Tech Briefs

Encapsulated Ball Bearings for Rotary Micro Machines

Microelectromechanical systems (MEMS)-fabricated silicon rotary elements for micro-motors, micro-generators, and micro-turbomachinery have received growing attention with applications in power conversion and actuation. Within these technologies, the bearing mechanism is the primary determinant of device performance and reliability. Active bearings, such as magnetic or electrostatic, have the advantage of being controlled during the operation, but at the cost of the accompanying circuitry. Passive bearings span a large range of velocities that include center-pin bushings with low revolution rates possible, and hydrostatic or hydrodynamic bearings with high revolution rates possible.

Posted in: Briefs, Mechanical Components, Microelectricmechanical device, Bearings

Development of High-Resolution Eddy Current Imaging Using an Electromechanical Sensor

An oscillating current flowing through a coil produces an oscillating magnetic field. When an electrically conducting material like a metal is brought close to the coil, the oscillating magnetic field produces eddy currents in the metallic material. The strength of the eddy current depends on the electrical conductivity of the material, the distance between the coil and the material, and the frequency of the excitation of the coil. The eddy currents in the electrical conductor produce a magnetic field opposing the magnetic field generated by the coil. The electrical impedance of the coil, placed in close proximity to a metal, is altered due to the eddy currents in the metal. Measurement of the change in the impedance is a method to determine the electrical conductivity of the metal.

Posted in: Briefs, Physical Sciences, Measurements, Sensors and actuators, Conductivity, Magnetic materials, Metals

Fuzzy Fiber Sensors for Structural Composite Health Monitoring

The onset of local damage in structures, such as delamination, cracking, and fastener loosening, can often be difficult to detect and has long-term implications on the performance of the composite structure. These structures are often exposed to a variety of conditions, including impact, shock loading, and extreme changes in temperature. Because of both manufacturing requirements and design specifications, large and complex sections often need to be joined together to form the final structures. It is important to understand the failure behavior of these joints under a variety of static and dynamic loading conditions.

Posted in: Briefs, Physical Sciences, Failure modes and effects analysis, Fiber optics, Sensors and actuators, Composite materials

Fatigue Crack Detection Via Load-Differential Guided Wave Methods

Guided waves (e.g., Lamb waves) have been considered for many structural health monitoring (SHM) applications because of their ability to travel long distances and maintain sensitivity to damage. One conventional approach to detect damage is to compare in situ signals to baselines recorded from the undamaged structure. By comparing current signals to damage-free baselines, signal changes caused by structural damage can be tracked. Such methods can handle some structural complexity, but have unwanted sensitivity to variations in environmental and operational conditions (e.g., temperatures and loads).

Posted in: Briefs, Physical Sciences, Failure modes and effects analysis, Waveguides, Fatigue

Distributed Fiber Optic Sensing for Homeland Security

To address the need to protect our borders and critical infrastructure, fiber optic sensing technology developed for antisubmarine warfare applications has been adapted to homeland security applications. Ground-based seismic sensing applications have significantly different requirements than traditional underwater acoustic applications. As a result, new optical interrogation and signal processing techniques are needed. Border and critical infrastructure sensor systems must be able to monitor long lengths (several km to several 10s of km) with reasonable spatial resolution (5 to 100 m), and have sufficient seismic sensitivity to detect targets of interest. A fiber optic distributed seismic sensor system was developed that is capable of meeting these requirements.

Posted in: Briefs, Physical Sciences, Architecture, Fiber optics, Security systems, Sensors and actuators

Direct-Write Polymer Nanolithography in Ultra-High Vacuum

The deposition of materials in vacuum is the foundational technology for creating modern electronic circuits; a vacuum being essential both to preserve the cleanliness of the substrate and the deposited materials, and to minimize the creation of defects. Consequently, most deposition techniques, from thermal evaporation to atomic layer deposition, require a high level of vacuum, preferably ultra-high vacuum (UHV), to be used effectively.

Posted in: Briefs, Manufacturing & Prototyping, Electronic equipment, Fabrication, Polymers

Operation and On-Chip Integration of Cavity-QED-Based Detectors for Single Atoms and Molecules

A new experimental platform for studies of transport and quantumlimited measurements of cold, trapped atomic gases was constructed. Using microfabrication processes, a silicon wafer was micromachined to allow for deposition of micrometer-scale electromagnet wires, and for the integration of closely spaced, highly reflective optical mirrors. With this device, nanokelvintemperature atomic gases were produced and placed with nanometer precision within a high-finesse optical resonator. This device was applied to the construction of a cavity optomechanical system with ultracold atomic gases, with the goals of understanding how to conduct quantum-limited measurements of the motion of a macroscopic mechanical object, and characterizing the new phenomena arising in such a hybrid optomechanical quantum system.

Posted in: Briefs, Manufacturing & Prototyping, Measurements, Optics, Storage, Gases, Silicon alloys