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The performance of an Unmanned Underwater Vehicle (UUV) is significantly influenced by the magnitude of self-generated noise, making it a crucial factor in advancing acoustic load technologies. Effective noise management, through the identification and separation of various self-noise types, is essential for enhancing a UUV's reception capabilities. This paper concentrates on the development of UUV self-noise separation techniques, with a particular emphasis on feature extraction and separation in multi-task learning environments. We introduce an enhancement module designed to leverage noise categorization for improved network efficiency. Furthermore, we propose a neural network-based multi-task framework for the identification and separation of self-noise, the efficacy of which is substantiated by experimental trials conducted in a lake setting. The results demonstrate that our network outperforms the Conv-tasnet baseline, achieving a 0.99 dB increase in Signal-to-Interference-plus-Noise Ratio (SINR) and a 0.05 enhancement in the recognized energy ratio. [ABSTRACT FROM AUTHOR]

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This study presents a predominantly numerical and theoretical investigation into the balance of tonal and broadband noise due to an isolated propeller in uniform motion. The predicted trends in the balance between tonal and broadband noise radiation with varying blade number and speed of rotation is supported by preliminary experimental measurements. Here, we assume that the dominant noise generation mechanisms are the tones due to steady loading and blade thickness, while the broadband noise is due to boundary layer scattering at the trailing edge. The study also provides a detailed comparison between the tonal and broadband formulations to highlight their similarities and differences. In this paper, we show that the main differences in the behaviour and character of the tonal and broadband spectra and directivities are due to the number of acoustic modes that can be excited. This paper presents a parametric study in which the variation in tonal and broadband noise is investigated as a function of blade tip Mach number (M t ) and blade number (B) whilst maintaining constant solidity and thrust. This study is repeated for three NACA airfoil profiles. It is found that tonal noise dominates at low blade number and low frequency and/or higher tip speeds, while broadband noise is the major contributor at high-frequencies and at high blade number and low tip speeds. The results show a clear distinction between the combinations of M t and B that are dominated by tonal and by broadband noise. These results are interpreted from fundamental principles relating to modal radiation efficiencies. We confirm this trend of balance between tonal and broadband noise with measured noise at different B and M t . The results of this paper will serve as useful guidelines for preliminary propeller design. [ABSTRACT FROM AUTHOR]

Automotive fans, small wind turbines, and manned and unmanned aerial vehicles (MAVs/UAVs) are just a few examples in which noise generated by the flow's interaction with aerodynamic surfaces is a major concern. The current work shows the potential of a new airfoil shape to minimize noise generation, maintaining a high lift-to-drag ratio in a prescribed Reynolds regime. This investigation uses a multifidelity approach: a low-fidelity semiempirical model is exploited to evaluate the sound pressure level (SPL). Fast evaluation of a low-cost function enables the computation of a large range of possible profiles, and accuracy is added to the low-fidelity response surface with high-fidelity CFD data. The constraint of maintaining a predefined range of the lift coefficient and lift-to-drag ratio ensures the possibility of using this profile in usual design procedures. [ABSTRACT FROM AUTHOR]

The current study was aimed at providing a detailed description of the major technical characteristics for electroencephalographic (EEG) equipment and their impact on quality of the recorded signal. Understanding the importance of the recording equipmenttechnical parameters will help medical professionals make the right choice while purchasing new equipment as well as correctly set the necessary recording parameters to ensure the maximum possible quality of EEG signal. In addition, the technical characteristics for EEG equipment available in Russia were compared. Such a comparison became possible after the full package of documents for registered medical equipment including data on relevant technical parameters began to be published at the Roszdravnadzor website since 2023.

The performance of an Unmanned Underwater Vehicle (UUV) is significantly influenced by the magnitude of self-generated noise, making it a crucial factor in advancing acoustic load technologies. Effective noise management, through the identification and separation of various self-noise types, is essential for enhancing a UUV’s reception capabilities. This paper concentrates on the development of UUV self-noise separation techniques, with a particular emphasis on feature extraction and separation in multi-task learning environments. We introduce an enhancement module designed to leverage noise categorization for improved network efficiency. Furthermore, we propose a neural network-based multi-task framework for the identification and separation of self-noise, the efficacy of which is substantiated by experimental trials conducted in a lake setting. The results demonstrate that our network outperforms the Conv-tasnet baseline, achieving a 0.99 dB increase in Signal-to-Interference-plus-Noise Ratio (SINR) and a 0.05 enhancement in the recognized energy ratio.

