Compact Noise Research Articles

Effect of Airfoil thickness on low-frequency gust-airfoil interaction noise

Interaction between turbulence and an airfoil is a significant aerodynamic noise source for many engineering applications when turbulence in the wake of upstream blades interacts with the leading edge of downstream blades. Modeling the oncoming turbulence as harmonic gusts is a common approach to studying the noise generated by turbulence-airfoil interaction. The airfoil can be considered a compact noise source, resulting in a dipole-like sound directivity pattern when the acoustic wavelength of gust-airfoil interaction is much larger than the airfoil chord length. However, the interaction becomes more complex when the acoustic wavelength is comparable to or smaller than the airfoil chord, as the airfoil cannot be treated as a compact source anymore and multiple lobes appear in the radiated sound directivity. This paper studies airfoil thickness effects using a computational aeroacoustics approach based on the spectral/hp element method for low-reduced frequency gusts. It is found that the sound pressure decreases with the increase of thickness for low reduced frequency gusts. To reveal its mechanism, a semi-analytical method and the convective FW-H equation are used for low reduced frequency to analyze the radiated noise. The interaction between sound sources on the airfoil surface is crucial for the thickness effect.

Advancing flow-duct noise control: Examples of innovative silencers

Two examples of innovative silencers for advanced duct noise control are presented. The first example is related to using metamaterials and the so-called ‘slow sound' to create a compact virtual Herschel-Quincke tube [1]. The second example revolves around a concept called the ‘modal filter' [2], which is designed to selectively damp a single propagating mode. For plane waves, optimal propagational damping is achieved by a wall impedance equal to the Cremer impedance. We will demonstrate how to compute the Cremer impedance, even for low frequencies, at which the classical solution is invalid [3]. Such an arrangement efficiently dampens both the plane (0,0) and the first radial mode (0,1). To further dampen the first two circumferential modes (1,0) and (2,0), a section with the Cremer impedance can be combined with a modal filter made of micro-perforated plates. These plates are inserted parallel to the flow direction and positioned at modal velocity maxima in the duct cross-section. We anticipate that both examples can be useful in industries requiring compact noise mitigation solutions in flow ducts. [1] https://doi.org/10.1016/j.jsv.2019.115045. [2] https://doi.org/10.1121/2.0000473. [3] https://doi.org/10.1121/1.5136952

A Practical Wave Optics Reflection Model for Hair and Fur

Traditional fiber scattering models, based on ray optics, are missing some important visual aspects of fiber appearance. Previous work [Xia et al. 2020] on wave scattering from ideal extrusions demonstrated that diffraction produces strong forward scattering and colorful effects that are missing from ray-based models. However, that work was unable to include some important surface characteristics such as surface roughness and tilted cuticle scales, which are known to be important for fiber appearance. In this work, we take an important step to study wave effects from rough fibers with arbitrary 3D microgeometry. While the full-wave simulation of realistic 3D fibers remains intractable, we developed a 3D wave optics simulator based on a physical optics approximation, using a GPU-based hierarchical algorithm to greatly accelerate the calculation. It simulates surface reflection and diffractive scattering, which are present in all fibers and typically dominate for darkly pigmented fibers. The simulation provides a detailed picture of first order scattering, but it is not practical to use for production rendering as this would require tabulation per fiber geometry. To practically handle geometry variations in the scene, we propose a model based on wavelet noise, capturing the important statistical features in the simulation results that are relevant for rendering. Both our simulation and practical model show similar granular patterns to those observed in optical measurement. Our compact noise model can be easily combined with existing scattering models to render hair and fur of various colors, introducing visually important colorful glints that were missing from all previous models.

