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 photothermally 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 m/ 0 C and 88.3m/bar respectively. Dynamic variations of temperature have been measured in the time domain, temperature changes down to 0.007 0 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 20000 s -1 .

Monitoring the Growth of a Microbubble Generated Photothermally onto an Optical Fiber by Means Fabry–Perot Interferometry

“…The technique known as photodeposition was used to immobilize ZnNPs on the optical fiber end [ 21 , 22 , 23 , 24 , 25 ]. In this technique, a source of continuous wave radiation is propagated through a single-mode optical fiber (125/9 µm), where the tip of the fiber is immersed in a solution of 4.5 mL of isopropyl alcohol with 10 mg of zinc powder (previously ultrasonified).…”

“…Here, the nanoparticles began to photodeposit on the tip of the optical fiber, and once a 3 dB optical loss was registered, the cuvette with the solution/nanoparticles was changed by another without nanoparticles (only alcohol). Due to the high absorption coefficient of the ZnNPs at the operating wavelength, the light was strongly absorbed by the nanoparticles, heating the solution until a microbubble was formed [ 21 , 22 , 25 ]. To record the formation and evolution of the microbubble, the cuvette was illuminated perpendicularly to the optical fiber, using a white light source to project the bubble’s shadow on a high-speed camera (Chronos 1.4 from Kron Technologies Inc., Brunaby, BC, Canada), with the help of a microscope lens.…”

“…A microbubble is a spherical shell which contains gas; therefore, microbubbles can be used as pressure probes because their size changes with pressure changes [ 24 , 25 ]. When the pressure pulses produced by a loudspeaker pass through the microbubble, they provoke a contraction and expansion in its volume.…”