Dynamic Impedance or Impact Echo is an acoustic echo sounding system which, in conjunction with UPV, is the primary technique used to assess the mechanical properties such as strength, integrity of materials; it can also be applied to deep structures, in the assessment of the form of masonry and concrete elements and to investigate the length and integrity of sheet piles.
It is directly appropriate to assessing the dimensions and integrity of concrete and stone, when used to set elements into whole body resonance, and measurements are made in the frequency domain rather than the time domain.
Tuned hammers are used to pass pulses of acoustic energy into the material of an element, causing it to resonate, and the response recorded in both the time and frequency domain to analyse the form and mechanical properties of the materials. The velocity of an acoustic wave within the material is proportional to its density and elastic modulus, thus accurate assessments of depth can be made even where steel is dense, and discontinuities (cracks) and voids found with relative ease.
Used in parallel with the radar, which may locate an object, this technique allows its mechanical properties to be evaluated at critical points within the overall arrangement - once the generalities of a structure has been found by radar, the continuity of acoustic response allows an integrity assessment.
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