Strategic distribution of resonators' parameters for broadband vibration mitigation

Locally resonant metamaterials have recently come to the fore as novel lightweight and compact Noise, Vibrations and Harshness (NVH) solutions. They can be designed/obtained by assembling nominally equal resonant elements, which are tuned to the desired frequency range, onto a host structure in a sub-wavelength manner. This combination leads to tunable frequency ranges, known as stop bands i.e. frequency regions where free wave propagation is not allowed. Nonetheless, these stop bands are typically only effective in a limited frequency region. In order to broaden the frequency range of noise and vibration reduction, an optimization procedure could be applied in order to obtain the ideal distribution of resonance frequencies and masses to achieve a minimal sound radiation over a certain frequency region. However, this approach typically requires a considerable computational time. For this reason, this paper proposes a set of guidelines that define a strategy for broadband NVH reduction without the use of optimization. The proposed strategy is applied to a finite plate with a predefined added grid for the resonator positions. The performance of the strategy is numerically analyzed by assessing the vibration response of the plate for multiple excitation locations and within different frequency ranges. The obtained responses are then compared to the response of the plate with an optimized grid of resonators. This study shows that the proposed strategy leads to a reasonable vibration reduction with similar levels with respect to the response obtained from optimization.

Variations with Mach number for gust–airfoil interaction noise

The interaction of turbulence with airfoil is an important noise source in many engineering fields, including helicopters, turbofans, and contra-rotating open rotor engines, where turbulence generated in the wake of upstream blades interacts with the leading edge of downstream blades and produces aerodynamic noise. One approach to study turbulence–airfoil interaction noise is to model the oncoming turbulence as harmonic gusts. A compact noise source produces a dipole-like sound directivity pattern. However, when the acoustic wavelength is much smaller than the airfoil chord length, the airfoil needs to be treated as a non-compact source, and the gust–airfoil interaction becomes more complicated and results in multiple lobes generated in the radiated sound directivity. Capturing the short acoustic wavelength is a challenge for numerical simulations. In this work, simulations are performed for gust–airfoil interaction at different Mach numbers using a high-fidelity direct computational aeroacoustic (CAA) approach based on a spectral/hp element method verified by a CAA benchmark case. It is found that the squared sound pressure varies approximately as the fifth power of Mach number, which changes slightly with the observer location. This scaling law can give a better sound prediction than the flat-plate theory for thicker airfoils. Furthermore, another prediction method, based on the flat-plate theory and CAA simulation, has been proposed to give better predictions than the scaling law for thicker airfoils.

Noise Effects in the Design of Digital Circuits Based on CNTFET

In this paper initially we present two CNTFET models: the first, already proposed by us and the second the Stanford model, recalling our method to match the output characteristics and transconductance characteristics between these two models. Then we briefly recall a compact noise model, proposed by us, used to simulate the performance of some digital CNTFET circuits, for which we present the DC, transient and noise analysis. In particular we examine a inverter gate and the proposed analysis allows to determine the optimal value of input voltage which makes the noise effects negligible.

Implementation of Noise Effects on CNTFET-based NOT Gate in Verilog-A

In this paper we initially present two CNTFET models: the first is already proposed by us and the second is the Stanford model, proposing a method to match the output characteristics and transconductance characteristics between these two models. Then we describe a compact noise model, used to simulate the performance of a NOT gate, in order to analyze how the noise sources constitute a significant limitation in the design of circuits based on CNTFET. All simulations are obtained using the programming language Verilog-A on the simulator Advanced Design System (ADS), highlighting the solutions proposed in order to use this software.

Compact hybrid noise control system: ANC system equipped with circular noise barrier using theoretically calculated control filter

