Narrow-band diffuse ultrasonic wavefield measurements in a network of reciprocal transducers for monitoring of a large concrete floor slab

Piezoelectric transducers were attached in a grid on the surface of an 8 x 2 x 0.08 m concrete floor slab. Through an automated, iterative scheme these were used to transmit and receive 50 kHz, continuous, sinusoidal signals, which were sampled by a multi-channel lock-in amplifier. The measured amplitude and phase were used to locate inflicted damage by detecting deviations from baseline measurements, acquired in a reference state. Superficial damage, in the range of centimeter, could easily be detected, even between the transducers placed the furthest apart, and could be located to a grid coordinate on the floor slab