A team from Langley Research Center in Hampton, VA, has been awarded the 2006 NASA Government Invention of the Year for an actuator and sensor system that is more durable than a piezoelectric system, and provides increased unidirectional control. In addition to being used in a number of NASA programs, the technology can be used in military, automotive, medical, and consumer product applications. The Invention of the Year is selected by NASA’s General Counsel, with the support of the Inventions and Contributions Board (ICB). For more information on the awards and this year’s winner and finalists, visit http://icb.nasa.gov/03-07-board/IOY2006/ index.htm.

MacroFiber Composite Actuator and Sensor (MFC)

Traditional actuation systems used in aerospace applications are hydraulic, pneumatic, and electromechanical devices. The MFC is an embodiment of a new type of piezoelectric device. The system’s piezocomposite technology allows integration and distribution of piezoelectric elements in both aerospace and nonaerospace products on a scale larger than what was possible previously. The MFC was developed by Richard Hellbaum, James High, Bruce Little, Paul Mirick, William Wilkie, Robert Bryant, and the late Antony Jalink and Robert Fox.

When voltage is applied to a piezoelectric device, an electric field is generated parallel to the piezoelectric fibers. This electric field produces a uniform mechanical strain proportional to the applied electric field up to a saturation point. Conversely, when the device is strained mechanically, a voltage is produced in response to the magnitude and direction of the applied load.

The space shuttle crawler/transporter has 16 cylinders with two bearings per cylinder. The MFC sensor was bonded to the bearing pin to measure cracks in the bearings.

Standard high-force electroactive ceramics such as piezoelectric wafers are brittle, are not electrically insulated, and come with electroded surfaces. They also are not packaged to protect them or the user from the operational environment. Also, the resulting force output and strain indication of conventional piezo wafers are nearly bi-directional and about 30% of what the MFC is capable of. A method that has been used to solve these issues is to assemble these piezoelectric materials as fibers, rather than wafers, and direct the electric field along the fiber axis. This approach provides flexibility, durability, environmental protection, and more unidirectional behavior and strain output.

Rather than using expensive round piezoelectric fibers, the MFC uses commercial piezoelectric wafers that are diced into square fibers and placed, prealigned, directly onto commercially produced polyimide copper films. There is no handling of the piezo material, and no fiber breakage.

The MFC was designed to be integrated into a system as an add-on component, or integrated during manufacturing. Its flat profile and use as both a sensor and actuator enable its use in critical or tight areas where the ability to selfpower wireless circuitry from the electricity generated from flexing the MFC enables additional health monitoring on complex rotating components, or in remote and hazardous environments.

As a conformable actuator, the MFC can be used to suppress vibration, cancel jitter or noise, or structurally stiffen or wrap the member or panel to which it is attached. Conversely, as a conformable sensor, it can sense the mechanical strains and generate the voltage signal that is proportional to the magnitude and rate of the applied load.

Since 1999, NASA has used MFC piezocomposites in a range of active vibration and shape-control applications including active damping of very large deployable spacecraft structures, buffet load alleviation on aircraft control surfaces, and controlling unsteady aerodynamics and noise on helicopter rotor blades. Sensor applications include impedance-based health monitoring of the space shuttle white room launch tower structures and the crawler/transporter roller bearings.

Recent commercial applications include energy harvesting for telemetry devices, automotive interior noise cancellation and structural damping on drive shafts, low-frequency woundhealing for medical applications, and active feedback of high-performance athletic equipment.

Recent commercial applications include energy harvesting for telemetry devices, automotive interior noise cancellation and structural damping on drive shafts, low-frequency woundhealing for medical applications, and active feedback of high-performance athletic equipment.


NASA Tech Briefs Magazine

This article first appeared in the June, 2007 issue of NASA Tech Briefs Magazine.

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