Ultrasonic detection and measurement of bubbles in the liquids.

In the area of fluid measurement by the use of ultrasonic wave propagation, the existence of gas bubbles in liquid causes some trouble, due to scattering and absorption of the wave. A new method for non-contact detection and measurement of bubbles in blood is developed utilizing the same phenomena. In this paper , a new apparatus for the measurement is described. Its theoretical analysis on the attenuation of ultrasonic wave in two-phase fluid is also discussed. Two different methods are tested, these are, (i) the measurement through the average attenuation of the transmitted wave, (ii) the measurement through the RMS fluctuation of the wave power. As a result of the experiment, the theory was verified and the method proved to be promising. The minimum detectable concentration of bubbles is 100 ppm. Development of this work is aimed at the detection of small bubbles in human blood during the dialysis treatment. In this application the advantage of this method is fully demonstrated, that is, the use of highly sensitive instruments not in direct contact with blood. Some results of field trials in a hospital are given. Also, a possible application to industrial measurement is mentioned. (A)