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Results for “Microwave techniques”

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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Microwave Imaging of Edge Conductivity in Graphene at Charge Neutrality and Quantum Hall States

Here, we report local conductivity imaging of edge states in monolayer graphene by millikelvin microwave impedance microscopy. At the charge-neutrality point, as the magnetic field increases, the local conductivity at the edge drops to zero more slowly than in the bulk. This behavior is consistent with the calculated spatial profile of the charge gap in the canted antiferromagnetic phase. For comparison, we also perform microwave imaging of integer quantum Hall states away from neutrality, which host dissipationless chiral edge channels. The evolution of the edge signal as a function of the bulk gap is fundamentally different between the Landau level filling factor 𝜈 = 0 and |𝜈| ≥ 1 integer quantum Hall states, which can be qualitatively explained by numerical simulations and theoretical analysis. Our results provide a comprehensive microscopic picture of the edge and bulk states as the Fermi level moves across the unique Landau-level spectrum of graphene.

Hall effect↗
DOE OSTI2025

Search for nonvirialized axions with 3.3 − 4.2 μ ⁢eV mass at selected resolving powers

The Axion Dark Matter eXperiment is sensitive to narrow axion flows, given axions compose a fraction of the dark matter with a non-negligible local density. Detecting these low-velocity dispersion flows requires a high spectral resolution and careful attention to the expected signal modulation due to Earth’s motion. Here, we report an exclusion on the local axion dark matter density in narrow flows of ρ a ≳ 0.03 GeV/cm 3 and ρ a ≳ 0.004 GeV/cm 3 for Dine-Fischler-Srednicki-Zhitnitski and Kim-Shifman-Vainshtein-Zakharov axion-photon couplings, respectively, over the mass range 3.3−4.2 μeV. Measurements were made at selected resolving powers to allow for a range of possible velocity dispersions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Theory of quasiparticle generation by microwave drives in superconducting qubits

Microwave drives play a central role in the control of superconducting quantum circuits, enabling qubit gates, readout, and parametric interactions. As the drive frequencies are typically an order of magnitude smaller than (twice) the superconducting gap, it is generally assumed that such drives do not disturb the BCS ground state. However, sufficiently strong drives can activate multiphoton pair-breaking processes that generate quasiparticles (QPs) and result in qubit errors. In this work, we present a theoretical framework for calculating the rates of multiphoton-assisted pair-breaking transitions induced by charge- or flux-coupled microwave drives. Through illustrative examples, we show that photon-assisted QP generation may affect novel high-frequency dispersive readout architectures, as well as Floquet-engineered superconducting circuits operating under strong driving.

circuit quantum electrodynamics↗
DOE OSTI2026

Nonequilibrium dynamics of two-level systems directly after cryogenic alternating bias

Two-level systems (TLSs) are a dominant decoherence mechanism in superconducting qubits, microwave kinetic inductance detectors, and quantum dots. TLSs are tunneling states commonly found in amorphous materials and interfaces, which interact electromechanically, leading to energy loss. Fluctuations in the frequency of the TLSs are a significant problem for qubit operation and force recalibration every few hours. In this study, we probe the effect of alternating bias at cryogenic temperatures on TLSs in a purpose-built LC oscillator. When an in situ alternating bias is applied, the steady-state spectra of the TLSs disappear. Spectroscopy reveals transient behavior, in which the TLS frequency fluctuates on the order of minutes. Thermal cycling above 10 K reverses these effects, restoring the TLS spectrum to its original state. Importantly, the intrinsic loss tangent of the LC oscillator remains unchanged before and after the application of the alternating bias. We propose that the disappearance of the steady-state spectrum is caused by nonequilibrium energy buildup from strain in the oxide film introduced by the pulsed voltage-bias sequence. Understanding this nonequilibrium energy could shed light on TLS fluctuations and reduce the calibration requirements for qubits.

general physics↗
DOE OSTI2025

Aqueous-Based Granulation Method Towards Syngas Production

An aqueous-based granulation method is developed to combat the structural changes associated with binder-based granulation techniques. Microwave-assisted methane reforming studies showed an improved catalyst efficiency for these aqueous-based granules compared to the powder catalysts. This granulation method has been extended to other practical applications (chemical looping gasification and air separations).

aqueous-based granulation↗
DOE OSTI2025

First Axionlike Particle Results from a Broadband Search for Wavelike Dark Matter in the 44 to 52 μ eV Range with a Coaxial Dish Antenna

