Broadband Noise Suppression Research Articles

All-polarization-maintaining divided pulse fiber oscillator mode-locked with the optical Kerr effect.

In this Letter, we investigate a Yb-doped mode-locked fiber oscillator that uses coherent pulse division and recombination to avoid excessive nonlinear phase shifts. The mode locking mechanism of the laser is based on the accumulation of a differential nonlinear phase between orthogonal polarization modes in the polarization-maintaining fiber segment. The inserted coherent pulse divider, based on YVO4 crystals rotated successively by 45°, enables stable and undistorted mode-locked steady states. The output pulse energy is increased from 89 pJ in the nondivided operation by ≈6.5 dB to more than 400 pJ with three divisions. A measurement of amplitude fluctuations reveals a simultaneous broadband noise suppression of up to ≈9 dB in the frequency range from 10 kHz to 2 MHz.

Level-set based topology optimization on acoustic balcony ceiling design of a simplified urban building for noise reduction.

Balconies can provide noise shielding for residents who live in high-rise apartment buildings. The efficiency of noise reduction induced by a balcony largely depends on the shape of the balcony ceiling. This study aims to optimize the shape of the ceiling of a two-dimensional simplified urban building to enhance noise mitigation by using level-set based topology optimization, which is capable of providing a distinct and smooth interface. Noise sources at both single and multi-frequency optimization are considered. In the single-frequency optimization, two peak frequencies in the spectrum of sound pressure level (SPL) at receivers on the fourth floor of an ordinary ceiling are selected. Results show that significant SPL reduction is attained by the optimized ceiling. In addition, broadband noise suppression at frequencies above the target value is also achieved. The underlying mechanism is that the optimized ceiling consisting of several concaves can redirect the incident wave propagating away from the balcony and effectively avoid forming a trapped mode within the area between the floor and the ceiling. Additionally, more effective noise reduction is achieved by the multi-frequency optimization. Thus, the proposed design strategy can be widely used in various applications of noise reduction in the field of building and environment.

Maze-like acoustic metamaterial for low-frequency broadband noise suppression

We propose the maze-like acoustic metamaterial (MLAMM) unit suitable for regulating the transformer noise. The influence of the length and width of the acoustic waveguide on the sound transmission loss (TL) is studied, and the TL and resonance frequencies of the MLAMM unit are calculated. The visco-thermal effect weakens the resonance transmission peak of the MLAMM unit. Finally, experiments verify that the proposed MLAMM unit has low-frequency broadband sound insulation performance, and the TL is about 25 dB in the frequency band of 100 Hz–500 Hz. The research provides a reasonable and effective solution for noise suppression of transformers.

Broadband Noise Suppression of Stationary Clocked DC/DC Converters by Injecting Synthesized and Synchronized Cancellation Signals

Active cancellation of disturbing signals is a common method in electromagnetic compatibility (EMC) of power electronic systems. In this paper, a new method of suppressing periodic disturbances is extended and applied. In this method, the disturbing harmonics are suppressed by a synthesized cancellation signal that is synchronized with the converter's operation. Here, the cancellation signal is synthesized from a number of destructive sine waves. The appropriate amplitudes and phases are found via a convenient and robust adaptive approach. As a special feature of this method, many troublesome effects, like delays or complex frequency characteristics, can be compensated easily. Therefore, this method does not suffer from the same limitations as previous active techniques. Until now, the method has only been proven for a small number of harmonics. In this study, it is applied to a wide frequency range of 150 kHz to 30 MHz of a 48-/12-V dc/dc converter, e.g., for automotive applications. An optimization strategy is developed from a causal model of the system. A test setup is realized, and the sensor's and injector's performances are discussed regarding the automotive EMC standard CISPR 25. Measurement results for the artificial network and the antenna are presented. The additional power losses are estimated.

