Passive Noise Research Articles

Trailing-edge noise reduction potential of a locally applied shallow dimpled surface

There is a strong need for airframe noise reduction methods that preserve the aerodynamic performance of lift-generating airframe components. Inspired by the drag reduction studies of van Nesselrooij et al. (2016) and Spalart et al. (2019), the current study explored the trailing-edge noise reduction potential of shallow dimples applied near the trailing edge of a NACA0012 airfoil (approximately the latter 18% of the chord). The effect of shallow dimples on the aerodynamic coefficients is studied by Reynolds Averaged Navier–Stokes (RANS). To investigate the noise reduction credentials of dimples, high-fidelity Overset-Large Eddy Simulations are carried out for a chord based Reynolds number Rec of 4.2 ×105 at zero angle of attack. Near-field analysis revealed that this local application of dimples eliminated the tonal vortex shedding noise, which is otherwise present in the reference configuration without dimples. Furthermore, the application of shallow dimples resulted in the breakdown of the span-wise coherence in the low-to-mid frequency range and a reduction in the convective velocity of the stream-wise convecting eddies. These effects have a favourable impact on the trailing edge noise reduction with a modest 1.8% increase in the overall drag (less than 1 drag count). The far-field sound characteristics revealed that the dimple treatment resulted in the reduction of overall sound pressure levels in the downstream radiation direction (≈ 5.5 dB) and an increase in the upstream radiation direction (≈ 3.5 dB). In a nutshell, this manuscript argues for the inclusion of shallow dimples to the list of potential candidates for passive noise reduction methods, such as serrations, porous materials, and finlets.

An 11.8-fJ/Conversion-Step Noise Shaping SAR ADC with Embedded Passive Gain for Energy-Efficient IoT Sensors.

Herein, we present a noise shaping successive-approximation-register (SAR) analog-to-digital converter (ADC) with an embedded passive gain multiplication technique. The noise shaping moves the in-band quantization noise from the signal band to out-of-band for improved signal-to-noise ratio (SNR). The proposed approach tackles the drawback of the previous active noise shaping (increased power and extra noise) and passive noise shaping (limited noise suppression and signal loss). Both noise shaping and gain multiplication are realized on-chip in an energy-efficient manner without an opamp. This approach uses only capacitors and switches in the finite impulse response (FIR) and infinite impulse response (IIR) filters. A comparator suppressing kickback noise is presented to handle the tradeoff between noise suppression and the filter capacitor size. The energy-efficient merged-capacitor switching (MCS) technique is effectively combined with rail-to-rail swing comparator and thermometer-coded capacitor array, which reduces the settling error in the digital to analog converter (DAC). The process-induced mismatch effect in the capacitive DAC is investigated using a behavioral model of the ADC. Additionally, we propose dynamic element matching (DEM) for the thermometer-coded capacitor array. The ADC is fabricated using a 0.18 μm CMOS process in an area of 0.26 mm2. Consuming 4.1 μW, the ADC achieves a signal-to-noise and distortion ratio (SNDR) of 66.5 dB and a spurious-free dynamic range (SFDR) of 79.1 dB. The figure-of-merit (FoM) of the ADC is 11.8 fJ/conversion-step.

Investigation of Fibrous Materials for Low Frequency and High-Frequency Passive Noise Reduction using Transfer Matrix Method

The concern about the adverse effects of noise pollution is enhancing day by day due to fast industrialization. Hence a wide variety of active and passive noise controllers made of natural and synthetic materials are widely used for various types of inevitable noise reduction. The different types of passive noise controllers fabricated using various techniques vary in their microstructure and surface morphology. In turn, they cause a difference in the noise-controlling mechanisms happening inside it, leading to its unique acoustic absorption characteristics. This article uses five different fibers of different fiber diameters to fabricate passive acoustic absorbers of different textures. The frequency response of their acoustic absorption coefficient is tested with the help of impedance tube apparatus using the transfer matrix method. Acoustic properties of coir fiber, basalt fiber, glass fiber, graphene fiber, and carbon fiber are investigated and compared. The present investigation focused on the influence of fiber diameter, the porosity, and the difference in the texture of these passive absorbers on the acoustic characteristics, frequency response of acoustic absorption coefficient, and the frequency corresponding to maximum absorption. The investigation also focuses on fabricating the passive absorbers for low-frequency noise reduction where only the active absorbers are available.

Scattering analysis of a partitioned membrane-bounded cavity with material contrast.

