Low frequency damping and ultrasonic attenuation in Ti3Sn-based alloys

1994 ◽  
Vol 9 (6) ◽  
pp. 1441-1448 ◽  
Author(s):  
Catherine R. Wong ◽  
Robert L. Fleischer
Keyword(s):  
High Temperature ◽  
Room Temperature ◽  
Ultrasonic Attenuation ◽  
Low Frequency ◽  
Basic Mechanism ◽  
Low Frequencies ◽  
High Frequencies ◽  
Young’S Moduli ◽  
High Temperature Alloys ◽  
Damping Behavior

Studies of high-temperature alloys in the Ti-Sn system based on the intermetallic compound Ti3Sn have identified alloys that damp strongly both at low frequencies (0.1 to 10 Hz) and high frequencies (5 to 20 MHz). The low frequency damping behavior shows loss factors as high as 0.04 at room temperature and Young's moduli that rise with temperature from 40 °C to 100 °C for two alloys. Although the basic mechanism or mechanisms of energy dissipation are presently unknown, the alloys are notable for unusual shapes of microhardness indentations. The deformations imply that large reversible strains can occur at temperatures from 23 °C to 1150 °C.

Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies

2011 ◽  
Author(s):  
Gundula B. Runge ◽  
Al Ferri ◽  
Bonnie Ferri
Keyword(s):  
Time Scale ◽  
Weighting Function ◽  
Control Strategies ◽  
Low Frequency ◽  
Low Frequencies ◽  
High Frequencies ◽  
Frequency Components ◽  
Computational Resources ◽  
Weighted Variable ◽  
Selection Of

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.

Evaluation of Thermal Degradation of 2.25Cr-1Mo Steel by High Frequency Ultrasonic Attenuation Measurement

2005 ◽  
Vol 475-479 ◽  
pp. 257-260 ◽  
Author(s):  
Jai Won Byeon ◽  
C.S. Kim ◽  
S.I. Kwun ◽  
S.J. Hong
Keyword(s):  
Attenuation Coefficient ◽  
High Frequency ◽  
Ultrasonic Attenuation ◽  
Attenuation Coefficients ◽  
Low Frequencies ◽  
High Frequencies ◽  
Noticeable Increase ◽  
Mean Size ◽  
Longitudinal Ultrasonic Wave ◽  
Degradation Time

It was attempted to assess nondestructively the degree of isothermal degradation of 2.25Cr-1Mo steel by using high frequency longitudinal ultrasonic wave. Microstructural parameter (mean size of carbides), mechanical property (Vickers hardness) and ultrasonic attenuation coefficient were measured for the 2.25Cr-1Mo steel isothermally degraded at 630°C for up to 4800 hours in order to find the correlation among these parameters. The ultrasonic attenuation coefficients at high frequencies (over 35MHz) were observed to increase rapidly in the initial 1000 hours of degradation time and then slowly thereafter, while the ones at low frequencies showed no noticeable increase. Ultrasonic attenuation at high frequencies increased as a function of mean size of carbides. Ultrasonic attenuation coefficient was found to have a linear correlation with the hardness, and suggested accordingly as a potential nondestructive evaluation parameter for assessing the mechanical strength reduction of the isothermally degraded 2.25Cr-1Mo steel.

High Temperature Anisotropic Magnetoresistive (AMR) Sensors

2015 ◽  
Vol 2015 (HiTEN) ◽  
pp. 000236-000243
Author(s):  
Bharat B. Pant ◽  
Lucky Withanawasam ◽  
Mike Bohlinger ◽  
Mark Larson ◽  
Bruce W. Ohme
Keyword(s):  
High Temperature ◽  
Transfer Function ◽  
Bias Voltage ◽  
Room Temperature ◽  
Closed Loop ◽  
Low Frequency ◽  
Low Noise ◽  
Noise Characteristics ◽  
Thermal Chamber ◽  
Increasing Temperature

