M. Ferrando

Medical imaging with a microwave tomographic scanner

A microwave tomographic scanner for biomedical applications is presented. It consists of a 64-element circular array with a useful diameter of 20 cm. Electronically scanning the transmitting and receiving antennas allows multiview measurements with no mechanical movement. Imaging parameters-a spatial resolution of 7 mm and a contrast resolution of 1% for a measurement time of 3 s-are appropriate for medical use. Measurements on tissue-simulating phantoms and volunteers, together with numerical simulations, are presented to assess the system for absolute imaging of tissue distribution and for differential imaging of physiological, pathological, and induced changes in tissues.<<ETX>>

High-frequency RCS of complex radar targets in real-time

This paper presents a new and original approach for computing the high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. The aircraft is modeled with I-DEAS solid modeling software using a parametric surface approach. High-frequency RCS is obtained through physical optics (PO), method of equivalent currents (MEC), physical theory of diffraction (PTD), and impedance boundary condition (IBC). This method is based on a new and original implementation of high-frequency techniques which the authors have called graphical electromagnetic computing (GRECO). A graphical processing approach of an image of the target at the workstation screen is used to identify the surfaces of the target visible from the radar viewpoint and obtain the unit normal at each point. High-frequency approximations to RCS prediction are then easily computed from the knowledge of the unit normal at the illuminated surfaces of the target. The image of the target at the workstation screen (to be processed by GRECO) can be potentially obtained in real time from the I-DEAS geometric model using the 3-D graphics hardware accelerator of the workstation. Therefore, CPU time for RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric model manipulations are left to the graphics hardware. This hybrid graphic-electromagnetic computing (GRECO) results in real-time RCS prediction for complex radar targets. >

GRECO: graphical electromagnetic computing for RCS prediction in real time

An innovative approach to computing the high-frequency radar cross sections (RCSs) of complex radar targets in real time, using a 3-D graphics workstation, is presented. The target (typically, an aircraft) is modeled with the I-IDEAS solid-modeling software, using a parametric-surface approach. The high-frequency RCS is obtained through physical optics (PO), the method of equivalent currents (MEC), the physical theory of diffraction (PTD), and the impedance boundary condition (IBC) techniques. The CPU time for the RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric-model manipulations are left to the graphics hardware.<<ETX>>

Planar and cylindrical active microwave temperature imaging: numerical simulations

A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems.

Temperature and Permittivity Measurements using a Cylindrical Microwave Imaging System

The capabilities of a cylindrical imaging system used in remote thermal sensing and dielectric constant measurements are investigated. The paper presents simulations of absolute and differential reconstructions of bodies within the Born approximation and of stronger diffracting objects. In addition a preliminary experiment is presented.

A Cylindrical System for Quasi-Real Time Microwave Tomography

A cylindrical system for biomedical microwave tomography is presented. The circular algorithms and some numerical reconstructions are discussed. Finally the experimental set-up is described and some preliminary measurements are presented.

Real-time radar cross section of complex targets by physical optics graphical processing

It is shown that the radar cross section (RCS) of complex targets can be obtained in real time using the hardware capabilities of a high-performance graphics workstation. Target geometry is modeled by a computer-aided-design package. The RCS is computed using the physical-optics high-frequency approximation. In order to validate the graphic processing of the surface integral, the results obtained for simple objects are compared with analytic evaluation of the physical-optics integral. A generic missile model is used to validate the physical-optics results for complex radar targets at high frequency. It is found that the RCS of complex targets at high frequency is predicted with reasonable accuracy by the physical-optics approximation.<<ETX>>

Microwave imaging of multilayer cylinders using optimization techniques

The authors present a novel approach to solving the problem of the reconstruction of arbitrary strong-scattering objects using optimization techniques. The algorithm is based on the minimization of the mean-squared error between the measured and calculated scattered fields from the reconstruction. The object is assumed to have cylindrical symmetry, and the radial profile of permittivity is to be determined. The validity of the proposed algorithm is investigated both numerically and experimentally. In the experimental part, a tomographic microwave system operating at 2.45 GHz was used to measure the scattered field produced by a dielectric cylinder. A comparison between the measured scattered field and the theoretical field corresponding to the optimized cylinder epsilon =61.62 tan delta =0.38 R=2.23 cm is shown, and the reconstruction error is negligible for the radius and below 10% for the dielectric constant and loss tangent.<<ETX>>

Feedback formulation for multiple scatterers

A numerical method for the scattering problem is presented that uses feedback formulation to model multiple interactions between objects, expressing incidents and scattered fields as sums of cylindrical modes, resulting in smaller matrix sizes. The method entails three steps: the characterization of each object, then the transformation of each emerging mode from one object into incident fields on the others and then the computation of the scattered fields.<<ETX>>

Cylindrical microwave imaging system

A cylindrical system for microwave tomography working at 2.45 GHz has been presented. In this setup, the body, immersed in water, is illuminated with a cylindrical wave and the measured scattered fields are processed by an algorithm for cylindrical geometries. Temperature and permittivity measurements were made using this system. The authors present the numerical simulations for different parameters and experimental images of biological bodies obtained with the system.<<ETX>>