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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

An electro-optic resonant modulator for coherent optical communication

A resonant cavity electro-optic phase modulator has been designed and implemented to operate at a data rate of 10 Mbps. The modulator consists of an electro-optic crystal located in a highly resonant cavity. The cavity is electro-optically switched on and off resonance, and the phase dispersion near the cavity resonance provides the output phase modulation. The performance of the modulator was measured by first heterodyne detecting the signal to an intermediate frequency, and measuring the spectral characteristics using an RF spectrum analyzer. The measured phase shift is shown to be in good agreement with the theoretical predictions. Further theoretical analysis shows that the design of the modulator can be scaled to operate at 100 Mbps.

Robinson, D. L.↗
NASA NTRS1992

Simultaneous equatorial measurements of waves and precipitating electrons in the outer radiation belt

Simultaneous wave and precipitating electron measurements near the equator in the outer radiation belt have been made from the CRRES satellite. The electron data of principal concern here were acquired in and about the loss cone with narrow angular resolution spectrometers covering the energy range 340 eV to 5 MeV. The wave data included electric field measurements spanning frequencies from 5 Hz to 400 kHz and magnetic field measurements from 5 Hz to 10 kHz. This paper presents examples in which the variations in electron fluxes in the loss cone and the wave intensities were correlated. These variations in electron flux were confined to pitch angles less than about 30 deg. The association between the flux enhancements and the waves is consistent with wave-induced pitch angle diffusion processes.

Imhof, W. L.↗
NASA NTRS1991

Infrared lidar windshear detection for commercial aircraft and the edge technique, a new method for atmospheric wind measurement

The edge technique, a new method for measuring small frequency shifts, is described. The technique allows high-accuracy measurement of atmospheric winds (0.2-1 m/s) with a high vertical resolution (10 m) using currently available technology. With the edge technique, a lidar system can be used to obtain range resolved measurements of the wind in the atmosphere from the ground, aircraft, or spaceborne platforms. The edge technique can be used with different lasers over a broad range of wavelengths.

Targ, Russell↗
DOE OSTI2021

“Frequency” and the PMU standard

The Phasor Measurement Unit (PMU) has revolutionized power system management by providing high-resolution, time-stamped, spatial, and temporal measure¬ments of the state of power systems. However, the standards defining the measured quantities have ambiguities that cause uncertainty, irreproducibility, and loss of interoperability during periods of change where the measurements should have the greatest value. This paper examines PMU frequency measurement to highlight the problems. It develops some suggestions for the scope and the next evolutionary improvements to the documentary standards. The aim is to improve the meaningfulness and trustworthiness of dynamic power system measurements.

Frequency, rate of change of frequency, definition↗
NASA NTRS2016

RFI and Remote Sensing of the Earth from Space

Passive microwave remote sensing of the Earth from space provides information essential for understanding the Earth's environment and its evolution. Parameters such as soil moisture, sea surface temperature and salinity, and profiles of atmospheric temperature and humidity are measured at frequencies determined by the physics (e.g. sensitivity to changes in desired parameters) and by the availability of suitable spectrum free from interference. Interference from manmade sources (radio frequency interference) is an impediment that in many cases limits the potential for accurate measurements from space. A review is presented here of the frequencies employed in passive microwave remote sensing of the Earth from space and the associated experience with RFI.

RFI↗
NASA NTRS1980

Coherence bandwidth loss in transionospheric radio propagation

In this report a theoretical model is developed that predicts the single-point, two-frequency coherence function for transionospheric radio waves. The theoretical model is compared to measured complex frequency correlation coefficients using data from the seven equispaced, phase-coherent UHF signals transmitted by the Wideband satellite. The theory and data are in excellent agreement. The theory is critically dependent upon the power-law index, and the frequency coherence data clearly favor the comparatively small spectral indices that have been consistently measured from the wideband satellite phase data. A model for estimating the pulse delay jitter induced by the coherence bandwidth loss is also developed and compared with the actual delay jitter observed on synthesized pulses obtained from the Wideband UFH comb. The results are in good agreement with the theory. The results presented in this report, which are based on an asymptotic theory, are compared with the more commonly used quadratic theory. The model developed and validated in this report can be used to predict the effects of coherence bandwidth loss in disturbed nuclear environments. Simple formulas for the resultant pulse delay jitter are derived that can be used in predictive codes.

