The use of ultrasonic images to evaluate the quality and degradation state of historical heritage by the identification of heterogeneities, defects or cracks is an attractive solution to the diagnosis of heritage buildings. In recent years, ultrasonic images and tomographic techniques have gained increasing importance in the evaluation of heritage building.
Ultrasonic waves are mechanical vibrations propagated in a frequency range superior to audible frequency (20 kHz), from 45 kHz to 100 MHz. Ultrasonic Tomography is a non-destructive technique based on ultrasonic wave propagation that allows the visualization of the section of a solid object by an image.
Tomographic techniques allow the visualization of the cross section of structures, thus enabling better detection of defects, cracks, or discontinuities in the material. To obtain a tomographic image is necessary to emit and receive multiple sonic rays that cover all cross sections, as shown in Figure 1. A tomographic image is obtained from projections through the object. These projections consist of velocity or attenuation measurements of ultrasonic pulses transmitted through the specimen.