Measurements at the Speed of Ultrasound

Starting with two ultrasonic measurements (speed of sound, intensity of sound), it is surprising how many variables can be determined, that are important in industrial processes, medicine, and elsewhere. This talk starts with the basics of ultrasonic waves, i.e., particle motions considered as analogs of the degrees of freedom of a simple molecule. Then we explore, in an intuitive nonmathematical manner, what happens when ultrasonic waves encounter or pass through various media: solids, liquids, gases, mixtures. "What happens" depends not only on the state and boundary conditions but on the "internal" conditions within the medium: temperature, pressure, flow. This leads us to consider how propagation of ultrasound has been used to determine these parameters as well as to identify liquid presence or level, quality of the medium, quality of the joint between adjacent media, etc. To determine flow velocity V to high accuracy, by sending sound with the flow and against the flow, it is necessary to achieve corresponding high accuracy in the determination of transit times in each direction, but this is not sufficient. As in life, one must choose the right path. Flow profile analysis teaches us that some paths are better than others, but there is no one right path. Further, there is no one right frequency or one right wave type. How does one find the best frequency and best wave type? While we seek simple solutions, preferably ones that are minimally intrusive (e.g., clamp-on flow or non-contact air-coupled NDT) the complexity of the problem may dictate the use of wetted or contact transducers, intrusive sensors, quadrature multipaths to efficiently average the flow over a pipe cross-section, or guided torsional waves responsive to the density of the adjacent fluid. Using examples from process control and nondestructive testing, solutions will be presented that include cryogenic extremes up to superheated steam and hot process temperatures well above the Curie point of commonly-used piezoelectric materials. Some of the points covered in the talk will be illustrated afterwards using commercially available equipment used to measure thickness, flows and flaws.

The talk is planned to be of 1 to 2 hr duration, depending on questions. Depending on audience interest, there may be a supplementary presentation at "half-time" by Prof. Mylvaganam, to illustrate alternative approaches to measuring the flow of flare gases and the level of liquid aluminum. Including demonstrations of equipment at the end, total time will be about 2 to 3 hr.

Target audience

Practicing engineers, researchers, graduate students who are interested in ultrasonic principles, techniques, applications and equipment currently available for measuring in the laboratory or in the field, industrial measurands, particularly flow, liquid level, thickness, flaws, disbonds. References for further information, in books available from Academic Press, include: Ch. 5 in Physical Acoustics 14 407-525 (1979); Ultrasonic Measurements for Process Control, 720 pp., 1989; Ch. 4, Physical Acoustics 23 275-470 (1999). Other references will be cited in the talk.

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