Signal Amplitude Variations Research Articles

Investigating the origins of pitch modulation in flute vibrato

Like most musicians, flute players often add vibrato to their playing for expressive effect. This is accomplished by a periodic modulation of the supplied air pressure resulting in significant amplitude and timbre variations of the resulting sound. However, a sizeable modulation in pitch also results in most cases with a width ranging from 20 to 50 cents of total variation. This work investigates the physical origins of this pitch variation based on an analysis of multiple databases of flute vibrato tones. Detailed tracking of the amplitude and pitch trajectories of each overtone is used to characterize the extent of amplitude and frequency modulation of each partial as well as their relative correlation. A high degree of correlation between amplitude and frequency modulation tracks suggests that both variations are controlled by the same physical parameter. However, the mechanisms for pressure-controlled pitch modulation are not well understood and many physically modeled synthesis algorithms do not produce this pitch variation when the input pressure is modulated. As such, this work systematically modifies existing physical models to reproduce the characteristics of recorded vibrato tones and evaluate potential mechanisms that may underlay the observed pitch modulations.

Elongated bubble velocity estimation in vertical liquid-gas flows using flow-induced vibration

The multiphase flow occurs in various major industrial fields and nature. Furthermore, due to the single and multiphase flow characteristics, they generate vibration on the structure conveying or subjected to the flow. This paper investigates in an experimental apparatus, the possibility to use the flow-induced vibration from a vertical liquid-gas two-phase flow conveyed by a pipe to obtain the elongated bubble velocity. The vibration signal analysis in time domain showed that the structural excitation due to the elongated bubble rising in the stagnant liquid was significant to be distinguished from other excitations. The time-frequency analysis of slug and churn flow showed a significant amplitude variation in a specific frequency band. Finally, it was possible to obtain the elongated bubble velocity with reasonable accuracy by cross-correlating the envelope of a vibration signal filtered in a particular frequency band of two accelerometers. Thus, this paper presents a non-invasive and simple to mount technique to estimate the elongated bubble velocity in stagnant and moving liquid conditions.

An accurate digital converter for lossy capacitive sensors

This paper presents an incremental delta-sigma based capacitance-to-digital converter for lossy capacitive sensors. The proposed converter consists of a capacitance-to-voltage converter followed by a single-bit incremental delta-sigma converter. Unlike conventional incremental-delta sigma converter where a fixed reference voltage signal is utilized, the proposed converter utilizes a reference signal which depends on the amplitude and frequency of the input excitation signal. The generated reference signal for the incremental-delta sigma converter reduces the error in the capacitance measurement due to variation in the excitation signal frequency and amplitude. In addition, the proposed converter utilizes a frequency-independent quadrature phase shifter circuit for the generation of reference π/2 phase-shifted signal for the phase-sensitive detection operation. Moreover, a modified clock counting approach is utilized to measure the sensor capacitance accurately. A prototype of the proposed circuit is fabricated using commercial off-the-shelf components and tested. The experimental results demonstrate that the circuit is able to measure the sensor capacitor in the range from 20 pF to 163 pF. The worst-case error in sensor capacitance measurement was less than 0.2%. Furthermore, the proposed converter experimentally provides a signal-to-noise ratio of 56.66 dB.

Global coastal attenuation of wind-waves observed with radar altimetry

Coastal studies of wave climate and evaluations of wave energy resources are mainly regional and based on the use of computationally very expensive models or a network of in-situ data. Considering the significant wave height, satellite radar altimetry provides an established global and relatively long-term source, whose coastal data are nevertheless typically flagged as unreliable within 30 km of the coast. This study exploits the reprocessing of the radar altimetry signals with a dedicated fitting algorithm to retrieve several years of significant wave height records in the coastal zone. We show significant variations in annual cycle amplitudes and mean state in the last 30 km from the coastline compared to offshore, in areas that were up to now not observable with standard radar altimetry. Consequently, a decrease in the average wave energy flux is observed. Globally, we found that the mean significant wave height at 3 km off the coast is on average 22% smaller than offshore, the amplitude of the annual cycle is reduced on average by 14% and the mean energy flux loses 38% of its offshore value.

