Millimeter wave inductive post filters,theory and results

This paper briefly details the work carried out on the modelling of inductive post filters. This type of filter approach is particularly attractive at millimeter wave frequencies due to its ease of manufacture, however for modelling no true wide band equivalent circuit would seem to be available. In order to overcome this limitation we have developed a rigorous wide band model. The accuracy of the model has been confirmed by numerous experimental measurements and the resulting computer program quickly enables both analysis and synthesis to be carried out. The speed and efficiency of this approach has allowed the effect of mechanical tolerances to be taken into account, thus reducing cost, complexity and assembly times.     

Design of a multiple-beam forming network using CORPS optimized for cellular systems

The design of beam-forming networks (BFNs) for a multibeam-steerable antenna array using Coherently Radiating Periodic Structures (CORPS) in cellular mobile communication systems is presented. In this paper, the CORPS technology is introduced and applied to the design of beam-forming networks in cellular systems for the first time. The CORPS-BFNs proposed show improved performance over the common way to feed antenna arrays used in mobile systems. In this design, the input ports of the feeding network design are optimized using the particle swarm optimization (PSO) algorithm. Two 2-beam design configurations of CORPS-BFN for a multibeam-steerable linear array on a cellular scenario are proposed and analyzed. Simulation results show the benefits of BFNs based on CORPS on a cellular mobile scenario based on the array factor response, in terms of side lobe level (SLL) and signal-to-interference (SIR) improvement capability. Furthermore, results for average SIR improvement, signal to interference plus noise power ratio (SINR) and BER are discussed.     

A four-shell diffusion phantom of the head for electrical impedance tomography

A four-shell head phantom has been built and characterized. Its structure is similar to that of nonhomogeneous concentric shell domains used by numerical solvers that better approximate current distribution than phantoms currently used to validate electrical impedance tomography systems. Each shell represents a head tissue, namely, skin, skull, cerebrospinal fluid, and brain. A novel technique, which employs a volume conductive impermeable film, has been implemented to prevent ion diffusion between different agar regions without affecting current distribution inside the phantom. Comparisons between simulations and phantom measurements performed over four days are given to prove both the adherence to the model in the frequency range between 10 kHz and 1 MHz and its long-term stability.     

Metal Organic Framework Crystals in Mixed‐Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance

Mixed‐matrix membranes comprising NH₂‐MIL‐53(Al) and Matrimid or 6FDA‐DAM have been investigated. The metal organic framework (MOF) loading has been varied between 5 and 20 wt%, while NH₂‐MIL‐53(Al) with three different morphologies, nanoparticles, nanorods, and microneedles has been dispersed in Matrimid. The synthesized membranes have been tested in the separation of CO₂ from CH₄ in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH₂‐MIL‐53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, i.e., NH₂‐MIL‐53(Al) nanoparticles, into the highly permeable 6FDA‐DAM has a larger effect, and the CO₂ permeability increases up to 85% with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with a CO₂/CH₄ separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non‐destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modeling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by focused ion beam scanning electron microscopy analysis.     

Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003? substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.     

Design of an enhanced access point to optimize TCP performance in Wi-Fi hotspot networks

In the last years, the number of Wi-Fi hotspots at public venues has undergone a substantial growth, promoting the WLAN technologies as the ubiquitous solution to provide high-speed wireless connectivity in public areas. However, the adoption of a random access CSMA-based paradigm for the 802.11 MAC protocol makes difficult to ensure high throughput and a fair allocation of radio resources in 802.11-based WLANs. In this paper we evaluate extensively via simulations the interaction between the flow control mechanisms implemented at the TCP layer and the contention avoidance techniques used at the 802.11 MAC layer. We conducted our study considering initially M wireless stations performing downloads from the Internet. From our results, we observed that the TCP downlink throughput is not limited by the collision events, but by the inability of the MAC protocol to assign a higher chance of accessing the channel to the base station. We propose a simple and easy to implement modification of the base station’s behavior with the purpose of increasing the TCP throughput reducing useless MAC protocol overheads. With our scheme, the base station is allowed to transmit periodically bursts of data frames towards the mobile hosts. We design a resource allocation protocol aimed at maximizing the success probability of the uplink transmissions by dynamically adapting the burst length to the collision probability estimated by the base station. By its design, our scheme is also beneficial to achieve a fairer allocation of the channel bandwidth among the downlink and uplink flows, and among TCP and UDP flows. Simulation results confirm both the improvement in the TCP downlink throughput and the reduction of system unfairness.     

