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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Evaluation of Variable-Depth Liners with Slotted Cores

An initial evaluation of variable-depth, slotted-core liners fabricated with conventional, flightworthy com-ponents is presented. Liners with two distinct chamber lengths provide significant broadband absorption and their impedances are, to first order, predictable with the NASA impedance prediction code. These liners employ film caps embedded in alternating chambers to provide a near-rigid boundary condition. This enables improved control of the liner design process. A number of additively-manufactured, bent-chamber liners are also investigated to explore the e˙ects of the bend on the liner impedance. The liner impedance is negligibly a˙ected by changes to the partition width, but is significantly a˙ected by changes to the slot height. This o˙ers an option for achieving low-frequency sound absorption with relatively thin liners.

acoustic↗
NASA NTRS2012

Fabrication of an Absorber-Coupled MKID Detector

Absorber-coupled microwave kinetic inductance detector (MKID) arrays were developed for submillimeter and far-infrared astronomy. These sensors comprise arrays of lambda/2 stepped microwave impedance resonators patterned on a 1.5-mm-thick silicon membrane, which is optimized for optical coupling. The detector elements are supported on a 380-mm-thick micro-machined silicon wafer. The resonators consist of parallel plate aluminum transmission lines coupled to low-impedance Nb microstrip traces of variable length, which set the resonant frequency of each resonator. This allows for multiplexed microwave readout and, consequently, good spatial discrimination between pixels in the array. The transmission lines simultaneously act to absorb optical power and employ an appropriate surface impedance and effective filling fraction. The fabrication techniques demonstrate high-fabrication yield of MKID arrays on large, single-crystal membranes and sub-micron front-to-back alignment of the micro strip circuit. An MKID is a detector that operates upon the principle that a superconducting material s kinetic inductance and surface resistance will change in response to being exposed to radiation with a power density sufficient to break its Cooper pairs. When integrated as part of a resonant circuit, the change in surface impedance will result in a shift in its resonance frequency and a decrease of its quality factor. In this approach, incident power creates quasiparticles inside a superconducting resonator, which is configured to match the impedance of free space in order to absorb the radiation being detected. For this reason MKIDs are attractive for use in large-format focal plane arrays, because they are easily multiplexed in the frequency domain and their fabrication is straightforward. The fabrication process can be summarized in seven steps: (1) Alignment marks are lithographically patterned and etched all the way through a silicon on insulator (SOI) wafer, which consists of a thin silicon membrane bonded to a thick silicon handle wafer. (2) The metal microwave circuitry on the front of the membrane is patterned and etched. (3) The wafer is then temporarily bonded with wafer wax to a Pyrex wafer, with the SOI side abutting the Pyrex. (4) The silicon handle component of the SOI wafer is subsequently etched away so as to expose the membrane backside. (5) The wafer is flipped over, and metal microwave circuitry is patterned and etched on the membrane backside. Furthermore, cuts in the membrane are made so as to define the individual detector array chips. (6) Silicon frames are micromachined and glued to the silicon membrane. (7) The membranes, which are now attached to the frames, are released from the Pyrex wafer via dissolution of the wafer wax in acetone.

Brown, Ari↗
NASA NTRS2010

Fabrication of an Absorber-Coupled MKID Detector and Readout for Sub-Millimeter and Far-Infrared Astronomy

We have fabricated absorber-coupled microwave kinetic inductance detector (MKID) arrays for sub-millimeter and far-infrared astronomy. Each detector array is comprised of lambda/2 stepped impedance resonators, a 1.5 micrometer thick silicon membrane, and 380 micrometer thick silicon walls. The resonators consist of parallel plate aluminum transmission lines coupled to low impedance Nb microstrip traces of variable length, which set the resonant frequency of each resonator. This allows for multiplexed microwave readout and, consequently, good spatial discrimination between pixels in the array. The Al transmission lines simultaneously act to absorb optical power and are designed to have a surface impedance and filling fraction so as to match the impedance of free space. Our novel fabrication techniques demonstrate high fabrication yield of MKID arrays on large single crystal membranes and sub-micron front-to-back alignment of the microstrip circuit.

