Surface-enhanced Raman spectroscopy (SERS) and related spectroscopies are powered primarily by the concentration of the electromagnetic (EM) fields associated with light in or near appropriately nanostructured electrically-conducting materials, most prominently, but not exclusively high-conductivity metals such as silver and gold. This field concentration takes place on account of the excitation of surface-plasmon (SP) resonances in the nanostructured conductor. Optimizing nanostructures for SERS, therefore, implies optimizing the ability of plasmonic nanostructures to concentrate EM optical fields at locations where molecules of interest reside, and to enhance the radiation efficiency of the oscillating dipoles associated with these molecules and nanostructures. This review summarizes the development of theories over the past four decades pertinent to SERS, especially those contributing to our current understanding of SP-related SERS. Special emphasis is given to the salient strategies and theoretical approaches for optimizing nanostructures with hotspots as efficient EM near-field concentrating and far-field radiating substrates for SERS. A simple model is described in terms of which the upper limit of the SERS enhancement can be estimated. Several experimental strategies that may allow one to approach, or possibly exceed this limit, such as cascading the enhancement of the local and radiated EM field by the multiscale EM coupling of hierarchical structures, and generating hotspots by hybridizing an antenna mode with a plasmonic waveguide cavity mode, which would result in an increased local field enhancement, are discussed. Aiming to significantly broaden the application of SERS to other fields, and especially to material science, we consider hybrid structures of plasmonic nanostructures and other material phases and strategies for producing strong local EM fields at desired locations in such hybrid structures. In this vein, we consider some of the numerical strategies for simulating the optical properties and consequential SERS performance of particle-on-substrate systems that might guide the design of SERS-active systems. Finally, some current theoretical attempts are briefly discussed for unifying EM and non-EM contribution to SERS.

Electromagnetic theories of surface-enhanced Raman spectroscopy

By using a coplanar waveguide (CPW) feed with a widened tuning stub, a square slot antenna for broadband operation is presented. Experimental results show that the impedance matching for the proposed antenna strongly depends on the location of the tuning stub in the square slot, and the impedance bandwidth is mainly determined by the width and length of the tuning stub. By properly choosing the location and the size of the tuning stub, a wide impedance bandwidth of 60% can be obtained, which is about 1.9 times that of a conventional CPW-fed square slot antenna with a simple tuning stub. Details of the experimental results are presented and discussed.

Broadband CPW-fed square slot antennas with a widened tuning stub

Wireless communication has led to an explosive growth of emerging consumer and military applications of radio frequency (RF), microwave and millimeter wave circuits and systems. Future personal (hand-held) and ground communications systems as well as communications satellites necessitate the use of highly integrated RF front-ends, featuring small size, low weight, high performance and low cost. Continuing chip scaling has contributed to the extent that off-chip, bulky passive RF components, such as high-Q inductors, ceramic and SAW filters, varactor diodes and discrete PIN diode switches, have become limiting. Micro-machining or MEMS technology is now rapidly emerging as an enabling technology to yield a new generation of high-performance RF-MEMS passives to replace these off-chip passives in wireless communication (sub)systems. This paper reviews the progress in RF-MEMS from a device and integration perspective. The worldwide state-of-the-art of RF-MEMS devices including switches, variable capacitors, resonators and filters are described. Next, it is stipulated how integration of RF-MEMS passives with other passives (as inductors, LC filters, SAW devices, couplers and power dividers) and, active circuitry (ASICs, RFICs) can lead to the so-called RF-MEMS system-in-a-package (RF-MEMS-SiP) modules. The evolution of the RF-MEMS-SiP technology is illustrated using IMEC's microwave multi-layer thin-film MCM-D technology which today already serves as a technology platform for RF-SiP.

https://iopscience.iop.org/article/10.1088/0960-1317/13/4/323/pdf

MEMS for wireless communications: 'from RF-MEMS components to RF-MEMS-SiP'

The data-science revolution is poised to transform the way photonic systems are simulated and designed. Photonic systems are, in many ways, an ideal substrate for machine learning: the objective of much of computational electromagnetics is the capture of nonlinear relationships in high-dimensional spaces, which is the core strength of neural networks. Additionally, the mainstream availability of Maxwell solvers makes the training and evaluation of neural networks broadly accessible and tailorable to specific problems. In this Review, we show how deep neural networks, configured as discriminative networks, can learn from training sets and operate as high-speed surrogate electromagnetic solvers. We also examine how deep generative networks can learn geometric features in device distributions and even be configured to serve as robust global optimizers. Fundamental data-science concepts framed within the context of photonics are also discussed, including the network-training process, delineation of different network classes and architectures, and dimensionality reduction. Neural networks can capture nonlinear relationships in high-dimensional spaces and are powerful tools for photonic-system modelling. This Review discusses how deep neural networks can serve as surrogate electromagnetic solvers, inverse modelling tools and global device optimizers.

