Dielectric Spectrum of CaCu3Ti4012 from the Giant Permittivity to its Negative Values

2013 ◽  
Vol 705 ◽  
pp. 52-55 ◽  
Author(s):  
Yurii Kabirov ◽  
Victor Gavrilyachenko ◽  
Evgeni Panchenko ◽  
Evgeni Milov ◽  
Anatoly Klenushkin
Keyword(s):  
Activation Energy ◽  
High Frequency ◽  
Low Frequency ◽  
Frequency Region ◽  
Dielectric Spectrum ◽  
Ceramic Technology ◽  
High Frequency Range ◽  
Frequency Range ◽  
One Step

The dielectric spectrum of CaCu3Ti4O12samples prepared by traditional "one step" ceramic technology is analyzed. It is established that the characteristic Debye-type dispersion with an activation energy 0, 075 eV manifests in the high-frequency range (f ~ 106Hz). In the low-frequency region (f< 102Hz) a transition from giant permittivity values to its negative values is detected in some samples. Conditions for such transition are discussed.

Electromagnetic Property of La0.7Sr0.3MnO3/Ag Composite at High Frequency

2015 ◽  
Vol 655 ◽  
pp. 182-185
Author(s):  
Ke Lan Yan ◽  
Run Hua Fan ◽  
Min Chen ◽  
Kai Sun ◽  
Xu Ai Wang ◽  
...  
Keyword(s):  
High Frequency ◽  
Single Phase ◽  
Low Frequency ◽  
Electromagnetic Property ◽  
High Frequency Range ◽  
Frequency Range ◽  
Free Electron Concentration ◽  
Theoretical Simulation ◽  
Electrical And Magnetic Properties ◽  
Three Phase

The phase structure, and electrical and magnetic properties of La0.7Sr0.3MnO3(LSMO)-xAg (xis the mole ratio,x=0, 0.3, 0.5) composite were investigated. It is found that the sample withx=0 is single phase; the samples withx=0.3 and 0.5 present three phase composite structure of the manganese oxide and Ag. With the increasing of Ag content, the grain size of the samples increases and the grain boundaries transition from fully faceted to partially faceted. The permittivity of spectrum (10 MHz - 1 GHz) and the theoretical simulation reveal that the plasma frequencyfpincrease with Ag content, due to the increasing of free electron concentration, which is further supported by the enhancement of conductivity. While for the permeability (μr'), theμr'decrease with the increasing of Ag content at low frequency range (f< 20 MHz), while at the relative high frequency range (f> 300 MHz), theμr'increased with Ag content. Therefore, the introduction of elemental Ag resulted in a higherμr'at the relative high frequency range.

Anderson-Stuart Model to Analyze AC and DC Conductivity of Lithium Zinc-Silicate Glass / Glass-Ceramics

2007 ◽  
Vol 280-283 ◽  
pp. 919-924
Author(s):  
M.S. Jogad ◽  
V.K. Shrikhande ◽  
A.H. Dyama ◽  
L.A. Udachan ◽  
Govind P. Kothiyal
Keyword(s):  
High Frequency ◽  
Glass Ceramics ◽  
Low Frequency ◽  
Frequency Region ◽  
Dc Conductivity ◽  
Frequency Range ◽  
High Frequency Region ◽  
Dc Conductivities ◽  
Conductivity Variation ◽  
Different Temperatures

AC and DC conductivities have been measured by using the real (e¢) and imaginary (e¢¢) parts of the dielectric constant data of glass and glass-ceramics (GC) at different temperatures in the rage 297-642K and in the frequency range 100 Hz to 10 MHz. Using Anderson –Stuart model, we have calculated the activation energy, which is observed to be lower than that of the DC conductivity. The analysis for glass/glass-ceramics indicates that the conductivity variation with frequency exhibits an initial linear region followed by nonlinear region with a maximum in the high-frequency region. The observed frequency dependence of ionic conductivity has been analyzed within the extended Anderson–Stuart model considering both the electrostatic and elastic strain terms. In glass/glassceramic the calculations based on the Anderson-Stuart model agree with the experimental observations in the low frequency region but at higher frequencies there is departure from measured data.

On-Board Aircraft Engine Bearing Prognostics: Enveloping or FFT Analysis?

