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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Mixed Linear/Square-Root Encoded Single-Slope Ramp Provides Low-Noise ADC with High Linearity for Focal Plane Arrays

Single-slope analog-to-digital converters (ADCs) are particularly useful for onchip digitization in focal plane arrays (FPAs) because of their inherent monotonicity, relative simplicity, and efficiency for column-parallel applications, but they are comparatively slow. Squareroot encoding can allow the number of code values to be reduced without loss of signal-to-noise ratio (SNR) by keeping the quantization noise just below the signal shot noise. This encoding can be implemented directly by using a quadratic ramp. The reduction in the number of code values can substantially increase the quantization speed. However, in an FPA, the fixed pattern noise (FPN) limits the use of small quantization steps at low signal levels. If the zero-point is adjusted so that the lowest column is onscale, the other columns, including those at the center of the distribution, will be pushed up the ramp where the quantization noise is higher. Additionally, the finite frequency response of the ramp buffer amplifier and the comparator distort the shape of the ramp, so that the effective ramp value at the time the comparator trips differs from the intended value, resulting in errors. Allowing increased settling time decreases the quantization speed, while increasing the bandwidth increases the noise. The FPN problem is solved by breaking the ramp into two portions, with some fraction of the available code values allocated to a linear ramp and the remainder to a quadratic ramp. To avoid large transients, both the value and the slope of the linear and quadratic portions should be equal where they join. The span of the linear portion must cover the minimum offset, but not necessarily the maximum, since the fraction of the pixels above the upper limit will still be correctly quantized, albeit with increased quantization noise. The required linear span, maximum signal and ratio of quantization noise to shot noise at high signal, along with the continuity requirement, determines the number of code values that must be allocated to each portion. The distortion problem is solved by using a lookup table to convert captured code values back to signal levels. The values in this table will be similar to the intended ramp value, but with a correction for the finite bandwidth effects. Continuous-time comparators are used, and their bandwidth is set below the step rate, which smoothes the ramp and reduces the noise. No settling time is needed, as would be the case for clocked comparators, but the low bandwidth enhances the distortion of the non-linear portion. This is corrected by use of a return lookup table, which differs from the one used to generate the ramp. The return lookup table is obtained by calibrating against a stepped precision DC reference. This results in a residual non-linearity well below the quantization noise. This method can also compensate for differential non-linearity (DNL) in the DAC used to generate the ramp. The use of a ramp with a combination of linear and quadratic portions for a single-slope ADC is novel. The number of steps is minimized by keeping the step size just below the photon shot noise. This in turn maximizes the speed of the conversion. High resolution is maintained by keeping small quantization steps at low signals, and noise is minimized by allowing the lowest analog bandwidth, all without increasing the quantization noise. A calibrated return lookup table allows the system to maintain excellent linearity.

Wrigley, Chris J.↗
NASA NTRS1987

Design and fabrication requirements for low noise supersonic/hypersonic wind tunnels

A schematic diagram of the new proposed Supersonic Low Disturbance Tunnel (SLDT) is shown. Large width two dimensional rapid expansion nozzles guarantee wide quiet test cores that are well suited for testing models at large angle of attack and for swept wings. Hence, this type of nozzle will be operated first in the new proposed large scale SLDT. Test results indicate that the surface finish of pilot nozzles is critical. The local roughness Reynolds number criteria R sub k is approx. = 10 will be used to specify allowable roughness on new pilot nozzles and the new proposed tunnel. Experimental data and calculations for M = 3.0, 3.5, and 5.0 nozzles give N-factors from 6 to 10 for transition caused by Goertler vortices. The use of N is approx. = 9.0 for the Goertler instability predicts quiet test cores in the new M = 3.5 and M = 6.0 axisymmetric long pilot nozzles that are 3 to 4 times longer than observed in the test nozzles to date. The new nozzles utilize a region of radial flow which moves the inflection point far downstream and delays the onset and amplification of the Goertler vortices.