Brown, Ari-David↗
NASA NTRS2010

Fabrication of an Absorber-Coupled MKID Detector and Readout for Sub-Millimeter and Far-Infrared Astronomy

We have fabricated absorber-coupled microwave kinetic inductance detector (MKID) arrays for sub-millimeter and farinfrared astronomy. Each detector array is comprised of lambda/2 stepped impedance resonators, a 1.5μm thick silicon membrane, and 380μm thick silicon walls. The resonators consist of parallel plate aluminum transmission lines coupled to low impedance Nb microstrip traces of variable length, which set the resonant frequency of each resonator. This allows for multiplexed microwave readout and, consequently, good spatial discrimination between pixels in the array. The Al transmission lines simultaneously act to absorb optical power and are designed to have a surface impedance and filling fraction so as to match the impedance of free space. Our novel fabrication techniques demonstrate high fabrication yield of MKID arrays on large single crystal membranes and sub-micron front-to-back alignment of the microstrip circuit.

far-infrared↗
NASA NTRSDate not supplied

Optimization of Variable Depth Acoustic Liners with Grazing Flow

Acoustic liners, typically used as a noise control treatment in the engine nacelles of conventional aircraft, are being considered for noise treatment in the proprotor ducts of a vertical takeoff and landing aircraft. This work considers a new optimization method to design an acoustic liner with variable depth cavities for broadband and low-frequency attenuation. This method, termed the direct optimization method, minimizes the radiated sound from a duct. In this paper, the new method is compared with an existing indirect method to design multiple variable depth acoustic liners. Acoustic impedances of liners designed using both methods are predicted using a semianalytical impedance model and impedance predictions for two designs are compared to experimental results acquired from grazing flow impedance testing. For the work presented here, liners designed using the indirect approach provide improved attenuation spectra over those designed using the direct approach but potential improvements to the performance of the direction optimization method are discussed.

Proprotor↗
NASA NTRS2019

Initial Developments of a Low Drag Variable Depth Acoustic Liner

The purpose of this study is to assess the acoustic performance and relative drag of a new type of variable depth liner containing pairs of resonators coupled together by shared inlet volumes just below the facesheet. This type of liner has the potential to achieve a targeted impedance with fewer openings in the facesheet, and therefore less drag, than previous designs. To better understand the limitations of the concept, three sets of samples were designed and tested in the NASA Langley normal incidence and grazing flow impedance tubes. Each set of samples consisted of a baseline variable depth liner with straight chambers, and a prototype liner with shared inlet volumes. Measurements conducted in both the normal incidence and grazing flow impedance tubes confirm that the prototype liner can achieve the same impedance as the baseline variable depth liner at discrete frequencies with 50% less open area. This results in a 75% reduction in the drag penalty relative to the baseline design. The proposed concept is not, however, able to achieve a flat, broadband impedance as effectively as the baseline liner. So, while the proposed concept is well suited for multitonal design metrics, tradeoffs must be made between liner drag and acoustic performance when broadband attenuation is required.

Schiller, Noah H.↗
NASA NTRS1987

Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit

The evolution and long-time stability of a double layer (DL) in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double layer potential structure. A simple model is presented in which this current redistribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double layer potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a one-dimensional simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.

Smith, Robert A.↗
NASA NTRS1987

Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit

The evolution and long-time stability of a double layer in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-layer potential structure. A simple model is presented in which this current re-distribution is effected by anomalous transport based on electrostatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-layer potential. The flank charging may be represented as that of a nonlinear transmission. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.

Smith, Robert A.↗
NASA NTRSDate not supplied

Evaluation of a Variable Facesheet Liner Configuration in Grazing Incidence for Broadband Noise Reduction

