Narrow-band Frequency Components Research Articles

Wavelet packet transform applied to active noise control system for mixed noise in nonlinear environment

The noise emitted from rotating machinery usually presents a mixture of broadband and narrowband frequency components. Hybrid functional link artificial neural network (HFLANN) system consisting of narrowband ANC (NANC) subsystem, broadband ANC (BANC) subsystem and sinusoidal noise canceller (SNC) subsystem is effective to suppress the mixed noise. However, in the conventional HFLANN system, the attenuation performance of broadband subsystem cannot meet the requirement, the narrowband subsystem cannot adapt to the nonlinear environment. To address the problems, an improved HFLANN (IHFLANN) system is proposed in this paper. By applying the wavelet packet (WP) structure, the broadband noise is decomposed into different frequency bands, which improves the attenuation performance of broadband subsystem. The FLANN structure is applied to the NANC subsystem to improve the steady-state performance in nonlinear environment. Meanwhile, to reduce the computational complexity, we introduce a simplified IHFLANN (SIHFLANN) system. Simulation results demonstrate the proposed systems achieve better attenuation performance and the simplified system reduces computational complexity without sacrificing the attenuation performance.

Многоадресные волоконные брэгговские структуры в радиофотонных сенсорных системах

The article describes the transition concept from addressable fiber Bragg structures and microwave-photonics sensor systems based on them to multicast fiber Bragg structures. The difference between multicast structures and address structures is that in the fiber Bragg structure formes three or more super narrow-band frequency components, spaced from each other by the microwave frequency. The central frequencies shift of multicast Bragg structures is determined by the result of processing the signal of optical frequencies beats at the photodetector, which parameters judge the applied physical fields. We see the solved problem of uniquely determining the central (Bragg) frequency shift of the multicast fiber Bragg structure, with a unique set of address frequencies.

Recursive Parametric Frequency/Spectrum Estimation for Nonstationary Signals With Impulsive Components Using Variable Forgetting Factor

This paper proposes a general and computationally efficient parametric model-based framework for recursive frequency/spectrum estimation and feature detection of nonstationary signals, which may contain different extents of nonstationarities and impulsive components. The estimation of time-varying frequency or spectrum is formulated as a time-varying linear model identification problem, where the spectral information is estimated from the model coefficients. We then employ a QR-decomposition-based recursive least M-estimate (QRRLM) algorithm for recursive estimation of the time-varying model coefficients in impulsive environment using M-estimation. New variable forgetting factor (VFF) schemes are developed to improve the tracking performance of the QRRLM method in nonstationary environment and we use theoretical derivation and simulations to prove that the proposed VFF schemes can approach the optimal VFF selection. The resultant VFF-QRRLM algorithm is able to restrain and isolate impulsive components whereas it is able to handle different extents of spectral variations. Simulation results show that the proposed VFF-QRRLM algorithm is more robust and accurate than conventional recursive least squares-based methods in estimating both time-varying narrowband frequency components and broadband spectral components with impulsive components. Potential applications of the proposed method can be found in power quality monitoring, online fault detection and speech analysis.

Time-Frequency Analysis of Transient-Evoked Otoacoustic Emissions in Children Exposed to Carboplatin Chemotherapy

The aims of this study were to characterize and quantify time-frequency changes in transient-evoked otoacoustic emissions (TEOAEs) recorded in children diagnosed with retinoblastoma who were receiving carboplatin chemotherapy. A signal processing technique, the wavelet transform (WT), was used to analyze TEOAE waveforms in narrow-band frequency components. Ten children (aged 3–72 months) diagnosed with unilateral or bilateral retinoblastoma were enrolled in the study. TEOAEs were acquired from the children with linear sequences of 70 dB peak equivalent SPL clicks. After WT analysis, TEOAE energy, latency and normalized energy in the narrow-band frequency components were compared before and during carboplatin chemotherapy treatment (average dose 1693 mg/m²). On a group basis, no significant differences (p > 0.05) in the TEOAE energy, latency or normalized energy before and after carboplatin treatment were observed. There were decreases in normalized energy on an individual basis in 10 out of 18 ears in the sample. Exposure to carboplatin chemotherapy did not cause significant changes in TEOAE energy, latency and normalized energy during treatment. However, long-term monitoring of hearing with measurements of TEOAEs is warranted, given the risks of delayed hearing loss in some children receiving carboplatin chemotherapy.