This paper proposes and investigates the feasibility of a compact noise control system for a wide frequency band, which can be easily installed and calibrated. Noise reduction over the workspace can be achieved by noise barriers, but becomes ineffective in low-frequency. Active noise control (ANC) is effective noise control method in low-frequency, so hybrid noise control systems combining a barrier and ANC were proposed. However, previous researches aimed at global noise control behind a large barrier for a stationary environment, which is very costly and difficult to reinstall. Despite its advantages in terms of space, cost, and mobility, a compact hybrid noise control system which is ANC system equipped with a compact size barrier for a specific space has been rarely studied due to the complex scattering effects and microphone arrangements in the control space. The present study aimed to investigate the feasibility of a compact hybrid noise control system using a theoretically calculated control filter, without microphones arrangement. Thus, can be various shapes of barrier and speaker arrangements, in this study, an axisymmetric structure is dealt with, since the theoretical equations had already been established and the computational amounts are reduced by simplifying it to two-dimensional problems. Theoretical noise reduction performance of a barrier, ANC, and the proposed noise control system are compared. Performance of ANC decreases with increasing frequency, and barrier is only effective in high-frequency bands. In contrast, the proposed noise control system achieved satisfactory noise reduction throughout the entire frequency range of interest. Following that, applying the theoretically calculated control filter was validated through experiments. The results showed that the proposed noise control system achieved a noise reduction of about 8 dB for a band-limited white noise in which the frequency range is 200–2000 Hz.

Low Frequency Noise Modeling and SPICE Implementation of Nanoscale MOSFETs

The physics-based compact gate and drain current noise models of nanoscale MOSFETs at low frequencies are presented. The models are primarily developed to be implemented in circuit simulators and are further applied to gain insight into the noise behavior of advanced MOSFETs. For a comprehensive evaluation of noise performance at low frequencies, the models describe all the important physical noise sources and effects which are observed in nanoscale MOSFETs with ultrathin gate oxides. The models account for the gate leakage current noise, the drain current noise, cross correlation effects between the gate and the drain, and quantum mechanical (QM) effects in the inversion layer. With the help of an accurate and generally applicable compact noise models, the compact noise models are successfully implemented into BSIM (Berkeley Short-channel IGFET Model) format and are validated through a comparison of simulation results and measurements.

Compact Noise Modeling Approach in Nano-scaled CSDG MOSFET for RF Switch

The Cylindrical Surrounding Double-Gate (CSDG) MOSFET can be used to design nanotechnology-based switches that can select the signals from various antennas from/to transmitting receiving sections. This model has the advantages of reduced noise for the various switching circuit application of nanotechnology and radio-frequency technology compared to Double-Gate (DG) MOSFET. In this research, a noise model of CSDG MOSFET has been designed and analyzed to apply the nanotechnology regime with the focus on various noises.

An opamp-free second-order noise-shaping SAR ADC with 4$$\times$$ passive gain using capacitive charge pump

This paper presents a compact and robust opamp-free noise shaping (NS) successive approximation register (SAR) analog-to-digital converter (ADC). The proposed NS SAR ADC adopts extra one passive feed-forward path summing in realizing second-order noise shaping with the minimum modification to a standard SAR. Compared with previous works, the noise sources of residue sampling and first-order integration on filter capacitors are obviated. It implements 4 $$\times$$ passive gain by capacitive charge-pump techniques that compensates the partial loss of residue voltage and relaxes the specifications of comparator. According to the behavioral modeling and simulation results, an ENOB of 16.88-bit is achieved based on a 10-bit DAC array, at the OSR of 16. Through utilizing the Monte Carlo simulation, the proposed ADC architecture is proven to be a robust system.

Compact noise-filtering volume gratings for holographic displays.

A compact noise filtering method for holographic head-mounted displays (HMDs) is proposed. Conventionally, twin, DC and high-order noise from the spatial light modulators is filtered by a spatial stop filter with a 4-f system. Since the 4-f system requires a long optical path length, the noise filtering system usually occupies most of the volume in holographic displays. In the proposed method, only thin angular stop filters (ASFs) are used for noise filtering. The ASFs do not require a bulky 4-f system while performing the same function as the conventional method. The proposed method is verified experimentally. Our study provides an important solution for realization of compact holographic HMDs.

