Frequency Mapping Technique Research Articles

Mel frequency mapping for intelligent diagnosis of rolling element bearings across different working conditions

The diagnosis of rolling bearing faults under constant operational conditions has garnered substantial scholarly interest, leading to the development of numerous robust and reliable diagnostic techniques. However, the dynamic and variable nature of industrial operating conditions complicates the acquisition of diagnostic data and renders fault prediction problematic, thus posing a formidable obstacle for fault diagnosis in unknown operational settings. Drawing an analogy from human communication, where listeners can comprehend speech irrespective of its speed or intensity, this paper aims to devise a methodology capable of distinguishing between various health states of machinery under fluctuating working conditions. To this end, we present a novel method, Mel Frequency Mapping Classification (MFMC), for nonlinear fault characteristic mapping and classification. This data-driven model, trained on datasets from known operational conditions, adapts well to new settings. Initially, vibration signals are converted from linear Hertz frequencies to nonlinear Mel frequencies through the Mel frequency mapping technique. Subsequently, the extracted fault signal features are transformed into Mel spectrograms, which serve as the input for the data-driven model. Finally, these Mel spectrograms are utilized as input variables for machine learning algorithms, specifically support vector machine (SVM) and multilayer perceptron (MLP), to accomplish automated, intelligent bearing diagnosis. To rigorously assess the efficacy of the proposed methodology in mechanical condition monitoring and intelligent diagnosis across diverse operational conditions, it was tested on two distinct datasets: CWRU and PU. These datasets encompass bearings with varying degrees and types of damage, situated in different components of the bearing, and operating under disparate conditions. Experimental results indicate that the proposed MFMC approach can obtain high cross-condition diagnosis accuracy on the training data under a single condition. This methodology offers a promising avenue for the intelligent diagnosis of mechanical equipment under cross-condition scenarios.

Influence of Coexistence of Pitting and Cracking Faults on a Two-Stage Spur Gear System

This work considers forced vibrations in a rotating structure consisting of a two-stage spur gear system with coexisting defects, specifically pitting and cracking. Numerical simulations and experimental analysis in various scenarios of the system in operation were conducted using the RPM–Frequency mapping technique. To identify fault characteristics, the analysis performed assumed the gear system had been misadjusted by a combination of pitting and cracking on the gear teeth. The correlation of the system-forced responses under regular and chaotic vibrations revealed that the system is far more sensitive to the crack than to the pitting when there are fluctuating harmonic peaks present at high vibration levels.

Synthesis design of quad‐band bandpass filter with mixed frequency transformation method

AbstractThis paper presents an analysis method to design quad‐band bandpass filters (BPFs) based on the mixed frequency transformation method. The frequency mapping technique is employed to obtain the design parameters by defining the frequency ranges of each passband. By using the proposed approach, the resonant angular frequencies and susceptance slope parameters can be obtained analytically. To validate our theory, a third‐order Chebyshev BPF and a fourth‐order elliptic BPF with different bandwidths are successfully synthesized. Moreover, a second‐order test BPF with a Chebyshev approximation and 20 dB passband return loss is synthesized, designed, fabricated, and measured. The measured insertion losses are 1.82, 2.01, 3.12, and 2.51 dB for each passband and measured return losses are better than 15.2 dB for all passbands. The measured results verify the designed BPF and also confirm the theoretical prediction.

An Approach for Individualized Cochlear Frequency Mapping Determined From 3D Synchrotron Radiation Phase-Contrast Imaging.

Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation. Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea. The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach. This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.

Partial Discharge Analysis of SF6/N2 Gas Mixture Filled MV Circuit Breaker Using Time–Frequency Map Clustering Technique

Breakdown of gas insulated switchgears due to partial discharges (PD) is a major threat for the safe and reliable operation of power system network. In recent times, PD based diagnostics has been widely adopted by electrical utilities in order to evaluate the health of high voltage insulation system. However, very few reports are only available on the PD characteristics of gas insulated medium voltage (MV) circuit breaker prototypes, in particular with mixture of gases, over a wide range of pressure and voltage stress. Deep analysis of nature of PD signals in mixture of gas insulation and its time–frequency characteristics is important in order to develop efficient online condition monitoring systems for circuit breakers. This paper is aimed at the analysis of PD characteristics of a 22 kV MV circuit breaker prototype filled with SF6/N2 gas mixtures using time–frequency (T-F) mapping and clustering technique. PD tests are carried out at different gas pressures (1–5 bar) and at different gas mixture ratios. Important PD parameters such as PD inception voltage, phase resolved PD (PRPD) pattern and PD repetition rate are evaluated. Clustering analysis of PD signals from the time–frequency mapping is carried out and formation of three different clusters consisting of short, long and repetitive PD pulses is identified. Online real time monitoring of individual cluster density will be helpful to understand the degradation of gas insulation of circuit breakers. Keeping in mind the minimal usage of SF6 gas, from the results, it is noted that 10% SF6 gas can be mixed with 90% N2 at 3 bar pressure to get satisfactory PD performance of a 22 kV medium voltage circuit breaker.

