Low-frequency Noise Research Articles

A Feedback Active Control Approach to Road Noise Based on a Single Microphone Sensor to Improve Automotive Cabin Sound Comfort

Tire–road noise deteriorates the sound quality of a vehicle’s interior and affects the driving safety and comfort. Obtaining low interior noise is a challenge for passenger car manufacturers. Traditional passive noise control (PNC) is efficient for canceling high frequency noise but not useful for low frequency noise, while active noise control (ANC), according to the residual error signal, can generate an anti-noise signal to reduce the original noise. Most research has focused on improving the control effect for a feedforward ANC system. However, this paper emphasizes a feedback ANC system based on a signal microphone sensor. There are two main contributions in this study to improve automotive cabin sound comfort. One is that the algorithm of the feedback ANC system using a single microphone sensor without a reference noise signal is proposed based on the Filtered-x Least Mean Square method. The other is that the algorithm applies additive random noise online to estimate the secondary path model. A simulation was implemented based on measured real road noise data, and the simulation results indicate that the proposed feedback ANC system with the single microphone sensor can effectively attenuate road noise. This study shows the feasibility of applying a feedback ANC system in automobiles to increase the cabin sound quality.

Study of the Extremely Low-Frequency Noise Characteristics of a Micro-Thrust Measurement Platform

The critical structural parameters are optimized and studied using the numerical simulation method to improve the resolution and stability of the Micro-Thrust Measurement Platform (MTMP). Under two different ground random vibration environments, the parameters, such as pivot thickness, pendulum rod length, and pivot structure, are focused on analyzing the influence of the system’s resolution and stability. The results show that when the thickness of the pivot is 0.04 mm or 0.2 mm, and the pendulum rod length is 2 m, the effect of ground random vibration on the MTMP is minimized. At 0.1 mHz, it can reach 0.0057 μN/Hz. In the series double-pivot structure, an appropriate increase in the distance between the sheets can further optimize the above conclusions. The results and analysis within this study can provide support for the engineering design of the MTMP.

Generative adversarial network-enhanced directional seismic wavefield decomposition and its application in reverse time migration

Reverse time migration (RTM) is an accurate method for imaging complex geologic structures without imposing any dip limitations. However, a large amount of high-amplitude low-frequency noise, which is mainly generated by the crosscorrelation of source and receiver wavefields propagating in the same directions, seriously contaminates the image quality. The causal imaging condition with separated up- and downgoing wavefields is an effective approach to reduce these low-frequency artifacts. Explicit up- and downgoing wavefield decomposition based on the Hilbert transform is computationally expensive due to additional wavefield extrapolation and storage for the imaginary parts. Directionally propagating wavefields have distinctive kinematic patterns such as traveltime and wavefront curvature, which provide us an opportunity to implement the wavefield decomposition using the statistical neural network method. Using extrapolated wavefields as the input and the decomposed up-, down-, left-, and rightgoing wavefields as the labeled data, we train a pair of generative adversarial networks to predict the directional wavefields. The training data sets are generated using seismic full-waveform modeling and explicit wavefield decomposition based on the Hilbert transform. Then, the decomposed directional wavefields are incorporated into a novel imaging condition that depends on the subsurface dip angles to compute the reflectivity perpendicular to the reflectors. Numerical experiments demonstrate that our method can produce accurate directional wavefield decomposition results and high-quality reflectivity images without low-wavenumber artifacts.

