The complex permittivity and resistivity of float-zone high-resistivity silicon were measured at microwave frequencies for temperatures from 10 up to 400 K employing dielectric-resonator and composite dielectric-resonator techniques. At temperatures below 25 K, where all free carriers are frozen out, loss-tangent values of the order of 2times10^-4 were measured, suggesting the existence of hopping conductivity or surface charge carrier conductivity in this temperature range. Use of a composite dielectric-resonator technique enabled the measurement of materials having higher dielectric losses (or lower resistivities) with respect to the dielectric-resonator technique. The real part of permittivity of silicon proved to be frequency independent. Dielectric losses of high-resistivity silicon at microwave frequencies are mainly associated with conductivity and their behavior versus temperature can be satisfactory described by dc conductivity models, except at very low temperatures

This review focuses on metal enhanced fluorescence (MEF) and its current and future applications in biotechnology. The mechanisms of MEF are discussed in terms of the additional radiative and nonradiative decay rates caused by the close proximity of the metal. We then review the current MEF materials and structures that show promise in bioapplications. The use of electromagnetic modelling to predict fluorescent rate enhancement is then considered. We then give particular focus to the recent work carried out in the homogeneous fabrication of metal nanoparticles using colloidal lithography. It is concluded that the use of computational electromagnetic modelling alongside homogeneous fabrication techniques will lead to predictable and controllable MEF, paving the way for increased applications in biotechnology.

New technological advancements in wireless networks have enlarged the number of connected devices. The unprecedented surge of data volume in wireless systems empowered by artificial intelligence (AI) opens up new horizons for providing ubiquitous data-driven intelligent services. Traditional cloud-centric machine learning (ML)-based services are implemented by centrally collecting datasets and training models. However, this conventional training technique encompasses two challenges: (i) high communication and energy cost and (ii) threatened data privacy. In this article, we introduce a comprehensive survey of the fundamentals and enabling technologies of federated learning (FL), a newly emerging technique coined to bring ML to the edge of wireless networks. Moreover, an extensive study is presented detailing various applications of FL in wireless networks and highlighting their challenges and limitations. The efficacy of FL is further explored with emerging prospective beyond fifth-generation (B5G) and sixth-generation (6G) communication systems. This survey aims to provide an overview of the state-of-the-art FL applications in key wireless technologies that will serve as a foundation to establish a firm understanding of the topic. Lastly, we offer a road forward for future research directions.

Potential utilization of proteins for early detection and diagnosis of various diseases has drawn considerable interest in the development of protein-based detection techniques. Metal induced fluorescence enhancement offers the possibility of increasing the sensitivity of protein detection in clinical applications. We report the use of tunable plasmonic silver nanostructures for the fluorescence enhancement of a near-infrared (NIR) dye (Alexa Fluor 790). Extensive fluorescence enhancement of ∼2 orders of magnitude is obtained by the nanoscale control of the Ag nanostructure dimensions and interparticle distance. These Ag nanostructures also enhanced fluorescence from a dye with very high quantum yield (7.8 fold for Alexa Fluor 488, quantum efficiency (Qy) = 0.92). A combination of greatly enhanced excitation and an increased radiative decay rate, leading to an associated enhancement of the quantum efficiency leads to the large enhancement. These results show the potential of Ag nanostructures as metal induced fluorescence enhancement (MIFE) substrates for dyes in the NIR “biological window” as well as the visible region. Ag nanostructured arrays fabricated by colloidal lithography thus show great potential for NIR dye-based biosensing applications. Open image in new window

The interaction of light with noble metal nanoparticles deposited onto the top surface of a semiconductor has been investigated using the finite-difference time-domain method. The scattering is calculated for spherical and hemispherical silver nanoparticles placed in a periodic two-dimensional array on the upper surface of a semi-infinite silicon substrate. The results show that the contact area between hemispherical particles and the silicon significantly reduces the forward scattering. The use of an oxide buffer layer to separate the particle from the semiconductor is investigated and is seen to be important if the forward scattering of light is to be enhanced.