Deep neural networks for the evaluation and design of photonic devices

An up-to-date literature overview on relevant approaches for controlling circuital characteristics and radiation properties of dielectric resonator antennas (DRAs) is presented The main advantages of DRAs are discussed in detail, while reviewing the most effective techniques for antenna feeding as well as for size reduction Furthermore, advanced design solutions for enhancing the realized gain of individual DRAs are investigated In this way, guidance is provided to radio frequency (RF) front-end designers in the selection of different antenna topologies useful to achieve the required antenna performance in terms of frequency response, gain, and polarization Particular attention is put in the analysis of the progress which is being made in the application of DRA technology at millimeter-wave frequencies

/pdf/dielectric-resonator-antennas-basic-concepts-design-3dxtctyxib.pdf

Dielectric Resonator Antennas: Basic Concepts, Design Guidelines, and Recent Developments at Millimeter-Wave Frequencies

A bow-tie slot antenna fed by CPW is introduced. It is designed to work in the Ku- band around 15.5 GHz. The proposed antenna is analysed both theoretically and experimentally. The presented results include the return loss and the radiation patterns. Two different geometries of the bow-tie antenna are presented and compared. The proposed antenna has several advantages such as a very large bandwidth, good control of its input impedance, and ease of fabrication. The proposed antenna has a dipole like radiation pattern which makes it suitable for mobile communication systems designed to work in the Ku- band.

Bow-tie slot antenna fed by CPW

A novel planar slot antenna is presented in this paper. The antenna provides dual-polarization and omnidirectional radiation patterns. Hence, it is suitable for hand-held equipments of wireless systems. The proposed antenna is optimized for operation at 5.2 GHz. The antenna, without ground plane extension, occupies an area of 2.17/spl times/2.17 cm/sup 2/. An impedance bandwidth of 10.6% is obtained, with a very good isolation between the two excitation ports. Appealing omnidirectional radiation patterns are maintained over the entire impedance bandwidth. The gains of the two polarizations are 2.59 and 3.52 dB, while the radiation efficiencies are 93% and 99.8%.

Dual-polarized omnidirectional planar slot antenna for WLAN applications

The performance of metal-insulator-metal (MIM) diodes is investigated. In this paper, we derive an analytical model that uses the Transfer Matrix Method based on the Airy Functions (AF-TMM) for the tunneling transmission probability through any number of insulating layers. The fast-computing AF-TMM simulator results show a complete matching with the numerical Non-Equilibrium Green's Function and a reasonable matching with previously published experimental results. This study shows the effect of the work function difference and insulator thickness on MIM diode performance. The advantage of using two insulator layers on enhancing the diode responsivity, resistance, and nonlinearity is also investigated.

Theoretical Study of Metal-Insulator-Metal Tunneling Diode Figures of Merit

A new technique for design centering of microwave circuits is introduced. This technique exploits the space-mapping interpolating surrogate (SMIS) with a modified ellipsoidal technique. The design centering solution for microwave circuits is obtained with a small number of fine model evaluations and, hence, the number of electromagnetic simulations is greatly reduced. Practical and demonstrative examples are included to show the efficiency of the new technique

The Ellipsoidal Technique for Design Centering of Microwave Circuits Exploiting Space-Mapping Interpolating Surrogates

In this letter, a new design for a planar antenna is introduced. The antenna is built using coplanar technology. It has dual-frequency operation: the first and second resonances are in the X- and Ku-bands, respectively. The proposed antenna has wideband behavior around both resonance frequencies. It has a dipole-like radiation pattern, which makes it suitable for phased-array applications. The analysis is carried out both theoretically and experimentally, and very good agreement is observed. The results include the return loss, the current distribution, the radiation patterns, and the antenna gain. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 22: 288–290, 1999.

Ezzeldin A. Soliman

Papers

Bow-tie slot antenna fed by CPW

Dual-polarized omnidirectional planar slot antenna for WLAN applications

Theoretical Study of Metal-Insulator-Metal Tunneling Diode Figures of Merit

The Ellipsoidal Technique for Design Centering of Microwave Circuits Exploiting Space-Mapping Interpolating Surrogates

CPW fed cusp antenna