Meta-barriers for ventilated sound reduction via transformation acoustics

Resolving the trade-off problem between wave obstructing and flow transport is an intriguing but challenging task that may find potential applications in many noise control scenarios. Herein, we present a meta-barrier for achieving broadband sound reduction yet keeping efficient ventilation based on transformation acoustics. The proposed meta-barrier consists of an internal core and a coating made of double-negative acoustic metamaterial with high damping dissipation. Unlike conventional barriers, the meta-barrier has a magnified scattering cross-section far beyond its actual size, allowing it to provide the coherent interference effect in addition to the enhanced blocking effect. The coherent interference effect can directly reduce the sound radiation efficiency of sound waves radiating from an aperture. Moreover, the inherent material loss in the coating has a positive effect on the sound reduction performance of the meta-barrier over a wide frequency range. The robust sound reduction performance of the meta-barrier is demonstrated numerically for the cases of large placed distances and wide-range incident angles. Experiments were conducted to confirm the effectiveness of a meta-barrier sample constructed of a plate-type double-negative acoustic metamaterial with multiple constituent layers for sound reduction and ventilation. The fabricated meta-barrier sample, with the wind-speed ratio of 75 %, can achieve superior sound attenuation in the frequency range of 500–1000 Hz. This work may inspire the design and development of passive acoustic devices to suppress low-frequency airborne noise while supporting large-area ventilation.

Design of a charge-sensitive amplifier for MEMS piezoelectric hydrophone

Hydrophone is an important part of sonar system and convert acoustic signal into electrical signal. However, the electrical signal generated by the hydrophone is relatively weak and cannot be directly used for underwater detection and communication. Therefore, it is necessary to preprocess the generated electrical signal. In this paper, a switched capacitor charge-sensitive amplifier for MEMS piezoelectric hydrophone is designed. In the structure, two single-channel charge amplifiers are used for time-division multiplexing. The noise sampling and charge amplification are performed separately in the same half cycle to achieve the effect of alternating output, thereby increasing the sampling rate and solving the problem of discontinuous output of the switched capacitor circuit. In the circuit design, virtual switch and two-phase non-overlapping clock are adopted to reduce the error caused by charge injection and clock feedthrough effect of CMOS switch. What’s more, the correlated double sampling technique is used to reduce the offset and low frequency noise of the circuit. The gain of the charge-sensitive amplifier designed in this study is 26 dB, the bandwidth is 0.8Hz∼17.6kHz, the equivalent input noise power spectral density is 115.6 nV/Hz at 0.1Hz, and the charge sensitivity is 2 mV / pC. The fitting line between the input charge and the amplitude of the output curve is similar to the theory. The simulation results show that the charge-sensitive amplifier proposed in this study meets the design requirements of the MEMS piezoelectric hydrophone readout circuit.

Analysis of wavy leading-edge noise reduction and source mechanism in rod-airfoil interactions

Inspired by the wings of owls and the tubercles present on humpback whales' flippers, leading-edge serrations have demonstrated the potential to mitigate airfoil–turbulence interaction noise. To deepen our understanding of the underlying mechanisms driving this noise reduction, we conducted compressible large-eddy simulations on a rod-airfoil configuration equipped with wavy leading edges (WLEs) of varying amplitudes. All tested serrations exhibited some degree of noise reduction, with the amplitude of the WLE exerting a significant influence on the overall noise reduction effect. Notably, the wavy airfoil with the largest amplitude demonstrated the most substantial noise reduction in the mid-frequency range, achieving a remarkable decrease in up to 2.2 dB in noise levels. Applying multi-process acoustic theory, we delved into sound production on surfaces and near-field structures responsible for generating noise sources. Our findings underscore a crucial mechanism contributing to noise reduction—the source cutoff effects manifested through the significant weakening of noise sources at hill regions along the serrations' surface. Stronger source cutoff effects were observed with larger WLE amplitudes. Furthermore, our study reveals that destructive relationships among sources also play a pivotal role in reducing flow noise. The reduction in mid-frequency noise results from a synergy of the source cutoff effect and destructive source relationships induced by WLEs, while the decrease in low-frequency noise primarily emanates from the source cutoff effect.

