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Fast and accurate simulations of transmission-line metamaterials using transmission-matrix method
Recently, two-dimensional (2D) periodically L and C loaded transmission-line
(TL) networks have been applied to represent metamaterials. The commercial
Agilent's Advanced Design System (ADS) is a commonly-used tool to simulate the
TL metamaterials. However, it takes a lot of time to set up the TL network and
perform numerical simulations using ADS, making the metamaterial analysis
inefficient, especially for large-scale TL networks. In this paper, we propose
transmission-matrix method (TMM) to simulate and analyze the TL-network
metamaterials efficiently. Compared to the ADS commercial software, TMM
provides nearly the same simulation results for the same networks. However, the
model-process and simulation time has been greatly reduced. The proposed TMM
can serve as an efficient tool to study the TL-network metamaterials.Comment: 15 pages, 13 figure
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Modeling of Traffic Excitation for System Identification of Bridge Structures
In long-term health monitoring of bridge structures, system identification is often performed based only on the system output (bridge vibration responses) because the system input (traffic excitation) is difficult to measure. To facilitate the identification of the bridge properties, traffic excitation is commonly modeled as spatially uncorrelated white noise. A physical model of a stationary stream of vehicles (moving loads) arriving in accordance with a Poisson process, traversing an elastic beam, shows that the traffic excitation is spatially correlated. Employing the dynamic nodal loading approach, this spatial correlation results in a frequency-dependent excitation spectrum density matrix, and shifts the response spectra obtained from those excited by spatially uncorrelated white noise. It is shown that the application of system identification techniques based on the conventional excitation model may result in misleading structural properties. Hence, this study further proposes an output-only gray-box identification technique for bridge structures, in which knowledge about the nature of the traffic excitation, such as its spatial correlation, is implanted into an autoregressive-moving-average (ARMA) model. The identifiability of the ARMA model so constructed is assured and the feasibility of the proposed identification technique is demonstrated by a numerical example
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