Assessment of methodologies for the solution of the Ffowcs Williams and Hawkings equation using LES of incompressible single-phase flow around a finite-size square cylinder

The acoustic analogy represents a powerful tool for the prediction of noise generated by the interaction between the flow and a moving body. It is based on decoupling the acoustic problem from the fluid dynamic one: the velocity and pressure fields, obtained through a separate numerical simulation, are used as source terms in an inhomogeneous wave equation whose solution reconstructs the noise in the far field. When the method is based on the fundamental Ffowcs Williams and Hawkings (FW-H) equation, different solving methodologies may be adopted.The present work considers the original FW-H equation and gives the advective formulation of the volume integral terms. The results are compared with those obtained with the Curle and porous formulations.To account for volume integrals, the assumption of compact noise source is needed. This assumption is common in literature, however, in the present work, a dimensional analysis is proposed, in order to indicate in a rigorous way the cases in which the compressibility delays can be avoided. The dimensional analysis is tested in the case of an acoustic monopole field. Successively, the FW-H porous formulation is compared with the original FW-H equation in the case of an irrotational advected vortex. This example puts in evidence the different response of the two methods in the case of a vortex crossing the acoustic domain.Then, different solution strategies of the FW-H are evaluated using a fluid dynamic dataset obtained through large eddy simulation of a turbulent flow around a finite-length cylinder with square section. The analysis allows to point out the strengths and drawback of the different techniques and to achieve, through the comparison of the different solutions, an accurate understanding of the noise source mechanisms taking place in the flow. Finally, a mixed procedure, merging the advantages of the porous formulation with the direct evaluation of the volume integral terms is proposed. It may be used in presence of significant time delays. Overall, the present study is oriented to the analysis of very low Mach number flows, although the complete porous method might be applicable in a more general framework. This aspect will require additional research in the future.

Oxide thickness dependent compact model of channel noise for E-mode AlGaN/GaN MOS-HEMT

In this paper, a compact channel noise model for gate recessed enhancement mode GaN based MOS-HEMT which is valid for all regions of operation is proposed. The compact noise model consists of high frequency thermal noise and low frequency flicker noise. The drain current, which is one of the most important parameters for compact noise model is developed by incorporating interface and oxide traps, mobility degradation due to vertical electric field, velocity saturation effect and self-heating effect. The flicker noise model is derived by considering mobility and carrier fluctuation due to traps present in both oxide and interface layer. The thermal noise and flicker noise models are validated by comparing the results with TCAD simulation and experimental results from literature respectively. Effect of thermal and flicker noise power spectral density (PSD) variation with different oxide thickness has also been analyzed.

A new compact circuit-level model of semiconductor lasers: investigation of relative intensity noise and frequency noise spectra

We introduce a new compact noise equivalent circuit model of semiconductor lasers (SLs) from the rate equation including Langevin noise sources. The noise sources are described in terms of the spectral properties of the relative intensity noise (RIN) and frequency/phase noise (FN). Unlike the previous noise equivalent circuit models, which are based on two different DC and small-signal circuit models, using only a single circuit model, the static and dynamic responses and also the noise characteristics of SLs, can be investigated. We examine the validity of the presented noise circuit model by comparing the simulated results with the analytical and numerical results available in the literatures.

A Compact Noise Model for C-CNTFETs

In this paper we present a compact noise model for C-CNTFETs implemented in Verilog-A. After a brief description of the main noise sources existing in CNTFETs, which constitute a significant limitation in the design of analogue and logic CNTFETs circuits, we enhance a model, already proposed by us, considering the noise sources. The simulation results allow to determine easily the different noise contributions and the noise figure. At last the proposed noise model is compared with the Landauer model, obtaining results comparable but with an improvement in terms of run time.

