Adjacent Frequency Components Research Articles

A frequency estimation method for two adjacent frequencies

The frequency-domain estimation methods are estimate frequency from main-lobe. One shortcoming of these methods lies in the fact that they are not suited to two adjacent frequency components. When the distance between two frequency components is less than 3 DFT bins, former methods are subject to severe spectral interference, which results in considerable errors of estimate. In this paper, a discovery is made that side-lobes have relatively smaller spectral interference as compared to main-lobe, for which a novel estimation method based on the first side-lobes is proposed. As demonstrated by simulation, the proposed method performs better in two adjacent frequency components estimation. When the distance between two frequency components reaches 1.5 bins, the maximum estimation error is approximately 0.07 bins for the two frequencies.

Instantaneous microwave frequency measurement with high-resolution based on stimulated Brillouin scattering

A novel photonic method of instantaneous microwave frequency measurement (IMFM) based on Stimulated Brillouin scattering (SBS) is proposed. The principle of the technique is the employment of SBS effect to amplify/attenuate two adjacent frequency components, which result in a definite amplitude comparison function (ACF). Using this technique, the frequency of an unknown RF signal can be precisely obtained. Experimental results show the measurement capability of the proposed method over a frequency range of 0.47–23 GHz with a higher resolution of 8 MHz.

주축 선회형 5축 가공기에서 가속도 센서를 이용한 채터 감지

Chatter is caused by the dynamic instability of a machining system. Chatter causes a variety of economic damages, including reduction of tool life, and damage to the machine tools and workpieces. In this study, we propose a method for detecting chatter in head-tilting 5 - axis machine tools. A sensor attached to a fixed part is considered, located at a remote place from the spindle. This study aimed to detect chatter without any prior knowledge of the involved dynamic system, such as tools, machine tools and workpieces. First, the acceleration signal under various machining conditions was analyzed: no change was observed to interfere with the chatter detection. However, with chatter occurring, beating of the acceleration signal was confirmed by two or more adjacent frequency components, which could be the basis of a very good chatter detection approach. Finally, using this concept, a mode diagram was proposed for chatter detection.

A Tunable Resolution MUSIC Algorithm for Interharmonics Analysis

The harmonic and interharmonic analysis recommendations are contained in the latest IEC standards on power quality. Measurement and analysis experiences have shown that great difficulties arise in the interharmonic detection and measurement with acceptable levels of accuracy. In order to improve the resolution of spectrum analysis, the traditional method (e.g. discrete Fourier transform) is to take more sampling cycles, e.g. 10 sampling cycles corresponding to the spectrum interval of 5 Hz while the fundamental frequency is 50 Hz. However, this method is not suitable to the interharmonic measurement, because the frequencies of interharmonic components are non-integer multiples of the fundamental frequency, which makes the measurement additionally difficult. In this paper, the tunable resolution multiple signal classification (TRMUSIC) algorithm is presented, which the spectrum can be tuned to exhibit high resolution in targeted regions. Some simulation examples show that the resolution for two adjacent frequency components is usually sufficient to measure interharmonics in power systems with acceptable computation time. The proposed method is also suited to analyze interharmonics when there exists an undesirable asynchronous deviation and additive white noise.

Analysis of velocity dispersion using full‐waveform multichannel sonic logging data: A case study