Cochlear active mechanisms in young normal-hearing subjects affected by Williams syndrome: Time–frequency analysis of otoacoustic emissions

The aim of this study was to investigate the functionality of cochlear active mechanisms in normal-hearing subjects affected by Williams syndrome (WS). Transient evoked otoacoustic emissions (TEOAEs) were recorded in a group of young WS subjects and a group of typically developing control subjects, all having normal-hearing thresholds and normal middle-ear functionality. We also analysed the narrow-band frequency components of TEOAEs, extracted from the broad-band TEOAE recordings by using a time–frequency analysis algorithm based on the Wavelet transform. We observed that TEOAEs and the frequency components extracted from TEOAEs measured in WS subjects had significantly lower energy compared to the controls. Also, the narrow-band frequency components of TEOAEs measured in WS subjects had slightly increased latency compared to the controls. Overall, results would suggest a subtle (i.e., sub-clinical) dysfunction of the cochlear active mechanisms in WS subjects with otherwise normal hearing. Also, results point out the relevance of using otoacoustic emissions in the audiological evaluation and monitoring of WS subjects to early identify possible subtle auditory dysfunctions, before the onset of mild or moderate hearing loss that could exacerbate language or cognitive impairments associated with WS.

Quantitative analysis of cochlear active mechanisms in tinnitus subjects with normal hearing sensitivity: Time–frequency analysis of transient evoked otoacoustic emissions and contralateral suppression

Objective The aim of this study was to analyze the fine structure of transient evoked otoacoustic emissions (TEOAEs) and contralateral suppression effects in tinnitus subjects with normal hearing in order to assess whether a minor cochlear or efferent dysfunction, possibly limited in narrow cochlear regions, might play a role in tinnitus. Methods TEOAEs were recorded, both in the absence and in the presence of contralateral acoustic stimulation, in 23 tinnitus patients with normal hearing sensitivity and in 31 non-tinnitus control subjects. The broad-band TEOAE recordings were analyzed by using an innovative algorithm and separated into a set of 33 narrow-band frequency components, that represent the different cochlear contributions to the whole TEOAE response. In each frequency component, three different parameters were analyzed and compared between tinnitus and non-tinnitus subjects, i.e., reproducibility, latency, and the suppression effects induced by contralateral acoustic stimulation. Results Significantly lower reproducibility was observed in the frequency components of the tinnitus subjects compared to the controls, whereas no significant differences in latency and in suppression effects were observed between tinnitus and non-tinnitus ears. Conclusions The analysis of the fine structure of TEOAEs revealed that the tinnitus subjects involved in this study might, possibly, have a minor dysfunction of the cochlear active mechanisms that resulted in frequency components with lower reproducibility. Conversely, the analysis of suppression effects in the narrow-band frequency components of TEOAE indicated that the subjects involved showed no relevant damage to the efferent regulatory mechanisms that control the cochlear activity, neither through the cochlea as a whole, nor in limited cochlear regions.

High-Performance Wireless via the Merger of CI Chip-Shaped DS-CDMA and Oscillating-Beam Smart Antenna Arrays

We introduce a novel merger of direct sequence code division multiple access (DS-CDMA) and smart antenna arrays. With regard to the DS-CDMA scheme, we employ carrier interferometry DS-CDMA (CI/DS-CDMA), a novel implementation of DS-CDMA where chips are decomposable into N narrowband frequency components. With regard to the antenna array, we deploy the oscillating-beam smart array. Here, applying proper time-varying phases to the array elements, we create small movement (oscillation) in the antenna array's pattern, while steering the antenna pattern main lobe to the position of the intended user. The oscillating antenna pattern creates a time-varying channel with a controllable coherence time. This, in turn, provides transmit diversity in the form of a time diversity gain at the mobile receiver side. At the receiver, three stages of combining are available: combining time components of the received signal within symbol duration Ts (each experiencing a different fade) to enhance performance via time diversity; combining frequency components which make up the CI/DS-CDMA chip to enhance the performance via frequency diversity; and combining across chips to eliminate the interfering users on the system. Merging CI/DS-CDMA with the oscillating-beam smart antenna at the base station, we achieve very high capacity via the merger of SDMA (available through directionality of the antenna array) and code division multiple access (inherent in CI/DS-CDMA), and very high performance via the construction of receivers that exploit both transmit diversity and frequency diversity. We present the performance gains of the proposed merger.

Quantification of the dynamic behavior over time of narrow-band components present in heart rate variability by means of the instantaneous amplitude and frequency

The statistical properties of the time- and frequency-domain characteristics of heart rate variability are known to vary over time. A method is presented to compute the time-varying spectral contents of the characteristic narrow-band frequency components of heart rate variability by means of the instantaneous amplitude and frequency at an optimal time resolution. The instantaneous frequency may show oscillatory, but also irregular periods in time. An index of the instantaneous bandwidth is computed to discriminate between oscillatory and irregular periods and to correct the instantaneous amplitude and frequency for irregular periods.

