Low-frequency Noise Reduction Research Articles

Portable Low-Frequency Noise Reduction Device for Both Small Open and Closed Spaces

Noise pollution has been given more attention due to its negative impacts on human health and disease. The portable low-frequency noise reduction device we developed in this research can provide an effective way for solving low-frequency noise pollution problem in the small space. This work describes the design principle and the prototype structures for two versions of V1.5 and V2.0 and builds the noise test systems for small spaces, respectively. These devices, installed on the outer surface of the small spaces, can automatically identify the noise spectrum and implement noise reduction by means of the active noise control (ANC) technology. The testing results indicate that the noise can be reduced 12 dB in the range of 250 Hz~400 Hz for the small closed space while, for the small open space, the best effect of 5.88 dB occurs in the optimal frequency of 450 Hz. These effects will be weakened with the increasing distance away from the source and show the obvious axisymmetric distribution in the inverted cone space.

Low Frequency Noise Reduction Using Multiple Transistors With Variable Duty Cycle Switched Biasing

Randomization of the trap state of defects present at the gate Si-SiO2 interface of MOSFET is responsible for the low-frequency noise phenomena such as random telegraph signal (RTS) and 1/ ${f}$ noise. Random activity of trapping and de-trapping of mobile charge carriers, in to these defects, can be reduced by switching the device ON and OFF periodically. The analysis of the low-frequency noise considers the non-stationary behavior of traps in time-periodic biasing conditions. In this paper, analysis of the low-frequency noise by deriving a model for RTS noise power spectral density for variable duty cycle switched biasing, is presented. It is concluded that the low-frequency noise can be reduced by using a multi-stage configuration of multiple transistors in place of a single transistor. In this configuration, each transistor has a decreased duty cycle and it is shown from simulation that the noise reduction obtained can be as large as 26 dB for a 40 stage configuration.

Suppression of Low-Frequency Electronic Noise in Polymer Nanowire Field-Effect Transistors.

The authors report on the reduction of low-frequency noise in semiconductor polymer nanowires with respect to thin-films made of the same organic material. Flicker noise is experimentally investigated in polymer nanowires in the range of 10-10(5) Hz by means of field-effect transistor architectures. The noise in the devices is well described by the Hooge empirical model and exhibits an average Hooge constant, which describes the current power spectral density of fluctuations, suppressed by 1-2 orders of magnitude compared to thin-film devices. To explain the Hooge constant reduction, a resistor network model is developed, in which the organic semiconducting nanostructures or films are depicted through a two-dimensional network of resistors with a square-lattice structure, accounting for the different anisotropy and degree of structural disorder of the active nanowires and films. Results from modeling agree well with experimental findings. These results support enhanced structural order through size-confinement in organic nanostructures as effective route to improve the noise performance in polymer electronic devices.

Spatial Stability Analysis of Subsonic Jets Modified for Low-Frequency Noise Reduction

This study performs a spatial stability analysis of several jets that have previously been investigated in terms of their noise radiation. The cases include a round jet and two chevron nozzle jets with varying penetration angle. The instability wave evolution in the near-nozzle region is examined to seek for clues as to how and why the mean flow azimuthal inhomogeneity introduced by chevrons modifies the low-frequency noise component. A biglobal stability analysis is performed to determine the most unstable modes on an initial plane. The downstream evolution of the most unstable modes is then computed via three-dimensional parabolized stability equations. The azimuthal mean flow inhomogeneity introduced by chevrons is found to modify instability wave growth rates and phase speeds. Findings indicate that the near-field hydrodynamic pressure oscillations of round jet instability modes are suppressed by chevron jets. For the same modal excitation amplitude at the inlet, the two chevron jets generate considerably lower pressure fluctuations than the round jet. It is also shown that the chevron jet with the lowest hydrodynamic pressure fluctuation levels is the jet with the lowest far-field low-frequency noise output among the three jets.

Low-frequency noise reduction in vertical MOSFETs having tunable threshold voltage fabricated with 60 nm CMOS technology on 300 mm wafer process

