Joe LoVetri - Academia.edu (original) (raw)
Papers by Joe LoVetri
International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
We introduce a non-linear inversion algorithm for use in microwave biomedical imaging when the ob... more We introduce a non-linear inversion algorithm for use in microwave biomedical imaging when the object of interest is surrounded by an arbitrarily shaped conducting enclosure. The algorithm utilizes the Gauss-Newton inversion method and a combined additive and multiplicative regularizer. The conducting enclosure is taken into account via a FEM-based forward solver which is able to efficiently model arbitrarily shaped boundaries. Results for the 2D scalar case are given when the enclosure is a circle, triangle, and square, and include simple and complex biological scatterers, based on synthetic data. The results show that the algorithm is capable of reconstructing objects in all cylinder types.
IEEE Transactions on Biomedical Engineering, 2010
In this paper, we describe a 2-D wideband microwave imaging system intended for biomedical imagin... more In this paper, we describe a 2-D wideband microwave imaging system intended for biomedical imaging. The system is capable of collecting data from 3 to 6 GHz, with 24 coresident antenna elements connected to a vector network analyzer via a 2 × 24 port matrix switch. As one of the major sources of error in the data collection process is a result of the strongly coupling 24 coresident antennas, we provide a novel method to avoid the frequencies where the coupling is large enough to prevent successful imaging. Through the use of two different nonlinear reconstruction schemes, which are an enhanced version of the distorted born iterative method and the multiplicative regularized contrast source inversion method, we show imaging results from dielectric phantoms in free space. The early inversion results show that with the frequency selection procedure applied, the system is capable of quantitatively reconstructing dielectric objects, and show that the use of the wideband data improves the inversion results over single-frequency data.
IEEE Transactions on Antennas and Propagation, 2000
ABSTRACT The contrast source inversion algorithm is formulated using the finite-element method fo... more ABSTRACT The contrast source inversion algorithm is formulated using the finite-element method for two-dimensional transverse electric microwave imaging problems. Edge-based triangular elements with vector basis functions are utilized to solve the TE electromagnetic problem. A single finite-element method (FEM) mesh is used to model both the electric field as well as the contrast-source and contrast variables used in the inverse problem. The electromagnetic field is modeled by taking the unknown values to be the tangential components of the transverse electric field along the edges of each triangular element. The unknown contrast-source and contrast variables are located at the centroids of every triangular element of the same FEM mesh, but only inside the imaging domain. The adaptation of the FEM-contrast source inversion (FEM-CSI) algorithm to 2D-TE problems on such an arbitrary mesh requires the implementation of special transformation operators which are presented herein. The algorithm's capabilities are demonstrated by inverting the Fresnel experimental TE datasets as well as synthetically generated data.
IEEE Transactions on Microwave Theory and Techniques, 2000
ABSTRACT The multiplicatively regularized Gauss-Newton inversion (GNI) algorithm is enhanced and ... more ABSTRACT The multiplicatively regularized Gauss-Newton inversion (GNI) algorithm is enhanced and utilized to obtain complex permittivity profiles of biological objects-of-interest. The microwave scattering data is acquired using a microwave tomography system comprised of 24 co-resident antennas immersed into a saltwater matching fluid. Two types of biological targets are imaged: ex vivo bovine legs and in vivo human forearms. Four different forms of the GNI algorithm are implemented: a blind inversion, a balanced inversion, a shape-and-location inversion, and a novel balanced shape-and-location inversion. The latter three techniques incorporate typical permittivity values of biological tissues as prior information to enhance the reconstructions. In those images obtained using the balanced shape-and-location reconstruction algorithm, the various parts of the tissue being imaged are clearly distinguishable. The reconstructed permittivity values in the bovine leg images agree with those obtained via direct measurement using a dielectric probe. The reconstructed images of the human forearms qualitatively agree with magnetic resonance imaging images, as well as with the expected dielectric values obtained from the literature.