Multifunctional Bandpass Filters With Reconfigurable and Switchable Band Control

A new series of multifunctional reconfigurable bandpass filters (BPFs) and their analytical synthesis design are presented in this paper. They feature frequency-adaptive characteristics in both their passbands and notched bands, as well as switchable-notched-band capability. Their basic filter architecture is discussed and modeled in a progressive manner. The initial circuit consists of a second-order Chebyshev-type filter to which two stubs are added to increase filtering selectivity through transmission-zero (TZ) creation. Subsequently, to produce an embedded notched band, stubs acting as band-stop structures are also inserted at the input–output terminals. The multifunctional properties of this filter scheme are analyzed attending to the resonance frequencies of the introduced stubs. When these resonance frequencies are tuned while keeping a constant spacing between them, a center-frequency reconfiguration with constant bandwidth is achieved; when the resonance frequency of the notched band is shifted to the TZ positions, the notched band is switched-off. The described filter synthesis methodology is based on the constant and frequency-mapping technique, where the dual-mapping functions are controlled to obtain reconfigurable/switchable properties from a low-pass prototype. For experimental-validation purposes, two reconfigurable lumped-element filter prototypes using the proposed synthesis technique are designed, manufactured, and tested. One exhibits a simple reconfigurable passband, whereas the other one adds a controllable/switchable embedded notched band that results in a quasi-elliptic-type dual-passband response. When compared to some related prior-art designs, these filters have the advantages of explicit design process, quantified analysis, and multifunctional responses.

Planar Multifrequency Wideband Bandpass Filters With Constant and Frequency Mappings

A new planar filter design technique with constant and frequency mappings has been proposed for multifrequency wideband bandpass filters (BPFs). The constant mapping treats components in the LC circuit (e.g., frequency invariant admittances, capacitors, and ideal inverters) as frequency dependent. It is consistent with practical planar circuits and caters to a wide frequency range. Following the classic single-to-multiband transformation, a new frequency mapping function is proposed by incorporating this constant mapping idea. With these two mapping functions, a direct relation between the LC circuit and its microstrip counterpart is established. Therefore, the multifrequency wideband BPF is readily designed from a low-passing LC circuit to the transmission line circuit. A laddertype Chebyshev filter and a trisection filter with the general Chebyshev response have been designed as examples. The first one is a dual-band case exhibiting a wide bandwidth for each passband. The second filter is a triple-band one showing a large frequency ratio between the first and third passband. Both examples experimentally validate the proposed constant and frequency mapping technique.

Time–distance domain transformation for Acoustic Emission source localization in thin metallic plates

Acoustic Emission used in Non-Destructive Testing is focused on analysis of elastic waves propagating in mechanical structures. Then any information carried by generated acoustic waves, further recorded by a set of transducers, allow to determine integrity of these structures. It is clear that material properties and geometry strongly impacts the result. In this paper a method for Acoustic Emission source localization in thin plates is presented. The approach is based on the Time–Distance Domain Transform, that is a wavenumber–frequency mapping technique for precise event localization. The major advantage of the technique is dispersion compensation through a phase-shifting of investigated waveforms in order to acquire the most accurate output, allowing for source-sensor distance estimation using a single transducer. The accuracy and robustness of the above process are also investigated. This includes the study of Young’s modulus value and numerical parameters influence on damage detection. By merging the Time–Distance Domain Transform with an optimal distance selection technique, an identification–localization algorithm is achieved. The method is investigated analytically, numerically and experimentally. The latter involves both laboratory and large scale industrial tests.

Snapshot MR technique to measure OEF using rapid frequency mapping.

Magnetic resonance (MR)-based oxygen extraction fraction (OEF) measurement techniques that use blood oxygen level-dependent (BOLD)-based approaches require the measurement of the R2' decay rate and deoxygenated blood volume to derive the local oxygen saturation in vivo. We describe here a novel approach to measure OEF using rapid local frequency mapping. By modeling the MR decay process in the static dephasing regime as two separate dissipative and oscillatory effects, we calculate the OEF from local frequencies measured across the brain by assuming that the biophysical mechanisms causing OEF-related frequency changes can be determined from the oscillatory effects. The Parameter Assessment by Retrieval from Signal Encoding (PARSE) technique was used to acquire the local frequency change maps. The PARSE images were taken on 11 normal volunteers, and 1 patient exhibiting hemodynamic stress. The mean MR-OEF in 11 normal subjects was 36.66±7.82%, in agreement with positron emission tomography (PET) literature. In regions of hemodynamic stress induced by vascular steal, OEF exhibits the predicted focal increases. These preliminary results show that it is possible to measure OEF using a rapid frequency mapping technique. Such a technique has numerous advantages including speed of acquisition, is noninvasive, and has sufficient spatial and temporal resolution.

