Ultrasonic Field Measurements

Both ultrasonic and radiographic techniques have shown appHcations which ate useful in determining residual stresses (27,28,33,34). Ultrasonic techniques use the acoustoelastic effect where the ultrasonic wave velocity changes with stress. The x-ray diffraction (xrd) method uses Bragg s law of diffraction of crystallographic planes to experimentally determine the strain in a material. The result is used to calculate the stress. As of this writing, whereas xrd equipment has been developed to where the technique may be conveniently appHed in the field, convenient ultrasonic stress measurement equipment has not. This latter technique has shown an abiHty to differentiate between stress reHeved and nonstress reHeved welds in laboratory experiments. 

Calorimetric methods are quite general they can be used under cavitating conditions and in either free or restricted ultrasonic fields. Essentially the technique consists of measuring the rate of temperature increase in the sonicated liquid and from this calculating the power input according to Eq. (7),... 

The accuracy of the method depends on the correct determination of the characteristics of the ultrasonic field, and accurate measurement of the temperature rise of an absorber of closely controlled energy equivalent. It is also essential that the absorbing medium has a high absorption coefficient and that the acoustic matching within the system is good. Castor oil is among the best liquids which have been used to calibrate transducers. 

Some of the important parameters which affect surface cleaning are (a) the size and nature of the support material and the coating, (b) the surface conditions of the support, (c) the time of treatment, and (d) the method by which the coating was applied. This last point is of crucial importance since the consistency of the method of coating determines the reproducibility and the accuracy of the method. It should be carefully standardized to allow comparative studies. The size of the item to be cleaned is also important. If it is too small it will be difficult to measure the amount of removed soil, and if it is too large it will dramatically disturb the ultrasonic field. A method used by ultrasonic cleaner manufacturers to assess cleaning power is to remove Tipp-Ex fluid from the screw threads. 

Direct measurement of the velocity or the amplitude of displacement of an imaginary particle submitted to an ultrasonic field is not easy. Filipczynski [132] suggested the use of a capacitance probe method in which the vibrations in the medium are picked up by a diaphragm. The displacement of the diaphragm is measured with an electrostatic microphone, and this is then related to the particle displacement. Sound intensity is given by the relation shown in Eq. (28) where r = particle displacement. The method can be used up to a frequency of 300 kHz. 

Marshakov et al. studied the effect of an ultrasonic field on the anodic dissolution of a variety of metals [120]. Anodic polarization curves were measured in 0.1—0.5 N HC1, NaCl, H2S04, and NajSC solutions in an ultrasonic field of 20 kHz frequency. The effect of ultrasound was different for various metals due to differential effects on the rate-controlling process. Anodic dissolution of Fe was actually slowed down in the presence of ultrasound because the rate-controlling adsorption of anions at the iron surface was inhibited. At a cadmium anode, the energy of metal atoms in a lattice was increased in the presence of ultrasound and, therefore, the ionization of cadmium was accelerated. Anodic dissolution of copper and silver... 

The kinetics of several well-known electrochemical reactions have been studied in the presence of an ultrasonic field by Altukhov et al. [142], The anodic polarization curves of Ag, Cu, Fe, Cd, and Zn in various solutions of HC1 and H2S04 and their salts were measured in an ultrasonic field at various intensities. The effect of the ultrasonic field on the reaction kinetics was found to be dependent on the mechanism of metal anodic dissolution, especially on the effect of this field on the rate-determining step of the reaction. The results showed that the limiting factor of the anodic dissolving of Cu and Ag is the diffusion of reaction products, while in the case of Fe it is the desorption of anions of solution from the anode surface, and at Cd the limiting factor is the rate of destruction of the crystal lattice. Similar results were obtained by Elliot et al. [ 143] who studied reaction geometry in the oxidation and reduction of an alkaline silver electrode. 

The evidence of the polymer adsorption on the surface of pigment particles and the formation of protective layers has been obtained by ESA method by experiments on measuring the -potential of the TiC>2 surface in aqueous dispersions in the presence of EFIEC (Table 2). It can be seen from the table that -potential becomes less negative in the presence of EHEC and still more approaches zero as a result of the treatment of dispersions in an ultrasonic field. This indicates the activation of polymer adsorption and the formation of stabilizing layers due to mechanochemical modification of particles. From the table it is also seen that as a consequence of mechanochemical treatment, the size of pigment particles in dispersions decreases, and dispersion becomes structurally more uniform, which leads to an increase of its stability even at increased temperature (experiment 4). 

SussELL A and Ashley K (2002) Field measurement of lead in workplace air and paint chip samples by ultrasonic extraction and portable anodic stripping voltammetry. J Environ Monit 4 156—161. SvENSSON BG, Sghutz a, Nilsson A and Skerfv-ING S (1992) Lead exposure in indoor firing ranges. Int Arch Occup Environ Health 64 219-221. Thornton 1, Davies DJA, Watt JM and Quinn MJ (1990) Lead exposure in young children from dust and soil in the United Kingdom. Environ Health Perspect 89 55-60. 

