- Professor, Georgia Institute of Technology.edit
Research Interests: Materials Engineering, Mechanical Engineering, Physics, Acoustics, Optics, and 15 moreModeling, Medicine, Surface Roughness, Classical Physics, Ultrasonics, Surface Waves, Diffraction, Technology and Engineering, Acoustic wave sensors, Rayleigh Waves, Rayleigh Wave, Diffraction Grating, Surface Wave, plane waves, and Planar
A diffraction grating is a spatial filter causing sound waves or optical waves to reflect in directions determined by the frequency of the waves and the period of the grating. The classical grating equation is the governing principle that... more
A diffraction grating is a spatial filter causing sound waves or optical waves to reflect in directions determined by the frequency of the waves and the period of the grating. The classical grating equation is the governing principle that has successfully described the diffraction phenomena caused by gratings. However, in this work, we show experimental observation of the so-called sub-harmonic diffraction in acoustics that cannot be explained by the classical grating equation. Experiments indicate two physical phenomena causing the effect: internal scattering effects within the corrugation causing a phase shift and nonlinear acoustic effects generating new frequencies. This discovery expands our current understanding of the diffraction phenomenon, and it also makes it possible to better design spatial diffraction spectra, such as a rainbow effect in optics with a more complicated color spectrum than a traditional rainbow. The discovery reveals also a possibly new technique to study nonlinear acoustics by exploitation of the natural spatial filtering effect inherent to an acoustic diffraction grating.
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Hellenistic theaters are well known for their marvelous acoustics. A numerical study reveals that the seat rows of the theater unexpectedly play an essential role in the acoustics, at least when the theater is not fully filled with... more
Hellenistic theaters are well known for their marvelous acoustics. A numerical study reveals that the seat rows of the theater unexpectedly play an essential role in the acoustics, at least when the theater is not fully filled with spectators. The seats, which constitute a corrugated surface, serve as an acoustic filter that passes sound coming from the stage at the expense of surrounding acoustic noise. Whether a coincidence or not, the famous theater of Epidaurus was built with optimized shape and dimensions.
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... Acknowledgement Nico F. Declercq is a postdoctoral fellow of the Fund for Scientific Research - Flanders (FWO - Vlaanderen). References ... IEEE-trans. on UFFC 52 (2005) 776791. [2] M. Hayes: Inhomogeneous plane waves. Arch. Ration.... more
... Acknowledgement Nico F. Declercq is a postdoctoral fellow of the Fund for Scientific Research - Flanders (FWO - Vlaanderen). References ... IEEE-trans. on UFFC 52 (2005) 776791. [2] M. Hayes: Inhomogeneous plane waves. Arch. Ration. Mech. Anal. 85 (1984) 4179. ...
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Research Interests: Physics, Gravitation, General Relativity, Stress, Anisotropy, and 15 moreHigher Order Thinking, Mathematical Sciences, Piezoelectric material, Classical Field Theory, Physical sciences, Slowness, Classical Mechanics, Einstein tensor, Gravitational Field, Gravitational energy, Piezoelectricity, Theoretical Model, Lithium Niobate, Higher order, and plane waves
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The acoustics education program at the Georgia Institute of Technology (Georgia Tech) is run by members of the Acoustics and Dynamics research area group from the School of Mechanical Engineering. We will briefly review the scope of this... more
The acoustics education program at the Georgia Institute of Technology (Georgia Tech) is run by members of the Acoustics and Dynamics research area group from the School of Mechanical Engineering. We will briefly review the scope of this program in terms of education and research activities
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International audienc
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Research Interests: Materials Engineering, Mechanical Engineering, Physics, Medicine, Feasibility Study, and 15 moreNondestructive testing, Fourier Analysis, Classical Physics, Feasibility Studies, Ultrasonics, Surface Waves, EVANESCENT WAVE, Feasibility, Fourier transform, Rayleigh Wave, Normal Distribution, Fourier Transformation, Ultrasonic Testing, Surface Wave, and plane waves
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When a bounded beam is incident on an immersed plate Lamb waves or Rayleigh waves can be generated. Because the amplitude of a bounded beam is not constant along its wave front, a specific beam profile is formed that influences the local... more
When a bounded beam is incident on an immersed plate Lamb waves or Rayleigh waves can be generated. Because the amplitude of a bounded beam is not constant along its wave front, a specific beam profile is formed that influences the local efficiency of energy conversion of incident sound into Lamb waves or Rayleigh waves. Understanding this phenomenon is important for ultrasonic immersion experiments of objects because the quality of such experiments highly depends on the amount of energy transmitted into the object. This paper shows by means of experiments based on monochromatic Schlieren photography that the area within the bounded beam responsible for Lamb wave generation differs from that responsible for Rayleigh wave generation. Furthermore it provides experimental verification of an earlier numerical study concerning Rayleigh wave generation.
