Electromagnetic imaging and sensing for food quality and safety assessment [Guest Editorial]

The six articles in this special present to the antennas and propagation community some of the emerging research activities on the application of EM-based technologies in such a societally relevant topic. The articles address food industry applications as different as sensing food quality and food spoilage indicators and monitoring food items to detect contaminants

Brain Stroke Microwave Imaging via an Efficient Implementation of the CSI-FEM Algorithm

Microwave imaging of the human head for stroke detection is demonstrated using the finite-element contrast source inversion method with enhanced discretization of the contrastsource variable. The linear basis functions used in the new discretization lead to a simple implementation of higher accuracy compared to discretizations wherein the contrast source variable is assumed to be constant over each tetrahedron of the 3D finite element mesh. These advantages are particularly important for stroke imaging because of the highly inhomogeneous nature of the human head. Results using synthetic data obtained from a realistic numerical model of the head show promise for stroke detection

Coulomb wave functions in the theory of the circular paraboloidal waveguide

In this paper it is shown how the Coulomb wave functions, commonly used in the description of a Coulomb field surrounding a nucleus, can be used in the description of electromagnetic fields that are symmetric with respect of + inside a paraboloidal waveguide. The Abraham potentials Q and U, which are useful in describing fields with rational symmetry, are used to simplify the problem. It is shown that these potentials must satisfy a partial differential equation that when separated yields the Coulomb wave equation of order L = 0. Electromagnetic fieldsdue to simple source distributions inside the paraboloid are expanded in terms of these functions. Specifically, solutions for current-loop sources locatedin the focal plane of the paraboloid are obtained. The case where the wall of the paraboloidal waveguide is assumed to be perfectly conducting is treated as well as the case where the wall has finite impedance. The finite paraboloid is also considered, and the far field is formulated using Huygen's principle. It is found that for the finite surface-impedance case, the far-field pattem due to a current loop operating at 100 MHz in the focal plane of a paraboloidal reflector of 1 m focal length is different from the perfectly conducting case. Specifically, the pattem seems to be more omnidirectional for the impedance case than for the perfectly conducting case. Numerical results are presented for relevant aspects of the problem

Fuzzy Logic Implementation of an Electromagnetic Interactions Modelling Tool

NRC publication: Ye

Computer techniques for electromagnetic interaction modelling.

Computer techniques for the modelling of complex electromagnetic interactions are explored. The main thesis is that these techniques, or methods, can be divided into two types: non-algorithmic and algorithmic techniques. Approximate algorithmic methods for the modelling of electromagnetic interactions have undergone great advances in the past twenty years but they are still only feasible for relatively small problems (i.e. where the space-time discretization produces and requires only a relatively small number of unknowns). The computer implementation of non-algorithmic methods have recently become a reality with the maturing of expert system technology and knowledge based engineering. In Part I of this thesis, a knowledge-based approach for the modelling of electromagnetic (EM) interactions in a system is described. The purpose is to determine any unwanted EM effects which could jeopardize the safety and operation of the system. Modelling the interactions in a system requires the examination of the compounded and propagated effects of the electromagnetic fields. A useful EM modelling approach is one which is incremental and constraint-based. The approach taken here subdivides the modelling task into two parts: (a) the definition of the related physical topology, and (b) the propagation of the electromagnetic constraints. A prototype of some of the EM constraints has been implemented in Quintus Prolog under NeWS on a Sun workstation. User interaction is through a topology drawing tool and a stack-based attribute interface similar to the HyperCard\sp{\rm TM} interface of the Apple Macintosh computer. In Part II, numerical methods which discretize the space-time region of interest and provide a solution to the electromagnetics problem, given appropriate initial and boundary conditions, are investigated. Specifically, time-domain finite difference methods as applied to Maxwell's equations are analyzed, compared and implemented. As the basis of this analysis, Maxwell's equations are expressed as a system of hyperbolic conservation laws. Analytical properties of these systems, based on the method of characteristics, are used to study the numerical solution of Maxwell's equations. Practical issues, such as computational efficiency and memory requirements, are discussed for the implementation of the finite difference schemes. Advanced programming techniques are used to implement all the finite difference schemes discussed. The schemes are used to solve the problem of the penetration of electromagnetic energy through a shield with a thick gap. A two-dimensional time-domain finite element method, implemented as the software package PDE/PROTRAN, is also applied to shielding problems. The software package is first validated for simple hyperbolic problems and is then applied to perfectly conducting shields with apertures

Novel Stopping Criteria for Optimization-Based Microwave Breast Imaging Algorithms

A discontinuous Galerkin formulation of the Contrast Source Inversion algorithm (DGM-CSI) for microwave breast imaging employing a frequency-cycling reconstruction technique has been modified here to include a set of automated stopping criteria that determine a suitable time to shift imaging frequencies and to globally terminate the reconstruction. Recent studies have explored the use of tissue-dependent geometrical mapping of the well-reconstructed real part to its imaginary part as initial guesses during consecutive frequency hops. This practice was shown to improve resulting 2D images of the dielectric properties of synthetic breast models, but a fixed number of iterations was used to halt DGM-CSI inversions arbitrarily. Herein, a new set of stopping conditions is introduced based on an intelligent statistical analysis of a window of past iterations of data error using the two-sample Kolmogorov-Smirnov (K-S) test. This non-parametric goodness-of-fit test establishes a pattern in the data error distribution, indicating an appropriate time to shift frequencies, or terminate the algorithm. The proposed stopping criteria are shown to improve the efficiency of DGM-CSI while yielding images of equivalent quality to assigning an often liberally overestimated number of iterations per reconstruction