Low-frequency ambient distributed acoustic sensing (DAS): case study from Perth, Australia

SUMMARYAmbient wavefield data acquired on existing (so-called ‘dark fibre’) optical fibre networks using distributed acoustic sensing (DAS) interrogators allow users to conduct a wide range of subsurface imaging and inversion experiments. In particular, recorded low-frequency (<2 Hz) surface-wave information holds the promise of providing constraints on the shear-wave velocity (VS) to depths exceeding 0.5 km. However, surface-wave analysis can be made challenging by a number of acquisition factors that affect the amplitudes of measured DAS waveforms. To illustrate these sensitivity challenges, we present a low-frequency ambient wavefield investigation using a DAS data set acquired on a crooked-line optical fibre array deployed in suburban Perth, Western Australia. We record storm-induced microseism energy generated at the nearby Indian Ocean shelf break and/or coastline in a low-frequency band (0.04−1.80 Hz) and generate high-quality virtual shot gathers (VSGs) through cross-correlation and cross-coherence interferometric analyses. The resulting VSG volumes clearly exhibit surface wave energy, though with significant along-line amplitude variations that are due to the combined effects of ambient source directivity, crooked-line acquisition geometry and the applied gauge length, fibre coupling, among other factors. We transform the observed VSGs into dispersion images using two different methods: phase shift and high-resolution linear Radon transform. These dispersion images are then used to estimate 1-D near-surface VS models using multichannel analysis of surface waves (MASW), which involves picking and inverting the estimated Rayleigh-wave dispersion curves using the particle-swarm optimization global optimization algorithm. The MASW inversion results, combined with nearby deep borehole information and 2-D elastic finite-difference modeling, show that low-frequency ambient DAS data constrain the VS model, including a low-velocity channel, to at least 0.5 km depth. Thus, this case study illustrates the potential of using DAS technology as a tool for undertaking large-scale surface wave analysis in urban geophysical and geotechnical investigations to depths exceeding 0.5 km.

Linear and Nonlinear Ultrasonic Techniques for Monitoring Stress-Induced Damages in Concrete

Abstract When stress in concrete exceeds certain threshold value, microcracks are nucleated, these microcracks can propagate and coalesce forming macrocracks, resulting in the gradual decay of the mechanical properties of concrete and eventual failure of the concrete structures. For safety concerns, one needs to develop suitable nondestructive testing methods capable of detecting past overloads of concrete structures during its service life. In this work, the stress-induced damage in concrete is monitored using ultrasonic techniques, exploiting the coupling between the stress level experienced by concrete and its wave propagation parameters. Cyclic compression tests with increasing maximum load level have been performed on specimens made of concrete with coarse-grained (CG) aggregates. Experimental results have been analyzed by two different ultrasonic methods—the linear and the nonlinear ultrasonic techniques. In linear ultrasonic technique, the stress level experienced by the specimens is related to the variations in signal amplitude and velocity of ultrasonic waves. In nonlinear ultrasonic method, the sideband peak count (SPC) technique is used for revealing the stress-induced damage corresponding to each load step. In comparison to linear ultrasonic parameters, the nonlinear ultrasonic parameter SPC-I appears to be more sensitive to the variations of the internal material structures during both loading and unloading phases. Moreover, the SPC technique has shown to be capable of identifying both the initial damage due to the evolution and nucleation of microcracks at the microscopic scale, and the subsequent damages induced by high overload, resulting in an irreversible degradation of the mechanical properties.

Chirped Gaussian pulse propagation with various data rates transmission in the presence of group velocity dispersion (GVD)

Abstract Linear/Measured chirped Gaussian pulse propagation is simulated at various data rates transmission in the presence of group velocity dispersion without amplification unit. The power variations (PVs) vs. frequency, time period are also clarified after 250 km fiber channel length and 10 Gb/s bit rate (BR) of for Gaussian pulse generators with linear chirp factor of 2 rad/s, measured chirp factor (alpha parameter of 2 rad/W, Adiabatic chirp of 10 s−1). Moreover the overall total light power after fiber, the overall total electrical power after APD receiver are studied and clarified for Gaussian pulse generators with linear chirp, measured chirp factor. PVs vs. frequency, time period are simulated after APD receiver for Gaussian pulse generators with linear chirp, measured chirp factor. Maximum signal amplitude variations vs. time after APD receiver for Gaussian pulse generators with linear chirp, measured chirp factor are also clarified with the numerical simulation results.