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International audienc
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Research Interests: Physics and Calibration
The difficulty of applying ultrasonic techniques to bi-material structures lies in the fact that different phenomena coexist, such as the non-linear effects caused by the adhesion properties between matrix-fibers and the diffraction... more
The difficulty of applying ultrasonic techniques to bi-material structures lies in the fact that different phenomena coexist, such as the non-linear effects caused by the adhesion properties between matrix-fibers and the diffraction effect caused by the periodicity of those structures. This work deals with the study of the combined effect of non-linear effects on a 3D bi-materials structure “polymer-titanium.” For this purpose, a Snapscan system is used which generates high amplitude pulses and receives signals composed of the fundamental mode and the higher harmonics. The transducers used are chosen according to the thickness and the periodicity scale of the sample. First, measurements in transmission are made where the transmitted ultrasonic waves are measured by changing the angle between the receiver and the sample. For each angle, a spectrogram is realized. The experimental observations on the spectrograms show that for small incident amplitudes we measure only the fundamental frequency. When the amplitude is gradually increased, high harmonics are generated due to the non-linear stress-strain relationship. Then, reflection measurements were made to measure the Bragg spectrum. The results show that the internal defects (due to lack of adhesion) disturb the periodicity of the structure and thus the Bragg spectrum. This non-destructive technique can be a valuable aid for the automotive industry, for example, in order to control their products during manufacturing process.
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This work was done on woven glass-fiber fabric reinforced composite samples. Those materials exhibit a complex anisotropic evolution of defects induced by several damage mechanisms. In order to non-destructively evaluate the damage... more
This work was done on woven glass-fiber fabric reinforced composite samples. Those materials exhibit a complex anisotropic evolution of defects induced by several damage mechanisms. In order to non-destructively evaluate the damage accumulation within this material, a methodology based on the measurement of the complete stiffness tensor is considered. After validation of the detectability of increasing damage state with this method, a new damage indicator is proposed to thoroughly quantify it. Samples were damaged by tensile tests (quasi-static and fatigue) at increasing stress levels along and out-of fibers axis. Afterwards, drop-weight impact is performed to consider several damage situations. Finally, an X-ray tomography is conducted to identify the damage mechanisms as well as the evolution of the void volume fraction. It is shown that this evolution has the same tendency with the ultrasonic damage indicator.
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A discussion of nondestructive techniques is presented for the investigation of complex media, with a focus on composite samples. Traditionally, one applies ultrasonic C-scans, or polar scans, which are easy to implement and to interpret.... more
A discussion of nondestructive techniques is presented for the investigation of complex media, with a focus on composite samples. Traditionally, one applies ultrasonic C-scans, or polar scans, which are easy to implement and to interpret. However, in many realistic cases, it is important to use more sophisticated approaches as C-scans often do not reveal any useful information. Typically, the early part of received signals is used to extract information, whereas the later part is considered either as noise or as a useless coda wave as in musical acoustics. Nevertheless, it appears that the coda part carries useful information about the medium, and therefore, it is important to explore techniques to extract that information. In addition, it turns out that the coda is very sensitive to material properties and damage as those sound waves interact longer with the material than early arrival waves. First, earlier results will be shown which compare experimental polar scans with numerical...