Studies on the Experimental Measurement of the Low-Frequency Aerodynamic Noise of Large Wind Turbines

With the continuous warming of the global climate, expanding the use of renewable energy has become one of the main social responsibilities. However, as the number of installed wind turbines and their physical dimensions continue to increase, the issue of generated noise has become increasingly significant in influencing the acceptance and endorsement of wind power projects by neighboring communities. In this paper, we investigated the noise generated by two wind turbine units with rated powers of 1.5 MW and 4.5 MW and analyzed the variations in low-frequency noise during their operation and shutdown periods. This research shows that the power of a single unit has a significant impact on the low-frequency noise emitted into the environment. Compared with 1.5 MW wind turbines, 4.5 MW wind turbines generate more low-frequency noise when operating at the same wind speed. Further analysis of the narrowband frequency spectra and one-third octave spectra of the measured noise indicates that the low-frequency noise from the 4.5 MW wind turbine increases significantly in the range of approximately 80 Hz to 300 Hz, with more pronounced variations below 250 Hz corresponding to changes in wind speed. However, the overall variations in low-frequency noise with wind speed are not as notable as those observed for the 1.5 MW wind turbine. Due to the relatively weak attenuation of low-frequency noise in the atmosphere, the higher low-frequency content of large wind turbines may cause more distress to residents near wind farms. The result of this study emphasizes that in the planning and design of wind power projects, in addition to considering the efficiency of single-unit power generation and the contribution of renewable energy, it is also necessary to pay full attention to noise emission issues to ensure that the project is widely supported and accepted in the community.

Selective modulation of electronic transport in VO2 induced by 10 keV helium ion irradiation

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping.

Geometric design and performance analysis of a foldcore sandwich acoustic metastructure for tunable low-frequency sound absorption

Acoustic metamaterial structures have received extensive attention for sound and vibration engineering applications from the scientific community in recent years. However, the real-life application of conventional acoustic metamaterial structures is frequently limited by fixed frequency bands and increased structural thicknesses in low-frequency noise reduction. In this study, we introduce an origami-based acoustic metamaterial structure that consists of a Miura-ori foldcore, along with a perforated and an unperforated panel. The proposed Miura-ori foldcore sandwich acoustic metastructure (MOF-SAM) exhibits adjustable low-frequency sound absorption capacities due to the foldability of the origami foldcore. Moreover, we employ numerical methods to investigate the sound absorption properties of the MOF-SAM, quantified by the sound absorption coefficient. The results indicate that the structure has a single absorption peak which is superior to that of acoustic structures composed of conventional honeycomb cores. The dissipation of acoustic energy is due to the structural vibrations of the metastructure and the losses in the folding process of the origami foldcore. The numerical results of this study show that the proposed sound absorption mechanism enables tunable low-frequency sound absorption. The geometric design and periodicity of the origami unit fragments offer multiple distinct absorption peaks and thus tunable acoustic performance. These findings of this study are expected to inspire novel designs for next-generation acoustic devices.

Stability-enhanced low-frequency fiber optic hydrophone based on an extrinsic Fabry-Perot interferometer

Fiber optic hydrophones (FOHs) offer the notable advantage of electromagnetic interference resistance. Nevertheless, overcoming the challenge of sustaining stable, high-performance operation in intricate underwater settings at a low cost remains a considerable obstacle for them. To circumvent the restrictions noted above, we employed a miniaturized FOH, utilizing an easily fabricated extrinsic Fabry-Perot interferometer (EFPI) which is made up of a composite chromium-aluminum (Cr-Al) membrane and fiber. The linear demodulation also suppresses the drift issue in the output spectrum. The average sound pressure sensitivity of the sensor, according to experimental findings, is around -139.15 dB re 1 V/µPa, while the equivalent noise sound pressure at 1 kHz is 51.52 dB re 1 µPa/Hz1/2. This sensor has a lot of potential because of features like sensitive low-frequency response and noise performance.

Synergistic effect of proton irradiation and electrical stress on high-speed 850 nm vertical-cavity surface-emitting lasers

The synergistic effect significantly impact VCSEL's reliability for potential applications in spatial data communication. The synergistic effect of 3 MeV proton irradiation and electrical stress on 850 nm high-speed VCSELs is investigated. The degradation of VCSEL slow down under the influence of bias current. However, device degradation is more pronounced during irradiation under high bias current density. Low frequency noise (LFN) analysis results indicate that defects induced by proton irradiation are the primary cause of the optical-electrical parameter degradation in the device. The bias current density significantly influences the final defect yield, leading to variations in the degree of degradation after irradiation at different bias currents. At a bias current density of 6.03 × 105 A/m2, the degradation of the modulation bandwidth is reduced in comparison to the unbiased state. A mechanism investigation into the synergistic effect of proton irradiation and electrical stress on VCSELs lends support for accurately evaluating the radiation hardness of optical communication system composed of VCSELs in harsh radiation environments.

