Random Rough Surface Effects Research Articles

Random rough surface effects on the performance of near-field thermophotovoltaic system

Surfaces roughness exists inevitably during manufacturing process, while how it affects the performance of the near-field thermophotovoltaic (NF-TPV) system is still unclear. In this work, we investigate the effect of rough surfaces on the performance of NF-TPV systems theoretically. Two typical NF-TPV systems with the same plasmonic emitter (Ga-doped ZnO, GZO) and different TPV cells (GaSb and InAs) are considered. The effective multilayer approach and analytical approximation model are applied to analyze near-field radiative heat transfer and the performance of the NF-TPV system. Near-field radiative heat transfer between the ideal GZO and TPV cell with smooth surfaces is through the TR-SPPs modes (interaction between the evanescent waves generated by total reflection and the surface plasmon polaritons), while the surface roughness excites the red-shift and the coupling of the TR-SPPs modes. The influence of surface roughness on the performance of the NF-TPV system depends on the cooperation between the resonance frequency of the emitter and the bandgap of TPV cell. Generally, roughness increases the power output for a given average emitter-cell distance, while the efficiency can be improved or reduced. This work will help the understanding and evaluation of the performance of NF-TPV systems with rough surfaces.

Random Rough Surface Effects on the Performance of Near-Field Thermophotovoltaic System

Random Rough Surface Effects on the Performance of Near-Field Thermophotovoltaic System

Roughness Effects on Fretting Fatigue

Fretting is a small oscillatory relative motion between two normal loaded contact surfaces. It may cause fretting fatigue, fretting wear and/or fretting corrosion damage depending on various fretting couples and working conditions. Fretting fatigue usually occurs at partial slip condition, and results in catastrophic failure at the stress levels below the fatigue limit of the material. Many parameters may affect fretting behaviour, including the applied normal load and displacement, material properties, roughness of the contact surfaces, frequency, etc. Since fretting damage is undesirable due to contacting, the effect of rough contact surfaces on fretting damage has been studied by many researchers. Experimental method on this topic is usually focusing on rough surface effects by finishing treatment and random rough surface effects in order to increase fretting fatigue life. However, most of numerical models on roughness are based on random surface. This paper reviewed both experimental and numerical methodology on the rough surface effects on fretting fatigue.

Random Rough Surface Effects in Waveguides Using Mode Matching Technique and the Method of Moments

To address the rough surface effects in high speed interconnects on printed circuit boards and microelectronic packages, we study the electromagnetic wave propagation in a parallel plate waveguide with rough surface walls, using a mode matching technique in combination with the method of moments (MoM). In the formulation, a line source in the smooth section of the waveguide excites a summation of modal fields. For each waveguide modal excitation, the modal response fields in the rough surface section of the waveguide are obtained by the solution of a set of coupled surface integral equations through MoM. Results are illustrated for a variety of roughness types including the very rough case based on exponential correlation functions. The results are compared with the previously developed analytical second-order small perturbation method (SPM2) result and the finite element method (FEM). It is shown that for rough surfaces with large slopes, the mode matching MoM model gives a smaller enhancement factor than SPM2. It is also shown that MoM can give accurate solutions even for the very rough case of exponential correlation functions. The MoM method of rough surface simulation in waveguide geometry requires much less computational resources than FEM.

Random Rough Surface Effects on Wave Propagation in Interconnects

To address the rough surface effects in high-speed interconnects on printed circuit boards (PCBs) and microelectronic packages, we study the electromagnetic wave propagation in a rough surface environment. In our model, the rough surface is characterized by a stochastic random process with correlation function or spectral density. This paper reviews the analytical theory, numerical simulations and experimental results based on such a model. We describe the rough surface characterization and the extraction of roughness parameters from 3D profile measurements. Initially we study the 2D case with the rough surface height function varying in only one horizontal direction and consider the case of plane wave incidence. Analytic second-order small perturbation method (SPM2) was used to obtain simple closed-form expressions for the absorption enhancement factor. The numerical transfer matrix (T-matrix) method and the method of moments (MoM) were also used. We next consider the case of the 3D problem with the rough surface height varying in both horizontal directions. We also used SPM2 to obtain a simple closed form expression for the enhancement factor. In interconnect problems, electromagnetic (EM) waves propagate in a guided wave environment. Thus, we next considered a waveguide model to study the effects of random roughness on wave propagation and compare with results from the plane wave formulation. Analytic SPM2 and numerical finite element method (FEM) with mode matching were used to obtain the enhancement factor. We also describe experimental results and correlation with the theoretical models. Finally, we explain how the enhancement factor concept used throughout lends itself to direct inclusion of rough surface effects in a wide variety of modeling problems.

Wave Propagation in a Randomly Rough Parallel-Plate Waveguide

We study the effects of random rough surface on electromagnetic wave propagation in a parallel-plate waveguide excited by a line source. The second-order small perturbation method is applied to derive a closed-form expression for the coherent wave propagation and the power loss. The derived result is expressed in terms of a double Sommerfeld integral. The double Sommerfeld integral is evaluated by direct numerical integration and by approximate methods. The results of the two methods are shown to be in good agreement with each other. Numerical results of coherent wave propagation and power loss are illustrated as a function of roughness characteristics and waveguide thickness. The enhancement factors are compared with previous results of plane-wave scattering. The waveguide model and the plane-wave model are in good agreement for moderate to large waveguide thicknesses. For small waveguide thickness, the waveguide model shows significantly different power loss as compared to the plane-wave model. Full-wave simulations by the finite-element method are used to validate the second-order small perturbation in waveguide model.

Efficient numerical modeling of random rough surface effects in interconnect resistance extraction

AbstractOwing to the decreasing skin depth in high‐speed analog and digital circuits, surface roughness is playing an increasingly important role in interconnect parasitic extraction. However, the random nature of surface roughness and the complicated electromagnetic behavior baffle satisfactory solutions to the extraction exercise. This paper utilizes a numerically formulated effective conductivity as an efficient measure of the rough surface effects in the resistance extraction to avoid the global discretization of interconnect surfaces. Two numerical methods based on different boundary element formulations are proposed to compute the mean effective conductivity for interconnects with random surface roughness. Numerical experiments compare these two methods in different rough surface patterns to evaluate their efficacy. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of random rough surface on absorption by conductors at microwave frequencies

The effects of a random rough surface on the absorption by a metallic surface at microwave frequencies are analyzed by using two methods: the analytic small perturbation method and the numerical method of moments method. The results show significant difference between absorption of a rough surface and that of a smooth surface. The absorption depends on the root mean square height, correlation length, and correlation function of the random rough surface. The similarities with and differences from Morgan's classical result and the Hammerstad and Bekkadal formula are discussed. It is shown that for multiscale rough surfaces, saturation of absorption does not occur, or occurs at much higher frequencies.