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009
We describe a 2D wide-band multi-frequency microwave imaging system intended for biomedical imagi... more We describe a 2D wide-band multi-frequency microwave imaging system intended for biomedical imaging. The system is capable of collecting data from 2-10 GHz, with 24 antenna elements connected to a vector network analyzer via a 2 times 24 port matrix switch. Through the use of two different nonlinear reconstruction schemes: the Multiplicative-Regularized Contrast Source Inversion method and an enhanced version of the Distorted Born Iterative Method, we show preliminary imaging results from dielectric phantoms where data were collected from 3-6 GHz. The early inversion results show that the system is capable of quantitatively reconstructing dielectric objects.
International Journal of Ultra Wideband Communications and Systems, 2010
Vivaldi antenna is widely known as a broadband antenna. In this paper, we investigate a modified ... more Vivaldi antenna is widely known as a broadband antenna. In this paper, we investigate a modified Vivaldi antenna with improved cross polarisation working in the ultra-wideband (UWB) frequency range (3.1-10.6 GHz) to be used as multiple probes for microwave tomography system. Our study includes investigation of radiation characteristics of the antenna, antenna design steps, fabrication sensitivity effects on the antenna performance and proposing and implementing a twenty-four antenna element system for fast data acquisition, including a novel method for frequency selection in microwave tomography applications. We also studied the fidelity parameter of the antennas inside the twenty-four element setup. The mutual coupling of adjacent elements, in spite of close proximity, is less than -17dB and fidelity variations for the antennas located in front of transmitter are less than 10%.
IEEE Antennas and Wireless Propagation Letters, 2011
Imaging with microwave tomography systems requires both the incident field within the imaging dom... more Imaging with microwave tomography systems requires both the incident field within the imaging domain as well as calibration factors that convert the collected data to corresponding data in the numerical model used for inversion. The numerical model makes various simplifying assumptions, e.g., 2-D versus 3-D wave propagation, which the calibration coefficients are meant to take into account. For an air-based microwave tomography system, we study two types of calibration techniques-incident and scattered field calibration-combined with two different incident field models: a 2-D line-source and an incident field from full-wave 3-D simulation of the tomography system. Although the 2-D line-source approximation does not accurately model incident field in our system, the use of scattered field calibration with the 2-D line-source provides similar or better images to incident and scattered field calibration with an accurate incident field. Thus, if scattered field calibration is used, a simple (but inaccurate) incident field is acceptable for our microwave tomography system. While not strictly generalizable, we expect our methodology to be applicable to most other microwave tomography systems.
Progress In Electromagnetics Research, 2013
The multiplicatively regularized finite-element contrast source inversion algorithm (MR-FEM-CSI) ... more The multiplicatively regularized finite-element contrast source inversion algorithm (MR-FEM-CSI) is used to solve the fullvectorial three-dimensional (3D) inverse scattering problem. The contrast and contrast-source optimization variables are located at the centroids of tetrahedra within the problem domain; whereas the electric field is expanded in terms of edge basis functions on the same tetrahedra. A dual-mesh is created in order to apply the multiplicative regularization. To handle large-scale problems the inversion algorithm is parallelized using the MPI library, with sparse matrix and vector computations supported by PETSc. The algorithm is tested using experimental datasets obtained from the Institut Fresnel database. A synthetic example shows that the technique is able to successfully image moisture hot-spots within a partially filled grain bin.
Medical Physics, 2013
Effective imaging of human tissue with microwave tomography systems requires a matching fluid to ... more Effective imaging of human tissue with microwave tomography systems requires a matching fluid to reduce the wave reflections at the tissue boundary. Further, in order to match the idealized mathematical model used for imaging with the complicated physical measurement environment, loss must be added to the matching fluid. Both too little and too much loss result in low-quality images, but due to the nonlinear nature of the imaging problem, the exact nature of loss-to-image quality cannot be predicted a priori. Possible optimal loss levels include a single, highly sensitive value, or a broad range of acceptable losses. Herein, the authors outline a process of determining an appropriate level of loss inside the matching fluid and attempt to determine the bounds for which the images are the highest quality. Our biomedical microwave tomography system is designed for 2D limb imaging, operating from 0.8 to 1.2 GHz. Our matching fluid consists of deionized water with various levels of loss introduced by the addition of table salt. Using two homogeneous tissue-mimicking phantoms, and eight different matching fluids of varying salt concentrations, the authors introduce quantitative image quality metrics based on L-norms, mean values, and standard deviations to test the tomography system and assess image quality. Images are generated with a balanced multiplicative regularized contrast source inversion algorithm. The authors further generate images of a human forearm which may be analyzed qualitatively. The image metrics for the phantoms support the claim that the worst images occur at the extremes of high and low salt concentrations. Importantly, the image metrics show that there exists a broad range of salt concentrations that result in high-quality images, not a single optimal value. In particular, 2.5-4.5 g of table salt per liter of deionized water provide the best reconstruction quality for simple phantoms. The authors argue that qualitatively, the human forearm data provide the best images at approximately the same salt concentrations. There exists a relatively large-range of matching fluid losses (i.e., salt concentrations) that provide similar image quality. In particular, it is not necessary to spend time highly optimizing the level of loss in the matching fluid.
