Conic optical fiber probe for generation and characterization of microbubbles in liquids

Abstract

A novel optical fiber probe has been developed to provide mechanical stability to microbubbles generated in fluids, the tip of the fiber is etched with hydrofluoric acid to pierce a truncated horn that fastens the microbubbles to the fiber tip and prevents misalignment or detachment caused by convection currents, vibrations or shocks in the liquid. Microbubbles are photo-thermally generated on the etched fiber and used as Fabry-Perot cavity sensor. Two methods were used to interrogate the probe: the first one, in the wavelength domain, is suitable for calibration in static or quasi static situations; the second one, in the time domain, can be used in dynamic environments. Experimental results in the wavelength domain show that the microbubble size rises linearly with temperature and decreases with the inverse of pressure; the average slopes are 27.1 μm/°C and 88.3 μm/bar respectively. Dynamic variations of temperature have been measured in the time domain, temperature changes down to 0.007 °C have been detected at a readout rate of 10 s-−1. Bubbles have been subjected to pressure shocks of 2.4 bar at a speed of 25 bar/s, pressure changes of 3.4 mbar have been resolved in the time domain at a readout rate of 20,000 s−1.