Improved monitoring of acoustic emissions in concrete structures by multi-triggering and adaptive acquisition time interval

• We propose the L-FAT to prevent the loss or partial acquisition of AE signals.
• L-FAT is designed as an adjunctive block to existing Acquisition System (AS).
• L-FAT allows multi triggering acquisition and adaptive acquisition time interval.
• The design criterion and actual creation of the L-FAT is discussed.
• Effectiveness of L-FAT with respect to traditional AS is experimentally assessed.

Damage evaluation by Acoustic Emission (AE) signals is a promising technique for the non-invasive and continuous monitoring of concrete structures. The triggered acquisition modality is adopted in order to reduce the amount of acquired data in continuous monitoring. However, two main inconveniences can occur: either loss or partial acquisition of AE signals. Propagation can attenuate the signal below the trigger level causing signal loss, while the occurrence of multiple AE events can cause the loss or partial acquisition of signal due to the unpredictability of the Acquisition Time Interval (ATI). In fact, lower trigger level and wider ATI are not valid solutions in all real contexts. The proposal of the paper consists in the introduction of the multi-triggering acquisition modality and adaptive evaluation of the ATI, with the proper hardware Logic Flat Amplifier and Trigger (L-FAT) generator block designed and pointed-out to this purpose. As an evolution of the previously pointed out FAT, it generates the logical trigger whatever the transducer detecting the AE signal and adapts the ATI to the width of the multiple AE events as a further improvement. The adaptive evaluation of the ATI is based on the property that the AE length in concrete is well established. This property is used to foresee the end of the last AE by restarting the countdown at each trigger condition. The hardware architecture, the operative modality and the actual realization of the L-FAT are presented. Experimental tests assess the effectiveness of the L-FAT to monitor all the AE events, reducing the amount of acquired data, and to improve the damage evaluation of concrete structures.