Rino, C. L.↗
NASA NTRS1981

Two-frequency /Delta k/ microwave scatterometer measurements of ocean wave spectra from an aircraft

A technique for remotely sensing the large-scale gravity wave spectrum on the ocean surface using a two frequency (Delta k) microwave scatterometer has been demonstrated from stationary platforms and proposed from moving platforms. This measurement takes advantage of Bragg type resonance matching between the electromagnetic wavelength at the difference frequency and the length of the large-scale surface waves. A prominent resonance appears in the cross product power spectral density (PSD) of the two backscattered signals. Ku-Band aircraft scatterometer measurements were conducted by NASA in the North Sea during the 1979 Maritime Remote Sensing (MARSEN) experiment. Typical examples of cross product PSD's computed from the MARSEN data are presented. They demonstrate strong resonances whose frequency and bandwidth agree with the surface characteristics and the theory. Directional modulation spectra of the surface reflectivity are compared to the gravity wave spectrum derived from surface truth measurements.

Johnson, J. W.↗
DOE OSTI2024

Measurement of the muon spin precession frequency using the straw tracking detectors at the Fermilab Muon g-2 experiment

The measurement of the anomalous magnetic dipole moment of the muon ($a_{\mu}$) has long stood as an excellent precision test of the Standard Model (SM). The Fermilab Muon g-2 experiment has recently finished data-taking and in July 2023 published its latest determination of $a_\mu$ with a world-leading precision of 0.2\,ppm. In this publication, it surpassed the systematic uncertainty goal defined in the TDR. The analyses of a dataset approximately four times larger than this recent publication is now underway. The principle measurement of the Muon g-2 experiment measures $a_{\mu}$ by taking the ratio of two frequencies; the anomalous precession frequency ($\omega_a$) and the muon-weighted magnetic field of the experiment's storage ring measured from the precession frequency of protons in water using nuclear magnetic resonance (NMR) probes. In all publications to date, $\omega_a$ has been determined using energy deposits in the 24 calorimeters. However, the Fermilab experiment has t wo straw tracker detectors measuring the time and momentum of charged particles which can in principle also be used to to measure $\omega_a$ and such a measurement can provide an invaluable cross-check of the calorimeter result with different, and reduced, systematic uncertainties. This thesis presents the first (blinded) determination of $\omega_a$ using just charged tracks from the straw tracking detectors as opposed to calorimeter energy deposits. This analysis was undertaken using the Run-2/3 dataset which represents approximately 25\% of the final dataset. A total uncertainty of 2.19\,ppm on $\omega_a$ was obtained which is dominated by the statistical uncertainty of 2.16\,ppm. Additionally two new methodologies important to the analysis of the straw tracking data have been developed: one to better determine the track arrival time ($t_0$) and one to determine the level of pileup in the tracking detectors. The new $t_0$ algorithm which incorporates angular information improves t he resolution on the determination of the $t_0$ by a factor of two and results in 19\% more tracks being successfully reconstructed. The data from the trackers is also used to determine the beam profile that weights the magnetic field in the determination of $a_\mu$ and in determining several of the systematic uncertainties in the calorimeter-based $\omega_a$ analysis. A detailed study of the impact of the internal alignment of the tracker, the $t_0$ and pileup on the determination of the beam position was undertaken and propagated through to an uncertainty in the $\omega_a$ determination. These uncertainties were used in the Fermilab Muon g-2 experiment's recent publication in Phys. Rev. Lett.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1978

Internal friction Q factor measurements in lunar rocks

In order to better interpret recently reported values for the variation of seismic Q as a function of depth below the lunar surface, we have developed apparatus and made laboratory measurements of Q as a function of hydrostatic pressure, temperature and frequency. Our measurements of the Q associated with shear deformations have demonstrated that the large difference in Q between well outgassed and volatile rich rocks persists to pressures corresponding to a depth of at least 50 km. Here we report new measurements of Q as a function of temperature, on the development of techniques to measure the Q associated with extensional deformations under hydrostatic pressure, on the derivation of theoretical relations between our laboratory Q values and the attenuation coefficient of seismic waves, and on the development of a model for mechanism of adsorption.

Tittmann, B. R.↗
NASA NTRS2001

Supersonic Pulsed Injection

An injector has been developed to provide high-speed high-frequency (order 10 kHz) pulsed a supersonic crossflow. The injector nozzle is formed between the fixed internal surface of the nozzle and a freely rotating three- or four-sided wheel embedded within the device. Flow-induced rotation of the wheel causes the nozzle throat to open and close at a frequency proportional to the speed of sound of the injected gas. Measurements of frequency and mass flow rate as a function of supply pressure are discussed for various injector designs. Preliminary results are presented for wall-normal injection of helium into a Mach-2 ducted airflow. The data include schlieren images in the injectant plume in a plane normal to the flow, downstream of injection.