Broadband noise suppression and feature identification of ECG waveforms using mathematical morphology and embedding theorem

The paper presents an adaptive morphological filter developed using multiscale mathematical morphology (MM) to reject broadband noise from ECG signals without affecting the feature waveforms. As a pre-processing procedure, the adaptive morphological filter cleans an ECG signal to prepare it for further analysis. The noiseless ECG signal is embedded within a two-dimensional phase space to form a binary image and the identification of the feature waveforms is carried out based on the information presented by the image. The classification of the feature waveforms is implemented by an adaptive clustering technique according to the geometric information represented by the image in the phase space. Simulation studies on ECG records from the MIT-BIH and BIDMC databases have demonstrated the effectiveness and accuracy of the proposed methods.

Postnatal maturation of contralateral DPOAE suppression in a precocious animal model (chinchilla) of the human neonate

Conclusion: In the neonatal chinchilla, the degree of contralateral distortion product otoacoustic emission (DPOAE) suppression and the latency and time constants of suppression are immature for 40–60 days. This suggests that olivocochlear efferent innervation of outer hair cells is not fully mature at birth in this animal model, and this may also be the case for human neonates. Objectives: To track postnatal changes in the dynamics of the olivocochlear efferent system in an animal model with cochlear development at birth similar to that in humans. Methods: Real-time measurements of contralateral DPOAE suppression were made in 79 ears of anaesthetized chinchillas, ranging in age from 1 day to 70 days. An adult control group (13 ears) was also tested. DPOAE (2f1-f2; f2 = 4.4 kHz; f2/f1 = 1.22) input/output functions were measured. Dynamics of contralateral broadband noise suppression were measured, including latency and suppression time constants. Results: DPOAE amplitude input/output functions are immature until 20–30 days postnatally. The maturation period for contralateral suppression amplitude is about 30 days. Latency of onset suppression was 40 ms at birth reducing to adult values (23 ms) at 40 days. The DPOAE suppression time constant was about 350 ms at birth and mature (230 ms) at 60 days.

Continuous production of glass-coated microwires and the applications for broadband noise suppression composite sheets

A system and a method were developed for continuous production of glass-coated microwires with controllable glass thickness and metallic core diameter. Fe–Si–Al flakes were fabricated by planetary ball milling using ethanol as a dispersant. A composite noise suppression sheet was prepared with glass-coated microwires combined with Fe–Si–Al flakes. The characteristics of the conduction noise suppression of the composite sheet were evaluated on a microstrip line in gigahertz frequencies. The conduction electromagnetic noise was effectively suppressed by the composite sheet in broad-band frequency region; the power loss is greater than 70% in the frequency range from 0.7 to 8.5GHz.

Stable and Efficient Generation of High Repetition Rate ($>$160 GHz) Subpicosecond Optical Pulses

A stable optical beat-signal with frequency >; 160 GHz is produced by injection-locking two narrow-linewidth semiconductor lasers emitting at frequencies spaced by the beat-frequency to a low-jitter 10-GHz optical comb. The generated beat-signal with broadband noise suppression of >; 75 dB is temporally compressed by factors of up to four in a high stimulated Brillouin scattering threshold aluminosilicate highly nonlinear fiber. The generated subpicosecond pulses have a root mean square (rms) timing jitter below 150 fs measured over 1 s.

Suppression of broadband noise radiated by a low-speed fan in a duct

Attenuation of ducted fan noise remains a technical challenge in the low frequency range as traditional duct lining becomes ineffective. This study proposes a reactive method to suppress the sound radiation from an axial-flow fan. The method is particularly effective in the low frequency region and covers a broad band. Its effect is derived from two mechanisms. One is the reduction in the confining effects of duct walls when the duct radius is increased; the other is the acoustic interference between the direct radiation from the fan and reflections by the duct junctions. This interference is always destructive for axial dipoles when the frequency approaches zero. This performance differs from normal passive control methods, which become totally ineffective toward zero frequency. An approximate plane-wave theory explains the essential physics of the method, and its quantitative prediction is found to agree well with a full numerical simulation using a spectral method of Chebyshev collocation. The latter is validated by experiment using an axial-flow fan in a duct of finite length. Broadband noise reduction is achieved while the flow speed is kept unchanged. Practical difficulties of implementation for a fan with high pressure increase are discussed.

