Fast Fourier Transform Spectrum Analysis Research Articles

Scanning ex situ solid-state magnetic resonance imaging on polymeric films using a static magnetic field gradient by an electromagnet.

A new technique for ex situ solid-state nuclear magnetic resonance imaging of polymeric films has been developed. This method uses the static magnetic field gradient generated by a water-cooled copper electromagnet. The imaging process involves scanning the sample in the plane of the film under a static magnetic field gradient. Two-dimensional (2D) 19F MRI measurements are attempted, where the fast Fourier transform (FFT) spectra of the second half of a Hahn echo peak is used for the depth (X-axis) direction, and the sample film is mechanically moved for the Y-axis, which is in-plane with respect to the film surface and normal to the inter-magnetic-pole line (Z-axis). The sample is a poly(tetrafluoroethylene) [PTFE] film with carved stripes on its surface. Furthermore, three-dimensional (3D) measurements of the film surface and thickness orientations were also performed for an analogous PTFE film. For 2D profiling on the film surface, 2D sample-moving was used. For depth profiling, FFT spectrum analysis was undertaken for each voxel situated at a specific (Y, Z) coordinate within the film. As a result, a 3D image of the sample and its corresponding geometry were obtained, although the scanning area was restricted to a part of the sample. Finally, numerical simulations of the spatial distribution of the static magnetic field were performed to confirm the validity of the present method.

Fast and efficient approach for multi-component quantum wells analysis based on FFT

Elaboration of the technology of the multicomponent Quantum Wells (QWs) based devices requires repeated time consuming diffraction curves analysis proceeded for each of the grown structures to determine their basis structural parameters. Optimization of the diagnostic procedures and making them more efficient is the key point from the manufacturer point of view. In this paper we present the use of Fast Fourier Transform (FFT) employed to fast determination of the thickness of epitaxial layers. The presented method combines the approach using the Rocking Curves (RC) measured by X-ray Diffraction (XRD) together with the analysis of the FFT spectrum. In this work GaInNAs/GaAs MQWs structures grown by atmospheric pressure-metalorganic vapour phase epitaxy (AP-MOVPE) were investigated. In the case of the series of the defined type samples, this method allows replacement of the time consuming simulation method used for diagnostic of the thickness of deposited layers in favor of FFT spectrum analysis.

Differences in fatigability of vastus medialis muscle between patients with limb symmetry index of

BackgroundA limb symmetry index (LSI) of ≥90% for the quadriceps is recommended for return to sports activity after anterior cruciate ligament reconstruction (ACLR). However, there is no information on differences in muscle fatigability between patients with LSI of <90% and ≥90%. The aim of this study was to assess the difference in quadriceps muscle fatigability on the involved side between post-ACLR patients with LSI of <90% and ≥90%. We hypothesized that there were differences between the two groups in muscle fatigability on the involved side reflecting difference in muscle fiber composition in the vastus medialis (VM) muscle. MethodsThe study subjects were 18 adult men who had undergone ACLR followed by rehabilitation therapy. LSI was <90% in 10 and ≥90% in 8 adult men. Surface electromyography (EMG) of the VM muscle was recorded during sustained quadriceps muscle isometric contraction. The median frequency (MF) was computed from the raw EMG signal using fast Fourier transform spectrum analysis. The MF slope was also calculated. ResultsThere were no differences in anthropometric characteristics, time since ACLR, anterior tibial translation and peak torque of knee extension on the involved side between the two groups. However, MF slope was significantly lower in the LSI ≥ 90% group than the <90% group. ConclusionOur results demonstrated fatigue-resistant vastus medialis in post-ACLR patients with LSI ≥90% compared to those with LSI <90%. The finding adds support to the use of ≥90% as the cutoff value for LSI for return of post-ACLR patients to sports activity.