ABSTRACTSeismic attenuation and velocity dispersion are potentially able to reveal the rock physical properties of the subsurface. Conventionally, a frequency‐independent quality factor (Q) is measured. This Q is equivalent to the total velocity dispersion in a seismic record and is inadequate for analysing the attenuation mechanism or rock physical properties. Here a new method is proposed to extract the velocity dispersion curves so that more attributes can be obtained from full‐waveform multichannel sonic logging data, especially the critical frequency (fc) if it is within the bandwidth of the data. This method first decomposes the seismic data into a series of frequency components, computes the semblance of each frequency component for different velocity values, cross‐correlates the semblance matrices of adjacent frequency components to get the velocity gradients, and finally integrates to obtain a velocity dispersion curve. Results of this method are of satisfactory accuracy and robustness. This method is applied to the data acquired in Mallik 5L‐38 gas hydrate research well in Mackenzie Delta, Northwest Territories, Canada. The observed P‐wave velocity dispersion compares well with the geological setting. In the gas hydrate zone (about 900 m–1100 m), high concentration of gas hydrate causes very strong velocity dispersion and a distinct fc at about 15 kHz, likely due to strong scattering of centimetre‐scale inclusions of gas hydrate; concurrently, water flow in connected cracks in some ranges of this zone adds a large part of velocity dispersion and a dimmer fc at about 9.5 kHz. Immediate underneath the gas hydrate zone, abundant free water in weakly laminated sediments causes quite strong velocity dispersion and an fc at about 6.5 kHz. Velocity dispersion is mild and without an obvious fc in sediments above the gas hydrate zone.

Concatenation underlies interactions between gamma and beta rhythms in neocortex

The neocortex generates rhythmic electrical activity over a frequency range covering many decades. Specific cognitive and motor states are associated with oscillations in discrete frequency bands within this range, but it is not known whether interactions and transitions between distinct frequencies are of functional importance. When coexpressed rhythms have frequencies that differ by a factor of two or more interactions can be seen in terms of phase synchronization. Larger frequency differences can result in interactions in the form of nesting of faster frequencies within slower ones by a process of amplitude modulation. It is not known how coexpressed rhythms, whose frequencies differ by less than a factor of two may interact. Here we show that two frequencies (gamma – 40 Hz and beta2 – 25 Hz), coexpressed in superficial and deep cortical laminae with low temporal interaction, can combine to generate a third frequency (beta1 – 15 Hz) showing strong temporal interaction. The process occurs via period concatenation, with basic rhythm-generating microcircuits underlying gamma and beta2 rhythms forming the building blocks of the beta1 rhythm by a process of addition. The mean ratio of adjacent frequency components was a constant – approximately the golden mean – which served to both minimize temporal interactions, and permit multiple transitions, between frequencies. The resulting temporal landscape may provide a framework for multiplexing – parallel information processing on multiple temporal scales.

A Comparative Study of Modal Parameter Identification Based on Wavelet and Hilbert-Huang Transforms

Modal parameter identification is an important topic in vibration-based structural health monitoring. This paper presents a comparative study of the modal parameter identification of structures based on the continuous wavelet transform (WT) using the modified complex Morlet wavelet function and the improved Hilbert–Huang transform (HHT). Special attention is given to some implementation issues, such as the modal separation and end effect in the WT, the optimal parameter selection of the wavelet function, the new stopping criterion for the empirical mode decomposition and the end effect in the HHT. The capabilities of these two techniques are compared and assessed by using three examples: a numerical simulation for a damped system with two very close modes; an impact test on an experimental model with three well-separated modes; and an ambient vibration test on the Z24-bridge benchmark problem. The results demonstrate that both methods are applicable for the system with well-separated modes when the time-frequency resolutions are sufficiently taken into account. For the system with very close modes, the WT method seems to be more effective than HHT. One reason is that the frequency separation of HHT is partially dependent on the decomposition performance of the preprocess tool. Therefore, if the adjacent frequency components are very close, it is difficult to design appropriate parameters for the filters to separate them clearly.

A New Method for Solving the Permutation Problem of Frequency-Domain Blind Source Separation

Frequency domain blind source separation has the great advantage that the complicated convolution in time domain becomes multiple efficient multiplications in frequency domain. However, the inherent ambiguity of permutation of ICA becomes an important problem that the separated signals at different frequencies may be permuted in order. Mapping the separated signal at each frequency to a target source remains to be a difficult problem. In this paper, we first discuss the inter-frequency correlation based method [1], and propose a new method using the continuity in power between adjacent frequency components of same source. The proposed method also implicitly utilizes the information of inter-frequency correlation, as such has better performance than the previous method.