Actual phenomena are, moreover, complicated by time factors which may be embodied in the term hysteresis. If the conditions in a macromolecular solution are suddenly changed (e.g., by addition of a non solvent or by a change of temperature) a certain time elapses before the new equilibrium condition is reached. This is also illustrated by recent experiments on the influence of ultrasonics on the viscosity of solutions of gelatin in water, rubber in toluene etc. If such solutions are subjected to the action of an ultrasonic field of moderate intensity, their viscosity measured at once after the treatment is markedly less than before, but, after a certain lapse of time, reassumes its initial value (or a value very near to it) The junction points are temporarily loosened due to microscopical agitation arising from the action of ultrasonic waves, but restore themselves to equilibrium condition at low rates of flow after a certain time. 

The power density Py is the characteristic quantity of turbulent flow. It determines the size of the smallest eddies and the intensity of microturbulence. In addition, it is a measure of the shear intensity in laminar flows or the intensity of cavitation in ultrasonic fields (see above). The power input P in the dispersion zone can be derived from the pressure drop (e.g. in pipes and nozzles) or can be measured caloricafly (e.g. for rotor-stator systems and ultrasonication Pohl 2005 Kuntzsch 2004). Additionally, P can be roughly approximated by the electric power consumption of the dispersion machine (e.g. for ultrasonication Mandzy et al. 2005 Sauter et al. 2008), even though the real values may be lower by a factor of 2 to 5. A further source of uncertainty is the volume of the dispersion zone (Vdisp). since the stress intensities are not uniformly distributed in dispersion apparatuses. In particular, this applies to agitated vessels, where the highest dissipation rates are obtained in the vicinity of the stirring instmment (Henzler and Biedermann 1996),... 

In general, the most widely used field technologies for inspection are ultrasonic thickness measurement, while for online methods they are corrosion test specimens, electrical resistance, and linear polarization probes. Both of the inspection methods and the first two online methods measure metal loss. The last method measures corrosion rate, but only in a sufficiendy conductive process environment, normally water. 

Progress has been made in the field of applied mathematics to invert this relation for the application mentioned here by techniques that establish a transformation between the data and the characteristics of the operator that describes the development of the ultrasonic field. To give the reader some insight, a sketch of an appropriate procedure for relating the measured acoustic field to the data is presented. The medium is characterized by an acoustic profile ... 

Ide, M., Ohdaira, E. and Ohtsuka, M. (1980) Miniature hydrophones for the measurement of ultrasonic field. Proceedings of the Tenth International Congress on Acoustics, Sydney, Australia, 19 20 July 1980, paper F-7.1. 

Ide, M. and Ohdaira, E. (1981) Wide frequency range miniature hydrophone for the measurement of pulse ultrasonic field, Jpn. J. App. Phys., 20, 205. ... 

Granz, B. (1987) PVDF receiving array for measurement of ultrasonic fields, Ferroelectrics, 75, 355. 

Possible nondestructive testing techniques for adhesively bonded structures and composite materials will be introduced along with a literature survey of successes and applications to date. Emphasis on ultrasonic inspection will also be highlighted, including such topics as ultrasonic wave generation, wave velocity, dispersion, reflection factor, wave refraction, attenuation, ultrasonic field analysis, resolution, thickness and defect location measurement, and C-scan testing. 

The parameters that best characterize an ultrasonic field are the wave frequency and the ultrasonic energy applied, with the latter being expressed as power, intensity, or acoustic pressure. The frequency does not represent a critical point because the variation of the applied frequency is usually less than 5-10% of the nominal frequency provided by the manufacturer. In contrast, the actual applied acoustic energy could be very different from the electrical consumption, and its direct measurement is difficult. In the literature, it is possible to identify a wide variety of methods for that purpose, but the results provided may be difficult to compare one with another. The majority of these methods are based on the measurement of physical or chemical changes produced by ultrasound, and a classification was proposed by Berlan and Mason (1996) ... 

In order to identify the influence of air velocity on the ultrasonic field and, therefore, on the ultrasound effects, the acoustic field inside the drying chamber was measured using a microphone (Riera et al, 2011). When measurements were taken without an air flow, an average sound pressure level of 154.3 dB was obtained for an electrical power applied to the transducer of 75W (30kWm ). However,... 

Rugged instruments based on portable computers are now available from many vendors. These systems, complete with motor-driven robotic devices to manipulate the transducer(s), have created the ability to measure wall thickness of corroded components at tens of thousands of points over 0.1 m, which can be converted into mass loss and pitting rates. This capabihty, coupled with increased precision of field measurements achievable with computer-controlled systems, has made these automated ultrasonic systems well suited for online corrosion monitoring [4]. 

Bridgman flexible bellows with slide wire 369 Brillouin scattering 719-726 broken aspects, textures 439 bubble domains, ultrasonic fields 557 building blocks, synthesis 98 bulk fluids, molecular modelling 77 bulk SHG, optical properties 577 bulk systems, large-scale simulation 83 buoyancy method, density measurements 332 Burgers vectors, defects 425,447... 

Piezoelectric polymer hydrophones have been proposed as probes (or mapping ultrasonic fields and determining acoustic field parameters in both water and biological media. Among the several PVDF hydrophones developed, the most widely used have been the original hoop membrane configuratioo (spot-poled membrane supported by means of a hoop) (40] and the needle-type probe (41]. While both can be used to assess ultrasonic field patterns in water, only the needle-type probe can be used for bioacoustic measurements, such as in vitro and in vivo evaluatkm of tissue properties. 

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