Ultrasonic wave generation

This micro device for ultrasonic mixing was made from two plates, one of which has a shallow open volume to give a micro chamber after assembly (see Figure 1.31) [22], The area that actually covers the micro chamber is considerably thinned compared with the remaining thickness of the top plate. On this diaphragm, a thin PZT membrane is deposited, which acts as ultrasonic wave generator. The micro chamber is connected to two inlet channels and one outlet channel. 

Figure 3. A QCM cell with a horn in it for ultrasonic wave generation.

Acoustic emission, a technique that involves analysis of ultrasonic waves generated by cracking (e.g. stress corrosion and corrosion fatigue) and deformation of material. 

A beam of ultrasonic waves generated by a transducer is directed on to the surface of the polymer which is immersed in a suitable liquid, for example water or silicone oil. Two refracted beams are produced, the higher velocity beam corresponding to a compressional or longitudinal wave, the other to a transverse or shear wave. There is also a reflected... 

Fig. 3. (a) The temporal dependence of the dillraclion of a CW He-Ne laser from a transient grating induced by two nano.second Nd YAG second harmonic laser pulses in a nematic film (PCB 40 m thick io-meotropically aligned) (after [17]). Time scale is 20 ns/div. Similar ultrasonic wave generation was also observed in a smectic liquid crystal film 117bj. (b) The dynamics of the thermal grating formation and decay in a nematic film as monitored by a CW He-Ne probe laser diffraction. The grating wave vector K - K2 is perpendicular to the director axis, (c) Same as in (b), but for K K2 along the director axis. 

I. C. Khoo and R. Normandin, Nanosecond laser induced optical wave mixing and ultrasonic wave generation in the nematic phase of liquid crystals, Opt. Lett., vol. 9, pp. 285-287, 1984 see also I. G. Khoo and R. Normandin, Nanosecond laser induced ultrasonic waves and erasable permanent gratings in smectic liquid crystal, J. Appl. Phys., vol. 55, pp. 1416-1418, 1984. 

Possible nondestructive testing techniques for adhesively bonded structures and composite materials will be introduced along with a literature survey of successes and applications to date. Emphasis on ultrasonic inspection will also be highlighted, including such topics as ultrasonic wave generation, wave velocity, dispersion, reflection factor, wave refraction, attenuation, ultrasonic field analysis, resolution, thickness and defect location measurement, and C-scan testing. 

The piezoelectric phenomena have been used to generate ultrasonic waves up to microwave frequencies using thin polyfvinylidene fluoride) transducers. In the audio range a new type of loudspeaker has been introduced using the transverse piezolectric effect on a mechanically biased membrane. This development has been of considerable interest to telephone engineers and scientists. 

Fig. 7. The impingement of this jet can create a localized erosion (and even melting) responsible for surface pitting and ultrasonic cleaning (68-70). A second contribution to erosion created by cavitation involves the impact of shock waves generated by cavitational collapse. The magnitude of such shock waves can be as high as 104 atmospheres, which will easily produce plastic deformation of malleable metals (77). The relative magnitudes of these two effects depends heavily on the specific system under consideration.

When zinc and a,a -dibromo-o-xylene are irradiated with ultrasonic waves at room temperature, synthetically useful quantities of the reactive intermediate, o xylylene, are generated which can be treated in situ with activated olefins to give good yields of cycloaddition products(30). Chew and Ferrier used this methodolgy to generate a-xylylene for the synthesis of optically pure functionalized hexahydroanthracenes(31). The reaction with lithium takes a different course(19). Rather than generate the -xylylene intermediate, ionic species are produced. The two fates of a, a -dibromo-o-xylene are presented in the scheme below ... 

Sonication using ultrasonic cleaner baths remains a popular extraction approach particularly for controlled-release products. In sonication, an ultrasonic wave of 20-40 kHz generated by a piezoelectric transducer is used to produce the formation and collapse of thousands of microscopic bubbles (cavitations) in the water bath to facilitate the break up of the solid particles and the subsequent dissolution of the API. Note that parameters such as the wattage power of the sonicator, presence of the perforated tray, depth of the water level, bath temperature and the number of sample flasks sonicated might all affect the extraction rate. For... 

The ultrasonic irradiation of a solution induces acoustic cavitation, a transient process that promotes chemical activity. Acoustic cavitation is generated by the growth of preexisting nuclei during the alternating expansion and compression cycles of ultrasonic waves. For example, in aqueous liquid, temperatures as high as 4300 K and pressures over 1000 atm are estimated to exist within... 

Figure 1. Ultrasonic compression and shear waves generated by the application of a sinusoidal force F(t) to the material.

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