Development and application of a novel class of hierarchicaltangential vector finite elements for electromagnetics

Tangential vector finite elements (TVFEs) overcome most of the shortcomings of node-based finite elements for electromagnetic simulations. For a triangular element, this paper proposes a class of hierarchical TVPEs that differ from traditional TVFEs. The hierarchical nature of the proposed TVFEs makes them ideally suited for employing an efficient selective field expansion (the lowest order TVFE employed within part of the computational domain and a higher order TVFE employed within the remaining part of the computational domain). This is an attractive feature not shared by nonhierarchical TVFEs for which a more traditional approach (the same TVFE employed throughout the computational domain) must be applied. For determining the scattering by composite cylinders, this paper argues that the performance (in terms of accuracy, memory, and, in most cases, CPU time) of the proposed class of hierarchical TVFEs when applying selective field expansion is superior to that of the lowest order TVFE and a traditional nonhierarchical TVFE. This is the case when an artificial absorber as well as a boundary integral is used for truncating the computational domain. A guideline is given as to how lowest and higher order TVFEs shall be combined for optimal performance of the proposed class of hierarchical TVFEs     

SAR reduction for handset with two-element phased array antennacomputed using hybrid MoM/FDTD technique

An investigation into a two-element phased antenna array mobile handset using the MoM/FDTD hybrid method is presented. The array is designed to provide a spatial null in the near field zone in the direction of the human head. Compared with an omnidirectional antenna, the overall efficiency and azimuth coverage are improved and the peak specific absorption rate in the head can be reduced by at least 10 dB     

A Review on Thin-film Sensing with Terahertz Waves

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy.     

P3HT based solution-processed pseudo bi-layer organic solar cell with enhanced performance

We present a solution-processed pseudo bi-layer organic solar cell with poly(3-hexyl thiophene) (P3HT) as donor and indene-C₆₀ bisadduct (ICBA) as acceptor. The devices were fabricated by sequential processing of the active components followed by a thermal annealing treatment. An efficiency of 5.9% was achieved under AM 1.5G irradiation (1000 W/m²). The obtained efficiency is attributed to an enhanced nanomorphology that arises from the inter-diffusion of the ICBA molecules into a layer of pre-organised polymer (P3HT) and also due to the subsequent crystallisation of the ICBA molecules. These processes facilitate efficient charge generation and extraction. Time of flight-secondary ion mass spectroscopy (TOF-SIMS) depth profiling was carried out for different thermal annealing treatments of these pseudo bi-layer devices, which reveals full inter-diffusion of ICBA into the polymer P3HT. Photo-CELIV (charge extraction by linearly increasing voltage) studies elucidates that the thermal annealing imparts crystallinity to the fullerene phase which results in the improvement of charge carrier mobility.     

Specific features of the sol-gel formation and optical properties of 3d metal/porous silicon composites

The composition and optical properties of composite materials based on porous silicon with iron, cobalt, and nickel deposited by the sol-gel technique are studied. It is shown that the deposition of metal-oxide films onto the surface of porous silicon enables stabilization of the photoluminescence and an increase in its intensity, as well as the storage of hydrogen in the porous layer.     

Strain Mapping at the Atomic Scale in Highly Mismatched Heterointerfaces

A complete characterization of dislocation network in a highly mismatched interface with high spatial resolution has been performed. The interface between InN quantum dots and a (0001) GaN substrate contains three noninteracting sets of regularly‐spaced misfit dislocations lying along <110> directions. The network has a “Star of David” form, with each star bounding a hexagonal region which is pseudomorphic. These misfit dislocations form a threading dislocation network at the island edges due to free surface forces.     

Surface‐Enhanced Raman Scattering Using Microstructured Optical Fiber Substrates

Microstructured optical fibers (MOFs) represent a promising platform technology for fully integrated next generation surface enhanced Raman scattering (SERS) sensors and plasmonic devices. In this paper we demonstrate silver nanoparticle substrates for SERS detection within MOF templates with exceptional temporal and mechanical stability, using organometallic precursors and a high‐pressure chemical deposition technique. These 3D substrates offer significant benefits over conventional planar detection geometries, with the long electromagnetic interaction lengths of the optical guided fiber modes exciting multiple plasmon resonances along the fiber. The large Raman response detected when analyte molecules are infiltrated within the structures can be directly related to the deposition profile of the nanoparticles within the MOFs via electrical characterization.     

Efficient wavelength conversion with high-power passivelyQ-switched diode-pumped neodymium lasers

Powerful CW diode-pumped Nd:YAG and Nd:YVO4 lasers Q-switched by Cr:YAG saturable absorbers demonstrate efficient (30%-60%) harmonic and parametric conversion, generating hundreds of milliwatts from ultraviolet to mid-infrared     

Finding cyclic redundancy check polynomials for multilevel systems

This letter describes a technique for finding cyclic redundancy check polynomials for systems for transmission over symmetric channels which encode information in multiple voltage levels, so that the resulting redundancy check gives good error protection and is efficient to implement. The codes which we construct have a Hamming distance of 3 or 4. We discuss a way to reduce burst error in parallel transmissions and some tricks for efficient implementation of the shift register for these polynomials. We illustrate our techniques by discussing a particular example where the number of levels is 9, but they are applicable in general     

Analysis of Iddq failures by spectral photon emission microscopy

In this work, a fast identification of I_ddq failures using spectroscopic photon emission microscopy (SPEMMI) is proposed. The spectra obtained from failure sites on the I_ddq failed chips were compared with the ones of known defective components. Four distinguishable spectra categories were identified. They were attributed to gate oxide breakdown, metal shorts, blackbody radiation, and ESD caused junction spiking. The focused ion beam (FIB) technique was used to look at the damage sites for confirmation of the SPEMMI results.