The acoustic performance of a silencer containing elastic membranes backed by cavities and porous material is investigated. The modeled waveguide configuration contains porous screens as well as the metallic fairings at interfaces between the inlet and outlet and the expansion chamber. The mode-matching solution is developed to analyze the attenuation of the silencer. The governing eigen-sub-systems are Sturm-Liouville and non-Sturm-Liouville types. In the latter case, the exploitation of generalized orthogonality conditions reveals the point-wise convergence of the solution to the governing eigen-systems. The study shows that by tuning the material parameters of the isotropic membranes and altering the bounding wall conditions, the performance of the physical device can be improved. It enables the model configuration to be adopted as a passive or reactive noise control device.

Noise Rejection Mode Imaging of Atomic Force Microscope

This paper presents an imaging mode of atomic force microscope (AFM) that is robust to the environmental acoustic noise. AFM operations are sensitive to external disturbances including acoustic noise, as disturbances to the probe-sample interaction directly results in distortions in the sample images obtained. Although conventionally passive noise cancellation has been employed, the passive-noise apparatus limits the function of AFM and its use in emerging applications. Moreover, residual noise still persists. In this work, we propose a noise rejection mode (NRM) of AFM imaging to avoid and eliminate the acoustic-caused disturbance to the imaging process. Contrary to other existing AFM imaging modes, in the proposed NRM approach, the set-point of the feedback loop for tracking the sample topography is adjusted online such that the AFM system is insensitive and thereby, robust to the environmental noise. Then, a feedforward controller is augmented to counter act the noise-caused vibration in the feedback loop. Both the set-point adjustment and the feedforward noise cancellation are implemented through finite-impulse-response (FIR) filters. Experimental examples are presented and discussed to illustrate the proposed technique.

Passive Noise Suppression in Yb-Doped Fiber Amplifier Based on Nonlinear Amplifying Loop Mirror

Passive Noise Suppression in Yb-Doped Fiber Amplifier Based on Nonlinear Amplifying Loop Mirror

Experimental Research on the Noise Characteristics of the Output Field of the Optical Filter Cavity

Precision measurement is an important direction of today's frontier scientific research. Using lasers to achieve high-precision target measurement has become an important way to improve measurement accuracy, which can be applied in various fields. However, for a certain application, the measurement accuracy will directly depend on the noise level of the laser source. Most applications require that the measurement frequency band is concentrated in the audio frequency band. In order to obtain a low-noise laser source with shot noise limited in the applied frequency band, active and/or passive noise reduction are the usual choice, i.e., active feedback control and filter cavity technique, and so on. Therefore, noise analysis and suppression techniques are the main concern of the precision measurement. The optical filter cavity acts as an optical low-pass filter, which can effectively suppress high-frequency noise beyond its linewidth. In this work, we found that the intensity noise of the output field of an optical filter cavity is higher than the noise floor of the laser. The main sources of noise are analyzed through experiments:(1) excess noise introduced by cavity length locking; (2) laser phase and pointing noises coupled to the intensity one by the cavity. To cancel the excess noise as much as possible, we optimize the feedback control loop by measuring the open-loop and closed-loop transfer functions of the MC, combined with the critical proportionality method. All the control loop are homemade, and the PID is designed with a FPGA board for expediently achieving a noise reduction up to 30 dB at the audio frequency. Then the control loop is optimized as the best condition without introducing the excess noise. Compared with the free-running laser, MC filters out the high-frequency noise, meanwhile converts the phase noise and pointing noise of input field into the intensity noise of the output field. Therefore, the power noise spectrum in the audio segment is still higher than that of the input optical field itself. In the future, an active control loop will be applied to suppress the noise power. The experimental results provide the basic means for applied research such as feedback control loop noise analysis, which will promote the development of precision measurement to higher measurement accuracy.

Experimental study on noise characteristics of audio frequency band in output field of optical filter cavity