We present the results from the first axionlike particle search conducted using a dish antenna. The experiment was conducted at room temperature and sensitive to axionlike particles in the 44 – 52 μ eV range (10.7–12.5 GHz). The novel dish antenna geometry was proposed by the BREAD Collaboration and previously used to conduct a dark photon search in the same mass range. To allow for axionlike particle sensitivity, the BREAD dish antenna was placed in a 3.9 T solenoid magnet at Argonne National Laboratory. In the presence of a magnetic field, axionlike dark matter converts to photons at the conductive surface of the reflector. The signal is focused onto a custom coaxial horn antenna and read out with a low-noise radio-frequency receiver. No evidence of axionlike dark matter was observed in this mass range and we place the most stringent laboratory constraints on the axion-photon coupling strength, g a γ γ , in this mass range at 90% confidence.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Microwave emission from geological materials - Observations of interference effects.

Microwave radiometric field observations were conducted at wavelengths of 21, 2.8, and 0.95 cm to determine the microwave penetration depth of a number of sands and gravels as a function of particle size and moisture content. Observations of a reflecting plate covered with varying thicknesses of test material exhibit a pronounced oscillatory behavior that is consistent with established electromagnetic theory for plane-parallel layered mediums. Utilization of this interference effect is proposed as a microwave radiometric technique for determining the bulk electrical properties of geologic materials, snow, ice, and other materials readily adapted to layering experiments.

Blinn, J. C., III↗
NASA NTRS1974

A theoretical and experimental investigation of cylindrical electrostatic probes at arbitrary incidence in flowing plasma

The theory for calculating the current collected by a negatively biased cylindrical electrostatic probe at an arbitrary angle of attack in a weakley ionized flowing plasma is presented. The theory was constructed by considering both random and directed motion simultaneous with dynamic coupling of the flow properties and of the electric field of the probe. This direct approach yielded a theory that is more general than static plasma theories modified to account for flow. Theoretical calculations are compared with experimental electrostatic probe data obtained in the free stream of an arc-heated hypersonic wind tunnel. The theoretical calculations are based on flow conditions and plasma electron densities measured by an independent microwave interferometer technique. In addition, the theory is compared with laboratory and satellite data previously published by other investigators. In each case the comparison gives good agreement.

Jenkins, R. V.↗
NASA NTRS1974

Directional spectra of ocean waves from microwave backscatter

The paper presents an analysis of two proposed microwave radar techniques for measuring ocean wave directional spectra. Tomiyasu's (1971) short pulse idea and Barrick's (1972) two-frequency correlation idea are regarded - independent of transmitted waveform - as essentially two alternative detection systems for modulated noise. Together, the two systems constitute a general detection system for modulated noise described some years ago by Parzen and Shiren (1956). A frequency domain analysis for backscatter on arbitrary incident waveform is given, and an interesting physical optics solution for the generalized fourth-order moments of the scattering matrix is obtained. It is shown that the present narrowband version of Barrick's two-frequency idea is impractical, and that the proper application of Barrick's idea is to wide band signals.

Jackson, F. C.↗
NASA NTRS1976

Scattering by spheres with nonisotropic refractive indices

Experimental scattering results using a microwave analog technique are described. Artificially constructed axially symmetric spheres with a graphite-like fine-layered composite structure and anisotropic refractive indices were employed to aid high-precision measurements of forward scattering under stable conditions (temperature, physical dimensions, electronic conditions) and to facilitate studies of the extinction and polarization of light by graphite particles in interstellar space. A theoretical approximation utilizing Mie theory for spheres with suitable orientation-dependent refractive indices is applied to account for changes in the complex forward-scattering amplitudes and phase in response to target orientation. The methods are extended to the full range of scattering angles, from the forward direction continuously to about 165 deg and at 180 deg. Agreement between experiment and prediction is close when the symmetry axis is parallel to the polarization.

Wang, R. T.↗
NASA NTRS1977

Technology advances in active and passive microwave sensing through 1985

The capabilities of passive and active microwave sensors are discussed. The Nimbus-G and Seasat-A scanning multichannel microwave spectrometer, the Seasat-A radar altimeter, scatterometer and synthetic aperture radar represent the first systematic attempt at exploring a wide variety of applications utilizing microwave sensing techniques and are indicators of the directions in which the pertinent technology is likely to evolve. The trend is toward high resolution multi-frequency imagers spanning wide frequency ranges and wide swaths requiring sophisticated receivers, real-time data processors and most importantly, complex antennas.

