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Results for “CARRIER MODULATION”
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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Linearity optimization in a class of analog phase modulators
This paper examines the ultimate modulating linearity attainable with a phase modulation technique based on the linear addition of quadrature phase carrier signals which have been multiplied by precisely defined nonlinear transformations of the modulating signal. Optimum gain coefficients are derived and plotted to permit implementation of analog phase modulators capable of exceptionally good linearity of phase deviations as large as 5 radians.
Feasibility Study of the Superconducting Gravity Gradiometer (SGG) Flight Test on the European Retrievable Carrier (EURECA)
A study was performed to determine the feasibility of conducting a flight test of the Superconducting Gravity Gradiometer (SGG) Experiment Module on one of the reflights of the European Retrievable Carrier (EURECA). EURECA was developed expressly to accommodate space science experimentation, while providing a high quality microgravity environment. As a retrievable carrier, it offers the ability to recover science experiments after a nominal six months of operations in orbit. The study concluded that the SGG Experiment Module can be accommodated and operated in a EURECA reflight mission. It was determined that such a flight test would enable the verification of the SGG Instrument flight performance and validate the design and operation of the Experiment Module. It was also concluded that a limited amount of scientific data could be obtained on this mission.
Atomically engineered epitaxial anatase TiO 2 metal-semiconductor field-effect transistors
Here, anatase TiO 2 is a promising material for a vast array of electronic, energy, and environmental applications, including photocatalysis, photovoltaics, and sensors. A key requirement for these applications is the ability to modulate its electrical properties without dominant dopant scattering and while maintaining high carrier mobility. Here, we demonstrate the room temperature field-effect modulation of the conducting epitaxial interface between anatase TiO 2 and LaAlO 3 (001), which arises for LaO-terminated LaAlO 3 , while the AlO 2- terminated interface is insulating. This approach, together with the metal-semiconductor field-effect transistor geometry, naturally bypasses the gate/channel interface traps, resulting in a high field-effect mobility μ FE of 3.14 cm 2 (V s) –1 approaching 98% of the corresponding Hall mobility μ Hall . Accordingly, the channel conductivity is modulated over 6 orders of magnitude over a gate voltage range of ~4 V.
Ultrasonic through-wall sensors
Aspects of ultrasonic through-wall data communication are described. In some aspects, a sensor device is located in an isolated environment behind a wall. A modulator generates a modulated sensor signal based on the binary sensor signal and a carrier signal. A coaxially aligned pair of electroacoustic transducers that transmits the modulated sensor signal through the wall of the isolated environment. A demodulator demodulates the modulated sensor signal to generate a demodulated binary sensor signal. A sensor data recovery component converts the demodulated binary sensor signal into an image or another sensor parameter.
Light-wave control of correlated materials using quantum magnetism during time-periodic modulation of coherent transport
Light–wave quantum electronics utilizes the oscillating carrier wave to control electronic properties with intense laser pulses. Without direct light–spin interactions, however, magnetic properties can only be indirectly affected by the light electric field, mostly at later times. A grand challenge is how to establish a universal principle for quantum control of charge and spin fluctuations, which can allow for faster-than-THz clock rates. Using quantum kinetic equations for the density matrix describing non–equilibrium states of Hubbard quasiparticles, here we show that time–periodic modulation of electronic hopping during few cycles of carrier–wave oscillations can dynamically steer an antiferromagnetic insulating state into a metalic state with transient magnetization. While nonlinearities associated with quasi-stationary Floquet states have been achieved before, magneto–electronics based on quasiparticle acceleration by time–periodic multi–cycle fields and quantum femtosecond/attosecond magnetism via strongly–coupled charge–spin quantum excitations represents an alternative way of controlling magnetic moments in sync with quantum transport.
The great solar anomaly ca. 1780-1800 - An error in compiling the record
The view that the sunspot index time sequence is of lessened validity prior to about 1850 is shown to be consistent with an error in the 1780-1800 time period when phase, offset of the Hale carrier sinusoid from zero mean, and the amplitude modulation envelope all show a lack of conformity with respect to the remainder of the record subsequent to the Maunder minimum. This lack of conformity is consistent with an error that delays one or more of the 11-year cycle minima but recovers phase subsequently. This type of error creates a strongly coherent set of companion changes in offset of the carrier from zero mean and in the amplitude modulation envelope.
Multiplex gas chromatography
The principles of the multiplex gas chromatography (GC) technique, which is a possible candidate for chemical analysis of planetary atmospheres, are discussed. Particular attention is given to the chemical modulators developed by present investigators for multiplex GC, namely, the thermal-desorption, thermal-decomposition, and catalytic modulators, as well as to mechanical modulators. The basic technique of multiplex GC using chemical modulators and a mechanical modulator is demonstrated. It is shown that, with the chemical modulators, only one gas stream consisting of the carrier in combination with the components is being analyzed, resulting in a simplified instrument that requires relatively few consumables. The mechanical modulator demonstrated a direct application of multiplex GC for the analysis of gases in atmosphere of Titan at very low pressures.
