Investigations on the Equivalent Magnetic Noise of Magneto(Elasto)Electric Sensors by Using Modulation Techniques

The equivalent magnetic noise of the magnetoelectric (ME) layered composite sensors has been investigated for various modulation techniques. The ME thin film response to an electric modulation or a magnetic modulation can be sensed by using either a charge amplifier or a coil wound around the sample and then demodulated by a synchronous detector. The equivalent magnetic noise for these excitations methods has been compared. As expected, the low-frequency fluctuations can be lowered when the magnetoelectric sensor is operated in a modulation mode. Results show that these methods can give the same level of equivalent magnetic noise for a certain strain-excitation. In theory, mechanical noise appears as the only dominant noise source after the demodulation process in the case of a certain strong amplitude excitation carrier signal. By using these modulation techniques, an equivalent magnetic noise level of 10-100 pT/Hz at 1 Hz was achieved with DC capability.

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Noise source location and scaling of subsonic upper-surface blowing

International Journal of Aeroacoustics ◽

10.1177/1475472x20930652 ◽

2020 ◽

Vol 19 (3-5) ◽

pp. 191-206

Author(s):

Trae L Jennette ◽

Krish K Ahuja

Keyword(s):

Strouhal Number ◽

Noise Source ◽

Low Frequency ◽

Directivity Pattern ◽

Source Location ◽

Dipole Source ◽

Frequency Noise ◽

Noise Sources ◽

Trailing Edge ◽

Trailing Edge Noise

This paper deals with the topic of upper surface blowing noise. Using a model-scale rectangular nozzle of an aspect ratio of 10 and a sharp trailing edge, detailed noise contours were acquired with and without a subsonic jet blowing over a flat surface to determine the noise source location as a function of frequency. Additionally, velocity scaling of the upper surface blowing noise was carried out. It was found that the upper surface blowing increases the noise significantly. This is a result of both the trailing edge noise and turbulence downstream of the trailing edge, referred to as wake noise in the paper. It was found that low-frequency noise with a peak Strouhal number of 0.02 originates from the trailing edge whereas the high-frequency noise with the peak in the vicinity of Strouhal number of 0.2 originates near the nozzle exit. Low frequency (low Strouhal number) follows a velocity scaling corresponding to a dipole source where as the high Strouhal numbers as quadrupole sources. The culmination of these two effects is a cardioid-shaped directivity pattern. On the shielded side, the most dominant noise sources were at the trailing edge and in the near wake. The trailing edge mounting geometry also created anomalous acoustic diffraction indicating that not only is the geometry of the edge itself important, but also all geometry near the trailing edge.

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Estimation of the Noise Source Level of a Commercial Ship Using On-Board Pressure Sensors

Applied Sciences ◽

10.3390/app11031243 ◽

2021 ◽

Vol 11 (3) ◽

pp. 1243

Author(s):

Hongseok Jeong ◽

Jeung-Hoon Lee ◽

Yong-Hyun Kim ◽

Hanshin Seol

Keyword(s):

Noise Source ◽

Pressure Sensors ◽

Low Frequency ◽

Frequency Resolution ◽

Source Strength ◽

Recording Time ◽

Source Level ◽

The One ◽

Hydrophone Array ◽

Good Agreement

The dominant underwater noise source of a ship is known to be propeller cavitation. Recently, attempts have been made to quantify the source strength using on-board pressure sensors near the propeller, as this has advantages over conventional noise measurement. In this study, a beamforming method was used to estimate the source strength of a cavitating propeller. The method was validated against a model-scale measurement in a cavitation tunnel, which showed good agreement between the measured and estimated source levels. The method was also applied to a full-scale measurement, in which the source level was measured using an external hydrophone array. The estimated source level using the hull pressure sensors showed good agreement with the measured one above 400 Hz, which shows potential for noise monitoring using on-board sensors. A parametric study was carried out to check the practicality of the method. From the results, it was shown that a sufficient recording time is required to obtain a consistent level at high frequencies. Changing the frequency resolution had little effect on the result, as long as enough data were provided for the one-third octave band conversion. The number of sensors affected the mid- to low-frequency data.

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A Study on Exhaust Muffler Using Counter-Phase Counteract

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.986-987.810 ◽

2014 ◽

Vol 986-987 ◽

pp. 810-813

Author(s):

Ying Li Shao

Keyword(s):

Mathematical Model ◽

Experimental Validation ◽

Noise Source ◽

Low Frequency ◽

Frequency Noise ◽

Expansion Chamber ◽

Band Noise ◽

Exhaust Noise ◽

Perforated Pipe ◽

The Mathematical Model

The exhaust noise, which falls into low-frequency noise, is the dominant noise source of a diesel engines and tractors. The traditional exhaust silencers, which are normally constructed by combination of expansion chamber, and perforated pipe or perforated board, are with high exhaust resistance, but poor noise reduction especially for the low-frequency band noise. For this reason, a new theory of exhaust muffler of diesel engine based on counter-phase counteracts has been proposed. The mathematical model and the corresponding experimental validation for the new exhaust muffler based on this theory were performed.

