In this paper, the correlation-based ultrasound imaging method called Excitelet is used in conjunction with a new Phase Coherence (PC) metric for medical imaging applications. In this shown that improved lateral resolution and a reduction of imaging artifacts are obtained when compared with Synthetic Aperture Focusing Technique (SAFT). Moreover, the phase content of the reflectivity map can be overlaid to the ultrasound image and allows distinguishing reflectors with different mechanical properties. This novel approach shows great potential for the imaging of specular reflectors and is supported with numerical and experimental imaging results.
This paper describes a novel way to exploit the correlation-based (CB) imaging algorithm Excitelet, based on correlation of measured signals with reference signals. In this study, reference signals are approximated using an experimental baseline instead of computing it. The reference signals are obtained by experimentally measuring the Full-Matrix Capture (FMC) with individual reflectors located at one point at a time of a determined imaging grid. This experimental CB (Exp CB) approach makes fewer model assumptions than the numerical CB (Num CB) method, meaning that the baseline is closer to reality, resulting in better spatial resolution and contrast of the imaging.
Guided-wave based Non-Destructive Evaluation (NDE) and Structural Health Monitoring (SHM) systems validation under realistic conditions or environment requires complex setups. Numerical or theoretical approaches are useful to save time and cost associated with experimental tests but the interaction with realistic geometrical (rivets, thickness changes, stiffeners, extrusions) or damage features (fatigue cracks, fillet cracks, delaminations, disbonds) must be accurately captured in order to be representative. In this paper, an experimental methodology is presented for estimating the far-field scattering of geometrical or damage features. The principle is based on the use of a Hankel transform of the measured 3D velocity field in order to evaluate with precision the scattered pattern using a spatially averaged method. Application to scattering of a hole with simulated machined and real fatigue cracks is proposed. It is observed that the simulated machined crack generally used as a reference standard can only model accurately the transmission behaviour while the scattering patterns are only similar when the wavelength is about the size of the crack, limiting the practical use of machined cracks for experimental validation of SHM or NDE systems.
In Structural Health Monitoring (SHM), classical imaging techniques rely on the use of analytical formulations to predict the propagation and interaction of guided waves generated using piezoceramic (PZT) transducers. For the implementation of advanced imaging approaches on composites structures, analytical formulations need to consider (1) the dependency of phase velocity and damping as a function of angle (2) the steering effect on guided wave propagation caused by the anisotropy of the structure and (3) the full transducer dynamics. In this paper, the analytical modeling of guided waves generation by a circular PZT and propagation on composite structures is investigated. This work, based on previous work from the authors, is intended to extend a semi- analytical formulation from isotropic to transversely isotropic plate-like structures. The formulation considers the dependency of the interfacial shear stress under the PZT as a function of radius, angular frequency and orientation on the composite structure. Validation is conducted for a unidirectional transversely isotropic structure with a bonded circular PZT of 10 mm in diameter. Amplitude curves and time domain signals of the A0 and S0 modes obtained from the proposed formulation and the classical pin-force model are first compared to Finite Element Model simulations. Experimental validation is then conducted using a 3D laser Doppler vibrometer for a non- principal direction on the composite. The results show the interest of considering a semi-analytical formulation for which the transducer dynamics where the shear stress distribution under the transducer is considered in order to reproduce more precisely the generation of guided waves on composite structures.
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