Tech Briefs

Fabrication of Buried Nanochannels From Nanowire Patterns

Sacrificial nanowires are buried, then etched away to form buried channels.

A method of fabricating channels having widths of tens of nanometers in silicon substrates and burying the channels under overlying layers of dielectric materials has been demonstrated. With further refinement, the method might be useful for fabricating nanochannels for manipulation and analysis of large biomolecules at single-molecule resolution. Unlike in prior methods, burying the channels does not involve bonding of flat wafers to the silicon substrates to cover exposed channels in the substrates. Instead, the formation and burying of the channels are accomplished in a more sophisticated process that is less vulnerable to defects in the substrates and less likely to result in clogging of, or leakage from, the channels.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Fabrication, Joining, Nanotechnology, Silicon alloys

Infrared Imaging System for Studying Brain Function

This would be an alternative to large, expensive, immobile fMRI systems.

A proposed special-purpose infrared imaging system would be a compact, portable, less-expensive alternative to functional magnetic resonance imaging (fMRI) systems heretofore used to study brain function. Whereas a typical fMRI system fills a large room, and must be magnetically isolated, this system would fit into a bicycle helmet.

Posted in: Briefs, TSP, Bio-Medical, Medical, Downsizing, Magnetic resonance imaging (MRI), Magnetic resonance imaging (MRI), Body regions, Nervous system

Diamond Smoothing Tools

Machined surfaces could be made much smoother.

Diamond smoothing tools have been proposed for use in conjunction with diamond cutting tools that are used in many finish-machining operations. Diamond machining (including finishing) is often used, for example, in fabrication of precise metal mirrors.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Mirrors, Tools and equipment, Cutting, Fabrication

Rarefying Spectra of Whispering-Gallery-Mode Resonators

Undesired families of resonances are damped by a relatively simple technique.

A method of cleaning the mode spectra of whispering - gallery - mode (WGM) optical resonators has been devised to make such resonators more suitable for use as narrow-band optical filters. The method applies, more specifically, to millimeter- sized whispering - gallery - mode optical resonators that are made of crystalline electro-optical materials and have ultrahigh values of the resonance quality factor (Q). The mode spectrum of such a resonator is typically dense, consisting of closely spaced families of modes; as such, the spectrum is not well suited for narrow-band filtering, in which there is a need for strong rejection of side modes. “Cleaning” as used here signifies rarefying the spectrum so that what remains consists mostly of a single desired family of modes or, at worst, a few mode families that are more widely spaced in frequency than are the mode families in the original, non-rarefied spectrum.

Posted in: Briefs, TSP, Physical Sciences, Architecture, Imaging, Imaging and visualization, Architecture, Imaging, Imaging and visualization, Refractory materials, Acoustics, Acoustics

Slot-Antenna/ Permanent-Magnet Device for Generating Plasma

Characteristics include uniformity of plasma, scalability, versatility, and long life.

A device that includes a rectangular - waveguide / slot - antenna structure and permanent magnets has been devised as a means of generating a substantially uniform plasma over a relatively large area, using relatively low input power and a low gas flow rate. The device utilizes electron cyclotron resonance (ECR) excited by microwave power to efficiently generate plasma in a manner that is completely electrodeless in the sense that, in principle, there is no electrical contact between the plasma and the antenna. Plasmas generated by devices like this one are suitable for use as sources of ions and/or electrons for diverse material-processing applications (e.g., etching or deposition) and for ion thrusters.

Posted in: Briefs, TSP, Physical Sciences, Antennas, Antennas

Large-Area Permanent-Magnet ECR Plasma Source

This device is a good source of ions for plasma processing applications.

A 40-cm-diameter plasma device has been developed as a source of ions for material-processing and ion-thruster applications. Like the device described in the immediately preceding article, this device utilizes electron cyclotron resonance (ECR) excited by microwave power in a magnetic field to generate a plasma in an electrodeless (noncontact) manner and without need for an electrically insulating, microwave-transmissive window at the source. Hence, this device offers the same advantages of electrodeless, windowless design — low contamination and long operational life.

Posted in: Briefs, TSP, Physical Sciences, Research and development

Broadband Achromatic Telecentric Lens

Lens works with a matched spectrometer for applications covering the entire solar-reflected spectrum.

A new type of lens design features broadband achromatic performance as well as telecentricity, using a minimum number of spherical elements. With appropriate modifications, the lens design form can be tailored to cover the range of response of the focal-plane array, from Si (400–1,000 nm) to InGaAs (400–1,700 or 2,100 nm) or InSb/HgCdTe reaching to 2,500 nm. For reference, lenses typically are achromatized over the visible wavelength range of 480–650 nm.

Posted in: Briefs, TSP, Physical Sciences, Calibration, Architecture, Optics, Architecture, Optics

Electro-Optical Modulator Bias Control Using Bipolar Pulses

Bias is automatically adjusted to maintain maximum extinction during “off” periods.

An improved method has been devised for controlling the DC bias applied to an electro-optical crystal that is part of a Mach-Zehnder modulator that generates low-duty-cycle optical pulses for a pulseposition modulation (PPM) optical datacommunication system. In such a system, it is desirable to minimize the transmission of light during the intervals between pulses, and for this purpose, it is necessary to maximize the extinction ratio of the modulator (the ratio between the power transmitted during an “on” period and the power transmitted during an “off” period). The present method is related to prior dither error feedback methods, but unlike in those methods, there is no need for an auxiliary modulation subsystem to generate a dithering signal. Instead, as described below, dither is effected through alternation of the polarity of the modulation signal.

Posted in: Briefs, TSP, Electronics & Computers, Optics, Optics

Fiber-Optic Strain Gauge With High Resolution And Update Rate

Changes in strain are correlated with changes in speckle patterns.

An improved fiber-optic strain gauge is capable of measuring strains in the approximate range of 0 to 50 microstrains with a resolution of 0.1 microstrain. (To some extent, the resolution of the strain gauge can be tailored and may be extensible to 0.01 microstrain.) The total cost of the hardware components of this strain gauge is less than $100 at 2006 prices. In comparison with prior strain gauges capable of measurement of such low strains, this strain gauge is more accurate, more economical, and more robust, and it operates at a higher update rate. Strain gauges like this one are useful mainly for measuring small strains (including those associated with vibrations) in such structures as rocket test stands, buildings, oilrigs, bridges, and dams. The technology was inspired by the need to measure very small strains on structures supporting liquid oxygen tanks, as a way to measure accurately mass of liquid oxygen during rocket engine testing.

Posted in: Briefs, Physical Sciences, Measurements, Fiber optics, Fiber optics, Test equipment and instrumentation

Temperature-Corrected Model of Turbulence in Hot Jet Flows

A standard turbulence model is corrected for total-temperature gradient and compressibility.

An improved correction has been developed to increase the accuracy with which certain formulations of computational fluid dynamics predict mixing in shear layers of hot jet flows. The CFD formulations in question are those derived from the Reynolds-averaged Navier-Stokes equations closed by means of a two-equation model of turbulence, known as the k−ε model, wherein effects of turbulence are summarized by means of an eddy viscosity. The need for a correction arises because it is well known among specialists in CFD that two-equation turbulence models, which were developed and calibrated for room-temperature, low Mach-number, plane-mixing-layer flows, under predict mixing in shear layers of hot jet flows. The present correction represents an attempt to account for increased mixing that takes place in jet flows characterized by high gradients of total temperature. This correction also incorporates a commonly accepted, previously developed correction for the effect of compressibility on mixing.

Posted in: Briefs, TSP, Information Sciences, Computational fluid dynamics, Turbulence

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