Folded horns have been conceived as alternatives to straight horns used as resonators and strain amplifiers in power ultrasonic systems. Such systems are used for cleaning, welding, soldering, cutting, and drilling in a variety of industries. In addition, several previous NASA Tech Briefs articles have described instrumented drilling, coring, and burrowing machines that utilize combinations of sonic and ultrasonic vibrational actuation. The main advantage of a folded horn, relative to a straight horn of the same resonance frequency, is that the folded horn can be made shorter (that is, its greatest linear dimension measured from the outside can be made smaller). Alternatively, for a given length, the resonance frequency can be reduced. Hence, the folded-horn concept affords an additional degree of design freedom for reducing the length of an ultrasonic power system that includes a horn.
Figure 1 depicts an ultrasonic actuator that includes a straight stepped horn, one that includes an inverted straight stepped horn of approximately the same resonance frequency, and one that includes a folded stepped horn of approximately the same resonance frequency. The main role of the straight stepped horn is to amplify longitudinal strain at its outermost end.
In the folded version, one can exploit bending strain in addition to longitudinal strain, and by adjusting the thickness of the folds, one can increase or decrease the contributions of bending displacements to the overall displacement at the tip. In this case, the folded-horn concept not only yields a shorter horn, but by enabling utilization of bending displacements, it also affords an additional degree of design freedom. Figure 2 shows an experimental folded-horn actuator of 16-kHz resonance frequency alongside a straight-horn actuator of 20-kHz resonance frequency.
This work was done by Stewart Sherrit, Stephen Askins, Michael Gradziel, Xiaoqi Bao, Zensheu Chang, Benjamin Dolgin, and Yoseph Bar-Cohen of Caltech and Tom Peterson of Cybersonics Inc. for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Mechanics category.NPO-30489.
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Folded Resonant Horns for Power Ultrasonic Applications
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Overview
The document discusses advancements in ultrasonic technology, specifically focusing on folded resonant horns as alternatives to traditional straight horns used in power ultrasonic applications. Developed by researchers at NASA's Jet Propulsion Laboratory, these folded horns are designed to enhance the efficiency and versatility of ultrasonic systems employed in various industries, including automotive, medical, textiles, and material fabrication.
Ultrasonic horns play a crucial role in amplifying the strain induced by piezoelectric elements in ultrasonic devices. The standard design of these horns has remained largely unchanged, typically featuring a tapered solid structure that amplifies limited displacement. However, traditional horns have limitations, particularly in size and resonance frequency. The folded horn design addresses these issues by allowing for a shorter overall length while maintaining or even reducing the resonance frequency, which is beneficial in applications where space is a premium.
The document highlights key findings from experiments comparing standard straight horns with folded horns. For instance, the standard horn used in the Ultrasonic Rock Abrasion Tool (URAT) resonated at approximately 20 kHz, while the folded horn resonated at around 16 kHz. However, the mechanical quality factor (Q) of the folded horn was significantly lower, resulting in reduced displacement at the tip compared to the straight horn. This lower Q was attributed to energy dissipation caused by screw threads in the horn's design, suggesting that further design improvements could enhance performance.
The folded horn design also allows for adjustments in tip displacement through bending contributions, providing designers with greater flexibility in optimizing performance. This innovation is expected to lead to more efficient ultrasonic devices, reducing manufacturing waste and improving the overall effectiveness of ultrasonic applications.
Overall, the document emphasizes the potential of folded resonant horns to revolutionize power ultrasonic systems by offering a more compact and efficient alternative to traditional designs. The research underscores the importance of continued innovation in ultrasonic technology to meet the evolving needs of various industries, ultimately contributing to advancements in manufacturing and material processing techniques.
