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Results for “microwave absorption”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The Ionization History of The Intergalactic Medium:

The funded project seeked a unified description of the ionization, physical structure, and evolution of the intergalactic medium (IGM) and quasar intervening absorption systems. We proposed to conduct theoretical studies of the IGM and QSO absorbers in the context of current theories of galaxy formation, developing and using numerical and analytical techniques aimed at a detailed modeling of cosmological radiative transfer, gas dynamics, and thermal and ionization evolution. The ionization history of the IGM has important implications for the metagalactic UV background, intergalactic helium absorption 21-cm tomography, metal absorption systems, fluctuations in the microwave background, and the cosmic rate of structure and star formation. All the original objectives of our program have been achieved, and the results widely used and quoted by the community. Indeed, they remain relevant as the level and complexity of research in this area has increased substantially since our proposal was submitted, due to new discoveries on galaxy formation and evolution, a flood of high-quality data on the distant universe, new theoretical ideas and direct numerical simulations of structure formation in hierarchical clustering theories.

Madau, Piero↗
DOE OSTI2020

Multimode Storage of Quantum Microwave Fields in Electron Spins over 100 ms

In this work, we report long coherence times (up to 300 ms) for near-surface bismuth donor electron spins in silicon coupled to a superconducting microresonator, biased at a clock transition. This enables us to demonstrate the partial absorption of a train of weak microwave fields in the spin ensemble, their storage for 100 ms, and their retrieval, using a Hahn-echo-like protocol. Phase coherence and quantum statistics are preserved in the storage.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Optically heralded microwave photon addition

Photons with optical frequencies of a few hundred terahertz are perhaps the only way to distribute quantum information over long distances. Superconducting qubits, which are one of the most promising approaches for realizing large-scale quantum machines, operate on microwave photons at frequencies that are ~40,000 times lower. To network these quantum machines across appreciable distances, we must bridge this frequency gap. Here we implement and demonstrate a transducer that can generate correlated optical and microwave photons. In this study, we use it to show that by detecting an optical photon we generate an added microwave photon with an efficiency of ~35%. Our device uses a gigahertz nanomechanical resonance as an intermediary, which efficiently couples to optical and microwave channels through strong optomechanical and piezoelectric interactions. We show continuous operation of the transducer with 5% frequency conversion efficiency, input-referred added noise of ~100, and pulsed microwave photon generation at a heralding rate of 15 Hz. Optical absorption in the device generates thermal noise of less than two microwave photons. Improvements of the system efficiencies and device performance are necessary to realize a high rate of entanglement generation between distant microwave-frequency quantum nodes, but these enhancements are within reach.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1979

Theory of the intercluster medium

A set of computer models for the evolution of intercluster matter (ICM) in expanding cosmologies which includes processes of electron impact ionization/excitation, radiative and dielectronic recombination, thermal bremsstrahlung, Compton scattering, and photoionization is presented. The thermal, ionization, and excitation histories of major constituents were found as functions of time, and predictions of emission spectra, the possible distortions of the cosmic 3 K microwave background, and optical depths of absorption troughs in QSO continua at various redshifts were obtained. It is concluded that the present Friedmann cosmology can be dominated by hot intercluster matter which would contain H and He in their cosmic ratio and traces of heavier elements. For a narrow range of parameters it is possible to generate cosmologies with a closure density of ICM which do not exceed the diffuse X-ray measurements. In open cosmologies distortion of the 3 K microwave background occurs, while closed cases show negligible change from the unperturbed spectrum.

Sherman, R. D.↗
NASA NTRS1980

Microwave, EUV, and X-ray observations of active region loops - Evidence for gyroresonance absorption in the corona

The combined data from 3.7 and 11 cm radio maps, EUV spectroheliograms, and X-ray photographs of an active region (McMath 12379) are analyzed. The near equality of the radio brightness temperatures and the electron temperature determined from the EUV and X-ray data implies that the radio emission is thermal. Since the free-free absorption is inadequate to account for this, the large optical depth must be produced by gyroresonance absorption. It is inferred that the magnetic scale height must be of the same order as the observed width of the coronal loops (one-billion cm). The scale of emission in the radio, and hence the scale of the absorbing region transverse to the line of sight, is also of this order.

