Showing papers by "École Polytechnique de Montréal published in 2005"

Guided-wave and leakage characteristics of substrate integrated waveguide

Abstract: The substrate integrated waveguide (SIW) technique makes it possible that a complete circuit including planar circuitry, transitions, and rectangular waveguides are fabricated in planar form using a standard printed circuit board or other planar processing techniques. In this paper, guided wave and modes characteristics of such an SIW periodic structure are studied in detail for the first time. A numerical multimode calibration procedure is proposed and developed with a commercial software package on the basis of a full-wave finite-element method for the accurate extraction of complex propagation constants of the SIW structure. Two different lengths of the SIW are numerically simulated under multimode excitation. By means of our proposed technique, the complex propagation constant of each SIW mode can accurately be extracted and the electromagnetic bandstop phenomena of periodic structures are also investigated. Experiments are made to validate our proposed technique. Simple design rules are provided and discussed.

Bilevel programming: A survey

Abstract: This paper provides an introductory survey of a class of optimization problems known as bilevel programming. We motivate this class through a simple application, and then proceed with the general formulation of bilevel programs. We consider various cases (linear, linear-quadratic, nonlinear), describe their main properties and give an overview of solution approaches.

Biomechanics of the knee joint in flexion under various quadriceps forces

Abstract: Bioemchanics of the entire knee joint including tibiofemoral and patellofemoral joints were investigated at different flexion angles (0° to 90°) and quadriceps forces (3, 137, and 411 N). In particular, the effect of changes in location and magnitude of restraining force that counterbalances the isometric extensor moment on predictions was investigated. The model consisted of three bony structures and their articular cartilage layers, menisci, principal ligaments, patellar tendon, and quadriceps muscle. Quadriceps forces significantly increased the anterior cruciate ligament, patellar tendon, and contact forces/areas as well as the joint resistant moment. Joint flexion, however, substantially diminished them all with the exception of the patellofemoral contact force/area that markedly increased in flexion. When resisting extensor moment by a force applied on the tibia, the force in cruciate ligaments and tibial translation significantly altered as a function of magnitude and location of the restraining force. Quadriceps activation generated large ACL forces at full extension suggesting that post ACL reconstruction exercises should avoid large quadriceps exertions at near full extension angles. In isometric extension exercises against a force on the tibia, larger restraining force and its more proximal location to the joint substantially decreased forces in the anterior cruciate ligament at small flexion angles whereas they significantly increased forces in the posterior cruciate ligament at larger flexion angles.

Fugitive Inks for Direct‐Write Assembly of Three‐Dimensional Microvascular Networks

Abstract: Microfluidic systems are essential to a broad range of technological applications, including biotechnology, [1] microelectronics , [2] sensors, [3] chemical reactors, [4] and autonomic materials. [5] Several approaches have emerged for fabricating two-dimensional (2D) [6] and three-dimensional (3D) [7] micro-fluidic devices, including photolithographic or soft-lithograph-ic techniques, [1b,2a,3c,4b,5b] laser micromachining, [7b] and derivative methods based on soft lithography. [7d±f] These techniques, however, have been confined to relatively thin device architec-tures (of only a few layers) and limited by materials constraints , [7b] poor resolution, [7c] or the need for extensive manual labor. [7d±f] We recently demonstrated the direct-write assembly of 3D microvascular networks, consisting of 16-layer structures with interconnected microchannels (200 lm in diameter) encapsulated in an epoxy matrix. [7a] Our approach involved the robotic deposition of a fugitive organic ink, which yields the desired microchannel network upon its subsequent removal from the matrix. Difficulties such as deformation of this fugitive-ink scaffold were encountered during assembly that prevented fabrication of larger 3D structures. Here, we report the development of a new fugitive ink that enables the direct-write assembly of 3D scaffolds (with more than a hundred layers) that retain their shape during fabrication and subsequent matrix infiltration under ambient conditions. The fabrication procedure of 3D microvascular networks (see Scheme 1) begins with the robotic deposition [8] of the fugitive ink onto a moving x±y platform, yielding a 2D pattern. After the initial layer is generated, the deposition nozzle, which is mounted on the z-stage, is raised a finite height and another layer is deposited. This process is repeated until the desired 3D scaffold is created. The interstitial pore space between patterned features is then infiltrated with a low-viscosity epoxy. Upon curing, the ink-based scaffold is removed, yielding an interconnected 3D microvascular network. The fugitive inks used in this directed assembly technique must satisfy several criteria. First, the ink must flow through a fine [**] The authors gratefully acknowledge funding for this project pro-Scheme 1. Schematic representation of the fabrication procedure for 3D microvascular networks by direct-write assembly: a) deposition of fugitive ink (in blue) through cylindrical nozzle; b) multilayer scaffold after ink deposition; c) resin infiltration into scaffold; d) resin solidification to form structural matrix; and e) 3D microvascular network created after removal of fugitive ink.