Effect of extraction on the acoustic vibrational properties of Picea jezoensis var. microsperma (Lindl.) W.C.Cheng &amp; L.K.Fu

The specific dynamic elastic modulus, acoustic radiation, logarithmic decrement, sound transmission parameter, and acoustic conversion efficiency of spruce wood (Picea jezoensis var. microsperma (Lindl.) W.C.Cheng & L.K.Fu) were improved by extraction treatment with deionized water, dichloromethane, benzyl alcohol, and ethanol. A larger improvement was achieved after extraction with benzoyl alcohol and dichloromethane extraction than by using ethanol and deionized water. It is necessary to improve the acoustic vibrational properties of wood to solve the problem of resource shortage of wood with excellent acoustic vibrational properties for the soundboards of musical instruments and to improve the use value of wood. The effects of extraction treatment with deionized water, dichloromethane, benzyl alcohol, and ethanol on the acoustic vibrational properties of spruce wood were evaluated. After the acoustic vibrational properties of untreated wood samples were measured using the free-free flexural vibration test method with a fast Fourier transform spectrum analyzer (FFT, CF-5220Z), extraction treatment of the wood samples was separately performed with deionized water, dichloromethane, benzyl alcohol, and ethanol for 15 days at room temperature and pressure, followed by drying. The acoustic vibrational properties of the treated wood samples were then measured, and the effect of extraction treatment on the acoustic vibrational properties was analyzed. The increase in the specific dynamic elastic modulus was highest (14.5%) after the benzyl alcohol treatment. The acoustic radiation clearly improved after the ethanol treatment (18.1%). The acoustic impedance of the wood treated by dichloromethane extraction decreased significantly (−4.35%), while the logarithmic decrement was significantly reduced (−52.0%) by benzyl alcohol treatment. From the viewpoint of energy utilization, with benzyl alcohol treatment, the acoustic conversion efficiency and transmission parameter increased by 124% and 125%, respectively. The degree of improvement in the acoustic vibrational properties of wood differed depending on the solvent used. Greater improvement was observed after extraction with benzoyl alcohol and dichloromethane as compared to ethanol and deionized water.

On multi-fault detection of rolling bearing through probabilistic principal component analysis denoising and Higuchi fractal dimension transformation

Bearing multi-fault detection from stochastic vibration signal is still a thorny task to dispose of because of the complex interplay between different fault components under severe noise interference. In such case, conventional techniques such as filter processing and envelope demodulation may cause undesired results. To overcome the limitation, this article explores a filtering-free technique combined probabilistic principal component analysis denoising with the Higuchi fractal dimension transformation to diagnose the bearing multi-faults. Fractal theory is used to optimize the model parameters and stabilize the random vibrational signal for fast Fourier transform spectrum analysis. Noise interference in the Higuchi transformation is capped using a probabilistic principal component analysis model whose parameters are optimized through embedding dimension Cao algorithm and correlation dimension Grassberger and Procaccia algorithm. The fault diagnostic scheme mainly falls into three steps. First, the original vibration signal is truncated into a series of sub-signal segments by moving window whose length is determined as twice the value of maximum time delay that is provided by examining the steady Higuchi fractal dimension value of a raw signal in a process of plotting the fractal dimension over a range of time delay. Then, the Higuchi approach is used to estimate the average fractal dimension for each segment to create a quasi-stationary Higuchi fractal dimension sequence on which, finally, the fault features are straightforwardly extracted by the fast Fourier transform algorithm. The effectiveness of the proposed method is validated using simulated and experimental compound bearing fault vibration signals. Some fault components may be clouded if applied Higuchi fractal dimension alone because of the noise interference, but using the probabilistic principal component analysis–Higuchi fractal dimension method leads to clear diagnostic results. It indicates that the proposed approach can be incorporated into bearing multi-fault extraction from raw vibration signals.

A Frequency-Correcting Method for a Vortex Flow Sensor Signal Based on a Central Tendency.

