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Time-domain measurement and analysis of mechanical step transitions in mode-tuned reverberation.

Arnaut, L R (2006) Time-domain measurement and analysis of mechanical step transitions in mode-tuned reverberation. NPL Report. DEM-EM 012

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This report presents experimental data and statistical analysis of time-domain measurements for a specific class of transient random electromagnetic fields. These transients are caused by mechanical (i.e., configurational) transitions between otherwise stationary states of a resonant cavity. They are produced by the discretized (stepwise) rotation of a mode tuner inside a reverberation chamber that is excited by a continuous time-harmonic source. Measured time-domain traces of the normalized amplitude of the received field during individual transitions are sampled, recorded, and transposed into stir sequences. Each constructed sequence is is stochastically wide-sense stationary and is characterized by an associated time delay, defining a specific age within the transitions. The cross-correlation function between sequences is found to permit an indirect detection of the average motion of the mode tuner, including mechanical oscillations, inertia, and backlash. The evolutions of the statistics of first order (probability distribution, mean value, standard deviation) and second order (autocorrelation function, correlation length, modulation index), as well as extreme-value sample statistics (maximum value), are derived from the sequences. These statistics show changes during the transitions that contain a deterministic (regular) contribution that can be correlated to the tuner motion. The measured fluctuations of the mean-normalized maximum received power are considerably larger than those estimated from measured fluctuations of the correlation length with presumed quasi-stationary ideal random fields. From the timedomain traces and stir sequences, the evolution of the rate of fluctuation and the modulation coefficient is determined. The influence of the operation frequency as well as various motor parameters is investigated. The effect of switching the source off/on (before/after each mechanical transition) on the maximum energy density is investigated, based on the measured chamber response to a pulse-amplitude modulated source field.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DEM-EM 012
Subjects: Electromagnetics
Last Modified: 02 Feb 2018 13:15
URI: http://eprintspublications.npl.co.uk/id/eprint/3858

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