Automotive fans, small wind turbines, and manned and unmanned aerial vehicles (MAVs/UAVs) are just a few examples in which noise generated by the flow’s interaction with aerodynamic surfaces is a major concern. The current work shows the potential of a new airfoil shape to minimize noise generation, maintaining a high lift-to-drag ratio in a prescribed Reynolds regime. This investigation uses a multifidelity approach: a low-fidelity semiempirical model is exploited to evaluate the sound pressure level (SPL). Fast evaluation of a low-cost function enables the computation of a large range of possible profiles, and accuracy is added to the low-fidelity response surface with high-fidelity CFD data. The constraint of maintaining a predefined range of the lift coefficient and lift-to-drag ratio ensures the possibility of using this profile in usual design procedures.

The self-noise level of a seismometer can determine the performance of the seismic instrument and limit the ability to use seismic data to solve geoscience problems. Accurately measuring and simultaneously comparing the self-noise models from different types of seismometers has long been a challenging task due to the constraints of observation conditions. In this paper, the self-noise power spectral density (PSD) values of nine types of seismometers are calculated using four months of continuous seismic waveforms from Malingshan seismic station, China, and nine self-noise models are obtained based on the probability density function (PDF) representation. For the seismometer STS-2.5, the self-noise levels on the horizontal channels (E–W and N–S) are significantly higher than that on the vertical channel (U–D) in the microseism band (0.1 Hz to 1 Hz), which is a computing bias caused by the misalignment between the sensors in the horizontal direction, while the remarkably elevated noise on the horizontal channels at the low frequencies (<0.6 Hz) may originate from the local variation of atmospheric pressure. As for the very broadband seismometers Trillium-Horizon-120 and Trillium-120PA, and the ultra-broadband seismometers Trillium-Horizon-360 and CMG-3T-360, there is a trade-off between the microseism band range and low-frequency range in the PSD curves of the vertical channel. When the level of self-noise in the microseism band is high, the self-noise at low frequencies is relatively low. Although compared with the other very broadband seismometers, the self-noise level of the vertical component of the STS-2.5 is 3 dB to 4 dB lower at frequencies less than 1 Hz, the self-noise level of the STS-2.5 at high frequencies (>2 Hz) is slightly higher than others. From our observations, we conclude that the nine seismometers cannot reach the lowest noise level in all frequency bands within the working range. [ABSTRACT FROM AUTHOR]

Airfoil self-noise is one of the dominant sources of airframe noises which causes limitations in many applications such as wind turbines. This paper investigates and quantifies the sensitivity of airfoil self-noise prediction to the grid resolution using large eddy simulation. Three-dimensional incompressible fluid flow around a NACA0012 airfoil at zero angle of attack with a chord-based Reynolds number of 6.4 x 105 is numerically analyzed in this paper. Far-field noise is predicted by Ffowcs-Williams & Hawkings model using the results of large eddy simulation. Three different grid sizes are used to investigate the effect of grid resolution on the accuracy of self-noise prediction. Results are compared with the experimental data of wind tunnel tests and noise measurements with microphones. Although the aerodynamic properties are calculated accurately in all grids, the grid resolution over the surface has a significant effect on the accuracy of the noise prediction. This effect of grid resolution is quantified in this paper. By the increase of grid points in the spanwise and streamwise directions on the surface, numerical noise prediction has approached the experimental data. The difference with the experimental data decreases from 20 dB to 3 dB in some frequencies. In addition, having doubled the number of surface grid points in both directions the average percentage of difference with the experimental data decreases from 5% to 2%. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of studying the samples of the electrochemical sensors of motion parameters on the base of Molecular Electronics Technology (MET). The sensors with microelectromechanical (MEMS) electrode assembly use electrolytes based on aqueous and non-aqueous solutions of potassium and lithium iodides. Electrolyte solutions contain impurities of ionic liquids and alcohols to achieve stable low-temperature operation and acceptable technical parameters of serial devices. The dependence of the general sensitivity and the shape of the amplitude-frequency characteristic on temperature have been studied. For the marginally acceptable samples, which had an acceptable temperature dependence of the conversion coefficient and low activation energies for the diffusion coefficient, the level of self-noise was found. The activation energy of the electrolyte diffusion coefficient was determined based on the analysis of the dependence of the background current on temperature. A conclusion was made regarding the possible prospects for using the studied solutions and components for operation in serial devices. [ABSTRACT FROM AUTHOR]

