Additional Noise Sources Research Articles

Aeolian noise of a cylinder in the critical regime.

The noise from the flow around a circular cylinder in the critical regime is investigated by combining a compressible wall-resolved large eddy simulation and a Ffowcs Williams and Hawkings analogy on solid and porous surfaces. This simulation is validated by comparing several flow parameters with previous experimental and numerical data in the same flow regime. Significantly reduced drag and increased vortex shedding Strouhal number (0.33) are observed. Two slightly asymmetric laminar separation bubbles (LSBs) on the cylinder surface at about 100° are shown to trigger turbulence through Kelvin-Helmholtz (KH) shear-layer instability. The latter contributes to a narrowband hump in the wall-pressure fluctuations with a tone at a Strouhal number of 27, which can be as intense as the dominant vortex shedding tone. The ratio of the corresponding Strouhal numbers is consistent with the proposed variation with the Reynolds number by Prasad and Williamson [(1997). J. Fluid Mech. 333, 375-402]. The dominant far-field noise source is still the vortex shedding dipolar tone radiating mostly at 90°. Yet, two additional broadband noise sources are evidenced in the wake, one at low frequencies caused by the wake oscillation and another one at high frequencies caused by the KH instability mostly directly toward the LSB locations.

Wide-band parametric amplifier readout and resolution of optical microwave kinetic inductance detectors

The energy resolution of a single photon counting microwave kinetic inductance detector can be degraded by noise coming from the primary low temperature amplifier in the detector's readout system. Until recently, quantum limited amplifiers have been incompatible with these detectors due to the dynamic range, power, and bandwidth constraints. However, we show that a kinetic inductance based traveling-wave parametric amplifier can be used for this application and reaches the quantum limit. The total system noise for this readout scheme was equal to ∼2.1 in units of quanta. For incident photons in the 800–1300 nm range, the amplifier increased the average resolving power of the detector from ∼6.7 to 9.3 at which point the resolution becomes limited by noise on the pulse height of the signal. Noise measurements suggest that a resolving power of up to 25 is possible if the redesigned detectors can remove this additional noise source.

Practical Prediction of CFO-Made OFDM Symbol Distortion

The Carrier Frequency Offset (CFO) is considered to be a major drawback of the Orthogonal Frequency-Division Multiplexing (OFDM) signal. So, in many practical situations, specifically with LTE-Advanced downlink introducing carrier aggregation, estimation of the CFO-induced OFDM symbol phase deviation, is of interest. However, this demands complex test equipment, such as e.g. a Vector Signal Analyzer (VSA), which might not be always and everywhere available. Therefore, we applied the link abstraction principle on the Bit Error Rate (BER) that is considered to be determined just by the CFO-caused phase deviation, i.e. as if the channel was noiseless and time-dispersion-free (so that evident bit errors occur just due to the actual CFO). Furthermore, as the CFO-caused squared phase deviation is linear with the instantaneous (per-OFDM-symbol) Peak-to-Average Power Ratio (PAPR), which is related to the Error Vector Magnitude (EVM) and so with BER, we develop a simple model for analytical BER-based estimating of CFO. In this sense, we considered the easy-to-measure BER degradation as resulting just from the according additive white Gaussian noise (AWGN) source, which abstracts the CFO distortion. The proposed analytical model is validated by according Monte-Carlo simulations.

Bandwidth extension of narrowband-signal intensity calculation using additive, low-level broadband noise.

