2011

Monolithic Flexure Pre-Stressed Ultrasonic Horns

Flexures are used rather than stress bolts, allowing one to apply pre-load to the piezoelectric material.

High-power ultrasonic actuators are generally assembled with a horn, backing, stress bolt, piezoelectric rings, and electrodes. The manufacturing process is complex, expensive, difficult, and time-consuming. The internal stress bolt needs to be insulated and presents a potential internal discharge point, which can decrease actuator life. Also, the introduction of a center hole for the bolt causes many failures, reducing the throughput of the manufactured actuators.

A new design has been developed for producing ultrasonic horn actuators. This design consists of using flexures rather than stress bolts, allowing one to apply pre-load to the piezoelectric material. It also allows one to manufacture them from a single material/plate, rapid prototype them, or make an array in a plate or 3D structure. The actuator is easily assembled, and application of prestress greater than 25 MPa was demonstrated.

The horn consists of external flexures that eliminate the need for the conventional stress bolt internal to the piezoelectric, and reduces the related complexity. The stress bolts are required in existing horns to provide pre-stress on piezoelectric stacks when driven at high power levels. In addition, the manufacturing process benefits from the amenability to produce horn structures with internal cavities. The removal of the pre-stress bolt removes a potential internal electric discharge point in the actuator. In addition, it significantly reduces the chances of mechanical failure in the piezoelectric stacks that result from the hole surface in conventional piezoelectric actuators. The novel features of this disclosure are:

1. A design that can be manufactured from a single piece of metal using EDM, precision machining, or rapid prototyping.
2. Increased electromechanical coupling of the horn actuator.
3. Higher energy density.
4. A monolithic structure of a horn that consists of an external flexure or flexures that can be used to pre-stress a solid piezoelectric structure rather than a bolt, which requires a through hole in the piezoelectric material.
5. A flexure system with low stiffness that accommodates mechanical creep with minor reduction in pre-stress.

This work was done by Stewart Sherrit, Xiaoqi Bao, Mircea Badescu, and Yoseph Bar- Cohen of Caltech, and Phillip Grant Allen of Cal Poly Pomona for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
• Innovative Technology Assets Management JPL
• Mail Stop 202-233
• 4800 Oak Grove Drive
• Pasadena, CA 91109-8099
• E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
NPO-47610

This Brief includes a Technical Support Package (TSP).

Monolithic Flexure Pre-Stressed Ultrasonic Horns (reference NPO-47610) is currently available for download from the TSP library.

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