A new method for estimating the self-noise of the measuring channel of a seismometer is proposed, taking into account the linear relationship between the signal and noise. The method extracts noise using records of two identical measuring channels on the example of the SM-3KV short-period seismometer with an operating frequency range of 0.5–40 Hz. The method was tested on model signals for channel noise with a normal distribution, as well as microseismic noise records recorded on a pedestal by seismometers with locked and free inertial masses. Work with the model signals demonstrated that the accuracy of the numerical result when assessing the level of isolated noise depends on the value of the cross-correlation of the initial seismograms. Consideration of this dependence when calculating the self-noise of real measuring channels yields a noise level similar to the standard method based on separation of the incoherent component of the initial signals. The noise values in the 0.5–40 Hz range with a locked mass of the seismometer are 2.1 ± 0.3 nm/s according to the standard method and 2.2 ± 0.4 nm/s according to the new methods. The obtained values do not contradict the manufacturer's data of the SM-3KV seismometer, which state that the self-noise level does not exceed 2 nm/s in the operating frequency range. [ABSTRACT FROM AUTHOR]

The self-noise level of a seismometer can determine the performance of the seismic instrument and limit the ability to use seismic data to solve geoscience problems. Accurately measuring and simultaneously comparing the self-noise models from different types of seismometers has long been a challenging task due to the constraints of observation conditions. In this paper, the self-noise power spectral density (PSD) values of nine types of seismometers are calculated using four months of continuous seismic waveforms from Malingshan seismic station, China, and nine self-noise models are obtained based on the probability density function (PDF) representation. For the seismometer STS-2.5, the self-noise levels on the horizontal channels (E–W and N–S) are significantly higher than that on the vertical channel (U–D) in the microseism band (0.1 Hz to 1 Hz), which is a computing bias caused by the misalignment between the sensors in the horizontal direction, while the remarkably elevated noise on the horizontal channels at the low frequencies (2 Hz) is slightly higher than others. From our observations, we conclude that the nine seismometers cannot reach the lowest noise level in all frequency bands within the working range.

Effect of broadband tuning in improving the performance characteristics, especially in receive mode, of a piezoelectric transducer working in the sonic frequencies is presented. The broadband tuning technique results in a frequency response function characteristic of a bandpass filter with significant improvements in SNR. When represented by an electrical equivalent circuit, the transducer resembles a half-section bandpass filter. Filter of higher order is obtained by adding external components for enhancing the bandwidth. The circuit parameters are determined from the measured electrical admittance of the transducer in the water. The transducer characteristics with broadband tuning network are simulated and validated experimentally. The impedance phase has improved from −70° to 0 ±20° over a broadband leading to an increase in power factor from 0.3 to close to 1. An enhancement of 3 dB in Source Level, 10 dB in Receiving Sensitivity, and 10 dB in Figure of Merit are obtained with 11 kHz increase in bandwidth. An improvement of 7 dB in the noise figure and SNR is also obtained in the receiving mode. The model results are in close agreement with the measured data validating the model. It is found that the broadband tuning network enhances the transducer performance simultaneously in transmitting and receiving modes. This is a significant improvement over conventional shunt tuning and is useful for stand-alone, energy-efficient sonars and two-way acoustic communication systems. The present studies demonstrate that broadband tuning methods in general, originally developed for RF and ultrasonic domains, are applicable in the sonic frequencies also. [ABSTRACT FROM AUTHOR]

In non-cooperative communication, the code frequency, the pulse shaping filter and other prior parameters are unknown to the receiver, which increases the challenge of non-cooperative receiving system design. A straightforward method may estimate these parameters in advance following traditional receiving systems. Estimation errors will undoubtedly be involved and passed between stages, which will decease system performance, especially in low signal-to-noise ratio (SNR) scenarios. To address this problem, this paper constructs a carefully designed optimization function for timing estimation that combines both the code frequencies and the timing parameters from multiple chips. Consequently, a feedback-based tracking model is proposed to solve such an optimization function. Finally, extensive simulation results validate the efficiency of the proposed method, which achieves ten times better accuracy than the traditional method and can partially overcome the influence of code frequency deviations.

Passive acoustic monitoring of wildlife requires sound recording systems. Several cheap, high-performance, or open-source solutions currently exist for recording soundscapes, but all rely on commercial microphones. Commercial microphones are relatively expensive, specialized for particular taxa, and often have incomplete technical specifications. We designed Sonitor, an open-source microphone system to address all needs of ecologists that sample terrestrial wildlife acoustically. We evaluated the cost and durability of our system and measured trade-offs that are seldom acknowledged but which universally limit microphones' functions: weatherproofing versus sound attenuation, windproofing versus transmission loss after rain, signal loss in long cables, and analog sound amplification versus directivity with acoustic horns. We propose five microphone configurations suiting different budgets (from 8 to 33 EUR per unit), and fulfilling different sound quality and flexibility requirements. The Sonitor system consists of sturdy acoustic sensors that cover the entire sound frequency spectrum of sonant terrestrial wildlife at a fraction of the cost of commercial microphones.

