scholarly journals Assessment of Fuel Cells’ State of Health by Low-Frequency Noise Measurements

Energies ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 8340
Author(s):  
Arkadiusz Szewczyk ◽  
Łukasz Gaweł ◽  
Kazimierz Darowicki ◽  
Janusz Smulko
Keyword(s):  
Fuel Cells ◽  
Spectral Density ◽  
Power Spectral Density ◽  
Flicker Noise ◽  
Low Frequency ◽  
Frequency Noise ◽  
State Of Health ◽  
Dc Voltage ◽  
Power Spectral ◽  
Set Up

We proposed applying low-frequency (flicker) noise in proton-exchange membrane fuel cells under selected loads to assess their state of health. The measurement set-up comprised a precise data acquisition board and was able to record the DC voltage and its random component at the output. The set-up estimated the voltage noise power spectral density at frequencies up to a few hundred mHz. We observed the evolution of the electrical parameters of selected cells of different qualities. We confirmed that flicker noise intensity varied the most (more than 10 times) and preceded changes in the impedance or a drop in the output DC voltage (less than 2 times). The data were observed for current loads (from 0.5 to 32 A) far from the permissible load. We deduce that the method can be utilised in industrial conditions to monitor the state of health of the selected cells by noise analysis. The method can be used in real-time when the flicker noise is measured within the range of a few Hz and requires a reasonable amount of averaging time to estimate its power spectral density. The presented method of flicker noise measurement has considerable potential for use in innovative ways of fuel cell quality monitoring.

Adaptive algorithms for measuring low-frequency noise parameters of semiconductor devices under mass control

2020 ◽  
pp. 59-64
Author(s):  
V. А. Sergeev ◽  
S. Е. Reschikoff
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Semiconductor Devices ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Filter Bandwidth ◽  
Spectrum Shape ◽  
Power Spectral ◽  
Shape Indicator

The solution of the problem of increasing the confidence and efficiency of quality control of semiconductor devices is considered. The analysis of conditions for measuring the power spectral density of low – frequency noise of semiconductor devices with a spectrum of the form (γ – the spectrum shape indicator) under mass quality control is presented. The error in measuring the power spectral density under the specified measurement conditions strongly depends on the value of the spectrum shape indicator. Adaptive algorithms for measuring low-frequency noise parameters are proposed for cases of a given limit error in measuring the power spectral density and a given time for a single measurement. The proposed algorithms include a preliminary estimation of the value of the spectrum shape indicator and subsequent measurement of the noise power spectral density at the optimal filter bandwidth. The optimal filter bandwidth is determined based on the results of a preliminary assessment of the spectrum shape indicator. For both cases, we obtained estimates of the gain in the sense of the average for the set (ensemble) of controlled products. The possibility of adaptive or cognitive adjustment of the measurement system parameters in the control process based on the results of evaluating sample averages in the training sample is discussed.

Reliability Evaluation of 4H-SiC JFETs Using I-V Characteristics and Low Frequency Noise

2013 ◽  
Vol 740-742 ◽  
pp. 934-937
Author(s):  
Hua Khee Chan ◽  
Rupert C. Stevens ◽  
Jonathan P. Goss ◽  
Nicholas G. Wright ◽  
Alton B. Horsfall
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Low Frequency ◽  
Frequency Noise ◽  
Noise Power ◽  
Low Frequency Noise ◽  
Noise Sources ◽  
Noise Power Spectral Density ◽  
Power Spectral ◽  
Noise Measurements

Two sets of 4H-SiC signal-lateral JFETs were thermally aged at 400°C and 500°C in furnaces open to air for 1000 hours. I"-" V and low frequency noise measurements were performed on these devices and the results were compared against the as-fabricated sample. The data from I"-" V characterisation demonstrates that the linear and saturated drain-source current decreases monotonically with stress temperature. In addition, the linear characteristics of the JFETs have shifted approximately 1.5V along the drain-source voltage axis. Whilst the devices thermally aged at 400°C show no degradation in magnitude and behaviour in Noise Power Spectral Density (NPSD), the NPSD of 500°C stressed devices has increase approximately 30dB and it shows a full frequency spectrum of 1/ƒ dependency up to 100 kHz. A further investigation of the noise origin reveals that the Normalised Noise Power Spectral Density (NNPSD) of the aged sample is directly proportional to RDSwhich is similar to the as-fabricated sample. Thus we hypothesize that the existing noise sources have intensified possibly due to the evolution of defects.

