Current Issue : January - March Volume : 2018 Issue Number : 1 Articles : 5 Articles
The existing acoustic emission (AE) source location methods assume that acoustic waves propagate along straight lines, and the source location is determined by average wave velocity. Because of the heterogeneity of materials, location results often fail to meet the accuracy requirement. For this reason, an AE source location method considering refraction in different media was proposed in this paper. According to sensor coordinates, the arrival time of acoustic waves, the velocities of acoustic waves in two kinds of media, the space-time relation equations of the AE source point and the measuring point were established by the precise coordinates of the AE source based on Snell�s law. The feasibility of the algorithm was verified by experiments, and the factors influencing location accuracy were also analysed. The results show that the algorithm proposed in this paper is applicable for both the same medium and different media, and the accuracy of localization is not affected by the ratio of wave velocities in two media or the distance from the AE source to the refraction surface....
A plasma actuator comprising a dielectric layer sandwiched between upper and lower\nelectrodes can induce a flow from the upper to lower electrode by means of an externally-applied\nelectric field. Our objective is to clarify the mechanism by which such actuators can control the cavity\ntone. Plasma actuators, with the electrodes elongated in the streamwise direction and aligned in the\nspanwise direction, were placed in the incoming boundary of a deep cavity with a depth-to-length\nratio of 2.5. By using this experimental arrangement, the amount of sound reduction (ââ?¬Å?control effectââ?¬Â)\nproduced by actuators of differing dimensions was measured. Direct aeroacoustic simulations\nwere performed for controlling the cavity tone by using these actuators, where the distributions\nof the body forces applied by the actuators were determined from measurements of the plasma\nluminescence. The predicted control effects on the flow and sound fields were found to agree\nwell with the experimental results. The simulations show that longitudinal streamwise vortices\nare introduced in the incoming boundary by the actuators, and the vortices form rib structures in\nthe cavity flow. These vortices distort and weaken the two-dimensional vortices responsible for\nproducing the cavity tone, causing the tonal sound to be reduced....
Acoustic standing waves have been widely used in trapping, patterning, and manipulating\nparticles, whereas one barrier remains: the lack of understanding of force conditions on particles\nwhich mainly include acoustic radiation force (ARF) and acoustic streaming (AS). In this paper,\nforce conditions on micrometer size polystyrene microspheres in acoustic standing wave fields\nwere investigated. The COMSOL�® Mutiphysics particle tracing module was used to numerically\nsimulate force conditions on various particles as a function of time. The velocity of particle movement\nwas experimentally measured using particle imaging velocimetry (PIV). Through experimental and\nnumerical simulation, the functions of ARF and AS in trapping and patterning were analyzed.\nIt is shown that ARF is dominant in trapping and patterning large particles while the impact\nof AS increases rapidly with decreasing particle size. The combination of using both ARF and\nAS for medium size particles can obtain different patterns with only using ARF. Findings of the\npresent study will aid the design of acoustic-driven microfluidic devices to increase the diversity of\nparticle patterning....
A passive surface acoustic wave (SAW) pressure sensor was developed for real-time\npressure monitoring in downhole application. The passive pressure sensor consists of a SAW\nresonator, which is attached to a circular metal diaphragm used as a pressure transducer. While the\nmembrane deflects as a function of pressure applied, the frequency response changes due to the\nvariation of the SAWpropagation parameters. The sensitivity and linearity of the SAWpressure sensor\nwere measured to be 8.3 kHz/bar and 0.999, respectively. The experimental results were validated\nwith a hybrid analyticalââ?¬â??numerical analysis. The good results combined with the robust design and\npackaging for harsh environment demonstrated it to be a promising sensor for industrial applications....
Acoustic levitation has the potential to enable novel studies due to its ability to hold a wide variety of\nsubstances against gravity under container-less conditions. It has found application in spectroscopy,\nchemistry, and the study of organisms in microgravity. Current levitators are constructed using\nLangevin horns that need to be manufactured to high tolerance with carefully matched resonant\nfrequencies. This resonance condition is hard to maintain as their temperature changes due to transduction\nheating. In addition, Langevin horns are required to operate at high voltages (>100 V) which\nmay cause problems in challenging experimental environments. Here, we design, build, and evaluate\na single-axis levitator based on multiple, low-voltage (ca. 20 V), well-matched, and commercially\navailable ultrasonic transducers. The levitator operates at 40 kHz in air and can trap objects above 2.2\ng/cm3 density and 4mmin diameter whilst consuming 10Wof input power. Levitation ofwater, fusedsilica\nspheres, small insects, and electronic components is demonstrated. The device is constructed\nfrom low-cost off-the-shelf components and is easily assembled using 3D printed sections. Complete\ninstructions and a part list are provided on how to assemble the levitator....
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