2009 ◽  
Author(s):  
Hai Qiu ◽  
Huageng Luo ◽  
Neil Eklund
Keyword(s):  
Spectrum Analysis ◽  
High Frequency ◽  
Characteristic Frequency ◽  
Low Frequency ◽  
Aircraft Engine ◽  
Frequency Region ◽  
Data Sampling ◽  
Frequency Range ◽  
Bearing Defect ◽  
Bearing Characteristic

Roller bearing prognosis requires the detection of a bearing defect signature in the earliest possible stage in order to avoid a minor or catastrophic mechanical failure. Defects can occur in any of the bearing parts, inner and outer race, cage and rolling elements. It is possible to identify the defective component of the bearing based on the specific vibration frequencies that are excited. However, the pattern of vibration spectrum changes as the bearing deteriorates through different stages. Depending on which failure stage the bearing is in, different techniques are required to find fault signatures in different frequency ranges. Techniques such as enveloping analysis that works in the high frequency region require higher data sampling rates and therefore more expensive data acquisition hardware than techniques conducted in low frequency region. This paper compares two popular rolling element bearing diagnostics techniques — spectrum analysis in the bearing characteristic frequency range and enveloping analysis in the high frequency range — using aircraft engine test rig data. The techniques are compared both in terms of the time of detection and data sampling requirement; this analysis provides guidance for technology adoption in future field deployment. Results demonstrate that enveloping analysis is able to detect bearing defects much earlier than the spectrum analysis, but it requires a higher data sampling rate. The bearing defect characteristic frequency is detectable in low frequency spectrum only in the late stage of the failure and it is contaminated by other harmonics such as shaft unbalance. From a practical perspective, the final choice of the technology adopted for deployment should be based on an analysis of hardware requirements and tolerance of detection latency.

SEA Subsystem Property Identification by Periodic FEM Approach

2011 ◽  
Vol 94-96 ◽  
pp. 1979-1982
Author(s):  
Jie Gao ◽  
Ke An Chen
Keyword(s):  
Dynamic Response ◽  
High Frequency ◽  
Periodic Structures ◽  
Low Frequency ◽  
Engineering Method ◽  
Complex Structures ◽  
High Frequency Range ◽  
Frequency Range ◽  
Remarkable Improvement ◽  
Property Identification

A study on SEA properties of periodically stiffened structure was accomplished based on the periodic theory. With application of certain software, a simulation was performed on a common periodically stiffened fuselage structure. The results indicate such modeling approach reflects relatively accurate property of subsystem in mid and high frequency range, while a remarkable improvement could also be expected in low frequency range, especially for complex structures. Such approach was approved as one reliable engineering method for solving dynamic response of periodic structures.

scholarly journals Specific Posture-Stabilising Effects of Vision and Touch Are Revealed by Distinct Changes of Body Oscillation Frequencies

2021 ◽  
Vol 12 ◽  
Author(s):  
Stefania Sozzi ◽  
Antonio Nardone ◽  
Marco Schieppati
Keyword(s):  
Frequency Analysis ◽  
High Frequency ◽  
Low Frequency ◽  
Control Mode ◽  
Spectral Amplitude ◽  
Median Frequency ◽  
High Frequency Range ◽  
Frequency Range ◽  
Foot Pressure ◽  
Eyes Closed

We addressed postural instability during stance with eyes closed (EC) on a compliant surface in healthy young people. Spectral analysis of the centre of foot pressure oscillations was used to identify the effects of haptic information (light-touch, EC-LT), or vision (eyes open, EO), or both (EO-LT). Spectral median frequency was strongly reduced by EO and EO-LT, while spectral amplitude was reduced by all “stabilising” sensory conditions. Reduction in spectrum level by EO mainly appeared in the high-frequency range. Reduction by LT was much larger than that induced by the vision in the low-frequency range, less so in the high-frequency range. Touch and vision together produced a fall in spectral amplitude across all windows, more so in anteroposterior (AP) direction. Lowermost frequencies contributed poorly to geometric measures (sway path and area) for all sensory conditions. The same subjects participated in control experiments on a solid base of support. Median frequency and amplitude of the spectrum and geometric measures were largely smaller when standing on solid than on foam base but poorly affected by the sensory conditions. Frequency analysis but not geometric measures allowed to disclose unique tuning of the postural control mode by haptic and visual information. During standing on foam, the vision did not reduce low-frequency oscillations, while touch diminished the entire spectrum, except for the medium-high frequencies, as if sway reduction by touch would rely on rapid balance corrections. The combination of frequency analysis with sensory conditions is a promising approach to explore altered postural mechanisms and prospective interventions in subjects with central or peripheral nervous system disorders.