Calculation of acoustic intensity using the phase and amplitude gradient estimator (PAGE) method has been shown to increase the effective upper frequency limit beyond the traditional p-p method when the source of interest is broadband in frequency [Torrie, Whiting, Gee, Neilsen, and Sommerfeldt, Proc. Mtgs. Acoust. 23, 030005 (2015)]. PAGE processing calculates intensity for narrowband sources without bias error up to the spatial Nyquist frequency [Succo, Sommerfeldt, Gee, and Neilsen, Proc. Mtgs. Acoust. 30, 030015 (2018)]. The present work demonstrates that for narrowband sources with frequency content above the spatial Nyquist frequency, additive low-level broadband noise can improve intensity calculations. To be effective, the angular separation between the source and additive noise source should be less than 30°, while using phase unwrapping with a smaller angular separation will increase the usable bandwidth. The upper frequency limit for the bandwidth extension depends on angular separation, sound speed, and probe microphone spacing. Assuming the signal-to-additive-noise ratio (SNRa) is larger than 10 dB, the maximum level and angular bias errors incurred by the additive broadband noise beneath the frequency limit-or up until probe scattering effects must be taken into account-are less than 0.5 dB and 2.5°, respectively. Smaller angular separation yields smaller bias errors.

Application of SVM Algorithm for Fetal ECG Extraction from a Single Maternal Abdominal Record

The electrical activity of the foetal cardiac muscles is known as foetal ECG (FECG), and it can provide crucial details on the health of the fetus's heart. A pregnant woman's belly can be used to non-invasively capture this signal during pregnancy. However, since additional sources of noise, including the maternal ECG generally overpower the FECG recording, it would be ineffective. However, a clean FECG may be retrieved from the abdominal recording if it is correctly processed, and FECG can be used to evaluate the functioning of the foetal heart. In order to extract foetal electrocardiogram (ECG) from a single abdomen record, a unique two-tier approach is presented in this work. The abdominal signal is processed through a smoothing filter in the first layer of the proposed approach in order to determine the maternal ECG's estimated value. Findings on synthetic and actual abdominal ECG data demonstrate that the intended technique can extract foetal ECG with signal quality equivalent or superior to that retrieved by multichannel based mechanisms. The anticipated maternal ECG is then nonlinearly matched with the abdominal signal through polynomial networks.

Optimal scheduling to minimize noise exposure in an oil and gas field

Noise analysis with different scenarios has been conducted for an oil and gas field to determine whether workers during sandblasting operations were fully protected from high noise to prevent ear injuries and downtime. The main purpose is to minimize noise doses affecting workers through an optimal scheduling algorithm. Data collected from a noise meter was fully evaluated and analyzed in terms of LAeq—A-weighted average energy equivalent sound pressure levels—and Lpk energy peak, in the audible range from 12.5 Hz to 20 kHz based on the one-third octave band frequencies. All noise results were found above the maximum permissible exposure limit 85 dB(A). Another important feature is the sharp rise observed in all weighted levels up to a mean value of 67 dB at low frequency of 80 Hz. A sharp decrease in the high frequency noise levels beyond 8 kHz is also observed. Comparisons between different scenarios are also presented. Additional noise sources such as compressors and air coolers add up an important fraction of the workers’ noise exposure dose and highly contribute to the hearing loss. Finally, a fair scheduling algorithm to optimize noise exposure time by minimizing the noise dose is proposed.

Impact of Microphone Configuration on Speech Perception of Cochlear Implant Users in Traffic Noise.

The aim of this study was to investigate the impact of microphone configuration and noise reduction algorithm on speech perception of cochlear implant (CI) users in a moving noise setup. Eleven CI users provided with Advanced Bionics implant systems participated in this study. All tests were conducted with three different microphone settings: (a) omnidirectional behind the ear (BTE), (b) inside the pinna (ITP), and (c) adaptive directional microphone (adaptive beamformer, ABF). Speech reception thresholds (SRTs) were measured using the Oldenburg sentence test in a moving noise source condition. Furthermore, the effect of a noise reduction algorithm on speech perception was measured in a condition with an additional static noise source. The ABF setting significantly improved SRT by 5.7 dB compared with the BTE microphone, and by 4.7 dB compared with the ITP microphone in the moving noise condition. In the presence of an additional static noise source, there was a significant improvement in SRT of 0.9 dB with the use of NR in addition to ABF. Adaptive beamforming can significantly improve speech perception in moving noise. Depending on the noise condition, the combination of ABF with NR can provide additional benefit.