Passive acoustic monitoring of wildlife requires sound recording systems. Several cheap, high-performance open-source solutions currently exist for recording soundscapes, but all of them are still reliant on commercial microphones. Commercial microphones are relatively expensive, specialized for particular taxa, and often have incomplete technical specifications. We designed Sonitor, an open-source microphone system to address all needs of ecologists that sample terrestrial wildlife acoustically. We evaluated the cost and durability of our system and measured trade-offs that are seldom acknowledged but which universally limit microphones' functions: weatherproofing versus sound attenuation, windproofing versus transmission loss after rain, signal loss in long cables, and analog sound amplification versus directivity with acoustic horns. We propose five microphone configurations suiting different budgets (from 8 to 33 EUR per unit), and fulfilling different sound quality and flexibility requirements. The Sonitor system consists of sturdy acoustic sensors that cover the entire sound frequency spectrum of sonant terrestrial wildlife at a fraction of the cost of commercial microphones.

Passive acoustic monitoring of wildlife requires microphones. Several cheap, high-performance open-source solutions currently exist for recording sounds, but all of them are still reliant on commercial microphones. Commercial microphones are relatively expensive, specialized on particular taxa, and often have opaque technical specifications. We designed Sonitor, an open-source microphone system to address all needs of ecologists that sample terrestrial wildlife acoustically. We evaluated the cost of our system and measured trade-offs that are seldom acknowledged but which universally limit microphones' functions: weatherproofing versus sound attenuation, windproofing versus transmission loss after rain, signal loss in long cables, and analog sound amplification and directivity with acoustic horns. We propose three microphone configurations suiting different budgets, sound qualities, and flexibility requirements, which all cover the entire sound frequency spectrum of sonant terrestrial wildlife at a fraction of the cost of commercial microphones.

The Hybrid-driven Underwater Glider (HUG) is a new type of submersible vehicle which combines the functions of traditional Autonomous Underwater Vehicles(AUV)and Autonomous Underwater Gliders(AUG). In order to study its noise source distribution and basic self-noise characteristics, a self-noise acquisition system based on the HUG was designed and developed, and a noise analysis test carried out in a free-field pool. In August 2016, the sea trial of the Petrel II glider was conducted in the South China Sea, with observation data at a depth range of 1 000 m as the research object. The self-noise data of the glider platform under different working conditions was obtained through the step-by-step operation method. The experimental analysis and results show that the self-noise acquisition system is stable. The contribution of mechanical noise to self-noise is greatest when the glider works in the gliding mode, while the self-noise band above 500 Hz is closely related to the work of the buoyancy adjustment unit, and peaks at 1 kHz. According to the analysis of the basic characteristics of self-noise, this provides some guidance for the implementation of vibration and noise reduction.

With the widespread availability of cell-phone recording devices and the availability of various powerful and easy-to-use digital media editing software,source cell-phone identification has become a hot topic in multimedia forensics.A novel cell-phone identification method was proposed based on the recorded speech.Firstly,device self-noise (DSN) was considered as the fingerprint of the cell-phone and estimated from the silent segments of the speech.Then,the mean of the noise's spectrum was extracted as the identification.Principal components analysis (PCA) was applied to reduce the feature dimension.Support vector machine (SVM) was adopted as the classifier to determine the source of the detecting speech.Twenty-four popular models of the cell-phones were evaluated in the experiment.The experimental results show that the average identification accuracy and recall of the method can reach up to 99.24% and demonstrate that the self-noise feature has more superior performance than the MFCC feature.

Underwater gliders travel through the ocean by buoyancy control, which makes their motion silent and involves low energy consumption. Due to those advantages, numerous studies on underwater acoustics have been carried out using gliders and different acoustic payloads have been developed. This paper aims to illustrate the use of gliders in underwater acoustic observation and target detection through experimental data from two sea trials. Firstly, the self-noise of the glider is analyzed to illustrate its feasibility as an underwater acoustic sensing platform. Then, the ambient noises collected by the glider from different depths are presented. By estimating the transmission loss, the signal receiving ability of the glider is assessed, and a simulation of target detection probability is performed to show the advantages of the glider over other underwater vehicles. Moreover, an adaptive line enhancement is presented to further reduce the influence of self-noise. Meanwhile, two hydrophones are mounted at both ends of the glider to form a simple array with a large aperture and low energy consumption. Thus, the target azimuth estimation is verified using broadband signals, and a simple scheme to distinguish the true angle from the port‒starboard ambiguity is presented. The results indicate that the glider does have advantages in long-term and large-scale underwater passive sensing. [ABSTRACT FROM AUTHOR]

