Velocity, ultrasonic

In an early study, Greenleaf et al. [4] reported reconstructions of ultrasonic velocity from time-of-flight profiles. Since then there has been periodic activity in using ultrasound to determine the transmission properties attenuation or refractive index. 

The angles has been represented in the figure 2. Cus being the ultrasonic velocity in the material. 

Ultrasonic techniques are an obvious choice for measuring the wall thickness. In the pulse-echo method times between echoes from the outer and inner surface of the tube can be measured and the wall thickness may be calculated, when the ultrasonic velocity of the material is known. In the prototype a computer should capture the measuring data as well as calculate and pre.sent the results. First some fundamental questions was considered and verified by experiments concerning ultrasonic technique (Table I), equipment, transducers and demands for guidance of the tube. 

Pandey et al. have used ultrasonic velocity measurement to study compatibility of EPDM and acrylonitrile-butadiene rubber (NBR) blends at various blend ratios and in the presence of compa-tibilizers, namely chloro-sulfonated polyethylene (CSM) and chlorinated polyethylene (CM) [22]. They used an ultrasonic interferometer to measure sound velocity in solutions of the mbbers and then-blends. A plot of ultrasonic velocity versus composition of the blends is given in Eigure 11.1. Whereas the solution of the neat blends exhibits a wavy curve (with rise and fall), the curves for blends with compatibihzers (CSM and CM) are hnear. They resemble the curves for free energy change versus composition, where sinusoidal curves in the middle represent immiscibility and upper and lower curves stand for miscibihty. Similar curves are obtained for solutions containing 2 and 5 wt% of the blends. These results were confirmed by measurements with atomic force microscopy (AEM) and dynamic mechanical analysis as shown in Eigures 11.2 and 11.3. Substantial earher work on binary and ternary blends, particularly using EPDM and nitrile mbber, has been reported. 

FIGURE 11,1 Ultrasonic velocity versus acrylonitrile-butadiene mbber/ethylene-propylene-diene monomer (NBR-EPDM) blend composition (a) no compatibiUzer, (b) with chloro-sulfonated polyethylene (CSM), and (c) with chlorinated polyethylene (CM). (From Pandey, K.N., Setua, D.K., and Mathur, G.N., Polym. Eng. Set, 45, 1265, 2005.)... 

From his initial work on the studies of solvent properties of non-aqueous solvents and later on the measurement of ultrasonic velocity, Prof. Pankaj switched over to sono-chemical studies in aqueous solutions involving inorganic systems, after his European Community Post-Doctoral Fellowship (1990 - 91) at the Department of Physics,... 

We wish to note that 0D can also be calculated from the measured ultrasonic velocities, and data should be equal to those obtained from specific heat measurements. The Debye s temperature evaluated from data of ultrasonic velocity is (see e.g. [14,15]) ... 

McClements, D.J. and Povey, M.J.W. 1987. Solid fat content determination using ultrasonic velocity measurements. Int. J. FoodSci. Technol. 22 491-499. 

Further evidence for the reality of a structural transition in the vicinity of Ira may be implied from a study by Satyanarayanamurty and Krishnamurty on ultrasonic velocities and compressibilities of aqueous solutions (131). They found that plots of the apparent molar compressibility (for metal nitrates) vs. square root concentration become linear only at concentrations above Ira. 

Ultrasonic velocity. The velocity at which an ultrasonic wave travels through a material... 

The velocity is therefore determined by two fundamental physical properties of a material its elastic modulus and density. The less dense a material or the more resistant it is to deformation the faster an ultrasonic wave propagates. Usually, differences in the moduli of materials are greater than those in density and so the ultrasonic velocity is determined more by the elastic moduli than by the density. This explains why the ultrasonic velocity of solids is greater than that of fluids, even though fluids are less dense [1],... 

The ultrasonic velocity is determined in one of two ways either the wavelength of ultrasound is measured at a known frequency (c = kf), or the time taken for a wave to travel a known distance is measured (c = d/t). Some of the techniques available for measuring the ultrasonic velocity of materials are discussed in section 3. 

