This study proposes a valley-positioning-assisted discrete cross-correlation algorithm for the fast cavity length interrogation of fiber-optic Fabry-Perot (FP) sensors. Because the number of template cavity lengths th...
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This study proposes a valley-positioning-assisted discrete cross-correlation algorithm for the fast cavity length interrogation of fiber-optic Fabry-Perot (FP) sensors. Because the number of template cavity lengths that require to be cross-correlated with the spectral function of the FP sensor is dramatically decreased by considering the interference order and discretization of the template function, the computation amount can be effectively reduced without sacrificing the interrogating resolution. The feasibility and performance of the proposed algorithm were successfully verified through simulations and experiments. In the cavity length range of 20-130 mu m, fiber-optic FP sensors were successfully interrogated with high performance. The maximum error is 3.97 nm, and the resolution reaches a value of 2.62 nm.
Owing to the transverse wind, a laser beam drifts when transmitting in an atmospheric channel. The moving speed of the light spot image at the receiving end was deduced using cross-correlation algorithm. By establishi...
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Owing to the transverse wind, a laser beam drifts when transmitting in an atmospheric channel. The moving speed of the light spot image at the receiving end was deduced using cross-correlation algorithm. By establishing experiments with communication distances of 1.3 km and 100 km, the relationship between the transverse wind and the moving speed of the spot particle image on the optical transmission path was obtained. The results show that the correlation coefficients between the transverse wind and spot particle image moving speed are 0.92 and 0.83, respectively, which proves the feasibility of using the cross-correlation algorithm to obtain the transverse wind speed in atmospheric turbulence. And from this approach, the transverse wind speed and the wind vector moving image on the transmission path can be analyzed easily. (C) 2022 Society of Photo-Optical Instrumentation Engineers (SPIE)
An inductive debris sensor can monitor a mechanical system's debris in real time. The measuring accuracy is significantly affected by the signal aliasing issue happening in the monitoring process. In this study, a...
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An inductive debris sensor can monitor a mechanical system's debris in real time. The measuring accuracy is significantly affected by the signal aliasing issue happening in the monitoring process. In this study, a mathematical model was built to explain two debris particles' aliasing behavior. Then, a cross-correlation-based method was proposed to deal with this aliasing. Afterwards, taking advantage of the processed signal along with the original signal, an optimization strategy was proposed to make the evaluation of the aliasing debris more accurate than that merely using initial signals. Compared to other methods, the proposed method has fewer limitations in practical applications. The simulation and experimental results also verified the advantage of the proposed method.
With the development of the information age, the transmission rate and transmission capacity of information continue to increase. As a wireless communication method to achieve high bit rate communication, space laser ...
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ISBN:
(数字)9781510649965
ISBN:
(纸本)9781510649965;9781510649958
With the development of the information age, the transmission rate and transmission capacity of information continue to increase. As a wireless communication method to achieve high bit rate communication, space laser communication plays an increasingly obvious role in global communications. In the current space laser communication system, the optical communication terminal uses a detector to detect the position of the received optical signal, and then the servo mechanism on it performs facula tracking. However, when a four-quadrant detector (4QD) is used to detect optical signal, the received optical signal generally contains three main types of noise, which are background radiation noise, shot noise and thermal noise. These three kinds of noise can be equivalent to Gaussian white noise. In this paper, a single-frequency cosine signal is used to modulate the intensity of the optical signal received by the 4QD, and then the modulated optical signal is detected by a spectrum analysis method based on the cross-correlation algorithm. This method reduces the relative error of the spectral line amplitude when the SNR is -5dB from 2.23% to 0.88%, and reduces the relative error of the spectral line amplitude when the SNR is -20dB from 17.6% to 5.49%. Therefore, this method can well suppress Gaussian white noise and improve the detection accuracy of modulated optical signal under extremely low SNR conditions.
The rotor unbalance of the magnetic levitated turbomolecular pump (MLTMP) can lead to undesirable rotor synchronous vibration, and thus seriously affect the instrumentation precision in the ultra-high vacuum condition...