• A model of the convective noise generation in the sensitive element of the electrochemical motion sensor has been developed. • An experimental sample of the planar electrochemical cell has been produced and tested. • The experimental behavior of the noise power spectral density is in good agreement with the modelling. The paper presents modeling and experimental study of the noise produced in planar sensitive element of electrochemical motion sensors. The experimental sample of the sensitive element has been produced using microelectronics methods. It has been manufactured as a narrow channel formed by two silicon plates with a set of electrodes placed on one of the plates. The channel is filled with water-based solution of potassium iodide with a small amount of iodine. In the end of the channel there are rubber membranes allowing the liquid to pass through the channel as the result of inertial forces associated with external motion. The liquid motion is converted into electrical response by the electrode system. The self-noise of the sample has been measured by comparing its output signals and output of the commercial low-noise seismometer, recorded side by side and followed by correlation analysis. The theoretical model uses equations of hydrodynamics and charge transfer in the concerned system. The stochastic behavior of the system is modeled by Langevin method applied to equations of hydrodynamics. The electrode current noise is calculated and is in a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

A mechanism model of carbon fiber electrode for detecting the ocean electric field is estab¬lished. Based on the proposed model, the stability of potential difference between carbon fiber electrodes is improved and its settling time is shorten by the parallel discharge resistances at both ends of signal am¬plifier. An uniform electric field was established to evaluate the influences of different parallel resistances on the detection performance of carbon fiber electrodes. The results show that the smaller the input resist¬ance is, the smaller the potential difference is, and the faster the self-noise settling is. The settling time of potential difference between electrodes is not greater than 2 h, the potential difference after settling is not greater than 0. 1 mV, and the self-noise level is in the range of 2 - 5 nV/ */liz at 1 Hz. [ABSTRACT FROM AUTHOR]

The performance of arrays of accelerometers is critical for various fields of engineering, but in contrast to that of isolated sensors, it cannot be easily evaluated. This is because it requires that both waveforms and instantaneous, especially extreme values of acceleration of all array sensors are accurately recorded without time lag. Although accelerometers are typically assumed to be characterized by white noise, this requirement is not easily satisfied, and there is evidence of serious problems with recorded accelerations, especially when used as input in structural analysis. For this reason, various techniques to overpass the problem of uncertainties, or even the faulty behavior of array sensors have been proposed. In our study we propose a simple and efficient method to test the performance of arrays of MEMS accelerometers which are currently used in various engineering applications. We made controlled experiments using identical, fully collocated MEMS sensors simultaneously recording source accelerations under common propagation effects, so that the timeseries of waveform differences unambiguously define sensor noise. Analysis of the sensors response indicates that dominant spectral frequencies are precisely defined by all sensors, but there were noticed significant waveform distortions due to dynamic noise of different types, mostly clipping below the saturation level of the sensor response. Dynamic noise tends to increase with the frequency level and to underestimate peak amplitude, while some sensors tend to be more prone to signal distortion than others. Such noise characteristics constrain some strategies to mitigate sensors errors. [ABSTRACT FROM AUTHOR]

Modern molecular electronic transfer (MET) angular motion sensors combine high technical characteristics with low cost. Self-noise is one of the key characteristics which determine applications for MET sensors. However, until the present there has not been a model describing the sensor noise in the complete operating frequency range. The present work reports the results of an experimental study of the self-noise level of such sensors in the frequency range of 0.01–200 Hz. Based on the experimental data, a theoretical model is developed. According to the model, self-noise is conditioned by thermal hydrodynamic fluctuations of the operating fluid flow in the frequency range of 0.01–2 Hz. At the frequency range of 2–100 Hz, the noise power spectral density has a specific inversely proportional dependence of the power spectral density on the frequency that could be attributed to convective processes. In the high frequency range of 100–200 Hz, the noise is conditioned by the voltage noise of the electronics module input stage operational amplifiers and is heavily reliant to the sensor electrical impedance. The presented results allow a deeper understanding of the molecular electronic sensor noise nature to suggest the ways to reduce it.

Seismometer self-noise levels were determined using Sleeman's three-sensor method in combination with the Welch method for different parameter combinations. The self-noise levels decreased with the increasing segment window length, which is equivalent to the subwindow length, and with the increasing segment overlap rate for different frequency points at a fixed band. After the statistical examination of 9800 different parameter combinations, a zone of reasonable self-noise calculation parameter combinations was identified. Reasons for the unsuitability of certain parameter combinations were explored with respect to their distortion of the seismometer's self-noise levels.