Tests were conducted in the NASA Langley Grazing Flow Impedance Tube (GFIT) to determine the broadband noise reduction capability of a variable facesheet liner. Three uniform liners were designed to achieve sound absorption over distinct frequency regimes at Mach 0.0. Each liner was fabricated and tested in the GFIT at sound pressure levels of 120 and 140 dB, and at tangential flow velocities up to Mach 0.5. A variable facesheet liner was fabricated to combine the geometries of these three liners, such that the facesheet geometry (hole diameter and porosity) was varied across the liner surface. The Prony method was used to educe the impedance of each sample, and these impedances were input to the CHE (Convected Helmholtz Equation) propagation code to predict the acoustic pressure profiles in the GFIT. Comparisons of predicted and measured acoustic pressure profiles were used to confirm the uniformity of all four liners, and to demonstrate the suitability of the CHE code in the analysis of the variable facesheet concept. Results showed good comparison at no flow and at Mach 0.3, and acceptable comparison at Mach 0.5. The variable facesheet liner provided enhanced broadband noise reduction at the no-flow condition for which it was designed, but further optimization is needed to target flow conditions.

acoustic↗
NASA NTRSDate not supplied

Evaluation of a Variable Facesheet Liner Configuration in Grazing Incidence for Broadband Noise Reduction

Abstract Tests were conducted in the NASA Langley Grazing Flow Impedance Tube (GFIT) to determine the broadband noise reduction capability of a variable facesheet liner. Three uniform liners were designed to achieve sound absorption over distinct frequency regimes at Mach 0.0. Each liner was fabricated and tested in the GFIT at sound pressure levels of 120 and 140 dB, and at tangential flow velocities up to Mach 0.5. A variable facesheet liner was fabricated to combine the geometries of these three liners, such that the facesheet geometry (hole diameter and porosity) was varied across the liner surface. The Prony method was used to educe the impedance of each sample, and these impedances were input to the CHE (Convected Helmholtz Equation) propagation code to predict the acoustic pressure profiles in the GFIT. Comparisons of predicted and measured acoustic pressure profiles were used to confirm the uniformity of all four liners, and to demonstrate the suitability of the CHE code in analysis of the variable facesheet concept. Results showed good comparison at no flow and Mach 0.3, and acceptable comparison at Mach 0.5. The variable facesheet liner provides enhanced broadband noise reduction at the no-flow condition for which it was designed, but further optimization is needed to target flow conditions.

acoustic↗
NASA NTRS1987

Cardiovascular dynamics during the initial period of head-down tilt

The cardiovascular response to 1 h of 60-deg head-down tilt was studied in 12 male subjects, ages 30-39 years, to simulate the early effects of weightlessness. Fluid shifts, hemodynamic variables, and indices of myocardial contractility were evaluated by utilizing electrocardiography, systolic time intervals, impedance cardiography, sphygmomanometry, and measurement of calf circumference. Most cardiovascular variables remained stable throughout the initial 30 min of the protocol, even though translocation of fluid from the legs to the thorax commenced immediately with the onset of head-down tilt. In contrast, minutes 30-60 were characterized by reduced stroke volume, cardiac output, mean stroke ejection rate, and Heather index concomitant with an elevation in mean arterial pressure. Intrathoracic fluid volume continued to increase, while leg volume continued to decrease. This latter physiological response suggests intrathoracic sequestration of fluid volume; blood was apparently redistributed to the pulmonary circulation rather than being retained in the great veins.

Tomaselli, Clare Marie↗
NASA NTRS2016

Evaluation of Novel Liner Concepts for Fan and Airframe Noise Reduction

This paper presents a review of four novel liner concepts: soft vanes, over-the-rotor liners, external liners, and flap side-edge liners. A number of similarities in the design and evaluation of these concepts emerged during these investigations. Since these were the first attempts to study these particular liner concepts, there was limited information to guide the design process. In all cases, the target frequencies (or frequency range) were known, but the optimum acoustic impedance and optimum liner placement were typically not known. For these cases, the maximum available surface was used and a c-impedance was targeted based on the assumption the sound field impinges on the surface at normal incidence. This choice proved fruitful for every application. An impedance prediction model was used to design variable-depth liner configurations, and a graphical design code (ILIAD) was developed to aid in this process. The ability to build increasingly complex liner configurations via additive manufacturing was key, such that multiple designs could quickly be tested in a normal incidence impedance tube. The Two-Thickness Method was used to evaluate available bulk materials, such that bulk liners could also be considered for each application. These novel liner concepts provide sufficient noise reduction to warrant further investigations.

