Ultrasound thermal effects

In this paper, the performanees of laser-ultrasound are estimated in order to identify lacks of weld penetration. The laser-ultrasonic technique is applied to cylindrical metallic strucmres (few mm thick) in a single-sided control. The results obtained for different materials (gold-nickel alloy and tantalum) are presented by B-sean views for which the control configuration is discussed with regard to the thermal effects at the laser impact. This testing is performed for different lacks of weld penetration (up to 0.5 mm for a thickness of 2 mm) even in the presence of the weld bead, which corresponds to an actual industrial problem. 

Wu et al. [12] used both microwave (MW) and ultrasound (US) methods individually and in combination to examine the combined effect. The rapid thermal effect of MW could be seen on polar chemicals and more OH radicals were produced due to US. Microwave irradiations have shown enhanced degradation effect when applied with sonication in absence of additional catalyst though the rate increased more in presence of H2O2. The rate order was found to be MW-US > MW > US. 

The absorption of ultrasound increases the temperature of the medium. Materials that possess higher ultrasound absorption coefficients, such as bone, experience severe thermal effects as compared to muscle tissue, which has a lower absorption coefficient [5]. The increase in the temperature of the medium upon ultrasound exposure at a given frequency varies directly with the ultrasound intensity and exposure time. The absorption coefficient of a medium increases directly with ultrasound frequency resulting in temperature increase. 

Hynynen, K., Vykhodtseva, N.I., Chung, A., Sorrentino, V, Colucci, V., and Jolesz, F.A. (1997) Thermal effects of focused ultrasound on the brain determination with MR Imaging. Radiology 204,247-253. 

Thermal Effects Due to the poor conductivity for ultrasounds (low module of elasticity and high quantity of air trapped inside) usually exhibited by the materials included in pharmaceutical formulations, a fast decay of ultrasonic energy to thermal energy is obtained. This process has been studied, monitoring the temperature inside the compression chamber by means of a thermistor. In the studied mixtures [87, 88], a fast rise in temperature was obtained in tenths of a second followed by a relatively fast decrease (see Figure 47). 

The peak temperature obtained for low ultrasonic energy (25 J) is below 80 °C, whereas for high energies (125-150 J) it is above 140 °C. In mixtures of keto-profen with acrylic polymers [90], the increase in temperature was slightly lower. In this respect it must be mentioned that a recent modification of the ultrasound-assisted tableting machine that involves the suppression of Teflon isolators in contact with the powder must result in a faster decrease in temperature inside the compression chamber. Thermal effects can cause the total or partial fusion of some components of the formulation. Nevertheless, in the assayed controlled-release formulations, the components are usually below its melting points. 

Ultrasound is known for its capacity to promote heterogeneous reactions (Ley and Low, 1989) mainly through greatly increased mass transport, interfacial cleaning and thermal effects. In addition, homogeneous chemical reactions have been reported to be modified (Suslick et ai, 1983 Luche, 1990 Colarusso and Serpone, 1996) for example the sonochemical generation of radical species in aqueous media is important in environmental detoxification (Kotronarou et al., 1991 Serpone et al., 1994). 

Tests involving new, more sophisticated measurement tools have provided new interpretations and equations for the cavitation phenomenon [14,15]. The thermal and non-thermal effects of non-inertial cavitation, and the chemical and mechanical effects of Inertial cavitation in relation to their impact on ultrasound safety have recently been Investigated [16]. 

Contribution of thermal effects to ultrasound-enhanced transport... 

The use of ultrasound (US) to enhance percutaneous absorption (so-called sonophoresis or phonophoresis) has been studied over many years, and is the basis of US propagation and US effects on tissue, and the use of US in transdermal delivery have been reviewed in detail. The proposed mechanisms by which US enhances skin penetration include cavitation, thermal effects and mechanical perturbation of the SC that is, US acts on the barrier function of the membrane. ... 

