Andrew E. Marble

Flow imaging of fluids in porous media by magnetization prepared centric-scan SPRITE

MRI has considerable potential as a non-destructive probe of porous media, permitting rapid quantification of local fluid content and the possibility of local flow visualization and quantification. In this work we explore a general approach to flow velocity measurement in porous media by combining Cotts pulsed field gradient flow encoding with SPRITE MRI. This technique permits facile and accurate flow and dispersion coefficient mapping of fluids in porous media. This new approach has proven to be robust in characterizing fluid behavior. This method is illustrated through measurements of flow in pipes, flow in sand packs and flow in porous reservoir rocks. Spatially resolved flow maps and local fluid velocity distribution were acquired.

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions.

Water transport and water management are fundamental to polymer electrolyte membrane fuel cell operation. Accurate measurements of water content within and across the Nafion layer are required to elucidate water transport behavior and validate existing numerical models. We report here a direct measurement of water content profiles across a Nafion layer under wetting and drying conditions, using a novel magnetic resonance imaging methodology developed for this purpose. This method, multi-echo double half k-space spin echo single point imaging, based on a pure phase encode spin echo, is designed for high resolution 1D depth imaging of thin film samples. The method generates high resolution (<8 microm) depth images with an SNR greater than 20, in an image acquisition time of less than 2 min. The high temporal resolution permits water content measurements in the transient states of wetting and drying, in addition to the steady state.

Designing Static Fields for Unilateral Magnetic Resonance by a Scalar Potential Approach

We present a method for designing single-sided magnets suitable for unilateral magnetic resonance (UMR) measurements. The method uses metal pole pieces to shape the field from permanent magnets in a target region. The pole pieces are shaped according to solutions to Laplaces equation, and can be designed using a combination of analytical methods and numerical optimization. The design leads to analytical expressions for the pole piece shapes and magnetic field. Here, we develop the method in Cartesian, polar, and spherical coordinates, and discuss the merits of each system. Finite magnet size has a substantial effect on the field quality in many cases, according to our simulations. We found that in order to achieve a compact magnet in which the static field closely matches that specified, a full 3-D design approach is necessary. A magnet designed by our method produces a static field with a constant gradient over a region 2 cm in diameter and 2 mm thick. This leads to a compact cylindrical magnet just over 11 cm in diameter, topped with a single metal pole piece. The design is validated through simulation. The simulated field is found to agree closely with that specified analytically through the design procedure

Stimulated Brillouin scattering modeled through a finite difference time domain approach

Stimulated Brillouin scattering (SBS), in an optical fiber, is a three-wave interaction (3WI) resulting from a coupling between light and acoustic waves. In a fiber optic sensing context, SBS results from the interaction between counterpropagating pulsed and continuous fields. We formulate a solution to the time dependant, one dimensional 3WI model in a SBS based fiber optic sensor. It is shown that a low complexity, first order finite difference time domain (FDTD) solution is capable of accurately modelling the dynamics of SBS with little computational effort. A modification to the first order scheme is proposed to combat numerical damping and dispersion, brought on by the low order of the solution. Examples are presented, validating the performance of our modelling technique. The effect of pulse power and risetime on the resulting scattering is examined, along with the effects of γa, an intrinsic fibre parameter related to the linewidth of the Brillouin spectrum. The spatial and temporal evolution of the acoustic field is illustrated; the effect of the steady state value of this field on the 3WI is investigated. The steady state acoustic field strength is related to the extinction ratio of the pulsed source, and it is found that this parameter has a significant influence on the scattering. This type of modelling provides a rapid means of investigating SBS as a tool in fiber optic sensing.

Anomaly detection of stationary targets in pan-sharpened IKONOS multispectral imagery

Multispectral (MS) and hyperspectral (HS) sensors can facilitate target or anomaly detection in clutter since natural clutter and man-made objects diff er in the energy they radiate across the electromagnetic spectrum. Previous research in anomaly detection has formulated two popular algorithms: those based on Gauss-Markov Random Fields (GMRF) and the so-called RX-detector. Performance of these algorithms is dependent on a number of issues including spatial resolution, spectral correlation between the imaging bands, clutter/target model accuracy and the acquired datas signal-to-noise ratio (SNR). This paper provides a comparison study of the anomaly detection performance of the RXdetector and the GMRF-based algorithm using: (1) 4m MS imagery acquired f rom the IKONOS satellite and (2) pansharpened 1m MS imagery created by fusing the 4m MS and the associated 1m panchromatic image sets. The study will be based on the detection performance for stationary and slow moving targets selected f rom imagery acquired during training exercises at Canadian Forces Base (CFB) Petawawa and CFB Wainwright, Canada.

Projection Pursuit Feature Analysis for Pan-Sharpened Multispectral Ikonos Imagery

Orbiting multispectral (MS) sensors can facilitate feature discrimination in clutter since natural clutter and man-made objects often differ in the energy they radiate across the electromagnetic spectrum. The projection pursuit technique (PP) has been previously proposed for assessing information content in large multivariate data sets such as hyperspectral (HS) imagery. Although the number of spectral bands is limited in MS data sets, this study investigates the suitability of PP for target detection. PP can highlight different features of interest in an image, improving and simplifying subsequent detection. This study uses two data sets: (1) 4 m MS IKONOS data and (2) pan-sharpened 1 m IKONOS MS imagery created by fusing the 4m MS and the associated 1 m panchromatic image sets. It is shown that PP based on the information divergence index can facilitate detection of certain targets, and emphasize features in MS data. This paves the way for an automated target detection and recognition system based around a PP preprocessing procedure

Flux guiding in an aluminum honeycomb lattice observed through magnetic resonance imaging

Using a finite integration (FI) electromagnetic model of a simulation software, a three dimensional section of aluminum honeycomb is analyzed. It is shown that, at 8 MHz, this structure behaves as a flux guide, preventing the attenuation of a penetrating magnetic field. The flux guiding effect was confirmed through MRI measurement of water inside an aluminum honeycomb panel. It was found that the aluminum lattice extended the range of the RF magnetic field used in MRI, allowing measurements to be made at a greater distance from a surface coil MRI probe than would otherwise be possible. The flux guiding effect is theorized to be the result of the structure of the aluminum honeycomb lattice. This structure parallels the construction of other engineered materials designed to have artificially high apparent permeability at certain frequencies.