Current Issue : July - September Volume : 2017 Issue Number : 3 Articles : 6 Articles
Artificially structured materials with unit cells at sub-wavelength scale, known as metamaterials, have been widely\nused to precisely control and manipulate waves thanks to their unconventional properties which cannot be found\nin nature. In fact, the field of acoustic metamaterials has been much developed over the past 15 years and still keeps\ndeveloping. Here, we present a topical review of metamaterials in acoustic wave science. Particular attention is given\nto fundamental principles of acoustic metamaterials for realizing the extraordinary acoustic properties such as negative,\nnear-zero and approaching-infinity parameters. Realization of acoustic cloaking phenomenon which is invisible\nfrom incident sound waves is also introduced by various approaches. Finally, acoustic lenses are discussed not only for\nsub-diffraction imaging but also for applications based on gradient index (GRIN) lens....
It has been shown that acoustic waves with helical wavefronts can carry angular momentum, which can\nbe transmitted towards a propagating medium. Such a wave field can be achieved by using a planar array\nof electroacoustic transducers, forming a given spatial distribution of phased sound sources which produce\nthe desired helical wavefronts. Here, we introduce a technique to generate acoustic vortices, based on the\npassive acoustic metasurface concept. The proposed metasurface is composed of space-coiled cylindrical unit\ncells transmitting sound pressure with a controllable phase shift, which are arranged in a discretized circular\nconfiguration, and thus passively transforming an incident plane wavefront into the desired helical wavefront.\nThis method presents the advantage of overcoming the restrictions on using many acoustic sources, and it is\nimplemented with a transmitting metasurface which can be easily three-dimensionally printed. The proposed\nstraightforward design principle can be adopted for easy production of acoustic angular momentum with minimum\ncomplexity and using a single source....
We have generated planar blast waves over the large area using carbon\nnanotubes(CNT)-poly-dimethylsiloxane(PDMS) optoacoustic transducer. Pulse laser\nis absorbed by CNT and converted to heat, and the heat is transferred to PDMS\ninducing its thermal expansion and blast wave generation. To theoretically describe\nthe planar blast wave generation, we build one-dimensional simulation model and\nfind analytical solutions for temperature and pressure distributions. The analytical\nsolution validated by the experimental data sheds light on how to improve the performance\nof the new transducer. Resonance of acoustic waves inside the transducer is\nalso discussed. The new optoacoustic transducer optimized based on the fundamental\nunderstandings will be useful in generating high quality blast waves for research\nand industrial applications....
Acoustical holography has been widely applied for noise sources location and sound field measurement. Performance of the\nmicrophones array directly determines the sound source recognition method. Therefore, research is very important to the\nperformance of the microphone array, its array of applications, selection, and how to design instructive. In this paper, based on\nacoustic holography moving sound source identification theory, the optimization method is applied in design of the microphone\narray, we select the main side lobe ratio and the main lobe area as the optimization objective function and then put the optimization\nmethod use in the sound source identification based on holography, and finally we designed this paper to optimize microphone\narray and compare the original array of equally spaced array with optimization results; by analyzing the optimization results and\nobjectives, we get that the array can be achieved which is optimized not only to reduce the microphone but also to change objective\nfunction results, while improving the far-field acoustic holography resolving effect. Validation experiments have showed that the\noptimization method is suitable for high speed trains sound source identification microphone array optimization....
Abstract. In this study, acoustic analysis and thermofluid performance of a Ranque-Hilsch Vortex Tube (RHVT) is\nexperimentally investigated under different orifice diameters at its cold tube. The orifice diameters used are 2mm,\n3 mm, 4 mm, 5 mm and 6 mm. The inlet pressure (gage) is set at 10 psi, 15 psi, 20 psi and 25 psi for each orifice\ndiameter. The sound produced by the tube is recorded using a microphone located outside the cold tube. The acoustic\nsignal is processed using Fast-Fourier Transform (FFT) to obtain the frequency representation. Main frequencies are\nthen extracted to constitute the signature of the signal for that specific configuration. It is observed that different\norifice diameters give different signatures. These signatures are then associated with the thermofluid performance of\nthe device to obtain the relation among the parameters....
This work deals with a theoretical analysis about the possibility of using linear and\nnonlinear acoustic properties to modify ultrasound by adding gas bubbles of determined sizes in\na liquid. We use a two-dimensional numerical model to evaluate the effect that one and several\nmonodisperse bubble populations confined in restricted areas of a liquid have on ultrasound by\ncalculating their nonlinear interaction. The filtering of an input ultrasonic pulse performed by\na net of bubbly-liquid cells is analyzed. The generation of a low-frequency component from a\nsingle cell impinged by a two-frequency harmonic wave is also studied. These effects rely on the\nparticular dispersive character of attenuation and nonlinearity of such bubbly fluids, which can be\nextremely high near bubble resonance. They allow us to observe how gas bubbles can change acoustic\nsignals. Variations of the bubbly medium parameters induce alterations of the effects undergone by\nultrasound. Results suggest that acoustic signals can be manipulated by bubbles. This capacity to\nachieve the modification and control of sound with oscillating gas bubbles introduces the concept of\nbubbly-liquid-based acoustic metamaterials (BLAMMs)....
Loading....