High-frequency Noise Spectrum Research Articles

Empirical Rotor Broadband Noise Prediction Using CFD Boundary Layer Parameter Extraction

In this study, for small unmanned aerial vehicle aeroacoustic predictions, an in-house acoustic code was extended for broadband noise using the empirical Brooks–Pope–Marcolini (BPM) method. The acoustic code was coupled with a comprehensive analysis tool (FLIGHTLAB) or Reynolds-averaged Navier–Stokes (RANS) method to predict the noise from a DJI 9443 CF rotor. The effects of two input parameters of the BPM method on the broadband noise were investigated, including the effective angle of attack and boundary layer parameters. The empirical formula for the boundary layer parameters was replaced with predictions using two-dimensional RANS, allowing arbitrary airfoils other than NACA0012. The boundary layer parameters were also predicted using three-dimensional RANS to capture a three-dimensional flow effect, which can be dominant in modern propellers operating at high rotational speeds. As a result, the three-dimensional effect on the boundary layer was confirmed to conflict with the BPM method, which was developed based on a two-dimensional chordwise flow database. Finally, mid- and high-frequency noise spectra were predicted from the three-dimensional hybrid RANS/LES simulation to be combined with the BPM results, thus improving the noise spectra predictions at midrange frequencies.

Stabilizing and Improving Qubit Coherence by Engineering the Noise Spectrum of Two-Level Systems

Superconducting circuits are a leading platform for quantum computing. However, their coherence times are still limited and exhibit temporal fluctuations. Those phenomena are often attributed to the coupling between qubits and material defects that can be well described as an ensemble of two-level systems (TLSs). Among them, charge fluctuators inside amorphous oxide layers contribute to both low-frequency $1/f$ charge noise and high-frequency dielectric loss, causing fast qubit dephasing and relaxation. Moreover, spectral diffusion from mutual TLS interactions varies the noise amplitude over time, fluctuating the qubit lifetime. Here, we propose to mitigate those harmful effects by engineering the relevant TLS noise spectral densities. Specifically, our protocols smooth the high-frequency noise spectrum and suppress the low-frequency noise amplitude via depolarizing and dephasing the TLSs, respectively. As a result, we predict a drastic stabilization in qubit lifetime and an increase in qubit pure dephasing time. Our detailed analysis of feasible experimental implementations shows that the improvement is not compromised by spurious coupling from the applied noise to the qubit.

Influence of grid resolution on the spectral characteristics of noise radiated from turbulent jets: Sound pressure fields and their decomposition

Jet noise remains a key target for aircraft noise reduction in the foreseeable future. While being extremely challenging, the requirement of predicting both low and high frequency noise spectra is increasingly important for design purposes. Novel approaches are needed to overcome the current numerical limitations in capturing the required broad noise spectra. Once sufficiently resolved, the energy contents of the numerically simulated near- and far-field sound pressure have intrinsic correlations among different levels of grid resolution. The present work explores the novel potential of such correlations to broaden the spectral prediction. The noise radiated from high subsonic turbulent jets is investigated using large-eddy simulation. The 3-D filtered compressible Navier-Stokes solutions are obtained for an axisymmetric and a serrated nozzle on successively refined multi-resolution grids, ranging from 5 to 80 million grid points. The radiated far-field sound is computed using the Ffowcs Williams – Hawkings (FW-H) surface integral method. Fourier decomposition for pressure near-field is applied to help identify the location of the sound source regions and the dominant directions of propagation, which provides a more thorough understanding of the effect of the grid resolution on the numerical cut-off frequencies of the far-field spectra. Further analysis of the far-field spectra and of their azimuthal modes confirms that a novel strategy to obtain a broadened overall sound spectrum is possible, at reduced computational cost, from a combination of multiple spectra from successively refined grids.

