Application Cases

Experiment Name: Single-Bubble Sonoluminescence Experiment

Experimental Objective:
To verify the phenomenon of sonoluminescence and establish a foundation for subsequent experiments.

Test Equipment:
RF power amplifier, signal generator, oscilloscope, piezoelectric ceramic, round-bottom flask, high-speed camera, etc.

Experimental Process:
A spherical flask with a capacity of approximately 100 mL is filled with water that has been specially treated to remove dissolved air. Piezoelectric ceramics are attached to both sides of the flask using adhesive. The signal generator produces an excitation signal, which is amplified by the RF power amplifier to drive the piezoelectric ceramics and generate ultrasonic waves. The signal frequency is adjusted to resonate the flask, creating an antinode of the ultrasonic standing wave at its center. A bubble is injected using a syringe, and it remains stationary at the antinode due to acoustic pressure. By carefully adjusting the acoustic intensity and turning off the lights, blue-white light spots can be observed with the naked eye in the dark, resembling stars in the night sky.

Figure 1-1: Block Diagram of the Single-Bubble Sonoluminescence Experiment

Experimental Results:
In the laboratory, the spectrum of single-bubble sonoluminescence can be measured, and it appears similar to blackbody radiation. Calculations indicate that at higher temperatures, bremsstrahlung radiation contributes more significantly, resulting in a continuous spectrum. At relatively lower temperatures, atomic or molecular line spectra become more prominent. Typically, in the temperature range of sonoluminescence, bremsstrahlung radiation dominates in the short-wavelength region, causing bright bubbles to emit blue-white light. In contrast, the line spectra of inert gas atoms are concentrated in the low-frequency range, leading to dimmer bubbles often appearing red. If the liquid is a sodium salt solution, sodium atoms may enter the bubble, exciting the sodium doublet lines, which can sometimes cause the bubble to appear yellow. By observing the sonoluminescence spectrum or the color of the bubble, the approximate temperature of the bubble can be estimated.

Experiments have shown that when a large number of cavitation bubbles emit light simultaneously in water, line spectra dominate the spectrum. However, in most cases, the spectrum of single-bubble sonoluminescence is continuous. This suggests that in the single-bubble scenario, the achieved temperature is significantly higher than that of individual bubbles in multi-bubble sonoluminescence. The situation differs in concentrated sulfuric acid. Figure 2-2 shows a photo of cavitating xenon bubbles emitting light in concentrated sulfuric acid. Readers can compare Figure 2-1 and Figure 2-2, noting that Figure 2-1 depicts a single argon bubble, while Figure 2-2 shows thousands of xenon bubbles. Recent theoretical studies indicate that in multi-bubble scenarios, interactions between bubbles suppress cavitation intensity. As a result, the compression process of the bubbles is constrained by surrounding bubbles, reducing its intensity and leading to lower internal temperatures compared to the single-bubble case.

Figure 2-1: Sonoluminescence of a Single Argon Bubble in Concentrated Sulfuric Acid (85%)

Figure 2-2: Flame-like Pattern Formed by Sonoluminescence of Numerous Cavitating Xenon Bubbles

Recommended RF Power Amplifier: ATA-8000

Figure: ATA-8000 Series RF Power Amplifier

Applications:
Nondestructive Testing, Sonodynamic Therapy, Focused Ultrasound, Ultrasonic Nebulization, Controlled Drug Release, Ultrasonic Medical Testing, Cell/Tumor Ablation

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