Precision measurement is an important direction of today’s frontier scientific research. Using lasers to achieve high-precision target measurement has become an important way to improve measurement accuracy, which can be used in various fields. However, for a certain application, the measurement accuracy will directly depend on the noise level of the laser source. Most of applications require that the measurement frequency band is concentrated in the audio frequency band. In order to obtain a low-noise laser source with shot noise limited in the applied frequency band, active and/or passive noise reduction is usually an option, i.e. active feedback control or filter cavity technique, etc. Therefore, noise analysis and suppression techniques are the main concern of the precision measurement. The optical filter cavity acts as an optical low-pass filter, which can effectively suppress high-frequency noise beyond its linewidth. In this work, we find that the intensity noise of the output field of an optical filter cavity is higher than the noise floor of the laser. The main sources of noise are analyzed experimentally, showing that 1) excess noise is introduced by cavity length locking, and 2) laser phase and pointing noises are coupled to the intensity one by the cavity. To cancel the excess noise as much as possible, we optimize the feedback control loop by measuring the open-loop and closed-loop transfer functions of the mode cleaner (MC), combined with the critical proportionality method. All the control loops are homemade, and the proportional-integral-derivative (PID) is designed with a field programmable gate array board for expediently achieving a noise reduction up to 30 dB at the audio frequency. Then the control loop is optimized to the best condition without introducing the excess noise. Compared with the free-running laser, MC filters out the high-frequency noise, meanwhile converts the phase noise and pointing noise of input field into the intensity noise of the output field. Therefore, the power noise spectrum in the audio band is still higher than that of the input optical field itself. In the future, an active control loop will be used to suppress the noise power. The experimental results provide the basic means for application research such as feedback control loop noise analysis, which will promote the development of precision measurement toward higher measurement accuracy.

A Digital Twin Architecture for Wireless Networked Adaptive Active Noise Control

The active noise control (ANC) is a complementary technique to the passive noise control (PNC) to reduce the low frequency noise. The ANC controller can be implemented by pre-trained filters or adaptive filters. The adaptive ANC controller is advantageous in its adaptation to environmental changes. However, the algorithm complexity of the adaptive ANC controller increases with the scale of ANC applications, making it difficult to be carried out on low-cost processors. To resolve this problem, cloud computing should be utilized in ANC systems, and thus the wireless networked ANC system is proposed. Since it is crucial for ANC controllers to generate the anti-noise wave in real time, this paper formulates a digital twin architecture that implements the control filter adaptation in the cloud and the anti-noise signal generation on the local controller, respectively. A digital twin filtered-reference least mean squares (DT-FxLMS) algorithm is proposed to coordinate the digital twin with the local controller. Simulation and experiment results demonstrate the effectiveness and efficiency of the wireless networked ANC system based on the digital twin architecture.

Hybrid active and passive noise control in ventilation duct with internally placed microphones module

A feedforward active noise control (ANC) system combined with the passive silencer is built to reduce the acoustic noise propagating through the ventilation duct. The passive silencer consists of two layers which are made of aluminum plate and the perforated panels respectively, the cavity between the two layers is filled with the melamine foam. To overcome the two issues encountered in the active noise control for ventilation duct, i.e., the turbulent flow noise and the acoustic feedback, the emphasis of ANC system is the internally placed microphones module. The module is made of a perforated panel shell filled with the melamine foam, the reference and error microphones are both placed in the melamine foam. The real experiments show that the passive silencer has more than 20 dB noise attenuation at frequencies above 600 Hz, ANC can obtain more than 10 dB noise attenuation from 70 Hz to 200 Hz (the maximum 17 dB at 150 Hz) when the wind speed increases from 5 m/s to 10 m/s. In addition, the module is easy to install and maintain, and its manufacturing cost is also acceptable.

Noise-resistant quantum communications using hyperentanglement

Quantum information protocols are being deployed in increasingly practical scenarios, via optical fibers or free space, alongside classical communications channels. However, entanglement, the most critical resource to deploy to the communicating parties, is also the most fragile to the noise-induced degradations. Here we show that polarization-frequency hyperentanglement of photons can be effectively employed to enable noise-resistant distribution of polarization entanglement through noisy quantum channels. In particular, we demonstrate that our hyperentanglement-based scheme results in an orders-of-magnitude increase in the SNR for distribution of polarization-entangled qubit pairs, enabling quantum communications even in the presence of strong noise that would otherwise preclude quantum operations due to noise-induced entanglement sudden death. While recent years have witnessed tremendous interest and progress in long-distance quantum communications, previous attempts to deal with the noise have mostly been focused on passive noise suppression in quantum channels. Here, via the use of hyperentangled degrees of freedom, we pave the way toward a universally adoptable strategy to enable entanglement-based quantum communications via strongly noisy quantum channels.

