ABSTRACT
It became clear very early that ultrasonic pulse echo on concrete requires very low frequency transducers (Neisecke 1991) to overcome the scattering problem in coarse aggregate concrete. Multi position experiments and synthetic aperture data analysis led to reliable thickness measurements of concrete slabs. In order to reduce testing times and to ease experiments, arrays of ten transducers were used. In the mid 90s a new type of transducer was developed in Russia (www.acsys.ru 2006) which did not require special coupling to the concrete surface (Fig. 1). Based on transversal excited ultrasound, testing became much easier to perform with the availability of these commercial products. The individual transducers have ceramic pin contact to the concrete, 12 transducers each are combined and form a large aperture for transmitting and receiving the signals.