Kundu, M. R.↗
NASA NTRS1971

Transfer of thermal microwaves in the atmosphere, volume 2

Figures and tabular information that are supplemental to a study on transfer of thermal microwaves in the atmosphere are presented. The numerical values for the absorption and scattering cross sections of a pure, liquid, water drop are given for drop diameters ranging up to 6 mm, and for various drop temperatures. These values were obtained through the Mie theory. For a Marshall-Palmer distribution of drop sizes, the volume absorption and scattering coefficients of rain are given for the same temperatures and microwave frequencies shown above and for contents of liquid water in the rain mass. Also, scattergrams are given of the katabatic and upwelling brightness temperatures of up to 582 model atmospheres over a calm ocean versus the equivalent depths of liquid water in cloud form, rain form, or combined cloud and rain form.

Paris, J. F.↗
DOE OSTI2023

Spatially-resolved dynamic sampling of different phasic magnetic resonances of nanoparticle ensembles in a magnetotactic bacterium Magnetospirillum magnetotacticum

Abstract Nanoscaled magnetic particle ensembles are promising building blocks for realizing magnon based binary logic. Element-specific real-space monitoring of magnetic resonance modes with sampling rates in the GHz regime is imperative for the experimental verification of future complex magnonic devices. Here we present the observation of different phasic magnetic resonance modes using the element-specific technique of time-resolved scanning transmission x-ray microscopy within a chain of dipolarly coupled Fe 3 O 4 nanoparticles (40–50 nm particle size) inside a single cell of a magnetotactic bacterium Magnetospirillum magnetotacticum . The particles are probed with 25 nm resolution at the Fe L 3 x-ray absorption edge in response to a microwave excitation of 4.07 GHz. A plethora of resonance modes is observed within multiple particle segments oscillating in- and out-of-phase, well resembled by micromagnetic simulations.

time-resolved scanning transmission x-ray microsco↗
NASA NTRS1971

Target contrast considerations in millimeter wave radiometry for airborne navigation

Target signal requirements for aircraft navigation systems that use radiometric receivers which map thermally emitted power radiated by terrain or power radiated by ground-based beacons are discussed. For selected millimeter wavelength bands, microwaves suffer relatively little degradation by absorption or scattering on passage through the atmosphere, despite extreme weather variations. Interest centers on 8-millimeter waves because of component availability, portability (small size), high image resolution, and all-weather capability at this wavelength. The idea of radiometric airborne navigation is introduced. Elements of radiometry, terrain radiation, and atmospheric transmission characteristics are reviewed. Data pertaining to these elements at 8 mm wavelength are collected. Calculation of radiometric contrasts is discussed for some simple models of terrain targets.

Mayer, A.↗
NASA NTRS1981

Effects of rain and fog on the Shuttle Ku-band microwave scanning beam landing system range and accuracy performance

The microwave Scanning Beam Landing System's (MSBLS) performance in fog and rain was studied. The fog and rain effects on the Shuttle Ku-band system were determined. Specifically, microwave attenuation, beam distortion, and coordinate errors resulting from operation of the MSBLS in poor weather conditions were evaluated. The main physical processes giving rise to microwave attenuation were found to be absorption and scattering by water droplets. The general theory of scattering and absorption used is discussed and a listing of applicable computer programs is provided.

Butler, D.↗
NASA NTRS2014

Impedance Matched Absorptive Thermal Blocking Filters

We have designed, fabricated and characterized absorptive thermal blocking filters for cryogenic microwave applications. The transmission line filter's input characteristic impedance is designed to match 50Ω and its response has been validated from 0-to-50GHz. The observed return loss in the 0-to-20GHz design band is greater than 20 dB and shows graceful degradation with frequency. Design considerations and equations are provided that enable this approach to be scaled and modified for use in other applications.

thermal blocking filters↗
NASA NTRS2014

Impedance Matched Absorptive Thermal Blocking Filters

We have designed, fabricated and characterized absorptive thermal blocking filters for cryogenic microwave applications. The transmission line filter's input characteristic impedance is designed to match 50 Omega and its response has been validated from 0-to-50GHz. The observed return loss in the 0-to-20GHz design band is greater than 20 dB and shows graceful degradation with frequency. Design considerations and equations are provided that enable this approach to be scaled and modified for use in other applications.