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014
International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
Abstract Thin-wire models for the FVTD algorithm are validated using various monopole configurati... more Abstract Thin-wire models for the FVTD algorithm are validated using various monopole configurations above a finite ground plane. The thin-wire model is derived from the original Holland-Simpson formulation, extended by Edelvik for the finite-element method, and ...
2009 13th International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
Page 1. Biomedical Microwave Inversion in Conducting Cylinders of Arbitrary Shapes Puyan Mojabi, ... more Page 1. Biomedical Microwave Inversion in Conducting Cylinders of Arbitrary Shapes Puyan Mojabi, Colin Gilmore, Amer Zakaria and Joe LoVetri Dept. ... 38, no. 2, 2003. [10] E. Chong and S. Zak, An Introduction to Optimization. New York: Wiley Interscience, 2001. ...
IEEE Antennas and Propagation Magazine, 2011
We present a repository of multi-static, near-field microwave scattering measurements. The data a... more We present a repository of multi-static, near-field microwave scattering measurements. The data are presented both raw (uncalibrated), and calibrated with a scattered-field calibration. Measurements were taken with 24 co-resident Vivaldi antennas in a single plane, inside an air-filled microwave tomography system. The antennas were linearly polarized in the vertical direction, and we intended for the two-dimensional transverse magnetic (scalar) approximation to apply. Data are presented for seven targets, both metallic and dielectric, with varying geometrical complexity. Data from simple geometric targets, useful for calibration using analytic equations, are given. The repository is available from the Web site: http://www.ece.umanitoba.ca/lovetri/EMILab/index.html.
Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation, 2012
ABSTRACT A microwave tomography system comprising twenty-four dipole antennas is evaluated for im... more ABSTRACT A microwave tomography system comprising twenty-four dipole antennas is evaluated for imaging animal tissues. The tissue and antennas are immersed into different salt-water solutions. Three solutions, exploiting different amount of conductivities, are used as matching fluid and the data at different frequencies are collected. Quantitative images are successfully reconstructed. Various parts of the tissue are discernible and they agree with the dielectric measurements obtained directly by a dielectric probe.
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2013
ABSTRACT This work investigate the use of MWI as a technique for monitoring the conditions of sto... more ABSTRACT This work investigate the use of MWI as a technique for monitoring the conditions of stored wheat and discuss the obstacles to be overcome for MWI to be a cost-effective solution to the grain spoilage problem. Experimental results obtained on a small scale, from a novel near-field MWI system developed in the Electromagnetic Imaging Lab (EIL) at the University of Manitoba, show that the difference between dry and wet grain can be detected in principle. The challenges of performing MWI imaging inside of full-size hopper bins, where the boundary of the imaging domain is modeled by a perfect electric conductor, are investigated. Included are: comparisons of the sensitivities of different measurement systems, including the microwave scatterer technique (MST); results from different inversion algorithms such as FEM-CSI and eigenfunction Gauss-Newton inversion; a discussion of antenna designs suitable for the pressures, sheer forces and abrasion conditions inside grain bins; and a discussion of calibration methods.