In this paper, DC and low-frequency noise (LFN) characteristics have been investigated with actual measurement data in both n- and p-type vertical MOSFETs (V-MOSFETs) for the first time. The V-MOSFETs which was fabricated on 300 mm bulk silicon wafer process have realized excellent DC performance and a significant reduction of flicker (1/f) noise. The measurement results show that the fabricated V-MOSFETs with 60 nm silicon pillar and 100 nm gate length achieve excellent steep sub-threshold swing (69 mV/decade for n-type and 66 mV/decade for p-type), good on-current (281 µA/µm for n-type 149 µA/µm for p-type), low off-leakage current (28.1 pA/µm for n-type and 79.6 pA/µm for p-type), and excellent on–off ratio (1 × 107 for n-type and 2 × 106 for p-type). In addition, it is demonstrated that our fabricated V-MOSFETs can control the threshold voltage (Vth) by changing the channel doping condition, which is the useful and low-cost technique as it has been widely used in the conventional bulk planar MOSFET. This result indicates that V-MOSFETs can control Vth more finely and flexibly by the combined the use of the doping technique with other techniques such as work function engineering of metal-gate. Moreover, it is also shown that V-MOSFETs can suppress 1/f noise ( of 10−13–10−11 µm2/Hz for n-type and 10−12–10−10 µm2/Hz for p-type) to one or two order lower level than previously reported nanowire type MOSFET, FinFET, Tri-Gate, and planar MOSFETs. The results have also proved that both DC and 1/f noise performances are independent from the bias voltage which is applied to substrate or well layer. Therefore, it is verified that V-MOSFETs can eliminate the effects from substrate or well layer, which always adversely affects the circuit performances due to this serial connection.

The role of absorptive silencer in reduction of low-frequency noise produced by a fan

Aims: In this study, the amount of the reduction in absorption silencer sound filled with Iranian absorbing materials and influence of thickness and density of adsorbent material in silence was investigated. Materials and Methods: We used galvanized channel 0.6 mm with 30 × 30 cm 2 dimension and axial fan. Length of absorptive silencer was 50 cm, and there used the mineral wool absorbent. Absorptive silencer as channel was designed to cross a section of channel and silencers after embedded the absorber be identical together. This study deals with a number of variables that affect performance of absorptive silencer in the channel and their impact on reducing the sound pressure level be examined. Results: In the frequencies 125 and 250 Hz a reduction of sound pressure level was found. While in frequency 500 Hz minimal reduction is achieved. In this study, an increase in the thickness of the absorbent material of absorption silencer, there was a little change in the volume decreasing but with increasing density from 80 to 100 Kg/m 3 better results were seen to reduce noise levels and it caused to increase NR rate. Conclusion: According to data from the present study we can used silencer with 5 cm thick and 100 Kg/m 3 density in the reduction of sound pressure level at frequencies lower than 250 Hz in the ventilation system as an effective device.

Application of a Helmholtz structure for low frequency noise reduction

In this work, we numerically investigate the existence of low-frequency band gaps in the Helmholtz resonance structure. Finite element method is utilized to calculate the band structure and transmission spectrum. Three band gaps and two neighboring partial band gaps are found from 0 to 4000 Hz. Geometrical parameters which may affect the band gap width or positions such as the inlet width and length are analyzed. Results indicate that the first band gap will become wider and higher with the increase of the inlet width of the resonators. However, variation trend of the first band gap is completely opposite when inlet length becomes longer. Calculated transmission spectrum validates the band structure well. This designed and calculated structure has potential application in the low-frequency noise reduction.

Structuring by electromagnetic forming and by forming with an elastomer punch as a tool for component optimisation regarding mechanical stiffness and acoustic performance

Ecological and economic reasons are forcing industry to improve efficiency and to save energy and resources. Especially for the automotive and transport industry – but also for all other industrial branches dealing with accelerated masses – lightweight design is a key issue for achieving this goal. In current product designs, insufficient geometric stiffness of the part often prohibits exploiting the full potential of weight reduction offered by modern materials. Ideally adapting the geometry to the load profile by implementing appropriate structures frequently allows wall thickness and weight reduction. At the same time, the acoustic properties can be improved in many cases, because the natural frequency of the modified structure is higher compared to a conventionally-designed structure, thus leading to a reduction of awkward low frequency noise (humming). To enable a target-oriented design, the influence of structures manufactured by elastomer tools and by electromagnetic forming (EMF) was analysed systematically. Knowledge about the influence of the structuring technology and the process parameters on the resulting structure properties and the part performance allows conclusions regarding the optimisation of the part functionality via a suitable selection and design of the process.

Experimental Analysis for Jet Noise Reduction of Chevron Pylon-Based Nozzles

The experimental analysis is conducted for jet noise reduction of separate flow chevron pylon-based nozzles at takeoff condition. The experimental results indicate that the pylon makes a noise reduction at low-frequency but produces an increase at high-frequency, together with an overall sound pressure reduction below the pylon. Compared to chevron nozzle without pylon, the adding of a pylon reduces noise benefit of chevron nozzles found in the isolated nozzle without a pylon. The best low-frequency noise reduction is located below the pylon where peak noise reduction is as high as about 1.3dB on frequency spectrum.