Various ultrasound intensities in the range of 0.1-2W/cm have been used for sonophoresis. In most cases, use of higher ultrasound intensities is limited by thermal effects. Several investigations have been performed to assess the dependence of sonophoretic enhancement on ultrasound intensity. Miyazaki, Mizuoka, and Takada. foimd a relationship between the plasma concentrations of indomethacin transported across the hairless rat skin by sonophoresis (therapeutic conditions) and the ultrasoimd intensity used for this purpose. Specifically, the plasma indomethacin concentration at the end of three hours after sonophoresis (0.25 W/cm ) was about 3-fold higher than controls at the same time. However, increasing intensity by 3-fold (to 0.75 W/cm ) further increased sonophoretic enhancement only by 33%. Mortimer, Trollope, and Roy found that application of ultrasoimd at IW/cm increased transdermal oxygen transport by 40%i while that at 1.5 W/cm and 2 W/cm induced an enhancement by 50%i and 55 /o, respectively. 

Ultrasound can be applied either in a continuous or a pulsed mode. A pulsed mode of ultrasound application is used many times because it reduces the severity of adverse side effects of ultrasound, such as thermal effects. However, pulsed application of ultrasound may have a significant effect on the efficacy of sonophoresis. As will be discussed later, cavitational effects, which play a crucial role in sonophoresis,... 

Absorption of ultrasound results in a temperature increase of the medium. Materials which posses higher ultrasound absorption coefficients, such as bones, experience severe thermal effects as compared to muscle tissues which have a lower absorption coefficient (a). 

As described earlier, ultrasound affects biological tissues via three main effects, thermal effects, cavitational effects, and acoustic streaming. Conditions under which these effects become critical are given below. ... 

Machet, L. Pinton, J. Patat, F. Arbeille, B. Pourcelot, L. Vaillant, L. In vitro phonophoresis of digoxin across hairless mice and human skin thermal effect of ultrasound. Int. J. Pharm. 1996, 133, 39 5. 

Ultrasound and electrochemistry provide a powerful combination for several reasons. Ultrasound is well known for its capacity to promote heterogeneous reactions, mainly through increased mass-transport, interfacial cleaning, and thermal effects. Effects of ultrasound in electrochemistry may be divided into several important branches (1) Ultrasound greatly enhances mass transport, thereby altering the rate, and sometimes the mechanism, of the electrochemical reactions. 

Compared with flow fields, ultrasound irradiation creates both solvodynamic and thermal effects. The latter may contribute to polymer degradation and mechanophore activation. Although, ideally, hot spots are quenched faster than the diffusion time of the polymer chain (less than 1 ps [110]), an effort to preclude thermal effects should be implemented in the experiment. 

Groote R, Jakobs RTM, Sijbesma RP (2012) Performance of mechanochemically activated catalysts is enhanced by suppression of the thermal effects of ultrasound. ACS Macro Lett 1 1012... 

In this chapter, we studied the effect of solid-phase modifiers on the thermal and cavitation effects occurring in pol5mier hydrogels on ultrasound exposure. Evaluation of thermal effects was carried out thermometric. Activity of cavitation processes was assessed by measuring the level of scattered noise, and on information about destruction of pol5mier matrix of the hydrogel. The effect of solid-phase sonosensitization was tested in experiments in vitro on bacterial cells and in vivo on mice. 

To estimate the thermal effects of an ultrasound field, an ultrasound emitter and a cylindrical sample (2.5 cm high and 3 cm in diameter) were positioned coaxially and immersed into a thermostated vessel with degassed water. A thermocouple was inserted from one sample end to the center along the S5mmetiy axis. Ultrasound was fed fi om another end using a... 

These data indicate the presence of two types of solid phase localization in the gel. In one case, the crystals are located at individual centers of polymer matrix (calcium salt of Theraphthal, (Fig. 22.1), in another, they are uniformly distributed over the matrix (iron hydroxide, (Fig. 22.2). This affects the magnitude of the thermal effects of ultrasound exposure. 

Thermal effects of ultrasound have been studied on samples of agarose gel modified with various modifiers. Figure 22.3 shows the dynamics of the temperature growth of agarose gel modified with calcium salt of Theraph-thal on ultrasound exposure. 

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