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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1970

Effect of filtering on noise and timing in nuclear particle detection

The relations between signal shaping, noise, and timing resolution in nuclear particle detection systems are examined in this paper. Mathematical analysis of five commonly used types of filters leads to numerical results for system noise components arising from sources in the preamplifier, detector, and bias resistors. These results are presented in the form of design curves for the various filters, showing the dependence of each output noise component on both the magnitude of the noise sources and the filter time constants. Three of the filters considered are simple RC types; the remaining two are combinations of delay lines and RC elements. The quantitative calculations specifically assume a silicon detector and a field-effect-transistor preamplifier. Those filters that exhibit bipolar step response are analyzed in terms of crossover timing resolution, based on the earlier noise calculations. Again, the results are summarized in sets of design curves for each filter. Finally, the comparative performance of the various filter types is discussed, and specific examples are given.

Gary, S. A.↗
NASA NTRS1986

Sensitive detection of narrowband pulses

Highly monochromatic signals, such as TV carriers, can be detected sensitively by using a narrow filter (b < or = 1 Hz) and performing power accumulation on its output. If instead a low-duty-cycle pulsed signal of the same total energy is present, the sensitivity of a square law device, followed by a thresholding operation (to eliminate most samples containing only noise), followed by the algorithm to be described, is greater by about 7 dB in typical cases. This is particularly interesting to SETI because such a pulsed signal is exactly what is sent by a rotating beacon with a directional antenna. Such a pulsed signal is, therefore, a good candidate for an extraterrestrial beacon. Software for detecting this signal type is now ready for field testing with the NASA Multichannel Spectrum Analyzer (MCSA).

NASA Discipline Number 52-60↗
NASA NTRS1985

Direct-detection optical communication with color coded pulse position modulation signaling

The performance characteristics of a direct-detection optical communication system which is based on a laser transmitter which produces single light pulses at selected nonoverlapping optical center frequencies are discussed. The signal format, called color coded pulse position modulation (CCPPM), uses more of the total available response bandwidth characteristics of the photodetector than does ordinary PPM signaling. The advantages of CCPPM signaling are obtained at the expense of an increased optical bandwidth of the transmitted signal and a more complicated transmitter and receiver structure. When the signal format is used in conjunction with block length Reed-Solomon codes, high data rates and reliable high-speed optical communications under conditions of optimal energy efficiency are obtained.

Davidson, F.↗
NASA NTRS1989

Digital Integrate-And-Dump Filter With Offset Sampling

Detection of weak signals improved slightly. Digital integrate-and-dump filter proposed for detection of weak rectangular-pulse signals corrupted by additive white Gaussian noise. Theory of filter takes account of degradation of performance caused by offset sampling.

Sadr, R.↗
NASA NTRS1985

Exploring results of the possibility on detecting cosmic ray particles by acoustic way

It has been demonstrated experimentally and theoretically that high energy particles produce detectable sounds in water. However, no one has been able to detect an acoustic signal generated by a high energy cosmic ray particle in water. Results show that transient ultrasonic signals in a large lake or reservoir are fairly complex and that the transient signals under water may arise mainly from sound radiation from microbubbles. This field is not explored in detail. Perhaps, the sounds created by cosmic ray particles hide in these ultrasonic signals. In order to develop the technique of acoustic detection, it is most important to make a thorough investigation of these ultrasonic signals in water.

Jiang, Y.↗
NASA NTRS2004

Signal Processing Variables for Optimization of Flaw Detection in Composites Using Ultrasonic Guided Wave Scanning

This study analyzes the effect of signal processing variables on the ability of the ultrasonic guided wave scan method at NASA Glenn Research Center to distinguish various flaw conditions in ceramic matrix composites samples. In the ultrasonic guided wave scan method, several time- and frequency-domain parameters are calculated from the ultrasonic guided wave signal at each scan location to form images. The parameters include power spectral density, centroid mean time, total energy (zeroth moment), centroid frequency, and ultrasonic decay rate. A number of signal processing variables are available to the user when calculating these parameters. These signal processing variables include 1) the time portion of the time-domain waveform processed, 2) integration type for the properties requiring integrations, 3) bounded versus unbounded integrations, 4) power spectral density window type, 5) and the number of time segments chosen if using the short-time fourier transform to calculate ultrasonic decay rate. Flaw conditions examined included delamination, cracking, and density variation.

