Issue << content << Multiple Ultrasonic Echo Signals in a Plate. Determination and Application

DOI: 10.12737/18049

2016. Vol.19. No. 1, pp. 36-39

Multiple Ultrasonic Echo Signals in a Plate. Determination and Application

V. T. Bobrov, V. G. Shevaldykin

Introduction. Multiple echo signals arise within a plate being tested with a normal ultrasonic transducer. Besides some weaker pulses with unequal recurrence intervals are seen on the screen. Although their amplitude is rather small, they can prevent the device, for example a thickness gauge, from normal operation. The task was to ascertain the reasons and to determine the points of time when these weak pulses arise.
Method. Any mechanical perturbation of the solid body’s surface generates a pair of ultrasound waves that propagate into its volume. The plate was tested with longitudinal and transversal ultrasonic waves originated by different normal transducers; the waves’ velocities in the plate material were known. Thus the time points when several initial pulses were to come to the oscillogram were calculated.
Results. The coincidence of the measured time points with the calculated ones showed that each small pulse is a result of ultrasonic signal propagation within the plate thickness: one or more times as a longitudinal wave and one or more times as a transversal wave. Strict determinateness of pulse registration points for all the pulses, depending only on the plate thickness and the actual sound velocities within the plate, allows the both velocities and a Poisson ratio to be measured using any of a normal transducer, including a piezoelectric transducer of longitudinal waves. When the ratio “transversal wave velocity / longitudinal wave velocity” is equal or close to 0.5, some pairs of pulses or more arise at the same point of time.
Conclusion. The given simple way to measure a velocity of both transversal and longitudinal waves makes it possible to evaluate physical and mechanical properties of the materials.
Keywords: ultrasonic pulses, multiple echo signals, longitudinal wave velocity, transversal wave, bottom echo, piezoelectric transducer, EMAT, Poisson ratio
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