IEEE Transactions on Microwave Theory and Techniques, 2014
ABSTRACT A novel 3-D dual-polarized microwave imaging system based on the modulated scattering te... more ABSTRACT A novel 3-D dual-polarized microwave imaging system based on the modulated scattering technique (MST) is presented. The system collects the magnitude and phase of the scattered field using 120 MST probes and 12 transmitter/collector antennas distributed around an object-of-interest in the near-field region. The 12 antennas form a middle circumferential layer while the printed MST probes are arranged on three circumferential layers including the middle layer. The antennas are linearly polarized double-layer Vivaldi antennas, each fixed inside its own cylindrical conducting cavity and slanted with respect to the vertical axis of the imaging chamber. The MST probes are etched on both sides of a thin substrate and loaded with five evenly distributed p-i-n diodes along their length. These are positioned vertically and horizontally so that the zzz - and phiphiphi -components of the electric field is measured. Field data are collected using MST, calibrated, and then inverted using a multiplicatively regularized finite-element contrast source inversion algorithm. The system performance is evaluated by collecting and inverting data from different 3-D targets.
International Journal of Biomedical Imaging, 2013
We present a pilot study using a microwave tomography system in which we image the forearms of 5 ... more We present a pilot study using a microwave tomography system in which we image the forearms of 5 adult male and female volunteers between the ages of 30 and 48. Microwave scattering data were collected at 0.8 to 1.2 GHz with 24 transmitting and receiving antennas located in a matching fluid of deionized water and table salt. Inversion of the microwave data was performed with a balanced version of the multiplicative-regularized contrast source inversion algorithm formulated using the finite-element method (FEM-CSI). T1-weighted MRI images of each volunteer's forearm were also collected in the same plane as the microwave scattering experiment. Initial "blind" imaging results from the utilized inversion algorithm show that the image quality is dependent on the thickness of the arm's peripheral adipose tissue layer; thicker layers of adipose tissue lead to poorer overall image quality. Due to the exible nature of the FEM-CSI algorithm used, prior information can be readily incorporated into the microwave imaging inversion process. We show that by introducing prior information into the FEM-CSI algorithm the internal anatomical features of all the arms are resolved, significantly improving the images. The prior information was estimated manually from the blind inversions using an ad hoc procedure.
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014
International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
We introduce a non-linear inversion algorithm for use in microwave biomedical imaging when the ob... more We introduce a non-linear inversion algorithm for use in microwave biomedical imaging when the object of interest is surrounded by an arbitrarily shaped conducting enclosure. The algorithm utilizes the Gauss-Newton inversion method and a combined additive and multiplicative regularizer. The conducting enclosure is taken into account via a FEM-based forward solver which is able to efficiently model arbitrarily shaped boundaries. Results for the 2D scalar case are given when the enclosure is a circle, triangle, and square, and include simple and complex biological scatterers, based on synthetic data. The results show that the algorithm is capable of reconstructing objects in all cylinder types.
IEEE Transactions on Biomedical Engineering, 2010
In this paper, we describe a 2-D wideband microwave imaging system intended for biomedical imagin... more In this paper, we describe a 2-D wideband microwave imaging system intended for biomedical imaging. The system is capable of collecting data from 3 to 6 GHz, with 24 coresident antenna elements connected to a vector network analyzer via a 2 × 24 port matrix switch. As one of the major sources of error in the data collection process is a result of the strongly coupling 24 coresident antennas, we provide a novel method to avoid the frequencies where the coupling is large enough to prevent successful imaging. Through the use of two different nonlinear reconstruction schemes, which are an enhanced version of the distorted born iterative method and the multiplicative regularized contrast source inversion method, we show imaging results from dielectric phantoms in free space. The early inversion results show that with the frequency selection procedure applied, the system is capable of quantitatively reconstructing dielectric objects, and show that the use of the wideband data improves the inversion results over single-frequency data.
IEEE Transactions on Antennas and Propagation, 2000
ABSTRACT The contrast source inversion algorithm is formulated using the finite-element method fo... more ABSTRACT The contrast source inversion algorithm is formulated using the finite-element method for two-dimensional transverse electric microwave imaging problems. Edge-based triangular elements with vector basis functions are utilized to solve the TE electromagnetic problem. A single finite-element method (FEM) mesh is used to model both the electric field as well as the contrast-source and contrast variables used in the inverse problem. The electromagnetic field is modeled by taking the unknown values to be the tangential components of the transverse electric field along the edges of each triangular element. The unknown contrast-source and contrast variables are located at the centroids of every triangular element of the same FEM mesh, but only inside the imaging domain. The adaptation of the FEM-contrast source inversion (FEM-CSI) algorithm to 2D-TE problems on such an arbitrary mesh requires the implementation of special transformation operators which are presented herein. The algorithm's capabilities are demonstrated by inverting the Fresnel experimental TE datasets as well as synthetically generated data.