In this paper, a Petrel II autonomous underwater glider (AUG) was used to analyze underwater noise spectrogram in the South China Sea. For ocean observations, AUG has an excellent performance such as being efficient in all weather conditions, lasting for long time periods, being able to be remote controlled, which creates favorable conditions for analyzing underwater noise characteristics. In order to measure the underwater noise, a newly developed and customized underwater passive acoustic monitoring system was firstly installed on the Petrel II glider and tested in the South China Sea trial in August 2016. The observation data at a depth of 1000 meters range were taken as the research object and were used to analyze the noise levels over a long period through the method of the short-time Fourier transform. At the same time, the noise data have been compared in time to the actions of the glider during the sea trial. However, AUGs also have limitations such as undesired instrument and flow noise. By adopting the step-by-step method, these self-noise data of Petrel II glider were acquired and analyzed quantitatively, and the basic characteristics of self-noise under different working conditions are depicted. Removing the corresponding self-noise, the noise data at different depths measured by the Petrel II glider could be used to estimate underwater ambient noise levels across depth. [ABSTRACT FROM AUTHOR]

A novel underwater electric field electrode is prepared with T300 carbon fiber heat-treated at 445°C, 465°Cand 485°C. The surface chemical state, electrochemical performance and detection performance of electric field electrode in NaCl solution are measured using X-ray photoelectron spectroscopy (XPS), electrochemical workstation and self-made noise measurement system. The impact of heat treatment on surface group content , cyclic voltammetry (CV) characteristics, exchange current density, response performance and electrode settling time is discussed. The detection mechanism of underwater carbon fiber detection electrode is analyzed. The group CO and COOR content of carbon fiber electrode increase as the heat treatment temperature increases; the heat treatment reduces the capacitance effect of electrode, increases its exchange current density, and improve its linear performance and settling speed. [ABSTRACT FROM AUTHOR]

The Vector Hydrophone (VH) is widely used to remotely detect underwater targets. Accurately measuring the self-noise of the VH provides an important basis for evaluating the performance of the detection system in which it is utilized, since the ability to acquire weak signals is determined by the VH self-noise level. To accurately measure the VH self-noise level in actual working conditions, the Dual-channel Transfer Function Method (DTFM) is proposed to reduce ambient background noise interference. In this paper, the underlying principles of DTFM in reducing ambient background noise is analyzed. The numerical simulations to determine the influence of ambient background noise, and the sensitivity difference of the two VHs on the measurement results are studied. The results of measuring the VH self-noise level in a small laboratory water tank by using DTMF indicate that ambient background noise interference can be reduced effectively by employing DTMF, more accurate self-noise level can be obtained as well. The DTMF provides an effective method for accurately measuring the self-noise level of VHs and also provides technical support for the practical application of the VH in underwater acoustics. [ABSTRACT FROM AUTHOR]

Modern molecular electronic transfer (MET) angular motion sensors combine high technical characteristics with low cost. Self-noise is one of the key characteristics which determine applications for MET sensors. However, until the present there has not been a model describing the sensor noise in the complete operating frequency range. The present work reports the results of an experimental study of the self-noise level of such sensors in the frequency range of 0.01-200 Hz. Based on the experimental data, a theoretical model is developed. According to the model, self-noise is conditioned by thermal hydrodynamic fluctuations of the operating fluid flow in the frequency range of 0.01-2 Hz. At the frequency range of 2-100 Hz, the noise power spectral density has a specific inversely proportional dependence of the power spectral density on the frequency that could be attributed to convective processes. In the high frequency range of 100-200 Hz, the noise is conditioned by the voltage noise of the electronics module input stage operational amplifiers and is heavily reliant to the sensor electrical impedance. The presented results allow a deeper understanding of the molecular electronic sensor noise nature to suggest the ways to reduce it. [ABSTRACT FROM AUTHOR]

The self-noise level of a seismometer can determine the performance of the seismic instrument and limit the ability to use seismic data to solve geoscience problems. Accurately measuring and simultaneously comparing the self-noise models from different types of seismometers has long been a challenging task due to the constraints of observation conditions. In this paper, the self-noise power spectral density (PSD) values of nine types of seismometers are calculated using four months of continuous seismic waveforms from Malingshan seismic station, China, and nine self-noise models are obtained based on the probability density function (PDF) representation. For the seismometer STS-2.5, the self-noise levels on the horizontal channels (E−W and N−S) are significantly higher than that on the vertical channel (U−D) in the microseism band (0.1 Hz to 1 Hz), which is a computing bias caused by the misalignment between the sensors in the horizontal direction, while the remarkably elevated noise on the horizontal channels at the low frequencies (<0.6 Hz) may originate from the local variation of atmospheric pressure. As for the very broadband seismometers Trillium-Horizon-120 and Trillium-120PA, and the ultra-broadband seismometers Trillium-Horizon-360 and CMG-3T-360, there is a trade-off between the microseism band range and low-frequency range in the PSD curves of the vertical channel. When the level of self-noise in the microseism band is high, the self-noise at low frequencies is relatively low. Although compared with the other very broadband seismometers, the self-noise level of the vertical component of the STS-2.5 is 3 dB to 4 dB lower at frequencies less than 1 Hz, the self-noise level of the STS-2.5 at high frequencies (>2 Hz) is slightly higher than others. From our observations, we conclude that the nine seismometers cannot reach the lowest noise level in all frequency bands within the working range.

