MEMs

Barium Ferrite Materials for Microwave Circulators

Barium ferrite thick disks have been fabricated for incorporation in self-biased microwave devices. The process uses barium ferrite nanopowder mixed with epoxy. The mix is placed on alumina substrates to fabricate 500 μm thick disks of BaM to achieve good magnetic properties such as magnetic saturations from 2,000 to 2,500 G and coercivities fom 3800 to 4000 Oe. In addition, the barium ferrite thick disks have been incorporated into microwave devices and successfully deposited into copper contact lines for testing and use.

Posted in: Briefs, Materials
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Lubrication Considerations for Military Equipment

Military equipment is subject to increasingly harsh environmental conditions and performance requirements. Simultaneously, engineers and equipment operators are demanding longer service life and less maintenance. The proper approach to lubrication is critical to minimizing equipment failures and meeting rigorous performance specifications. While a multitude of environmental and technical variables may affect lubricant selection and use, the following considerations are important to address whenever a new lubricant is selected:

Posted in: Briefs, Materials
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Thermal Characterization of Thin Films for MEMS Applications

Dielectric thin films play a very important role in the development of microelectromechanical systems (MEMS). These dielectric materials often are used as insulating layers in devices, major components in MEMS structures, or even as materials strictly used for fabrication processes in a clean-room environment. In these applications, heat is often a crucial factor. Whether it be heat transfer through a device to stimulate operation, a device being exposed to certain temperatures during fabrication, or any other manner of heat transfer, these thermal processes are critical to device operation in MEMS. As such, thermal properties of these thin film dielectrics, especially thermal conductivity, are very important parameters to insure proper device operation.

Posted in: Briefs, Materials, Microelectricmechanical device, Heat transfer, Insulation, Materials properties
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Optical Microwave-Signal-Channelization Technique Analyzed

In a recent study, a proposed technique for optical frequency-band channelization of a microwave signal or other wide-band radio signal in a receiver was analyzed and compared with prior electronic and acousto-optical techniques. In frequency-band channelization, which is commonly used in wide-band radio receivers, a received signal is divided into narrow frequency bands (channels) and the signal in each channel is detected by a relatively narrow-band sub-receiver. In principle, frequency-band channelization offers benefits of reduced noise bandwidth and processing gain in the narrowband sub-receivers, leading to increased sensitivity, such that the wide-receiver could have a sensitivity approaching that of a narrow-band receiver. The quality of the channelization ultimately determines the performance of the receiver.

Posted in: Briefs, Electronics & Computers
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High-Cycle Life Testing of RF MEMS Switches

The electromechanical, RF, and charging properties of an "air-gap" capacitive switch enable it to be utilized in high-cycle life testing. Monitoring both high-speed and low-speed switching characteristics provides insight into quantifying the lifetime properties of the switch, and enable estimation of switching lifetime under a variety of operating conditions.

Posted in: Briefs, Electronics & Computers
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Reduced Power Laser Designation Systems

This work contributes to the Micropulse Laser Designation (MPLD) project to develop a six-pound eye-safe micro-pulse laser system to locate, identify, range, mark, and designate stationary and moving targets. MPLD uses laser pulses of much lower energy and higher repetition rates than in existing laser designation systems. Because of this, MPLD presents a range of new circuit design and signal processing problems.

Posted in: Briefs, Photonics
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Continuous-Wave Laser Diodes Based on a Novel InGaAsNSb Material System

Laser sources operating in the spectral region from 2 to 3.5 μm are in demand for ultra-sensitive laser spectroscopy, medical diagnostics, home security, industrial process monitoring, infrared countermeasures, and optical wireless communications. Currently, solid-state lasers and optical parametric oscillators and amplifiers are used as coherent light sources in this spectral region.

Posted in: Briefs, Photonics
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Photon Counting Chirped Amplitude Modulation Ladar

This work is a follow-up to prior efforts to develop a method using Geiger-mode avalanche photodiode (GM-APD) photon counting detectors in chirped amplitude modulation (AM) ladar receivers to yield sensitivities approaching the shot noise limit. Such sensitivities represent about four orders of magnitude improvement over the sensitivities of the currently used unity-gain, opto- electronic mixing (OEM) metal-semiconductor-metal (MSM) detectors. These sensitivity improvements may enable compact, low-power, eye-safe, and/or long-range ladar with low-cost, low-bandwidth readout integrated circuits for foliage and camouflage penetration, target ID, manned and unmanned ground and air vehicle navigation, 3D face recognition, battle damage assessment, and change detection.

Posted in: Briefs, Photonics
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SparkJet Actuators for Controlling Flows

SparkJet actuators are under investigation as means of controlling flows — especially supersonic and hypersonic flows. In one important class of potential applications, SparkJet actuators would be used to effect rapid and flexible steering of advanced aerospace vehicles. Effective manipulation of flow fields in aerospace systems could afford significant benefits, including increases in performance, maneuverability, payload, and range, as well as reductions in overall costs. These macro-scale benefits would be achieved through the use of SparkJet actuators to alter such phenomena as laminar-to-turbulent transition, turbulence, and flow separation on a micro scale.

Posted in: Briefs, Mechanical Components
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Stability of Rotors Supported by Hydrodynamic Film Bearings

The document, "Hydrodynamic Fluid Film Bearings and Their Effect on the Stability of Rotating Machinery" represents a lecture in a series "Design and Analysis of High-Speed Pumps," held in 2006 under the auspices of the North Atlantic Treaty Organization. The document introduces the basic principles of hydrodynamic lubrication and the fundamental equation of classical lubrication theory, then proceeds through derivation of the static and dynamic performance characteristics of short cylindrical journal bearings, with application to the dynamic forced performance of a rigid rotor supported on plain bearings. The Sommerfeld number is introduced and shown to define the relation among load, speed, and equilibrium eccentricity of a journal within a radial bearing. Rotordynamic force coefficients (direct and cross-coupled stiffnesses) are introduced and the relationships between them and instabilities of the rotor-and-bearing system are thoroughly discussed. The relationship between the whirl frequency ratio (the ratio between the frequency of undesired orbital rotor motion about the nominal journal axis and the frequency of rotation) and the threshold rotational frequency for instability is discussed. The document concludes with a review of practical journal-bearing configurations, including summaries of their major advantages and disadvantages and brief descriptions of typical applications.

Posted in: Briefs, Mechanical Components
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