Further assessment of a time domain impedance boundary condition for the numerical simulation of noise-absorbing materials

In regard to the mitigation of environmental noise across major industry sectors, the present study focuses on the numerical prediction of passive noise reduction devices. Here, it is further explored how the noise attenuation induced by locally reacting noise absorbing materials (also called acoustic liners) can be simulated using a time domain highly accurate Computational AeroAcoustics (CAA) method. To this end, it is assessed how a classical Time Domain Impedance Boundary Condition (TDIBC) can effectively model acoustic liners of practical interest, including when the latter are exposed to realistic conditions (grazing flow and noise excitation). The investigation consists in numerically reproducing two experimental campaigns initially performed at NASA Langley Research Center. Two different materials are considered (honeycomb superimposed with perforate or wiremesh resistive face-sheet), each being characterized by a specific noise attenuation behaviour ( e.g. dependency on the flow conditions and/or noise excitation). Each material is tested under various flow conditions ( e.g. grazing flow of Mach up to 0.5) and/or noise source excitation ( e.g. multiple tones of level up to 140 dB each). The results demonstrate the ability of the underlying CAA/TDIBC approach to simulate realistic acoustic liners in non-trivial configurations, with enough physical accuracy ( e.g. correct capture of the noise attenuation characteristics) and numerical robustness ( e.g. absence of instabilities). The study also reveals that, independent from the CAA/TDIBC approach itself, some specific pre-processing tasks (e.g. impedance eduction and subsequent TDIBC calibration) may play a bigger role than expected, in practice.

Моделирование пассивных помех в РЛС с цифровой антенной решеткой

The problem of imitation modeling of passive interference is considered in the context of devel-oping algorithms for space-time processing of broadband signals in a radar system with a digital antenna array. Spectral and correlation characteristics of passive noise are discussed in the frame-work of Gaussian, polynomial (fractional rational) and exponential models. Due to the broadband nature of probing signals, the formation of the antenna array directional pattern is carried out by controlling the time delays of oscillations arriving at the array elements, which is implemented in the frequency domain through complex weighting factors. Modeling of passive interference as a sta-tionary complex random process is performed in discrete "slow" time, with each complex vector of samples being spaced from neighboring vectors by the value of the repetition period of the probing pulses. The known method for modeling passive interference based on a shaping recursive filter is unsuitable for use in the case of an interference spectrum other than rational. The method for model-ing the vector of correlated samples using the Cholesky expansion of the noise covariance matrix is inapplicable when the correlation coefficient is close to one. A method is proposed for modeling masking extended passive interference of a wide class based on filtering a sequence of complex pseudo-random vectors in the frequency domain with the use of a fast Fourier transform.

Mechanical sharing dual-comb fiber laser based on an all-polarization-maintaining cavity configuration.

We present a mechanical sharing, dual-comb fiber laser based on an all-polarization-maintaining cavity configuration and a nonlinear amplifying loop mirror mode-locking mechanism. This simple setup yields dual-optical frequency combs with a high level of mutual coherence without active servo control. We realized a high relative stability with a standard deviation of 0.27 Hz and a relative beat note between the dual-frequency combs with a full-width at half-maximum of ∼50Hz. Dual-frequency combs were found to have high relative stability and mutual coherence owing to passive common-mode noise suppression using a mechanical sharing laser cavity. This laser configuration can significantly simplify dual-comb spectroscopy.

Acoustic notch filtering earmuff utilizing Helmholtz resonator arrays.

In recent years, noisy bustling environments have created situations in which earmuffs must soundproof only specific noise while transmitting significant sounds, such as voices, for work safety and efficiency. Two sound insulation technologies have been utilized: passive noise control (PNC) and active noise control (ANC). However, PNC is incapable of insulating selective frequencies of noise, and ANC is limited to low-frequency sounds. Thus, it has been difficult for traditional earmuffs to cancel out only high-frequency noise that people feel uncomfortable hearing. Here, we propose an acoustic notch filtering earmuff utilizing Helmholtz resonator (HR) arrays that provides a sound attenuation effect around the tuneable resonant frequency. A sheet-like sound insulating plate comprising HR arrays is realized in a honeycomb structure. Since the resonant frequency is determined by the geometry of the HR arrays, a highly audible sound region can be designed as the target frequency. In this research, the acoustic notch filtering performance of the proposed HR array plate is investigated in both simulations and experiments. Furthermore, the fabricated earmuffs using the novel HR array plates achieve a sound insulation performance exceeding 40 dB at the target frequency, which is sufficiently high compared to that of conventional earmuffs. The experimental results confirm that the proposed device is a useful approach for insulating frequency-selective sound.

A 2.4 GHz sub 1-mW highly linear differential LNA using balun transformer gm-boosting technique

This paper presents a passive gm-boosting differential low noise amplifier (LNA) for low power applications using a single-to-double transformer. This LNA improves noise figure and linearity with no extra power penalty by using the front-end balun together with noise and distortion cancelation. To address the excess power and noise that are introduced by the auxiliary amplifier, both the current reuse and resistive feedback techniques are used. The input balun provides the differential signals from the single ended input signal and boosts the gm of the amplifier. gm-boosting together with the distortion reduction technique improve both the second and third order nonlinearity. The detailed analysis and simulations including Gain, NF, and Linearity in a standard 65nm CMOS technology are given. Simulation results reveal that the LNA achieves over 23.5 dB gain, 2.8 dB NF, IIP3 and IIP2 of +4.3 dBm and +46 dBm, respectively. It consumes 620 µW from a 0.8 V supply voltage while the total effective die area is 0.21mm2.