Femtosecond laser ablation of gold in water: influence of the laser-produced plasma on the nanoparticle size distribution

Abstract: Femtosecond laser radiation has been used to ablate a gold target in pure deionized water to produce gold colloids. The dimensional distribution of nanoparticles is characterized by the simultaneous presence of two distinct particle populations: one with low dispersion, having a mean particle size of 5–20 nm, and one with high dispersion, having a much larger particle size. By changing the target position with respect to the radiation focus, we study the influence of the plasma formed after the laser pulse in front of the target, during nanofabrication process. We show that the most intense plasma is produced by positioning the target slightly before the geometric focal point. Here, the plasma intensity was found to correlate with the amount of ablated material as well as with the mean size of nanoparticles associated with the second, highly dispersed, distribution of nanoparticles; this suggests the involvement of plasma-related processes in the ablation of material, and the formation of relatively large particles. The thermal heating of the target by the plasma, and its mechanical erosion by the collapse of a plasma-induced cavitation bubble are discussed as possible ablation mechanisms. The gold nanoparticles produced in ultrapure water are of importance for biosensing applications.

A fully integrated low-power BPSK demodulator for implantable medical devices

Abstract: During the past decades, research has progressed on the biomedical implantable electronic devices that require power and data communication through wireless inductive links. In this paper, we present a fully integrated binary phase-shift keying (BPSK) demodulator, which is based on a hard-limited COSTAS loop topology, dedicated to such implantable medical devices. The experimental results of the proposed demodulator show a data transmission rate of 1.12 Mbps, less than 0.7 mW consumption under a supply voltage of 1.8 V, and silicon area of 0.2 mm/sup 2/ in the Taiwan Semiconductor Manufacturing Company (TSMC) CMOS 0.18-/spl mu/m technology. The transmitter satisfies the requirement of applications relative to high forward-transferring data rate, such as cortical stimulation. Moreover, the employment of BPSK demodulation along with a passive modulation method allows full-duplex data communication between an external controller and the implantable device, which may improve the controllability and observability of the overall implanted system.

Novel substrate integrated waveguide cavity filter with defected ground structure

Abstract: An open-structure eigenvalue problem of substrate integrated waveguide (SIW) cavity structures is investigated in detail by using a finite-difference frequency-domain method, and the quality (Q) factor of such SIW cavities is given. Based on the concept of a defected ground structure, a new class of SIW cavity bandpass filters are designed, fabricated, and measured around 5.8 GHz. With their fabrication on standard printed circuit boards, such filters present the advantages of high-Q factor, high power capacity, and small size. Simulated and measured results are presented and discussed to show promising performances of the proposed filters.

An overview of scheduling algorithms in MIMO-based fourth-generation wireless systems

Abstract: In this article an overview of the scheduling algorithms proposed for fourth-generation multiuser wireless networks based on multiple-input multiple-output technology is presented. In MIMO systems a multi-user diversity gain can be extracted by tracking the channel fluctuations between each user and the base station, and scheduling transmission for the "best" user. Based on this idea, several opportunistic scheduling schemes that attempt to improve global capacity or satisfy users with different QoS requirements have been proposed. Transmit beamforming procedures aimed at increasing the channel fluctuations have been proposed. The simultaneous exploitation of both spatial and multi-user diversity is not straightforward; however, it may be achieved by a refined selection of the "best" user. In addition, a multiple access gain can be obtained from a simple SDMA/TOMA system. Finally, several resource allocation schemes are discussed for this hybrid multiple access system.

Multilayered substrate integrated waveguide (MSIW) elliptic filter

Abstract: This letter presents the design and experiment of a novel elliptic filter based on the multilayered substrate integrated waveguide (MSIW) technique. A C-band elliptic filter with four folded MSIW cavities is simulated by using high frequency structure simulator software and fabricated with a two-layer printed circuit board process, the measured results show good performance and in agreement with the simulated results.

