Tuning infrared emission from microstrip arrays

Earlier work has shown that a narrow-frequency-band, wide-angle emission is produced by an array of metal patches supported on a thin dielectric layer covering a ground plane. The modes responsible for this emission are local plasmons trapped under the metal patches. As the dielectric layer thickness, $h_d$, is increased, the resonant emission fades in strength because the plasmon modes can no longer be trapped under a single patch. Further increases in $h_d$, making it comparable to the light wavelength in the dielectric layer, lead to a collection of new emission peaks. These are narrower than the one peak found for small $h_d$ but they are not well separated. We have found that some of these peaks can be suppressed over a narrow range of $h_d$. This leaves one with well-separated, narrow-band emission peaks. We have identified the physical mechanism for this selective suppression of emission peaks

The Study of Quantum Interference in Metallic Photonic Crystals Doped with Four-Level Quantum Dots

In this work, the absorption coefficient of a metallic photonic crystal doped with nanoparticles has been obtained using numerical simulation techniques. The effects of quantum interference and the concentration of doped particles on the absorption coefficient of the system have been investigated. The nanoparticles have been considered as semiconductor quantum dots which behave as a four-level quantum system and are driven by a single coherent laser field. The results show that changing the position of the photonic band gap about the resonant energy of the two lower levels directly affects the decay rate, and the system can be switched between transparent and opaque states if the probe laser field is tuned to the resonance frequency. These results provide an application for metallic nanostructures in the fabrication of new optical switches and photonic devices

Theoretical And Experimental Analysis Of Transmission And Enhanced Absorption Of Frequency Selective Surfaces In The Infrared

A comparative study between theory and experiment is presented for transmission through lossy frequency selective surfaces (FSSs) on silicon in the 2-15 μm range. Important parameters controlling the resonance shape and location are identified: dipole length, spacing, impedance, and dielectric surroundings. Their separate influence is exhibited. The primary resonance mechanism of FSSs is the resonance of the individual metallic patches. There is no discernable resonance arising from a feed-coupled configuration. The real part of the element\u27s impedance controls the minimum value of transmission, while scarcely affecting its location. Varying the imaginary part shifts the location of resonance, while only slightly changing the minimum value of transmission. With such fine-tuning, it is possible to make a good fit between theory and experiment near the dipole resonance on any sample. A fixed choice of impedance can provide a reasonable fit to all samples fabricated under the same conditions. The dielectric surroundings change the resonance wavelength of the FSS compared to its value in air. The presence of FSS on the substrate increases the absorptivity/emissivity of the surface in a resonant way. Such enhancement is shown for dipole and cross arrays at several wavelengths

Intragastric balloon: is there any place left for It in the treatment of obesity?

Intragastric balloon (IGB) is used in the treatment of obesity for more than 20 years, both as a self-standing procedure and as a bridge treatment to bariatric surgery. The indications and results are well known, due to its characteristics as a non-surgical, endoscopic, minimally invasive and temporary treatment. Recently new models of IGB appeared on the market, and FDA approved for the first time in 2015 two models as treatment of obesity in the United States. Spatz™ Adjustable Balloon System is the first adjustable IGB, tolerated for 12 months, available from 2005. Between 2013-2015 thirty overweighted/obese patients were treated with Spatz3™, maintained in place for approximately 12 months, with a minimum follow-up of 6 months. The results, complications and efficacy of the Spatz3™ balloon are presented, together with an extended review of the literature. IGB represents a useful tool in the treatment of obesity, when patient’s selection is careful done

On computing nonlinear wave-wave interactions: open questions and latest developments

Although great advances have been made over the last five decades in modelling the nonlinear wave-wave interactions, the topic is far from being exhausted. Despite considerable progress, many open questions remain. This paper gives a brief summary of problems in the understanding and modelling of nonlinear wave-wave interactions. Recent developments together with suggestions for further research are also discussed. The discussion is confined to a few outstanding issues: (a) Although nonlinear energy transfer can be predicted with rigorous theories such as that of resonant weakly nonlinear interaction between sets of four waves (i.e. the kinetic or Boltzmann equation by Hasselmann) or directly from the hydrodynamic equations based on first principles with no assumptions involved, it is not yet completely clear whether the solutions converge to the same universal solution. Despite a few results available in literature there are still unresolved controversies, discrepancies and challenges that we aim discussing in this paper along with some recent developments. (b) To date, there is no clear view on the role of near-resonant interactions in the evolution of nonlinear waves. Recent works point out to expectations that near-resonant interactions, rather than the exact resonance, dominate the temporal nonlinear evolution. Even though one can in principle account for near-resonant interaction in the spatio-temporal domain, its practical use in an operational wave prediction model is far from being established. This paper will discuss the latest development within the framework of a novel wave-action transfer model that would cover near-resonant interactions and Stokes corrections, as well as the associated computational challenges and the open questions that must be addressed. (b) Currently, quite a few exact, quasi-exact and approximate methods exist to compute the nonlinear fourwave interaction. However, usually only one approximate method is in use to compute the non-linear quadruplet wave-wave interactions for a discrete wind wave spectrum usually in third-generation wave prediction models. Up untill now no comprehensive and more importantly objective comparison has been performed to determine the best (both in terms of performance and accuracy) method for computing the nonlinear four-wave interactions in a discrete spectral model. A good understanding of these methods is crucial for the interpretation of the results of the numerical aspects. In this paper we outline and discuss the foundation of an inter-comparison study that should provide answers to a range of basic questions as well as provide a systematic analysis of the characteristics of these methods

4H-SiC Schottky Diodes for Temperature Sensing Applications in Harsh Environments

© (2011) Trans Tech Publications, Switzerland.4H-SiC Schottky Barrier Diodes (SBDs) with remarkable electrical performance have been fabricated and characterised. A barrier height about 1.64V and an ideality factor close to 1 are extracted from the forward characteristics measured at several temperatures. These essential Schottky contact parameters are obseived to be constant with temperature. A temperature probe with a simple and innovative scheme is designed and applied. The probe uses SiC SBDs as temperature sensor in the 20-400° C range, with measured sensitivities varying from 1.3 mV/K to 2.8 m V/K. The probe is meant to monitorize the temperature inside the furnaces, in the cement industry