Ultrasonic pressure wave

Sonication This involves the generation of shear forces in a cell sample in the vicinity of a titanium probe (0.5 mm in diameter and 10 cm long) that vibrates at 20,000 Hz. The device contains a crystal of lead zirconate titanate that is piezoelectric, i.e., it expands and contracts when an oscillatory electric field is applied to it from an electronic oscillator. The ultrasonic pressure waves cause microcavitation in the sample, and this disrupts the cell membranes, usually in a few seconds. 

The technique presented above has been extensively evaluated experimentally using ultrasonic data acquired from a test block made of cast stainless steel with cotirse material structure. Here we briefly present selected results obtained using two pressure wave transducers, with refraction angles of 45° and 0°. The -lOdB frequency ranges of the transducers were 1.4-2.8 MHz and 0.7-1.4 MHz, respectively. The ultrasonic response signals were sampled at a rate of 40 MHz, with a resolution of 8 bits, prior to computer processing. 

Pressure waves of the same nature as sound waves but of greater frequency, i.e., shorter wavelength, and therefore inaudible. Ultrasonic waves have been used for the detection of ply separations and other voids in rubber-textile composites such as tyres, and for thickness measurement of coatings, etc., where access is possible from only one side. 

In ultrasonic standing wave atomization, increasing the amplitude of the sonotrodes and/or the gas pressure reduces the mass median diameter of the droplets generated.[143]... 

N.B. A shock pulse (shock or pressure wave) develops when two pieces of moving metal contact each other in an initial impact. This shock pulse is in the ultrasonic frequency range and typically occurs at around 36 kHz. The amplitude of the shock pulse is proportional to the velocity of the impact. 

After the leakage has been created, the flat expansion pressure waves are propagated in two converse sides. These waves have sonic speed and after clashing to the upstream and downstream boundaries, return to the form of compression or expansion wave depending on the edge type (Fig. 1). In the leak location, depending whether the ratio of pressure to ambient pressure is more or less than the CPR quantity, the equation of which is showed in equation (1), the flow will be sonic and ultrasonic or subsonic respectively. 

Ultrasonic sound waves propagating in a liquid solution create repetitive pressure/density variations. Some versions measure the absorption of sound energy and others involve the scattering of a light beam. They are useful for very fast reactions, but each instrument tends to be limited to a small time range. Although operation at high pressures is possible, such an application would be very specialized. 

Ultrasonic meters are of two types transit time and Doppler shift. In the first type a high-frequency pressure wave is beamed at an angle across the pipe. The velocity of the wave is found from its time of transit. When the wave is transmitted in the direction of the flow, its velocity is increased, and vice versa. From the change in transit time from that in a quiescent fluid the fluid velocity can be determined. Transit-time meters are applicable to clean fluids only. 

Ultrasonic techniques are so numerous that a comprehensive discussion is not possible. Since an ultrasonic wave is an adiabatic pressure wave, in general both a temperature and a pressure perturbation of the system occurs. In most nonaqueous solvents, the temperature perturbation is of primary importance, because chemical equilibria are generally much more sensitive to temperature changes than to pressure changes. In aqueous solutions, however, the pressure perturbation is usually of primary importance, because the thermal-expansion coefficient of water is very small, so that the pressure wave is almost isothermal. A serious disadvantage of ultrasonic methods is that rather large volumes of solution are required for low-frequency measurements and relatively high concentrations (> 10" M) of reactants are required at all frequencies. Recent experimental innovations have alleviated these problems to some extent. The most common ultrasonic... 

It is well known that some amounts of cavities or small bubbles are present in rubber during any type of mbber processing (Kasner and Meinecke, 1996). The formation of bubbles can be nucleated by precursor cavities of appropriate size (Gent and Tompkins, 1969). The proposed models (Isayev et al., 1996a,c,d Yashin and Isayev, 1999,2000) were based upon a mechanism of rubber network breakdown caused by cavitation, which is created by high intensity ultrasonic waves in the presence of pressure and heat. Driven by ultrasound, the cavities pulsate with amplitude depending mostly upon the ratio between ambient and ultrasonic pressures (acoustic cavitation). 

Vis coiner tial losses (Fig. lb). As an ultrasonic wave passes through an emulsion it causes the droplets to oscillate backwards and forwards because of the density difference between them and the surrounding liquid. The movement of the droplets leads to the generation of a dipolar pressure wave the energy of the new wave is not detected and hence contributes to measmed attenuation. In addition, the oscillation is damped because of the viscosity of the siuround ing liquid, and so some of the ultrasonic energy is lost as heat. 

Ultrasonic standing wave (USW) manipulatiOTi is a simple and useful method for handling, separating, and concentrating large groups of cells. A USW creates a pressure node that will attract particles or cells. As with DEP, a cell can experience either an attractive or repulsive acoustic force depending on its material parameters. This can be used either to trap objects locally over an ultrasonic transducer, concentrate them within a fluidic channel, or separate different types of objects from each other. Successful separation of human erythrocytes from human lipid vesicles has been reported (Fig. 5). 

It is well known that the ultrasonic standing wave can exert forces on particles and have been used in many fields including chemical and materials engineering to separate or enrich suspended particles in a medium at well-defined positions. The force produced by ultrasonic standing waves moves particles to either the pressure node or antinodes of the standing wave depending on the density and compressibility of the particles and the medium. 

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