Dichotic presentation of speech signal using a critical filter bank for bilateral sensorineural hearing impairment

Sensorineural hearing-impaired listeners face a particular problem in view of a decrease in the frequency resolving capacity of an ear due to the spread of masking of frequency components by adjacent frequency components. Filtering a speech signal by a bank of critical band filters and adding signals from alternate bands for presenting to the two ears is likely to reduce the effect of the spread of masking along the cochlear partition, and thus may help in improving the speech intelligibility. This processing scheme has been implemented with 18 critical bands for experimental evaluation through listening tests. The scheme was found to be helpful in improving recognition scores and transmission of speech features in listening tests with normal hearing subjects with simulated sensorineural hearing loss. Listening tests were carried out using 12 vowel–consonants–vowel and consonant–vowel nonsense syllables presented in quiet (no masking noise), on ten subjects with mild to very severe sensorineural hearing loss. The stimulus response confusion matrices were analyzed using relative improvement in recognition scores and information transmission analysis. The relative improvement in recognition scores is up to 25%. Information transmission analysis indicated that the overall improvement is contributed to by improvements in transmission of the speech feature of voicing, place, and manner. The mean response time has also been found to decrease significantly.

Fast and accurate method to measure interharmonics in power systems

AbstractIn order to improve the resolution of spectrum analysis, the traditional method is to take more sampling periods, e. g. 50 sampling periods corresponding to the spectrum interval of 1 Hz. This method is not suitable to the inter‐harmonic measurement, because most interharmonics vary rather quickly with the time and so the analysis results based on long time sampling may be useless. In this paper the zero‐padding technique with short sampling time is used to resolve interharmonics, and the zoom FFT is used to decrease the computation time in order to meet the needs of real‐time measurement. The simulating computation shows that the resolution for two adjacent frequency components is usually sufficient to measure harmonics and interharmonics in power systems with acceptable short sampling and computation time. This method is also suited to analyse harmonics and interharmonics when there exists an undesirable asynchronous deviation between the sampling period and the signal period.

Adaptive smoothing: An improved method for spectral analysis and its application to seizure EEG

We describe the data adaptive smoothing method, an improved method for multichannel spectral analysis of seizure EEG. After Fast Fourier Transform of EEG data, spectra were computed by smoothing over adjacent frequency components. Using cross-validatory maximum likelihood criteria, unsmoothed spectral data were used to select the level of smoothing (spectral window effective bandwidth) required to minimize bias and variance errors. The statistical assumptions of this method are consistent with the statistical properties of seizure EEG. On computer simulation of seizure EEG, the smoothing level predicted by this method correlates strongly with the optimum smoothing level. The utility of the method is demonstrated by application to seizure EEG. The consistency of the method's statistical assumptions, the success in selection of the optimum smoothing level, and the variability in optimum smoothing required for seizure EEG suggest that the adaptive smoothing method is a useful method for multichannel spectral analysis.

Model for Phase Perception of Complex Tones

Plomp and Steeneken recently published results on the effect of phase on the timbre of complex tones consisting of 10 harmonically related frequency components [J. Acoust. Soc. Amer. 46, 409–421 (1969)]. The (rank order) similarity judgments obtained in triadic comparisons by eight subjects were represented geometrically in a multidimensional space using Kruskal's monotonic scaling procedure. In order to understand the observed effects of phase on timbre, it is assumed that the ear can detect in these comparison tests differences in the degree of amplitude modulation of all triplets of adjacent frequency components falling into the same critical band. Each 10-tone complex is thus characterized by eight amplitude modulation indices (corresponding to the harmonic triplets 1,2,3; 2,3,4; 3,4,5; ⋯; 8,9,10). The Euclidean distances between two stimuli in this multidimensional “modulation space” are found to correlate well with the Euclidean distances in the perceptual space based on the similarity judgments.