Pointe-Claire, Canada
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Hendaoui A.,University of Québec | Emond N.,University of Québec | Chaker M.,University of Québec | Haddad E.,MPB Communications Inc.
Applied Physics Letters | Year: 2013

This paper describes a VO2-based smart structure with an emittance that increases with the temperature. A large tunability of the spectral emittance, which can be as high as 0.90, was achieved. The transition of the total emittance with the temperature was fully reversible according to a hysteresis cycle, with a transition temperature of 66.5 °C. The total emittance of the device was found to be 0.22 and 0.71 at 25 °C and 100 °C, respectively. This emittance performance and the structure simplicity are promising for the next generation of energy-efficient cost-effective passive thermal control systems of spacecrafts. © 2013 American Institute of Physics.

Zandi K.,Ecole Polytechnique de Montréal | Wong B.,MPB Communications Inc. | Zou J.,MPB Communications Inc. | Kruzelecky R.V.,MPB Communications Inc. | And 2 more authors.
Proceedings of the IEEE International Conference on Micro Electro Mechanical Systems (MEMS) | Year: 2010

A novel in-plane Silicon-On-insulator (SOI) optical accelerometer using a Fabry-Perot microcavity with two distributed Bragg reflectors (DBR) is presented, in which one DBR mirror is attached to two suspended proof masses. As a consequence of acceleration, the relative displacement of the movable mirror with respect to the fixed one changes the cavity length and modifies the Fabry-Perot resonance. All of the device components are fabricated by using one single fabrication step. The sensor performance could reach μg resolution with a demonstrated 2.5 nm/g sensitivity and 400 μg resolution. ©2010 IEEE.

Hendaoui A.,INRS - Institute National de la Recherche Scientifique | Emond N.,INRS - Institute National de la Recherche Scientifique | Dorval S.,INRS - Institute National de la Recherche Scientifique | Chaker M.,INRS - Institute National de la Recherche Scientifique | Haddad E.,MPB Communications Inc.
Current Applied Physics | Year: 2013

This work involves the study of the positive emittance-switching (i.e. emittance that increases with increasing the temperature) of thermochromic VO2 films deposited using reactive pulsed laser deposition (RPLD) on Al substrates. The temperature dependence of the emittance of a 260 nm-thick VO2 film on Al substrate revealed a maximum of the emittance of 0.29 around 68°C. It is attributed to an increase in the infrared radiation absorption by the VO2 film due to the coexistence of both insulating and metallic phases in the vicinity of the transition temperature of VO 2. The emittance tunability between 25°C and 68°C is 0.21. Since practical SRD application requires both high emittance at high temperature and large tunability, we demonstrate, by both simulation and fabrication, that these goals can be accomplished to some extent by a top dielectric a-Si:H/SiO2 λ/4 stack layer. In fact, the addition of a-Si:H/SiO2 λ/4 overlayer results in an increase of the maximum value of the emittance by 114% (from 0.29 to 0.62) as well as an increase of the tunability by 81% (from 0.21 to 0.38). This work reports an important improvement of the positive emittance-switching efficiency of the VO2-based structures and holds promise for a new generation of smart radiator devices (SRDs) for a passive thermal control of spacecrafts. © 2013 Elsevier B.V. All rights reserved.

Gong S.,York University | Zhu Z.H.,York University | Haddad E.I.,MPB Communications Inc.
Journal of Applied Physics | Year: 2013

