Microwave Diffraction Tomography Research Articles

An Improved Antenna Calibration Methodology for Microwave Diffraction Tomography in Limited-Aspect Configurations

This work underlines the importance of properly modeling the directivity of the antennas and proposes an improved calibration strategy in the framework of microwave diffraction tomography. Experiments to prove the effectiveness of the approach are carried out with a system comprising two ultrawideband linear antenna arrays. In the configurations presented herein, targets are in the near-field of the arrays and small aperture angles are considered ( ~ 40 deg). Multi-frequency multi-view multi-static quantitative inversions are performed using the modified <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> gradient method. The calibration approach reconstructs the directivity of the antennas using measured incident fields. The novelty consists in taking the reconstructed antenna pattern into account within the inversion algorithm both at transmission and at reception through a multipolar expansion of, respectively, the incident field and the data equation Green function. The results show that a fine modeling of the directivity of the antennas is paramount to image and separate scatterers, particularly when placed closer than the resolution limit of the system and beyond the Born approximation regime.

Reconstruction with Computerized Microwave Diffraction Tomography by Using Circular Measurement System in the Far-Field Region

This paper deals with far-field microwave imaging of a dielectric object satisfying the Born approximation. The results of computer simulations obtained with a circular measuring geometry are given. The computational efficiency of this method is also shown.

Effect of View Angle Variations in Vector Diffraction Tomography

Under the Born approximation, the effect of view angle variations on image reconstruction in vector diffraction tomography is investigated. This paper deals with internal image reconstructions of infinitely long lossless and lossy dielectric cylinders placed in free space. Emphasis is placed on showing how both the co-polarized and the cross-polarized diffracted terms vary with incidence angle in the image reconstruction because any oblique incidence on a curved surface always produces depolarization. The cross-polarized component was found to contain object information on edges, i.e., the boundary position of the cylinder. It is shown that polarization utilization will play an important role in precise image reconstruction in microwave diffraction tomography.

Magical Microwaves—The Exploitation of the Century

The celebrated discoveries of Maxwell, Hertz and many others heralded a century rich in the exploitation of ideas to create electronic systems beneficial to mankind. This address focuses on the recent exploitation of electromagnetics concerning the sensing of images, generation of force and dispensing of heat thus highlighting important trends in the kindred RF and microwave industries. A recapitulation of the milestones in the advances over the century emphasises the interdependence of theory, material development and system innovation. Today's CAD/CAM and chip-integration philosophies have taken the batch-oriented microwave component industry to the threshold of mass production. Improving both the accuracy of electromagnetic design equations and the manufacturing technology are critical issues, and the revolutionary antenna phased array technology well illustrates these challenges. The diverse advances in passive and active image sensing systems rely heavily on signal processing, and examples include the radiometric sensing of temperature and microwave diffraction tomography in medical diagnostics, and the synthetic aperture radar scanning of the earth. A complementary topic concerns the disguise of radar target signatures, mainly in defence, and the use of ingenious electromagnetic wave scattering behaviour. Equally daunting is the invention of microwave sources with astronomical power levels that make defensive electromagnetic beam weapons a possibility, and fascinating experiments on electromagnetic rocket launchers and guns for space scenarios have been reported. Finally commonplace microwave domestic cooking is seen to be but one of a multitude of applications including pest control, seed germination and cancer therapy. Skill shortages, achieving the potential of CAD in mass production, and exploiting the emerging technologies, are some of the stimulating challenges ahead.

Wide-band microwave diffraction tomography under Born approximation

Studies of the diffraction tomography of dielectric objects in forward and backward scattering using a frequency diversity technique in the microwave region are presented. Numerical results show that the image reconstructed in the backward scattering case is better than that obtained in the forward scattering case. This shows that this cost-effective technique has potential in medical and nondestructive testing applications. >

