Electrochemical tomography as a nondestructive technique to study localized corrosion of metals

We present an approach, termed electrochemical tomography (ECT), for the in-situ study of corrosion phenomena in general, and for the quantification of the instantaneous rate of localized corrosion in particular. Traditional electrochemical techniques have limited accuracy in determining the corrosion rate when applied to localized corrosion, especially for metals embedded in opaque, porous media. One major limitation is the generally unknown anodic surface area. ECT overcomes these limitations by combining a numerical forward model, describing the electrical potential field in the porous medium, with electrochemical measurements taken at the surface, and using a stochastic inverse method to determine the corrosion rate, and the location and size of the anodic site. Additionally, ECT yields insight into parameters such as the exchange current densities, and it enables the quantification of the uncertainty of the obtained solution. We illustrate the application of ECT for the example of localized corrosion of steel in concrete.

Coupled Field Thermoelectric Simulation of High Voltage Ceramic Cap and Pin Disc Type Insulator Assembly

Transmission of high power at high voltages over very long distances has become very imperative. At present, throughout the globe, this task performed by overhead transmission lines. The dual task of mechanically supporting and electrically isolating the live phase conductors from the support tower is performed by insulators. The electrical potential, field and temperature distribution along the insulators governs the possible effects, which is quite detrimental to the system. However, a reliable data on electrical potential, field and temperature distribution in commonly employed insulators are rather scarce or access individually for thermal or electrical load only. Considering this, the present work has made an attempt to study accurately, thermal and electrical characteristics of 11 kV single cap and pin type ceramic disc distribution insulator assembly used for high voltage transmission. The coupled field thermo electrical finite element by using commercially available FEM software Ansys-11 is employed for the required field computations. This new set of ANSYS coupled-field elements enables users to accurately and efficiently analyze thermoelectric devices. This paper review the finite element formulation, which in addition to Joule heating, includes Seebeck, Peltier, Thomson effects and electrical load, i. e. by considering thermal and electric loads acting simultaneously. The Electrical voltage, electrical field and temperature distribution is deduced and compared with various other/individual analyses.

Accurate Prediction of Thermal Resistance of FET by Detailed Modeling of Heat Generation and Backend Stackup

In typical thermal modeling of a FET (field effect transistor) structure, the power could be modeled as the heat generation, which is averaged under the entire gate length (gate averaged). However, it is found from the electrical potential field within the channel that the heat generation is actually distributed all the way from source to drain with a heavy concentration around the gate edge at the drain side. In a typical case, the peak of the heat distribution is almost four times of the gate averaged. Therefore, accurate modeling of the heat generation averaging over a much smaller region near the gate edge (edge averaged) makes a significant difference. This paper focuses on the comparison of the edge averaged versus the gate averaged modeling development. Furthermore, the detailed topology of the backend stackup layers and their relative impacts on heat dissipation paths are evaluated and the practical simplification is proposed in the modeling development. The result shows that, for a single gate FET die, the thermal resistance is found to be 26% more than that of the gate averaged approach. For a multiple gate FET die, both methods give the same surface temperature on the top surface layer. However, the temperature difference (ΔTjs) between the junction and the top surface is different between the two heat averaging approaches and the edge averaged approach prediction doubles that of the gate averaged approach. It is also found that ΔTjs is independent of number of gates and only depends on the backend stackup details between source and drain.

Evaluation of Continuum Mechanics for Electroosmotic Flow in Nanosize Structures

Development of nano-devices for various applications has drawn great attention recently driven by the need of miniaturizing the devices for the integration and automation of Biochips or Lab-on-a-Chip devices. Fundamental understanding of transport phenomena in nanofluidic channels is critical for systematic design and precise control of such devices. The goal of this study is to develop a theoretical model to study electroosmotic flow in nanochannels. Instead of using the Boltzmann distribution, the conservation condition of ion number and the Nernst equation are used in this new model to find the ionic concentration field in the nanochannels. A correct boundary condition for the concentration field at the wall of the channel is developed and the symmetry condition of the potential field at the center of the nanochannel is applied to this model. The ionic concentration field, electrical potential field and flow field are obtained by numerically solving this model. Comparisons of area-average velocity between the numerical simulations and experimental results reported in literature are provided.

2-D and 3-D interpretation of electrical tomography measurements, Part 1: The forward problem

We have developed a computer code to model the electrical potential field for borehole‐to‐borehole measurements. This scheme supports a large class of model geometries including 2-D and 3-D structures embedded in a homogeneous half‐space. It enables the computation of the electrical potential at any point due to a direct current injection at any source point within the model. A new boundary integral formulation is used that generates a sparse linear system. The sparsity is exploited in order to optimize the memory size and the computation time needed to solve the forward problem. This formulation is new because two unknown quantities—the electrical potential and a current‐related quantity—are solved for each interface. The numerical accuracy of this code has been extensively tested. Simulations of a simple model geometry are used to gain insight on when 3-D phenomena differ from those of 2-D models.