Morphology effects on spin-dependent transport and recombination in polyfluorene thin films
Here, we have studied the role of spin-dependent processes on conductivity in polyfluorene (PFO) thin films by preforming continuous wave (cw) electrically detected magnetic resonance (EDMR) spectroscopy at temperatures between 10 K and room temperature using microwave frequencies between about 1 GHz and 20 GHz, as well as pulsed EDMR at the X band (10 GHz). Variable frequency EDMR allows us to establish the role of spin-orbit coupling in spin-dependent processes whereas pulsed EDMR allows for the observation of coherent spin motion effects. We used PFO for this study in order to allow for the investigation of the effects of microscopic morphological ordering since this material can adopt two distinct intrachain morphologies: an amorphous (glassy) phase, in which monomer units are twisted with respect to each other, and an ordered (β) phase, where all monomers lie within one plane. In thin films of organic light-emitting diodes, the appearance of a particular phase can be controlled by deposition parameters and solvent vapor annealing, and is verified by electroluminescence spectroscopy. Under bipolar charge-carrier injection conditions, we conducted multifrequency cw EDMR, electrically detected Rabi spin-beat experiments, and Hahn echo and inversion-recovery measurements. Coherent echo spectroscopy reveals electrically detected electron-spin-echo envelope modulation due to the coupling of the carrier spins to nearby nuclear spins. Our results demonstrate that, while conformational disorder can influence the observed EDMR signals, including the sign of the current changes on resonance as well as the magnitudes of local hyperfine fields and charge-carrier spin-orbit interactions, it does not qualitatively affect the nature of spin-dependent transitions in this material. In both morphologies, we observe the presence of at least two different spin-dependent recombination processes. At room temperature and 10 K, polaron-pair recombination through weakly spin-spin coupled intermediate charge-carrier pair states is dominant, while at low temperatures, additional signatures of spin-dependent charge transport through the interaction of polarons with triplet excitons are seen in the half-field resonance of a triplet spin-1 species. This additional contribution arises since triplet lifetimes are increased at lower temperatures. We tentatively conclude that spectral broadening induced by hyperfine coupling is slightly weaker in the more ordered β-phase than in the glassy phase since protons are more evenly spaced, whereas broadening effects due to spin-orbit coupling, which impacts the distribution of g-factors, appear to be somewhat more significant in the β-phase.
Electroabsorption optical modulator
An electroabsorption modulator incorporates waveguiding regions along the length of the modulator that include quantum wells where at least two of the regions have quantum wells with different bandgaps. In one embodiment of the invention, the regions are arranged such that the quantum wells have bandgaps with decreasing bandgap energy along the length of the modulator from the modulator's input to its output. The bandgap energy of the quantum wells may be decreased in discrete steps or continuously. Advantageously, such an arrangement better distributes the optical absorption as well as the carrier density along the length of the modulator. Further advantageously, the modulator may handle increased optical power as compared with prior art modulators of similar dimensions, which allows for improved link gain when the optical modulator is used in an analog optical communication link.
Minority Carrier Lifetime Studies of Narrow Bandgap Antimonide Superlattices
In this study optical modulation response and photoluminescence spectroscopy were used to study mid-wave Ga-free InAs/InAsSb superlattices. The minority carrier lifetimes in the different samples varied from 480 ns to 4700 ns, partly due to different background doping concentrations. It was shown that the photoluminescence intensity can be used as a fast non-destructive tool to predict the material quality. It was also demonstrated that it is crucial to use a low excitation power in the photoluminescence measurements in order to get a good correlation between the photoluminescence intensity and the minority carrier lifetime.
Temperature-dependent efficiency droop of blue InGaN micro-light emitting diodes
Temperature-dependent trends in radiative and Auger recombination coefficients have been determined at different injection carrier concentrations using InGaN micro-light emitting diodes 40 μm in diameter. The differential lifetime was obtained first from the measured modulation bandwidth and was then employed to calculate the carrier concentration in the quantum well active region. When the temperature increases, the carrier concentration increases, but both the radiative and Auger recombination coefficients decrease. In addition, the temperature dependence of radiative and Auger recombination coefficients is weaker at a higher injection carrier concentration, which is strongly related to phase space filling.
