Tech Briefs

Efficient Ionizer for an Array of Mass Spectrometers

Electron- and ion-beam optics are designed to maximize generation and extraction of ions.An electron-beam ionizer has been designed to deliver ions to the entrance apertures of nine miniature quadrupole mass spectrometers in an array. A similar electron-beam ionizer could also be designed for an array of more or fewer mass spectrometers. Principal issues that had to be addressed in formulating the design were (1) generation of a collimated, suitably dimensioned electron beam that passes near all the entrance apertures so that ions are generated for each aperture at a sufficient rate; (2) application of suitable extraction potentials to nearby, suitably configured electrodes so that a large flux of ions can be extracted from the electron-beam region wherein the analyte is ionized; and (3) choosing a configuration and potentials for a system of electrostatic lenses (that is, assemblies of electrodes and apertures) to transport and focus the extracted ions into beams of desired diameters and kinetic energies that impinge on the entrance apertures of the mass spectrometers at the desired angles.

Posted in: Briefs, Physical Sciences

Read More >>

Analyzing Rocket Exhaust by Atomic-Absorption Spectroscopy

To save time and money, instrumentation was assembled from commercially available parts. A computer-controlled instrumentation system has been developed for use in measuring concentrations of various atomic species in the exhaust gases of a space-shuttle main engine on a test stand. The system is based on established techniques of atomic-absorption spectroscopy (AAS). Although the design of the system is specific to this rocket-engine-testing application, it may be adaptable to other applications that involve similar geometry, physical conditions, and chemical constituents of flowing gases.

Posted in: Briefs, TSP, Physical Sciences

Read More >>

Adjustable Optics for Spectral Analysis of Rocket Exhaust

Source and receiver probes are aimed along a common line of sight.The figure presents additional information on the optics of the atomic-absorption-spectroscopy (AAS) system described in the preceding article. The optics include (1) a periscopic optical subsystem for access to a measurement optical axis in a plane different from that of the input and output optical axes and (2) mechanical and optoelectronic features for aligning the input and output optics.

Posted in: Briefs, TSP, Physical Sciences

Read More >>

Thickness-Independent Ultrasonic Characterization of Tubes

This single-transducer technique was previously applied to plates only.A technique for ultrasonic characterization of plates has been extended to tubes and curved structures in general. In this technique, as explained in more detail below, one performs measurements that yield a thickness-independent value of local through-the-thickness speed of sound in a specimen. From such measurements at numerous locations across the specimen, one can construct a map of velocity as a function of location. The gradients of velocity indicated by such a map indicate through-the-thickness-averaged microstructural parameters that affect the speed of sound. Such parameters include the pore volume fraction, mass density, fiber volume fraction (in the case of a composite material), and chemical composition.

Posted in: Briefs, TSP, Physical Sciences

Read More >>

Detecting Metal Ions by Voltammetry Using Diamond Electrodes

Multiple ion species can be detected in a single voltammetric scan over a wide potential range. Experiments have demonstrated the feasibility of detecting multiple species of toxic metal ions and other ions of interest dissolved in water, by means of voltammetry with electrically conductive artificial diamond electrodes. Diamond is attractive as an electrode material because it is highly chemically stable and exhibits the greatest useable range of potential (from +2 to –2 V in aqueous solution) than any known material.

Posted in: Briefs, Physical Sciences

Read More >>

Preconditioning the Helmholtz Equation for a 2-D Duct

Numerical solutions converge quickly to exact steady-state solutions.A preconditioning technique has been developed for numerical solution of the Helmholtz equation as applied to the steady-state propagation of sound in a semi-infinite, two-dimensional (2-D) rigid duct. As explained below, the technique involves the use of two pseudo-time parameters in a finite-difference approximation of the equation that describes the propagation of sound. The use of these parameters makes the solution proceed much faster than in older transient- and steady-state-analysis-based numerical solution methods.

Posted in: Briefs, TSP, Information Sciences

Read More >>

Analytic Technique for Separation of Cochannel FM Signals

In the absence of noise, two signals can be separated perfectly. A digital processing technique for separating two cochannel frequency-modulation (FM) signals involves a partial algebraic solution that gives the phases of the two signals to within one of two possibilities, plus the use of a two-state trellis algorithm to trace the most likely correct sequence of possibilities. Other techniques for separating cochannel FM signals do not yield perfect separation under any circumstances; however, the present technique can yield perfect separation in the absence of noise.

Posted in: Briefs, Information Sciences

Read More >>

The U.S. Government does not endorse any commercial product, process, or activity identified on this web site.