IEEE Transactions on Microwave Theory and Techniques, 2000
ABSTRACT The multiplicatively regularized Gauss-Newton inversion (GNI) algorithm is enhanced and ... more ABSTRACT The multiplicatively regularized Gauss-Newton inversion (GNI) algorithm is enhanced and utilized to obtain complex permittivity profiles of biological objects-of-interest. The microwave scattering data is acquired using a microwave tomography system comprised of 24 co-resident antennas immersed into a saltwater matching fluid. Two types of biological targets are imaged: ex vivo bovine legs and in vivo human forearms. Four different forms of the GNI algorithm are implemented: a blind inversion, a balanced inversion, a shape-and-location inversion, and a novel balanced shape-and-location inversion. The latter three techniques incorporate typical permittivity values of biological tissues as prior information to enhance the reconstructions. In those images obtained using the balanced shape-and-location reconstruction algorithm, the various parts of the tissue being imaged are clearly distinguishable. The reconstructed permittivity values in the bovine leg images agree with those obtained via direct measurement using a dielectric probe. The reconstructed images of the human forearms qualitatively agree with magnetic resonance imaging images, as well as with the expected dielectric values obtained from the literature.
Annual International Conference of the IEEE Engineering in Medicine and Biology Society, 2009
We describe a 2D wide-band multi-frequency microwave imaging system intended for biomedical imagi... more We describe a 2D wide-band multi-frequency microwave imaging system intended for biomedical imaging. The system is capable of collecting data from 2-10 GHz, with 24 antenna elements connected to a vector network analyzer via a 2 times 24 port matrix switch. Through the use of two different nonlinear reconstruction schemes: the Multiplicative-Regularized Contrast Source Inversion method and an enhanced version of the Distorted Born Iterative Method, we show preliminary imaging results from dielectric phantoms where data were collected from 3-6 GHz. The early inversion results show that the system is capable of quantitatively reconstructing dielectric objects.
International Journal of Ultra Wideband Communications and Systems, 2010
Vivaldi antenna is widely known as a broadband antenna. In this paper, we investigate a modified ... more Vivaldi antenna is widely known as a broadband antenna. In this paper, we investigate a modified Vivaldi antenna with improved cross polarisation working in the ultra-wideband (UWB) frequency range (3.1-10.6 GHz) to be used as multiple probes for microwave tomography system. Our study includes investigation of radiation characteristics of the antenna, antenna design steps, fabrication sensitivity effects on the antenna performance and proposing and implementing a twenty-four antenna element system for fast data acquisition, including a novel method for frequency selection in microwave tomography applications. We also studied the fidelity parameter of the antennas inside the twenty-four element setup. The mutual coupling of adjacent elements, in spite of close proximity, is less than -17dB and fidelity variations for the antennas located in front of transmitter are less than 10%.
IEEE Antennas and Wireless Propagation Letters, 2011
Imaging with microwave tomography systems requires both the incident field within the imaging dom... more Imaging with microwave tomography systems requires both the incident field within the imaging domain as well as calibration factors that convert the collected data to corresponding data in the numerical model used for inversion. The numerical model makes various simplifying assumptions, e.g., 2-D versus 3-D wave propagation, which the calibration coefficients are meant to take into account. For an air-based microwave tomography system, we study two types of calibration techniques-incident and scattered field calibration-combined with two different incident field models: a 2-D line-source and an incident field from full-wave 3-D simulation of the tomography system. Although the 2-D line-source approximation does not accurately model incident field in our system, the use of scattered field calibration with the 2-D line-source provides similar or better images to incident and scattered field calibration with an accurate incident field. Thus, if scattered field calibration is used, a simple (but inaccurate) incident field is acceptable for our microwave tomography system. While not strictly generalizable, we expect our methodology to be applicable to most other microwave tomography systems.