An unprecedented quinoid–donor–acceptor strategy to boost the carrier mobilities of semiconducting polymers for organic field-effect transistors
Quinoidal–aromatic conjugated polymers hold great application potential in organic field-effect transistors (OFETs). However, the development of high mobility quinoidal–aromatic conjugated polymers still lags behind the more popular donor–acceptor (D–A) conjugated polymers, mainly owing to the lack of a rational design strategy and efficient building block. Herein, a novel quinoid–donor–acceptor (Q–D–A) strategy is demonstrated to modulate the energy-level and boost the charge carrier transport mobility of conjugated polymers as opposed to the D–A system. On the basis of this strategy, a quinoidal–aromatic conjugated polymer, namely PAQM-BT, is designed and synthesized. With the combined use of quinoid, donor and acceptor units in the backbone, the resulting Q–D–A polymer PAQM-BT displays the narrowest bandgap with the deepest-lying lowest unoccupied molecular orbital (LUMO) energy level, highest backbone coplanarity, enhanced thin-film crystallinity and smallest effective hole mass ($m^*_h$) in comparison with the corresponding D–A polymer PT3B1 and quinoid–donor (Q–D) polymer PAQM-3T. Benefitting from the more effective intra- and inter-chain charge transport, as corroborated by experiment and theoretical calculations, OFET devices based on PAQM-BT exhibit a highly boosted hole mobility of up to 5.10 cm 2 V -1 s -1 , which is one and four orders of magnitude higher than that of PAQM-3T and PT3B1, respectively, and is among the highest for quinoidal–aromatic conjugated polymers. Finally, the potent Q–D–A strategy not only allows the energy level to be modulated but also leads to effective charge carrier transport, opening up possibilities to the development of high mobility quinoidal–aromatic conjugated polymers based on a variety of quinoids, donors, and acceptors.
Ubiquitous Interplay Between Charge Ordering and High-Temperature Superconductivity in Cuprates
Copper-oxide superconductors have a complex electronic structure. A charge density order has been observed in two cuprate families; however, it has been unclear whether such an order exists in Bi-based compounds (see the Perspective by Morr). Comin et al. (p. 390, published online 19 December) and da Silva Neto et al. (p. 393, published online 19 December) address this question in single-layer and double-layer Bibased cuprates, respectively. For both families of materials, surface measurements by scanning tunneling spectroscopy agree with bulk measurements obtained through resonant elastic x-ray scattering, which suggests the formation of short-range correlations that modulate the charge density of the carriers over a range of dopings. Thus, charge ordering may represent a common characteristic of the major cuprate families.
ACCObeam: Acoustic Collimated Ultrasonic Beam
A passive, linear arrangement of a sonic crystal-based apparatus and method including a 1D sonic crystal, a nonlinear medium, and an acoustic low-pass filter, for permitting unidirectional broadband ultrasound propagation as a collimated beam for underwater, air or other fluid communication are described. The signal to be transmitted is first used to modulate a high-frequency ultrasonic carrier wave which is directed into the sonic crystal side of the apparatus.
On the optimality of the MAP estimation loop for carrier phase tracking BPSK and QPSK signals
Starting with MAP estimation theory as a basis for optimally estimating carrier phase of BPSK and QPSK modulations, it is shown in this paper that the closed loop phase trackers, which are motivated by this approach, are indeed closed loop optimum in the minimum mean-square phase tracking jitter sense. The corresponding squaring loss performance of these so-called MAP estimation loops is compared with that of more practical implementations wherein the hyperbolic tangent nonlinearity is approximated by simpler functions.
Hybrid Analog/Digital Receiver
Advanced hybrid analog/digital receiver processes intermediate-frequency (IF) signals carrying digital data in form of phase modulation. Uses IF sampling and digital phase-locked loops to track carrier and subcarrier signals and to synchronize data symbols. Consists of three modules: IF assembly, signal-processing assembly, and test-signal assembly. Intended for use in Deep Space Network, but presumably basic design modified for such terrestrial uses as communications or laboratory instrumentation where signals weak and/or noise strong.
NASA 60 GHz intersatellite communication link definition study. Addendum A: Mixed baseband and IF signals
As part of a definition study for a 60 GHz intersatellite communications link system (ICLS), baseline design concepts for a channelized crosslink were identified. The crosslink would allow communications between geostationary satellites of the planned Tracking and Data Acquisition System (TDAS) and would accommodate a mixture of frequency translation coherent links (bent pipe links) and baseband-in/baseband-out links (mod/demod links). A 60 GHz communication system was developed for sizing and analyzing the crosslink. For the coherent links this system translates incoming signals directly up to the 60 GHz band; trunks the signals across from one satellite to a second satellite at 60 GHz then down converts to the proper frequency for re-transmission from the second satellite without converting to any intermediate frequencies. For the baseband-in/baseband-out links the baseband data is modulated on to the 60 GHz carrier at the transmitting satellite and demodulated at the receiving satellite. The frequency plan, equipment diagrams, and link calculations are presented along with results from sizing and reliability analyses.