Increase in electromyogram low-frequency power in nonfatigued contracting skeletal muscle

1986 ◽  
Vol 61 (3) ◽  
pp. 1012-1017 ◽  
Author(s):  
A. R. Bazzy ◽  
J. B. Korten ◽  
G. G. Haddad
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Biceps Brachii ◽  
Low Frequency ◽  
Biceps Brachii Muscle ◽  
Power Spectral ◽  
Loaded Breathing ◽  
Low Frequency Power ◽  
The Relationship ◽  
Frequency Power

We studied the relationship between changing elbow joint angle and the power spectral density of the biceps brachii muscle electromyogram (EMG) during submaximal isometric contractions. For this purpose, we recorded the EMG of the biceps brachii muscle with surface electrodes in 13 subjects. Each subject held a 2.8-kg weight and contracted the biceps isometrically for 30 s at one of two lengths. The length of the muscle was changed by flexing the forearm toward the upper arm to form an angle of 135 degrees (L1) or 45 degrees (L2). We found that the mean centroid frequency (fc) of the EMG power spectral density was 26% lower at L1 than at L2 (P less than 0.01). For each subject there was no significant change in fc during the isometric contraction at either angle. In addition, in nine subjects who sustained fatiguing contractions of the biceps with a 6-kg load, fc decreased by 15% (P less than 0.025). These data suggest that a change in the length at which a muscle contracts isometrically can alter or induce indirectly an alteration in the frequency content of its EMG. This finding may have important implications for the assessment of respiratory muscle EMG especially during loaded breathing.

Limitations of the Power Spectral Density as an Indicator of Test Severity

2011 ◽  
Vol 54 (2) ◽  
pp. 116-128 ◽  
Author(s):  
Mark Paulus
Keyword(s):  
Experimental Data ◽  
Spectral Density ◽  
Frequency Shift ◽  
Natural Frequency ◽  
Power Spectral Density ◽  
Low Frequency ◽  
Poor Correlation ◽  
Frequency Change ◽  
Power Spectral

This paper presents a set of experimental data comparing repetitive shock (RS) vibration, single-axis electrodynamic (ED) vibration, and multi-axis ED vibration. It was found that multi-axis testing is more severe than single-axis testing at the same level. In addition, weaknesses were found in the RS system at low frequency. Smoothing of the data or poor line resolution was also shown to change the overall severity of a test. A poor correlation was shown between the power spectral density (PSD) and the rate of natural frequency change (RFC) over a wide frequency shift. The change in natural frequency caused the initial PSD to be an ineffective indicator of test severity. Quantification of the severity of the test profile can be accomplished through characterization of the RFC.

The Comparisons of Heart Rate Variability and Perceived Exertion During Simulated Cycling with Various Viewing Devices

2008 ◽  
Vol 17 (6) ◽  
pp. 575-583 ◽  
Author(s):  
Shih-Fong Huang ◽  
Po-Yi Tsai ◽  
Wen-Hsu Sung ◽  
Chih-Yung Lin ◽  
Tien-Yow Chuang
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Spectral Density ◽  
Power Spectral Density ◽  
Perceived Exertion ◽  
Low Frequency ◽  
Control Group ◽  
Threshold Intensity ◽  
Power Spectral ◽  
Significant Difference

Sympathovagal modulation during immersion in a virtual environment is an important influence on human performance of a task. The aim of this study is to investigate sympathovagal modulation using heart rate variability and perceived exertion during exercise in a virtual reality (VR) environment. Sixteen young healthy volunteers were tested while using a stationary bicycle and maintained at an anaerobic threshold intensity for exercise sessions of approximately 10 min duration. Four randomized viewing alternatives were provided including desktop monitor, projector, head mounted device (HMD), and no simulation display. The “no simulation display” served as the control group. A quick ramp exercise test was conducted and maintained at an anaerobic threshold intensity for each session to evaluate power spectral density and rating of perceived exertion (RPE). The sampled heart rate data were rearranged by cubic spline interpolation into power spectrums spanning the ultra-low frequency (ULF) to high frequency (HF) range. A significant difference was found between the no-display and projector groups for total power (TP) and very low frequency (VLF) components. In particular, there was a significant difference when comparing HMD and no-display exercise RPE curves within 6 min of cycling and at the termination of the exercise. A significant difference was also achieved in projector vs. control group comparison at the termination of the exercise. Our results indicate that the use of HMD and the projected VR during cycling can reduce the TP and VLF power spectral density through a proposed decrease in the renin-angiotensin system, with the implication that this humoral effect may enable anaerobic exercise for longer durations through a reduction in sympathetic tone and subsequent increased blood flow to the muscles.

Analysis of turbulence power spectra and velocity correlations in a pipeline with obstructions

2017 ◽  
Vol 28 (02) ◽  
pp. 1750019 ◽  
Author(s):  
A. T. da Cunha Lima ◽  
I. C. da Cunha Lima ◽  
M. P. de Almeida
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Cross Sections ◽  
Power Spectra ◽  
Low Frequency ◽  
Frequency Range ◽  
Frequency Space ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Low Frequency Power

We calculate the power spectral density and velocity correlations for a turbulent flow of a fluid inside a duct. Turbulence is induced by obstructions placed near the entrance of the flow. The power spectral density is obtained for several points at cross-sections along the duct axis, and an analysis is made on the way the spectra changes according to the distance to the obstruction. We show that the differences on the power spectral density are important in the lower frequency range, while in the higher frequency range, the spectra are very similar to each other. Our results suggest the use of the changes on the low frequency power spectral density to identify the occurrence of obstructions in pipelines. Our results show some frequency regions where the power spectral density behaves according to the Kolmogorov hypothesis. At the same time, the calculation of the power spectral densities at increasing distances from the obstructions indicates an energy cascade where the spectra evolves in frequency space by spreading the frequency amplitude.