Numerical methods for large-scale nonlinear optimization

Abstract: Recent developments in numerical methods for solving large differentiable nonlinear optimization problems are reviewed. State-of-the-art algorithms for solving unconstrained, bound-constrained, linearly constrained and non-linearly constrained problems are discussed. As well as important conceptual advances and theoretical aspects, emphasis is also placed on more practical issues, such as software availability.

A new six-port junction based on substrate integrated waveguide technology

Abstract: A six-port junction based on the substrate integrated waveguide (SIW) technology is proposed and presented. In this design of such a junction, the SIW is first converted to an equivalent rectangular waveguide, then regular rectangular waveguide design techniques are used. In this structure, an SIW power divider and SIW hybrid 3-dB coupler are designed as fundamental building blocks. A six-port junction circuit operating at 24 GHz is fabricated and measured. Good agreement between simulated and measured results is found for the proposed six-port junction.

Biomechanics of changes in lumbar posture in static lifting.

Abstract: Study design In vivo measurements and model studies are combined to investigate the role of lumbar posture in static lifting tasks. Objectives Identification of the role of changes in the lumbar posture on muscle forces, internal loads, and system stability in static lifting tasks with and without load in hands. Summary of background data Despite the recognition of the causal role of lifting in spinal injuries, the advantages of preservation or flattening of the lumbar lordosis while performing lifting tasks is not yet clear. Methods Kinematics of the spine and surface EMG activity of selected muscles were measured in 15 healthy subjects under different forward trunk flexion angles and load cases. Apart from the freestyle lumbar posture, subjects were instructed to take either lordotic or kyphotic posture as well. A kinematics-based method along with a nonlinear finite element model were interactively used to compute muscle forces, internal loads and system stability margin under postures, and loads considered in in vivo investigations. RESULTS.: In comparison with the kyphotic postures, the lordotic postures increased the pelvic rotation, active component of extensor muscle forces, segmental axial compression and shear forces at L5-S1, and spinal stability margin while decreasing the passive muscle forces and segmental flexion moments. Conclusion Alterations in the lumbar lordosis in lifting resulted in significant changes in the muscle forces and internal spinal loads. Spinal shear forces at different segmental levels were influenced by changes in both the disc inclinations and extensor muscle lines of action as the posture altered. Considering internal spinal loads and active-passive muscle forces, the current study supports the freestyle posture or a posture with moderate flexion as the posture of choice in static lifting tasks.

A Trust-Region Method for Nonlinear Bilevel Programming: Algorithm and Computational Experience

Abstract: We consider the approximation of nonlinear bilevel mathematical programs by solvable programs of the same type, i.e., bilevel programs involving linear approximations of the upper-level objective and all constraint-defining functions, as well as a quadratic approximation of the lower-level objective. We describe the main features of the algorithm and the resulting software. Numerical experiments tend to confirm the promising behavior of the method.

Analysis and design of current probe transition from grounded coplanar to substrate integrated rectangular waveguides

Abstract: The transition between a grounded coplanar waveguide (GCPW) and a substrate integrated rectangular waveguide (SIRW) is investigated in this paper. The proposed scheme makes use of a current probe to transfer power between the two dissimilar transmission lines. A computer-aided-design-oriented analytical model is developed in order to optimize the geometrical dimensions of the transition. By using the GCPW instead of the microstrip line to interface the SIRW, substrate thickness can be increased without incurring a penalty due to transmission loss. Therefore, it is possible to achieve higher Q components. Experiments at 28 GHz show that an effective bandwidth of 10% can easily be obtained. The insertion loss is less than 0.73 dB over the bandwidth of interest.

Deembedding static nonlinearities and accurately identifying and modeling memory effects in wide-band RF transmitters

Abstract: In this paper, a robust modeling technique for memoryless wide-band radio frequency transmitters using a dynamic exponential weighted moving average algorithm is developed and tested. To improve the relatively limited accuracy of the conventional Wiener model in predicting the response of dynamic nonlinear transmitters, a new augmented Wiener model is proposed along with its parameter-identification procedure. The accuracy of the augmented Wiener model is compared with that of the conventional Wiener model by using an L-band 60-W peak-envelope-power GaAs field-effect-transistor push-pull amplifier-based transmitter, which is driven by a two-carrier wide-band code-division multiple-access signal.