Cutler, A. D.↗
NASA NTRS2010

The NASA Langley Isolator Dynamics Research Lab

The Isolator Dynamics Research Lab (IDRL) is under construction at the NASA Langley Research Center in Hampton, Virginia. A unique test apparatus is being fabricated to support both wall and in-stream measurements for investigating the internal flow of a dual-mode scramjet isolator model. The test section is 24 inches long with a 1-inch by 2-inch cross sectional area and is supplied with unheated, dry air through a Mach 2.5 converging-diverging nozzle. The test section is being fabricated with two sets (glass and metallic) of interchangeable sidewalls to support flow visualization and laser-based measurement techniques as well as static pressure, wall temperature, and high frequency pressure measurements. During 2010, a CFD code validation experiment will be conducted in the lab in support of NASA s Fundamental Aerodynamics Program. This paper describes the mechanical design of the Isolator Dynamics Research Lab test apparatus and presents a summary of the measurement techniques planned for investigating the internal flow field of a scramjet isolator model.

Middleton, Troy F.↗
NASA NTRSDate not supplied

2-D Lunar Microwave Radiance Observations From the NOAA-20 ATMS

Reported here are disk-integrated Moon surface microwave brightness temperature (Tb) retrievals covering the frequency range of 23–183 GHz. FullMoon observations obtained from the advanced technology microwave sounder (ATMS) onboard the NOAA-20 satellite during a special spacecraft pitch–maneuver operation forms the basis of the retrievals. Instrument nonlinearity, Earth sidelobe contamination, cosmic background radiation, and reflector thermal emission corrections are applied to the observations to obtain accurate values of the Moon’s Tb at all frequencies. The measured full Moon Tb ranges from ~240 to 293 K with frequency increases from 23 to 183 GHz. A clear frequency trend is detected when the brightness temperature increases.

Hu Yang↗
NASA NTRS2024

Piezoelectric impedance-based high-accuracy damage identification using sparsity conscious multi-objective optimization inverse analysis

Two elements are essential in structural health monitoring utilizing dynamic responses: response measurement with high-frequency contents, i.e., small characteristic wavelengths, that can adequately reflect damage features, and effective inverse identification analysis that is however oftentimes under-determined. The advancement of smart structure integration has led to active interrogation through frequency-sweeping piezoelectric impedance measurement at high frequency range. In this research we develop a multi-objective optimization formulation for the identification of damage location and severity utilizing piezoelectric impedance. While one optimization objective is to match the response measurement with finite element model prediction in the damage parametric space, the other is the number of locations of damage, i.e., the sparsity of damage index as the solution vector, since damage usually occurs within a small number of locations. This multi-objective formulation fits well the under-determined nature of damage identification, as it naturally provides multiple solutions as basis for further elucidation. The challenge remaining is how to find a small solution set that can include the actual damage scenario. Here we develop a novel inverse identification framework utilizing the intelligent swarm optimizer which possesses flexibility for enhancement. We first embed a sparsity enforcement process into the population generation of the optimizer, which yields a solution repository intrinsically possessing sparsity. We then apply reinforcement learning so the agents can adaptively opt for local strategies with the aim of enriching the searching patterns to diversify the solutions. Through the incorporation of a Q-table, searching toward more promising directions will be rewarded. Our case analyses employing experimental data indicate that this sparsity-conscious multi-objective particle swarm optimization technique can lead to a small solution set which generally encompasses the true damage scenario. This effectively solves the structural damage identification problem with piezoelectric impedance measurement.

