Vector-electromagnetic scattering from metal surfaces using the infinite-slope Kirchhoff approximation

This paper presents calculations of a new formulation of the 3D Kirchhoff approximation which allows calculation of the scattering of vector waves from 2D rough surfaces containing infinite slopes. Results are presented for scattering from metal surfaces with rectangular surface structures. This type of surface has applications, for example, in remote sensing and in testing or imaging of printed circuits. Some preliminary calculations for rectangular-shaped grooves in a plane are presented for the 2D surface method.

An efficient geometric modeling method has been proposed for investigation on the properties of the electromagnetic (EM) scattering from two-dimensional (2D) rough surface. In this approach, the plane surface related to the rough surface is firstly modeled by the non-uniform rational B-spline (NURBS) surface through the computer aided geometric design (CAGD). Then the rough surface is reconstructed with the parameters of the plane surface and its height function. The method of moments (MOM) is adopted to solve the electric field integral equation (EFIE) with the rooftop basis function and line matching technique. Moreover, based on the message passing interface (MPI) platform, the parallel MOM algorithm is presented to reduce the simulation time of a single-processor. The conjugate gradient method (CGM) is developed to solve the matrix equation and parallelized with the impedance matrix divided to different processors by lines according to the property of MPI. The validity of this approach is shown by comparing to the flat triangular patch. Some numerical simulations are also exhibited and analyzed.

Surface-enhanced Raman scattering (SERS) spectroscopy is a popular technique for detecting chemicals in small quantities. Rough metallic surfaces with nanofeatures are some of the most widespread and commercially successful substrates for efficient SERS measurements. A rough metallic surface creates a high-density random distribution of so-called "hot spots" with local optical field enhancement causing Raman signal to increase. In this Letter, we revisit the classic SERS experiment [Surf. Sci.158, 229 (1985)SUSCAS0039-602810.1016/0039-6028(85)90297-3] with rough metallic surfaces covered by a thin layer of copper phthalocyanine molecules. As a modification to the classic configuration, we apply an adaptive wavefront correction of a laser beam profile. As a result, we demonstrate an increase in brightness of local SERS hot spots and redistribution of Raman signal over the substrate area. We hypothesize that the improvement is due to optimal coupling of the shaped laser beam to the random plasmonic nanoantenna configurations. We show that the proposed adaptive-SERS modification is independent of the exact structure of the surface roughness and topography, works with many rough surfaces, and gives brighter Raman hot spots in comparison with conventional SERS measurements. We prove that the adaptive SERS is a powerful instrument for improving SERS sensitivity.

This work focuses on the application of a multivariable model predictive controller that regulates thin film surface roughness and mean slope to a two-dimensional kinetic Monte-Carlo thin film growth model using both substrate temperature and deposition rate as manipulated inputs. The description of the thin film growth involving both adsorption and surface migration is first given. Surface roughness and surface slope are defined as the root-mean-squares of the surface height profile and the surface slope profile, respectively. The dynamics of the evolution of the thin film surface height profile are assumed to be described by an Edwards-Wilkinson-type equation (a second-order stochastic partial differential equation) in two spatial dimensions. Analytical solutions of the expected surface roughness and surface slope are obtained on the basis of the Edwards-Wilkinson equation and are used in the controller design. The model parameters of the Edwards-Wilkinson equation depend on the substrate temperature and deposition rate. This dependence is used in the formulation of the predictive controller to predict the influence of the control action on the surface roughness and slope at the end of the growth process. The model predictive controller involves constraints on the magnitude and rate of change of the control action and optimizes a cost that involves penalty on both surface roughness and mean slope from the set-point values. The controller is applied to the two-dimensional kinetic Monte-Carlo thin film growth model and is shown to successfully regulate surface roughness and mean slope to set-point values at the end of the deposition.

Compared with scattering from a rough surface only, composite scattering from a target above a rough surface has become so practical that it is a subject of great interest. At present, this problem has been solved by some numerical methods which will produce an enormous calculation amount. In order to overcome this shortcoming, the reciprocity theorem (RT) and the method of equivalent edge currents (MEC) are used in this paper. Due to the advantage of RT, the difficulty in computing the secondary scattered fields is reduced. Simultaneously, MEC, a high-frequency method with edge diffraction considered, is used to calculate the scattered field from the cone-cylinder target with a high accuracy and efficiency. The backscattered field and the polarization currents of the rough sea surface are evaluated by the Kirchhoff approximation (KA) method and physical optics (PO) method, respectively. The effects of the backscattering radar cross section (RCS) and the Doppler spectrum on the size of the target and the windspeed of the sea surface for different incident angles are analysed in detail.