Stochastic Gravitational-wave Background from Binary Black Holes and Binary Neutron Stars and Implications for LISA

Abstract The advent of gravitational-wave and multimessenger astronomy has stimulated research on the formation mechanisms of binary black holes (BBHs) observed by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo. In the literature, the progenitors of these BBHs could be stellar-origin black holes (sBHs) or primordial black holes (PBHs). In this paper, we calculate the stochastic gravitational-wave background (SGWB) from BBHs, covering the astrophysical and primordial scenarios separately, together with the one from binary neutron stars (BNSs). Our results indicate that PBHs contribute a stronger SGWB than that from sBHs, and the total SGWB from both BBHs and BNSs has a high possibility of being detected by the future observing runs of LIGO/Virgo and the Laser Interferometer Space Antenna (LISA). On the other hand, the SGWB from BBHs and BNSs also contributes an additional source of confusion noise to LISA’s total noise curve, and then weakens LISA’s detection abilities. For instance, the detection of massive black hole binary (MBHB) coalescences is one of the key missions of LISA, and the largest detectable redshift of MBHB mergers can be significantly reduced.

Flow and acoustics of an isothermal supersonic 2:1 rectangular jet with an adjacent surface

In integrated airframe/propulsion system configurations, additional noise sources can be created from the interactions between the jet flow and the adjacent airframe surfaces. Another situation of surfaces of close proximity occur during takeoff and landing when the ground is close enough to cause the jet-surface interference. The impact of a plate oriented parallel to the axis of a 2:1 rectangular supersonic jet (De = 20.65mm) at the minor axis side is studied. Plate offset (h) distances of h = 0, 1, 2, and 3 equivalent diameters from the nozzle lip to the surface are included. The impact of the plate is studied at nozzle pressure ratios (NPRs) of 2.5–4.5 when the design Mach number is 3.67, at a temperature ratio of TR = 1.1. Mean and turbulent flow field data are acquired using streamwise particle image velocimetry (PIV). Trends of shock cell spacing, potential core length, and shear layer development are analyzed. Near and far field data are taken and correlated with the flow field details. The offset from the nozzle is shown to vary flow and acoustic properties and impact screech tones.

An Experimental Study and Theoretical Simulation of Jet-Wing Interaction Noise

The use of high-bypass-ratio engines in civil aviation has resulted in the occurrence of an additional noise source associated with noise of interaction between a jet and an airplane wing. A theoretical model is proposed for predicting the characteristics of interaction noise based on the near-field parameters for an isolated jet. The required near-field characteristics were obtained experimentally in the AC-2 anechoic chamber of the Central Aerohydrodynamic Institute (TsAGI) using a system of azimuthal microphone arrays. Noise in the far-field zone was also measured for both an isolated jet and a jet with a closely located plate simulating a wing. The results of comparing the directivities and spectra of interaction noise obtained using the proposed model and measured experimentally are in good agreement.

Aerodynamic noise reduction using dual-jet planar air curtains

In this paper, dual-jet planar air curtains are demonstrated to be able to successfully remove aerodynamic noise radiated from tandem rods in a crossflow. Single-jet air curtains have shown significant promise as a low noise technology but can introduce additional noise sources such as lip and mixing noise. In this work, dual-jet air curtains are shown to address these obstacles, achieving the same shielding height with a significantly lower overall system noise. Providing high amplitude tonal and broadband noise, tandem rods are chosen as the test case and the fluid mechanics and acoustics associated with their shielding by air curtains are examined both experimentally and numerically. Particle image velocimetry and flow visualisation methods allow the flow fields to be examined, and a numerical analysis with computational fluid dynamics to be validated. Barely examined in the literature to date, the trajectory of planar jets in crossflow are studied here and compared to a basic semi-empirical model. The accurate identification of the trajectory allows a method for an optimum shielding height and dual jet velocity combination to be proposed and tested. Acoustic beamforming and 1/3 octave band analysis are performed for diagnostic noise source localisation and comparative evaluation. It is demonstrated that a judicious choice of flow parameters can result in the complete removal of the aerodynamic noise with almost no acoustic penalty.