Acoustic Emission Behaviors of Carbon-Cloth/Epoxy Composites in Compression Test

2011 ◽  
Vol 480-481 ◽  
pp. 421-426
Author(s):  
Chao Lu ◽  
Peng Ding ◽  
Zheng Hua Chen
Keyword(s):  
Acoustic Emission ◽  
Compression Test ◽  
High Frequency ◽  
Wavelet Packet ◽  
Low Frequency ◽  
Matrix Cracking ◽  
Carbon Cloth ◽  
High Frequency Range ◽  
Frequency Range ◽  
The Matrix

In this paper, we use acoustic emission (AE) system to collect the AE signals and analyze the damage evolution during the monotonic compression test. Based on the experimental correlation diagram of the load and characters of the acoustic emission, the reference load of failure was found. The experimental results also revealed the characters of the source of the acoustic emission signals after the wavelet packet decomposition and frequency spectrum analysis. The frequency range of the matrix cracking is on the range of 125~187.5 kHz, while the frequency range of layer debonding is wide, it is not just on the low-frequency range but on the high-frequency range. The frequency of fiber breakage is on the high frequency range, nearly on the range of 375~437.5 kHz.

Effects of whole body heating on dynamic baroreflex regulation of heart rate in humans

2000 ◽  
Vol 279 (5) ◽  
pp. H2486-H2492 ◽  
Author(s):  
C. G. Crandall ◽  
R. Zhang ◽  
B. D. Levine
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Heat Stress ◽  
Transfer Function ◽  
High Frequency ◽  
Low Frequency ◽  
Whole Body ◽  
High Frequency Range ◽  
Frequency Range ◽  
Transfer Function Analysis

The purpose of this project was to identify whether dynamic baroreflex regulation of heart rate (HR) is altered during whole body heating. In 14 subjects, dynamic baroreflex regulation of HR was assessed using transfer function analysis. In normothermic and heat-stressed conditions, each subject breathed at a fixed rate (0.25 Hz) while beat-by-beat HR and systolic blood pressure (SBP) were obtained. Whole body heating significantly increased sublingual temperature, HR, and forearm skin blood flow. Spectral analysis of HR and SBP revealed that the heat stress significantly reduced HR and SBP variability within the high-frequency range (0.2–0.3 Hz), reduced SBP variability within the low-frequency range (0.03–0.15 Hz), and increased the ratio of low- to high-frequency HR variability (all P < 0.01). Transfer function gain analysis showed that the heat stress reduced dynamic baroreflex regulation of HR within the high-frequency range (from 1.04 ± 0.06 to 0.54 ± 0.6 beats · min−1 · mmHg−1; P < 0.001) without significantly affecting the gain in the low-frequency range ( P = 0.63). These data suggest that whole body heating reduced high-frequency dynamic baroreflex regulation of HR associated with spontaneous changes in blood pressure. Reduced vagal baroreflex regulation of HR may contribute to reduced orthostatic tolerance known to occur in humans during heat stress.

Stroke volume effect of changing arterial input impedance over selected frequency ranges

1985 ◽  
Vol 248 (4) ◽  
pp. H477-H484 ◽  
Author(s):  
K. Sunagawa ◽  
W. L. Maughan ◽  
K. Sagawa
Keyword(s):  
Stroke Volume ◽  
High Frequency ◽  
Input Impedance ◽  
Characteristic Impedance ◽  
Low Frequency ◽  
Volume Effect ◽  
High Frequency Range ◽  
Frequency Range ◽  
Windkessel Model ◽  
End Diastolic Volume

We investigated the effect of changing arterial input impedance over three selected frequency ranges on stroke volume (SV) in nine isolated canine left ventricles. The input impedance was simulated with a three-element Windkessel model (i.e., resistance, characteristic impedance, and compliance) and was imposed on the ventricles with a servo-controlled loading system. Under a constant end-diastolic volume [33.1 +/- 1.5 (SE) ml], we changed the modulus of the afterloaded impedance over a low frequency range (below 0.13 Hz) by changing the resistance, over a transitional frequency range (in which the impedance modulus decreases from total resistance to characteristic impedance) by changing the compliance, and over a high frequency range (above 2.0 Hz) by changing the characteristic impedance. Each of the impedance components was changed from control to 50 and 200% of control. SV sensitively decreased from 16.1 +/- 0.7 to 7.4 +/- 0.5 ml in response to the increase in the low-frequency impedance modulus. SV was relatively insensitive, however, to the same percent increase in the impedance modulus over the transitional frequency range (from 11.2 +/- 0.6 to 12.3 +/- 0.7 ml) and over the high frequency range (from 11.9 +/- 0.6 to 11.6 +/- 0.7 ml). The average relative sensitivities of SV to the increase and decrease in impedance moduli in these frequency ranges were 1.2:0.12:0.04. We conclude that the modulus of impedance in the low frequency range is, by far, a more important determinant of SV than those in the transitional and high frequency ranges.