Reduction of Low-Frequency Noise in Tunneling-Magnetoresistance Sensors With a Modulated Magnetic Shielding

The high-noise level at low frequency in magnetic tunnel junction (MTJ) sensors is the key problem for their applications in measuring the low values of static magnetic field. In this paper, we investigated a shielding-type flux chopper to resolve the 1/f noise issue. By the using a cylindrical chopper with its axis perpendicular to the sensing direction of MTJ sensor, the noise at 1 Hz was reduced from 4 to 0.3 nT/√Hz by chopping the magnetic flux at 5 kHz. The reduction in noise can be qualitatively explained by the 1/f behavior and the chopping efficiency. The proposed method is promising in enhancing the detectivity of MTJ sensor for sensing the static geomagnetic field.

Implement an Indoor Low Frequency Noise Reduction System Based on FXLMS Algorithm

In order to solve the hazards of indoor low-frequency noise on the human body, the low-frequency noise reduction system is designed for a confined space by using the active control theory, and the process of adaptive noise elimination is achieved through the FX-LMS algorithm. The system hardware is integrated with the sound sensor, the complex programmable logic devices, the digital to analog converter and micro control unit to build the core circuit. Furthermore, the processing software of noise reduction is implemented by the FXLMS. Through the system test, the result shows that the noise reduction system can effectively reduce the low frequency noise intensity in the confined space.

Multilayer-split-tube resonators with low-frequency band gaps in phononic crystals

In this paper, low-frequency band gaps in two-dimensional Helmholtz resonant phononic crystals (PCs) composed of multilayer-split-tube resonators are investigated. The band structures, transmission spectra, and pressure field of the acoustic modes of these PCs are calculated by using a finite element method (FEM). The numerical results show that the first band gap of the structure is from 88 to 140 Hz. The transmission spectra are in accordance with those of the dispersion relation calculations. The acoustic modes of the bands are analyzed to reveal the nature of this phenomenon. It is found that the interaction between the local resonance and the traveling wave modes in proposed structure is responsible for the formation of the first band gap. The influences of the structural parameters on the band gaps are investigated by using FEM and the electrical circuit analogy. Numerical results show that the band gaps can be modulated in an even wider frequency range by changing the structural parameters, such as the rotation angle, the number of tubes, and the radius of the outer tube. The structural design results provide an effective way for phononic crystals to obtain the low-frequency band gaps, which have potential application in the low-frequency noise reduction.

Investigation of Low-Frequency Noise in p-type Nanowire FETs: Effect of Switched Biasing Condition and Embedded SiGe Layer

The low-frequency noise (LFN) of a p-type nanowire FET (p-NWFET) was characterized and compared with that of an n-type NWFET (n-NWFET) in terms of dominant noise source and its location in the channel region. An inverse proportional dependence of the noise level on channel diameter was observed in the p-NWFET but not in the n-NWFET. The LFN was observed to be mainly generated by Hooge mobility fluctuation in the p-NWFET. Under a switched biasing condition, p-NWFET showed no substantial LFN reduction (in contrast to the n-NWFET), indicating that the carrier number fluctuation was insignificant. This was due to the compressive stress induced by embedded SiGe with heavier transverse effective hole mobility.

(Invited) Planar Field Effect Transistor Biosensors: Toward Single Molecular Detection and Clinical Applications

In this research, a recessed gate AlGaN/GaN heterojunction field effect transistor (HFET) is demonstrated for biodetection sensitivity improvement. The measurements are performed on a zero-bias gate configuration to eliminate the noise and electrochemical activities from the gate electrode. A detection limit in terms of the concentration is demonstrated at 16 aM on a gate-recessed AlGaN/GaN bioHFET for streptavidin (SA) detection. The reduction of low frequency noise contributes to the signal to noise ratio (SNR) improvement. The recessed AlGaN/GaN bioHFETs have also been characterized in direct detection of biomarkers in physiological fluids at low concentrations for early-stage transplant rejection diagnostics. The electrical measurement results from recessed AlGaN/GaN bioHFETs are consistent with the patients’ clinical behavior.

A robust numerical approach for prediction of turbofan engine noise

Noise from the aircraft jet engines is still the dominant source in takeoff condition. Government regulations of community noise are getting more stringent, creating significant challenges for aircraft manufacturers to meet these requirements. Expensive nature of experiments as well as accessing to powerful computers have provided new impetus for computational studies. In this paper, an efficient and robust numerical scheme, namely the Lattice Boltzmann Method was used to simulate the sound created by typical internal mixing nozzles with forced mixers. The simulation includes capturing the time-resolved flow characteristics and large scale turbulent structures. The sub grid scales were modeled using the renormalization group (RNG) forms of the standard k-ε equations. Several test cases including cold and hot core flow experiments conducted by NASA were selected for computational setup and validation purposes. The far field sound was predicted using a surface integral method. The near-field simulation results such as the jet centerline velocity decay and turbulence intensities as well as far-field sound were qualitatively in agreement with experimental results. The far-field sound analysis suggested significant low-frequency noise reduction for the lobed mixers, as well as significant reduction in overall sound pressure level (OASPL) in comparison with the simple confluent nozzle configurations.