Suppression of broadband noise at mode locking in driven vortex matter

We measure voltage noise generated by current-driven vortices for fields corresponding to the solid phase when at equilibrium including the peak-effect regime, focusing on a change in broadband noise (BBN) as the vortex system undergoes a mode-locking (ML) resonance. For all the fields steplike structure indicative of ML is observed in the $I\text{\ensuremath{-}}V$ curves. We find that BBN at high frequencies (but well below the ac drive frequency) is suppressed inside the ML steps. The results are consistent with the view that the mode-locked state is a frozen solid pinned in the moving frame of reference.

Role of the efferent medial olivocochlear system in contralateral masking and binaural interactions: an electrophysiological study in guinea pigs.

Contralateral broadband noise (BBN) elevates ipsilateral auditory thresholds (central masking) and reduces the amplitude of ipsilateral brainstem auditory evoked potentials (BAEPs). Binaural interactions are complex psychophysical phenomena, but binaural interaction components are easily extracted from BAEPs to monaural versus binaural click stimulation. However, contralateral, or binaural, acoustical stimulation is known to activate simultaneously the crossed and uncrossed medial olivocochlear (MOC) efferent systems and decrease activity in both cochleas. Particularly, contralateral BBN stimulation suppresses in part ipsilateral peripheral activity. What is the role of such contralaterally induced peripheral suppression in the overall changes in central BAEPs observed during contralateral masking or binaural stimulation? Compound action potentials (CAPs) of the auditory nerve and BAEPs were recorded simultaneously in awake guinea pigs from electrodes chronically implanted on the round window of the cochlea and the surface of the brain. Peripheral and central measures of contralateral masking and binaural interactions were obtained from responses to monaural or binaural clicks, with or without contralateral BBN, recorded before, during, and after the reversible blockade of the MOC function following a single intramuscular injection of gentamicin. Contralateral BBN effectively reduced the amplitudes of CAP and of all BAEP peaks. CAP to ipsilateral click did not, however, change significantly from monaural to binaural click stimulation; still, normal binaural interaction components developed in the BAEPs. When the medial efferent function was blocked by gentamicin, the normal contralateral BBN suppression of CAP and of the earliest BAEP peak was lost; however, the later BAEP peaks were suppressed by contralateral BBN as before gentamicin, and the central binaural interaction components were unchanged. In these experimental conditions, the MOC efferent system seems to play little role in centrally recorded contralateral masking and binaural interactions.

Distributed balanced photodetectors for broad-band noise suppression

A novel velocity-matched distributed balanced photodetector with a 50-/spl Omega/ coplanar waveguide output transmission line has been experimentally demonstrated in the InP/InGaAs material system. Distributed absorption and velocity matching are employed to increase the saturation photocurrent. A common-mode rejection ratio greater than 27 dB has been achieved. The radio-frequency (RF) link experiment conducted at 4.16 GHz shows that the relative intensity noise of the laser has been suppressed by more than 24 dB and shot-noise limited performance has been achieved. Significant improvement of signal-to-noise ratio has been observed over a wide range of frequencies and phase mismatch of input RF signals.

Diagnostic Evaluation of Jet Noise Suppression Mechanisms

A unified aeroacoustic jet noise prediction method has been developed based on the modeling of principal noise generation and emission mechanisms from first principles. It is demonstrated herein that this jet noise prediction method is a useful diagnostic tool for assessing the relative importance of the various mechanisms for a given nozzle type. The relative contributions of 1) turbulent mixing noise suppression, 2) shock-cell broadband noise suppression, 3) convective amplification suppression, and 4) fluid shielding attenuation have been evaluated for a high element number multichute suppressor to arrive at a plausible explanation for how multielement suppressors suppress jet noise. This explanation, an alternative view to historical conceptions of jet noise suppression, suggests an approach to designing low noise suppressor nozzles.