Fluid pressure measurement using bubbles insonified by two frequencies

Abstract

The double frequency method, where bubbles rising through a fluid are illuminated simultaneously with a ‘pump’ frequency swept through the resonance frequency range and a megahertz imaging frequency, is used to measure pressure changes in fluids non-invasively. The bubble echo spectrum is centred at the imaging frequency with side bands at separations equal to the pump frequency. If the ambient pressure is changed, the bubbles undergo changes in their sizes. This would alter the resonant frequency of the bubble and hence the peak of the echo at the sum (or difference) frequency. By observing shifts in the frequency of the peak amplitude of the side bands it is shown that fluid pressure changes can be measured accurately.