Overview of the MPEG Reconfigurable Video Coding Framework

Video coding technology in the last 20 years has evolved producing a variety of different and complex algorithms and coding standards. So far the specification of such standards, and of the algorithms that build them, has been done case by case providing monolithic textual and reference software specifications in different forms and programming languages. However, very little attention has been given to provide a specification formalism that explicitly presents common components between standards, and the incremental modifications of such monolithic standards. The MPEG Reconfigurable Video Coding (RVC) framework is a new ISO standard currently under its final stage of standardization, aiming at providing video codec specifications at the level of library components instead of monolithic algorithms. The new concept is to be able to specify a decoder of an existing standard or a completely new configuration that may better satisfy application-specific constraints by selecting standard components from a library of standard coding algorithms. The possibility of dynamic configuration and reconfiguration of codecs also requires new methodologies and new tools for describing the new bitstream syntaxes and the parsers of such new codecs. The RVC framework is based on the usage of a new actor/ dataflow oriented language called CAL for the specification of the standard library and instantiation of the RVC decoder model. This language has been specifically designed for modeling complex signal processing systems. CAL dataflow models expose the intrinsic concurrency of the algorithms by employing the notions of actor programming and dataflow. The paper gives an overview of the concepts and technologies building the standard RVC framework and the non standard tools supporting the RVC model from the instantiation and simulation of the CAL model to software and/or hardware code synthesis.     

Design of different planar geometries of antenna arrays for isoflux radiation in GEO satellites

The synthesis of different planar geometries of antenna arrays for isoflux radiation is presented in this paper. This synthesis considers the reduction of the side lobe level and the isoflux radiation requirements for Geostationary Earth Orbit satellites. The behavior of the radiation is studied in three geometries of two-dimensional antenna arrays such as uniform planar arrays, aperiodic planar arrays (APA) and concentric ring arrays (CRA). The well-known methods of genetic algorithm and particle swarm optimization are utilized for the optimization problem. In this way, the designs of APA and CRA presented in this paper could provide an acceptable solution for reducing the antenna hardware and simplifying the power feeding even more than results presented previously in the literature.     

A miniature vibrotactile sensory substitution device for multifingered hand prosthetics

A multisite, vibrotactile sensory substitution system, that could be used in conjunction with artificial touch sensors in multifingered prostheses, to deliver sensory feedback to upper limb amputees is presented. The system is based on a low cost/power/size smart architecture of off-the-shelf miniaturized vibration motors; the main novelty is that it is able to generate stimuli where both vibration amplitude and frequency as well as beat interference can be modulated. This paper is aimed at evaluating this system by investigating the capability of healthy volunteers to perceive-on their forearms-vibrations with different amplitudes and/or frequencies. In addition, the ability of subjects in spatially discriminating stimulations on three forearm sites and recognizing six different combinations of stimulations was also addressed. Results demonstrate that subjects were able to discriminate different force amplitudes exerted by the device (accuracies greater than 75%); when both amplitude and frequency were simultaneously varied, the pure discrimination of amplitude/frequency variation was affected by the variation of the other. Subjects were also able to discriminate with an accuracy of 93% three different sites and with an accuracy of 78% six different stimulation patterns.     

Fast and air stable near-infrared organic detector based on squaraine dyes

In search for an organic material suitable for the detection of near-infrared electromagnetic radiation and at the same time capable of air stable operation of related devices, so to address the many applications envisaged with this technology (remote control, chemical/biological sensing, optical communication, spectroscopic and medical instruments), we explore the performance of a blend of hydrazone end-capped symmetric squaraines and phenyl C₆₁ butyric acid methyl ester. We succeed in developing air stable solution-processed devices with external quantum efficiency in the NIR as high as 3.5% and response times of few hundreds of nanoseconds. Essential to these achievements has been a detailed characterization of the devices performed by correlating the optoelectronic performances to the morphology of the layers (extracted from AFM measurements) and to the charge carrier mobility (extracted from transistor structures), enabling their optimization at the chemical level, by tailoring the squaraine substitution pattern, and at the device level, by tuning the blend composition. We show that a good balance between holes and electrons mobility is essential for high EQE and fast response speed, and that a smooth morphology is mandatory to achieve long term air stability and operability with no need for encapsulation.