Airborne ultrasound

The gas-driven transducers are simply whistles with high frequency output. Dog whistles and sirens can be given as the two examples of gas-driven transducers. These transducers can be used to break down foams and agglomerates of dust and for the acceleration of drying processes. However, these types do not have any significant chemical applications, as it is not possible to achieve a sufficiently high-pressure intensity in airborne ultrasound by this method. 

For large scale (200 L capacity plating tank) it proved impossible to apply airborne ultrasound and therefore the ultrasound was introduced into the plating tank (Fig. 6.13). The transducers consisted of two banks of three mounted in dummy tanks and delivered in total 1.4 kW into 135 L making the overall ultrasonic intensity 0.01 W cm The cathode consisted of a steel bar (5 cm diameter and 20 cm length) and 4 large lead anodes (diameter 3.7 cm and length 39 cm) were used. On sonication... 

Neither type of transducer has any significant chemical application because it is not possible to achieve a sufficiently high intensity in airborne ultrasound by this method. Despite this, applications do exist for airborne ultrasound but the source must be very powerful - usually a sonic horn. In this way one can obtain intensities of a fraction of a... 

Questions are sometimes raised about the potential harmful effects of ultrasound produced by laboratory-scale devices. Available data indicates that airborne ultrasonic fields do not appear to be hazardous to humans. There are, in fact, no known physiological effects from airborne ultrasound. Ultrasonic sickness appears to be largely psychosomatic. 

This same airborne ultrasound which can be used to destroy smokes is also capable of defoaming liquids by placing the acoustic source above the liquid surface upon which the foam is being generated. The methodology has proved so effective... 

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 contrast, contact as well as airborne ultrasound application avoids the occurrence of external cavitation and thus reduces the risk of related effects such as radical formation and oxidation. Thus, to the present author s knowledge, no important quality impairment due to such ultrasound-assisted processes has yet been reported. Soria et al. (2010) found only minor changes in the reducing sugar... 

Broadband microphones (from the audible range to ultrasound), which can be achieved in a converter using the piezoelectric properties 33 in the thickness direction, have aheady been applied as transducer elements in an airborne ultrasound transducer (Yasuno et al. 2010). Application to ultrasonic probes for medical use is also expected. 

Two types of ultrasonic systems are available that can be used for predictive maintenance structural and airborne. Both provide fast, accurate diagnosis of abnormal operation and leaks. Airborne ultrasonic detectors can be used in either a scanning or contact mode. As scanners, they are most often used to detect gas pressure leaks. Because these instruments are sensitive only to ultrasound, they are not limited to specific gases as are most other gas leak detectors. In addition, they are often used to locate various forms of vacuum leaks. 

Ultrasonic extraction is especially efficient with environmental and industrial hygiene samples however, in addition to the inapplicability to the extraction of some metals and the inability to quantitatively extract heavy metals from very large bulk environmental samples [14,15], ultrasounds occasionally produce ionic species that were absent from the original sample. The new species give unidentified signals that yield spurious analytical results such is the case with the extraction of ionic species from airborne particulate matter [23], where the new ions formed prevent accurate determination of those initially present in the sample. 

Many procedures report the contribution of ultrasounds or microwaves to quantitatively extract the trapped compounds. For example, a low temperature microwave-assisted extraction method (MAE) was reported to determine PAHs in airborne particulate matter (Karthikeyan et al. 2006). The procedure requires a... 

The use of high-intensity ultrasound in the chemical laboratory has grown enormously during the past decade and has a diverse set of applications. Human exposure to ultrasound with frequencies of between 16 and 100 kilohertz (kHz) can be divided into three distinct categories airborne conduction, direct contact through a liquid coupling medium, and direct contact with a vibrating solid. 

Ultrasound through airborne conduction does not appear to pose a significant health hazard to humans. However, exposure to the associated high volumes of audible sound can produce a variety of effects, including fatigue, headaches, nausea, and tinnitus. When ultrasonic equipment is operated in the laboratory, the apparatus must be enclosed in a 2-cm-thick wooden box or in a box lined with acoustically absorbing foam or tiles to substantially reduce... 

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