Nonlinear RF circuits and systems simulation when driven by several modulated signals

The simulation of nonlinear RF circuits and systems driven by digitally modulated signals with a large number of carriers is addressed by combining the envelope transient harmonic balance method with the artificial frequency mapping technique. The co-simulation of low-pass equivalent behavioral models with circuit based models is addressed by simulating the overall wireless communication path. Several application examples are considered, in particular, the modeling of complete wireless communications circuits and systems incorporating the radio channel model.

Distribution of lipid deposits around aortic branches of mice lacking LDL receptors and apolipoprotein E.

Mice with inactivated genes are increasingly used as models of human atherosclerosis. The aim of the present study was to determine whether the characteristic age-related distributions of lipid deposition seen around human arterial branches are replicated in such mice. Lesions occur downstream of branch ostia in immature human aortas, but these regions are spared in adult vessels, with lesions occurring more frequently at the sides or upstream of the branches. We determined the pattern of lipid staining around 102 intercostal branch ostia from apolipoprotein E/low density lipoprotein receptor double-knockout mice aged 9 to 20 weeks by using en face microscopy and a frequency-mapping technique. Lesion prevalence was high in the ostium and the region immediately surrounding it. Frequencies were 2.12+/-0.30 (mean+/-SEM, n=11) times higher upstream than downstream (P<0.01), but the pattern did not resemble the adult human pattern: there were no peaks in frequency at the sides or upstream of the branch, and there was no sparing downstream. Furthermore, a patch of sparing upstream of the branch was seen, which has not been reported for human vessels, and there was no trend toward a more upstream pattern with age. We conclude that knockout mice may not be a suitable model in which to investigate localizing factors.

Distribution of Disease around the Aortocoeliac Branch of White Carneau Pigeons at Different Ages

The distribution of atherosclerotic lesions in the human aorta changes with age. Lipid deposition tends to occur downstream of branch sites in immature vessels but upstream of them at later ages. Comparable age-related distributions of spontaneous and induced lesions have been demonstrated in rabbit aortas. Spontaneous disease is known to develop upstream of the aortocoeliac branch in mature White Carneau pigeons. Using a frequency mapping technique, we investigated whether the same pattern or a downstream one occurs in immature pigeons. Lesions in hatchlings occurred upstream of the branch, to the left of the midline. By 5 months, these lesions had expanded, and a second upstream area, to the right of the midline, was also affected. At later ages, disease frequencies increased in both of these regions but not elsewhere. Thus, contrary to findings in rabbit and human aortas, there was no evidence for a switch from a downstream to an upstream distribution with age. The two rabbit distributions have been attributed to the similar age-related patterns seen in the permeability of the arterial wall; the mature but not the immature pattern of permeability is NO-dependent. The absence of the juvenile disease pattern in pigeons suggests that they might show the NO-dependent pattern of permeability at all ages.

Regular and Chaotic Dynamics of Triaxial Stellar Systems

We use Laskar's frequency mapping technique to study the dynamics of triaxial galaxies with central density cusps and nuclear black holes. For ensembles of 10^4 orbits, we numerically compute the three fundamental frequencies of the motion, allowing us to map out the Arnold web. We also compute diffusion rates of stochastic orbits in frequency space. The objects of fundamental importance in structuring phase space are found to be the 3-dimensional resonant tori; even when stable, such tori are not necessarily associated with periodic orbits as in systems with only two degrees of freedom. Boxlike orbits are generically stochastic, but some tube orbits are stochastic as well. The spectrum of diffusion rates for box-like orbits at a given energy is well approximated as a power law over at least six decades. Models with high central concentrations -- steep central cusps or massive black holes -- exhibit the most stochasticity. A black hole with a mass of 0.3% the mass of the galaxy is as effective as the steepest central density cusp at inducing stochastic diffusion. There is a transition to global stochasticity in box-like phase space when the mass of a central black hole exceeds 2% the galaxy mass. We predict a greater average degree of dynamical evolution in faint ellipticals, due to their high central densities and short crossing times. The evolution time is estimated to be shorter than a galaxy lifetime for absolute magnitudes fainter than about -19 or -20, consistent with the observed change in many elliptical galaxy properties at this luminosity.