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Characteristics of Low-Frequency Horizontal Noise of Ocean-Bottom Seismic Data

Seismological Research Letters ◽

10.1785/0220200349 ◽

2021 ◽

Author(s):

Chao An ◽

Chen Cai ◽

Lei Zhou ◽

Ting Yang

Keyword(s):

Water Waves ◽

Noise Source ◽

Random Noise ◽

Low Frequency ◽

Ocean Bottom ◽

Coherent Noise ◽

Infragravity Waves ◽

Low Frequencies ◽

Bottom Currents ◽

Ocean Bottom Seismographs

Abstract Horizontal records of ocean-bottom seismographs are usually noisy at low frequencies (< 0.1 Hz). The noise source is believed to be associated with ocean-bottom currents that may tilt the instrument. Currently horizontal records are mainly used to remove the coherent noise in vertical records, and there has been little literature that quantitatively discusses the mechanism and characteristics of low-frequency horizontal noise. In this article, we analyze in situ ocean-bottom measurements by rotating the data horizontally and evaluating the coherency between different channels. Results suggest that the horizontal noise consists of two components, random noise and principle noise whose direction barely changes in time. The amplitude and the direction of the latter are possibly related to the intensity and direction of ocean-bottom currents. Rotating the horizontal records to the direction of the principle noise can largely suppress the principle noise in the orthogonal horizontal channel. In addition, the horizontal noise is incoherent with pressure, indicating that the noise source is not ocean surface water waves (infragravity waves). At some stations in shallow waters (<300 m), horizontal noise around 0.07 Hz is found to be linearly proportional to the temporal derivative of pressure, which is explained by forces of added mass due to infragravity waves.

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A charge amplifier with noise peaking suppression and gain drop compensation utilizing a Quasi-Miller RC network

AEU - International Journal of Electronics and Communications ◽

10.1016/j.aeue.2019.05.029 ◽

2019 ◽

Vol 107 ◽

pp. 252-256

Author(s):

Zhen Gu ◽

Xiaojun Bi

Keyword(s):

Charge Amplifier ◽

A Charge

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Design and performances of a shielded liquid helium insert with an optically heated variable temperature stage for the study of low frequency magnetic noise inHTcsuperconductors

The European Physical Journal Applied Physics ◽

10.1051/epjap:2001134 ◽

2001 ◽

Vol 13 (3) ◽

pp. 225-228 ◽

Cited By ~ 2

Author(s):

X. Ridereau ◽

M. Lam Chok Sing ◽

D. Bloyet

Keyword(s):

Liquid Helium ◽

Variable Temperature ◽

Low Frequency ◽

Magnetic Noise

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The Effect of Airfoil Shape on Trailing Edge Noise

Journal of Theoretical and Computational Acoustics ◽

10.1142/s2591728518500202 ◽

2019 ◽

Vol 27 (02) ◽

pp. 1850020 ◽

Cited By ~ 1

Author(s):

Seongkyu Lee

Keyword(s):

Boundary Layer ◽

Noise Source ◽

Source Region ◽

Low Frequency ◽

Suction Side ◽

Frequency Noise ◽

Pressure Side ◽

Trailing Edge ◽

Trailing Edge Noise ◽

Naca0012 Airfoil

This paper investigates the effect of airfoil shape on trailing edge noise. The boundary layer profiles are obtained by XFOIL and the trailing edge noise is predicted by a TNO semi-empirical model. In order to investigate the noise source characteristics, the wall pressure spectrum is decomposed into three components. This decomposition helps in finding the dominant source region and the peak noise frequency for each airfoil. The method is validated for a NACA0012 airfoil, and then five additional wind turbine airfoils are examined: NACA0018, DU96-w-180, S809, S822 and S831. It is found that the dominant source region is around 40% of the boundary layer thickness for both the suction and pressure sides for a NACA0012 airfoil. As airfoil thickness and camber increase, the maximum source region moves slightly upward on the suction side. However, the effect of the airfoil shape on the maximum source region on the pressure side is negligible, except for the S831 airfoil, which exhibits an extension of the noise source region near the wall at high frequencies. As airfoil thickness and camber increase, low frequency noise is increased. However, a higher camber reduces low frequency noise on the pressure side. The maximum camber position is also found to be important and its rear position increases noise levels on the suction side.

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