Magnetic field sensors are employed in down-hole oil, gas, and geothermal well-drilling applications for azimuth sensing, orientation/rotation sensing, and magnetic anomaly detection. Key requirements of these applications include high measurement accuracy in the near-DC frequency regime, high-operating temperatures, high mechanical shock and vibration, and severe size constraints. Silicon manufacturing processes enable the development of rugged components with small size compatible with assembly processes used for adjacent electronics in hermetically sealed hybrid and/or ceramic packages. Silicon-based magnetic sensors include Anistotropic Magnetoresistive (AMR), Giant Magnetoresistive (GMR) and Tunnelling Magnetoresistive (TMR) sensors. Commercially available GMR and TMR sensors generally cannot be operated much above 150°C. While GMR and TMR have enabled great areal density growth for magnetic recording industry over the past two decades, AMR sensors provide high accuracy measurements in the near-DC regime above 150°C. This is in part due to simplicity of their construction, but also due to their low noise characteristics at low frequencies compared to GMR and TMR. This paper will describe the extension of Honeywell's low noise AMR sensors into high temperature regime up to 225°C. Sensors being reported have room temperature bridge resistance of ~700 Ω, open loop sensitivity of ~2.5 mV/V-Gauss, with a temperature coefficient of sensitivity of −2500 ppm/°C. The low-frequency minimum detectable field monotonically increases with increasing temperature. At room temperature it is ~2.2 μG/√Hz@1 Hz and reaches a value of ~26μG/√Hz@1 Hz at 225°C. Signal and noise density both increase with increasing sensor bias voltage such that low-frequency signal-to-noise ratio does not vary in the bias voltage range of 2.5 V to 10V. These sensors have also been configured in a closed loop format using low noise electronics. Measurements of closed loop transfer function in the range of ±0.8 Gauss were made. The sensor was placed in a thermal chamber while the feedback electronics were placed outside at room temperature. The linearity of the transfer function is quite excellent; deviation from linearity increases monotonically with increasing temperature reaching < 0.002% of full scale or 29 μGauss at 225°C. Closed loop operation of a typical sensor shows 1-σ measurement variability of 21 μGauss at 220°C. By a combination of averaging and closed loop operation an input step from 0 to 75 μGauss is replicated at the output to within 0.1 μG at 225°C.

scholarly journals Laboratory measurements of low- and high-frequency elastic moduli in Fontainebleau sandstone

Geophysics ◽  
2013 ◽  
Vol 78 (5) ◽  
pp. D369-D379 ◽  
Author(s):  
Emmanuel C. David ◽  
Jérome Fortin ◽  
Alexandre Schubnel ◽  
Yves Guéguen ◽  
Robert W. Zimmerman
Keyword(s):  
Bulk Modulus ◽  
Elastic Moduli ◽  
High Pressures ◽  
Low Frequency ◽  
Frequency Dispersion ◽  
Low Frequencies ◽  
High Frequencies ◽  
Fontainebleau Sandstone ◽  
Wave Velocities ◽  
Water Saturated

The presence of pores and cracks in rocks causes the fluid-saturated wave velocities in rocks to be dependent on frequency. New measurements of the bulk modulus at low frequencies (0.02–0.1 Hz) were obtained in the laboratory using oscillation tests carried out on two hydrostatically stressed Fontainebleau sandstone samples, in conjunction with ultrasonic velocities and static measurements, under a range of differential pressures (10–95 MPa), and with three different pore fluids (argon, glycerin, and water). For the 13% and 4% porosity samples, under glycerin- and water-saturated conditions, the low-frequency bulk modulus at 0.02 Hz matched well the low-frequency and ultrasonic dry bulk modulus. The glycerin- and water-saturated samples were much more compliant at low frequencies than at high frequencies. The measured bulk moduli of the tested rocks at low frequencies (0.02–0.1 Hz) were much lower than the values predicted by the Gassmann equation. The frequency dispersion of the P and S velocities was much higher at low differential pressures than at high pressures, due to the presence of open cracks at low differential pressures.

Permeability and borehole Stoneley waves: Comparison between experiment and theory

Geophysics ◽  
1989 ◽  
Vol 54 (1) ◽  
pp. 66-75 ◽  
Author(s):  
Kenneth W. Winkler ◽  
Hsui‐Lin Liu ◽  
David Linton Johnson
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
Theoretical Models ◽  
Oil Field ◽  
Stoneley Wave ◽  
Biot Theory ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
High Frequencies ◽  
Theoretical Predictions

We performed laboratory experiments to evaluate theoretical models of borehole. Stoneley wave propagation in permeable materials. A Berea sandstone and synthetic samples made of cemented glass beads were saturated with silicone oils. We measured both velocity and attenuation over a frequency band from 10 kHz to 90 kHz. Our theoretical modeling incorporated Biot theory and Deresiewicz‐Skalak boundary conditions into a cylindrical geometry and included frequency‐dependent permeability. By varying the viscosity of the saturating pore fluid, we were able to study both low‐frequency and high‐frequency regions of Biot theory, as well as the intermediate transition zone. In both low‐frequency and high‐frequency regions of the theory, we obtained excellent agreement between experimental observations and theoretical predictions. Velocity and attenuation (1/Q) are frequency‐dependent, especially at low frequencies. Also at low frequencies, velocity decreases and attenuation increases with increasing fluid mobility (permeability/viscosity). More complicated behavior is observed at high frequencies. These results support recent observations from the oil field suggesting that Stoneley wave velocity and attenuation may be indicative of formation permeability.