A vortex flow meter employs a sensor based on the piezoelectric vibration principle to realize vortex signal acquisition, and therefore the measurement results are susceptible to vibration noise. In this paper, the generalized mode method is proposed based on the central tendency characteristic of the vortex signal and combined with the existing filter bank method. The method combining filter bank with the generalized mode is designed and applied in the signal-processing system of the vortex flow meter, which makes up for the defect that the filter bank method cannot filter out the noise in the sub-band. The simulation experiments verify the feasibility and anti-interference performance of the algorithm. Meanwhile, a comparison with two FFT (Fast Fourier Transform) spectrum analysis methods shows that the algorithm designed in this paper requires a smaller sample size and achieves better real-time performance. The actual anti-vibration experiment and calibration experiment verify that the signal-processing system of a vortex flow meter ensures good accuracy and repeatability.

Micro-vibration measurement based on current modulation and secondary feedback self-mixing interference technology

The secondary feedback self-mixing interference (2FSMI) technology used to measure the micro-vibrations of objects is more accurate than the self-mixing interference (SMI) technique, and current modulation is a commonly used modulation method. Therefore, current modulation and 2FSMI technology are combined to measure micro-vibrations with different amplitudes within a wavelength. First, the interference signal is current-modulated by a sawtooth wave. Second, the collected signal is preprocessed. Third, the preprocessed signal is subject to fast Fourier transform spectrum analysis. Finally, the micro-displacement of the vibrating object is reconstructed. Experimental results show that the maximum error of this method in reconstructing the micro-displacement of a vibrating object is less than 13 nm, which is approximately half that of the SMI technique. Moreover, this method can reconstruct not only sinusoidal vibrations but also arbitrary waveform vibrations. Therefore, using this method to measure object vibration can yield high measurement accuracy without increasing the experimental device.

Properties of Paraspinal Muscles in Japanese High School Baseball Players With Terminal-Stage Lumbar Spondylolysis

BackgroundLumbar spondylolysis is a defect in the pars interarticularis that is common in young athletes; the stress distribution at the pars interarticularis is the highest in extension and rotation movements. The paraspinal muscles play an important role in stabilization of the lumbar spine; however, no study has assessed the properties of paraspinal muscles in athletes with lumbar spondylolysis. ObjectiveTo evaluate the properties of paraspinal muscles in athletes with lumbar spondylolysis. DesignCross-sectional study. SettingLaboratory. ParticipantsSix high school baseball players with terminal-stage lumbar spondylolysis and 11 high school baseball players without organic lumbar lesions of similar anthropometric characteristics. MethodsAll subjects performed the unsupported trunk holding test combined with surface electromyographic (EMG) power spectral analysis until exhaustion. The results of EMG power spectral analysis were compared between the spondylolysis and control groups. Main Outcome MeasurementsThe median frequency (MF) was computed from the raw EMG signal of the erector spinae and multifidus during trunk holding test using fast Fourier transform spectrum analysis. The initial MF and MF slope were calculated. ResultsNo significant differences in endurance time were found between the spondylolysis and control groups. The initial MF and the MF slopes of the erector spinae and multifidus were significantly lower in the spondylolysis group than in the control group. ConclusionsThe results suggest lower fast-twitch motor unit recruitment in the erector spinae and multifidus of high school baseball players with terminal-stage lumbar spondylolysis compared with the control. Level of EvidenceIV

Prediction of Natural Frequency of Gas Turbine Disc

In the present paper, Natural frequencies of gas turbine disc determined by Holzer’s method as well as Fast Fourier Transform spectrum analyzer are compared. Hub is a circular disc made up of Aluminium alloy to whose outer periphery blades are welded. Disk’s inner end is coupled with a shaft. Thus the Natural frequencies of this component can be kept at a minimum range. Also this material exhibits good properties such as low embrittlement, low toxicity, easy formation of complex shapes and some other economical issues. Many gas turbine models have adopted mild steel hub. Reduction of torsional vibrations in the circular disc results in decreased Natural frequency of gas turbine assembly. This paper also discuss the information to find stiffness, damping ratio and amplitude.

