Lamb wave transducers made of piezoelectric macro-fiber composite (original) (raw)
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Properties of interdigital transducers for Lamb-wave based SHM systems
2011
1 Recently, an intensive research activity has been observed concerning the application of guided waves to long range ultrasound (LRUT) and structural health monitoring. Guided waves propagating in plates, known as Lamb waves, have appeared to be suitable for monitoring and condition evaluation of planar structures. Lamb waves can be generated using different types of actuators including piezoelectric or electromagnetic acoustic transducers. In this paper a novel type of piezoelectric transducers is presented based on macro-fiber piezocomposite (MFC). Contrary to the previously presented MFC transducers the transducers presented here are provided with interdigital electrodes matched to certain wavelength. Two different designs of interdigital transducers (IDT) made of MFC substrate are presented in the paper together with the results of numerical simulations and experimental tests. INTRODUCTION Applications of guided ultrasonic waves to nondestructive testing (NDT) and structural he...
Investigation of the 3D displacement characteristics for a macro-fiber composite transducer (MFC-P1)
Materiali in tehnologije, 2018
The accurate three-dimensional (3D) displacement profile of a contact-type ultrasonic transducer ensures that the transducer is free of defects during its manufacturing or installation. It also ensures the applicability of the transducer in structural health monitoring (SHM) and non-destructive testing (NDT). Since its invention in 1996 by NASA, the macro-fiber composite (MFC) transducer was positively accepted by researchers due to its lightweight, flexibility, durability and reliability. As it can be embedded quite easily on the structure under inspection, there are different ways to which it can be used for the detection of defects in the composite materials using guided Lamb waves. The objective of the presented work was to investigate the operational performance of an unloaded macro fiber composite (MFC) transducer of P1-type by estimating its 3D displacement components. The 3D spatial displacements of vibrating MFC were investigated using a Polytec 3D scanning laser vibrometer (PSV-500-3D-HV) in order to determine the directions/planes along which the ultrasonic guide waves would be generated most effectively. The behaviour of the MFC transducer of P1 type based on the displacement characteristics confirmed that it works in d33 (elongation) mode, as specified in the manufacturer's specifications. Keywords: macro fiber composite, ultrasonic NDT, spatial displacements, Lamb waves, 3D-scanning laser vibrometer Natan~en tridimenzionalni profil (3D) premikov kontaknega ultrazvo~nega pretvornika omogo~a, da je le-ta brez napak med izdelavo ali namestitvijo. To namre~zagotavlja uporabnost pretvornika za strukturno zdravstveno opazovanje (angl. SHM) in neporu{no testiranje materialov (angl. NDT). NASA je leta 1996 izumila ultrazvo~ni kompozitni pretvornik na osnovi makrovlaken (MFC; angl.: Macro-Fiber Composite). Raziskovalci so potem pretvornik kmalu pozitivno sprejeli zaradi njegove majhne mase, prilagodljivosti, trajnosti in zanesljivosti. Obstajajo razli~ni na~ini njegove uporabe za odkrivanje napak v kompozitnih materialih z uporabo kontroliranih Lambovih valov, ker ga je zelo lahko namestiti na preiskovano strukturo. Predmet raziskave predstavljene v tem~lanku, so lastnosti obratovanja neobremenjenega MFC-pretvornika tipa P1 z oceno njegovih 3D-premikov. Prostorske premike vibrirajo~ega MFC so avtorji preiskovali s 3D-laserskim skenirnim vibrometrom Polytec (PSV-500-3D-HV) in s tem dolo~ili smeri in ravnine, vzdol`katerih so vodeni ultrazvo~ni valovi najbolj u~inkovito generirani. Potrdili so, da le-ta deluje v na~inu d33 (raztezek) in da so karakteristike obna{anja MFC pretvornika tipa P1 v skladu s proizvajal~evo specifikacijo. Klju~ne besede: kompozit iz makrovlaken, ultrazvo~na neporu{na preiskava (NDT), prostorski premiki, Lambovi valovi, 3D-laserski skenirni vibrometer
The Abstracts of ATEM : International Conference on Advanced Technology in Experimental Mechanics : Asian Conference on Experimental Mechanics
Active Fiber Composites (AFC) consist of one layer of piezoelectric ceramic fibers embedded in an epoxy matrix and sandwiched between two sets of interdigitated electrodes. They show orthotropic mechanical properties due to their design and manufacturing. The small thickness and the conformability to curved surfaces make them suitable for applications in structural health monitoring (SHM) with acoustic nondestructive testing methods. The piezoelectric properties of the AFC allow for both actuation and sensing capabilities with the same element which enables emitting and receiving of structural waves (e.g., Lamb waves) for monitoring of critical structural elements. Before realizing specific applications for AFC in SHM systems, it is necessary to characterize the transfer behavior of AFC bonded on a structure for excitation and sensing of transient waves which propagate in the structure. To characterize this behavior experimentally, the acoustic wave field in a thin, planar structure excited from surface bonded AFC is explored with a laser interferometer. Surface velocities at different positions around an AFC bonded on an aluminum plate during transient excitation are recorded. The transfer function is calculated for different angles from the fiber direction of the AFC for both the first symmetric and the first antisymmetric Lamb wave mode. The sensing process is also investigated: structural waves generated by surface bonded piezoelectric ceramic discs are measured likewise with laser interferometry in the vicinity of the AFC and with the AFC itself. Results show, that the emitting and receiving capabilities of the AFC decrease with increasing angle from the fiber direction of the AFC. Typical maxima and minima in the transfer function depend on the length of the AFC.