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The rotor unbalance of the magnetic levitated turbomolecular pump (MLTMP) can lead to undesirable rotor synchronous vibration, and thus seriously affect the instrumentation precision in the ultra-high vacuum condition. The accurate identification and elimination of rotor unbalance is the primary issue for system stable operation at high speeds. This article proposes a method for rotor unbalance self-identification without using external information, and designs a model parameter correction procedure to improve the rotor balancing precision. First, the complex coefficient method is utilized to establish the rotor dynamic model under the regular controller, and the numerical equivalence between the correction mass centrifugal force and magnetic bearings force is used to obtain the rotor unbalance. Then, the rotor synchronous responses based on rotor radial displacement and bearing control currents are extracted through the cross-correlation algorithm. To further improve the rotor unbalance measurement accuracy, the stiffness coefficient values are also corrected by introducing virtual trial weights. Finally, the experimental results conducted on a MLTMP prototype verify the effectiveness of the proposed method in the self-identification of rotor unbalance.
The threshold value comparative method is generally used in the measurement of delay time in the ultrasonic pulse echo method. The measurement error is large since the threshold method is easy to turn error with the i...
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The threshold value comparative method is generally used in the measurement of delay time in the ultrasonic pulse echo method. The measurement error is large since the threshold method is easy to turn error with the interference. So in this paper, cross-correlation algorithm is used to calculate the delay time. The overlap retaining method and improved real sequence fast Fourier transform algorithm are used to calculate the cross-correlation of the transmitted sequence and received sequence, so the calculated amount and measurement error are reduced, and the accuracy of the ultrasonic level meter is improved.
At present, the co-phasing detection algorithms for segmented mirrors struggle to balance the measurement range and accuracy. This paper proposes a coarse co-phasing measurement method using the incoherent properties ...
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At present, the co-phasing detection algorithms for segmented mirrors struggle to balance the measurement range and accuracy. This paper proposes a coarse co-phasing measurement method using the incoherent properties of a broadband (400-800 nm) light source combined with the incoherence of two semicircular diffraction patterns of visible light as a template to detect the piston error, and a narrowband algorithm for fine co-phasing measurement. The diversity factors between template patterns and actual diffraction patterns can be calculated by the cross-correlation algorithm. This proposed method addresses long measurement time caused by low target flow rate and is characterized by wide measurement range, high precision and high energy utilization. The method is theoretically researched and simulated and an experimental system which was constructed to verify the effectiveness of this method achieves 15 nm detection accuracy, and the measurement range using the proposed method can match the measurement range of the actuator.
In free space optical (FSO) communication, acquisition, tracking and pointing (ATP) is the key technology to maintain a high-quality FSOlink. Specifically, the detection of pointing angle deviation greatly affects the...
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In free space optical (FSO) communication, acquisition, tracking and pointing (ATP) is the key technology to maintain a high-quality FSOlink. Specifically, the detection of pointing angle deviation greatly affects the performance of ATP, especially under weak receiving power. However, the separated beacon laser beam commonly used in ATP will increase the structural complexity of the terminal such as the size, weight, and power. It is unwanted in some limited applications such as satellite. To improve the pointing accuracy with weak signal in beaconless FSO communication, we propose a delta-sigma enabled beaconless cross-correlation (CCR) method with four-quadrant detectors. In the proposed method, a low-frequency sine analog signal for CCR calculation is modulated into a 1-bit digital signal by delta-sigma modulation and then inserted into the communication data as a training sequence. The root means square error (RMSE) of the pointing angle deviation measurement is 14.17 mu rad with the incident optical power of-40 dBm. Compared with the direct intensity method, of which RMSE is 67.61 mu rad, the proposed method can effectively improve the pointing accuracy with weak power without a beacon laser in FSO communication.
This work presents an Adaptive Large Scale Particle Image Velocimetry method (ALSPIV), which measures surface velocity of a physical model experiment with complex flow pattern. In the experiment, the eleven low-cost, ...
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This work presents an Adaptive Large Scale Particle Image Velocimetry method (ALSPIV), which measures surface velocity of a physical model experiment with complex flow pattern. In the experiment, the eleven low-cost, high-resolution surveillance cameras are adopted to achieve a large-scale flow field in real time. The lenses of them are shined perpendicularly on water surface to minimize perspective distortion. A camera calibration method is also designed to enhance measurement accuracy. In addition, an adaptive cross-correlation algorithm can contribute to cross-correlation and a lower signal-to-noise ratio. Finally, an experimental method is employed to verify the ALSPIV method's accuracy, and the surface velocity distributions under three different steady flows are measured to demonstrate its applicability. Results show that the method is demonstrated to be a low-cost and automatic flow diagnostic tool and an accurate means of measuring surface velocities in the physical model experiments of flood propagation with complex flow patterns.
Slug flow is commonly encountered in industrial flows, its characteristics like strong intermittence and high pressure drop are usually harmful to the industrial process and facilities. Slug flow has more characterist...
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