Guided wave excitation by a CLoVER transducer for structural health monitoring: theory and experiments

Abstract

The guided wave (GW) field excited by a wedge-shaped, anisotropic piezocomposite transducer, surface-bonded on an isotropic substrate is investigated with applications to large area structural health monitoring. This investigation supports the development of the composite long-range variable-direction emitting radar (CLoVER) transducer. The analysis is based on the three-dimensional equations of elasticity, and the solution yields expressions for the field variables that are able to capture the multimodal nature of GWs. The assumption of uncoupled dynamics between the actuator and substrate is used, and their interaction is modeled through shear tractions along the transducer's radial edges. A similar problem is modeled using three-dimensional finite element simulations to assess the spatial and transient accuracy of the solution. Experimental tests are also conducted on pristine structures to validate the accuracy of the theoretical approach. The experimental studies employ CLoVER transducers developed in-house, and their manufacturing procedure is briefly described. Frequency response experiments based on piezoelectric sensors are conducted to assess the performance of the solution in the frequency domain. These tests are complemented by laser vibrometer measurements that allow the spatial and temporal evolution of the solution to be evaluated. The numerical simulations and experimental tests show that the wave time of arrival, radial attenuation, and azimuthal distribution are well captured by the theoretical solution.

Toward the Upscaling of Guided Waves-Based NDE and SHM in Aeronautics

“…The methodologies to locate impact based on guided waves can be mainly classified in three groups: (i) inverse methods that locate the impact via model updating, by using neural networks, genetic algorithms, or time reversal [3][4][5][6]; (ii) hyperbolic positioning algorithms that locate impact by using the difference in time-of-flight (ToF), i.e., time difference of arrival (TDoA), of the wavefronts captured by different sensors and proper triangulation algorithms [7][8][9][10][11][12][13]; and (iii) direct strategies which allow to locate the wave source by capturing the wave direction of arrival (WDA) without recurring to the waves ToF [14][15][16][17].…”

Inkjet fabrication of spiral frequency-steerable acoustic transducers (FSATs)

“…The main drawback of phased arrays is the considerable amount of hardware and data handling required to independently control each element. As an alternative, active and passive structure interrogation through devices with inherent directional capabilities was proposed, respectively by firing individual wedge sectors of a ring-shaped composite long-range variable-direction emitting radar (CLoVER) transducer, 5 and by directional sensing of incoming waves using macro-fiber composite piezoelectric rosettes. 6 The wavenumber spiral frequency steerable acoustic transducer (WS-FSAT) recently proposed by the authors 7,8 provides an interesting option for directional structure inspection with further reduction of hardware requirements down to a single, differential channel.…”

Experimental demonstration of spiral frequency-steerable acoustic sensors

“…However, individually controlling each array element leads to significant hardware complexity, power consumption and data rate requirements. Alternative devices with inherent directional properties include the CLoVER transducer [4] featuring individually activated wedge sections of a piezo-composite ring pattern, as well as rosette configurations of microfiber composite (MFC) devices [5]. Whereas these solutions still involve multiple channels, recently proposed FSATs incorporate directional capabilities into one-or two-channel devices [6,7,8] with peculiar geometries.…”