scholarly journals Modeling of the MET Sensitive Element Conversion Factor on the Intercathode Distance

Sensors ◽  
2020 ◽  
Vol 20 (18) ◽  
pp. 5146
Author(s):  
Maksim Ryzhkov ◽  
Vadim Agafonov
Keyword(s):  
High Frequency ◽  
Sensitive Element ◽  
Conversion Factor ◽  
Conversion Coefficient ◽  
Low Frequency ◽  
Frequency Region ◽  
Frequency Range ◽  
System Parameters ◽  
A Cell ◽  
Transforming Cell

MET sensors for measuring motion parameters are used in many scientific and technical fields. Meanwhile, the geometries of the transforming cell applied practically are far from optimal, and the influence of many geometric parameters on the sensitivity has not been studied. These parameters include the intercathode distance in a four-electrode conversion cell. In this paper, a mathematical model that allows calculating the behavior of the conversion coefficient depending on the frequency for a cell with flat electrodes at different intercathode distances is constructed. The stationary current is shown to decrease monotonically with the decreasing intercathode distance at the constancy of other system parameters. At the same time, the signal current decreases in the low-frequency region and increases in the high-frequency range. Taking into account the results obtained, practically speaking, it is advisable to reduce the intercathode distance to the technologically possible minimum, which makes the frequency response more uniform and reduces the current consumed by the sensitive element.

scholarly journals The effect of rock permeability and porosity on seismoelectric conversion: experiment and analytical modelling

2019 ◽  
Vol 219 (1) ◽  
pp. 328-345 ◽  
Author(s):  
Rong Peng ◽  
Bangrang Di ◽  
Paul W J Glover ◽  
Jianxin Wei1 ◽  
Piroska Lorinczi ◽  
...  
Keyword(s):  
Coupling Coefficient ◽  
High Frequency ◽  
Low Frequency ◽  
Low Permeability ◽  
High Frequency Range ◽  
Frequency Range ◽  
Rock Permeability ◽  
Rock Samples ◽  
Experimental Apparatus ◽  
Porosity And Permeability

SUMMARY The seismoelectric method is a modification of conventional seismic measurements which involves the conversion of an incident poroelastic wave to an electromagnetic signal that can be measured at the surface or down a borehole. This technique has the potential to probe the physical properties of the rocks at depth. The problem is that we currently know very little about the parameters which control seismoelectric conversion and their dependence on frequency and permeability, which limits the development of the seismoelectric method. The seismoelectric coupling coefficient indicates the strength of seismoelectric conversion. In our study, we focus on the effects of the reservoir permeability, porosity and frequency on the seismoelectric coupling coefficient through both experimental and numerical modellings. An experimental apparatus was designed to record the seismoelectric signals induced in water-saturated samples in the frequency range from 1 to 500 kHz. The apparatus was used to measure seismoelectric coupling coefficient as a function of porosity and permeability. The results were interpreted using a microcapillary model for the porous medium to describe the seismoelectric coupling. The relationship between seismoelectric coupling coefficients and the permeability and porosity of samples were also examined theoretically. The combined experimental measurements and theoretical analysis of the seismoelectric conversion has allowed us to ascertain the effect of increasing porosity and permeability on the seismoelectric coefficient. We found a general agreement between the theoretical curves and the test data, indicating that seismoelectric conversion is enhanced by increases in porosity over a range of different frequencies. However, seismoelectric conversion has a complex relationship with rock permeability, which changes with frequency. For the low-permeability rock samples (0–100 × 10−15 m2), seismoelectric coupling strengthens with the increase of permeability logarithmically in the low-frequency range (0–10 kHz); in the high-frequency range (10–500 kHz), the seismoelectric coupling is at first enhanced, with small increases of permeability leading to small increases in size in electric coupling. However, continued increases of permeability then lead to a slight decrease in size and image conversion again. For the high-permeability rock samples (300 × 10−15–2200 × 10−15 m2), the seismoelectric conversion shows the same variation trend with low-permeability samples in low-frequency range; but it monotonically decreases with permeability in the high-frequency range. The experimental and theoretical results also indicate that seismoelectric conversion seems to be more sensitive to the changes of low-permeability samples. This observation suggests that seismic conversion may have advantages in characterizing low permeability reservoirs such as tight gas and tight oil and shale gas reservoirs.

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