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

Over the past three decades a new spectroscopic technique with unique possibilities has emerged. Based on coherent and time-resolved detection of the electric field of ultrashort radiation bursts in the far-infrared, this technique has become known as terahertz time-domain spectroscopy (THz-TDS). In this review article the authors describe the technique in its various implementations for static and time-resolved spectroscopy, and illustrate the performance of the technique with recent examples from solid-state physics and physical chemistry as well as aqueous chemistry. Examples from other fields of research, where THz spectroscopic techniques have proven to be useful research tools, and the potential for industrial applications of THz spectroscopic and imaging techniques are discussed.

Terahertz spectroscopy and imaging – Modern techniques and applications

The substrate integrated waveguide (SIW) technique makes it possible that a complete circuit including planar circuitry, transitions, and rectangular waveguides are fabricated in planar form using a standard printed circuit board or other planar processing techniques. In this paper, guided wave and modes characteristics of such an SIW periodic structure are studied in detail for the first time. A numerical multimode calibration procedure is proposed and developed with a commercial software package on the basis of a full-wave finite-element method for the accurate extraction of complex propagation constants of the SIW structure. Two different lengths of the SIW are numerically simulated under multimode excitation. By means of our proposed technique, the complex propagation constant of each SIW mode can accurately be extracted and the electromagnetic bandstop phenomena of periodic structures are also investigated. Experiments are made to validate our proposed technique. Simple design rules are provided and discussed.

Guided-wave and leakage characteristics of substrate integrated waveguide

Substrate-integrated waveguide (SIW) technology represents an emerging and very promising candidate for the development of circuits and components operating in the microwave and millimetre-wave region. SIW structures are generally fabricated by using two rows of conducting cylinders or slots embedded in a dielectric substrate that connects two parallel metal plates, and permit the implementation of classical rectangular waveguide components in planar form, along with printed circuitry, active devices and antennas. This study aims to provide an overview of the recent advances in the modelling, design and technological implementation of SIW structures and components.

Review of substrate-integrated waveguide circuits and antennas

The integrated planar technique has been considered as a reliable candidate for low-cost mass production of millimeter-wave circuits and systems. This paper presents new concepts that allow for a complete integration of planar circuits and waveguide filters synthesized on a single substrate by means of metallized post (or via-hole) arrays. Analysis of the synthesized integrated waveguide and design criteria are presented for the post pitch and diameter. A filter design method derived from a synthesis technique using inductive post is presented. An experimental three-pole Chebyshev filter having 1-dB insertion loss and return loss better than 17 dB is demonstrated. Integrating such planar and nonplanar circuits on a substrate can significantly reduce size, weight, and cost, and greatly enhance manufacturing repeatability and reliability.

Single-substrate integration technique of planar circuits and waveguide filters

Breast cancer is a leading disease worldwide, and the success of medical therapies is heavily related to the availability of breast cancer imaging techniques. While current methods, mainly ultrasound, x-ray mammography, and magnetic resonance imaging, all exhibit some disadvantages, a possible alternative investigated in recent years is based on microwave and mm-wave imaging system. A key point for these systems is their reliability in terms of safety, in particular exposure limits. This paper presents a feasibility study for a mm-wave breast cancer imaging system, with the aim of ensuring safety and compliance with the widely adopted European ICNIRP recommendations. The study is based on finite element method models of human tissues, experimentally characterized by measures obtained at one of the most important European clinical center for cancer treatments. Results prove the feasibility of the system, which can meet the exposure limits while providing the required dynamic range to let the receiver detect the cancer anomaly. In addition, the dosimetric quantities used at the present and their maximum limits at mm-waves are taking into discussion and the possibility of needing moderns quantities and limitations is discussed.

Breast cancer imaging at mm-waves: Feasibility study on the safety exposure limits

We present a new algorithm well suited for the modal analysis of arbitrarily shaped cavities filled with a lossless, isotropic and homogeneous medium. The electric-wall condition is enforced on the field produced by an unknown current sheet, distributed over the cavity wall, and the resulting Electric Field Integral Equation (EFIE) is solved using the method of the moments (MM). Thanks to the special form of the kernel of the EFIE, the algebraic problem can be rearranged to yield the resonating frequencies and the associated currents as eigenvalues and eigenvectors of a standard linear eigenvalue problem. The algorithm yields all resonances up to the maximum frequency of interest by a single evaluation of the MM matrices. For this reason CPU times are reasonably short, even in finding many resonances of quite complicated cavities. The cavity shape is modelled using triangular patches and the code is interfaced with a commercial mechanical CAD.<<ETX>>

A new 3-D electromagnetic solver for the design of arbitrarily shaped accelerating cavities

This paper describes the behaviour of a planar antenna, composed by an open-ended waveguide as primary feed and a frequency selective surface (FSS) located in front of it. In particular the frequency responses adopting a capacitive or an inductive FSS are compared, showing that the latter exhibits a significant bandwidth improvement. In addition, an alternative design method is proposed and it is proven to be more effective than the standard geometrical optics approach in predicting the performance of such structures. (5 pages)

Design of a Large Bandwidth Planar Antenna using Inductive Frequency Selective Surfaces

Substrate Integrated Waveguide, an emerging technology for microwave and mm-wave circuits, can be used to manufacture several different devices, in particular couplers. A straightforward implementation for SIW couplers is based on a narrow-wall multi-hole architecture. This paper presents a semi-analytical approach, based on the quantitative determination of the SIW side leakage, to design this type of SIW couplers with arbitrary coupling. The proposed approach is verified against full-wave simulations.

http://ieeexplore.ieee.org/iel7/6679726/6686544/06686820.pdf

Substrate Integrated Waveguide couplers: A semi-analytical design approach based on side leakage

In this paper, the slotted slant ridge resonator together with different strategies for their manufacturing with 3D printing technology is illustrated The slant ridge resonator consists of a ridge with a slot inserted in a rectangular waveguide Both ridge and slot resonant modes are exploited to obtain a second order filter response (doublet) capable of two poles and two transmission zeros The structure allows an excellent control in terms of both bandwidth and transmission zero positioningThe manufacturing strategies considered in the paper consists in the 3D printing of the slotted ridge with different supports Ridge and support are then electroplated and finally inserted in a metallic rectangular waveguide ensuring the metal contact between support and waveguide Measured results demonstrating the feasibility of the method are shown

Luca Perregrini

Papers

Breast cancer imaging at mm-waves: Feasibility study on the safety exposure limits

A new 3-D electromagnetic solver for the design of arbitrarily shaped accelerating cavities

Design of a Large Bandwidth Planar Antenna using Inductive Frequency Selective Surfaces

Substrate Integrated Waveguide couplers: A semi-analytical design approach based on side leakage

Different Strategies for the Additive Manufacturing of Slotted Slant Ridge Filtering Doublet