Anomalous Decimeter Radio Noise from the Region of the Atmospheric Front: I. Characteristics of the Detected Radio Noise and Meteorological Parameters of the Frontal Cloudiness

An extraordinary experimental fact is presented and analyzed, namely, a rather intense broadband radio noise detected during the passage of an atmospheric front through the field of view of UHF antennas. Local atmospheric properties and possible sources of the extraordinary noise, including the thermal noise from cloudiness and extra-atmospheric sources, are considered. A conclusion is made about the presence of an additional nonthermal source of radio noise in the frontal cloudiness. According to the proposed hypothesis, these are multiple electric microdicharges on hydrometeors in the convective cloud.

Levitated optomechanics with a fiber Fabry–Perot interferometer

In recent years, quantum phenomena have been experimentally demonstrated on variety of optomechanical systems ranging from micro-oscillators to photonic crystals. Since single photon couplings are quite small, most experimental approaches rely on the realization of high finesse Fabry–Perot cavities in order to enhance the effective coupling. Here we show that by exploiting a, long path, low finesse fiber Fabry–Perot interferometer ground state cooling can be achieved. We model a 100 m long cavity with a finesse of 10 and analyze the impact of additional noise sources arising from the fiber. As a mechanical oscillator we consider a levitated microdisk but the same approach could be applied to other optomechanical systems.

Noise Limits in Thin-Film Magnetoelectric Sensors With Magnetic Frequency Conversion

To enable the measurement of low-frequency magnetic signals with cantilever type thin-film magnetoelectric sensors, magnetic frequency conversion transfers the frequency of the desired signal into the mechanical resonance of the cantilever. The system electronics for the realization of this approach and the approach itself introduce additional noise sources as compared with direct detection, which lowers the limit of detection. In this paper, the magnetic frequency conversion noise sources are reviewed, discussed, and evaluated for our setup. The model for the nonlinear transfer process is implemented in the time domain. This enables the consideration of the pump noise in a noise equivalent circuit. For the sensor type under investigation, the dominant noise near its optimal working point originates from the pump source. If the noise of the pump can be decreased and magnetic excess noise is not dominant, the noise limit is the thermal-mechanical noise of the sensor. The implementation of a filter after the excitation source decreases the limit of detection to 60 pT/ $\sqrt {\text {Hz}}$ at 10 Hz.

Time-dependent probability density functions and information geometry in stochastic logistic and Gompertz models

A probabilistic description is essential for understanding growth processes in non-stationary states. In this paper, we compute time-dependent probability density functions (PDFs) in order to investigate stochastic logistic and Gompertz models, which are two of the most popular growth models. We consider different types of short-correlated multiplicative and additive noise sources and compare the time-dependent PDFs in the two models, elucidating the effects of the additive and multiplicative noises on the form of PDFs. We demonstrate an interesting transition from a unimodal to a bimodal PDF as the multiplicative noise increases for a fixed value of the additive noise. A much weaker (leaky) attractor in the Gompertz model leads to a significant (singular) growth of the population of a very small size. We point out the limitation of using stationary PDFs, mean value and variance in understanding statistical properties of the growth in non-stationary states, highlighting the importance of time-dependent PDFs. We further compare these two models from the perspective of information change that occurs during the growth process. Specifically, we define an infinitesimal distance at any time by comparing two PDFs at times infinitesimally apart and sum these distances in time. The total distance along the trajectory quantifies the total number of different states that the system undergoes in time, and is called the information length. We show that the time-evolution of the two models become more similar when measured in units of the information length and point out the merit of using the information length in unifying and understanding the dynamic evolution of different growth processes.