cryogenic microwave applications↗
DOE OSTI2021

Linking optical spectra to free charges in donor/acceptor heterojunctions: cross-correlation of transient microwave and optical spectroscopy

The primary photoexcited species in excitonic semiconductors is a bound electron–hole pair, or exciton. An important strategy for producing separated electrons and holes in photoexcited excitonic semiconductors is the use of donor/acceptor heterojunctions, but the degree to which the carriers can escape their mutual Coulomb attraction is still debated for many systems. Here, we employ a combined pump–probe ultrafast transient absorption (TA) spectroscopy and time-resolved microwave conductivity (TRMC) study on a suite of model excitonic heterojunctions consisting of mono-chiral semiconducting single-walled carbon nanotube (s-SWCNT) electron donors and small-molecule electron acceptors. Comparison of the charge-separated state dynamics between TA and TRMC photoconductance reveals a quantitative match over the 0.5 microsecond time scale. Charge separation yields derived from TA allow extraction of s-SWCNT hole mobilities of ca. 1.5 cm 2 V -1 s -1 (at 9 GHz) by TRMC. We find that the correlation between the techniques conclusively demonstrates that photoinduced charge carriers separated across these heterojunctions do not form bound charge transfer states, but instead form free/mobile charge carriers.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Modeling the electron cyclotron emission radiation signature from suprathermal electrons in a tokamak

An Electron Cyclotron Emission (ECE) modeling code has been developed to model ECE radiation with an arbitrary electron momentum distribution, a small oblique angle, both ordinary (O-mode) and extraordinary polarizations (X-mode), and multiple cyclotron frequency harmonics. The emission and absorption coefficients are calculated using the Poynting theorem from the cold plasma dispersion and the electron–microwave interaction from the full anti-Hermitian tensor. The modeling shows several ECE radiation signatures that can be used to diagnose the population of suprathermal electrons in a tokamak. First, in an n = 2 X-mode (X2) optically thick plasma and oblique ECE view, the modeling shows that only suprathermal electrons, which reside in a finite region of the velocity and space domains, can effectively generate cyclotron emissions to the ECE receiver. The code also finds that the O1 mode is sensitive to suprathermal electrons of both a high v ⊥ and v || , while the X2 mode is dominantly sensitive to suprathermal electrons of a high v ⊥ . Finally, the modeling shows that an oblique ECE system with both X/O polarization and a broad frequency coverage can be used to effectively yield information of the suprathermal electron population in a tokamak.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1974

Solar absorptance of second surface mirrors for high angles of incidence

Recent measurements have indicated an increase rather than a decrease in the solar absorptivity of second surface mirrors at angles of incidence greater than 80 deg. These observations stimulated an analytical effort which revealed that the increase does occur. Using electromagnetic wave theory, the solar absorptance equations for the mirror configurations commonly encountered in application are developed. An increase in mirror solar absorptance has also been deduced from the temperatures of a second surface mirrored radiator being monitored on the Nimbus E microwave spectrometer experiment. Test and calculated results substantiating the solar absorptance increase are presented.

Stultz, J. W.↗
DOE OSTI2021

Plasma generation by household microwave oven for surface modification and other emerging applications

A simple and inexpensive method to generate plasma using a kitchen microwave oven is described in this paper. The microwave-generated plasma is characterized by spectroscopic analysis and compared with the absorption spectra of a gas discharge tube. A Paschen-like curve is observed as the microwave plasma initiation time is plotted as a function of the pressure of the plasma chamber. We have also demonstrated that this microwave-generated air plasma can be used in a multitude of applications such as: (a) surface modification of a substrate to change its wettability; (b) surface modification to change electrical/optical properties of a substrate; and (c) enhancement of adhesive forces for improved bonding of polymeric microfluidic molds, such as bonding polydimethylsiloxane (PDMS) chips to glass covers. These simple techniques of plasma generation and subsequent surface treatment and modification applications may bring new opportunities leading to new innovations not only in advanced labs, but also in undergraduate and even high school research labs.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