Predicting robust complete and full band gaps in three-dimensional frame structures

Vibration can cause structural damage in dynamic systems when not designed properly. Recently, several approaches are emerging in structural dynamics as possible alternatives for passive vibration and noise control, such as phononic crystals and metamaterials. In this work, a three-dimensional frame that presents intersection of longitudinal, flexural and torsional band gaps is investigated. For periodic structures, the Irreducible Brillion Zone (IBZ) gives information for any possible angle of propagation of a wave. The manufacturing process induces variability along each three-dimensional frame element. The present study verifies the robustness of the band gaps of the three-dimensional structure against spatially varying geometry and mechanical properties. The spatial random fields are modeled using the expansion optimal linear estimator (EOLE). Bayesian statistics is used to infer on the stochastic response simulated using the Monte Carlo method combined with the EOLE. The three-dimensional frame is modeled via Euler-Bernoulli beam and ordinary shaft theories as well as with Timoshenko and Saint-Venant theories. It is shown that the three-dimensional frame structure exhibits a complete (for all waves) and full (throughout the IBZ) robust band gap against the proposed variability. Both models are able to predict this robust band gap.

Experimental and numerical investigations of ventilated acoustic metamaterial based in-parallel arrangement of Helmholtz resonator for façade screen

Understanding urban noise as a serious environmental problem in urban centers, the development and application of noise control strategies have demanded a recent effort by several researches. In this case, the development of acoustic metamaterial artificially designed to manipulate the wave phenomena has become a recent topic, aiming at optimized responses, and enables the development of subwavelength devices with potential application in passive ventilation and noise mitigation, providing better environmental conditions in buildings. The present paper intends to contribute to the knowledge in this field by investigating the concept of an acoustic metamaterial with negative bulk modulus based in a parallel arrangement of Helmholtz Resonators. Experimental and numerical investigations are carried out to determine the acoustic potential of the proposed meta structure in terms of sound absorption and sound transmission loss. The developed concept exhibits significant benefits in the properties of sound transmission loss, and seems a potential application for noise control at specific frequency bands (mainly at low to middle frequency) in building façades.

Wavenumber domain analysis of full-band energy harvesting and damping dissipation characteristics of plate embedded with heterogeneous ABH array

The Acoustic Black Hole (ABH) structure has been developed as a promising approach for passive vibration attenuation and noise control. The basic theory of ABH effect hinges on the geometry thickness gradual decreasing according to the power law. This feature of structure reduces flexural wave speed, resulting in "trapping" flexural wave into ABH indentation to achieve energy focalizing. In this work, the FE model of a plate embedded with ABH indentation and damp structure is established and excited by a series of harmonic forces respectively. The characteristics of energy distribution in this plate in full frequency band are investigated by the power flow method and wavenumber domain analysis. By transforming the spatial vibratory energy into wavenumber domain, the ABH effect is analyzed and compared with a uniform panel. Meanwhile, the dissipation effect of vibration and sound radiation energy has been studied with addition of damping material. Furthermore, the energy harvesting and dissipation performances of a plate embedded with heterogeneous ABH array are investigated in order to demonstrate the influence of ABH structure parameters and configuration. The research will be beneficial for the vibration energy control in full frequency band.

Design of noise barriers for the mitigation of construction noise

Noise pollution is a major problem in many major cities in particular a small island state like Singapore with residential buildings very close to the major trunk roads and expressways. The problem is aggravated by the ongoing city redevelopment and construction of new mass rapid transit lines. Construction noise is therefore a common theme of public complaints and therefore there is an increased interest in the development of more effective mitigation measure for construction noise. In this work, a Flat-tip jagged-edge profile was investigated and applied on the edge of a cantilever (slanted up for 45 degrees, facing the noise source) which was mounted at the top of a passive noise barrier. Besides the numerical simulations, the full sized prototypes were also experimentally tested on a construction sites with noise generated by a boring machine. Both numerical simulations and experimental results showed that this barrier with a slanted Flat-tip jagged cantilever would perform better than the traditional barrier having a Straight-edge cantilever of same height, with a maximum additional attenuation of 5.0 dBA experimentally obtained. The barrier with slanted Flat-tip jagged cantilever could also extend the shadow zone behind the barrier to higher levels of the building.