Optical grating-based interferometric sensors have been the subject of prior investigations, with recent work focused on micromachined microphone applications. The silicon structure is similar in construction to capacitive microelectromechanical-system microphones, with the exception that the microphone backplate contains an optical-diffraction grating at the center. The grating serves as a beam splitter in this system, allowing only a portion of the incident light to pass to the diaphragm and back, enabling interferometric readout of diaphragm displacements. A cited advantage of this system is the ability to design highly perforated backplates with low mechanical damping and with the ability to realize low thermal-mechanical noise. Grating backplates, however, have their own unique optical design constraints different from capacitive sensors. This paper details a rigorous finite element computational fluid dynamics model for flow resistance of a grating backplate. The model is validated for a case study backplate fabricated in the epitaxial layer of a 2-μm silicon-on-insulator wafer. The dynamics of the backplate are studied in isolation from other microphone elements by mounting the backplate in close proximity to a rigid optical-reflector and using electrostatic actuation to vibrate the backplate for extraction of compliance, resonance frequency, and quality factor. [ABSTRACT FROM AUTHOR]

The records of ground motion, measured by broadband seismometers, serve for a wide range of scientific research activities. Accordingly, the knowledge of key parameters of seismometers is important for providing reliable results. In most common quality control procedures, the tested seismometer is installed side by side with the reference seismometer. Then, a three-dimensional matrix transforming recordings from one unit to another is needed. The quality of a design of this transformation matrix depends on the mathematical background of a chosen procedure, on the quality of a recorded seismic signal, and on the used bandwidth. In this paper, we present five different mathematical techniques to calculate transformation matrices. One of these techniques is applied in the time domain while the four others use the frequency domain. The methods were verified by two different cases, where different pairs of seismometers were installed on different locations. In all cases, the procedure, reducing the 'average' self-noise gives the best result, regards to the decision criteria. [ABSTRACT FROM AUTHOR]

Deep reactive ion etch (DRIE) processes are performed on both sides of a silicon-on-insulator (SOI) wafer to realize piezoelectric accelerometers consisting of 20-\mum-thick epitaxial silicon cantilevers with bulk silicon masses at the tip. Sol-gel deposition of lead-zirconate-titanate (PZT) is used to realize an 800-nm-thick film on the top surface of the beams. Prior to accelerometer characterization, a system identification procedure based on laser Doppler vibrometry is performed, providing a complete description of the devices and predicted sensitivities. Frequency response measurements confirm device sensitivities in the 3.4–50 pC/g range in the flat-band (depending on device geometry), and resonance frequencies in the 60-Hz–1.5-kHz range. The self-noise for the longest beam of 8.5 mm is measured as 1.7 \mug/\sqrtHz at 30 Hz and is limited by dielectric loss of the PZT film which is estimated to have a \tan\delta of 0.02. Scaling relationships for this particular device geometry are presented to provide insight into possible future design directions. \hfill[2012\--0300] [ABSTRACT FROM PUBLISHER]

This paper deals with the goodness of the Gaussian assumption when designing second-order blind estimation methods in the context of digital communications. The low- and high-signal-to-noise ratio (SNR) asymptotic performance of the maximum likelihood estimator—derived assuming Gaussian transmitted symbols—is compared with the performance of the optimal second-order estimator, which exploits the actual distribution of the discrete constellation. The asymptotic study concludes that the Gaussian assumption leads to the optimal second-order solution if the SNR is very low or if the symbols belong to a multilevel constellation such as quadrature-amplitude modulation (QAM) or amplitude-phase-shift keying (APSK). On the other hand, the Gaussian assumption can yield important losses at high SNR if the transmitted symbols are drawn from a constant modulus constellation such as phase-shift keying (PSK) or continuous-phase modulations (CPM). These conclusions are illustrated for the problem of direction-of-arrival (DOA) estimation of multiple digitally-modulated signals. [ABSTRACT FROM AUTHOR]

