scholarly journals Dynamic frequency-noise spectrum measurement for a frequency-swept DFB laser with short-delayed self-heterodyne method

2015 ◽  
Vol 23 (22) ◽  
pp. 29245 ◽  
Author(s):  
Qian Zhou ◽  
Jie Qin ◽  
Weilin Xie ◽  
Zhangweiyi Liu ◽  
Yitian Tong ◽  
...  
Keyword(s):  
Noise Spectrum ◽  
Frequency Noise ◽  
Heterodyne Method ◽  
Spectrum Measurement ◽  
Dfb Laser ◽  
Dynamic Frequency

scholarly journals Estimation of the Laser Frequency Noise Spectrum by Continuous Dynamical Decoupling

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Manchao Zhang ◽  
Yi Xie ◽  
Jie Zhang ◽  
Weichen Wang ◽  
Chunwang Wu ◽  
...  
Keyword(s):  
Noise Spectrum ◽  
Laser Frequency ◽  
Frequency Noise ◽  
Dynamical Decoupling

scholarly journals Numerical and experimental analyses of intake silencer and its effects on turbocharger compressor performance

2019 ◽  
Vol 11 (3) ◽  
pp. 168781401982667 ◽  
Author(s):  
Chen Liu ◽  
Yipeng Cao ◽  
Yang Liu ◽  
Wenping Zhang ◽  
Pingjian Ming ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Transmission Loss ◽  
Pressure Ratio ◽  
Pressure Fluctuations ◽  
Noise Spectrum ◽  
Acoustic Mode ◽  
Frequency Noise ◽  
Reduced Pressure ◽  
Compressor Rotor ◽  
Compressor Performance

Numerical studies of a marine diesel engine intake silencer are conducted to evaluate its performance, and effects of the silencer on the turbocharger compressor performance are also discussed. The results show that the duct acoustic mode method can be used in the silencer transmission loss prediction, and the predicted noise reduction and main frequency range agree with the measurements fairly well. However, it is found that the silencer compromises the compressor performance by shortening its operating range. It is found that the static pressure on the compressor blade surface is decreased, thus the compressor total-to-total pressure ratio and isentropic efficiency are reduced. Pressure fluctuations at compressor rotor and stator inlets enhanced when a silencer is installed, which means the trend of pressure spectrum in the rotor and stator passage is changed. Compared with the results of a compressor in natural aspiration, it is found that the silencer can significantly reduce high-frequency noise. In particular, it is quite effective in tonal noise reduction. In addition, the compressor inlet noise spectrum indicates that noise radiation characteristics are different with a silencer installed.

scholarly journals High-Resolution Seafloor Absolute Pressure Gauge Measurements Using a Better Counting Method

2016 ◽  
Vol 33 (9) ◽  
pp. 1859-1874 ◽  
Author(s):  
Spahr C. Webb ◽  
Scott L. Nooner
Keyword(s):  
High Frequency ◽  
Frequency Standard ◽  
Noise Spectrum ◽  
Interval Length ◽  
Absolute Pressure ◽  
Frequency Noise ◽  
Counting Method ◽  
Iir Filter ◽  
Quartz Oscillator ◽  
Number Of Cycles

AbstractVibrating quartz force transducers are the critical component of most deep-sea pressure and depth gauges in use in oceanography, producing a frequency output that varies with pressure. Accurate and low drift pressure measurements can be obtained by precisely measuring this frequency. In most implementations, the frequency is determined by counting the number of cycles of a high-frequency standard oscillator occurring during a large number of cycles of the lower-frequency quartz force oscillator. Resolution is limited by the sampling interval (length of counting) and the frequency of the frequency standard. Alternative counting methods can provide significant (20–40 dB) improvements in resolution at sampling rates above 1 Hz. Each counting method can be described as a different filter applied to the output of a counter of the frequency standard gated at each transition of the transducer quartz oscillator. Improvements in resolution can be understood as the result of minimizing the aliasing of higher-frequency counting noise into the spectrum below the Nyquist frequency. A simple multipole infinite impulse response (IIR) filter designed to limit spectral leakage of high-frequency noise minimizes the noise spectrum and thereby optimizes the resolution of the pressure output. The resultant noise spectrum rises as frequency squared above 1 Hz, independent of the sampling rate. At frequencies below 1 Hz, it is limited by noise in the electronics driving the force transducer quartz oscillator. Resolution increases with frequency of the frequency standard up to about 200 MHz, plateauing for higher frequencies due to other noise sources (likely electronic).

Noise Test and Countermeasures Research of Locomotive Cab

2011 ◽  
Vol 317-319 ◽  
pp. 1197-1200
Author(s):  
Yan Liu ◽  
Wen Liu ◽  
Bing Yang ◽  
Xiao Pai Zhang ◽  
Ping Zhang ◽  
...  
Keyword(s):  
Low Frequency ◽  
Good Health ◽  
Electrical Equipment ◽  
Intermediate Frequency ◽  
Noise Spectrum ◽  
Channel Noise ◽  
Frequency Noise ◽  
Frequency Range ◽  
Noise Test ◽  
Analysis System

The locomotive cab noise has became an important factor in good health of the drivers through analyzing noise hazards of the locomotive cab, and the noise also can reduce working efficiency, easy to produce hidden trouble on security. Use Multi-channel Noise Test and Analysis System, measure the locomotive cab noise and analyze the results of the noise test, then get the conclusions from the noise spectrum: Locomotive cab noise occurs mainly in the low frequency range and intermediate frequency range; Wheel-rail noise and cooling room noise mainly are low frequency noise; Electrical equipment of the first locomotive cab contribute a major noise. Results of this study provide the basis for the vibration and noise reduction design of the locomotive cab.

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