Low-frequency noise control using layered granular aerogel and limp porous media

2021 ◽  
Vol 263 (4) ◽  
pp. 2724-2729
Author(s):  
Yutong Xue ◽  
Amrutha Dasyam ◽  
J. Stuart Bolton ◽  
Bhisham Sharma
Keyword(s):  
Noise Control ◽  
Glass Fibers ◽  
Low Frequency ◽  
Normal Incidence ◽  
Frequency Noise ◽  
Fibrous Materials ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Fibrous Media ◽  
Impedance Tube Method

The acoustic absorption of granular aerogel layers with a granule sizes in the range of 2 to 40 μm is dominated by narrow-banded, high absorption regions in the low-frequency range and by reduced absorption values at higher frequencies. In this paper, we investigate the possibility of developing new, low-frequency noise reduction materials by layering granular aerogels with traditional porous sound absorbing materials such as glass fibers. The acoustic behavior of the layered configurations is predicted using the arbitrary coefficient method, wherein the granular aerogel layers are modeled as an equivalent poro-elastic material while the fibrous media and membrane are modeled as limp media. The analytical predictions are verified using experimental measurements conducted using the normal incidence, two-microphone impedance tube method. Our results show that layered configurations including granular aerogels, fibrous materials, and limp membranes provide enhanced sound absorption properties that can be tuned for specific noise control applications over a broad frequency range.

scholarly journals Low Frequency Noise Remove from EEG Signal

2020 ◽  
Vol 9 (1) ◽  
pp. 1510-1513
Keyword(s):  
Human Brain ◽  
Random Noise ◽  
Low Frequency ◽  
Frequency Noise ◽  
Eeg Signal ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Average Value ◽  
Different Types ◽  
The Brain

The electrical activity of the brain recorded by EEG which used to detect different types of diseases and disorders of the human brain. There is contained a large amount of random noise present during EEG recording, such as artifacts and baseline changes. These noises affect the low -frequency range of the EEG signal. These artifacts hiding some valuable information during analyzing of the EEG signal. In this paper we used the FIR filter for removing low -frequency noise(<1Hz) from the EEG signal. The performance is measured by calculating the SNR and the RMSE. We obtained RMSE average value from the test is 0.08 and the SNR value at frequency(<1Hz) is 0.0190.

Low Frequency Absorption of Additively Manufactured Cylinders

2019 ◽  
Author(s):  
Sophie R. Kaye ◽  
Ethan D. Casavant ◽  
Paul E. Slaboch
Keyword(s):  
Low Frequency ◽  
Normal Incidence ◽  
Frequency Noise ◽  
Outer Diameter ◽  
Acoustic Absorption ◽  
Frequency Range ◽  
Large Space ◽  
Low Frequencies ◽  
Cylinder Length ◽  
Hollow Cylinders

Abstract Attenuating low frequencies is often problematic, due to the large space required for common absorptive materials to mitigate such noise. However, natural hollow reeds are known to effectively attenuate low frequencies while occupying relatively little space compared to traditional absorptive materials. This paper discusses the effect of varied outer diameter, and outer spacing on the 200–1600 Hz acoustic absorption of additively manufactured arrays of hollow cylinders. Samples were tested in a 10 cm diameter normal incidence impedance tube such that cylinder length was oriented perpendicular to the incoming plane wave. By varying only one geometric element of each array, the absorption due to any particular parameter can be assessed individually. The tests confirmed the hypothesis that minimizing cylinder spacing and maximizing cylinder diameter resulted in increased overall absorption and produced more focused absorption peaks at specific low frequencies. Wider cylinder spacing produced a broader absorptive frequency range, despite shifting upward in frequency. Thus, manipulating these variables can specifically target absorption for low frequency noise that would otherwise disturb listeners.

Impact of Proton Irradiation on Power 4H-SiC MOSFETs

2020 ◽  
Vol 1004 ◽  
pp. 1074-1080
Author(s):  
Alexander A. Lebedev ◽  
Vitalii V. Kozlovski ◽  
Leonid Fursin ◽  
Anatoly M. Strel'chuk ◽  
Mikhail E. Levinshtein ◽  
...  
Keyword(s):  
Proton Irradiation ◽  
Removal Rate ◽  
Low Frequency ◽  
Frequency Noise ◽  
Electrical Characteristics ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Maximum Value ◽  
Noise Spectroscopy ◽  
Noise Density

Impact of 15 MeV proton irradiation on electrical characteristics and low frequency noise has been studied in high-power vertical 4H-SiC MOSFETs of 1.2 kV-class at doses 1012 £ F £ 1014 cm-2. The maximum value of the field-effect mobility µFЕ depends weakly on F up to F = 2×1013 cm-2. At F = 4×1013 cm-2, the character of the µFЕ(Vg) dependence changes radically. The maximum µFЕ decreases approximately threefold. The dose Fcr corresponding to the complete degradation of the device is about 1014 cm-2. It can be estimated as Fcr» he/n0, where he is the electron removal rate and n0 is the initial electron concentration in the drift layer. In the entire frequency range of analysis f, gate voltages, and drain-source biases, the frequency dependence of the current spectral noise density SI(f) follows the law SI ~ 1/f. From the data of noise spectroscopy, the density of traps in the gate oxide Ntv has been estimated. In non-irradiated structures, Ntv » 5.4×1018 cm-3eV-1. At Ф = 6×1013 cm-2, the Ntv value increases to Ntv » 7.2×1019cm-3eV-1. The non-monotonic behavior of the output current Id and the level of low frequency noise on dose F has been demonstrated.

RESEARCH AND MAPPING OF LOW FREQUENCY NOISE GENERATED BY POWER PLANTS OF INDUSTRIAL ENTREPRISES

Akustika ◽  
2021 ◽  
pp. 103
Author(s):  
Andrey Vasilyev
Keyword(s):  
Power Plants ◽  
Low Frequency ◽  
Environmental Noise ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Frequency Range ◽  
Noise Mapping ◽  
Industrial Enterprises ◽  
Noise Measurements ◽  
Urban Territory

Environmental noise level from industrial enterprises is constantly increasing, especially in low frequency range. This paper presents the results of research and mapping of low frequency noise generated by power plants of industrial enterprises. Environmental noise mapping results of urban territory of Samara region of Russia are also presented. Results of noise measurements during industrial enterprises operation (on the example of “KuibyshevAzot” company) are showing that in some measuring points there were exceeding values compared with Russian sanitary norms requirements. The most serious problem is low frequency noise impact.

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