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Concept

Fréquence de répétition des impulsions radar

Résumé

La fréquence de répétition des impulsions radar (PRF, Pulse Repetition Frequency) est le nombre d'impulsions transmises chaque seconde par un radar. Son inverse appelé « période inter–impulsions » (PRT, Pulse Repetition Time) mesure le temps écoulé entre le début d'une impulsion et le début de la suivante. La fréquence de répétition des impulsions est une notion importante car elle détermine à la fois la distance maximale de détection de la cible et le maximum de vitesse Doppler qui peut être déterminé avec précision par le radar. Par extension, la fréquence de répétition des impulsions peut s'appliquer dans le domaine des ondes sonores et lumineuses. Définition Les ondes électromagnétiques (par exemple radio ou lumineuses) sont des phénomènes à fréquence unique conceptuellement purs, tandis que les impulsions peuvent être mathématiquement considérées comme composées d'un certain nombre de fréquences pures qui s'additionnent et s'annulent dans des interactions qui créent un

Source officielle

https://fr.wikipedia.org/wiki/Fr%C3%A9quence_de_r%C3%A9p%C3%A9tition_des_impulsions_radar

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High Performance InP-Based Quantum Dash Semiconductor Mode-Locked Lasers for Optical Communications

Anthony Martinez

Several applications are pushing the development of high performance mode-locked lasers: generation of short pulses for extremely high bit rate transmission at 100 Gb/s and beyond, all-optical clock recovery at 40 Gb/s and beyond, generation of millimeter wave signals through mode-beating on a high speed photodiode, optical sampling for analog-to-digital conversion, and generation of wavelength-division-multiplexing channels. This paper will report on new advances in InP-based quantum dash mode-locked lasers, which largely surpass the performance of their bulk or quantum well counterparts in terms of the mode-beating spectral purity and the bandwidth of optical spectrum. In particular, we will describe the quantum dash nanostructures used for the mode-locked lasers and the dependence of the mode-locking properties on detailed quantum dash structures. We will demonstrate that these quantum dash lasers can be actively mode-locked, generating sub-picosecond or picosecond pulses at different repetition frequencies with extremely low timing jitter. They can also be used to achieve all-optical clock recovery, with timing jitter compliant with International Telecommunication Union (ITU) standards even for highly degraded input optical signal-to-noise ratio. Finally, we demonstrate that, owing to the very wide and flat optical spectrum and the low relative-intensity noise level of the mode-locked laser, error-free transmission over 50 km single mode fiber has been achieved for eight wavelength division multiplexing ITU channels at 10 Gb/s with a channel spacing of 100 GHz. (C) 2009 Alcatel-Lucent.

2009

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The detection of cavitation in hydraulic machines by use of ultrasonic signal analysis

Mohamed Farhat, Michelle Susanne Frei, Pascal Damian Odermatt

This presentation describes an experimental approach for the detection of cavitation in hydraulic machines by use of ultrasonic signal analysis. Instead of using the high frequency pulses (typically 1MHz) only for transit time measurement different other signal characteristics are extracted from the individual signals and its correlation function with reference signals in order to gain knowledge of the water conditions. As the pulse repetition rate is high (typically 100Hz), statistical parameters can be extracted of the signals. The idea is to find patterns in the parameters by a classifier that can distinguish between the different water states. This classification scheme has been applied to different cavitation sections: a sphere in a water flow in circular tube at the HSLU in Lucerne, a NACA profile in a cavitation tunnel and a Francis model test turbine both at LMH in Lausanne. From the signal raw data several statistical parameters in the time and frequency domain as well as from the correlation function with reference signals have been determined. As classifiers two methods were used: neural feed forward networks and decision trees. For both classification methods realizations with lowest complexity as possible are of special interest. It is shown that three signal characteristics, two from the signal itself and one from the correlation function are in many cases sufficient for the detection capability. The final goal is to combine these results with operating point, vibration, acoustic emission and dynamic pressure information such that a distinction between dangerous and not dangerous cavitation is possible.

International Association For Hydraulic Research2014

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A Low-Power, Low Data-Rate, Ultra-Wideband Receiver Architecture for Indoor Wireless Systems

Cyril Botteron, Frédéric Chastellain, Pierre-André Farine, Alexander Heubi, Christian Robert, Paul Saad, Uroschanit Yodprasit

Abstract—In this paper, a novel architecture for a low data-rate, low power consumption Impulse Radio (IR) Ultra- Wideband (UWB) receiver is presented in which the received UWB signal is downconverted to a given intermediate frequency (IF) rather than at baseband. This way, the requirement to implement two separate paths for the in-phase and the quadrature components is removed and the power consumption can be reduced. From the IF, the signal is converted to the digital domain by a set of 24 Redundant Signed Digit (RSD) Analog to Digital Converters (ADCs) working at the pulse repetition rate. The digitized signal is then correlated with a predefined template prior to be fed to the bit detector. The trade-offs for the selection of the IF are highlighted and the BER performance of the proposed receiver is evaluated using simulations in 802.15.3a multipath channels. The expected power consumption for the implementation of the receiver using a CMOS process is also provided.

2008

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