Aastha Trehan

Near-Field Microwave Imaging Based on Aperture Raster Scanning With TEM Horn Antennas

The design, fabrication, and characterization of an ultrawideband (UWB) antenna for near-field microwave imaging of dielectric objects are presented together with the imaging setup. The focus is on an application in microwave breast tumor detection. The new antenna operates as a sensor with the following properties: 1) direct contact with the imaged body; 2) more than 90% of the microwave power is coupled directly into the tissue; 3) UWB performance; 4) excellent de-coupling from the outside environment; 5) small size; and 6) simple fabrication. The antenna characterization includes return loss, total efficiency, near-field directivity, fidelity, and group velocity. The near-field imaging setup employs planar aperture raster scanning. It consists of two antennas aligned along each others boresight and moving together to scan two parallel apertures. The imaged object lies between the two apertures. With a blind de-convolution algorithm, the images are de-blurred. Simulation and experimental results confirm the satisfactory performance of the antenna as an UWB sensor for near-field imaging.

TEM Horn Antenna for Ultra-Wide Band Microwave Breast Imaging

A novel TEM horn antenna placed in a solid dielectric medium is proposed for microwave imaging of the breast. The major design requirement is that the antenna couples the microwave energy into the tissue without being immersed itself in a coupling medium. The antenna achieves this requirement by: 1) directing all radiated power through its front aperture, and 2) blocking external electromagnetic interference by a carefully designed enclosure consisting of copper sheets and power absorbing sheets. In the whole ultra-wide band the antenna features: 1) good impedance match, 2) uniform field distribution at the antenna aperture, and 3) good coupling efficiency.

Near-field detection at microwave frequencies based on self-adjoint response sensitivity analysis

A new detection method is proposed for the localization of electrically small scatterers in a known background medium. The method requires the knowledge of the electric field distribution inside the known background medium where no scatterers are present. It is based on a self-adjoint response sensitivity computation which can be performed in real time. Using the E-field distribution in the background medium, it provides three-dimensional maps of the Frechet derivative within the imaged volume. The peaks and dips in these maps identify the locations where the permittivity and conductivity of the measured medium differ from those in the background medium. The background medium can be heterogeneous. In a homogeneous-medium example, the performance of the detection algorithm is studied in terms of the number of transmission/reception points, the dielectric contrast of the scatterer compared to the background medium, and the size of the scatterer. Its resolution is also addressed. The detection of a small scatterer in a heterogeneous background is demonstrated.

Near-field microwave imaging based on planar aperture scanning

A near-filed microwave imaging setup is investigated. The setup benefits from the high near-field directivity and good efficiency of a recently proposed ultra-wide band TEM horn antenna. The setup employs planar aperture scanning. It consists of two antennas aligned along each others boresight and moving together to scan two parallel apertures. The imaged object lies between the two apertures. With a blind de-convolution algorithm, the images are de-blurred. Simulation and experimental results confirm the satisfactory performance of this setup for near-field microwave imaging with possible application in breast cancer diagnosis.

Detection at microwave frequencies based on self-adjoint sensitivity analysis

A novel general formulation of the response sensitivity analysis is proposed and implemented in a computationally efficient algorithm for the detection of electrically small scatterers in a known background medium. The responses of the background medium where no scatterers are present are modeled via ultra-wideband time-domain simulation. Using these modeled responses and the measured responses of the examined object, 3D derivative maps are obtained within the objects volume. The minima or maxima in these maps indicate the locations where the voxel permittivities and conductivities differ significantly between the measured and modeled media. Localization of the scatterers in a complex heterogeneous example is successfully conducted. The limitations of the detection algorithm and its resolution are studied using a homogeneous background example in terms of the number of transmission/reception points, the dielectric contrast and the size of the scatterer.

Ultra-wide band TEM horn antenna for microwave imaging of the breast

In this paper, a novel UWB TEM horn antenna enclosed in a dielectric medium has been proposed for microwave imaging in breast cancer detection. It obviates the use of coupling medium. Also, the outer surface of the dielectric enclosure has been covered by copper sheets and a microwave absorbing sheet to decouple the antenna from surrounding interferences. The design is accomplished through full-wave simulation and then experimentally tuning for good impedance match. An effort has been made to achieve small size within a few centimeters while maintaining good impedance match and directing microwave power toward the breast.

Accuracy assessment of photogrammetry surface reconstruction for improving microwave imaging

This paper examines the capability of photogrammetry to model the surface shape of 3-D glycerin phantoms of some canonical shapes as well as random shapes. This study aims to investigate the accuracy assessment for practical scenarios where the breast shapes and sizes vary significantly due to genetic, age, and medical factors as well as surgical intervention. The measured and simulated S-parameters are compared in the ultra-wide band (UWB) frequency range from 3.1-10.6 GHz for a set-up that contains two UWB antennas, a glycerin phantom emulating the breast, and isopropyl alcohol as the coupling medium.

Detection using microwaves and self-adjoint sensitivity analysis

A novel general formulation of the response sensitivity analysis has been proposed recently. This sensitivity-analysis method has enabled the development of a conceptually new detection algorithm. The performance of this algorithm was tested on a realistic breast-tumour detection problem through ultra-wideband time-domain simulations. The detection relies on images obtained from the response derivatives with respect to the voxel permittivities and conductivities in the modelled “background” medium, which is a close approximation of the healthy (or normal) breast tissue. Abnormal regions in the object under test are successfully detected and localized after increasing sufficiently the number of transmission/reception points.

Microwave imaging for breast cancer diagnosis based on planar aperture scanning

The contrast between the electrical properties of the components of a dielectric body enables its imaging using microwave measurements. In a typical active imaging scenario, microwave power is radiated via an antenna and the scattered power is picked by one or more antennas. The scattered signals are then analyzed to detect and identify significant scatterers (targets).

Systematic fidelity assessment of antennas for near-field microwave imaging

Recently, ultra-wideband (UWB) systems for near-field microwave imaging (MWI) have been reported. The Federal Communications Commission has allocated the bandwidth from 3.1 GHz to 10.6 GHz for such UWB applications [1]. Therefore, the time-domain (TD) assessment of UWB antennas and systems is crucial.