Parametric FIR Design of Propagation Loss Filters in Digital Waveguide String Models

One of the attractive features of sound synthesis by physical modeling is the potential to build acoustic-sounding digital instruments that offer more flexibility and different options in its design and control than their real-life counterparts. In order to develop such virtual-acoustic instruments, the models they are based on need to be fully parametric, i.e., all coefficients employed in the model are functions of physical parameters that are controlled either online or at the (offline) design stage. In this letter we show how propagation losses can be parametrically incorporated in digital waveguide string models with the use of zero-phase FIR filters. Starting from the simplest possible design in the form of a three-tap FIR filter, a higher-order FIR strategy is presented and discussed within the perspective of string sound synthesis with digital waveguide models.

A scalable packet sorting circuit for high-speed WFQ packet scheduling

A novel implementation of a tag sorting circuit for a weighted fair queueing (WFQ) enabled Internet Protocol (IP) packet scheduler is presented. The design consists of a search tree, matching circuitry, and a custom memory layout. It is implemented using 130-nm silicon technology and supports quality of service (QoS) on networks at line speeds of 40 Gb/s, enabling next generation IP services to be deployed.

Quantum efficiency in GaAs Schottky photodetectors with enhancement due to surface plasmon excitations

The overall quantum efficiency in surface plasmon (SP) enhanced Schottky barrier photodetectors is examined by considering both the external and internal yield. The external yield is considered through calculations of absorption and transmission of light in a configuration that allows reflectance minimization due to SP excitation. Following a Monte Carlo method, a procedure is presented to estimate the internal yield while taking into account the effect of elastic and inelastic scattering processes on excited carriers subsequent to photon absorption. The relative importance of internal photoemission and band-to-band contributions to the internal yield is highlighted along with the variation of the yield as a function of wavelength, metal thickness and other salient parameters of the detector. (C) 2002 Elsevier Science Ltd. All rights reserved.

Scheme for enhancing efficiency in resonant-cavity Schottky photodetectors

It is shown that structuring the top layers of a resonant cavity Schottky photodetector in a way that allows coupling between the wavevector of incident radiation and that of electron-collective oscillations (plasmons) at the surface of the metallic electrode leads to practically zero reflectance in the case of front illuminated devices. This is expected to result in a consequential enhancement in the quantum efficiency in these photodetectors. (C) 2001 Elsevier Science Ltd. All rights reserved.

On the Distribution of Signal Phase in Body Area Networks

In this letter, we investigate the distribution of the phase component of the complex received signal observed in practical experiments using body area networks. Two phase distributions, the recently proposed kappa-mu and eta-mu probability densities, which together encompass the most widely used fading models, namely Semi-Gaussian, Rayleigh, Hoyt, Rice, and Nakagami-m, have been compared with measurement data. The kappa-mu distribution has been found to provide the best fit over a range of on-body links, while the user was mobile. The experiments were carried out in two dissimilar indoor environments at opposite ends of the multipath spectrum. It has also been found that the uniform phase distribution has not arisen in anyone of the experiments.

Progress in proton radiography for diagnosis of ICF-relevant plasmas

Proton radiography using laser-driven sources has been developed as a diagnostic since the beginning of the decade, and applied successfully to a range of experimental situations. Multi-MeV protons driven from thin foils via the Target Normal Sheath Acceleration mechanism, offer, under optimal conditions, the possibility of probing laser-plasma interactions, and detecting electric and magnetic fields as well as plasma density gradients with similar to ps temporal resolution and similar to 5-10 mu m spatial resolution. In view of these advantages, the use of proton radiography as a diagnostic in experiments of relevance to Inertial Confinement Fusion is currently considered in the main fusion laboratories. This paper will discuss recent advances in the application of laser-driven radiography to experiments of relevance to Inertial Confinement Fusion. In particular we will discuss radiography of hohlraum and gasbag targets following the interaction of intense ns pulses. These experiments were carried out at the HELEN laser facility at AWE (UK), and proved the suitability of this diagnostic for studying, with unprecedented detail, laser-plasma interaction mechanisms of high relevance to Inertial Confinement Fusion. Non-linear solitary structures of relevance to space physics, namely phase space electron holes, have also been highlighted by the measurements. These measurements are discussed and compared to existing models.

Spatial evolution of a q-Gaussian laser beam in relativistic plasma

In a recent experimental study, the beam intensity profile of the Vulcan petawatt laser beam was measured; it was found that only 20% of the energy was contained within the full width at half maximum of 6.9 mu m and 50% within 16 mu m, suggesting a long-tailed non-Gaussian transverse beam profile. A q-Gaussian distribution function was suggested therein to reproduce this behavior. The spatial beam profile dynamics of a q-Gaussian laser beam propagating in relativistic plasma is investigated in this article. A non-paraxial theory is employed, taking into account nonlinearity via the relativistic decrease of the plasma frequency. We have studied analytically and numerically the dynamics of a relativistically guided beam and its dependence on the q-parameter. Numerical simulation results are shown to trace the dependence of the focusing length on the q-Gaussian profile.