Detection Method of Fatigue Damage in Carbon Steel Using Laser Ultrasonics

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of ultrasonic vibration on the specimen surface. From the comparison of the broadband ultrasonic waveforms among five stages of fatigue damage, the attenuation coefficient of the longitudinal wave by the intrinsic material attenuation increased progressively with increasing the number of fatigue cycle. Ultrasonic attenuation at 2.5, 5.0, 7.5 and 10.0MHz were also calculated by Fourier transformation in order to compare the decay of the longitudinal wave among these frequency components. From the results, ultrasonic attenuation increased as the number of fatigue cycle increased, in both broadband and narrowband frequency components. Therefore, the measurement of broadband and narrowband ultrasonic wave obtained by the laser ultrasonic technique would be effective as the detection method of fatigue damage in nuclear power plant components.

Detection Method of Fatigue Damage in Carbon Steel Using Laser Ultrasonics.

Ultrasonic attenuation was measured by the laser ultrasonic technique among the carbon steel specimens which were subjected to five stages of fatigue damage by constant cyclic tensile stress amplitude. Irradiation of a Q-switched laser was used for ultrasonic generation, and a laser interferometer which consists of a frequency-doubled continuous wave laser and a Fabry-Perot etalon was used for detection of ultrasonic vibration on the specimen surface. From the comparison of the broadband ultrasonic waveforms among five stages of fatigue damage, the attenuation coefficient of the longitudinal wave by the intrinsic material attenuation increased progressively with increasing the number of fatigue cycle. Ultrasonic attenuation at 2.5, 5.0, 7.5 and 10.0MHz were also calculated by Fourier transformation in order to compare the decay of the longitudinal wave among these frequency components. From the results, ultrasonic attenuation increased as the number of fatigue cycle increased, in both broadband and narrowband frequency components. Therefore, the measurement of broadband and narrowband ultrasonic wave obtained by the laser ultrasonic technique would be effective as the detection method of fatigue damage in nuclear power plant components.

The measurement of steady-state visual evoked cortical potentials using an adaptive noise canceller

A new software method for measuring steady-state visual evoked cortical potentials (VECPs) has been developed using the principle of adaptive noise cancelling. The steady-state VECP is composed of narrow-band frequency components at harmonics of the stimulus frequency. In clinical recordings, these signal components are masked by wide-band noise, predominantly electroencephalographic activity and muscle noise. The stimulus frequency is exactly known and by using a reference sinusoid at the stimulus frequency (or its harmonics) the adaptive noise canceller (ANC) is able to cancel uncorrelated noise components from the recording. In effect, the ANC functions as an adaptive narrow-band-pass filter at the reference frequency. The performance of the ANC has been evaluated using both simulated and physiological signals. The output of the ANC provides temporal information on the signal amplitude and phase, and can be used to calculate the reliability of signal detection. For this application, the ANC has a number of advantages over the fast Fourier transform: it is a more sensitive detector, it requires fewer calculations, it is less computationally intensive, it requires less memory and it can be implemented in real time.

Structure of random velocity fluctuations in a two-dimensional vortex-street wake.

This paper describes experimentall the structure of random components of the velocity fluctuations in the vortex-street wake of a thin normal plate at a Reynolds number of 23 OOO. Measurements were made by a phase-averaging technique at positions eight heights downstream of the plate. The random components were defined as the corresponding instantaneous velocities subtracted by their phase-averaged values, viz. the periodic components. The random components were decomposed into several narrow-band frequency components, whose contributions to the Reynolds shearing stress are found to generally attain a maximum at saddles associated with the periodic components. Moreover the Reynolds shearing stress is dominated by the low-frequency components whose longitudinal length scale is greater than that of the periodic components. These facts raise a doubt as to the well·documented idea that most of Reynolds shearing stress is produced by the vortex stretching near the saddles. The low-frequency random components may possibly be produced by a modulation of the shape, strength and position of each realization of the periodic components.

Turbulent Pressure Field in a Co-Annular Jet

Single-point and two-point fluctuating static pressure measurements have been made in the initial mixing and transition regions in a co-annular circular jet. Space scales, correlation and time scales in the convected frame, and convection velocities have been determined for both broad-band and narrow-band frequency components. Analytical functionals describing the structural behavior of the turbulent pressure field have been developed from the data which are suitable for direct application in predicting the sound power level radiated from this turbulent field. Effects of both area and velocity ratios are incorporated in the model. A b BB dc,dEp x> y Nomenclature = anisotropy factor = mixing layer width = broad band = diameter of core or of bypass nozzle = decay coefficients in axial, radial, and lateral directions, respectively = broad-band axial length scale for pressure = narrow-band radial and lateral