Roth, Don J.↗
NASA NTRS1998

Noncontact Acousto-Ultrasonics for Material Characterization

A NdYAG 1064 nm, laser pulse was employed to produce ultrasonic waves in specimens of SiC/SiC and SiC/Ti 6-4 composites which are high temperature materials of interest for aerospace applications. Air coupled transducers were used to detect and collect the signals used for acousto-ultrasonic analysis. Conditions for detecting ultrasonic decay signals were examined. The results were compared to those determined on the same specimens with contact coupling. Some non-contact measurements were made employing conventional air focused detectors. Others were performed with a more novel micromachined capacitance transducer. Concerns of the laser-in technology include potential destructiveness of the laser pulse. Repeated laser pulsing at the same location does lead to deterioration of the ultrasonic signal in some materials, but seems to recover with time. Also, unlike contact AU, the frequency regime employed is a function of laser-material interaction rather than the choice of transducers. Concerns of the air coupled-out technology include the effect of air attenuation. This imposes a practical upper limit to frequency of detection. In the case of the experimental specimens studied ultrasonic decay signals could be imaged satisfactorily.

Kautz, Harold E.↗
NASA NTRS2002

An expert system for fault management assistance on a space sleep experiment

The expert system, Principal Investigator-in-a-box, or [PI], was designed to assist astronauts or other operators in performing experiments outside their expertise. Currently, the software helps astronauts calibrate instruments for a Sleep and Respiration Experiment without contact with the investigator on the ground. It flew on the Space Shuttle missions STS-90 and STS-95. [PI] displays electrophysiological signals in real time, alerts astronauts via the indicator lights when a poor signal quality is detected, and advises astronauts how to restore good signal quality. Thirty subjects received training on the sleep instrumentation and the [PI] interface. A beneficial effects of [PI] and training reduced troubleshooting time. [PI] benefited subjects on the most difficult scenarios, even though its lights were not 100% accurate. Further, questionnaires showed that most subjects preferred monitoring waveforms with [PI] assistance rather than monitoring waveforms alone. This study addresses problems of complex troubleshooting and the extended time between training and execution that is common to many human operator situations on earth such as in power plant operation, and marine exploration.

NASA Discipline Neuroscience↗
NASA NTRS2009

Advanced Laser Based Measurements in Porous Media Combustion

We present measurements using dual-pump dual-broadband coherent anti-Stokes Raman scattering spectroscopy (DP-DBB-CARS) inside a porous media burner. This work continues our previous measurements in such combustion systems. The existing setup was significantly modified with the aim of providing improved data quality and data rate, reduction of interferences and additional species information. These changes are presented and discussed in detail. The CARS technique was expanded to a dual-pump dual-broadband CARS system which in principle enables acquisition of temperatures together with relative H2/N2- and O2/N2- species concentrations. Experimental complexity was reduced by the use of a modified spectrometer enabling the detection of both signals, vibrational and rotational CARS, with only one detection system.

Tedder, Sarah A.↗
NASA NTRS1980

The recognition of extraterrestrial artificial signals

Considerations in the design of receivers for the detection and recognition of artificial microwave signals of extraterrestrial origin are discussed. Following a review of the objectives of SETI and the probable reception and detection characteristics of extraterrestrial signals, means for the improvement of the sensitivity, signal-to-noise ratios and on-line data processing capabilities of SETI receivers are indicated. The characteristics of the signals likely to be present at the output of an ultra-low-noise microwave receiver are then examined, including the system background noise, terrestrial radiations, astrophysical radiations, accidental artificial radiations of terrestrial origin, and intentional radiations produced by humans and by extraterrestrial intelligence. The classes of extraterrestrial signals likely to be detected, beacons and leakage signals, are considered, and options in the specification of gating and thresholding for a high-spectral resolution, high-time-resolution signal discriminator are indicated. Possible tests for the nonhuman origin of a received signal are also pointed out.

Seeger, C. L.↗
NASA NTRS1992

Detecting Lamb waves with broadband acousto-ultrasonic signals in composite structures

Lamb waves can be produced and detected in ceramic matrix composites (CMC) and metal matrix composites (MMC) plates using the acousto-ultrasonic configuration employing broadband transducers. Experimental dispersion curves of lowest symmetric and lowest antisymmetric modes behave in a manner analogous to the graphite/polymer theoretical curves. In this study a basis has been established for analyzing Lamb wave velocities for characterizing composite plates. Lamb wave disperison curves and group velocities were correlated with variations in axial stiffness and shear stiffness in MMC and CMC. For CMCs, interfacial shear strength was also correlated with the first antisymmetric Lamb mode.

Kautz, Harold E.↗
NASA NTRS2005

Lunar Seismic Detector to Advance the Search for Strange Quark Matter

Detection of small seismic signals on the Moon are needed to study lunar internal structure and to detect possible signals from Strange Quark m&er transit events. The immediate objective is to create a prototype seismic detector using a tunnel diode oscillator with a variable capacitor attached to a proof mass. The device is designed to operate effectively on the Moon, which requires a low power consumption to operate through lunar night, while preserving sensitivity. The goal is capacitance resolution of better than 1 part in 10' and power consumption of less than 1 watt.