Cuprate High Temperature Superconductors and the Vision for Room Temperature Superconductivity

SPIN ◽  
2017 ◽  
Vol 07 (02) ◽  
pp. 1750006 ◽  
Author(s):  
Dennis M. Newns ◽  
Glenn J. Martyna ◽  
Chang C. Tsuei
Keyword(s):  
High Temperature ◽  
High Frequency ◽  
Room Temperature ◽  
Phonon Frequency ◽  
High Temperature Superconductors ◽  
Low Frequency ◽  
Unconventional Superconductivity ◽  
Superconducting Transition ◽  
Strongly Coupled ◽  
Room Temperature Superconductivity

Superconducting transition temperatures of 164 K in cuprate high temperature superconductors (HTS) and recently 200 K in H3S under high pressure encourage us to believe that room temperature superconductivity (RTS) might be possible. In considering paths to RTS, we contrast conventional (BCS) SC, such as probably manifested by H3S, with the unconventional superconductivity (SC) in the cuprate HTS family. Turning to SC models, we show that in the presence of one or more van Hove singularities (vHs) near the Fermi level, SC mediated by classical phonons ([Formula: see text]phonon frequency) can occur. The phonon frequency in the standard [Formula: see text] formula is replaced by an electronic cutoff, enabling a much higher [Formula: see text] independent of phonon frequency. The resulting [Formula: see text] and isotope shift plot versus doping strongly resembles that seen experimentally in HTS. A more detailed theory of HTS, which involves mediation by classical phonons, satisfactorily reproduces the chief anomalous features characteristic of these materials. We propose that, while a path to RTS through an H3S-like scenario via strongly-coupled ultra-high frequency phonons is attractive, features perhaps unavailable at ordinary pressures, a route involving SC mediated by classical phonons which can be low frequency may be found.

scholarly journals High Frequency Performance of Piezoelectric Diaphragms for Impedance-Based SHM Applications

2020 ◽  
Vol 2 (1) ◽  
pp. 16
Author(s):  
Guilherme Rezende ◽  
Fabricio Baptista
Keyword(s):  
High Frequency ◽  
Structural Damage ◽  
Low Cost ◽  
Low Frequency ◽  
Experimental Tests ◽  
Piezoelectric Transducers ◽  
Low Frequencies ◽  
High Frequencies ◽  
Electromechanical Impedance ◽  
Damage Indices

Piezoelectric transducers are used in a wide variety of applications, including damage detection in structural health monitoring (SHM) applications. Among the various methods for detecting structural damage, the electromechanical impedance (EMI) method is one of the most investigated in recent years. In this method, the transducer is typically excited with low frequency signals up to 500 kHz. However, recent studies have indicated the use of higher frequencies, usually above 1 MHz, for the detection of some types of damage and the monitoring of some structures’ characteristics that are not possible at low frequencies. Therefore, this study investigates the performance of low-cost piezoelectric diaphragms excited with high frequency signals for SHM applications based on the EMI method. Piezoelectric diaphragms have recently been reported in the literature as alternative transducers for the EMI method and, therefore, investigating the performance of these transducers at high frequencies is a relevant subject. Experimental tests were carried out with piezoelectric diaphragms attached to two aluminum bars, obtaining the impedance signatures from diaphragms excited with low and high frequency signals. The analysis was performed using the real part of the impedance signatures and two basic damage indices, one based on the Euclidean norm and the other on the correlation coefficient. The experimental results indicate that piezoelectric diaphragms are usable for the detection of structural damage at high frequencies, although the sensitivity decreases.

Comparison of multiple-layer versus multiple-cavity microperforated panels for sound absorption at low frequency

2021 ◽  
Vol 69 (4) ◽  
pp. 341-350
Author(s):  
Pedro Cobo ◽  
Francisco Simón ◽  
Carlos Colina
Keyword(s):  
Sound Absorption ◽  
Low Frequency ◽  
Single Layer ◽  
Helmholtz Resonator ◽  
Layer Versus ◽  
Low Frequencies ◽  
High Frequencies ◽  
Multiple Layer ◽  
Band Absorption ◽  
Microperforated Panels

Microperforated panels (MPPs) are recognized as suitable absorbers for noise control applications demanding special clean and health requirements.While it is relatively easy to design single-layer MPPs for sound absorption in one-to-two octave bands at medium-high frequencies, the performance for low frequencies (below 600 Hz) leads to a rather narrow-band absorption, similar to that of a Helmholtz resonator. However, multiple-layer MPPs can be designed as sound absorbers that yield low-frequency absorption in a wide frequency band. Recently, multiple-cavity perforated panels have been proposed to improve the performance of MPPs in the low-frequency range. In this article, the capability of multiple-layer and multiple-cavity MPPs to provide sound absorption at low frequencies is analyzed.

