of the method, a closed-form expression is derived for the solution of the telegrapher's equations for the microstrip transducers. The insertion loss is then obtained from this solution as a function of three transmission line parameters, i. e., the propagation constant and the characteristic impedance of the YIG-loaded microstrip line and the mutual inductance between the two microstrips. In the second step, these transmission line parameters are numerically computed by applying a full-wave method of moments technique. The theoretical results obtained have been found to be in good agreement with experimental results.

Francisco Medina

Papers

Advances on circuit modeling of extraordinary transmission

Analytical modelling and experimental verification of Fabry-Pérot resonances in multilayer sub-wavelength partially-reflecting surfaces

Compact Multilayered Balanced-to-Balanced Dual- and Tri-Band Diplexers Based on Magnetically Coupled Open-Loop Resonators

On the Computation of the Dispersion Diagram of Symmetric Periodic One-dimensional Structures

A new method for the computation of the insertion loss of magnetostatic-surface wave transducers