Megasonic Transducer Voltage Control for Uniform Acoustic Field
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Solution Overview
Problem
Megasonic systems face challenges in achieving uniform acoustic field distribution and minimizing cavitation erosion and surface damage during the cleaning of delicate articles, due to high frequency sound waves exhibiting higher attenuation and uneven interference patterns.
Innovation Solution
The use of multiple rows of piezoelectric elements with adaptive voltage control and specific geometric arrangements, such as circular elements positioned to minimize acoustic pressure differences, along with pulsed control signals and additional transducers for improved uniformity, ensures consistent acoustic pressure across the surface being cleaned.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high frequency megasonic waves are used for cleaning, then cavitation erosion and surface damage are reduced, but acoustic field uniformity deteriorates due to higher attenuation and beam effects
Solution Approach 1:
The transducer surface is divided into multiple independently controllable piezoelectric element groups arranged in rows. Each group can be driven with different voltages to compensate for attenuation variations across the acoustic field, thereby achieving uniform energy distribution while maintaining high frequency operation
Solution Approach 2:
Different regions of the transducer surface are assigned different driving voltages based on their position and attenuation characteristics. Elements in regions with higher attenuation receive higher voltages, while those in regions with lower attenuation receive lower voltages, creating a non-uniform driving pattern that results in uniform acoustic field distribution
2Productivity
If continuous wave megasonic systems are used, then cleaning action is maintained, but cavitation erosion increases due to violent and random cavitation effects
Solution Approach 1:
The megasonic system uses amplitude-modulated pulsed waveforms instead of continuous waves. The periodic modulation creates controlled cycles of cavitation bubble formation and collapse, maintaining cleaning effectiveness while reducing random violent cavitation events that cause surface damage
Solution Approach 2:
The amplitude-modulated continuous wave (AMCW) technique maintains continuous acoustic field presence while modulating the energy delivery. This ensures continuous cleaning action through sustained cavitation activity while the modulation controls the intensity to prevent excessive erosion
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces surface damage and enhances cleaning efficiency by achieving uniform acoustic field distribution, minimizing interference effects, and optimizing bubble activity for effective cleaning without damaging delicate surfaces.
Implementation Method 1
The transducers of available systems involve, as an active element, a piezoelectric ceramic or polymer driven at its resonant frequency by a single frequency continuous-wave generator. This active element converts electrical energy to acoustic energy
Implementation Method 2
Cavitation is generally known and defined as the activity of bubbles (e.g., gas bubbles) in a liquid. Such activity includes growth, pulsation and/or collapse of bubbles in a liquid. The occurrence of transient cavitation can release high amounts of energy towards an area surrounding the cavitation. One of the best-known applications of cavitation may be the removal of particles from a surface of a substrate
Data Source
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AI summary
This invention relates to a system for delivering megasonic energy to a liquid, comprising: - one or more megasonic transducers, each transducer having a single operating frequency within an ultrasound bandwidth and comprising two or more groups of piezoelectric elements arranged in one or more rows; and - a megasonic generator means for driving the one or more transducers at frequencies within the bandwidth, the generator means being adapted for changing the voltage applied to each group of piezoelectric elements so as to achieve substantially the same maximum acoustic pressure for each group of piezoelectric elements, the generator means and transducers being constructed and arranged so as to produce ultrasound within the liquid. Such a system may be part of an apparatus for cleaning a surface of an article such as a semiconductor wafer or a medical implant.