Low-frequency extension of Amiet׳s theory for compact airfoil noise predictions

Amiet׳s theory is an airfoil noise prediction technique adopted in the industrial design of applications such as wind-turbines, turbomachinery, ventilation systems and drones. This methodology uses Schwarzschild׳s technique in an iterative procedure where the second calculation can only be computed in terms of approximate analytical expression. After two iterations Amiet׳s noise prediction is precise at high-frequencies, however generally overestimated in the frequency range where the airfoil is considered a compact noise source – acoustic wavelength comparable to the chord. This paper applies two extra iterations of Schwarzschild׳s technique to improve the methodology convergence in the compact airfoil regime. This approach is combined with analytical correction formulas derived to maintain the solution accuracy after four iterative application of Schwarzschild׳s technique. Results show that, in the compact airfoil regime, two extra iterations contribute to improved noise prediction convergence and enhanced agreement with experimental data.

An optoelectronic oscillator based on series resonance cavity

Commercial and military applications of microwave and millimeter-wave sources in aerospace, radar, navigation, and communication system require high spectrum purity and low phase-noise oscillators. The optoelectronic oscillator (OEO) emerges as an excellent low noise source that has attracted great attention in recent years. In this paper, a novel technique is proposed for single-mode selection in an optoelectronic oscillator, which uses a microwave cavity as the mode selector. It consists of a pump laser and a feedback circuit including an intensity modulator, an optical fiber delay lines, a photodetector, an amplifier, a filter and two drilling cables. The drilling cable is fabricated by drilling open holes on a coaxial cable using a drilling machine. By changing the radius of the drilling holes, the designed reflection coefficient can be obtained. By simulation, the constructed microwave resonator that consists of a filter and two drilling cables has a higher Q value and only the modes that satisfy the oscillation conditions of the loop will be selected. The basic principle is analyzed theoretically and experimentally. By comparing with traditional structure of OEO, it is shown that the novel structure can effectively improve the side-mode suppression ratio. In addition, the stability of the oscillation frequency is easier to control than the parallel structure. In this experiment, the output of a 10 GHz single-mode signal with a side-mode suppression ratio of 72 dB and a phase noise of -122 dBc/Hz@10 kHz from the carrier is obtained. Meanwhile, phase-lock techniques are used to compensate the drift of cavity length. Then the radio frequency (RF) stability of the oscillation frequency is measured using an RF spectrum analyzer, and the RF stability over 3 hours for the OEO is less than 4 Hz. This scheme has the advantages of traditional OEO with low noise since no extra active devices are needed, and it suppresses the side-mode noise also effectively. In addition, this system is promising for the development of compact, high frequency, low cost and low noise OEOs.

Compact noise modelling for common double‐gate metal–oxide–semiconductor field‐effect transistor adapted to gate‐oxide‐thickness asymmetry

On the basis of the quasi-linear relationship between the surface potentials of a common double-gate metal-oxide-semiconductor field-effect transistor, a compact noise model, which is adapted to gate-oxide-thickness asymmetry, is proposed. The proposed model includes a physics-based thermal and flicker noise model. The effect of the lateral and vertical electric fields on the mobility degradation has also been taken into account for accurate noise prediction in short-channel devices. The thermal noise model is compared with the technology computer aided design (TCAD) simulation data and good agreement is observed. The proposed noise model appears to be efficient for analogue circuit simulation.

A compact, multichannel, and low noise arbitrary waveform generator.

A new type of high functionality, fast, compact, and easy programmable arbitrary waveform generator for low noise physical measurements is presented. The generator provides 7 fast differential waveform channels with a maximum bandwidth up to 200 MHz frequency. There are 6 fast pulse generators on the generator board with 78 ps time resolution in both duration and delay, 3 of them with amplitude control. The arbitrary waveform generator is additionally equipped with two auxiliary slow 16 bit analog-to-digital converters and four 16 bit digital-to-analog converters for low frequency applications. Electromagnetic shields are introduced to the power supply, digital, and analog compartments and with a proper filter design perform more than 110 dB digital noise isolation to the output signals. All the output channels of the board have 50 Ω SubMiniature version A termination. The generator board is suitable for use as a part of a high sensitive physical equipment, e.g., fast read out and manipulation of nuclear magnetic resonance or superconducting quantum systems and any other application, which requires electromagnetic interference free fast pulse and arbitrary waveform generation.