Study on Dynamic Response Test of Long Span PC Girder Bridge under the Operating Conditions

2013 ◽  
Vol 275-277 ◽  
pp. 984-988
Author(s):  
Xiao Dong Chen ◽  
Xia Ping Liu ◽  
Zhuo Sun ◽  
Ka Hong Cai ◽  
Hong Yang
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
System Development ◽  
Low Frequency ◽  
Vibration Signal ◽  
Frequency Domain Analysis ◽  
Spectral Density Function ◽  
Operating Conditions ◽  
Measured Signal ◽  
Power Spectral

In this paper, based on the Guangzhou Pazhou Bridge ,the acceleration and dynamic deflection was tested synchronously under normal operating conditions. Power spectral density analysis of the measured signal was done with frequency domain analysis methods.The measured value was compared with the finite element calculated value.The studies are as follows: first, the acceleration and deflection power spectral density function shows a multimodal distribution；the vibration frequency is concentrated in the low frequency range；the bridge vibration energy is concentrated in the first three frequency.Second, the actual operating conditions of Pazhou Bridge is good and it has a good bearing capacity. Third，the bridge impact coefficient measured maximum value is much greater than the national specification values.The researchs can provide the basic data for study on bridge health monitoring system development and bridge vibration signal separation technique.

scholarly journals Evaluation procedure for blowing machine monitoring and predicting bearing SKFNU6322 failure by power spectral density

2021 ◽  
Vol 23 (3) ◽  
pp. 522-529
Author(s):  
Javier Castilla-Gutiérrez ◽  
Juan Carlos Fortes Garrido ◽  
Jose Miguel Davila Martín ◽  
Jose Antonio Grande Gil
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Vibrational Energy ◽  
Low Frequency ◽  
Evaluation Procedure ◽  
Correct Operation ◽  
Industrial Sites ◽  
Machine Monitoring ◽  
Power Spectral ◽  
The Comparative Study

This work shows the results of the comparative study of characteristic frequencies in terms of Power Spectral Density (PSD) or RMS generated by a blower unit and the SKFNU322 bearing. Data is collected following ISO 10816, using Emonitor software and with speed values in RMS to avoid high and low frequency signal masking. Bearing failure is the main cause of operational shutdown in industrial sites. The difficulty of prediction is the type of breakage and the high number of variables involved. Monitoring and analysing all the variables of the SKFNU322 bearing and those of machine operation for 15 years allowed to develop a new predictive maintenance protocol. This method makes it possible to reduce from 6 control points to one, and to determine which of the 42 variables is the most incidental in the correct operation, so equipment performance and efficiency is improved, contributing to increased economic profitability. The tests were carried out on a 500 kW unit of power and It was shown that the rotation of the equipment itself caused the most generating variable of vibrational energy.

scholarly journals A Study of Low-Frequency, Wind-Driven, Coastal-Trapped Waves along the Southeast Coast of Australia

2018 ◽  
Vol 48 (2) ◽  
pp. 301-316 ◽  
Author(s):  
Fanglou Liao ◽  
Xiao Hua Wang
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Wind Stress ◽  
Energy Flux ◽  
Low Frequency ◽  
Coastal Trapped Waves ◽  
Southeast Coast ◽  
Power Spectral ◽  
Alongshore Wind Stress ◽  
Alongshore Wind

AbstractCoastal-trapped waves (CTWs) along the southeast coast of Australia were investigated based on a frictional, wind-driven long-wave theory. It was found that low-frequency sea level anomalies (SLAs) were continuously propagating from the south coast up along the east coast as CTWs, mainly forced by the alongshore wind stress. Three main subinertial peaks existed in the spectral characteristics of the SLAs, with periods of 14.2, 10.2, and 7.8 days, respectively. Power spectral density distributions of the peaks showed that the CTW amplitudes varied significantly along the southeast coast. For idealized linear and exponential shelves, a theoretical analysis indicated that the fundamental factor influencing the eigenvector of mode 1, and therefore the CTW amplitude, was the offshore water depth. This theoretical work was well supported by eight sensitivity cases. Four additional cases were conducted, and time-averaged energy fluxes were calculated to identify the energy source of the CTWs in the Australian Coastal Experiment (ACE) region. It was shown that both the local wind stress and the wind stress in Bass Strait contributed to the CTWs in the ACE region, with the latter playing a more important role. The remaining CTW energy came from remote forcing farther west of Bass Strait. The energy flux calculation also showed that the CTW energy flux was almost constant along the investigated coast because of the balance between frictional dissipation and the energy gain from the alongshore wind stress; the significant variations in the power spectral density (PSD) of the subinertial peaks were mainly due to the variations in the modal eigenvectors caused by the shelf geometry.

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