Guided Waves (GW) inspection is a popular methodology employed by many Structural Health Monitoring (SHM) systems. GW inspection is typically achieved through phased arrays featuring a large number of piezoelectric transducers. The weight penalty, the complex circuitry, and maintenance concerns associated with wiring a large number of transducers have to be addressed for widespread field deployment of these type of SHM systems. Drastic hardware simplification and cost reduction of Guided wave (GWs) based systems can be achieved by using shaped transducers that present inherent directional capabilities when generating and sensing elastic waves. In particular, Frequency steerable acoustic transducers (FSATs) are based on a spatial filtering effect which is frequency-dependent, so that a direct relationship can be established between the direction of propagation and the spectral content of the transmitted/received differential signals [1]. However, in the first practical realizations of FSATs, two main limitations appeared: i) waves are excited or sensed contemporarily in one direction and in the opposite direction (180° ambiguity), ii) just a relatively rude approximation of the desired directivity has been achieved, resulting in a wave generation/detection even in directions other than the desired one. In this work, a new generation of FSATs is proposed, which allows overcoming the above mentioned limitations. In particular, the 180° ambiguity is eliminated by combining the information of 2 differential signals rather than one [1], as happened for the 1st generation FSATs. The result of this combination is a signal whose spectrum peaks at a frequency “f_d”. The piezoelectric load distribution of the 2nd generation FSAT is designed so that the value of “f_d” varies as a function of the wave direction of propagation in the whole angular range [0-360°]. The proposed embedded system allows to operate on composite panels tackling anisotropic and dispersive propagation, and to implement a SHM system with lower weight and size w.r.t. the actual structural monitoring systems. References [1] E. Baravelli et al., IEEE TIM, 62(8), 2013. [2] L. De Marchi et al., “Piezoelectric sensor, method and apparatus for guided waves inspections in real time,” 2015, temporary patent no. MI2015A000556.
A New Generation of Frequency Steerable Transducers for Lamb Waves Inspections / De Marchi, Luca; Testoni, Nicola; Marzani, Alessandro. - STAMPA. - (2016), pp. 1-8. (Intervento presentato al convegno 19th World Conference on Non-Destructive Testing (WCNDT 2016) tenutosi a Munich, Germany nel 13-17 June 2016).
A New Generation of Frequency Steerable Transducers for Lamb Waves Inspections
DE MARCHI, LUCA;TESTONI, NICOLA;MARZANI, ALESSANDRO
2016
Abstract
Guided Waves (GW) inspection is a popular methodology employed by many Structural Health Monitoring (SHM) systems. GW inspection is typically achieved through phased arrays featuring a large number of piezoelectric transducers. The weight penalty, the complex circuitry, and maintenance concerns associated with wiring a large number of transducers have to be addressed for widespread field deployment of these type of SHM systems. Drastic hardware simplification and cost reduction of Guided wave (GWs) based systems can be achieved by using shaped transducers that present inherent directional capabilities when generating and sensing elastic waves. In particular, Frequency steerable acoustic transducers (FSATs) are based on a spatial filtering effect which is frequency-dependent, so that a direct relationship can be established between the direction of propagation and the spectral content of the transmitted/received differential signals [1]. However, in the first practical realizations of FSATs, two main limitations appeared: i) waves are excited or sensed contemporarily in one direction and in the opposite direction (180° ambiguity), ii) just a relatively rude approximation of the desired directivity has been achieved, resulting in a wave generation/detection even in directions other than the desired one. In this work, a new generation of FSATs is proposed, which allows overcoming the above mentioned limitations. In particular, the 180° ambiguity is eliminated by combining the information of 2 differential signals rather than one [1], as happened for the 1st generation FSATs. The result of this combination is a signal whose spectrum peaks at a frequency “f_d”. The piezoelectric load distribution of the 2nd generation FSAT is designed so that the value of “f_d” varies as a function of the wave direction of propagation in the whole angular range [0-360°]. The proposed embedded system allows to operate on composite panels tackling anisotropic and dispersive propagation, and to implement a SHM system with lower weight and size w.r.t. the actual structural monitoring systems. References [1] E. Baravelli et al., IEEE TIM, 62(8), 2013. [2] L. De Marchi et al., “Piezoelectric sensor, method and apparatus for guided waves inspections in real time,” 2015, temporary patent no. MI2015A000556.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
