ABSTRACT
Because violins are traditionally hand-crafted using wood, each one is unique. This makes the design of repeatable experiments studying some aspects of its dynamic behavior unfeasible. To tackle this problem, an adjustable finite element (FE) model of a violin soundbox using the geometry and behavior of the "Titian" Stradivari was developed in this paper. The model is parametric, so its design and material properties can be varied for before/after comparisons in both the frequency and time domains. Systematic simulations revealed that f-holes set lower in the top, as seen in some Stradivari violins (e.g., Hellier, Cremonese), raise the frequency of the Hill (a feature in the bridge mobility); conversely, the higher set f-holes seen in some Guarneri violins (e.g., Principe Doria) reduces such frequency. This agrees with the widespread belief that the high-frequency response of Stradivari violins is stronger than Guarneri violins. Changes in the response of the system were quantified once each part of the design was added, calling attention to the influence of the blocks on the behavior of signature modes, especially in the frequency and shape of B1 +. A text file of the FE model is available in supplemental materials; it runs in ANSYS (free version), for which guides are included.
ABSTRACT
The optical behavior exhibited by bimetallic nanoparticles was analyzed by the influence of ultrasonic and nonlinear optical waves in propagation through the samples contained in an ethanol suspension. The Au-Pt nanoparticles were prepared by a sol-gel method. Optical characterization recorded by UV-vis spectrophotometer shows two absorption peaks correlated to the synergistic effects of the bimetallic alloy. The structure and nanocrystalline nature of the samples were confirmed by Scanning Transmission Electron Microscopy with X-ray energy dispersive spectroscopy evaluations. The absorption of light associated with Surface Plasmon Resonance phenomena in the samples was modified by the dynamic influence of ultrasonic effects during the propagation of optical signals promoting nonlinear absorption and nonlinear refraction. The third-order nonlinear optical response of the nanoparticles dispersed in the ethanol-based fluid was explored by nanosecond pulses at 532 nm. The propagation of high-frequency sound waves through a nanofluid generates a destabilization in the distribution of the nanoparticles, avoiding possible agglomerations. Besides, the influence of mechanical perturbation, the container plays a major role in the resonance and attenuation effects. Ultrasound interactions together to nonlinear optical phenomena in nanofluids is a promising alternative field for a wide of applications for modulating quantum signals, sensors and acousto-optic devices.
ABSTRACT
A strong influence of mechanical action in nonlinear optical transmittance experiments with bimetallic nanoparticles integrated by gold and platinum was observed. The nanostructured samples were synthesized by a sol-gel method and contained in an ethanol suspension. UV-VIS spectroscopy evaluations, Transmission electron microscopy studies and input-output laser experiments were characterized. A two-photon absorption effect was induced by nanosecond pulses at 532 nm wavelength with an important contribution from the plasmonic response of the nanomaterials. All-optical identification of acoustical waves was remarkably improved by optical nonlinearities. High sensitivity for instrumentation of mechano-optical signals sensing particular fluids was demonstrated by using a variable carbon dioxide incorporation to the system.
ABSTRACT
This paper was based on a theoretical framework to determine strong and weak radiation by a guitar top plate, vibrating through deflections hard to analyze: multipolar mode shapes. The air-structure interaction was examined in terms of edge modes or corner modes, and considering even or odd number modes. A numerical model was implemented and experimentally calibrated, exhibiting several advantages exploring the coupling between vibratory and acoustic waves in a top plate. Two analyses were applied detecting high or low radiation efficiency for the structure. First, the addition of volume velocity for odd numbers of poles and cancellation for even numbers were examined. In fact, both behaviors can happen at the same time, as it was shown for a corner radiator case used as an example. Second, the ratio between bending and acoustic wavenumbers was explored. To illustrate the importance of this ratio, some theoretical features of a more efficient radiator than the corner mode were exposed in an edge mode example. Labeling multipolar mode shapes as efficient or inefficient radiators showed to be a useful alternative analyzing the top plate behavior. It can be applied knowing the nodal lines of the vibration pattern and estimating the bending and acoustic wavelengths.