Galitzki, Nicholas B.↗
DOE OSTI2022

Expediting DECam Multimessenger Counterpart Searches with Convolutional Neural Networks

Searches for counterparts to multimessenger events with optical imagers use difference imaging to detect new transient sources. However, even with existing artifact-detection algorithms, this process simultaneously returns several classes of false positives: false detections from poor-quality image subtractions, false detections from low signal-to-noise images, and detections of preexisting variable sources. Currently, human visual inspection to remove the false positives is a central part of multimessenger follow-up observations, but when next generation gravitational wave and neutrino detectors come online and increase the rate of multimessenger events, the visual inspection process will be prohibitively expensive. We approach this problem with two convolutional neural networks operating on the difference imaging outputs. The first network focuses on removing false detections and demonstrates an accuracy of 92% on our data set. The second network focuses on sorting all real detections by the probability of being a transient source within a host galaxy and distinguishes between various classes of images that previously required additional human inspection. We find the number of images requiring human inspection will decrease by a factor of 1.5 using our approach alone and a factor of 3.6 using our approach in combination with existing algorithms, facilitating rapid multimessenger counterpart identification by the astronomical community.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1989

Design and simulated performance of a CARS spectrometer for dynamic temperature measurements using electronic heterodyning

A new design for generating CARS signals and for the detection and processing of these signals is presented and evaluated. The design is based on electronic heterodyning of the CARS spectrum of nitrogen at two selected narrowband frequencies, ratioing the resulting signal strengths, and comparing this ratio with a theoretically derived temperature scale. A reference cell is incorporated into the design for system calibration and for accurate temperature measurements. The spectrometer is found capable of measuring temperature in the submillisecond time scale with an accuracy of 10 percent in the 1000-2000 K temperature range. A typical result using the Hg(x)Cd(1-x)Te photomixer for T = 1500 K, Delta T = 50 K is a SNR of 21 dB and a data collection rate of 300 Hz.

Deen, M. Jamal↗
NASA NTRS2004

Pseudo-Random Modulation of a Laser Diode for Generating Ultrasonic Longitudinal Waves

Laser generated ultrasound systems have historically been more complicated and expensive than conventional piezoelectric based systems, and this fact has relegated the acceptance of laser based systems to niche applications for which piezoelectric based systems are less suitable. Lowering system costs, while improving throughput, increasing ultrasound signal levels, and improving signal-to-noise are goals which will help increase the general acceptance of laser based ultrasound. One current limitation with conventional laser generated ultrasound is a material s damage threshold limit. Increasing the optical power to generate more signal eventually damages the material being tested due to rapid, high heating. Generation limitations for laser based ultrasound suggests the use of pulse modulation techniques as an alternate generation method. Pulse modulation techniques can spread the laser energy over time or space, thus reducing laser power densities and minimizing damage. Previous experiments by various organizations using spatial or temporal pulse modulation have been shown to generate detectable surface, plate, and bulk ultrasonic waves with narrow frequency bandwidths . Using narrow frequency bandwidths improved signal detectability, but required the use of expensive and powerful lasers and opto-electronic systems. The use of a laser diode to generate ultrasound is attractive because of its low cost, small size, light weight, simple optics and modulation capability. The use of pulse compression techniques should allow certain types of laser diodes to produce usable ultrasonic signals. The method also does not need to be limited to narrow frequency bandwidths. The method demonstrated here uses a low power laser diode (approximately 150 mW) that is modulated by controlling the diode s drive current and the resulting signal is recovered by cross correlation. A potential application for this system which is briefly demonstrated is in detecting signals in thick composite materials where attenuation is high and signal amplitude and bandwidth are at a premium.

Madaras, Eric I.↗
NASA NTRS1993

Upper limits for gravitational radiation from supermassive coalescing binaries

We report a search for waves from supermassive coalescing binaries using a 10.5 day Pioneer 10 data set taken in 1988. Depending on the time to coalescence, the initial frequency of the wave, and the length of the observing interval, a coalescing binary waveform appears in the tracking record either as a sinusoid, a 'chirp', or as a more complicated signal. We searched our data for coalescing binary waveforms in all three regimes. We successfully detected a (fortuitous) 'chirp' signal caused by the varying spin rate of the spacecraft; this nicely served as a calibration of the data quality and as a test of our analysis procedures on real data. We did not detect any signals of astronomical origin in the millihertz band to an upper limit of about 7 x 10 exp -15 (rms amplitude). This is the first time spacecraft Doppler data have been analyzed for coalescing binary waveforms, and the upper limits reported here are the best to date for any waveform in the millihertz band.

Anderson, J. D.↗