Влияние волнообразного износа рельса на виброакустические характеристики при движении подвижного состава

According to the papers of the German and French specialists, the rail corrugation stimulates increasing the rail sound radiation intensity. Besides, the consideration of the rail corrugation actually explains the high-frequency noise spectrum. The rail corrugation is characterized by two key parameters — the corrugation amplitude and spacing. The corrugation occurrence leads to the high-frequency impact on the rail under the rolling stock operation, since the influence frequency represents motion speed/corrugation spacing ratio. Lagrange equations are used to define the force impact on the rail under the rolling stock operation. Rail vibration velocities are obtained from the differential equations of the bending oscillations for various methods of the rail laying: on the slab track, on timber and concrete sleepers. It is shown that the motion speed effects to a greater extent on the noise level increase involving the corrugation.

EFFECT OF GATE-ALL-AROUND TRANSISTOR GEOMETRY ON THE HIGH-FREQUENCY NOISE: ANALYTICAL DISCUSSION

By means of the Ramo–Shockley–Pellegrini theorem, an analytical discussion on how different geometries of gate-all-around 1D ballistic transistors affect their time-dependent current and their (intrinsic) high-frequency noise spectrum is presented. In particular, it is shown that the frequency range where the high-frequency noise spectrum is meaningful increases when the lateral area is decreased.

Relaxation processes in solid-state two-qubit gates

We consider a solid-state two-qubit gate subject to relaxation processes originated by transverse and longitudinal fluctuations of the single-qubit Hamiltonians. We model each noise component as a bosonic bath characterized by a specific power spectrum. We specialize our analysis to a i - SWAP gate implemented by Josephson qubits in a fixed coupling scheme. For high-frequency noise spectra extrapolated from single-qubit experiments we estimate the efficiency of the i - SWAP gate from the decay of anti-correlations between single-qubit switching probabilities.

Analytical model of high-frequency noise spectrum in Schottky-barrier diodes

We propose an analytical model for the high-frequency noise of Schottky-barrier diodes (SBD). The high-frequency spectrum is shown to be governed by collective motions of carriers in the neutral region of the SBD caused by the self-consistent electric field. The model is validated by comparison with Monte Carlo simulations of GaAs SBDs operating from barrier-limited to flatband conditions.

The Current Noise Spectrum of Copper-doped Germanium at 20 K

The current noise spectrum of copper-doped germanium has been measured from 30 c/s to 16 kc/s and from 5 Mc/s to 50 Mc/s. From the generation-recombination noise level, the capture cross section for holes by the ionized copper atoms is 8.1 × 10-14 cm2; the high frequency noise spectrum indicates that the carrier lifetime is single valued. In a suitably cleaned crystal no 1/f noise was observed above 30 c/s; excess 1/f noise occurred only when the surface of the crystal was contaminated with a metallic deposit, or a damaged surface layer was present.

Evaluation of Two Loudness Computational Procedures for Broad-Band Noises

Two loudness computational procedures for octave-band analyses of broad-band noises were examined in terms of their ability to predict equal-loudness adjustments. The first procedure employs the 1942 American Standard loudness function, pure-tone equal-loudness contours, and assumes complete additivity of loudness. The second procedure employs a slightly modified loudness function, octave-band noise equal-loudness contours, and assumes only partial additivity of loudness. The procedures were evaluated against equal-loudness adjustments between each of nine spectral noises and a wide-band “white” noise. The nine spectral noises were produced by passing white noise through a series of frequency emphasis, or tilting, circuits ranging from −12 db to +12 db per octave spectral tilt. The first procedure systematically overestimates the loudness of low-frequency noise spectra and underestimates the loudness of high-frequency noise spectra. A substantial portion of the systematic discrepancy of the first procedure is removed by re-evaluating the loudness of the highest noise frequencies (4.8 to 9.6 kc) in line with the octave-band noise contours. The second procedure avoids the systematic errors of the first procedure and substantially improves the over-all accuracy of loudness prediction—reducing the decibel error by about 2 to 1.

Range Extender for General Radio 760A Sound Analyzer

This attachment extends the range of the GR 760A sound analyzer to one megacycle by means of an oscillator and a tuned mixer which beat high frequency signals down to a frequency accepted by the analyzer. The apparatus is easily constructed, simple to operate, and has proved to be both reliable and flexible. This article describes the circuits and physical arrangements, and discusses the calibration and use of the attachment in the study of high frequency noise spectra.