Interferometric Fiber Optic Probe for Measurements of Cavitation Bubble Expansion Velocity and Bubble Oscillation Time

Abstract

Cavitation bubbles are used in medicine as a mechanism to generate shock waves. The study of cavitation bubble dynamics plays a crucial role in understanding and utilizing such phenomena for practical applications and purposes. Since the lifetime of cavitation bubbles is in the range of hundreds of microseconds and the radii are in the millimeter range, the observation of bubble dynamics requires complicated and expensive equipment. High-speed cameras or other optical techniques require transparent containers or at least a transparent optical window to access the region. Fiber optic probe tips are commonly used to monitor water pressure, density, and temperature, but no study has used a fiber tip sensor in an interferometric setup to measure cavitation bubble dynamics. We present how a fiber tip sensor system, originally intended as a hydrophone, can be used to track the expansion and contraction of cavitation bubbles. The measurement is based on interference between light reflected from the fiber tip surface and light reflected from the cavitation bubble itself. We used a continuous-wave laser to generate cavitation bubbles and a high-speed camera to validate our measurements. The shock wave resulting from the collapse of a bubble can also be measured with a delay in the order of 1 µs since the probe tip can be placed less than 1 mm away from the origin of the cavitation bubble. By combining the information on the bubble expansion velocity and the time of bubble collapse, the lifetime of a bubble can be estimated. The bubble expansion velocity is measured with a spatial resolution of 488 nm, half the wavelength of the measuring laser. Our results demonstrate an alternative method for monitoring bubble dynamics without the need for expensive equipment. The method is flexible and can be adapted to different environmental conditions, opening up new perspectives in many application areas.

Nucleation of a Vapor Phase and Vapor Front Dynamics Due to Boiling-Up on a Solid Surface

“…However, the observed oscillations are not associated with changes in the density of the medium, appearing rather as a result of interference of the reflected rays. The traveling interference pattern shown in Figure 4, which is characteristic of the interferometers with a moving reflector, is due to the formation of an additional reflected signal as a result of the superposition of the origin and propagation of the phase interface with the reflected light waves from the stationary end of the fiber [34]. Each oscillation period in the recorded signal (Figure 4) corresponds to a shift of the vapor front by half the wavelength of the probing radiation.…”

“…In turn, the refractive index decreased with a reduction in the density of the medium. The dynamics of the changes in the density of the medium were assessed by tracking the changes in the average intensity of the reflected radiation according to the photodetector signal following the activating pulse [26,34]. During the fiber-optic densitometry experiments with superheated liquid following activation of boiling-up, high-frequency oscillations were observed at the output of the high-speed photodetector of reflected radiation.…”

Simulation of light scattering on a deformed gas bubble

“…Moreover, the smaller the bubbles, the larger the interfacial surface that cleans the liquid from impurities [5], [6], [7], [8]. To study the factors influencing the size of gas bubbles suspended in a liquid, a system for measuring this size is needed, for example, based on the principle of light scattering in a two-phase liquid [9], [10], [11], [12]. Optical examination of a two-phase liquid is the least invasive, since light makes minimal changes to the medium being examined.…”

“…When a large bubble breaks into smaller ones, deformations occur on its surface. For non-invasive measurement of deformations, it is necessary to modify existing methods for measuring the parameters of the dispersed phase in a continuous medium [10,11]. To modify measurement methods, theoretical studies of the scattering of an electromagnetic field on a deformed dispersed inclusion (in this case, a bubble) are necessary, which are described below.…”

A high sensitivity fiber optic acoustic sensor based on incident-angle sensing: application to detect snoring signals

“…Compared with ordinary piezoelectric acoustic sensors, fiber optic acoustic sensors (FOAS) have the advantages of strong anti-electromagnetic interference ability, corrosion resistance, and high sensitivity, which make FOAS a unique advantage in the medical field. For example, the hydrophone can be used in the application of ultrasonic acupuncture tracking [1,2] , empty bubble dynamics [3] , and measuring myocardial cell acoustic signals [4] . In some specific occasions, such as MRI, FOAS also has an irreplaceable effect in detecting voice signals.…”