Low-frequency vibration reduction of an underwater metamaterial plate excited by a turbulent boundary layer

Flow-induced structural noise is an important component of hydrodynamic noise of underwater structures. Local resonance metamaterials are considered to have excellent performance and enormous potential in the field of low-frequency vibration and noise control. To verify its potential, the paper derived the underwater band gap of a lateral local resonance (LLR) plate through the plane wave expansion (PWE). Then, utilizing the modal superposition approach and Rayleigh integral technique, the vibro-acoustic response of a LLR plate under a turbulent boundary layer (TBL) excitation is obtained. Finite element certification is also conducted through an uncorrelated wall plane wave technique. Parametric study is conducted to analyse the factors which influence the control effects. The result shows that the plate exhibits excellent suppression performance for flow-induced vibration at band gap frequencies. The band gaps and suppression ranges generated by the underwater metamaterial plate, are dramatically narrowed due to the thick fluid load. The paper provides theoretical guidance for the control of flow-induced structural vibration and the application of acoustic metamaterials.

Entropy Model of Rosin Autonomous Boolean Network Digital True Random Number Generator

A True Random Number Generator (TRNG) is an important component in cryptographic algorithms and protocols. The Rosin Autonomous Boolean Network (ABN) digital TRNG has been widely studied due to its nice properties, such as low energy consumption, high speed, strong platform portability, and strong randomness. However, there is still a lack of suitable entropy models to deduce the requirement of design parameters to ensure true randomness. The current model to evaluate the entropy of oscillator-based TRNGs is not applicable for Rosin ABN TRNGs due to low-frequency noise. This work presents a new, suitable stochastic model to evaluate the entropy of Rosin ABN TRNGs. Theoretical analysis and simulation experiments verify the correctness and the effectiveness of the model, and, finally, the appropriate sampling parameters for Rosin ABN TRNGs are given for sufficient entropy per random bit to ensure true randomness.

Source identification from unperceived low-frequency noise emissions at a Madrid home

People may be exposed to energy sources that they cannot perceive with their senses, but which may be harmful to their organism, and therefore, individuals cannot avoid them. One of these energy sources is the sound, particularly sound out of the hearing range (20–20000 Hz). Although the sounds are imperceptible for frequencies below 200 Hz unless they have high intensities. Sound with frequencies below 200 Hz is called “low frequency sound”.This study focuses on low frequency sound generated by artificial sources, and specially in sound located in urban areas. Specifically in the measurement and detection of low frequency sources from the perspective of individuals who are manifesting the symptoms associated with their exposure.To this end, a household of Madrid with individuals who have symptoms is taken as sample. This home did not have large potential sources of low-frequency sounds near its location, such as streets with high intensity of traffic or the subway in order to better contrast other possible sources that are not so obvious.The results show high levels of sound emission at the lowest frequency range (20–200 Hz). These results also show that filters should not be applied to remove non-audible frequency spectrums, such as A type, because it omits sounds in urban areas that could affect people.Data treatment incorporates analysis methods based on machine learning which allow differentiate between sources without measuring on them. Finally, further developments must incorporate measurements bellow 20 Hz and will increase the numbers of households sampled.

