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

In this presentation it will be discussed how to obtain analytical or quasi-analytical equivalent circuits to deal with periodic structures such as frequency selective surfaces and/or metasurfaces. Both the topology and the values of the involved elements of these circuits are obtained from a basic rationale to solve the corresponding integral equation. This procedure, besides providing a very efficient analysis/design tool, allows for a good physical insight into the operating mechanisms of the structure in contrast with the almost blind numerical scheme of commercial simulators.

Physically-insightful equivalent circuit models for electromagnetic periodic structures

In this paper the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an LC series resonator modelling the feed plus two capacitively coupled LC parallel resonators accounting for the radiating patches. Then, a de-embedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modelling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments.

Design of Broadband Aperture-Coupled Stacked Microstrip Antennas using Second-Order Filter Theory

In this paper, a transmission-line model is developed for the computation of the insertion loss of magnetostatic-surface wave transducers and measurements are carried out by the authors to check this model. In a first step of the analysis, closed-form expressions for the solution of the telegrapher's equations for the two microstrip transducers are obtained. The insertion loss is then derived 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, these quantities being, in general, complex. In a second step, these transmission-line parameters are numerically computed by applying a full-wave method-of-moments technique. Thus, the theoretical results obtained are found to be in good agreement with experimental results.

Insertion loss of magnetostatic-surface wave transducers $transmission-line model and experiment

Coupled‐resonators are widely used for implementing narrowband bandpass filters, which are essential components for many RF/microwave applications. This chapter starts by designing a balanced single‐band bandpass filter based on conventional coupled resonators. Next, several types of common‐mode (CM) rejection stages (which are the basic unit cells of artificial differential lines with CM rejection) are cascaded with the basic filter to verify how effectively CM rejection is significantly improved without altering the differential‐mode (DM) response. The chapter demonstrates that differential lines providing CM rejection over a desired frequency band can be used to improve the response of balanced filters with poor CM performance. This has been done for both single‐band and dual‐band implementations. The LC‐loaded lines are intended to be applied to reject the CM transmission in a balanced dual‐band bandpass filter. The filter itself are implemented using two pairs of coupled resonators.

Coupled‐resonator balanced bandpass filters with common‐mode suppression differential lines

This paper reports on differential printed transmission lines which yield a very good matching for differential-mode and strong rejection for the common-mode. The new differential lines are inspired on the concept of metamaterial transmission lines. Circuit model predictions, electromagnetic simulations and experimental results are quite satisfactory.

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Francisco Medina

Papers

Physically-insightful equivalent circuit models for electromagnetic periodic structures

Design of Broadband Aperture-Coupled Stacked Microstrip Antennas using Second-Order Filter Theory

Insertion loss of magnetostatic-surface wave transducers $transmission-line model and experiment

Coupled‐resonator balanced bandpass filters with common‐mode suppression differential lines

Microstrip/CPW differential lines for common-mode suppression