Ten Lectures on Impact-Echo

Quantitative ultrasonic evaluation of concrete structures using one-sided access

“…Conventional impact echo (IE) is a commonly used elastic wave based method which involves generation of compression, shear, and Rayleigh waves using a mechanical impact at the surface [3,4,9]. The waves reflected from internal changes in acoustic impedance or external boundaries and recorded on the surface, where the impact was generated, give information about the structure using signal interpretation techniques normally based on spectral analysis [10].…”

“…Testing with this method can be time consuming and only allows for one signal pair to be sent and received per scan. With only one mechanical impact signal and spectral analysis methods that require multiple reflections at the same boundary, there are difficulties in evaluating the complex geometries required for irregular flaw detection [3,4,9]. Hardware such as air coupled impact echo have been developed to allow for more productive measurements and multiple measurement pairs [11,12,13].…”

“…The results of this limited information can lead to reliability problems due to the sensitivity to small shifts of source and sensor positions [4]. Ultrasonic array technology provides an opportunity to mitigate the issues with limited transducer pairs, signal variability, and sensor positional shift instability, using a self-contained arrangement of sending and receiving transducer pairs at set spacing.…”

“…To accomplish this task, the impact-echo signature analysis (IESA) method [4], was modified for the reconstruction methods used in this study. While Schubert and Koehler stated that a priori knowledge of a reference signal where no scatterers are present is not generally available, the Kirchoff migration methods described in section 4 provide intuitive reference scans.…”

“…Although ultrasound has been used for evaluation of concrete structures since the 1940s, earlier applications of this technology have experienced difficulties. Traditional ultrasonic methods relied on time consuming liquid coupling and could not achieve the necessary penetration depths in concrete materials due to the heterogeneity causing excessive attenuation of the wavefront [3][4][5].…”