Low-Frequency Sound Absorption Potential of Subwavelength Absorbers Based on Coupled Micro-Slit Panels

Due to space limitations during installation, reducing low-frequency noise has always been a challenging area. Sub-wavelength structures are typically favored in such scenarios for noise reduction. This paper explores the potential of micro-slit panels (MSP) for low-frequency sound absorption. To further optimize the panel thickness, coupled MSPs (CMSP) with a distance between two MSPs of less than 1 mm are proposed. Firstly, the low-frequency absorption performances of a single MSP based on two optimized schemes – the cavity-depth optimal scheme (COS) and the panel thickness optimal scheme (TOS) – are examined and compared with those of existing ultrathin metamaterials. The results demonstrate that MSP has significant potential for low frequency sound absorption, and COS allows for a smaller overall structural thickness but a larger panel thickness than TOS. Secondly, to reduce the panel thickness, the CMSP is developed and the theoretical model of its acoustic impedance is established and validated by experiments. Then, based on the theoretical model, the low-frequency absorption potential of CMSP is optimized using COS. The results show that both the overall thickness and the panel thickness of the CMSP absorber are reduced while maintaining better performance. Furthermore, the proposed absorber achieves a subwavelength scale since its total thickness can be as small as 0.138λ.

Ultralow-Noise Chopper Amplifier for Seafloor E-Field Measurement.

The seafloor E-field signal is extremely weak and difficult to measured, even with a high signal-to-noise ratio. The preamplifier for electrodes is a key technology for ocean-bottom electromagnetic receivers. In this study, a chopper amplifier was proposed and developed to measure the seafloor E-field signal in the nanovolt to millivolt range at significantly low frequencies. It included a modulator, transformer, AC amplifier, high-impedance (hi-Z) module, demodulator, low-pass filter, and chopper clock generator. The injected charge in complementary metal-oxide semiconductor (CMOS) switches that form the modulator is the main source of 1/f noise. Combined with the principles of peak filtering and dead bands, a hi-Z module was designed to effectively reduce low-frequency noise. The chopper amplifier achieved an ultralow voltage noise of 0.6 nV/rt (Hz) at 1 Hz and 1.2 nV/rt (Hz) at 0.001 Hz. The corner frequency was less than 100 mHz, and there were few 1/f noises in the effective observation frequency band used for detecting electric fields. Each component is described with relevant tradeoffs that realize low noise in the low-frequency range. The amplifier was compact, measuring Ø 68 mm × H 12 mm, and had a low power consumption of approximately 23 mW (two channels). The fixed gain was 1500 with an input voltage range of 2.7 mVPP. The chopper amplifiers demonstrated stable performance in offshore geophysical prospecting applications.

Analysis of cardiovascular function in diabetic patients using EEMD-ICA fusion multi-scale percussion entropy.

Diabetes is a chronic disease that can lead to a variety of complications and even cause death. The signal characteristics of the photoplethysmography signals (PPG) and electrocardiogram signals (ECG) can reflect the autonomic and vascular aspects of the effects of diabetes on the body. Based on the complex mechanism of interaction between PPG and ECG, a set of ensemble empirical mode decomposition-independent component analysis (EEMD-ICA) fusion multi-scale percussion entropy index (MSPEI) method was proposed to analyze cardiovascular function in diabetic patients. Firstly, the original signal was decomposed into multiple Intrinsic Mode Function (IMFs) by ensemble empirical mode decomposition EEMD, principal components of IMF were extracted by independent component analysis (ICA), then the extracted principal components were reconstructed to eliminate the complex high and low frequency noise of physiological signals. In addition, the MSPEI was calculated for the ECG R-R interval and PPG amplitude sequence.(RRI and Amp) The results showed that, compared with EEMD method, the SNR of EEMD-ICA method increases from 2.1551 to 11.3642, and the root mean square error (RMSE) decreases from 0.0556 to 0.0067. This algorithm can improve the performance of denoising and retain more feature information. The large and small scale entropy of MSPEI (RRI,Amp) was significantly different between healthy and diabetic patients (p< 0.01). Compared with arteriosclerosis index (AI) and multi-scale cross-approximate entropy (MCAE): MSPEISS (RRI,Amp) indicated that diabetes can affect the activity of human autonomic nervous system, while MSPEILS (RRI,Amp) indicated that diabetes can cause or worsen arteriosclerosis. Multi-scale Percussion Entropy algorithm has more advantages in analyzing the influence of diabetes on human cardiovascular and autonomic nervous function.