This paper investigates the effect of carbon nanotube (CNT) deformation on the electrical conductivity of CNT polymer composites at crossed nanotube junctions using a revised 3-dimensional CNT percolating network model. Two aspects of the work are considered. The first is concerned with the effect of CNT deformation on its intrinsic and contact resistances at CNT-CNT junctions. An analytical model based on electron ballistic tunneling theory and Landauer-Büttiker formula is proposed to describe the variation of CNT-CNT contact resistance at the CNT-CNT junction in terms of local deformation of CNT walls and CNT-CNT distance. In addition, a model exclusively based on experimental data to describe the change of CNT intrinsic resistance in terms of its cross-section deformation is adopted. The second is concerned with the relationship among the CNT-CNT distance, the angle between two adjacent CNTs, and the dimensions of local deformation of CNT walls and its impact on the corresponding intrinsic and contact resistance of CNTs near and at a CNT-CNT junction. Finally, Monte Carlo simulations are conducted to evaluate these effects on the electrical conductivity of nanocomposites for different CNT weight fractions. Our results reveal that the local deformation of CNT walls plays a significant role in the evaluation of electrical conductivity of CNT polymer composites. The intrinsic resistance in the deformed part of CNTs near a CNT-CNT junction increases much faster than the decrease of CNT-CNT contact resistance at the same junction when two CNTs are getting closer, resulting in a net increase of resistance at the junction. Numerical results show that the current model agrees with existing experimental data better than existing models without considering the effect of CNT deformation, which tends to overestimate the electrical conductivity of CNT polymer composites containing homogeneously dispersed percolating CNT network. © 2013 AIP Publishing LLC.

Turitsyn S.K.,Aston University | Turitsyn S.K.,Novosibirsk State University | Bednyakova A.E.,Novosibirsk State University | Fedoruk M.P.,Novosibirsk State University | And 2 more authors.
Nature Photonics | Year: 2015

An important group of nonlinear processes in optical fibre involve the mixing of four waves due to the intensity dependence of the refractive index. It is customary to distinguish between nonlinear effects that require external/pumping waves (cross-phase modulation and parametric processes such as four-wave mixing) and those arising from self-action of the propagating optical field (self-phase modulation and modulation instability). Here, we present a new nonlinear self-action effect - self-parametric amplification - which manifests itself as optical spectrum narrowing in normal dispersion fibre, leading to very stable propagation with a distinctive spectral distribution. The narrowing results from inverse four-wave mixing, resembling an effective parametric amplification of the central part of the spectrum by energy transfer from the spectral tails. Self-parametric amplification and the observed stable nonlinear spectral propagation with a random temporal waveform can find applications in optical communications and high-power fibre lasers with nonlinear intracavity dynamics. © 2015 Macmillan Publishers Limited.

Hendaoui A.,INRS - Institute National de la Recherche Scientifique | Emond N.,INRS - Institute National de la Recherche Scientifique | Dorval S.,INRS - Institute National de la Recherche Scientifique | Chaker M.,INRS - Institute National de la Recherche Scientifique | Haddad E.,MPB Communications Inc.
Solar Energy Materials and Solar Cells | Year: 2013

One of the major challenges facing the use of thermochromic coatings as efficient Smart Radiator Devices (SRDs) for a passive energy-efficient thermal control of spacecrafts is the limited high temperature emittance that can be achieved with present devices. Through an elegant choice of the thickness of an SiO2 layer being part of a VO2-based SRD multilayer structure, we obtained an emittance as high as 0.80 at high temperature, while maintaining a large emittance tunability. More interestingly, by doping VO 2 with tungsten (W), the transition temperature of pure VO 2 occurring originally at about 68 C could be decreased down to about 19.5 C with 2.9 at% of W. The average decrease rate of the transition temperature was found to be ~16.5 C per 1 at% of W. This reduction was accompanied by a displacement of the emittance transition region that can be tailored over a wide range of temperatures, and by a shrinking of the hysteresis width. This work constitutes an important breakthrough toward practical applications of thermochromic VO2-based smart coatings for passive energy-efficient thermal control of spacecrafts close to room temperature. © 2013 Elsevier B.V.