Solids usually have larger ultrasonic velocities and acoustic impedance, than liquids, which have larger values than gasses. Air has a very low acoustic impedance compared to liquids or solids which means that it is difficult to transmit ultrasound from air into a condensed material. This can be a problem when ultrasound is used to test dry materials, e.g., biscuits or egg shells. A small gap of air between an ultrasonic transducer and the sample to be tested can prevent ultrasound from being transmitted into the material. For this reason coupling materials (often aqueous or oil based) can be placed between the transducer and sample to eliminate the effects of the air gap, or alternatively soft-tip ultrasonic transducers can be used. 

Each echo has traveled a distance twice the cell length d further than the previous echo and so the velocity can be calculated by measuring the time delay t between successive echoes c = 2d/t. The cell length is determined accurately by calibration with a material of known ultrasonic velocity, e.g. distilled water 2d = cw.tw (where the subscripts refer to water). The attenuation coefficient is determined by measuring the amplitudes of successive echoes A = A0e-2cxd, and comparing them to the values determined for a calibration material. A number of sources of errors have to be taken into account if accurate measurements are to be made, e.g., diffraction and reflection (see below). 

In the empirical approach the ultrasonic parameters of a range of samples with known properties are measured. Empirical relationships are then established between the property of interest and the measurable ultrasonic parameters. A typical example of this approach is the determination of the sugar content of fruit drinks [18]. A series of sugar solutions of different sugar concentration are prepared and their ultrasonic velocities are measured. This data is then used to make up a calibration curve which relates the sugar content to the... 

Figure 9. Dependence of ultrasonic velocity of the sugar content of a series of aqueous glucose solutions at 20°C [18].

Thus a measurement of the ultrasonic velocity and density can be used to determine the adiabatic compressibility (or bulk modulus) of the material. For homogeneous solids measurements of the compression and shear velocities can be used to determine the bulk and shear moduli (see section 2.4). The Young s modulus of rod-like materials (e.g. spaghetti) can be determined by measuring the velocity of ultrasound. 

For ideal mixtures there is a simple relationship between the measurable ultrasonic parameters and the concentration of the component phases. Thus ultrasound can be used to determine their composition once the properties of the component phases are known. Mixtures of triglyceride oils behave approximately as ideal mixtures and their ultrasonic properties can be modeled by the above equations [19]. Emulsions and suspensions where scattering is not appreciable can also be described using this approach [20]. In these systems the adiabatic compressibility of particles suspended in a liquid can be determined by measuring the ultrasonic velocity and the density. This is particularly useful for materials where it is difficult to determine the adiabatic compressibility directly, e.g., powders, biopolymer or granular materials. Deviations from equations 11 - 13 in non-ideal mixtures can be used to provide information about the non-ideality of a system. 

Figure 11. Dependence of ultrasonic velocity on the tristeann concentration of tristearin/paraffin oil mixtures at 18°C.

Figure 14. Dependence of the ultrasonic velocity on temperature for a fatty material.

The solid fat content of a material can be determined by measuring its ultrasonic velocity J L... 

Ultrasonic Doppler velocimetry, 3 Ultrasonic velocity profiler (UVP) measurements, 1, 2, 4. See also Gas-liquid interface Ultrasound echo intensity, 10-11, 13-15, 20... 

Ultrasound tomography (UST), 205 Ultrasound transducer arrangement, 14 Urea-formaldehyde microcapsules, 67 UVP-DUO systems, 2, 7, 12-13 UVP measurements. See Ultrasonic velocity profiler (UVP) measurements... 

Ultrasound-based Gas-liquid Interface Detection in Gas-liquid Two Phase Flows (by Prof. Yasushi Takeda et al.) introduces two ultrasonic-based detection methods for gas-liquid interface of gas-liquid two-phase flows in horizontal pipes, based on ultrasonic velocity profiler (UVP) measurements. One approach using ultrasonic peak echo intensity information to predict gas-liquid interface has wider application range and has been validated. Another approach based only on liquid velocity information is a relatively new technique and is still at intermediate stage of an ongoing development. 

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