Dynamics and control of aggregate thin film surface morphology for improved light trapping: Implementation on a large-lattice kinetic Monte Carlo model

The aim of this work is to design an off-line system, method and experimental set-up for predicting surface roughness (Ra) of metal surfaces with the help of audio signals. The frictional contact between a metal surface and sharp pencil like scratching tool will produce audio signals which vary based on the roughness of the surface. The samples considered to design and validate the concept are work pieces machined with metal cutting processes such as Turning and Grinding. Several audio signals are generated from various types of metal surfaces produced by these processes after the completion of the machining process away from the machining area in an enclosed chamber. The audio waves are captured with the help of a microphone fixed inside the chamber. These audio signals are processed to generate the surface pattern of the relevant surface. The audio signals are then converted to spectrogram and normalized histogram plots with the help of MATLAB, based on which the roughness of the surfaces is predicted. An experimental set-up is designed which provides a sound-proof environment to capture and record the audio signals. The proposed system, method and set-up are validated with the actual surface roughness of the chosen surfaces measured with the help of a surface roughness measurement instrument.

The roughness of the material surface affects the THz nondestructive testing results. Roughness of the surface can be ignored in the microwave region, but should be considered in the terahertz frequency domain. The effect of scattering caused by rough surface at terahertz frequency on the reflection spectrum was studied and discussed. By consideration of the reflection model of a single sample, the reflection signal of a rough surface can be correlated with that of a smooth surface by using the Kirchhoff approximation. In addition, the glucose tablets with different roughness were measured by THz-TDS (Terahertz time domain spectroscopy) system and their reflection spectra were analyzed. The reflection spectrum results show that due to the roughness of the surface, diffuse scattering generated by the rough surface weakens the intensity of the reflection spectrum at the receiver. In order to reduce the influence of the roughness on the spectrum, a spectral Gaussian compensation method was proposed, which can restore the spectral characteristics of the smooth surface. The power spectrum of 360 mesh roughness was increased by about 3 dB and 9 dB at 0.5 THz and 1 THz, respectively. Therefore, it can be envisaged that the proposed rough-surface spectral compensation method has a specific reference value in the development of the THz nondestructive testing technology in the future.

This study analyzed 15 patients who underwent revision for loosening at the stem-cement interface. The femoral components were from the same manufacturer and had grit-blast roughened surfaces. An apparent radiographic deficiency in the cement mantle was present in at least one zone in 1 3 patients. In 9 of 12 patients with localized osteolysis, the osteolysis developed in a zone with an apparent radiographic cement mantle defect. Loosening occurred due to tension failure of the stem-cement interface followed by axial subsidence and movement into relative retroversion. Motion between the stem and the cement mantle fueled an abrasive wear mechanism between the roughened metal surface and the cement mantle, generating excessive metal and cement particles that gained access to endosteal bone via defects in the cement mantle and resulting in localized osteolysis. Although the roughened surface played a central role in these failures, it is unlikely the layer of polymethylmethacrylate (precoat) played a role in the mechanism of failure. In some cases, debonding occurred as a result of tension failure of the metal-precoat interface. In others, tension failure occurred within the cement mantle, leaving the precoat and some cement from the mantle on the stems. There was no difference in the mechanism of failure of stems with precoat proximally compared to stems with precoat proximally and distally. One stem had no precoat; findings in this patient were indistinguishable from the others. The significance of debonding depends on the surface roughness of the stem. Debonding carries a poorer prognosis with a rougher stem surface because of abrasive wear with the generation of numerous metal and cement particulates, which can lead to rapid osteolysis if there are cement mantle defects. Stems with a higher metal-cement bond strength may require a higher quality cement mantle for long-term success.