Magical microwaves: the exploitation of the century

The celebrated discoveries of Maxwell, Hertz and many others heralded a century rich in the exploitation of ideas to create electronic systems beneficial to mankind. This address focuses on the recent exploitation of electromagnetics concerning the sensing of images, generation of force and dispensing of heat thus highlighting important trends in the kindred RF and microwave industries. A recapitulation of the milestones in the advances over the century emphasises the interdependence of theory, material development and system innovation. Today&apos;s CAD/CAM and chip-integration philosophies have taken the batch-oriented microwave component industry to the threshold of mass production. Improving both the accuracy of electromagnetic design equations and the manufacturing technology are critical issues, and the revolutionary antenna phased array technology well illustrates these challenges. The diverse advances in passive and active image sensing systems rely heavily on signal processing, and examples include the radiometric sensing of temperature and microwave diffraction tomography in medical diagnostics, and the synthetic aperture radar scanning of the earth. A complementary topic concerns the disguise of radar target signatures, mainly in defence, and the use of ingenious electromagnetic wave scattering behaviour. Equally daunting is the invention of microwave sources with astronomical power levels that make defensive electromagnetic beam weapons a possibility, and fascinating experiments on electromagnetic rocket launchers and guns for space scenarios have been reported. Finally commonplace microwave domestic cooking is seen to be but one of a multitude of applications including pest control, seed germination and cancer therapy. Skill shortages, achieving the potential of CAD in mass production, and exploiting the emerging technologies, are some of the stimulating challenges ahead.

Microwave tomography: an algorithm for cylindrical geometries

The letter presents an efficient algorithm in cylindrical coordinates for microwave diffraction tomography. In comparison with algorithms in cartesian co-ordinates, the mechanical rotation of the object is avoided and higher-quality images are obtained with similar processing time.

Implementation of microwave diffraction tomography for measurement of dielectric constant distribution

Diffraction tomography is a process that can infer the internal structure of an object from multiple views of its diffraction shadow. The procedure is sensitive to variations in the object&apos;s refractive index and there is interest in using the technique to measure permittivity distributions within dielectric objects and to image soft tissues for biomedical applications. To allow the inversion to proceed, a number of conditions have to be met. These determine the type of object to be studied, the geometry of the microwave system and surrounding environment. The optimal resolution distance obtainable is half a wavelength, but this can rarely be achieved because of practical limitations. Some procedures, however, are available to improve the practical resolution. One, which is suitable for microwave tomography, is to use multifrequency data and to combine the resulting images. A system operating over the X-Band microwave frequency range is described and some results for test objects in air are given

The Effects of Attenuation on the Born Reconstruction Procedure for Microwave Diffraction Tomography (Short Paper)

The effects of attenuation on the Born inversion process for diffraction tomography are investigated. The exact forward scattered fields for a Iossy dielectric cylinder in a Iossy medium are calculated and are then used to reconstruct an image of the scattering object. As accurate image is produced only when the cylinder acts as a small perturbation on the dielectric constant of the external medium. Results indicate that even small losses have a significant effect on the resolution of the image. It is possible, however, to eliminate image distortion by matching the loss tangent of the outside medium to that within the cylinder.

Microwave Diffraction Tomography for Biomedical Applications (Further Comments)

The comment made by Drs. L. Larsen, T. Guo, and W. Guo is worth noting and requires further explanations. Our reconstruction process is effectively based on a spectral domain approach, but does not involve identity, which is no longer valid inside the object under investigation. Instead, we use the relation existing between the Fourier-Transform of the normalized current distribution and the Fourier-Transform of the scattered field in the plane of measurement. The relevant equations are derived in and a paper has been submitted for publication in the IEEE Transactions on Antennas and Propagation.

Microwave Diffraction Tomography for Biomedical Applications (Comments)

In the above paper, and a subsequent publication, Bolomey et al. suggested a very useful technique of biological tomography which may provide a fast image reconstruction at low cost. In a more recent work, Bolomey also presented some interesting results of a reconstructed image of a pony kidney. The virtue of the suggested technique lies in the rapidity of data collection by modulated scattering Here we would like to point out that more theoretical study is still needed on the interpretation of the reconstructed image.

Microwave Diffraction Tomography for Biomedical Applications

This short paper points out the realizability of a method suitable for quasi real-time coherent microwave tomography for biomedical applications.