Statistical models of fading signals propagated through the ionospheric satellite channels

Statistical models of satellite ionospheric radio channels are considered in the article, the influence of which causes fading of signals during their propagation (amplitude and phase variations of signals) due to random temporal and spatial fluctuations of the electron density of ionospheric irregularities. These models are based on the use of empirical laws regarding the densities of the amplitudes and phases of digital signals from the output of signal demodulators. A technique for estimating the probability of erroneous reception of digital signals with phase shift keying using the considered fading models is presented. Estimates of energy losses end errorperformance degradation during propagation along ionospheric satellite radio channels with scintillation index parameters typical for the P- and L-frequency bands, with respect to propagation in free space, have been made.

Numerical simulation of lower ionospheric reflection parameters by using International Reference Ionosphere (IRI) model and validation with Very Low Frequency (VLF) radio signal characteristics

Sub-Ionospheric Very Low Frequency (VLF) radio wave propagation characteristics are the major tool to study the lower ionospheric heights mainly D-region. Wait’s 2-component exponential model is a well-known mechanism to understand the basic characteristics of this layer based on VLF remote sensing. This model deals with two major ionospheric parameters, namely, ‘steepness parameter’ (β) and ‘effective reflection height’ (h′). ‘International Reference Ionospheric (IRI)’ is a famous model for the terrestrial ionosphere that provides mostly the altitude profile temperature of the electron and ions globally. In this manuscript, we use such electron density profiles based on IRI outcomes during a quiet ionospheric condition. We choose our VLF reception location ‘Ionospheric and Earthquake Research Center & Optical Observatory’ (IERCOO), Sitapur (Lat 22.5° N, Lon 87.48° E) to compute the electron density from IRI model. By using the Wait’s exponential model with a log-linear fitting of electron density, we compute the β and h′ from their fundamental definition. With an automation technique, we repeat this process several times and generate a complete data set of such parameters for different time of the day during the summer and winter seasons of the year 2016. To get a qualitative comparison with the VLF signal amplitude variation with β and h′, we choose the Indian VLF transmitter VTX of frequency 18.2 kHz (Lat 8.26°N and 77.44°E). By computing similar data sets for other four receiving locations in India, we replicate the VLF signal amplitude profiles using Long Wavelength Propagation Capability (LWPC) model which matches with the observed signal profile satisfactorily.

High-Resolution Detection of Wavelength Shift Induced by an Erbium-Doped Fiber Bragg Grating

We analyze theoretically and verify experimentally a high-resolution and low-cost method to detect wavelength shift induced by an Erbium-doped fiber Bragg grating. A π-phase-shifted fiber Bragg grating on a temperature controlling setup is employed to achieve tunable single-sideband modulation. To further enhance measurement stability and diminish operational complexity, an asymmetric phase-shifted fiber Bragg grating is developed to reflect wide single-sideband modulation signals and avoid the tuning of the optical carrier wavelength. Through the using of microwave photonics technique, the wavelength shift of the Erbium-doped fiber Bragg grating induced by laser pumping is mapped onto the amplitude variation of the beat signal. The results indicate 1 GHz frequency shift, corresponding to 0.008 nm wavelength shift in the 1550 nm band, is able to be detected. The resolution can be further improved by using a more accurate temperature controlling system. Furthermore, our approach offers an alternative method to detect weak temperature and strain changes on chips or other sensing systems with high accuracy.

LTP Modeling of Single-Phase $T/4$ Delay-Based PLLs

A large number of single-phase phase-locked loops (PLLs) require generating a 90° phase-shifted version of their single-phase input signal. Among the wide variety of options, using a quarter-cycle transfer delay is particularly popular. In recent years, several single-phase transfer delay-based PLLs (TD-PLLs) have been proposed in the literature. The major difference between different TD-PLLs lies in the way they have adapted to frequency changes. Regardless of this structural difference, a common trend in investigating TD-PLLs is obtaining a linear time-invariant (LTI) model and analyzing it. Obtaining such a model, however, is often based on neglecting the input signal amplitude variations and double-frequency oscillations in the transient behavior of TD-PLLs, which results in some inaccuracies. To deal with this problem, the linear time-periodic (LTP) modeling of TD-PLLs is presented in this letter. It is demonstrated that the LTP model does not have the limitations of the LTI one and can provide much higher accuracy, but at the cost of a higher model complexity.

