Microwave Imaging

CHAPTER FOUR

Imaging Configurations and Model Approximations

4.1 OBJECTIVES OF THE RECONSTRUCTION

In practical applications, the objectives of the inspection can be very different. In certain cases, it can be sufficient to locate the unknown scatterers by retrieving their spatial positions starting from measurement of the scattered field performed outside an investigation domain. Methods aimed at solving this problem are actually not imaging methods, but mainly localization methods (e.g., those based on radar concepts and on smart antennas that can estimate the directions of arrival of signals related to the presence of the objects).

In other cases, the aim of the inspection is to retrieve the shape of the object, which in certain applications (discussed in the following sections) is sufficient information, as the values of the object's dielectric parameters are unnecessary or obvious. An example is represented by nondestructive testing, evaluations, and quality control of materials and products (see Chapter 10), where knowledge of the position and shape of a defect is often sufficient for deciding whether the structure of apparatus under test can be still used. Moreover, the information on the shape and, consequently, on the dimensions of a defect can also be an indication for determining the residual life of the apparatus or system.

However, the most ambitious goal of the inspection is to obtain complete images of the objects under test. Such images, when using microwaves, are ...