Thermodynamic modeling of the Fe-S system

Abstract: A thorough review and critical evaluation of phase equilibria and thermodynamic data for all phases in the iron-sulfur (Fe-S) binary system at 1 bar pressure has been made over the entire composition range for temperatures from 25 °C to above the liquidus. The Gibbs energies of ten phases have been modeled, and optimized model parameters have been obtained that reproduce all data simultaneously within experimental error limits. For the liquid phase, the recently extended modified quasi-chemical model is applied for the first time to a liquid metal-sulfur phase. A two-sublattice model within the framework of the compound energy formalism is used for the high-temperature monosulfide pyrrhotite solution. A substitutional model is used for the dissolution of S in solid iron. The Gibbs energies of six stoichiometric compounds are also modeled.

Substrate integrated waveguide (SIW) linear phase filter

Abstract: A planar four-pole linear phase filter centered at 10GHz based on substrate integrated waveguide (SIW) is proposed. The filter is composed of four side-by-side horizontally oriented SIW cavities, which are coupled in turn by evanescent waveguide sections with three direct coupling and one cross coupling between the first and fourth SIW cavities. The SIW cavities are fed by microstrips through coupling slots. A curve-fitting technique is adopted to improve the efficiency of the design process. The measured results are presented and compared with the results simulated by a high-frequency structure simulator. Good agreement between the simulated and measured results is observed.

Feature identification: a novel approach and a case study

Abstract: Feature identification is a well-known technique to identify subsets of a program source code activated when exercising a functionality. Several approaches have been proposed to identify features. We present an approach to feature identification and comparison for large object-oriented multi-threaded programs using both static and dynamic data. We use processor emulation, knowledge filtering, and probabilistic ranking to overcome the difficulties of collecting dynamic data, i.e., imprecision and noise. We use model transformations to compare and to visualise identified features. We compare our approach with a naive approach and a concept analysis-based approach using a case study on a real-life large object-oriented multi-threaded program, Mozilla, to show the advantages of our approach. We also use the case study to compare processor emulation with statistical profiling.

Super-compact multilayered left-handed transmission line and diplexer application

Abstract: A novel super-compact multilayered (ML) composite-right/left-handed (CRLH) transmission line (TL) is proposed. This ML architecture consists of the periodic repetition of pairs of U-shaped parallel plates connected to a ground enclosure by meander lines. The parallel plates provide the left-handed (LH) series capacitance, and the meander lines provide the LH shunt inductance, while the right-handed parasitic series inductance and shunt capacitance are generated by the metallic connections in the direction of propagation and by the voltage gradient from the TL to the ground enclosure, respectively. In contrast to previously reported planar LH or CRLH TLs, the ML TL has its direction of propagation along the vertical direction, perpendicular to the plane of the substrates. This presents the distinct advantage that large electrical length can be achieved over an extremely short TL length and small transverse footprint. The LH-range characteristics of the multilayer CRLH TL are analyzed by the finite-element method and finite-difference time-domain (FDTD) full-wave simulations. In addition, the CRLH equivalent-circuit model is applied to gain simple insight into the behavior of the structure. Finally, the theoretical results are confirmed by experiments using the initial prototype with the very small length (thickness) of 0.016/spl lambda//sub g/ and footprint of 0.06/spl lambda//sub g//spl times/0.08/spl lambda//sub g/ (/spl lambda//sub g/=/spl lambda//sub 0///spl radic//spl epsiv//sub r/=235 mm at the center of the LH band, 0.4 GHz). The proposed miniaturized ML line can find applications in bandpass filters, delay lines, and numerous phase-advance components. As an example of application, a 1-GHz/2-GHz diplexer, composed of two ML CRLH TLs, is demonstrated. The ML CRLH TL proposed here presents a great potential for the development of novel microwave components taking profit of new multilayer technologies such as low-temperature co-fired ceramic technology.

Critical thermodynamic evaluation and optimization of the CaO–MgO–SiO2 system

Abstract: A complete literature review, critical evaluation and thermodynamic modeling of phase diagrams and thermodynamic properties of all oxide phases in the CaO–MgO–SiO 2 system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model, and the Gibbs energies of the olivine and pyroxene solid solutions are modeled using the compound energy formalism. A set of optimized model parameters of all phases is obtained which reproduces all available and reliable thermodynamic and phase-equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures over the entire composition range. The complex phase relationships in the system have been elucidated, and discrepancies among the data have been resolved. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate all thermodynamic properties and any phase diagram section or phase equilibrium of interest.