Yang Zhang↗
NASA NTRS2021

Wide Bandwidth Radiometer Sensitivity for Remote Sensing of Ocean Salinity

Modern microwave radiometers have demonstrated the feasibility of monitoring surface salinity from space and also the need for better accuracy in cold water. Accuracy could be improved by adding measurements at lower frequencies (lower than the measurement at 1.4 GHz currently used) and closer to the peak in sensitivity of brightness temperature to changes in salinity. Proposals to accomplish this have focused on wide bandwidth receivers which include at the low end frequencies close to the peak in sensitivity. This strategy involves trade-offs, some obvious such as radio frequency interference (RFI) when operating outside the protected band at 1.4 GHz and the loss of spatial resolution at lower frequencies. Others stemming from the interdependence of the retrieval of salinity on water temperature and surface roughness are more subtle. The objective of this manuscript is to examine this interdependence and its implications to future wide bandwidth instruments for remote sensing of salinity from space.

microwave radiometry↗
NASA NTRS2010

Fully Printed High-Frequency Phased-Array Antenna on Flexible Substrate

To address the issues of flexible electronics needed for surface-to-surface, surface-to-orbit, and back-to-Earth communications necessary for manned exploration of the Moon, Mars, and beyond, a room-temperature printing process has been developed to create active, phased-array antennas (PAAs) on a flexible Kapton substrate. Field effect transistors (FETs) based on carbon nanotubes (CNTs), with many unique physical properties, were successfully proven feasible for phased-array antenna systems. The carrier mobility of an individual CNT is estimated to be at least 100,000 sq cm/V(dot)s. The CNT network in solution has carrier mobility as high as 46,770 sq cm/V(dot)s, and has a large current-density carrying capacity of approx. 1,000 mA/sq cm , which corresponds to a high carrying power of over 2,000 mW/ sq cm. Such high carrier mobility, and large current carrying capacity, allows the achievement of high-speed (>100 GHz), high-power, flexible electronic circuits that can be monolithically integrated on NASA s active phasedarray antennas for various applications, such as pressurized rovers, pressurized habitats, and spacesuits, as well as for locating beacon towers for lunar surface navigation, which will likely be performed at S-band and attached to a mobile astronaut. A fully printed 2-bit 2-element phasedarray antenna (PAA) working at 5.6 GHz, incorporating the CNT FETs as phase shifters, is demonstrated. The PAA is printed out at room temperature on 100-mm thick Kapton substrate. Four CNT FETs are printed together with microstrip time delay lines to function as a 2-bit phase shifter. The FET switch exhibits a switching speed of 0.2 ns, and works well for a 5.6-GHz RF signal. The operating frequency is measured to be 5.6 GHz, versus the state-of-the-art flexible FET operating frequency of 52 MHz. The source-drain current density is measured to be over 1,000 mA/sq cm, while the conventional organic FETs, and single carbon nanotube-based FETs, are typically in the mA to mA/sq cm range. The switching voltage used is 1.8 V, while the state-of-the-art flexible FET has a gate voltage around 50 V. The gate voltage can effectively control the source-drain current with an ON-OFF ratio of over 1,000 obtained at a low Vds bias of 1.8 V. The azimuth steering angles of PAA are measured at 0deg, -14.5deg, -30deg, and 48.6deg. The measured far-field patterns agree well with simulation results. The efficiency of the 2-bit 2-element PAA is measured to be 39 percent, including the loss of transmission line, FET switch, and coupling loss of RF probes. With further optimization, the efficiency is expected to be around 50-60 percent.

Chen, Yihong↗
NASA NTRS1980

Applications of acoustics in the measurement of coal slab thickness

The determination of the possibility of employing acoustic waves at ultrasonic frequencies for measurements of thicknesses of slabs of coal backed by shale is investigated. Fundamental information concerning the acoustical properties of coal, and the relationship between these properties and the structural and compositional parameters used to characterize coal samples was also sought. The testing device, which utilizes two matched transducers, is described.

Hadden, W. J., Jr.↗
NASA NTRS1994

Plate mode velocities in graphite/epoxy plates

Measurements of the velocities of the extensional and flexural plate modes were made along three directions of propagation in four graphite/epoxy composite plates. The acoustic signals were generated by simulated acoustic emission events (pencil lead breaks or Hsu-Neilson sources) and detected by by broadband ultrasonic transducers. The first arrival of the extensional plate mode, which is nondispersive at low frequencies, was measured at a number of different distances from the source along the propagation direction of interest. The velocity was determined by plotting the distance versus arrival time and computing its slope. Because of the large dispersion of the flexural mode, a Fourier phase velocity technique was used to characterize this mode. The velocity was measured up to a frequency of 160 kHz. Theoretical predictions of the velocities of these modes were also made and compared with experimental observations. Classical plate theory yields good agreement with the measured extensional velocities. For predictions of the dispersion of the flexural mode, Mindlin plates theory, which includes the effects of shear deformation and rotatory inertia was shown to give better agreement with the experimental measurements.

Prosser, W. H.↗