Tech Briefs

Printed Multi-Turn Loop Antennas for RF Biotelemetry

Compact antennas afford hemispherical coverage at any linear polarization.

Printed multi-turn loop antennas have been designed for contactless powering of, and reception of radio signals transmitted by, surgically implantable biotelemetric sensor units operating at frequencies in the vicinity of 300 MHz. In the original intended application of these antennas, the sensor units would be microelectromechanical systems (MEMS)-based devices now being developed for monitoring physiological parameters of humans during space flights. However, these antennas and the sensor units could just as well be used for physiological monitoring on Earth.

Posted in: Briefs, TSP, Bio-Medical, Medical, Antennas, Microelectricmechanical device, Microelectromechanical devices, Telemetry, Antennas, Microelectricmechanical device, Microelectromechanical devices, Telemetry, Human factors

Retaining Rings for Industrial Fastening Applications

Retaining rings are selected based on material, finish, and a variety of application parameters.

A discussion of retaining rings inevitably must begin with a debunking of myths; namely, that one style of retaining ring will function better than all other types in all instances. No one retaining ring style is better than another. Rather, the parameters of an application actually determine which retaining ring is best to use, and this can vary from assembly to assembly. Selecting the correct type of retaining ring based on variables such as installation/removal requirements, anticipated thrust load, and end-play take-up can ensure the retaining ring chosen will perform reliably, while significantly reducing fastener costs.

Posted in: Briefs, Mechanical Components, Mechanics, Fastening, Parts

Glass/BNNT Composite for Sealing Solid Oxide Fuel Cells

Boron nitride nanotubes contribute to strength and fracture toughness.

A material consisting of a barium calcium aluminosilicate glass reinforced with 4 weight percent of boron nitride nanotubes (BNNTs) has shown promise for use as a sealant in planar solid oxide fuel cells (SOFCs). The composition of the glass in question in mole percentages is 35BaO + 15CaO + 5Al2O3 + 10B2O3 + 35SiO2. The glass was formulated to have physical and chemical properties suitable for use as a planar- SOFC sealant, but has been found to be deficient in one aspect: it is susceptible to cracking during thermal cycling of the fuel cells. The goal in formulating the glass/BNNT composite material was to (1) retain the physical and chemical advantages that led to the prior selection of the barium calcium aluminosilicate glass as the sealant while (2) increasing strength and fracture toughness so as to reduce the tendency toward cracking.

Posted in: Briefs, TSP, Materials, Fuel cells, Composite materials, Glass, Nanomaterials

Improved Single-Source Precursors for Solar-Cell Absorbers

Deposition properties and final compositions can be tailored.

Improved single-source precursor compounds have been invented for use in spray chemical vapor deposition (spray CVD) of chalcopyrite semiconductor absorber layers of thin-film solar photovoltaic cells. The semiconductors in question are denoted by the general formula CuInxGa1–xSySe2–y, where x≤1 and y≤2. These semiconductors have been investigated intensively for use in solar cells because they exhibit longterm stability and a high degree of tolerance of radiation, and their bandgaps correlate well with the maximum photon power density in the solar spectrum. In addition, through selection of the proportions of Ga versus In and S versus Se, the bandgap of CuInxGa1–xSySe2–y can be tailored to a value between 1.0 and 2.4 eV, thus making it possible to fabricate cells containing high and/or graded bandgaps.

Posted in: Briefs, TSP, Materials, Solar energy, Semiconductors

Spray CVD for Making Solar-Cell Absorber Layers

Spray CVD combines the advantages of metalorganic CVD and spray pyrolysis.

Spray chemical vapor deposition (spray CVD) processes of a special type have been investigated for use in making CuInS2 absorber layers of thin-film solar photovoltaic cells from either of two subclasses of precursor compounds:
[(PBu3) 2Cu(SEt)2In(SEt)2] or [(PPh3)2Cu(SEt)2 In(SEt)2] . CuInS2 is a member of the class of chalcopyrite semiconductors described in the immediately preceding article. [(PBu3)2Cu(SEt)2In(SEt)2] and [(PPh3)2 Cu(SEt)2In(SEt)2] are members of the class of single-source precursors also described in the preceding article.