Multi-Point Disturbance Detection and High-Precision Positioning of Polarization-Sensitive Optical Time-Domain Reflectometry

Compared with its counterparts, polarization sensitive optical time-domain reflectometry (P-OTDR) has two typical problems in terms of multi-point disturbance detection and high precision positioning, which restrict its practical applications. In this paper, we propose a novel method by using two-dimensional (2-D) image processing and statistical clustering. In place of the traditional spatial or temporal signal analysis way, the idea employs the temporally and the spatially uneven/inconsistent evolving patterns induced by the multiple individual events, and the proposed method is carried out to accumulate the temporally differentiated OTDR traces and then build up a 2-D temporal-spatial evolving graph, by using edge detection and automatic clustering to distinguish different disturbing points with precise locations. Through series of multi-point disturbance tests, the proposed method has been proved to have better performance than the conventional direct differentiation method and the fast Fourier transform spectrum analysis.

Age-related sex differences in erector spinae muscle endurance using surface electromyographic power spectral analysis in healthy humans

Background contextPrevious studies reported that the erector spinae muscle is more resistant to fatigue in healthy adult women than in men. However, no study has reported changes in back muscle fatigue with aging in healthy men and women. PurposeThe aim of this study was to evaluate age-related changes in muscle fatigue of erector spinae muscle in men and women. Study design/settingThis cross-sectional study was conducted in a laboratory. Patient sampleFifty-three healthy subjects (11 elderly men, 11 elderly women, 17 young men, and 14 young women) without low back pain history. Outcome measuresThe median frequency (MF) and mean power frequency (MPF) during trunk holding test were derived from the raw electromyographic (EMG) signal using Fast Fourier Transform spectrum analysis program. The rates of changes in MF and MPF were calculated. MethodsSubjects performed the unsupported trunk holding test until exhaustion. The results of power spectral analysis of the EMG activity of the left erector spinae muscle were compared in both age groups and sexes. ResultsThe endurance time in young men was significantly shorter than in young women. The slopes of MF and MPF in young men were significantly higher than in young women. There were no significant differences in MF and MPF slopes of elderly men and elderly women. Furthermore, the MF and MPF slopes were significantly lower in elderly men than young men but similar in the two women groups. ConclusionsAge-related changes in the slopes of MF and MPF of erector spinae muscle occur in healthy men but not in healthy women.

Theta Power Spectral Analysis of Electroencephalography in Infantile Spasms: Before and After ACTH Treatment

Background Infantile spasms (ISs) were thought to be a kind of intractable seizure, and diagnosed with one or many of the following: nodding spasm clusters, mental retardation, or showing up as interictal hypsarrhythmia on electroencephalograms. While these spasms represent a major therapeutic challenge, limited parameters are available to evaluate their status before and after treatment. The American Academy of Neurology/Child Neurology Society recommends that administration of adrenocorticotropic hormone (ACTH) is effective for short-term treatment of children with IS. To determine whether there were differences in EEG manifestations, we performed a power spectral analysis of the EEG of hypsarrhythmia to determine the effects of ACTH, before and after its administration. Methods After obtaining informed consents from guardians, we recruited children younger than 3 years of age, who fulfilled both the definition of IS and were receiving other antiantiepileptic drugs (valproic acid, vigabatrin, lamotrigine, etc.) in Taipei Medical University-affiliated hospitals from November 2009 to June 2012. Patients with IS were administered synthetic ACTH subcutaneously for 2 weeks following a 6-week tapering-off period. The data were later analyzed by fast Fourier transformation (FFT) analysis. Results The average EEG voltage of five patients before ACTH treatment for all the brain regions ranged from 92.21 to 153.02 μV (mean: 106.64 ± 12.36 μV; n = 5). We found that the frequency corresponding to the theta wave power (7.8 Hz) showed a prominent elevation in all of the five IS patients with hypsarrhythmia. Before commencing ACTH treatment, the theta wave power was in the range of 14.77–27.52 μV (mean: 21.05 ± 2.15 μV; n = 5). Two weeks after ACTH treatment, the theta wave power decreased to a range of 1.81–6.01 μV (mean 3.81 ± 0.67; n = 5). Thus, we conclude that administration of ACTH induced a significant decrease in the theta wave power (mean decrease: −80.95 ± 3.42%; p Conclusion Performing an FFT spectrum analysis of an EEG such as EEG of the hypsarrhythmia can serve as an objective tool to understand specific signal processing in children with IS. This is the first finding to discover the inhibitory effect of ACTH on the theta wave power. The inter-relationship between ACTH and theta power needs to be elucidated in the future studies.

