Ultrasonic wave characteristics

It is of interest to note that the lengthy and complex calculation Debye made was published in the same (first) edition of the Journal of Chemical Physics as an article by Bernal and Fowler, who first suggested several seminal concepts about the structure of water that are now commonly accepted in solution theory. The velocity amplitude is measured in cm s". It is the ratio of the pressure of the ultrasonic wave to the characteristic acoustic impedance of the media. 

Most ultrasonic material analyses rely on measurements of some characteristic of ultrasonic waves propagating through the sample that provides information on the interaction of ultrasonic waves with the inside of the sample, thus enabling analysis of its physical and chemical properties. 

Tsidzi, K. 1997. Propagation characteristics of ultrasonic waves in foliated rocks. BidL bit. Association of Eng. Geology, 56 103-113. 

High-intensity ultrasound has the ability to alter a material s characteristics due to interactions between the sound wave and the food product at a structural level. Transmission of the ultrasonic wave takes place by the oscillation of medium particles, and the damping of ultrasound energy in deeper tissue layers forms the basis of the modification of tissue structures, leading to an impact on simultaneously occurring mass and heat transfer processes during drying. 

As pointed out, the characteristics of ultrasonic waves applied in a medium determine the effects produced. So, there are ultrasound applications that use low ultrasound intensities (<1 Wcm ) and high frequencies (>1 MHz) which do not affect the medium significantly. In these cases, the change in the characteristics of ultrasound waves traveling through the medium is used to determine the medium s properties. As they constitute a nondestructive inspection technique, low-intensity ultrasound applications have been the subject of intensive research and development over the past few years (Benedito et al., 2002 Benedito et al, 2004 Ninoles et al., 2011). 

Table 1.41 lists the main characteristics of HR-US. As ultrasonic waves are synthesised electronically, it is easy to change their wavelength, quite unlike optical techniques. Ultrasonic velocity and attenuation can be measured simultaneously at different wavelengths as a function of time. US analysis... 

Many different types of ultrasonic transducers are available, differing in diameter of the probe, frequency, and frequency bandwidth. Each transducer has a characteristic resonant frequency at which ultrasonic waves are most effectively generated and received. Narrow bandwidth transducers are capable of penetrating deep, as well as detecting small flaws. However, these transducers do a poor job of separating echos. Broad bandwidth transducers exhibit excellent echo separation bnt poor flaw detection and penetration (3). Transducers of a frequency range of 2-5 MHz are most conunon. For plastic materials, transducers in the range of 1-2 MHz seem to yield the best results. 

Some of the problems often encountered during ultrasonic inspection of plane specimens are also found on cylindrical specimens. For example, problems associated with the directional characteristic of the ultrasonic transducer. Furthermore, the discontinuity influences the shape and propagation direction of a reflected pulse, causing wave mode transformation. In addition, the specimen influences the shape and amplitude of the reflected pulse by sound absorption. 

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