Sima Noghanian

A Wideband Microwave Tomography System With a Novel Frequency Selection Procedure

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.

A Survey of Wireless Communications and Propagation Modeling in Underground Mines

Mining and mineral exploration play important roles in the global economy. In mining operations, communication systems play vital roles in ensuring personnel safety, enhancing operational efficiency and process optimization. Over the period 1920-2012, this article surveys the evolution of wireless communications in underground mines, the developments of the underlying technology, and progress in understanding and modeling the underground wireless propagation channel. Current and future trends in technology, applications and propagation modeling are also identified. About ninety relevant references have been reviewed that consider: 1) the emergence of technology and applications, 2) analytical, numerical and measurement-based propagation modeling techniques, and 3) implications of the physical environment, antenna placement and radiation characteristics on wireless communication system design. Affected systems include narrowband, wideband/ultra-wideband (UWB) and multiple-antenna systems. The paper concludes by identifying open areas of research.

Analysis of Incident Field Modeling and Incident/Scattered Field Calibration Techniques in Microwave Tomography

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.

Angle-of-Arrival Statistics of a Three-Dimensional Geometrical Scattering Channel Model for Indoor and Outdoor Propagation Environments

In this letter, a three-dimensional geometrical scattering channel model is introduced to simultaneously describe the angular distribution of multipath waves in the azimuth and the elevation angles. The angle-of-arrival probability density functions of the received multipath waves are provided. These functions facilitate independent control of the angular spread in both the azimuth and the elevation angles via the models parameters. To establish the model verification, it has been compared against the results from a site-specific propagation prediction technique at indoor and outdoor wireless communication environments.

A Novel Microwave Tomography System Based on the Scattering Probe Technique

In this paper, we introduce a novel microwave tomography system, which utilizes 24 double-layered Vivaldi antennas, each of which is equipped with a diode-loaded printed-wire probe. By biasing the probes diodes, the impedance of the probe is modified, allowing an indirect measurement of the electric field at the probes locations. Each printed-wire probe is loaded with five equally spaced p-i-n diodes, in series. We show that electric field data collected in this way within the proposed tomography system can be used to reconstruct the dielectric properties of an object of interest. Reconstructions for various objects are shown. Although the results are still preliminary, sufficient experimentation has been done to delineate the advantages of such an indirect method of collecting scattered-field data for tomographic imaging purposes.

Heterogeneous breast phantom development for microwave imaging using regression models

As new algorithms for microwave imaging emerge, it is important to have standard accurate benchmarking tests. Currently, most researchers use homogeneous phantoms for testing new algorithms. These simple structures lack the heterogeneity of the dielectric properties of human tissue and are inadequate for testing these algorithms for medical imaging. To adequately test breast microwave imaging algorithms, the phantom has to resemble different breast tissues physically and in terms of dielectric properties. We propose a systematic approach in designing phantoms that not only have dielectric properties close to breast tissues but also can be easily shaped to realistic physical models. The approach is based on regression model to match phantoms dielectric properties with the breast tissue dielectric properties found in Lazebnik et al. (2007). However, the methodology proposed here can be used to create phantoms for any tissue type as long as ex vivo, in vitro, or in vivo tissue dielectric properties are measured and available. Therefore, using this method, accurate benchmarking phantoms for testing emerging microwave imaging algorithms can be developed.

Angle and Time of Arrival Statistics of a Three Dimensional Geometrical Scattering Channel Model for Indoor and Outdoor Propagation Environments

In this paper, a three dimensional geometrical scattering channel model for indoor and outdoor wireless propagation environments is introduced. It is based on the assumption that the scatterers are distributed within a spheroid, in which the mobile station and base station are located at the spheroid’s foci. This model captures both the spatial and temporal statistical distributions of the received multipath signals. Several angle of arrival and time of arrival probability density functions of the received multipath signals are provided in compact forms. The angle of arrival probability density functions are obtained in terms of both the azimuth and elevation angles. Numerical results are presented to illustrate and verify the derived expressions. To validate the model, it has been compared against some of the available two dimensional models and measured data. Received 11 August 2010, Accepted 6 October 2010, Scheduled 21 October 2010 Corresponding author: Mohammad Alsehaili (msehaili@ee.umanitoba.ca). 192 Alsehaili et al.

Using a priori Information for Regularization in Breast Microwave Image Reconstruction

Regularization methods are used in microwave image reconstruction problems, which are ill-posed. Traditional regularization methods are usually problem-independent and do not take advantage of a priori information specific to any particular imaging application. In this paper, a novel problem-dependent regularization approach is introduced for the application of breast imaging. A real genetic algorithm (RGA) minimizes a cost function that is the error between the recorded and the simulated data. At each iteration of the RGA, a priori information about the shape of the breast profiles is used by a neural network classifier to reject the solutions that cannot be a map of the dielectric properties of a breast profile. The algorithm was tested against four realistic numerical breast phantoms including a mostly fatty, a scattered fibroglandular, a heterogeneously dense, and a very dense sample. The tests were also repeated where a 4 mm × 4 mm tumor was inserted in the fibroglandular tissue in each of the four breast types. The results show the effectiveness of the proposed approach, which to the best of our knowledge has the highest resolution amongst the evolutionary algorithms used for the inversion of realistic numerical breast phantoms.

Sampling rate reduction for 60 GHz UWB communication using compressive sensing

60 GHz ultra wide-band (UWB) communication is an emerging technology for high speed short range communications. However, the requirement of high-speed sampling increases the cost of receiver circuitry such as analog-to-digital converter (ADC). In this paper, we propose to use a compressive sensing framework to achieve a significant reduction of sampling rate. The basic idea is based on the observation that the received signals are sparse in the time domain due to the limited multipath effects at 60 GHz wireless transmission. According to the theory of compressive sensing, by carefully designing the sensing scheme, sub-Nyquist rate sampling of the sparse signal still enables exact recovery with very high probability. We discuss an implementation for a low-speed A/D converter for 60 GHz UWB received signal. Moreover, we analyze the bit error rate (BER) performance for BPSK modulation under RAKE reception. Simulation results show that in the single antenna pair system model, sampling rate can be reduced to 2.2% with 0.3dB loss of BER performance if the input sparsity is less than 1%. Consequently, the implementation cost of ADC is significantly reduced.

A diamond shaped small planar ultra wide band (UWB) antenna for microwave Imaging Purpose

There has been a flourishing prospect of UWB technology in recent years in both communication and other purposes like microwave imaging and radar applications. Antenna in UWB imaging systems plays a significant role and it is quite challenging to design a proper antenna satisfying all the constraints required for microwave imaging applications. Recent studies of UWB antenna structures are specially concentrated on microstrip (Choi et al., 2004), slot (Liu et al., 2005) and planar monopole antennas (Wong et al., 2004). In this work, a small (30 x 30 mm2) printed microstrip fed monopole antenna has been designed, fabricated and some antenna parameters measurements like return loss, voltage standing wave ratio (VSWR), radiation pattern and group delay have been performed to test the validity of simulation and verify eligibility of the antenna for microwave imaging purpose.