Posted in: Briefs, TSP, Materials, Solar energy, Spraying, Chemicals, Gases

Making Ternary Quantum Dots From Single-Source Precursors

Relative to a prior process, this process is simpler and safer.

A process has been devised for making ternary (specifically, CuInS2) nanocrystals for use as quantum dots (QDs) in a contemplated next generation of highefficiency solar photovoltaic cells. The process parameters can be chosen to tailor the sizes (and, thus, the absorption and emission spectra) of the QDs.

Posted in: Briefs, TSP, Materials, Solar energy, Product development, Fabrication, Refractory materials

A Method of Assembling Compact Coherent Fiber-Optic Bundles

The method is based on hexagonal close packing.

A method of assembling coherent fiber-optic bundles in which all the fibers are packed together as closely as possible is undergoing development. The method is based straightforwardly on the established concept of hexagonal close packing; hence, the development efforts are focused on fixtures and techniques for practical implementation of hexagonal close packing of parallel optical fibers.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Fiber optics, Fiber optics, Assembling

Manufacturing Diamond Under Very High Pressure

Pure or doped diamond is crystallized from molten carbon and in solid state.

A process for manufacturing bulk diamond has been made practical by the invention of the High Pressure and Temperature Apparatus capable of applying the combination of very high temperature and high pressure needed to melt carbon in a sufficiently large volume. The rate of growth achievable in this process is about ten times the rate achievable in older processes. Depending on the starting material and temperature-and-pressure schedule, this process can be made to yield diamond in any of a variety of scientifically and industrially useful forms, including monocrystalline, polycrystalline, pure, doped, and diamond composite. (Doping makes it possible to impart desired electrical and optical properties, including semiconductivity and color.) The process can also be used to make cubic boron nitride.

Posted in: Briefs, TSP, Manufacturing & Prototyping, Manufacturing processes

Compact Fuel-Cell System Would Consume Neat Methanol

Size, mass, and parasitic power consumption would be reduced.

In a proposed direct methanol fuelcell electric- power-generating system, the fuel cells would consume neat methanol, in contradistinction to the dilute aqueous methanol solutions consumed in prior direct methanol fuel-cell systems. The design concept of the proposed fuel-cell system takes advantage of (1) electro-osmotic drag and diffusion processes to manage the flows of hydrogen and water between the anode and the cathode and (2) evaporative cooling for regulating temperature. The design concept provides for supplying enough water to the anodes to enable the use of neat methanol while ensuring conservation of water for the whole fuel-cell system. By rendering unnecessary some of the auxiliary components and subsystems needed in other direct methanol fuel-cell systems for redistributing water, diluting methanol, and regulating temperature, this fuel-cell design would make it possible to construct a more compact, less massive, more energy-efficient fuel-cell system.

Posted in: Briefs, TSP, Physical Sciences, Downsizing, Water, Electric power, Fuel cells, Methanol, Product development

Ring-Resonator/Sol-Gel Interferometric Immunosensor

Light would make multiple passes through the sensing volume.

A proposed biosensing system would be based on a combination of (1) a sensing volume containing antibodies immobilized in a sol-gel matrix and (2) an optical interferometer having a ring resonator configuration. The antibodies would be specific to an antigen species that one seeks to detect. The binding of the antigens to the immobilized antibodies would change the index of refraction of the sensing volume, which would be mounted in one of the interferometer arms. The interferometer would measure the change in the index of refraction, thereby indirectly measuring the concentration of the antigen species of interest.

Posted in: Briefs, TSP, Physical Sciences, Measurements, Medical, health, and wellness, Test equipment and instrumentation

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