Ultrasound physical characteristics

The ultrasound fields are generated by a focused, MRI compatible piezoelectric transducer (19). The physical characteristics of the transducer determine the size of the focal spot and can be tailored for the experimental needs. For example, we have performed successful experiments with 100-mm diameter, 80-mm radius of curvature transducers with a frequency of 0.7 MHz (see Note 1). 

High-frequency, low-power ultrasound generally within the frequency range 0.5-20 MHz can be used to evaluate foodstuffs in terms of physical characteristics such as the degree of emulsification or the concentration of solids or gas. In... 

In contrast, the disturbance caused by the ultrasound oscillator induces characteristic oscillations within the given liquid column, corresponding to its geometry and its physical characteristics. Expression defining a number of possible values of the liquid column oscillation frequencies is obtained as a solution of the corresponding rate potential function for the standing wave formed on the meniscus surface, in the form [1-2] ... 

It is difficult to pinpoint the specific macromolecular characteristics that allow response to ultrasound. Many polymers of varying composition, architecture, polarity, Tg, and so on, have been demonstrated to alter their behavior when exposed to ultrasonic stimulation. As opposed to magnetoresponsive polymers, foreign additives are not required [136]. However, polymers existing in a few specific physical states are mostly considered. Polymeric systems that respond to ultrasound have generally been gels or other nonswoUen macroscopic solids, polymeric micelles, or layer-by-layer (LbL) coated microbubbles. 

The particular and interesting characteristics of ultrasound waves in chemical reactions arise from the physical phenomenon known as acoustic cavitation. Cavitation is the production, growth, and collapse of microbubbles in a liquid when a large negative pressure is applied to it [10,11]. As can be seen in Figure 3, the formation of cavitation bubbles is initiated during the rarefaction cycle. 

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