A6.3 - Sound Velocity Profiles in Fluids for Process Monitoring

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings SENSOR 2011
A6 - Ultrasonic Sensors I
M. Lenz, E. Kühnicke - Technische Universität Dresden (Germany)
147 - 152


In conventional methods the sound velocity is determined by means of the back wall echo or a reflector at a known position. This paper presents a novel approach for combined measurement of sound velocities and distances in fluids with scattering particles. In contrast to conventional methods, the knowledge about the sound field is exploited to characterise the fluid, and solely the echoes from the scattering particles are used to determine sound velocity.

The basic idea is that the information on the transducer’s focus position and the corresponding time of flight suffice to determine the sound velocity of the fluid and that in turn, sufficient information on the focus position is comprised in the echo signals.

Proof of concept for these statements is given by theory, simulations, and experiments with a focusing transducer and an annular array. The following experiments are explained in detail:

(1) Measurements of the sound velocity c in four fluids covering the wide range between 1116 and 2740 m/s. The results show good agreement with values published elsewhere.
(2) Measurements in water, where c is adjusted by temperature. Sound velocity is varied between 1431 and 1555 m/s with increments of less than 10 m/s. The measured statistical variation of 1.4 m/s corresponds to a relative uncertainty not worse than 0.1%.
(3) Measurements with an annular array, where the focus distance was varied by time-shifted superposition of the receive signals belonging to the different elements of an annular array.

The results indicate that the novel method is even capable of measuring profiles of the sound velocity along the ultrasonic beam noninvasively.