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[IEEE 2018 IEEE International Ultrasonics Symposium (IUS) - Kobe, Japan (2018.10.22-2018.10.25)] 2018 IEEE International Ultrasonics Symposium (IUS) - Looking at the Skull in a New Light: Rayleigh-Lamb Waves in Cranial Bone
摘要： Current knowledge on the ultrasound wave propagation in the cranial bone is restricted to far-field observations. In order to extend our understanding on how ultrasound waves propagate in the skull, we use short laser pulses to excite ultrasound waves in water-immersed ex vivo mouse and human skulls and explored their near-field. The laser pulses ( 10 ns duration) of 532 nm are absorbed by a small layer of black burnish deposited on the skull’s inner surface and generate ultrasound waves due to the thermoelastic effect. The acoustic near-field is mapped using a needle hydrophone close to the skull surface, following a three-dimensional scanning path derived from a previous pulse-echo scan of the skull with a spherically focused ultrasound transducer. The results for mouse and human skulls show different wave propagation regimes according to their differences in size, thickness, and internal structure. Leaky and non-leaky waves have been observed for both skull samples. Zero order Lamb modes were observed in the mouse skull, whereas Rayleigh-Lamb higher order modes can be observed in the human skull sample, presumably propagating in the outer cortical bone layer. Good agreement is found between the experiments and the multilayered flat plate model.
关键词： Skull Bone,Lamb Waves,Near Field,Surface Acoustic Waves,Rayleigh Waves,Plate waves,Laser ultrasonics
更新于2025-09-23 15:22:29
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Spatial distribution of the phononic crystal modes excited by a moving laser source
摘要： In this paper, we have presented the dispersion curve of Lamb waves in an aluminum plate with a periodic rectangular corrugation experimentally. A mode selection method was applied to generate Lamb waves in the region of the corrugated periodic structure using a moving continuous wave laser, and the signal can be detected at any point in the excitation region. The relationship between the phase velocity and the frequency is observed. It is found that the intensity distribution of the dispersion curves in the experimental results is related to the slope of the dispersion curves as well as the selection of the detection point. Vibrations at a series of locations were detected, re?ecting the change in energy that Lamb waves undergo in the process of propagation through the periodic structure, which is different from the existing method of single-point excitation and detection. The spatial distribution of the mode amplitude at the resonances points, in particular induced by the Bragg re?ection, has been studied.
关键词： dispersion curve,phononic crystal,Bragg reflection,laser ultrasonic method,Lamb waves
更新于2025-09-11 14:15:04
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Quantum Dot Optomechanics in Suspended Nanophononic Strings
摘要： The optomechanical coupling of quantum dots and flexural mechanical modes is studied in suspended nanophononic strings. The investigated devices are designed and monolithically fabricated on an (Al)GaAs heterostructure. Radio frequency elastic waves with frequencies ranging between f = 250 and 400 MHz are generated as Rayleigh surface acoustic waves on the unpatterned substrate and injected as Lamb waves in the nanophononic string. Quantum dots inside the nanophononic string exhibit a 15-fold enhanced optomechanical modulation compared to those dynamically strained by the Rayleigh surface acoustic wave. Detailed finite element simulations of the phononic mode spectrum of the nanophononic string confirm that the observed modulation arises from valence band deformation potential coupling via shear strain. The corresponding optomechanical coupling parameter is quantified to 0.15 meV nm?1. This value exceeds that reported for vibrating nanorods by approximately one order of magnitude at 100 times higher frequencies. Using this value, a derived vertical displacement in the range of 10 nm is deduced from the experimentally observed modulation. The results represent an important step toward the creation of large scale optomechanical circuits interfacing single optically active quantum dots with optical and mechanical waves.
关键词： nanomechanics,optomechanics,quantum dots,Lamb waves,hybrid quantum systems
更新于2025-09-11 14:15:04
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A Guided Wave Sensor Enabling Simultaneous Wavenumber-Frequency Analysis for Both Lamb and Shear-Horizontal Waves
摘要： Guided waves in plate-like structures have been widely investigated for structural health monitoring. Lamb waves and shear horizontal (SH) waves, two commonly used types of waves in plates, provide different benefits for the detection of various types of defects and material degradation. However, there are few sensors that can detect both Lamb and SH waves and also resolve their modal content, namely the wavenumber-frequency spectrum. A sensor that can detect both waves is desirable to take full advantage of both types of waves in order to improve sensitivity to different discontinuity geometries. We demonstrate that polyvinylidene difluoride (PVDF) film provides the basis for a multi-element array sensor that detects both Lamb and SH waves and also measures their modal content, i.e., the wavenumber-frequency spectrum.
关键词： shear horizontal waves,Lamb waves,PVDF sensor,wavenumber-frequency analysis
更新于2025-09-09 09:28:46
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Analysis of Second-Harmonic Generation of Low-Frequency Dilatational Lamb Waves in a Two-Layered Composite Plate
摘要： We analyze the effect of second-harmonic generation (SHG) of primary Lamb wave propagation in a two-layered composite plate, and then investigate the influence of interfacial properties on the said effect at low frequency. It is found that changes in the interfacial properties essentially affect the dispersion relation and then the maximum cumulative distance of the double-frequency Lamb wave generated. This will remarkably influence the efficiency of SHG. To overcome the complications arising from the inherent dispersion and multimode natures in analyzing the SHG effect of Lamb waves, the present work focuses on the analysis of the SHG effect of low-frequency dilatational Lamb wave propagation. Both the numerical analysis and finite element simulation indicate that the SHG effect of low-frequency dilatational Lamb wave propagation is found to be much more sensitive to changes in the interfacial properties than primary Lamb waves. The potential of using the SHG effect of low-frequency dilatational Lamb waves to characterize a minor change in the interfacial properties is analyzed.
关键词： composite plate,interfacial properties,low frequency,second-harmonic generation,Lamb waves
更新于2025-09-09 09:28:46
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Double-Negative Pillared Elastic Metamaterial
摘要： We present a single-phase double-sided pillared metamaterial with effective mass density and elastic modulus simultaneously negative. The negative effective mass density is achieved owing to the combination of the symmetric bending resonance and the antisymmetric compressional resonance of both pillars, whereas the negative effective elastic modulus results from their symmetric compressional resonance. Comparisons with the single-sided pillared structure are made. The dependence of the width of the double-negative band against the geometric parameters of the unit cell is also investigated. In addition, the negative refraction and the zero-index refraction of the symmetric Lamb wave in the deep-subwavelength scale are observed, while at the same frequency, the propagation of the antisymmetric Lamb wave is forbidden.
关键词： deep-subwavelength scale,zero-index refraction,negative refraction,Lamb waves,elastic metamaterial
更新于2025-09-09 09:28:46