Surface Electromagnetic Fields Research Articles

Scattering of an induced surface electromagnetic field by fatigue cracks in ferromagnetic metals

In crack detection and sizing by the alternating current field measurement technique, U-shaped wires or coils excited by a high-frequency AC current source can be used to induce the surface field in the workpiece. The authors present a modeling technique for the interaction of a fatigue crack in a ferromagnetic metal with the surface field resulting from an inducer with two U-shaped wires. This work is an extension of a previous modeling technique to have developed for infinitely long (one-dimensional) cracks. In the present technique, the boundary of the fatigue crack is approximated by a circular arc, leading to a formulation for an efficient computation of the field-flaw interaction. Various numerical and experimental results supporting the modeling and illustrating the behavior of the magnetic field and electric potential at the metal surface around circular-arc cracks are presented. >

Analysis of surface electromagnetic fields of wavelength-sized surface relief gratings

The complex values of the electromagnetic fields along surface relief gratings for TE polarization are rigorously evaluated. The amplitude and phase of the surface field show the dependence upon various factors including the incident angle, complex refractive index of the material and the depth of the slots. The results are analyzed and given physical explanations. It is found that for wavelength-sized slots the edges and walls have significant effects on the surface electromagnetic field distributions.

Polarization-modulation electronic absorption study of copper phthalocyanine films on silver by surface plasmon resonance spectroscopy

Electronic absorption measurements with a polarization-modulation technique were performed on evaporated Ag films coated with copper phthalocyanine in the Kretschmann ATR prism geometry. It is shown that excitations of the extended surface plasmon polariton and the transverse localized plasmon of the Ag films produce a substantial augmentation in the electronic absorption intensity of the dye as a result of the enhancement of surface electromagnetic fields. The experiments showed no significant interaction between the dye molecules and the substrate, probably due to the presence of surface contaminants. It is also shown that the molecules are oriented perpendicular rather than parallel with respect to the substrate.

A study of the leakage of surface electromagnetic fields through holes and cracks in metal plates

This paper considers the problems of thin-skin surface currents applied to conducting plates that have through holes or through cracks in them. The surface field distributions depend on the parameter m ═ ( μ 0 / μ ) ( l / δ ), where μ 0 / μ is the ratio of the free space to the specimen magnetic permeability and l / δ is the ratio of the flaw length dimension l to the skin depth δ . When m is small the fields are surface Laplacian distributions that can be computed by using methods of conformal mapping. The paper gives these distributions for circular holes and through cracks. Experiments are described for both these geometries, which confirm the incident and the leakage field distributions calculated for the two faces of the plate.

Description of an Aircraft Lightning And Simulated Nuclear Electromagnetic Pulse (NEMP) Threat Based on Experimental Data

Most modern aircraft are designed to withstand a direct lightning strike. To accomplish this protection, the aircraft must have an external conductive path with a given skin thickness and a minimum amount of exposed areas and antennas that could allow energy coupling to the inside. Additionally, some modern military aircraft are also designed to operate in a nuclear electromagnetic pulse (NEMP) environment. This paper provides experimental lightning data and NEMP scalemodel data to characterize both phenomena. The lightning data were obtained by measuring the surface electromagnetic fields on a CV-580 research aircraft during an actual lightning strike. The aircraft was struck by lightning 48 times in central Florida between 1500- and 18 000-ft altitude during the summers of 1984 and 1985. One of these lightning events, for which an extensive set of data was available, has been analyzed. For this event, the maximum measured values were as follows: time rate of change of the surface magnetic flux density, 3750 T/s; total normal current density, 20 A/m2; peak current, 4.7 kA; and rate of rise of the current, 38 kA/ps. The NEMP data were obtained by measuring the surface electromagnetic fields during a simulated NEMP test in a 1:74 scale model of the same aircraft. During scale-model NEMP simulation, the maximum values measured were as follows: time rate of change of the surface magnetic flux density, 40 000 T/s; and total normal current density, 90 A/m2. The analyses of these results should provide new insights for combined lightning and NEMP protection.

Spin-polarized nuclei as probes of electromagnetic field distributions on solid surfaces

Recent experiments using thermal beams of nuclear-spin-polarized alkali atoms adsorbed on hot metal surfaces show that polarized nuclei are sensitive probes of surface electromagnetic field distributions. The high polarization of the probe beams, when coupled with the efficiency of atomic physics techniques used for monitoring the polarization of desorbed particles, makes possible a variety of interesting spinrelaxation experiments on single-crystal surfaces, including nuclear magnetic resonance. Extension of the current experimental method to semiconductor and insulator surfaces at arbitrary temperatures appears to be straightforward. The information from spin-polarized nuclear surface spectroscopy (SPNSS) will allow detailed tests of charge-density profiles now available in self-consistent surface structure calculations. Moreover, the variety of presently available polarized nuclear species suggests that the chemistry of many interesting adsorbate-surface systems could also be profitably investigated by this technique. The use of spin-polarized hydrogen nuclei in particular offers enticing prospects for fundamental studies in catalysis, surface structure and basic two-dimensional physics.