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The interaction of (in)homogeneous plane waves with a singly corrugated surface has been tackled before. It was shown that inhomogeneous waves are the only kind of waves that are able to really stimulate leaky critical waves, such as... more
The interaction of (in)homogeneous plane waves with a singly corrugated surface has been tackled before. It was shown that inhomogeneous waves are the only kind of waves that are able to really stimulate leaky critical waves, such as leaky Rayleigh waves, while plane waves are the only waves that can actually stimulate Scholte Stoneley waves. Recently, a model is developed that describes the interaction of (in)homogeneous plane waves with a doubly corrugated surface ('egg crate'). However, since plane waves extend to infinity, they cannot exist in reality, whence it is necessary to extend the model to bounded beams and to investigate what special features might hence occur in reality. Here, the decomposition of a 3D gaussian beam is performed into plane waves using the Fast Fourier Transform. The interaction of a normally incident gaussian beam with the doubly corrugated surface is investigated with special attention for the directivity of excited Scholte Stoneley waves. Thi...
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Metamaterials are intensely explored for their capabilities to modify sound beams. In addition to frequency filtering, acoustic lenses offer intriguing possibilities for shaping sound beams. For the time being, the versatility of... more
Metamaterials are intensely explored for their capabilities to modify sound beams. In addition to frequency filtering, acoustic lenses offer intriguing possibilities for shaping sound beams. For the time being, the versatility of metamaterials remains limitless. In beam-shape adaptation, however, their complexity suggests that manufacturers of transducers could benefit from combining metamaterials with more conventional materials. This paper investigates the transmission of a circumscribed beam through a stratum of anisotropic material to examine the change in beam shape after transmission. The incident sound is presumed to originate from a conventional transducer, possibly coated with a metamaterial to modify the sound field, before being transmitted through the anisotropic layer. Different incident beam shapes, such as conical-like, Gaussian, and pillar beams, are investigated. While the results are not exhaustive, they demonstrate the beam shape’s adaptability.
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Wiring, of different degrees of complexity, is a dominant part of mechanical support in constructions, electromagnetic and telecommunication signal transmission cables, among other applications. Single and manifold twisted wires are... more
Wiring, of different degrees of complexity, is a dominant part of mechanical support in constructions, electromagnetic and telecommunication signal transmission cables, among other applications. Single and manifold twisted wires are prominent examples of such utilities and are susceptible to mechanical irritations and deterioration. They require ultrasonic non-destructive testing and health monitoring. The objective is to develop an ultrasound-based technique to automatically measure the number of twists per meter in winded wire strands implementable in the industry, to be used during an ultrasonic scan and provide the number of twists per meter during cable production, for instance, to verify that calibration is still in place. Fourier transformation is applied as an expedited non-destructive testing method of twisted wires. Digital signal processing to obtain spatial and time spectral representation recognition due to amplitude variance, induced by the varying distance between the...
Background. Donated blood is routinely preserved for about six weeks. After that, a considerable amount of unused blood is discarded for safety. We carried out sequential measurements of the ultrasonic parameters (Velocity of propagation... more
Background. Donated blood is routinely preserved for about six weeks. After that, a considerable amount of unused blood is discarded for safety. We carried out sequential measurements of the ultrasonic parameters (Velocity of propagation of ultrasound, its attenuation, and relative nonlinearity coefficient B/A) for red blood cells (RBCs) bags in their physiological preserving conditions in the blood bank, in a given experimental setup, to investigate the gradual deteriorations in the biomechanical properties of RBCs. Materials and Methods. We discuss our primary findings, which indicate the applicability of ultrasound techniques as a quantitative quick, non-invasive routine check for the validity of sealed blood bags. The technique can be applied during and beyond the regular preservation period, thus enabling deciding for each bag to either further preserve or withdraw. Results and Discussion. Considerable increases in the velocity of propagation (ΔV = 966 m s−1) and ultrasound att...
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The acoustics education program at the Georgia Institute of Technology (Georgia Tech) is run by members of the Acoustics and Dynamics research area group from the School of Mechanical Engineering. We will briefly review the scope of this... more
The acoustics education program at the Georgia Institute of Technology (Georgia Tech) is run by members of the Acoustics and Dynamics research area group from the School of Mechanical Engineering. We will briefly review the scope of this program in terms of education and research activities