Benjamin R. Lavoie

Low-loss surface modes and lossy hybrid modes in metamaterial waveguides

Abstract We show that waveguides with a dielectric core and a lossy metamaterial cladding (metamaterial-dielectric guides) can support hybrid ordinary-surface modes previously only known for metal-dielectric waveguides. These hybrid modes are potentially useful for frequency filtering applications as sharp changes in field attenuation occur at tailorable frequencies. Our results also show that the surface modes of a metamaterial-dielectric waveguide with comparable electric and magnetic losses can be less lossy than the surface modes of an analogous metal-dielectric waveguide with electric losses alone. Through a characterization of both slab and cylindrical metamaterial-dielectric guides, we find that the surface modes of the cylindrical guides show promise as candidates for all-optical control of low-intensity pulses.

Estimating the Effective Permittivity for Reconstructing Accurate Microwave-Radar Images

We present preliminary results from a method for estimating the optimal effective permittivity for reconstructing microwave-radar images. Using knowledge of how microwave-radar images are formed, we identify characteristics that are typical of good images, and define a fitness function to measure the relative image quality. We build a polynomial interpolant of the fitness function in order to identify the most likely permittivity values of the tissue. To make the estimation process more efficient, the polynomial interpolant is constructed using a locally and dimensionally adaptive sampling method that is a novel combination of stochastic collocation and polynomial chaos. Examples, using a series of simulated, experimental and patient data collected using the Tissue Sensing Adaptive Radar system, which is under development at the University of Calgary, are presented. These examples show how, using our method, accurate images can be reconstructed starting with only a broad estimate of the permittivity range.

Slow light with three-level atoms in metamaterial waveguides

Metamaterial is promising for enhancing the capability of plasmonic devices. We consider a cylindrical waveguide with three-level \Lambda\ atoms embedded in the dielectric core. By comparing metal cladding vs metamaterial cladding of a waveguide with \Lambda\ atoms in the core, we show that, for a fixed amount of slowing of light due to electromagnetically induced transparency, the metamaterial cladding outperforms in terms of the inherent loss.

Evaluation of Image Reconstruction Algorithms for Confocal Microwave Imaging: Application to Patient Data

Confocal Microwave Imaging (CMI) for the early detection of breast cancer has been under development for over two decades and is currently going through early-phase clinical evaluation. The image reconstruction algorithm is a key signal processing component of any CMI-based breast imaging system and impacts the efficacy of CMI in detecting breast cancer. Several image reconstruction algorithms for CMI have been developed since its inception. These image reconstruction algorithms have been previously evaluated and compared, using both numerical and physical breast models, and healthy volunteer data. However, no study has been performed to evaluate the performance of image reconstruction algorithms using clinical patient data. In this study, a variety of imaging algorithms, including both data-independent and data-adaptive algorithms, were evaluated using data obtained from a small-scale patient study conducted at the University of Calgary. Six imaging algorithms were applied to reconstruct 3D images of five clinical patients. Reconstructed images for each algorithm and each patient were compared to the available clinical reports, in terms of abnormality detection and localisation. The imaging quality of each algorithm was evaluated using appropriate quality metrics. The results of the conventional Delay-and-Sum algorithm and the Delay-Multiply-and-Sum (DMAS) algorithm were found to be consistent with the clinical information, with DMAS producing better quality images compared to all other algorithms.

Adaptive Monostatic System for Measuring Microwave Reflections from the Breast

A second-generation monostatic radar system to measure microwave reflections from the human breast is presented and analyzed. The present system can measure the outline of the breast with an accuracy of ±1 mm and precisely place the microwave sensor in an adaptive matter such that microwaves are normally incident on the skin. Microwave reflections are measured between 10 MHz to 12 GHz with sensitivity of 65 to 75 dB below the input power and a total scan time of 30 min for 140 locations. The time domain reflections measured from a volunteer show fidelity above 0.98 for signals in a single scan. Finally, multiple scans of a breast phantoms demonstrate the consistency of the system in terms of recorded reflection, outline measurement, and image reconstruction.

Comparison of radar-based microwave imaging algorithms applied to experimental breast phantoms

Microwave imaging is a promising imaging modality for the early detection of breast cancer. The two most important signal processing components of a radar-based microwave imaging system are the early-time artifact removal and the image reconstruction algorithm. Several image reconstruction algorithms have been developed and their performance has been evaluated in a number of studies. However, most of these evaluation studies were either performed on numerical breast phantoms or used an idealized artifact removal algorithm. In this paper, a range of both data independent and data adaptive imaging algorithms are evaluated using experimental breast phantoms in combination with a realistic artifact removal algorithm. The clutter rejection capabilities of each algorithm are assessed in the presence of experimental noise and residual artifacts using a range of appropriate image quality metrics.

Hybrid mode tunability in metamaterial nanowaveguides

Abstract. We employ the properties of metamaterials to tailor the modes of metamaterial-dielectric waveguides operating at optical frequencies. We survey the effects of three-dimensional isotropic metamaterial structural parameters on the refractive index of metamaterials and on the hybrid modes in slab metamaterial-dielectric waveguides. Hybrid modes refer to hybrid ordinary-surface plasmon polariton modes in the waveguide structures. We investigate how robust metamaterials are to fluctuations in their structural parameters; specifically, we examine the effects of Gaussian errors on the metamaterials electromagnetic behavior. Our survey enables us to determine the allowable fluctuation limits and from this to identify appropriate unit-cell structure for further applications of metamaterials in waveguide technologies.

Characterization of surface-plasmon polaritons at lossy interfaces

We characterize surface-plasmon polaritons at lossy planar interfaces between one dispersive and one nondispersive linear isotropic homogeneous media, i.e., materials or metamaterials. Specifically we solve Maxwells equations to obtain strict bounds for the permittivity and permeability of these media such that satisfying these bounds implies surface-plasmon polaritons successfully propagate at the interface, and violation of the bounds impedes propagation, i.e., the field delocalizes from the surface into the bulk. Our characterization of surface-plasmon polaritons is valuable for checking viability of a proposed application, and, as an example, we employ our method to falsify a previous prediction that surface-plasmon propagation through a surface of a double-negative refractive index medium occurs for any permittivity and permeability; instead we show that propagation can occur only for certain medium parameters.

An Analysis of the Assumptions Inherent to Near-Field Beamforming for Biomedical Applications

Microwave imaging for biomedical applications is a growing field that shows promise in early patient studies. Interpretation of preclinical imaging results is difficult, in part due to an incomplete understanding of the imaging operator. In this paper, near-field beamforming is demonstrated to be analogous to synthetic aperture radar, and both imaging methods are shown to depend on several simplifying assumptions. The influence of these assumptions is analyzed using analytical and simulated models, and the results are confirmed in an experimental setup. These observations are further explored in application to simulations of realistic breast models as well as patient data.

Performance of leading artifact removal algorithms assessed across microwave breast imaging prototype scan configurations

Microwave imaging is a promising imaging modality for the detection of early-stage breast cancer. One of the most important signal processing components of microwave radar-based breast imaging is early-stage artifact removal. Several artifact removal algorithms have been reported in the literature. However, the neighbourhood-based skin subtraction and hybrid artifact removal algorithms have shown particularly promising results in different realistic 3D breast phantoms. For the first time in this paper, both algorithms have been evaluated and compared using the scan approaches of the most common microwave breast imaging prototype systems. The tests include 3D numerical as well as experimental breast phantoms scanned with hemispherical, cylindrical and adaptive scanning patterns. The efficacy of both algorithms has been evaluated across a range of appropriate performance metrics.