Modeling and Analysis of Noise Sources for Thin-Film Magnetoelectric Sensors Based on the Delta-E Effect

We present a comprehensive noise model for an electromechanical resonator that is utilized as a magnetic field sensor. The cantilever-type sensor is coated with a magnetostrictive film that exhibits a change in elastic modulus E with a magnetic field and therefore detunes the resonator—the so-called delta-E effect. The noise model contains all relevant noise sources from the operational electronics, the wiring, and the sensor itself. Measurements show good agreement up to a certain excitation voltage, where an additional dominant noise source appears. It is identified as originating from the magnetic film. With the results of the model, the operational parameters of such sensors are discussed. The model predicts that the limit of detection at 10 Hz for the present sensors can be improved to 60 pT/(Hz) $^{1/2}$ if the magnetic noise is eliminated.

Investigation of single and twin jet interactions with plates with cut-outs

The design and testing of the launch vehicle structure and its subsystems to withstand the lift-off acoustic loads is quite a daunting task in itself. Any effort to minimize these loads can prove to be highly beneficial as it directly influences the design, weight, and qualification of the launch vehicle components and hence the overall vehicle operating cost and time. The components of launch pad such as the launch platform and jet blast deflector are known to be the principal noise sources of the intense acoustic loads generated during lift-off. They contribute to the overall noise levels experienced by the launch vehicle by either reflecting the noise generated by the jet exhaust or by creating additional sources of noise. Earlier studies showed that the presence of cut-outs in the launch platform significantly affects the overall acoustic loads experienced by the launch vehicle. The present paper attempts to characterize the influence of cut-outs in the launch platform on the noise levels experienced by the launch vehicle, by investigating single and twin jets impinging on flat plates with and without cut-outs at varying lift-off distances. The results from acoustic measurements carried out in the near and far-field of scaled down single and twin jet launch vehicle models are discussed. The paper also attempts to relate changes in acoustic field, brought about by the different platform configurations, to the changes in flow field through flow visualization using the schlieren technique.

Nonperturbative environmental influence on dephasing

Environmental noise leads to dephasing and relaxation in a quantum system. Often, a rigorous treatment of multiple noise sources within a system-bath approach is not possible. We discuss the influence of environmental fluctuations on a quantum system whose dynamics is dephasing already due to a phenomenologically treated additional noise source. For this situation, we develop a path-integral approach, which allows us to treat the system-environment coupling in a numerically exact way, and additionally we extend standard perturbative approaches. We observe strong deviations between the numerically exact and the perturbative results even for weak system-bath coupling. This shows that standard perturbative approaches fail for additional, even weak, system-bath couplings if the system dynamics is already dissipative.

Doubly stochastic (pseudo)gene expression in the regulation of cancer

We extend a model of the regulation of cancer by gene and pseudogene messenger RNAs to take into account cell-to-cell variability. This introduces an additional randomness to the intensity of the intracellular noise. The intracellular stochasticity is modelled via an additive white noise source and the intercellular stochasticity, or randomness, is modelled via a steady-state -distribution for the intracellular noise intensity. The doubly stochastic process is treated numerically and displays a difference compared with the single stochastic (pseudo)gene expression process, which is the randomness-induced shift of the onset of even–odd oscillations in the number of molecules. Similarities to experimental outcomes in the related literature are pointed out.

The stable state properties and mean first-passage time of tristable system driven by non-correlated additive and multiplicative non-Gaussian noise

The effects of the system parameters on the stable-state probability density and mean first-passage time (MFPT) are investigated for a tristable system, driven by non-correlated additive and multiplicative non-Gaussian noise sources. The expression of the stable state probability density function (PDF) and MFPT of the system is derived. The results show that the intensity of multiplicative and additive noise sources cannot give rise to noise-induced transitions on the tristable system. The effects of the system parameter b on MFPT are investigated in two directions. In addition, in the behavior of the MFPT, we observe the noise enhanced stability (NES) and resonant activation (RA) of the tristable system induced by non-correlated addictive and multiplicative non-Gaussian noise.