Ultrasound sound

Ultrasound sound at frequencies above the audible range (i.e., above about 20 kHz). 

Ultrasound-assisted drying processes can be based on sound transmission in air (airborne ultrasound), liquids (osmotic solutions) or solids (contact ultrasound). Sound transmission and sound emitter designs must be adapted to the respective applications and have, together vdth the transmission medium, a major influence on process design and performance. 

In general a thickness measurement using ultrasound is done by measuring the time of flight of the ultrasonic pulse and calculating the thickness of the objeet multiplying the time and the known constant sound velocity in the material. 

The previous subsection described single-experiment perturbations by J-jumps or P-jumps. By contrast, sound and ultrasound may be used to induce small periodic perturbations of an equilibrium system that are equivalent to periodic pressure and temperature changes. A temperature amplitude 0.002 K and a pressure amplitude 5 P ss 30 mbar are typical in experiments with high-frequency ultrasound. Fignre B2.5.4 illustrates the situation for different rates of chemical relaxation with the angular frequency of the sound wave... 

The easily accessible frequency range of sound and ultrasound waves confines the range of applicability of... 

The chemical effects of ultrasound do not arise from a direct interaction with molecular species. Ultrasound spans the frequencies of roughly 15 kH2 to 1 GH2. With sound velocities in Hquids typically about 1500 m/s, acoustic wavelengths range from roughly 10 to lO " cm. These are not molecular dimensions. Consequently, no direct coupling of the acoustic field with chemical species on a molecular level can account for sonochemistry or sonoluminescence. 

The source and detector of ultrasound in an ultrasound medical imager is called a transducer. The transducer is a piezoelectric crystal which physically changes its dimensions when a potential is appHed across the crystal (38). The appHcation of a force to the piezoelectric crystal which changes its dimensions creates a voltage in the crystal. AppHcation of an oscillating potential to the crystal causes the dimensions of the crystal to oscillate and hence create a sound at the frequency of the oscillation. The appHcation of an oscillating force to the crystal creates an alternating potential in the crystal. 

Foam can also be broken with a rotating perforated basket [Lem-lich, Principles of Foam Fractionation, in Periy (ed.), Progre.ss in Separation and Purification, vol. 1, Interscience, New York, 1968, chap. 1]. If the foamate is aqueous (as it usually is), the operation can be improved by discharging onto Teflon instead of glass [Haas and Johnson, Am. In.st. Chem. Fng. J., II, 319 (1965)]. A turbine can be used to break foam [Ng, Mueller, and Walden, Can. J. Chem. Fng., 55, 439 (1977)]. Foam which is not overly stable has been broken by running foamate onto it [Brunner and Stephan, Ind. Fng. Chem., 57(5), 40 (1965)]. Foam can also be broken by sound or ultrasound, a rotating disk, and other means [Ohkawa, Sakagama, Sakai, Futai, and Takahara,y. Ferment. Technol, 56,428, 532 (1978)]. 

Its unit is hertz (s ), corresponding one cycle per second. Pure tone consists of one frequency, but normally all sounds are a mixture of many frequencies. In the audio range, frequency varies normally from 20 Hz to 16000 Hz. The size of the audio range depends on the sensitivity of the listener s ears. When the frequency is below 20 Hz, it is called infrasound, while for frequencies over 16000 Hz, it is called ultrasound. 

The role of cavitation in ultrasound degradation has been confirmed repeatably in most experiments where cavitation was prevented, either by applying an external hydrostatic pressure, by degassing the solution, by reducing the sound intensity or the temperature, polymer chain scission was also largely suppressed [117]. 

Perturbation of a spin-state equilibrium by ultrasound results in the absorption of sound, the absorption coefficient a (neper cm ) being determined as a function of frequency /(Hz) according to ... 

Ultra-sound emissions typically occur when male rodents are exposed to female odours or altricial neonates to maternal sources (Whitney, 1974 Conely and Bell, 1978). Without the VNO, sexually inexperienced male mice do not utter emissions at ultra-high frequencies (UHF), whereas those with prior experience vocalise after VN-x, as discussed above (Chap. 5). Female mouse urine contains a unique UHF-eliciting component which is non-volatile but ephemeral (Sipos et al., 1995). The signal is degraded by oxidation and disappears within 15 to 18 hours of deposition. Direct contact with freshly voided urine must occur before males will vocalise (sexually experienced or inexperienced). At least one of the olfactory systems is needed for UHF to be elicited by fresh urine complete deafferentation abolishes the response (Sipos et al., 1993). Exposure to females permits UHF to be elicited by other than chemical cues (Labov and Wysocki, 1989). Nocturnal or cryptic species conceivably use ultrasound to advertise male presence whether this is to deter other males or assist with female location is unclear. 

Renal ultrasound (uses sound waves to assess size, position, and abnormalities of the kidney dilatation of the urinary tract can be seen with postrenal ARF)... 

Positive urine human chorionic gonadotropin followed by positive ultrasound, fetal heart sounds, and/or fetal movement. Pregnancy Dating and Gestational Age Calculated from the first day of the last menstrual period. 

Abstract Acoustic cavitation is the formation and collapse of bubbles in liquid irradiated by intense ultrasound. The speed of the bubble collapse sometimes reaches the sound velocity in the liquid. Accordingly, the bubble collapse becomes a quasi-adiabatic process. The temperature and pressure inside a bubble increase to thousands of Kelvin and thousands of bars, respectively. As a result, water vapor and oxygen, if present, are dissociated inside a bubble and oxidants such as OH, O, and H2O2 are produced, which is called sonochemical reactions. The pulsation of active bubbles is intrinsically nonlinear. In the present review, fundamentals of acoustic cavitation, sonochemistry, and acoustic fields in sonochemical reactors have been discussed. 

An acoustic wave (sound) is a propagation of pressure oscillation in medium such as air or liquid water with the sound velocity [1]. Ultrasound is inaudible sound and its frequency of pressure oscillation is above 20 kHz (20,000 oscillations per second) [2]. For convenience, an acoustic wave above 10 kHz in frequency is sometimes called an ultrasonic wave. 

As ultrasonic frequency increases, the acoustic field is more restricted above an ultrasonic transducer. Roughly speaking, when the wavelength of ultrasound (2 = c/f, where c is the sound velocity in the liquid and/is the ultrasonic frequency) is much smaller than the radius of the transducer, the acoustic field is restricted above the transducer. It should be noted that the sound velocity in a bubbly liquid is smaller or occasionally larger than that in liquid without bubbles [87, 88]. 

An ultrasonic horn has a small tip from which high intensity ultrasound is radiated. The acoustic intensity is defined as the energy passing through a unit area normal to the direction of sound propagation per unit time. Its units are watts per square meter (W/m2). It is related to the acoustic pressure amplitude (P) as follows for a plane traveling wave [1]. 

Acoustic cavitation In this case, the pressure variations in the liquid are effected using the sound waves usually ultrasound (16 kHz to 100 MHz). The chemical changes taking place due to the cavitation induced by the passage of sound waves are commonly known as sonochemistry. 

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