HTS Motors in Aircraft Propulsion: Design Considerations

Current high temperature superconducting (HTS) wires exhibit high current densities enabling their use in electrical rotating machinery. The possibility of designing high power density superconducting motors operating at reasonable temperatures allows for new applications in mobile systems in which size and weight represent key design parameters. Thus, all-electric aircrafts represent a promising application for HTS motors. The design of such a complex system as an aircraft consists of a multi-variable optimization that requires computer models and advanced design procedures. This paper presents a specific sizing model of superconducting propulsion motors to be used in aircraft design. The model also takes into account the cooling system. The requirements for this application are presented in terms of power and dynamics as well as a load profile corresponding to a typical mission. We discuss the design implications of using a superconducting motor on an aircraft as well as the integration of the electrical propulsion in the aircraft, and the scaling laws derived from physics-based modeling of HTS motors.

QR decomposition-based matrix inversion for high performance embedded MIMO receivers

Real-time matrix inversion is a key enabling technology in multiple-input multiple-output (MIMO) communications systems, such as 802.11n. To date, however, no matrix inversion implementation has been devised which supports real-time operation for these standards. In this paper, we overcome this barrier by presenting a novel matrix inversion algorithm which is ideally suited to high performance floating-point implementation. We show how the resulting architecture offers fundamentally higher performance than currently published matrix inversion approaches and we use it to create the first reported architecture capable of supporting real-time 802.11n operation. Specifically, we present a matrix inversion approach based on modified squared Givens rotations (MSGR). This is a new QR decomposition algorithm which overcomes critical limitations in other QR algorithms that prohibits their application to MIMO systems. In addition, we present a novel modification that further reduces the complexity of MSGR by almost 20%. This enables real-time implementation with negligible reduction in the accuracy of the inversion operation, or the BER of a MIMO receiver based on this.

Designed ultrafast optical nonlinearity in a plasmonic nanorod metamaterial enhanced by nonlocality

All-optical signal processing enables modulation and transmission speeds not achievable using electronics alone(1,2). However, its practical applications are limited by the inherently weak nonlinear effects that govern photon-photon interactions in conventional materials, particularly at high switching rates(3). Here, we show that the recently discovered nonlocal optical behaviour of plasmonic nanorod metamaterials(4) enables an enhanced, ultrafast, nonlinear optical response. We observe a large (80%) change of transmission through a subwavelength thick slab of metamaterial subjected to a low control light fluence of 7 mJ cm(-2), with switching frequencies in the terahertz range. We show that both the response time and the nonlinearity can be engineered by appropriate design of the metamaterial nanostructure. The use of nonlocality to enhance the nonlinear optical response of metamaterials, demonstrated here in plasmonic nanorod composites, could lead to ultrafast, low-power all-optical information processing in subwavelength-scale devices.

Artificial Impedance Surfaces for Reduced Dispersion in Antenna Feeding Systems

An impedance surface is presented that reduces the dispersion experienced upon propagation of broadband pulses within rectangular waveguides. The surface impedance is selected so that, within a frequency range, the transverse resonance condition is satisfied for longitudinal wavenumber that varies linearly with frequency. A synthesis procedure for practical surface topologies consisting of periodic dipole arrays is described. An example involving a finite structure is employed to illustrate the reduced dispersion. Numerical simulation results obtained from in-house mode-matching method as well as HFSS are presented. A prototype is fabricated and tested experimentally validating the theoretical predictions.

Sub-Wavelength Profile 2-D Leaky-Wave Antennas With Two Periodic Layers

A fast and accurate analysis and synthesis technique for high-gain sub-wavelength 2-D Fabry-Perot leaky-wave antennas (LWA) consisting of two periodic metallodielectric arrays over a ground plane is presented. Full-wave method of moments (MoM) together with reciprocity is employed for the estimation of the near fields upon plane wave illumination and the extraction of the radiation patterns of the LWA. This yields a fast and rigorous tool for the characterisation of this type of antennas. A thorough convergence study for different antenna designs is presented and the operation principles of these antennas as well as the radiation characteristics are discussed. Moreover, design guidelines to tailor the antenna profile, the dimensions of the arrays as well as the antenna directivity and bandwidth are provided. A study on the radiation efficiency for antennas with different profiles is also presented and the trade off between directivity and radiation bandwidth is discussed. Numerical examples are given throughout to demonstrate the technique. A finite size antenna model is simulated using commercial software (CST Microstripes 2009) which validates the technique.

Helical resonator filters with improved power handling capabilities for space applications

The power-handling capabilities of helical resonator filters for space applications are discussed. Emerging difficulties due to the multipaction effects are highlighted. A method is proposed to increase specified power handling without significantly sacrificing the size/quality factor. Experimental verification is attained by means of a fabricated prototype for which measured filter response and multipaction test results are obtained and presented.