Piezo-composite transducer for mode and direction selectivity of Lamb waves
2018
Ultrasonic-based SHM (Structural Health Monitoring) applications commonly rely on the use of piezo-electric patches to emit and receive ultrasonic waves. The objective is to study the propagation of the waves through a structure to assess its structural integrity. Because of the elevated number of echoes and possible modes of propagation of the waves within the structure, those applications suffer from a burden of signal processing. This paper presents a composite piezo-electric patch that was designed and successfully tested for reducing the complexity of the SHM detection schemes by selecting the mode and direction of the Lamb waves received. The piezo-composite is composed of a row of eight independent ceramic pillars separated with polymer, so it is a 1-D matrix of independent piezo-patches. Used with adequate electronics and signal processing, it was shown that it allowed selecting the direction and the mode of the Lamb waves.
Sensors and Actuators A: Physical, 2005
In this work a new technology for designing and manufacturing ultrasonic interdigital transducers (IDT) is presented. The piezoelectric material used is a metallised piezopolymer film made of polyvinylidene fluoride (PVDF) with electrode pattern obtained with a laser ablation process. Piezopolymer transducer prototypes are designed with wavelength of 8 mm to operate with Lamb waves (symmetrical S 0 mode). An experimental validation of the piezopolymer IDT design is demonstrated with a transmitter-receiver IDT pair embedded in a 3 mm thick carbon fiber reinforced plastic (CFRP) composite laminate.
Active fiber composites for the generation of Lamb waves
Ultrasonics, 2009
Active fiber composites (AFC) are thin and conformable transducer elements with orthotropic material properties, since they are made of one layer of piezoelectric ceramic fibers. They are suitable for applications in structural health monitoring systems (SHM) with acoustic non-destructive testing methods (NDT). In the presented work the transfer behavior of an AFC as an emitter of transient elastic waves in plate-like structures is investigated. The wave field emitted by an AFC surface bonded on an isotropic plate was simulated with the finite-difference method. The model includes the piezoelectric element and the plate and allows the simulation of the elastic wave propagation. For comparison with the model experiments using a laser interferometer for non-contact measurements of particle velocities at different points around the AFC on the surface of the plate were performed. Transfer functions defined as the ratio of the electric voltage excitation signal and the resulting surface velocity at a specific point are separately determined for the two fundamental Lamb wave modes. In order to take the orthotropic behavior of the AFC into account the transfer functions are determined for several points around the AFC. Results show that the AFC is capable to excite the fundamental symmetric and antisymmetric Lamb wave mode. The antisymmetric mode is mainly radiated in the direction of the piezoelectric fibers, while the symmetric mode is spread over a larger angle. The amplitudes of the emitted waves depend on the frequency of the excitation as well as on the geometric dimensions of the transducer.
Composite Structures, 2002
The paper presents a set of numerical results on the use of surface mounted piezoelectric transducers to analyse the effects of impact damage and delamination of plate-like structures on the Lamb wave mode. The effects of the size, properties and orientation of the damage upon a propagating Lamb wave is qualitatively determined. In this paper, impact damage was simulated by a local change in the stiffness of the material in the structure and a delamination. The effects on the transmission of the incident Lamb wave when it propagates through a region of change in density are analysed. This paper will also demonstrate how the properties of a propagating Lamb wave can be affected by the existence of a delamination in a plate.
Modeling and experimental study of transducers made with piezoelectric composite material
Le Journal de Physique IV, 1999
The topic of this work is the experimental and theoretical study of a cylindrical acoustic transducer made with a 1.3 piezoelectric composite material. This material consists in PZT ceramic rods embedded in a polymer matrix. A modeling of this ideal transversally periodic structure is proposed. It is based on a finite element approach derived from homogenization techniques mainly used for composite material studies. The analysis focuses on a representative unit cell with specific boundary conditions on the lateral surfaces taking accurately into account the periodicity of the structure. The first step proposed is the development of a tridimensional Fortran code especially adapted for this problem. It then allowed the set up of different nonredundant linear combinations of degrees of freedom that could be linked to the ANSYS FEM code allowing to progress toward the modeling of the complete problem. The motion of the faces of an experimental transducer vibrating in the quasi-static mode has been analyzed using Laser Doppler vibrometry technique. Experimental and modeling results are in good agreement and justify the proposed approach.
Optimized piezoelectric sensor for a specific application: Detection of Lamb waves
Sensors and Actuators A: Physical, 2006
This work is devoted to the development and the optimization of a new piezoelectric sensor using Lamb waves destined to aerospace structures health monitoring. In such systems, Lamb waves are usually excited and received by thin single piezoelectric transducers. One of the most critical tasks in health monitoring is to identify all the generated Lamb waves in order to ease the damage estimation. A possible solution is to measure the Lamb wave signal at different locations along the propagation direction. So, the development of a distributed sensing technology using metallic multi-electrode deposited on a piezoelectric substrate was a key element, which built the bridge between the sensors signals and the structural integrity interpretation.