FFT Spectrum Analyzer Project for Teaching Digital Signal Processing With FPGA Devices

This paper presents a course on digital signal processing with field-programmable gate arrays (FPGA) devices. The course integrates two separate disciplines, digital signal processing (DSP) and very large scale integration (VLSI) design, and focuses on the development of a sophisticated DSP design from simulation to fixed-point implementation. The structure and methodology used in the proposed course are oriented to the design and implementation of an fast Fourier transform (FFT) spectrum analyzer. This application covers most topics included in a DSP course and gives better results that those obtained with typical courses performing independent multiple simple experiments. The project is divided into modules that show specific learning necessities and determine the course contents and organization. Each laboratory part is dedicated to design and implements the block of the analyzer related to the theoretical content presented in the class. At the end of the course the students have designed all the pieces in the DSP project and have completed and verified the system. The used methodology enables students and engineers to understand and develop complex fixed-point applications, looking for the best signal processing algorithms on hardware implementations, and also results in more motivated and active students.

Precision Measurements of AC Josephson Voltage Standard Operating Margins

Recent advances in circuit design and fabrication of superconducting integrated circuits have enabled us to demonstrate an ac Josephson voltage standard (ACJVS) that generates both ac and dc waveforms up to 242-mV peak voltage. Using a Fast Fourier Transform spectrum analyzer and an ac-dc transfer standard, we characterize ACJVS operating margins by performing "flat-spot" measurements at the level of a part in 10/sup 6/ for all eight bias parameters. By verifying that every bias parameter has a "flat-spot" (i.e., a range of bias values over which the measured ACJVS output is precisely constant), we demonstrate that all Josephson junctions on the chip are operating properly.

Characterizing tuning forks as nanomechanics sensorsthrough thermal noise spectra measured by a personal computersound card

A minimal and convenient experimental set-up is described,which allows an easy characterization of crystal tuning forks,especially after the modifications introduced to exploit them assensors in nanomechanics and in force microscopy techniques. Thesystem uses the thermal noise of the crystal as test signal, asimple frequency converter for translating the signal itself intothe audio-frequency band, and a PC sound card to acquire it andeventually perform a fast Fourier transform spectrum analysis on thenoise samples. Our results show that the main decrease of theQ-factor of the tuning fork is caused by its acoustical couplingto the environment, while small masses added to either or bothprongs only produce minor variations.

Inexpensive technique for accurate determination of elastic properties by free decay in circular plates

Rapid determinations of elastic modulus are often made in the lab by measuring the resonances of regular bars of the material. When this is done, the most accurate results are obtained by suspending the specimen with as close to free conditions as possible. A circular plate supported by a taut wire through a central hole behaves accurately as an annular plate with both edges free. For low-loss materials, 10–20 modes are easily detected with an inexpensive microphone when such a plate is struck. Furthermore, the analytical solution for a thick, annular plate can be programmed readily in computational tools such as mathcad, matlab, or mathematica. (Even for plates traditionally considered thin—thickness-to-diameter ratios less than 0.1—thin-plate theory can produce significant errors for higher-order modes.) The first two resonance frequencies can be used to determine the elastic modulus and Poisson’s ratio and the higher modes can be used to assess the uncertainty or to uncover anisotropy. The resonance frequencies can be measured with a fast Fourier transform spectrum analyzer and an understanding of the response of such an analyzer to a slowly decaying sinusoid. [Work supported by the Naval Sea Systems Command.]

