Thursday, December 24, 2009

MEMS & NEMS Rotary Devices Made with Multiwall Carbon Nanotubes by M.I.T. and Draper Laboratory Researchers, Discovery Enables Complex Nano Drive and Sensing Mechanisms


Researchers from the Charles Stark Draper Laboratory, Inc (Cambridge, MA) and Massachusetts Institute of Technology (M.I.T., Cambridge, MA) divulge nano-rotary devices made with  multiwall carbon nanotubes in U.S. Patent Application 20090317233.  A rotor may be coupled to an outer wall of a multiwall nanotube, be spaced apart from the substrate, and be free to rotate around an elongate axis of the multiwall nanotube.

The nano-rotary device may be employed as a flywheel in a flywheel energy storage mechanism, as an optical chopper to periodically interrupt a light beam (for example with the rotation of the vanes through the light beam), as a turbine to extract energy from fluid flow, as a gas compressor to increase the pressure of a gas, and/or as a flow sensor to sense a rate of fluid flow. For example, the vanes of the rotary device may be pushed by a fluid and the rotary device used to extract energy fro it (in the case of a turbine) or used to drive a rotary potentiometer or similar device (in the case of a flow sensor).

Commercial micro-electro-mechanical systems ("MEMS") now reach the sub-millimeter to micrometer size scale. There is, however, also great interest in nanometer scale electromechanical systems. Nanostructures are of great interest not only for their basic scientific richness, but also because they have the potential to revolutionize critical technologies.

Certain types of bearing structures are employed in MEMS and nano-electro-mechanical systems ("NEMS") to allow for relative motion (e.g., linear or rotational) between two parts, but each has its limitations. For example, silicon-on-silicon sliding bearings generally have friction, lifetime, and debris issues. Gas bearings may have very low friction, but their design is typically complex and they generally are not operable in vacuum. For their part, ball bearings have size and wobble limitations.

Rotational actuators are of particular interest for several applications. For example, a dynamically tuned gyroscope, also known as a dry tuned gyroscope ("DTG"), typically includes a motor (e.g., an electromagnetic motor) that spins a shaft to which a rotor is attached. In some implementations, the shaft is supported by ball bearings. As mentioned, however, such ball bearings typically cannot be made small enough for some applications. In addition, they may consume greater amounts of power than desired due to undesirably high friction. Jeweled bearings and precisely machined pivots may be used instead, but, again, they typically increase the overall size of the DTG to larger than what is desired for many applications.

Rotational actuators that employ carbon nanotubes have been described. However, such actuators typically feature a rotor whose rotation axis is parallel to a top surface of the substrate. This arrangement is generally difficult to integrate with MEMS and NEMS processing, is difficult to manufacture, limits the applications of a device in which the actuator is employed, and limits the potential geometries for other features of the device (e.g., actuation and readout mechanisms).

A needs exist for improved nano and micro bearing structures and for methods of manufacturing and using the same.  The M.I.T. carbon nanotube rotary bearing meets that need.

The M.I.T. rotary bearing features a multiwall nanotube (e.g., a carbon nanotube that includes an outer cylindrical wall and one or more concentric inner cylindrical walls). The multiwall nanotube may be attached to a substrate, and a rotor may be connected to the outer wall of the nanotube. In addition, a long axis of the nanotube may be oriented substantially perpendicular to a top surface of the substrate such that an axis of rotation of the rotor is also substantially perpendicular to the top surface of the substrate.

According to inventors David J Carter, Marc S. Weinberg, Eugene Cook, Peter Miraglia and Zoltan S Spakovszky,  this arrangement advantageously allows for well-controlled nanotube growth and/or placement, and integrated structure fabrication using standard MEMS/NEMS fabrication techniques. It also allows for the design of rotationally-symmetric rotors for high rotation speed, gives precise control over the rotor's geometry and mass (e.g., over its diameter and thickness), and enables the fabrication of relatively complex drive and sense mechanisms (e.g., multiple drive electrodes for an electrostatic drive, structures patterned above and below the rotor for an electrostatic or electromagnetic drive, and/or magnetic or capacitive readouts).


2 comments:

  1. Use of nanotechnology is increasing day by day. Carbon nanotubes are widely used in various industries.
    Multi Wall Carbon Nanotubes is layers of graphene. It is in cylindrical shape.

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