Jones, M. G.↗
NASA NTRS2015

Evaluation of Variable-Depth Liner Configurations for Increased Broadband Noise Reduction

This paper explores the effects of variable-depth geometry on the amount of noise reduction that can be achieved with acoustic liners. Results for two variable-depth liners tested in the NASA Langley Grazing Flow Impedance Tube demonstrate significant broadband noise reduction. An impedance prediction model is combined with two propagation codes to predict corresponding sound pressure level profiles over the length of the Grazing Flow Impedance Tube. The comparison of measured and predicted sound pressure level profiles is sufficiently favorable to support use of these tools for investigation of a number of proposed variable-depth liner configurations. Predicted sound pressure level profiles for these proposed configurations reveal a number of interesting features. Liner orientation clearly affects the sound pressure level profile over the length of the liner, but the effect on the total attenuation is less pronounced. The axial extent of attenuation at an individual frequency continues well beyond the location where the liner depth is optimally tuned to the quarter-wavelength of that frequency. The sound pressure level profile is significantly affected by the way in which variable-depth segments are distributed over the length of the liner. Given the broadband noise reduction capability for these liner configurations, further development of impedance prediction models and propagation codes specifically tuned for this application is warranted.

Jones, M. G.↗
NASA NTRSDate not supplied

An Initial Assessment of Variable Depth Liner Optimization for Ducted Proprotor Applications

The rise of the Urban Air Mobility market has spurred the design of a new generation of novel aircraft. To aid industry and researchers interested in these types of aircraft, the Revolutionary Vertical Lift Technology project at NASA has developed a fleet of reference vehicles for system studies. A new six-passenger reference vehicle has recently been added to the research portfolio that has ducted proprotors for propulsors. The ducts present an opportunity to apply acoustic treatment to the interior of the duct that could target both tonal and broadband noise, representative of the sound produced by this type of propulsor. In this paper, design methodologies are presented to design a variable depth liner for this application. An optimizer is used to design multiple liners with variable chamber depths. Experimental results from normal impedance testing are compared to numerical predictions using the optimizer model and a finite element model. Results show that an optimizer can be used to design an acoustic liner with favorable performance for a broad range of frequencies, which could be appropriate for a ducted proprotor application.

Matthew B Galles↗
NASA NTRS1975

Signal conditioning circuit apparatus

A signal conditioning circuit is described including operational amplifier, a variable source of offset potential, and four resistive impedance. The circuit has constant input impedance independent of gain and offset adjustments. Gain change is effected by varying one of the impedances in an amplifier feedback circuit; offset adjustment is effected through variation of the offset potential source.

Holland, V. B.↗
NASA NTRS1975

Duct acoustics and acoustic finite element method

A comprehensive solution method - Acoustic Finite Element Method - has been proposed. In order to generate confidence in the method proposed, the problem of influence of shear flow in a two-dimensional channel on sound propagation from an arbitrary source distribution has been theoretically formulated. From the preliminary investigation of application of acoustic finite element method, it seems that it can provide solutions to problems concerning the transmission of sound in variable area ducts, or in ducts in which the boundary layer depends on the streamwise variable, or in ducts with discontinuities in lining impedance and with end termination impedances, both the inlet and exhaust jet flows being taken into account.

Kapur, A.↗
NASA NTRS1983

Preliminary evaluation of thematic mapper sensor characteristics relative to land cover/land use discrimination

Preliminary experimental results of airborne thematic mapper (TM) data taken to quantify the effect of three major TM sensor parameters, spectral, spatial, and radiometric resolution, six months after launch of Landsat-4 are reported. The flight took place on Nov. 2, 1982 over Washington, D.C., and data gathered were compared with ground reference data from color airborne photography on a 1:40,000 scale. Analyses proceeded by deleting one band from each of four data sets, thus making the data equivalent to MSS data. Attention was directed to land cover/use classes in a quick-look format. A per-pixel maximum likelihood scheme was found to increase the recognition and dicrimination categorization capabilities. Finer spatial resolution, however, impeded classification due to increased within-class variability of the field-center pixels, which also incresed class overlap in the spectral data base. Improved data analyses techniques are therefore needed to exploit the available higher spatial resolution of the TM.

Williams, D. L.↗