Beckwith, Ivan E.↗
NASA NTRS1988

Design and fabrication requirements for low-noise supersonic/hypersonic wind tunnels

Analyses of NASA Langley experimental results obtained from efforts to develop a low disturbance wind tunnel by means of linear stability theory have shown that the amplification of Gortler vortices on the concave walls of nozzles at Mach numbers from 3 to 5 are the cause of transition. The theory is used to design advanced nozzles for Mach numbers of 3.5 and 6 which can generate substantially longer quiet test regions. Transition on the nozzle walls is noted to be extremely sensitive to nozzle wall roughness and contamination.

Beckwith, I. E.↗
DOE OSTI2023

Non-reciprocal acoustoelectric microwave amplifiers with net gain and low noise in continuous operation

Abstract Piezoelectric acoustic devices that are integrated with semiconductors can leverage the acoustoelectric effect, allowing functionalities such as gain and isolation to be achieved in the acoustic domain. This could lead to performance improvements and miniaturization of radio-frequency electronic systems. However, acoustoelectric amplifiers that offer a large acoustic gain with low power consumption and noise figure at microwave frequencies in continuous operation have not yet been developed. Here we report non-reciprocal acoustoelectric amplifiers that are based on a three-layer heterostructure consisting of an indium gallium arsenide (In 0.53 Ga 0.47 As) semiconducting film, a lithium niobate (LiNbO 3 ) piezoelectric film, and a silicon substrate. The heterostructure can continuously generate 28.0 dB of acoustic gain (4.0 dB net radio-frequency gain) for 1 GHz phonons with an acoustic noise figure of 2.8 dB, while dissipating 40.5 mW of d.c. power. We also create a device with an acoustic gain of 37.0 dB (11.3 dB net gain) at 1 GHz with 19.6 mW of d.c. power dissipation and a non-reciprocal transmission of over 55 dB.

42 ENGINEERING↗
DOE OSTI2025

Spontaneous generation of athermal phonon bursts within bulk silicon causing excess noise, low energy background events, and quasiparticle poisoning in superconducting sensors

Solid state phonon detectors used in the search for dark matter and coherent neutrino nucleus interactions (CE $v$ NS) require excellent energy resolution (eV-scale or below) and low backgrounds. An unknown source of phonon bursts, the low energy excess (LEE), dominates other above-threshold backgrounds and generates excess shot noise from subthreshold bursts. Here, in this paper, we measure these phonon bursts for 12 days after cooldown in two nearly identical 1 cm 2 silicon detectors that differ only in the thickness of their substrate (1 vs 4 mm thick). We find that both the channel-correlated shot noise and near-threshold shared LEE relax with time since cooldown. Additionally, both the correlated shot noise and LEE rates scale linearly with substrate thickness. When combined with previous measurements of other silicon phonon detectors with different substrate geometries and mechanical support strategies, these measurements strongly suggest that the dominant source of both above and below threshold LEE is the bulk substrate. By monitoring the relation between bias power and excess phonon shot noise, we estimate that the energy scale for subthreshold noise events is 0.68 ± 0.38 meV. In our final dataset, we report a world-leading energy resolution of 258.5 ± 0.4 meV in the 1 mm thick detector. Simple calculations suggest that these silicon substrate phonon bursts are likely a significant source of quasiparticle poisoning in superconducting qubits operated in well shielded and vibration free environments.