Effects of Periodic Materials on Distance Attenuation in Wall–Slab Structures: An Experiment

This research examines the application of periodic materials in wall–slab structures to mitigate impact noise and vibration propagation, a prevalent issue in multifamily housing. Traditional methods, such as floating floors, have proven insufficient in addressing low-frequency impact noises and in facilitating the identification of noise origins, leading to increased resident annoyance. Periodic materials, known for their effectiveness in controlling plane waves in civil engineering, were applied to the intermediate slab of a wall–slab experimental setup. The research involved assessing the attenuation of noise and vibration over distance before and after the application of periodic materials by measuring indoor sound pressure levels and the natural vibration amplitude of the structure’s members upon impact. The results showed that periodic materials not only facilitated distance attenuation but also significantly diminished noise and vibration throughout the structure, without the side effects of vibration amplification seen in prior civil engineering applications. This indicates a practical advancement in using these materials, offering a novel approach to sound insulation and enabling more precise impact source localization. Ultimately, this study contributes to improving urban living by suggesting a method to enhance acoustic comfort in multifamily housing, underlining the importance of further exploration in architectural applications of periodic materials.

Discrete Distribution Model of Ship Noise Source in Shipping Channel

Ship noise plays an important role in low-frequency ocean ambient noise. With the increasingly busy sea traffic, the randomness of the spatiotemporal distribution characteristics of ship noise is also increasing. However, most ships sail in a relatively fixed range in different sea areas. Most of the previous studies assumed that the ship noise sources in shipping channel satisfy a uniformly distribution, actually all kinds of large ships are not uniformly distributed in the shipping channel, and there are also many small boats distributed on the channel that contribute significantly to low-frequency ocean ambient noise. The channel within a certain sea area will be divided into different regions, and ship information (AIS) in different regions will be analyzed statistically in this paper. It is assumed that the ship noise sources in different channel regions are discrete point noise sources that obey a certain spatiotemporal statistical distribution, combined with the noise source level models of different types of ships to form a discrete source model of ship noise in shipping channel. Using the ray propagation theory considering the horizontal refraction of sound energy, the vertical distribution of the ship noise level in this sea area is calculated, and compared with the vertical noise level distribution of ship noise source uniform distribution model, the variation range of noise level vertical distribution of two models is close calculated noise level (such as maximum and minimum values) is consistent with the measured data. The discrete source model of ship noise established in this paper may provide a technical support for predicting low-frequency ambient noise characteristics near the channel.

A novel paradigm examining the remote induction of nocebo effects online.

Side effect information is routinely communicated online. However, limited experimental evidence exists regarding the role of this information in generating maladaptive health outcomes (i.e., the nocebo effect). A novel paradigm was developed to remotely induce the nocebo effect via provision of online side effect information. Participants were given information regarding the positive effects of low frequency noise (LFN). A proportion were additionally warned of LFN-induced side effects. Study 1 (N = 423) investigated the source of information (listed vs. socially communicated side effects), while Study 2 (N = 560) investigated the role of positive and negative affects on attenuating and exacerbating the nocebo effect. Pooled analysis (N = 983) explored the effect of negative and positive expectations on both the nocebo effect and positive outcomes. Across studies, a significant nocebo effect in the warned side effects occurred after LFN exposure. This did not vary by source of information (Study 1) nor was it attenuated via the induction of positive affect (Study 2). Both studies demonstrated a reduction in positive outcomes among those receiving side effect information. Pooled analysis revealed that negative, but not positive, expectations mediated the nocebo effect. Positive and negative expectations interacted to predict positive outcomes. Holding negative expectations appeared to block positive health outcomes. Specifically, when negative expectations were above average, there was no effect of positive expectations on positive outcomes. Nocebo effects were remotely generated via minimal provision of side effect information. Pooled analysis revealed that future interventions should target positive and negative expectations to reduce side effects. (PsycInfo Database Record (c) 2024 APA, all rights reserved).