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Beamforming is widely used in structural health monitoring (SHM) systems for impact or damage localization. Beamforming directionality is achieved by the constructive interference of sensor wavefronts, which results in a significant amplification of the measured signal in a particular direction. For beamforming applications, the cost per sensor is typically significant, because of the sensor itself, and the associated electronics. Therefore, in order to minimize the cost of SHM in practice, it is highly desirable to reduce the number of sensors. Beamforming with an array of sensors requires an advanced signal processing technique to detect the direction-of-arrival (DOA). In addition, by deploying more sensors, better detection accuracy can be achieved. In this paper, the non-equidistant linear sensor array is proposed, to obtain lower costs while guaranteeing reasonable detection accuracy. In addition, the proposed sensor deployment scheme is able to reduce the effects of “spatial aliasing,” which phenomenon is typically encountered in the equidistant linear sensor array layout. To validate the performance of the proposed non-equidistant linear array technique in SHM applications, several finite element models (FEM) simulation and experimental investigations are carried out. Different sensor array layouts are also compared to optimize the performance of the non-equidistant linear array.

This study proposes a new sensor cluster configuration for localizing an acoustic source in a plate using uniform linear array beamforming and T-shaped sensor clusters. This technique requires neither the properties of the plate material nor a dense array of sensors to find the direction of arrival of the acoustic source. It functions by placing four sensors in a cluster in the shape of the letter “‘T” over a small region of the plate. Uniform linear array beamforming-based source localization is carried out by the constructive interference of different sensor signals. However, this approach has the disadvantage of a very low resolution when the direction of arrival approaches certain values. The L-shaped sensor clusters use the information from the time difference of arrival between the sensors to estimate the direction of arrival, which has a high resolution in all directions except for the direction that is very close to vertical to the cluster. In this study, we numerically and experimentally demonstrate that the proposed T-shaped sensor cluster can accurately localize the acoustic source with no blind area. We also detail its superior performance compared to both uniform linear array beamforming and L-shaped clusters. In the experimental investigation, the maximum deviation of impact source localization was reduced significantly, from 54° to 4° for an aluminum plate, and from 42° to 3° for a composite plate. Furthermore, this novel combined sensor array layout requires only a few sensors, which can significantly reduce the cost of structural health monitoring practice.

Lamb waves have the advantages of long propagation distance and low power loss, which are widely used in the field of structural health monitoring. However, the Lamb waves generated by conventional methods usually contain various modes, and the multi-modes Lamb waves always cause troubles for damage detection and localization. This research proposes a novel single-A0 mode Lamb wave generation technique: the actuator is attached on the side face of the beam structure, and the sensor is attached on the top or bottom surface, which is perpendicular to the side face, so the single-A0 mode Lamb wave can be generated. Due to the mode conversion effect of Lamb wave when it passes through a crack, the existence of crack can be determined by checking the existence of S0 mode. In addition, the location of the crack can also be localized accurately using the proposed algorithm. Numerical and experimental investigations are carried out to demonstrate the performance of the proposed method.

Beamforming or phased array is widely used in structural health monitoring (SHM) systems for source localization. This localization is achieved by the constructive interference of signals measured by sensors in different positions. The uniform linear array (ULA) is one of the most commonly used beamforming array layouts due to its low complexity and high reliability. Unfortunately, ULA has the disadvantage of very low resolution when the direction of arrival (DOA) approaches certain directions. In order to overcome this problem, the double L-shape array is employed by adding only one sensor to the ULA. This sensor array uses the time difference of arrival information to estimate the DOA, which has high resolution in all directions except for the direction very close to vertical. Due to the blind area of the ULA beamforming and double L-shape sensors array, we combine the two methods and proposes a novel combined sensor array configuration which has no blind area at all. In addition, this novel combined sensor array layout uses a fewer number of sensors, which can reduce the cost of SHM practice significantly. Several numerical investigations are carried out to demonstrate the performance of the proposed sensor array.