Ultrasonic tomography

The method is based on the reflection of short pulses of ultrasonic elastic waves by cracks, cavities, reinforcements and other discontinuities present in the material (pulse-echo method). The intensity of the waves reflected by these inhomogeneities depends on their contrast with respect to the base material in terms of acoustic impedance (acoustic impedance Z = density x speed of the elastic waves). The air present in the voids has almost zero acoustic impedance and the pulses are integrally reflected: R = (Z2 – Z1) / (Z1 + Z2) = – 1. Weaker indications (R ~ 0.5) are obtained in correspondence with the reinforcing bars, whose acoustic impedance is approximately 4-5 times that of the concrete.
Thanks to the repeated application of the principle through a series of equally spaced pulse emission-reception sensors, the instrument processes a 2D tomography along a section orthogonal to the surface of the structural element (B-scan), allowing the identification of defects and pathologies even on structures accessible from one side only (pavements, tunnels, etc.). Among the main purposes of this method it is possible to include: thickness measurements of elements accessible from only one side (walls, building cladding slabs, flooring, etc.); localization of voids and cavities; identification of masonry morphologies (solid masonry, two / three-layered masonry, etc.); identification of any laminations inherent to the material, veins of the stone; evaluation of the effectiveness of consolidation interventions; identification of cracks parallel to the surface (provided they are deeper than 50 mm).