Barath, F. T.↗
NASA NTRS1978

The Chesapeake Bay: A challenge to the remote sensing community

The use of remote sensing in studying, monitoring, and understanding the Chesapeake Bay was examined. References to multispectral scanning, laser techniques, infrared microwave, and radar were made. These aspects were then analyzed with multidimensional models, digital analysis, and holographic projections.

James, C. E.↗
NASA NTRS1977

Technology advances in active and passive microwave sensing through 1985

As a result of a growing awareness by the remote sensing community of the unique capabilities of passive and active microwave sensors, these instruments are expected to grow in the next decade in numbers, versatility and complexity. The Nimbus-G and Seasat-A Scanning Multichannel Microwave Spectrometer (SMMR), the Seasat-A radar altimeter, scatterometer and synthetic aperture radar represent the first systematic attempt at exploring a wide variety of applications utilizing microwave sensing techniques and are indicators of the directions in which the pertinent technology is likely to evolve. The trend is toward high resolution multi-frequency imagers spanning wide frequency ranges and wide swaths requiring sophisticated receivers, real-time data processors and most importantly, complex antennas.

Barath, F. T.↗
NASA NTRS1978

Remote sensing of snowpack with microwave radiometers for hydrologic applications

A microwave remote sensing of snowpack experiment is described and some preliminary data presented. A mobile field laboratory consisting of a four-frequency (5, 10.7, 18 and 37 GHz), all with dual linear (vertical and horizontal) polarizations, microwave radiometer system attached to a truck-mounted aerial lift was used to study the microwave emission characteristics of snowpacks in the Colorado Rocky Mountains during the winter of 1977-78. The influence of snowpack physical parameters such as water equivalent, grain size, and melt-freeze cycle on its microwave brightness temperature and its implications to the application of microwave radiometric technique to remote sensing of snowpack for runoff prediction are discussed.

Shiue, J. C.↗
NASA NTRS1979

Improvement of scanning radiometer performance by digital reference averaging

Most radiometers utilize a calibration technique in which measurements of a known reference are subtracted from measurements of an unknown source so that common-mode bias errors are cancelled. When a radiometer is scanned over a varying scene, it produces a sequence of outputs, each being proportional to the difference between the reference and the corresponding input. A reference averaging technique is presented that employs a simple digital algorithm which exploits the asymmetry between the time-variable scene inputs and the nominally constant reference input by averaging many reference measurements to decrease the statistical uncertainty in the reference value. This algorithm is, therefore, optimized by an asymmetric chopping sequence in which the scene is viewed for more than one-half of the duty cycle (unlike the analog Dicke technique). Reference averaging algorithms are well within the capabilities of small microprocessors. Although this paper develops the technique for microwave radiometry, it may be beneficial for any system which measures a large number of unknowns relative to a known reference in the presence of slowly varying common-mode errors.

Bremer, J. C.↗
NASA NTRS1978

Ocean waves

Ocean wave data can be obtained from such active microwave probe techniques as monostatic HF and VHF, bistatic HF, HF synthetic aperture radar, altimeters, satellite and airborne synthetic aperture radar, carrier wave or pulsed dual-frequency radars, and coastal surveillance radar. Approaches to texture analysis of ocean wave imagery are discussed, with attention given to transform techniques or spatial frequency analysis, and the analysis of second-order gray level statistics. In addition, recommendations are made for further work on the modulation of short gravity waves by longer waves as a function of wind speed and wave direction, and the derivation of transfer functions for the ocean response of dual-frequency radars.

Bartsch, N.↗
NASA NTRS1979

Rough surface wavelength measurement through self mixing of Doppler microwave backscatter

A microwave backscatter technique is presented that has the ability to sense the dominant surface wavelength of a random rough surface. The purpose of this technique is to perform this measurement from an aircraft or spacecraft, wherein the horizontal velocity of the radar is an important parameter of the measurement system. Attention will be directed at water surface conditions for which a dominant wavelength can be defined, then the spatial variations of reflectivity will have a two dimensional spectrum that is sufficiently close to that of waves to be useful. The measurement concept is based on the relative motion between the water waves and a nadir looking radar, and the fact that while the instantaneous Doppler frequency at the receiver returned by any elementary group of scatterers on a water wave is monotonically changing, the difference in the Doppler frequency between any two scattering 'patches' stays approximately constant as these waves travel parallel to the major axis of an elliptical antenna footprint. The results of a theoretical analysis and a laboratory experiment with a continuous wave (CW) radar that encompasses several of the largest waves in the illuminated area show how the structure in the Doppler spectrum of the backscattered signal is related to the surface spectrum and its parameters in an especially direct and simple way when an incoherent envelope detector is the receiver.

Weissman, D. E.↗