Tech Briefs

Interferometric Quantum-Nondemolition Single-Photon Detectors

These detectors would function independently of frequency.

NASA’s Jet Propulsion Laboratory, Pasadena, California

Two interferometric quantum-nondemolition (QND) devices have been proposed: (1) a polarization-independent device and (2) a polarization-preserving device. The prolarization-independent device works on an input state of up to two photons, whereas the polarization-preserving device works on a superposition of vacuum and single-photon states. The overall function of the device would be to probabilistically generate a unique detector output only when its input electromagnetic mode was populated by a single photon, in which case its output mode would also be populated by a single photon.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Measurements, Lasers

Ring-Down Spectroscopy for Characterizing a CW Raman Laser

Parameters of operation can be obtained from a single ring-down scan.

NASA’s Jet Propulsion Laboratory, Pasadena, California

A relatively simple technique for characterizing an all-resonant intracavity continuous- wave (CW) solid-state Raman laser involves the use of ring-down spectroscopy. As used here, “characterizing” signifies determining such parameters as threshold pump power, Raman gain, conversion efficiency, and quality factors (Q values) of the pump and Stokes cavity modes.

Posted in: Briefs, ptb catchall, Tech Briefs, Photonics, Calibration, Lasers, Spectroscopy

Advances in Measurement of Skin Friction in Airflow

This system implements a combination of established experimental techniques and advanced image processing.

The surface interferometric skin-friction (SISF) measurement system is an instrument for determining the distribution of surface shear stress (skin friction) on a wind-tunnel model. The SISF system utilizes the established oil-film interference method, along with advanced image-data-processing techniques and mathematical models that express the relationship between interferograms and skin friction, to determine the distribution of skin friction over an observed region of the surface of a model during a single wind-tunnel test.

Posted in: Briefs, Test & Measurement, Mathematical models, Test equipment and instrumentation, Wind tunnel tests, Aerodynamics

Calibration Test Set for a Phase-Comparison Digital Tracker

Four equal-amplitude signals are generated at selectable phase increments of 0.1°.

An apparatus that generates four signals at a frequency of 7.1 GHz having precisely controlled relative phases and equal amplitudes has been designed and built. This apparatus is intended mainly for use in computer-controlled automated calibration and testing of a phase-comparison digital tracker (PCDT) that measures the relative phases of replicas of the same Xband signal received by four antenna elements in an array. (The relative direction of incidence of the signal on the array is then computed from the relative phases.) The present apparatus can also be used to generate precisely phased signals for steering a beam transmitted from a phased antenna array.

Posted in: Briefs, TSP, Electronics & Computers, Calibration, Antennas, Test equipment and instrumentation

Arrays of Miniature Microphones for Aeroacoustic Testing

MEMS microphones are mounted on flexible printed-circuit boards.

A phased-array system comprised of custom-made and commercially available microelectromechanical system (MEMS) silicon microphones and custom ancillary hardware has been developed for use in aeroacoustic testing in hard-walled and acoustically treated wind tunnels. Recent advances in the areas of multi-channel signal processing and beam forming have driven the construction of phased arrays containing ever-greater numbers of microphones. Traditional obstacles to this trend have been posed by (1) the high costs of conventional condenser microphones, associated cabling, and support electronics and (2) the difficulty of mounting conventional microphones in the precise locations required for high-density arrays. The present development overcomes these obstacles.

Posted in: Briefs, Electronics & Computers, Microelectromechanical devices, Acoustics, Test equipment and instrumentation, Wind tunnel tests

Wireless Acoustic Measurement System

This system supplants older, less-capable, cable-connected systems.

A prototype wireless acoustic measurement system (WAMS) is one of two main subsystems of the Acoustic Prediction/ Measurement Tool, which comprises software, acoustic instrumentation, and electronic hardware combined to afford integrated capabilities for predicting and measuring noise emitted by rocket and jet engines. The other main subsystem is described in the article on page 24.

Posted in: Briefs, Electronics & Computers, Acoustics, Noise measurement, Jet engines, Rocket engines, Test equipment and instrumentation

Spiral Orbit Tribometer

Friction and lubricant degradation rate can be quantified rapidly.

The spiral orbit tribometer (SOT) bridges the gap between full-scale life testing and typically unrealistic accelerated life testing of ball-bearing lubricants in conjunction with bearing ball and race materials. The SOT operates under realistic conditions and quickly produces results, thereby providing information that can guide the selection of lubricant, ball, and race materials early in a design process.

Posted in: Briefs, TSP, Mechanical Components, Mechanics, Life cycle analysis, Tribology, Bearings, Performance tests, Test equipment and instrumentation

Predicting Rocket or Jet Noise in Real Time

Measurement data can be analyzed in real time.

A semi-empirical theoretical model and a C++ computer program that implements the model have been developed for use in predicting the noise generated by a rocket or jet engine. The computer program, entitled the Realtime Rocket and Jet Engine Noise Analysis and Prediction Software, is one of two main subsystems of the Acoustic Prediction/Measurement Tool, which comprises software, acoustic instrumentation, and electronic hardware combined to afford integrated capabilities for real-time prediction and measurement of noise emitted by rocket and jet engines. [The other main subsystem, consisting largely of acoustic instrumentation and electronic hardware, is described in “Wireless Acoustic Measurement System,” which appears elsewhere in this section.

Posted in: Briefs, Information Sciences, Prognostics, Acoustics, Noise measurement, Jet engines, Rocket engines

Computational Workbench for Multibody Dynamics

PyCraft is a computer program that provides an interactive, workbench-like computing environment for developing and testing algorithms for multibody dynamics. Examples of multibody dynamic systems amenable to analysis with the help of PyCraft include land vehicles, spacecraft, robots, and molecular models. PyCraft is based on the Spatial-Operator-Algebra (SOA) formulation for multibody dynamics. The SOA operators enable construction of simple and compact representations of complex multibody dynamical equations. Within the PyCraft computational workbench, users can, essentially, use the high-level SOA operator notation to represent the variety of dynamical quantities and algorithms and to perform computations interactively. PyCraft provides a Python-language interface to underlying C++ code. Working with SOA concepts, a user can create and manipulate Python-level operator classes in order to implement and evaluate new dynamical quantities and algorithms. During use of PyCraft, virtually all SOA-based algorithms are available for computational experiments.

Posted in: Briefs, TSP, Software, CAD, CAM, and CAE, Mathematical models, Test equipment and instrumentation

SiC Multi-Chip Power Modules as Power-System Building Blocks

Fault-tolerant power-supply systems could be constructed and expanded relatively inexpensively.

The term “SiC MCPMs” (wherein “MCPM” signifies “multi-chip power module”) denotes electronic power-supply modules containing multiple silicon carbide power devices and silicon-on-insulator (SOI) control integrated-circuit chips. SiC MCPMs are being developed as building blocks of advanced expandable, reconfigurable, fault-tolerant power-supply systems. Exploiting the ability of SiC semiconductor devices to operate at temperatures, breakdown voltages, and current densities significantly greater than those of conventional Si devices, the designs of SiC MCPMs and of systems comprising multiple SiC MCPMs are expected to afford a greater degree of miniaturization through stacking of modules with reduced requirements for heat sinking. Moreover, the higher-temperature capabilities of SiC MCPMs could enable operation in environments hotter than Si-based power systems can withstand.

Posted in: Briefs, Semiconductors & ICs, Downsizing, Integrated circuits, Semiconductor devices, Thermal management

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