MPB Communications Inc. | Date: 2010-06-08

The emittance value is a measure of an amount of energy expelled from a given surface area relative to a black-body reference. Depending on the specific coating a change in the emittance value is actively or passively effected. There are known active variable emittance thermal control coatings. However, such coatings are actually panels housing a mixture of both high and low emissivity materials that are electrically manipulated to control the emittance value of the panel. These coatings are classified as either electrochromic or electrophorectic. Both electrochromic and electrophorectic coatings require an applied voltage to cause a change in the emittance value of the coating. By contrast, aspects of the present invention do not include active variable emittance thermal control coatings. Aspects of the present invention do include passive variable emittance thermal control coatings and materials. In accordance with aspects of the present invention passive means that the variable emittance value changes in response to changes in the environment without active control (e.g. neither a voltage nor a current is applied). More specifically, in accordance with one aspect of the invention a passive variable emittance thermochromic material is provided that has a relatively low emittance value at low temperatures and a relatively high emittance value at high temperatures.

There is provided a system for remote pumping of a Raman fiber amplifier comprising a pump laser located remotely from the Raman fiber amplifier and a laserhead and one or more optical fibers to optically couple the high power pump light from the remote pump laser to the Raman fiber amplifier where a seed laser light is amplified wherein the pump laser for producing a high power laser light of a predetermined pump wavelength comprises a first fiber laser emitting light at the predetermined pump wavelength and one (second) or two (third) laser emitting light at a wavelength lower than the predetermined pump wavelength and multiplexed with light from the first laser into an optical fiber providing Raman gain at the predetermined pump wavelength to convert the second (and optionally also the third) laser light to light at the predetermined pump wavelength.

Benkahoul M.,INRS - Institute National de la Recherche Scientifique | Chaker M.,INRS - Institute National de la Recherche Scientifique | Margot J.,University of Montréal | Haddad E.,MPB Communications Inc. | And 4 more authors.
Solar Energy Materials and Solar Cells | Year: 2011

Thermochromic VO2 thin films were deposited on various substrates, namely quartz, Si, and Al, using RF reactive magnetron sputtering deposition. IR thermometry measurements reveal that the emissivity properties of the system VO2/substrate strongly depend on the IR optical properties of the substrate. VO2 films deposited on a highly IR reflective substrate such as Al, present an emissivity dependence on temperature that is opposite to that of VO2 deposited on an IR transparent substrate, like quartz and Si. XPS and Raman measurements show that VO 2 undergoes a crystalline structure transition from monoclinic to tetragonal when deposited on Al, quartz, and Si. They also confirm that the transition is accompanied by a change from an insulator or semiconductor state to a metallic state. The emissivity performance of VO2/Al as compared to that of VO2/quartz and VO2/Si is attributed to the higher IR reflective properties of Al in comparison to quartz and Si. The increase of emissivity with temperature makes the VO2/Al system of strong interest as a passive smart radiator device for thermal control of spacecraft. © 2011 Elsevier B.V. All rights reserved.

Agency: European Commission | Branch: FP7 | Program: CP-FP | Phase: SPA.2012.3.1-01 | Award Amount: 1.87M | Year: 2013

Fueled by mass market demand, terrestrial consumer electronics continue to drive technology advancement in the field of microelectronics devices. Many of these technologies are spearheaded by the contributions of Small and Medium Enterprise (SME). There is a clear opportunity to revolutionize space technologies by leveraging advancement in the commercial electronics market. However, despite the obvious benefits to the space industry, it remains difficult for SMEs to get involved due to the significant cost, effort, time, and paper work to qualify parts for space applications. A trend toward smaller and cheaper satellites allows for a novel approach to space qualification and testing. Nanosatellites (between 1kg and 10kg) can be launched at a relatively low cost as piggy back payloads for larger satellite missions. Since the cost of failure is an order of magnitude lower than conventional satellites, nanosatellites offer an ideal platform for high risk demonstration missions. The aim of this project is to flight qualify a wide range of SME payloads in a 3U 3kg nanosatellite platform operating at a 700km orbit. The primary purpose of this spacecraft is as a technology demonstrator. Each SME in the consortium will be responsible for contributing a particular spacecraft subsystem. The University of Surrey will integrate these systems into the nanosatellite platform, and will also be responsible for the ADCS and CMGs of the satellite. ISIS will oversee the launch opportunity and deployment of the satellite. Astrium, as a Large System Integrator (LSI), will help roadmap the technology demonstrated in this mission to future applications within the European space framework.

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