The application of quadrature demodulation techniques for the investigation of flows

Müller, H.; Strunck, V.; Dopheide, D.

doi:10.1016/s0955-5986(97)00008-3

Cited by 11 publications

(13 citation statements)

References 10 publications

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“…In principle, the QDT allows precise frequency measurements of a pair of signals in quadrature, independently of the number of signal periods available [3][4][5][6][7]. Therefore, also low signal frequencies can be measured in a time-resolved way in the signal base band.…”

Section: Introductionmentioning

confidence: 99%

Statistical frequency measuring error of the quadrature demodulation technique for noisy single-tone pulse signals

Czarske

2001

Meas. Sci. Technol.

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The standard deviation of the centre frequency of a signal is investigated for the quadrature demodulation technique (QDT). Signal frequencies can be measured by QDT unaffected by the amount of available signal periods. It can be used for the measurement of nonstationary signals generated by laser Doppler velocimeters. The dependence of the frequency measuring error on the averaging time of noisy single-tone Gaussian pulse signals is analysed. Assuming a quantum noise process, it is shown that the minimum measuring error results for an averaging time of approximately 1/ e 2 of the pulse duration of the signal. Alternatively, defined weighting of the measured values leads to a monotonically decreasing measuring error with increasing averaging time until the Cramer-Rao lower bound is reached. Therefore, the weighted QDT provides the lowest measuring error of all linear unbiased frequency estimators. It allows the evaluation of small frequency changes of laser Doppler signals, e.g. from micro-turbulent flows. The theory presented here is verified by Monte Carlo simulations and experiments.

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Section: Introductionmentioning

confidence: 99%

Statistical frequency measuring error of the quadrature demodulation technique for noisy single-tone pulse signals

Czarske

2001

Meas. Sci. Technol.

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“…5. The idea of this back-mixing technique was already described in a Special Issue of FMI about optical techniques for fluid flow measurement by the authors, see Müller et al (1996b) and will be summarized here therefore only briefly. The resulting quadrature signal pair at the output of the mixer unit is completely free of any frequency shift influences and any frequency fluctuations of the laser diodes and permits the magnitude and sign of velocities to be determined precisely.…”

Section: Directional 2 W Mopa Lda System and Experimental Resultsmentioning

confidence: 99%

Realization of high performance LDA-systems using optical amplifiers, high power semiconductor lasers and optical fiber lasers

Dopheide

Többen

Strunck

et al. 2000

J Vis

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Advanced novel techniques for sophisticated LDA applications are presented in this paper.By applying laser sources with high output powers like MOPA-lasers (master oscillator power amplifier), fiber lasers and booster fiber amplifiers to increase the laser power in the measuring volume and by amplifying the scattered light power with optical fiber preamplifiers to increase the sensitivity of the receiving units, the signal-to-noise-ratio of laser Doppler signals is drastically improved and the overall performance of a laser Doppler anemometer is significantly enhanced.

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“…Hence, three beat frequencies detected by PD1 and PD2 are given by (14) (15) (16) Here, the beat frequency can be discriminated with PD3. Because the amplitude of and are identical, is lying parallel to the axis and (17) where is the angle between the direction of and the axis.…”

Section: B Beat Frequency Detectionmentioning

confidence: 99%

“…Several approaches have been reported for directional discrimination without optical modulators [12]- [14], although these approaches are for one-dimensional velocity measurement. In this paper, 2-D laser Doppler velocimetry without polarization discrimination, wavelength discrimination or frequencyshift discrimination is proposed.…”

Section: Introductionmentioning

confidence: 99%

Laser Doppler Velocimetry for Two-Dimensional Directional Discrimination by Monitoring Scattered Beams in Different Directions

Maru

Fujii

2011

IEEE Sensors J.

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2-D laser Doppler velocimetry without polarization discrimination, wavelength discrimination or frequency-shift discrimination is proposed. In the proposed velocimetry, scattered beams in different directions are monitored with two detection blocks in order to discriminate the direction of velocity. The principle of the proposed velocimetry is described and the discrimination of velocity direction is theoretically analyzed by simulation. The simulation result indicates that the direction of velocity can be discriminated by using the proposed velocimetry as well as the magnitude of velocity.

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The application of quadrature demodulation techniques for the investigation of flows

Cited by 11 publications

References 10 publications

Statistical frequency measuring error of the quadrature demodulation technique for noisy single-tone pulse signals

Statistical frequency measuring error of the quadrature demodulation technique for noisy single-tone pulse signals

Realization of high performance LDA-systems using optical amplifiers, high power semiconductor lasers and optical fiber lasers

Laser Doppler Velocimetry for Two-Dimensional Directional Discrimination by Monitoring Scattered Beams in Different Directions

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