This letter deals with the compensation of the self-noise (jitter) in a nondata-aided (blind) feedforward symbol-timing estimator using two samples per symbol for linearly modulated waveforms transmitted through additive white Gaussian noise channels. The main contribution of this letter is the derivation of an appropriate prefilter to achieve nearly jitter-free digital blind feedforward timing recovery. Computer simulations illustrate that the proposed prefiltering scheme improves significantly the performance at mid and high signal-to-noise ratios. [ABSTRACT FROM AUTHOR]

The objective of this paper is to expose the computational aeroacoustics (CAA) community to the current unresolved issues in modeling and predicting fan noise. The paper includes a description of the sources of fan noise and a discussion of the current status of the fan noise prediction methods and their shortcomings. The discussion is focused on the issues and includes sufficient details to help outline the scope of the fan noise problem and define the level of fidelity required for meaningful CAA simulations. [ABSTRACT FROM AUTHOR]

This correspondence presents a new technique to compute efficiently the spectra of the in-phase (I) and quadrature (Q) components as well as the cross-spectrum of the in-phase and quadrature (I-Q) components of self-noise appearing at the output of the zero-memory, high-order nonlinear (NL) device employed in a clock recovery system. It is known that these spectra play an important role in the phase jitter performance of the clock regenerator. The results are very general and applicable to many cases of practical interest. Numerical examples and computer simulations provided show that the new approach yields very accurate results and is much faster than the usual computer simulation method. In addition, we give a theorem to show that for the signal shapes having linear phase, the cross-power spectrum of self-noise is zero. We also provide a general expression for the jitter variance of the generated clock signal in terms of the power spectra of self-noise in-phase and quadrature components. It is shown that the cross-power spectrum will also contribute to timing jitter if the selected signaling shape does not have any symmetry in time domain. The optimal periodic sampling instants are determined by the axis crossings of the clock signal in the positive direction. The axis is set at a level whereby the jitter variance takes on a minimum value. It is concluded that when the cross-power spectrum is zero for all frequencies then the optimal sampling instants occur at the positive zero crossings of the clock signal and only the Q noise contributes to the timing jitter performance. [ABSTRACT FROM AUTHOR]

An equivalent circuit analysis is presented to predict the acoustic characteristics of resonant hydrophones and the factors leading to their degradation. The circuit parameters of a Tonpilz transducer, operated as a resonant hydrophone in the receiving mode, are determined from the measured complex electrical admittance in water at frequencies in the vicinity of resonance. The parameters are refined by non-linear regression method and used to calculate the receiving sensitivity in the same band. External components such as insulation resistance, cable capacitance and input impedance of the preamplifier are included in the model and their loading effects on the receiving sensitivity are determined. The detrimental effect of drop in insulation resistance on the performance of the resonant hydrophone is studied quantitatively. The cut-off values of insulation resistance at various frequencies and capacitances are prescribed that would mark the end-of-life of the hydrophone. In the present case, the acceptable lower limit of R i is found to be 1 MΩ at 100 Hz and 10 kΩ at 30 kHz. The model results are validated by experiments and are found to agree well with the measured data. The equivalent circuit model of hydrophones will be useful to optimize the hydrophone- preamplifier combination of underwater acoustic systems by minimizing the receiver noise and enhancing the signal to noise ratio. [ABSTRACT FROM AUTHOR]

In this paper we revisit the early-late timing recovery scheme developed for filter bank based multicarrier transmission. A substantial improvement is proposed for the case where the receiver contains a decision-feedback equalizer. We show how the timing error detector has to be modified to account for the high level of self-noise and how this self-noise can be mitigated thanks to the introduction of a correction term. We investigate the tracking performance of this new synchronizer for high bit rate transmission over copper wires. [ABSTRACT FROM PUBLISHER]

Passive acoustic monitoring of wildlife requires sound recording systems. Several cheap, high-performance, or open-source solutions currently exist for recording soundscapes, but all rely on commercial microphones. Commercial microphones are relatively expensive, specialized for particular taxa, and often have incomplete technical specifications. We designed Sonitor, an open-source microphone system to address all needs of ecologists that sample terrestrial wildlife acoustically. We evaluated the cost and durability of our system and measured trade-offs that are seldom acknowledged but which universally limit microphones' functions: weatherproofing versus sound attenuation, windproofing versus transmission loss after rain, signal loss in long cables, and analog sound amplification versus directivity with acoustic horns. We propose five microphone configurations suiting different budgets (from 8 to 33 EUR per unit), and fulfilling different sound quality and flexibility requirements. The Sonitor system consists of sturdy acoustic sensors that cover the entire sound frequency spectrum of sonant terrestrial wildlife at a fraction of the cost of commercial microphones., Competing Interests: No competing interests were disclosed., (Copyright: © 2021 Darras K et al.)