Low-frequency locally resonant band-gaps in phononic crystal plates with periodic spiral resonators

In this paper, low-frequency band-gaps (BGs) in a phononic crystal (PC) thin plate with periodic spiral resonators are investigated numerically and experimentally. The formation mechanisms of the BGs in the proposed structure are explained based on the modal analysis. We find that the interaction between the local resonances and the traveling wave modes in the plate is responsible for the formation of the BG in low-frequency range. This interaction strength greatly affects the bandwidth of the BG, of which the lower edge depends on the corresponding local resonance frequency. It is shown that the out-of-plane BG can be modulated by changing the geometrical parameters. The proposed PC plate is demonstrated to possess a broad out-of-plane BG in low-frequency range from 42 Hz to 150 Hz, by combining the numerical calculations with experimental measurements. The structure design and its results provide an effective way for phononic crystals to obtain broad BGs in low-frequency range, which has potential applications in the low-frequency vibration and noise reduction.

J045073 圧電吸音板のLR回路による周波数調整([J045-07]知的材料・構造システム(7))

This paper proposes a frequency tuning method of the piezoelectric sound absorbing panel. The piezoelectric elements on the panel shunted with an inductance and a resistance work like a dynamic vibration absorber. The sound absorbing panel transforms sound energy into the vibration energy, and this vibration energy is dissipated through the resistance using electrical resonance. Because the piezoelectric sound absorbing panel has high sound absorption coefficient around its natural frequency, this method can be used for low-frequency noise reduction. However, the frequency at which the sound absorption coefficient becomes 1 was automatically determined in the method proposed in the previous research. Therefore, this paper proposes the frequency tuning method of the piezoelectric sound absorbing panel using the LR circuit. The governing equations were theoretically derived, and the optimum values of the LR circuit were formulated. Theoretical analysis was validated through simulations and experiments.

Onset and universality of turbulent drag reduction in von Karman swirling flow

We report the results of experiments on turbulent drag reduction (TDR) in swirling flow of water and water-sucrose polymer solutions, where Re and Wi as well as polymer concentration ϕ are varied. The friction coefficients Cf and Cp defined through average torque and rms of pressure fluctuations prms for different elasticity El = Wi/Re and ϕvs.Re/Rec collapse onto universal curves in accord with theory, where Rec is Re at TDR onset. The transition lines to the TDR state, Rec − El and Rec − ϕ, are measured and relevant physics is discussed. Power spectra for Γ and p at Re/Rec > 1 show a drastic reduction of low-frequency noise and the emergence of a peak corresponding to the main vortex frequency in accord with TDR.

Extremum-Seeking Control of Jet Noise

An extremum-seeking algorithm is used to optimise a fluidic jet-noise controller. The control device, called a fluidevron, produces reductions in jet noise that are comparable with those achieved using conventional microjets, but the underlying flow-physics have been found to be different (Laurendeau et al. [1]). The extremum-seeking algorithm is used to optimise the control either for maximum low-frequency noise-reduction, or for maximum overall noise-reduction. This is achieved through a specification of the frequency-range over which noise reduction is sought. The extremum-seeking performs well, producing integrated low-frequency noise reduction gains on the order of 2.5 dB at 60 degrees (angle measured with respect to the dowstream jet axis) when tuned for maximum low-frequency benefit, and an overall reduction of 1.5 dB, where the high frequency penalty is virtually eliminated, when tuned for maximum spectral range. Farfield microphone spectra at different polar stations show that the control effect is omnidirectional. This implies that there is no directional bias in the response of the source mechanisms to the actuation. Finally, the relationship between noise reduction and flow-rate is studied and found to be non-linear. The source mechanisms are most receptive at low flow-rate, a saturation point being reached after which the actuation no longer has control authority over the source dynamics.

Comparative Study of Biaxial and Uniaxial Mechanical Stress Influence on the Low Frequency Noise of Fully Depleted SOI nMOSFETs Operating in Triode and Saturation Regime

This paper presents an experimental comparative study of uniaxial and biaxial strain techniques influence on the low frequency noise of planar fully depleted SOI nMOSFETs operating in linear and saturation regimes. The comparison between devices from the same technology with these two strained techniques demonstrated a reduction of low frequency noise for devices with both strain technologies in linear regime for shorter devices (below 410 nm). In saturation regime the reduction of low frequency noise for uniaxial and biaxial strain also occurs, but does not depend on the channel length, and the reduction of low frequency noise in favor of both strain technologies is more pronounced for channel length of 160 nm.