Chang, C. L. [Argonne National Laboratory 1 , 9700↗
NASA NTRS1995

Low-Noise Wide Bandwith, Hot Electron Bolometer Mixers for Submillimeter Wavelengths

Recently a novel superconductive hot-electron micro-bolometer has been proposed which is both fast and sensitive (D. E. Prober, Appl. Phys. Lett. 62, 2119, 1993). This device has several important properties which make it useful as a heterodyne sensor for radioastronomy applications at frequencies above 1 THz. The thermal response time of the device is fast enough, several 10's of picoseconds, to allow for IF's of several GHz. This bolometer mixer should operate well up to at least 10 THz. There is no energy gap limitation as in an SIS mixer, since the mixing process relies on heating of the electron gas. In fact, rf power is absorbed more uniformly above the gap frequency. The mixer noise should be near quantum-limited, and the local oscillator (LO) power requirement is very low: / 10 nW for a Nb device. One of the unique features of this device is that it employs rapid electron diffusion into a normal metal, rather than phonon emission, as the thermal conductance that cools the heated electrons. In order for diffusion to dominate over phonon emission, the device must be short, less than 0.5.

Bolometer Mixers↗
NASA NTRS1977

Fabrication of ultra-low-noise amplifier

Three construction techniques reduce noise temperature of microwave parametric amplifier. Techniques include electroformed idler cavity, screw-tuned idler, and low-loss matching section.

Kraemer, E.↗
NASA NTRS1996

Computerized Design and Analysis of Face-Milled, Uniform Tooth Height, Low-Noise Spiral Bevel Gear Drives

A new method for design and generation of spiral bevel gears of uniform tooth depth with localized bearing contact and low level of transmission errors is considered. The main features of the proposed approach are as follows: (1) the localization of the bearing contact is achieved by the mismatch of the generating surfaces. The bearing contact may be provided in the longitudinal direction, or in the direction across the surface; and (2) the low level of transmission errors is achieved due to application of nonlinear relations between the motions of the gear and the gear head-cutter. Such relations may be provided by application of a CNC machine. The generation of the pinion is based on application of linear relations between the motions of the tool and the pinion being generated. The relations described above permit a parabolic function of transmission errors to be obtained that is able to absorb almost linear functions caused by errors of gear alignment. A computer code has been written for the meshing and contact of the spiral bevel gears with the proposed geometry. The effect of misalignment on the proposed geometry has also been determined. Numerical examples for illustration of the proposed theory have been provided.

Litvin, F. L.↗
NASA NTRS1996

Computerized Design and Analysis of Face-Milled, Uniform Tooth Height, Low-Noise Spiral Bevel Gear Drives

A new method for design and generation of spiral bevel gears of uniform tooth depth with localized bearing contact and low level of transmission errors is considered. The main features of the proposed approach are as follows: (1) The localization of the bearing contact is achieved by the mismatch of the generating surfaces. The bearing contact may be provided in the longitudinal direction, or in the direction across the surface; and (2) The low level of transmission errors is achieved due to application of nonlinear relations between the motions of the gear and the gear head-cutter. Such relations may be provided by application of a CNC machine. The generation of the pinion is based on application of linear relations between the motions of the tool and the pinion being generated. The relations described above permit a parabolic function of transmission errors to be obtained that is able to absorb almost linear functions caused by errors of gear alignment. A computer code has been written for the meshing and contact of the spiral bevel gears with the proposed geometry. The effect of misalignment on the proposed geometry has also been determined. Numerical examples for illustration of the proposed theory have been provided.

Litvin, F. L.↗
NASA NTRS1979

The low-noise 115-GHz receiver on the Columbia-GISS 4-ft radio telescope

The superheterodyne millimeter-wave radiometer on the Columbia-GISS 4-ft telescope is described. This receiver uses a room-temperature Schottky diode mixer, with a resonant-ring filter as LO diplexer. The diplexer has low signal loss, efficient LO power coupling, and suppresses most of the LO noise at both sidebands. The receiver IF section has a parametric amplifier as its first stage with sufficient gain to overcome the second-stage amplifier noise. A broad-banded quarter-wave impedance transformer minimizes the mismatch between mixer and paramp. At 115 GHz, the SSB receiver noise temperature is 860 K, which is believed to be the lowest figure so far reported for a room-temperature receiver at this frequency.

Cong, H.-I.↗