Impedance Of Rods Research Articles

Análisis de Sobretensiones Resultantes de Descargas Atmosféricas para Suelos Dependientes de la Frecuencia

En este trabajo se presenta un estudio comparativo de la impedancia de un electrodo vertical enterrado en un suelo homogéneo donde los parámetros eléctricos (resistividad y permisibilidad) son dependientes de la frecuencia en relación a los mismos con parámetros constantes. Para su cálculo, es llevado en consideración que el electrodo vertical se puede interpretar como una línea de transmisión (LT) cuyos los parámetros eléctricos son distribuidos por unidad de longitud. Así, la impedancia del electrodo es computada como siendo la impedancia harmónica de LT en función de la frecuencia. Una vez obtenidas las impedancias de aterramiento del electrodo, y empleando una técnica de mínimos cuadrados, se las representan por circuitos eléctricos directamente en el dominio del tiempo. La ventaja de usar este tipo de representación es que el modelo puede insertarse fácilmente en software del tipo EMTP para el análisis de los transitorios electromagnéticos. Así, se calculan las elevaciones de potencial en el aterramiento para una descarga atmosférica incidente en el electrodo. Adicionalmente, una descarga atmosférica es inyectada en el topo de una torre de transmisión aterrada por un electrodo vertical, para evaluar las tensiones en los brazos de la estructura y en su base. Los resultados muestran que las tensiones son significativamente modificadas por la presencia del suelo con parámetros dependientes de la frecuencia, en especial las amplitudes, y que un análisis preciso del transitorio en los sistemas eléctricos debe llevar en cuenta ese fenómeno.

Theory of multiresonant metamaterials forA0Lamb waves

We develop an analytical wave approach to describe the physics properties of multiresonant metamaterials for Lamb waves propagating in plates. The metamaterial that we characterize consists of a 10 by 10 uniform, periodic array of long rods attached to the surface of the plate that forms the substrate in which antisymmetric ${A}_{0}$ Lamb waves are excited. We show that the ${A}_{0}$ Lamb wave propagation through the metamaterial can be accurately modeled using a simplified theory that replaces the two-dimensional array with a one-dimensional beam with a linear array of 10 rods. The wave propagation problem is solved rigorously for this one-dimensional system using the scattering matrix for a single rod. The exact eigenvalues of the system are approximated in a long wavelength expansion to determine a simple expression for the effective wave number and dispersion of the metamaterial. The modeled dispersion is compared with an experimental measurement of the dispersion inside the metamaterial with excellent agreement. The multiresonant rods, restricted to longitudinal vibration consistent with ${A}_{0}$ Lamb waves excited in the plate, produce two wide stop bands in the frequency domain from 0 to 10 kHz where the stop or passband boundaries align with the minima and maxima of the rod's impedance. We show that a negative effective density is obtained in the stop band. With the simple yet highly accurate relations given in this paper we have a tool to develop more complex metamaterials with rods and plates of different properties.

Impedance response and modeling of composites containing aligned semiconductor whiskers: Effects of dc-bias partitioning and percolated-cluster length, topology, and filler interfaces

Impedance spectroscopy and modeling were used to investigate the partitioning of 0-40 V dc bias in composites containing alumina and different volume fractions of silicon carbide whiskers (SiCw), which formed low-connectivity percolated clusters. Differences in response between long (∼25 cm) composite rods and thin (∼1.7 mm) slices thereof were interpreted in terms of the relative contributions to the impedance from the electrodes and SiCw-percolated clusters of the composite samples. Bias had minimal effect on the impedance of rods, because its distribution across the long percolated clusters within translated to low electric fields at the SiCw-SiCw interfaces. The impedance of thin slices was more sensitive to bias and was mainly due to such interfaces. The associated dc resistance and effective capacitance decreased significantly with increasing dc bias. A model for symmetrical Schottky energy barriers at interfaces fit the capacitance trend and outputted a parameter Φi/κ¯i. Different models for the non-linear current-voltage behavior were related to each other and indicated weak varistor-like behavior, i.e., 1.15 ≤ αV ≤ 2.57. With increasing SiCw content and composite dc conductivity, Φi/κ¯i increased and the varistor non-linearity strength αV decreased. Also, the exponent t describing conductivity divergence at percolation was reduced at large dc bias. A new model of percolated clusters was proposed and correctly predicted the qualitative character and some quantitative aspects of these experimental results. The model is based on tendencies of the current distribution, which are expected from the topological structure and contrast between interface/whisker electrical behavior. Accordingly, it outputs the voltage-distribution tendencies.

Percussive energy transfer in pneumatic top hammer rock drills

ABSTRACT A mathematical model of pneumatic roll drills is introduced. This model takes into account the local deformation of impact ends of piston and shank adapter. For this model, there is a good agreement between theoretical and experimental results. Two dimensionless parameters related to the mass of piston, the local deformation of impact ends, characteristic impedance of rod, and force-penetration characteristic at bit-rock interface, are introduced. The analysis indicates that the checking of these dimensionless parameters and letting them be in certain ranges are helpful for the design of pneumatic rock drills to achieve high efficiency of energy transfer.