Pre-Stall Waves: Precursors to Stall Inception in a Contra-Rotating Axial Fan

2020 ◽  
Author(s):  
Manas Madasseri Payyappalli ◽  
A. M. Pradeep
Keyword(s):  
Low Frequency ◽  
Intermediate Frequency ◽  
Axial Fan ◽  
Frequency Spectra ◽  
Low Frequencies ◽  
Stall Inception ◽  
High Frequencies ◽  
Inflow Condition ◽  
Design Speed ◽  
High Frequency Waves

Abstract Stall in a compressor or a fan is often associated with pre-stall waves, that could act as precursors. The present study aims to understand in detail the pre-stall waves leading to instabilities in a low aspect ratio, low hub-tip ratio contra-rotating axial fan. Apart from a clean inflow condition, experiments on the contra-rotating fan are also carried out for two radial distortion conditions, namely, hub-radial and tip-radial distortions, and three circumferential distortion conditions, namely, simple-circumferential, hub-complex-circumferential and tip-complex-circumferential distortions. The results primarily concluded that operating rotor-2 at a speed higher than the design speed could possibly suppress the pre-stall disturbances. Towards the fully developed stall, the waves that are associated with low frequencies speed up and thus these waves become intermediate frequency waves. The fluid phenomena that trigger the stall are associated with high frequencies and these subsequently stretch to low frequencies at the onset of fully developed stall. The low-frequency waves and high frequency waves compromise to reach an intermediate frequency range during the fully developed stall. Further, it is observed that disturbances associated with low frequencies as well as high frequencies co-exist during the fully developed stall regime. There is also a region in the frequency spectra where no disturbances are excited and this region appears to be a “no excitation zone”. This paper thus concludes that there possibly exists a mechanism through which the energy is transferred between different frequencies during the pre-stall and fully developed stall regimes.

Sympathetic stimulation elicits increased or decreased VO2 in the perfused rat hindlimb via alpha 1-adrenoceptors

1997 ◽  
Vol 272 (5) ◽  
pp. H2146-H2153 ◽  
Author(s):  
J. L. Hall ◽  
J. M. Ye ◽  
M. G. Clark ◽  
E. Q. Colquhoun
Keyword(s):  
High Frequency ◽  
Pressor Response ◽  
Low Frequency ◽  
Sympathetic Nerves ◽  
High Frequency Stimulation ◽  
Arterial Infusion ◽  
Low Frequencies ◽  
High Frequencies ◽  
Low Frequency Stimulation ◽  
Frequency Stimulation

The effects of lumbar sympathetic nerve stimulation on oxygen uptake (VO2) in curarized muscle of the perfused rat hindlimb were investigated. Stimulation of sympathetic nerves elicited vasoconstriction at all frequencies. Importantly, this was associated with changes in VO2 that were generally stimulatory at low frequencies (0.5-2 Hz) and inhibitory at high frequencies (5-10 Hz). Both the pressor response and the changes in VO2 were almost completely blocked by the alpha 1/alpha 2-blocker phentolamine (1.0 microM) but were not affected by the beta 1/beta 2-blocker DL-propranolol (2.0 microM). The alpha 2-blocker yohimbine (0.1 microM) did not significantly affect either the pressor or VO2 response. The alpha 1-antagonist prazosin (0.1 microM) abolished the vasoconstriction with low-frequency stimulation and inhibited > 90% of the vasoconstriction with high-frequency stimulation. Intra-arterial infusion of phenylephrine (alpha 1-agonist), but not of UK-14304 (alpha 2-agonist), also elicited a similar biphasic response in VO2 during vasoconstriction. The changes in VO2 at both low- and high-frequency stimulation were fully reversed by prazosin. The vasodilator sodium nitroprusside also showed similar effects to prazosin in blocking both VO2 and vasoconstriction. Thus sympathetic control of VO2 in the perfused rat hindlimb appears to be initiated by activation of predominantly vascular alpha 1-adrenoceptors.

Sign in / Sign up

Export Citation Format

Share Document