Evaluation of the Uncertainty of Passive Cavitation Measurements for Blood–Brain Barrier Disruption Monitoring

Exposure to ultrasound combined with intravenous injection of microbubbles is a technique that can be used to temporarily disrupt the blood–brain barrier. Transcranial monitoring of cavitation can be done with one or more passive cavitation detectors (PCDs). However, the positioning of the PCDs relative to the cavitation site and the attenuation of these signals by the skull are two sources of error in the quantification of cavitation activity. The aim of this study was to evaluate in vitro the amplitude variation of cavitation signals that can be expected for an excised porcine skull model. The variation caused by the relative positioning of the PCD with respect to the cavitation site was quantified. A position-based correction of the signal amplitude was evaluated. Pig skull samples were used to assess variation in signal amplitude caused by bone. The overall coefficient of variation of the signals owing to these measurement biases was estimated at 30.8%.

Infrared Infusion Monitor Based on Data Dimensionality Reduction and Logistics Classifier

This paper presents an infrared infusion monitoring method based on data dimensionality reduction and a logistics classifier. In today’s social environment, nurses with hospital infusion work are under excessive pressure. In order to improve the information level of the traditional medical process, hospitals have introduced a variety of infusion monitoring devices. The current infusion monitoring equipment mainly adopts the detection method of infrared liquid drop detection to realize non-contact measurements. However, a large number of experiments have found that the traditional infrared detection method has the problems of low voltage signal amplitude variation and low signal-to-noise ratio (SNR). Conventional threshold judgment or signal shaping cannot accurately judge whether droplets exist or not, and complex signal processing circuits can greatly increase the cost and power consumption of equipment. In order to solve these problems, this paper proposes a method for the accurate measurement of droplets without increasing the cost, that is, a method combining data drop and a logistics classifier. The dimensionalized data and time information are input into the logistics classifier to judge the drop landing. The test results show that this method can significantly improve the accuracy of droplet judgment without increasing the hardware cost.

Investigating the performance of an amplitude-independent algorithm for detecting the hand muscle activity of stroke survivors

To make robotic hand devices controlled by surface electromyography (sEMG) signals feasible and practical tools for assisting patients with hand impairments, the problems that prevent these devices from being widely used have to be overcome. The most significant problem is the involuntary amplitude variation of the sEMG signals due to the movement of electrodes during forearm motion. Moreover, for patients who have had a stroke or another neurological disease, the muscle activity of the impaired hand is weak and has a low signal-to-noise ratio (SNR). Thus, muscle activity detection methods intended for controlling robotic hand devices should not depend mainly on the amplitude characteristics of the sEMG signal in the detection process, and they need to be more reliable for sEMG signals that have a low SNR. Since amplitude-independent muscle activity detection methods meet these requirements, this paper investigates the performance of such a method on people who have had a stroke in terms of the detection of weak muscle activity and resistance to false alarms caused by the involuntary amplitude variation of sEMG signals; these two parameters are very important for achieving the reliable control of robotic hand devices intended for people with disabilities. A comparison between the performance of an amplitude-independent muscle activity detection algorithm and three amplitude-dependent algorithms was conducted by using sEMG signals recorded from six hemiparesis stroke survivors and from six healthy subjects. The results showed that the amplitude-independent algorithm performed better in terms of detecting weak muscle activity and resisting false alarms.

Distributed Feedback Laser (DFB) for Signal Power Amplitude Level Improvement in Long Spectral Band

Abstract This study outlines the distributed feedback laser for signal power amplitude level improvement in the long spectral band of 1550 nm wavelength within supporting pumped wavelength of 1480 nm. The bias and modulation peak currents based distributed feedback laser are varied in order to test the signal power level, peak signal amplitude variations after the fiber-optic channel and light detectors. The signal power level, peak signal amplitude is measured against spectral wavelength and time bit period variations. The study emphasis the signal power level, peak signal amplitude are enhanced for the best selection values of both a bias current at 45 mA and modulation peak current at 0.5 mA.

An improved backtracking search optimization algorithm for cubic metric reduction of OFDM signals

Abstract The large amplitude variations of OFDM signals generate in-band distortion and out-of-band radiation. In recent years, cubic metric (CM) has been verified as a more accurate metric to measure the amplitude variations. In this paper, the PTS technique is used to decrease the CM of OFDM signals. To overcome the search complexity of an exhaustive search based PTS technique, we introduce an improved backtracking search (IBS) optimization algorithm. Simulations are conducted to show the advantages of the proposed IBS based PTS approach compared with the conventional OFDM, and several state-of-the-art methods in terms of search complexity and CM reduction performance.

