Gabriel Cormier

Real-coded genetic algorithm for Bragg grating parameter synthesis

We propose to use a genetic algorithm to determine the physical parameters of Bragg gratings from their reflection spectra for both design purposes and fiber sensor applications. A real-coded genetic algorithm is used for inversion purposes, along with an F-matrix formalism for synthesis of uniform, chirped, and apodized gratings. An example of bandpass filter design is also studied. The method is easily applicable and shows promising results.

Genetic algorithm for ellipsometric data inversion of absorbing layers

A new data reduction method is presented for single-wavelength ellipsometry. A genetic algorithm is applied to ellipsometric data to find the best fit. The sample consists of a single absorbing layer on a semi-infinite substrate. The genetic algorithm has good convergence and is applicable to many different problems, including those with different independent measurements and situations with more than two angles of incidence. Results are similar to those obtained by other inversion techniques.

Design of X-Band GaN Phase Shifters

This paper presents two different types of high-power gallium-nitride (GaN) phase shifters designed for X-band (8-12 GHz), but offering good performance over a much wider band. The first is a 22.5° switched-filter phase shifter, which has much wider bandwidth than is typically found with this configuration, while maintaining low insertion loss (<; 2 dB), good return loss ( >11.15 dB), and an amplitude imbalance of less than 1.03 dB across X-band. The 1-dB compression point was higher than laboratory equipment was able to measure ( >38 dBm) and the phase shifter monolithic microwave integrated circuit exhibited an input-referred third-order intercept point (IIP3) of 46.2 dBm. The second phase shifter is a novel design, which promises wide bandwidth (in our case, limited by the single-pole double-throw switch we have also designed), but which achieves decent insertion loss (5 dB), good return loss (better than 11 dB), and very low phase variation (1°) across X-band, also with 22.5° phase shift. It offers a 1-dB compression point of 30.1 dBm and an IIP3 of 46.3 dBm. The components for a 45 ° differential phase shift using the same structure were also fabricated and verified with measurements. The high-power phase shifters have been fabricated in a 0.5- μm GaN HEMT process and were designed using an accurate customized switch field-effect transistor model.

Wind Speed Prediction for a Target Station using Neural Networks and Particle Swarm Optimization

In this study, artificial neural networks (ANN) and particle swarm optimization (PSO) were applied to predict the average daily wind speed measured at a meteorological tower installed June 2005 at the Greater Moncton Sewerage Commission, in Moncton, New Brunswick, Canada. Wind speeds were collected covering the period between June 2005 and December 2008. Five reference airport meteorological stations were used as input for the neural network and PSO. The artificial neural network modeling was done using the Matlab® neural network toolbox, while the PSO algorithm is an in-house program written in Matlab®. The daily wind speeds generated by the ANN model and PSO were compared with the actual measured data. It was found that with six months of input data, both the ANN and the PSO were able to predict the short term daily wind speed for the following 36 months at the target station. The PSO obtained a smaller error compared to the neural network. The PSO algorithm was also able to find the best combination of input variables automatically, while the ANN used manually-selected input variables.

High-power X-band GaN switched-filter phase shifter

This paper presents a high-power switched-filter GaN phase shifter, designed for X-band and offering good performance from 8-16 GHz. The manufactured 0°/22.5° switched-filter phase shifter has much wider bandwidth than is typically found with this configuration, while maintaining low insertion loss (<; 2 dB), good return loss (> 11.15 dB) and an amplitude imbalance of less than 1.03 dB across X-band. The 1 dB compression point was higher than laboratory equipment was able to measure (> 38 dBm) and the phase shifter MMIC exhibited an IIP3 higher than 46 dBm. The proposed high-power phase shifter has been fabricated in a 0.5 μm GaN HEMT process and was designed using an accurate, customized switch FET model.

Particle swarm optimization for ellipsometric data inversion of samples having an arbitrary number of layers

A method is presented for performing the inversion of ellipsometric data using a hybrid approach involving a particle swarm optimization algorithm and a Levenberg-Marquardt algorithm. A sample may be composed of any number of layers of transparent or absorbing materials on a substrate. The method described is applicable to single- or multiple-angle, single-wavelength ellipsometry. The results of the particle swarm optimization algorithm agree well with previously published data calculated using different ellipsometric inversion algorithms, and converges for wide ranges of initial parameter estimates.

Improved determination of the optical constants of anisotropic thin films by ellipsometry using ant colony fitting algorithms

Birefringent TiO2 thin films were characterized using spectroscopic ellipsometry. Ellipsometric data were fitted to a model, taking into account the anisotropic nature of the film and the coherence length of the source being shorter than the thickness of the substrate. Using a conventional gradient-based algorithm often produced a wrong set of optical constants corresponding to a local minimum of the objective function, unless the initial guess was carefully chosen. Using an optimization algorithm inspired by the foraging behavior of ants makes it possible to systematically find that small region in the parameter space where the best solution lies, without a priori knowledge of the optical properties of the sample. The proposed method is especially suitable for samples with unknown optical properties or complex materials, such as anisotropic thin films, for which a large number of parameters are needed to describe them.

Development of a Model for a Microwave GaInP\/GaAs HBT

This article presents the development of a nonlinear model for a microwave gallium indium phosphide (GaInP)/gallium arsenide (GaAs) heterojunction bipolar transistor (HBT). This model tied for first prize in the Microwave Transistor Modeling student competition held during the 2014 IEEE Microwave Theory and Techniques Society International Microwave Symposium (IMS2014) in Tampa, Florida.

Extraction of a Model for a Microwave Power pHEMT

This article presents the development of a large-signal transistor model for a power microwave pseudomorphic high-electron mobility transistor (pHEMT). This model won the first prize in the Microwave Transistor Modeling student competition held during the 2013 IEEE Microwave Theory and Techniques Society (MTT-S) International Microwave Symposium (IMS2013) in Seattle, Washington.

Miniature single-sideband subharmonically-pumped 60 GHz direct upconverter in a uniplanar GaAs pHEMT technology using inductive and capacitive loading techniques

This paper presents a novel, compact, single-sideband (SSB) subharmonically-pumped (SHP) direct upconverter developed in a uniplanar 0.18 mu m GaAs technology. A total of 100 MHz in-phase and quadrature signals directly modulate the second harmonic of a 30 GHz carrier signal, producing a 60.1 GHz output. Two pairs of antiparallel diodes reduce feed-through of the 30 GHz local oscillator (LO) signal to the mixers RF output. Novel structures patterned in the center conductor of a coplanar waveguide (CPW) provide matching and size-reduction simultaneously. The 2.1mm(2) circuit also uses a miniaturized Wilkinson divider based on asymmetric coplanar stripline and a standard CPW 90 degrees coupler. The SSB SHP direct upconverter exhibits a conversion loss of 10 dB, a lower-sideband rejection of 15 dB and 2f(LO) suppression of approximately 25 dB over a wide frequency range from 52-61 GHz.