Progress In Electromagnetics Research, 2013
The multiplicatively regularized finite-element contrast source inversion algorithm (MR-FEM-CSI) ... more The multiplicatively regularized finite-element contrast source inversion algorithm (MR-FEM-CSI) is used to solve the fullvectorial three-dimensional (3D) inverse scattering problem. The contrast and contrast-source optimization variables are located at the centroids of tetrahedra within the problem domain; whereas the electric field is expanded in terms of edge basis functions on the same tetrahedra. A dual-mesh is created in order to apply the multiplicative regularization. To handle large-scale problems the inversion algorithm is parallelized using the MPI library, with sparse matrix and vector computations supported by PETSc. The algorithm is tested using experimental datasets obtained from the Institut Fresnel database. A synthetic example shows that the technique is able to successfully image moisture hot-spots within a partially filled grain bin.
Medical Physics, 2013
Effective imaging of human tissue with microwave tomography systems requires a matching fluid to ... more Effective imaging of human tissue with microwave tomography systems requires a matching fluid to reduce the wave reflections at the tissue boundary. Further, in order to match the idealized mathematical model used for imaging with the complicated physical measurement environment, loss must be added to the matching fluid. Both too little and too much loss result in low-quality images, but due to the nonlinear nature of the imaging problem, the exact nature of loss-to-image quality cannot be predicted a priori. Possible optimal loss levels include a single, highly sensitive value, or a broad range of acceptable losses. Herein, the authors outline a process of determining an appropriate level of loss inside the matching fluid and attempt to determine the bounds for which the images are the highest quality. Our biomedical microwave tomography system is designed for 2D limb imaging, operating from 0.8 to 1.2 GHz. Our matching fluid consists of deionized water with various levels of loss introduced by the addition of table salt. Using two homogeneous tissue-mimicking phantoms, and eight different matching fluids of varying salt concentrations, the authors introduce quantitative image quality metrics based on L-norms, mean values, and standard deviations to test the tomography system and assess image quality. Images are generated with a balanced multiplicative regularized contrast source inversion algorithm. The authors further generate images of a human forearm which may be analyzed qualitatively. The image metrics for the phantoms support the claim that the worst images occur at the extremes of high and low salt concentrations. Importantly, the image metrics show that there exists a broad range of salt concentrations that result in high-quality images, not a single optimal value. In particular, 2.5-4.5 g of table salt per liter of deionized water provide the best reconstruction quality for simple phantoms. The authors argue that qualitatively, the human forearm data provide the best images at approximately the same salt concentrations. There exists a relatively large-range of matching fluid losses (i.e., salt concentrations) that provide similar image quality. In particular, it is not necessary to spend time highly optimizing the level of loss in the matching fluid.
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014
International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
Abstract Thin-wire models for the FVTD algorithm are validated using various monopole configurati... more Abstract Thin-wire models for the FVTD algorithm are validated using various monopole configurations above a finite ground plane. The thin-wire model is derived from the original Holland-Simpson formulation, extended by Edelvik for the finite-element method, and ...
2009 13th International Symposium on Antenna Technology and Applied Electromagnetics and the Canadian Radio Science Meeting, 2009
Page 1. Biomedical Microwave Inversion in Conducting Cylinders of Arbitrary Shapes Puyan Mojabi, ... more Page 1. Biomedical Microwave Inversion in Conducting Cylinders of Arbitrary Shapes Puyan Mojabi, Colin Gilmore, Amer Zakaria and Joe LoVetri Dept. ... 38, no. 2, 2003. [10] E. Chong and S. Zak, An Introduction to Optimization. New York: Wiley Interscience, 2001. ...
IEEE Antennas and Propagation Magazine, 2011
We present a repository of multi-static, near-field microwave scattering measurements. The data a... more We present a repository of multi-static, near-field microwave scattering measurements. The data are presented both raw (uncalibrated), and calibrated with a scattered-field calibration. Measurements were taken with 24 co-resident Vivaldi antennas in a single plane, inside an air-filled microwave tomography system. The antennas were linearly polarized in the vertical direction, and we intended for the two-dimensional transverse magnetic (scalar) approximation to apply. Data are presented for seven targets, both metallic and dielectric, with varying geometrical complexity. Data from simple geometric targets, useful for calibration using analytic equations, are given. The repository is available from the Web site: http://www.ece.umanitoba.ca/lovetri/EMILab/index.html.
