Sound fields

Finally, by volumetric imaging Three-dimensional information was obtained by stacking reflection tomograms from multiple planes. Using this stacking technique, cubic voxels were obtained and could be numerically dissected in any plane. Although there are several attractive features related to this technique, there are also several questions which need to be addressed before it can be used for industrial applications. For example, the applied sound field must be further characterized. 

This is because on one hand, heav wave is weaker and on the other hand, photoelastic testing method is unfavorable for observing the sound field of axial symmetry. The sound field (see Fig.4) excited by strip ciystal in solid is observed with photoelastic testing method. The wavefront of head wave can be see in Fig.4, which is a circumstantial evidence of wavefront of head wave excited just by point-shape crystal. We can calculate... 

Resonant Sound Absorbers. Two other types of sound-absorbing treatments, resonant panel absorbers and resonant cavity absorbers (Helmholtz resonators), are used in special appHcations, usually to absorb low frequency sounds in a narrow range of frequencies. Resonant panel absorbers consist of thin plywood or other membrane-like materials installed over a sealed airspace. These absorbers are tuned to specific frequencies, which are a function of the mass of the membrane and the depth of the airspace behind it. Resonant cavity absorbers consist of a volume of air with a restricted aperture to the sound field. They are tuned to specific frequencies, which are a function of the volume of the cavity and the size and geometry of the aperture. 

Rotating vanes are provided in the rooms to ensure diffuse sound fields. Sound is introduced into the source room, the average sound pressure level is measured in one-third octave bands in both rooms, and the sound-transmission loss is calculated as follows, where and die average sound... 

The qualitative analysis developed in the previous section is now complemented by examining correlations between the sound field and the flame dynamics. This is accomplished by comparing time traces of pressure fluctuation p and light emission I signals recorded during the various experiments. Results are displayed in Figures 5.2.11 and 5.2.12, respectively, for the various... 

Dahnke S, Keil F (1998) Modeling of sound fields in liquids with a nonhomogeneous distribution of cavitation bubbles as a basis for the design of sonochemical reactors. Chem Eng Technol 21 873-877... 

Prosperetti A (1984) Bubble phenomena in sound fields part two. Ultrasonics 22 115... 

Fig. 15.4 Initial growth in sonoluminescence intensity from a pulsed sound field...

The effect of ultrasound on liquid-liquid interfaces between immiscible fluids is emulsification. This is one of the major industrial uses of ultrasound (74-76) and a variety of apparatus have been devised which will generate micrometer-sized emulsions (9). The mechanism of ultrasonic emulsification lies in the shearing stresses and deformations created by the sound field of larger droplets. When these stresses become greater than the interfacial surface tension, the droplet will burst (77,78). The chemical effects of emulsification lie principally in the greatly increased surface area of contact between the two immiscible liquids. Results not unlike phase transfer catalysis may be expected. 

A primary limitation of sonochemistry remains its energy inefficiency. This may be dramatically improved, however, if a more efficient means of coupling the sound field with preformed cavities can be found. The question of selectivity in and control of sonochemical reactions, as with any thermal process, remains a legitimate concern. There are, however, clearly defined means of controlling the conditions generated during cavitational collapse, which permit the variation of product distributions in a rational fashion. 

However, this can only be an estimate since it is unlikely that a bubble in a sound field vhll feel a constant pressure, Pq, exerted during its collapse (acoustic pressure is time dependent, i. e. P = P sin 27tft) nor will it be an empty void, being filled with either gas or vapour. As such, Eq. 2.25 must be modified (Eq. 2.27). 

Acoustic intensity has a dramatic influence on the observed rates of sonochemical reactions. Below a threshold value, the amplitude of the sound field is too small to induce nucleation or bubble growth. Above the cavitation threshold, increased intensity of irradiation (from an immersion horn, for example) will increase the effective volume of the zone of liquid which will cavitate, and thus, increase the observed sonochemical rate. 

Fukusima K, Sanssen D, Kikuchi E (1972) Sound field characteristics related to operation of ultrasonic converters. In Kikuchi E (ed) Ultrasonic converters. Mir, Moscow, p 353... 

Sonic. Gas generates an intense sound field into which liquid is directed. Similar to two-fluid but with greater tolerance for solids. Similar to two-fluid. 

The late reverberation is characterized by a dense collection of echoes traveling in all directions, in other words a diffuse sound field. The time decay of the diffuse reverberation can be broadly described in terms of the mid frequency reverberation time. A more accurate description considers the energy decay relief of the room. This yields the frequency response envelope and the reverberation decay time, both functions of frequency. The modal approach reveals that reverberation can be described statistically for sufficiently high frequencies. Thus, certain statistical properties of rooms, such as the mean spacing and height of frequency maxima, are independent of the shape of the room. 

Bech, 1995] Beth, S. (1995). Perception of Reproduced Sound Audibility of Individual Reflections in a Complete Sound Field, II . In Proc. Audio Eng. Soc. Conv. Preprint 4093. 

---