Surface-dressed optical Bloch equations are solved for a two-level atom near or adsorbed on a rough surface, which is modeled as a hemispheroid protrusion on a perfectly conducting surface. Effects of the laser bandwidth are included by means of a phase-diffusion model. The presence of the surface roughness generates a dephasing broadening mechanism on the adatomic resonance fluorescence spectrum, which can be strongly enhanced by plasmon resonances depending on the shape of the hemispheroid. The dependence of the electrodynamics of the adatom on the adatom-hemispheroid distance is also evaluated.

Titanium alloys are considered as 'metals of future' because of their exceptional properties such as high strength to weight ratio, high specific strength, corrosion resistance etc and there is a crucial need to develop cost effective methods for their machining. The present paper highlights the analysis of variation of objective functions namely, metal removal rate, surface roughness and dimensional deviation depending upon the process parameters of wire electric discharge machining in machining of Ti 6-2-4-2 alloy. Box-Behnken designs are used to plan and analyse the experiments. Mathematical models are developed for metal removal rate, surface roughness and dimensional deviation using regression technique and consequently opted for optimisation of objective functions. As the parametric effect on metal removal rate, surface roughness and dimensional deviation is opposite, the problem is considered a multi objective optimisation problem. Pareto optimal solutions satisfying the conflicting objective functions are obtained using non-dominated sorting algorithm -II. The solutions obtained so can be utilised as machining recommendations to set levels of process parameters to satisfy the set of aforesaid process yield criteria.

In present work, abrasive waterjet machining has been used to machine adhesively bonded titanium-carbon fiber-reinforced plastics-titanium hybrid laminate with varying traverse speed, jet pressure, and stand-off distance. The effect of varying abrasive waterjet machining parameters on cut quality has been quantified by material removal rate, metal composite interface damage factor, taper ratio ( T r), and surface roughness (Ra). Response surface methodology along with central composite design has been used to analyze the influence of process parameters on output responses. Additionally, analysis of variance was performed to identify the significant parameters on the output responses. For better abrasive waterjet cut quality, the optimal values of process parameters obtained were 200 MPa jet pressure, 237.693 mm/min traverse speed, and 1 mm stand-off distance. The corresponding material removal rate, metal composite interface damage factor, taper ratio, and surface roughness are 5.388 mm3/s, 1.41, 1.16, and 3.827 µm, respectively. Furthermore, validation tests have been performed with obtained optimal parameters that deliver satisfactory outcomes with an error of 5.35%, 3.07%, 2.29%, and 0.39% for material removal rate, metal composite interface damage factor, taper ratio, and surface roughness, respectively.

The effects of surface roughness on the optical properties of metals have been discussed by comparing experimental results of ellipsometry with theoretical results from the homogeneous effective medium model (HEM), the monolayer effective medium model (MEM) and the gradual density layer model (GDL). A gradual increase of |rp/rs|(=p) has been observed with the increase in surface roughness at a higher angle than θB and gradual decrease at lower angle than θB, where θB is the pseudo-Brewster's angle. Though HEM models do not explain the roughness effect on optical properties, MEM model and GDL model show good explanations for the optical effects from rough metal surface, when Δd<<λ.

The ultrashort pulsed (USP) laser microwelding of sapphire/lnvar36 alloy controlled by the surface roughness of metal was investigated for the first time. The surface roughness (Sa) of Invar alloys gradually decreased from 0.944 to 0.029 μm from the prime surface to grounded and polished surface. However, the joint shear strength first increased and then decreased with the lowered Sa, the maximum shear strength reached 107.87 MPa at the Sa ∼ 0.131 μm. Compared to other surfaces with low Sa, the relatively high surface roughness enhanced the interfacial thermal deposition both spatially and temporally which in turn promoted the diffusion of interface elements and the formation of jagged mechanical interlocking structures. Therefore, the appropriate rough metal surface was beneficial for the enhancement of sapphire/metal dissimilar joints. This report is of great significance in simplifying the surface preparation process in the USP laser microwelding of transparent hard and brittle materials with metals, therefore promoting this technique from lab to industry.

Based on the Kirchhoff's approximation, analytical expressions for pulse scattering mutual coherence function (MCF) and the Double Frequency Scattering Section (DFSS) from moving rough random surface are presented. From expressions, we find that the MCF and DFSS have related with the coherence bandwidth frequency difference, and the speed of the rough surface. Some important scattering characteristics of calculations based on the analytical solutions will be further discussed in details.