Spectral electromyographic fatigue analysis of back muscles in healthy adult women compared with men

Objective and Design: To investigate the difference in back muscle endurance between normal adult women and men using surface electromyographic (EMG) power spectral analyses. Methods: Forty-five healthy subjects (22 men and 23 women) were studied during an unsupported trunk holding test for 120 seconds. Recording surface electrodes were placed over each erector spinae muscle at L1 level. Outcome Measures: Median frequency (MF), mean power frequency (MPF), and zero crossing rate (ZCR) were evaluated using the ME3000P Fast Fourier Transform spectrum analysis program. The rate of change was determined for each parameter during the test, and correlation was examined by Pearson's correlation. Results: The negative slopes of all indices of back muscle fatigue were significantly steeper in men than in women. Conclusion: Our results indicated that the trunk holding test combined with EMG power spectral analysis of lumbosacral muscles is useful for the evaluation of fatigue performance of these muscles. Our results also showed a higher muscle endurance in healthy adult women than in men.

Spectrum analysis for introductory musical acoustics

A “real time” fast Fourier transform spectrum analyzer facilitates several experiments for an introductory course in musical acoustics. With its rapidly updated display, the time-dependent vibrations of an aluminum bar are easily studied. Using longer time acquisitions and correspondingly higher resolution facilitates the study of string inharmonicities, resonant energy transfer, and sound radiation patterns in guitar acoustics.

A SETI Search of Nearby Solar-Type Stars at the 203-GHz Positronium Hyperfine Resonance

The development of advanced millimeter-wave technology has made it possible to construct low-noise receivers and high-power transmitters comparable to those available at much lower frequencies. This technology, plus certain physical characteristics of the millimeter-wave spectrum, suggests possible advantages for use of this wavelength range for interstellar communications. As a result, a SETI (search for extraterrestrial intelligence) type search has been conducted for narrow-bandwidth signals at frequencies near the positronium hyperfine spectral line (203.385 GHz), a potential natural reference frequency. A total of 40 solar-type stars within 23 parsecs were observed, in addition to three locations near the galactic center. No detections were made at the detection threshold of 2.3 × 10-19 W/m2 in each of two orthogonal linear polarizations. Future observations will be made with a higher resolution fast Fourier transform spectrum analyzer (FFTSA), which should improve sensitivity by an order of magnitude and reduce required observing time.

Real time cure monitoring of composite structures using the techniques of mechanical impedence analysis

AbstractA dynamic mechanical apparatus, based on the concept of mechanical impedance analysis (MIA), was constructed for real‐time cure monitoring of composites. The frequency response function (FRF), in terms of the inertance, impedance or admittance value, can be obtained from the ratio of the Fourier Transforms of excitation and response signals. Spectra during curing of several different kinds of composite materials were obtained with the Fast Fourier Transform spectrum analyzer while the material was continually excited with a random input generated by an electro‐magnetic shaker. The dynamic properties, such as storage modulus (E′) and loss tangent (tan δ), of the composite can be obtained from the FRF spectra as a function of cure time and temperature. Variations of the inertance spectra with cure time, reflecting the changes in the dynamic mechanical properties, for the composite materials under various isothermal cure conditions are discussed. Optimal cure cycles of a new resin can be determined by characterizing the phase transformation of the material, which can be identified from the MIA measurement results. The MIA technique is found to be a sensitive and direct means for monitoring the overall cure state of composites. The signals obtained can be integrated in real‐time in a closed‐loop feedback control system for composite fabrication.