Monolithic Flexure Pre-Stressed Ultrasonic Horns
- Created on Tuesday, 01 November 2011
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
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
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
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