Proceedings of the 2012 IEEE International Symposium on Antennas and Propagation, 2012
ABSTRACT A microwave tomography system comprising twenty-four dipole antennas is evaluated for im... more ABSTRACT A microwave tomography system comprising twenty-four dipole antennas is evaluated for imaging animal tissues. The tissue and antennas are immersed into different salt-water solutions. Three solutions, exploiting different amount of conductivities, are used as matching fluid and the data at different frequencies are collected. Quantitative images are successfully reconstructed. Various parts of the tissue are discernible and they agree with the dielectric measurements obtained directly by a dielectric probe.
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
2013 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2013
ABSTRACT This work investigate the use of MWI as a technique for monitoring the conditions of sto... more ABSTRACT This work investigate the use of MWI as a technique for monitoring the conditions of stored wheat and discuss the obstacles to be overcome for MWI to be a cost-effective solution to the grain spoilage problem. Experimental results obtained on a small scale, from a novel near-field MWI system developed in the Electromagnetic Imaging Lab (EIL) at the University of Manitoba, show that the difference between dry and wet grain can be detected in principle. The challenges of performing MWI imaging inside of full-size hopper bins, where the boundary of the imaging domain is modeled by a perfect electric conductor, are investigated. Included are: comparisons of the sensitivities of different measurement systems, including the microwave scatterer technique (MST); results from different inversion algorithms such as FEM-CSI and eigenfunction Gauss-Newton inversion; a discussion of antenna designs suitable for the pressures, sheer forces and abrasion conditions inside grain bins; and a discussion of calibration methods.
IEEE Transactions on Microwave Theory and Techniques, 2014
ABSTRACT A novel 3-D dual-polarized microwave imaging system based on the modulated scattering te... more ABSTRACT A novel 3-D dual-polarized microwave imaging system based on the modulated scattering technique (MST) is presented. The system collects the magnitude and phase of the scattered field using 120 MST probes and 12 transmitter/collector antennas distributed around an object-of-interest in the near-field region. The 12 antennas form a middle circumferential layer while the printed MST probes are arranged on three circumferential layers including the middle layer. The antennas are linearly polarized double-layer Vivaldi antennas, each fixed inside its own cylindrical conducting cavity and slanted with respect to the vertical axis of the imaging chamber. The MST probes are etched on both sides of a thin substrate and loaded with five evenly distributed p-i-n diodes along their length. These are positioned vertically and horizontally so that the zzz - and phiphiphi -components of the electric field is measured. Field data are collected using MST, calibrated, and then inverted using a multiplicatively regularized finite-element contrast source inversion algorithm. The system performance is evaluated by collecting and inverting data from different 3-D targets.
International Journal of Biomedical Imaging, 2013
We present a pilot study using a microwave tomography system in which we image the forearms of 5 ... more We present a pilot study using a microwave tomography system in which we image the forearms of 5 adult male and female volunteers between the ages of 30 and 48. Microwave scattering data were collected at 0.8 to 1.2 GHz with 24 transmitting and receiving antennas located in a matching fluid of deionized water and table salt. Inversion of the microwave data was performed with a balanced version of the multiplicative-regularized contrast source inversion algorithm formulated using the finite-element method (FEM-CSI). T1-weighted MRI images of each volunteer's forearm were also collected in the same plane as the microwave scattering experiment. Initial "blind" imaging results from the utilized inversion algorithm show that the image quality is dependent on the thickness of the arm's peripheral adipose tissue layer; thicker layers of adipose tissue lead to poorer overall image quality. Due to the exible nature of the FEM-CSI algorithm used, prior information can be readily incorporated into the microwave imaging inversion process. We show that by introducing prior information into the FEM-CSI algorithm the internal anatomical features of all the arms are resolved, significantly improving the images. The prior information was estimated manually from the blind inversions using an ad hoc procedure.
2014 USNC-URSI Radio Science Meeting (Joint with AP-S Symposium), 2014
2014 XXXIth URSI General Assembly and Scientific Symposium (URSI GASS), 2014