Seasonal Variations of the Amplitude of the VLF Radio Signals and the Intensity of the Atmospheric Electric Field in Cryolithozone Conditions

It is performed an analysis of seasonal variations of the parameters of the underlying surface under cryolithozone conditions far from industrial interference at the SHICRA SB RAS radiophisical polygon near Yakutsk. Seasonal variations of the parameters of atmospheric electricity and the very low frequency (VLF) radio waves propagation from 2009 to 2018 are presented. It is obtained that for summer season the atmospheric electric field near the earth’s surface has a recession due to summer defrosting of the upper layer of permafrost and underlying surface conductivity changes and an increasing of radon output permeability. There is a slight decreasing of amplitude of VLF radio navigation signals received in Yakutsk in summer period. There is an asymmetry in seasonal daytime variations of the VLF signal amplitude. The VLF amplitude during autumn equinox more closely to summer solstice. The asymmetry determined by the season electron density profiles of the ionospheric D region.

THE RESEARCH FOR AN IDENTIFICATION OF CRACK – LIKE CORROSION – MECHANICAL DEFECT BY ACOUSTIC IN-LINE INSPECTION TOOLS

Problem of an identification of cracks in dents or corrosion damage, which is considered as a crack – like corrosion – mechanical defect type, is considered for acoustic in – line inspection tools during an in – line inspection of oil pipelines. For this purpose, a theoretical model has been provided and considered as a vertical notch with a convex base. For modeling an interaction of acoustic waves with the defect model there has been used a corresponded formula of an acoustic equation at a ray – acoustic approximation. Considering used simplifying assumptions there have obtained certain boundary conditions for acoustic equation of the crack – like corrosion mechanical defect. Based on this theoretical model here an experimental research were provided at specially manufactured test specimen which contained vertical notches with base of different curvature. At the specimen there are has been obtained a difference of echo signals amplitude from convex and flat surface based notches. Obtained results showed a sufficient agreement with provided by theoretical modeling and approve an adequacy of the proposed model for a theoretical description of considered interaction shear waves with the defect imitation. According to obtained trend of an echo – signal amplitude variation a method for identification of cracks in dents or corrosion damage during an oil pipeline inspection by inline inspection tools has been provided.

Identification of Multiple First-Order Continuous-Time Dynamic Models From Special Segments in Historical Data

Continuous-time dynamic models are often required for controller design, process monitoring, and operation optimization. This paper proposes an approach to estimate unknown parameters of multiple first-order continuous-time dynamic models from special segments in historical data. The approach is composed by two main steps. First, special segments are defined as the ones with two ends in steady states and the middle part having significant amplitude variations in transient states; the special segments are found automatically by exploiting a piece-wise linear representation technique from a large amount of historical data samples. Second, static gains are estimated by solving a set of linear equations based on steady-state values of inputs and outputs; sums of time constants and delays are obtained by solving another set of linear equations based on integrals of model output errors from data samples in transient states; the sums are used as an optimization constraint for maximizing the fitness value between measured and simulated outputs, from which separated estimates of time constants and delays are yielded. Numerical examples are provided to illustrate the proposed approach and compare with existing ones.

Flow pattern classification in liquid-gas flows using flow-induced vibration

The multiphase flow is not only the most common flow in nature but also occurs in various major industrial fields. Furthermore, in many industrial plants, the single and multiphase flows generates vibration and noise. In the context of two-phase flows, a specific case of multiphase flow, the flow pattern determination is crucial to their analysis, and despite the recent progress and developments in flow-induced vibration for two-phase flows, it is still considered an open topic. This paper develops a novel algorithm for flow pattern classification using the vibration signal from a vertical pipe conveying a liquid-gas two-phase flow to determine the flow pattern. An experimental apparatus and procedure were developed to perform this investigation. The analysis in the frequency domain showed a distinct frequency band activity for slug and churn flows. The analysis in time domain showed a significant amplitude variation for these flow patterns. Finally, by using the RMS and Pearson correlation coefficient, it was possible to classify the studied cases accurately. The results present a non-intrusive technique to identify the flow pattern in two-phase liquid-gas vertical flows.