Infrared absorption study of adsorbed species at metal/water interface by use of the Kretschmann configuration

An infrared ATR technique using the Kretschmann configuration for exciting the surface electromagnetic field has been applied for the in-situ observation of adsorbed species at metal/aqueous solution interface. When an evaporated Ag film of about 10 nm in thickness is in contact with an acidic solution of mercaptobenzothiazole (MBT), the vibrational bands of a surface complex, Ag(I)MBT, are enhanced in intensity irrespective of the polarization state of the radiation. The polarization independence of the absorption enhancement can well be explained in terms of the excitation of transverse collective electron resonance associated with Ag islands. When a Ag film of 19 nm in thickness is used, absorption of the Ag(I)MBT complex is enhanced by p-polarized radiation only. The absorption intensity is maximum at an angle of incidence of 70° at which the background reflectivity is minimum. This enhancement involves the excitation of surface plasmon polaritons. Nearly the same results were obtained when Cu was used in the place of Ag.

Surface electromagnetic fields around surface flaws in metals

In an earlier paper(3) it was shown mathematically and confirmed by experiment that when a uniform surface alternating conduction current is incident on a spherical cap indentation at the surface of a metal there is no perturbation to the current flow on the plane surface outside the cap. It is shown here that this result is true of all axisymmetric surface cavities which are interrogated by any form of surface Laplacian current flow. The result applies, for example, to surface cavities in the form of right cylindrical stopped holes or to conical pits. The paper describes experiments confirming the result in those two cases for uniform incident currents. It also describes the case of an annular cylindrical hole where the theory predicts that a uniform surface current of lower strength than the incident uniform current is established on the central part of the surface plane. This gives rise to a linear variation in surface probe readings in a center line traverse which is also confirmed by experiment. These results are in marked contrast to the perturbations to the surface currents produced by surface cracks, which have been described in earlier work(2) by the use of unfolding algorithms.

Surface Electromagnetic Fields in the "Semi-Classical Infinite Barrier" Model: Collective and Single-Particle Response

The electromagnetic field near a metal surface is calculated within the "SCIB" model, which replaces the surface by a specular reflection condition on a homogeneous system and assumes the conduction electrons to respond according to Lindhard's dielectric function. The longitudinal fields included in the model are separated into contributions from a collective plasmon mode and from non-collective particle-hole excitations producing Friedel-type oscillations. The analytical properties of Lindhard's function in the complex k-plane are exploited to prove that these contributions sum in such a manner that, in contrast to previous erroneous statements, the normal component of the total electric field is continuous and no singular surface charges occur. Numerical results are presented which show that in a large frequency regime most of the electronic response is carried by the plasmon mode. These results, which refute earlier speculations about the physical implications of the SCIB model, are compared with other model calculations of surface fields.

Total internal reflection fluorescent microscopy.

This review discusses applications of fluorescence microscopy using totally internally reflected excitation light. When totally internally reflected in a transparent solid at its interface liquid, the excitation light beam penetrates only a short distance into the liquid. This surface electromagnetic field, called the 'evanescent wave', can selectively excite fluorescent molecules in the liquid near the interface. Total internal reflection fluorescence (TIRF) has been used to examine the cell/substrate contact regions of primary cultured rat myotubes with acetylcholine receptors labelled by fluorescent alpha-bungarotoxin and human skin fibroblasts labelled with a membrane-incorporated fluorescent lipid. TIRF examination of cell/surface contacts dramatically reduces background from cell autofluorescence and debris. TIRF has also been combined with fluorescence photobleaching recovery and correlation spectroscopy to measure the chemical kinetic binding rates and surface diffusion constant of fluorescent labelled serum protein binding (at equilibrium) to a surface.

The solution of 3-dimensional induction heating problems using an integral equation method

The boundary integral equation method is applied to the solution of the induction heating of three dimensional objects. Two methods are explored. The first uses a direct solution of the electric field integral equation and the second uses a combination of the electric and magnetic equations and represents the tangential components of the surface electromagnetic field by three scalar surface potentials. Both fields and potentials are given a finite element representation. Results for some simple cases are considered.

Surface electromagnetic fields

Recent progress in the theory of surface electromagnetic fields is reviewed. Difficulties are noted in applying the textbook theory of refraction to fields withinA˚of a surface. These difficulties have been overcome with the development of a nonlocal description of surface optics, that has largely been applied to free-electron metal surfaces. Various model versions of non-local surface optics are described and quantitatively compared. Opportunities for, and actual contact between the theory of surface electromagnetic fields and experiment are described. Directions for future research in the area are discussed.

The role of surface roughness in surface enhanced raman spectroscopy (SERS): the importance of multiple plasmon resonances

The interaction of light with clusters and random distributions of metal hemispheroids on a perfect conducting flat surface is studied. Significant SERS enhancements are found to arise from multiple plasmon contributions to the surface electromagnetic fields.

Enhancement in Raman intensity by use of surface plasmons

The excitation of surface plasmons at silver electrodes by attenuated total reflection allows one to intensify the Raman signal from adsorbed molecules. The enhancement of the Raman intensity as a result of the amplification of the surface electromagnetic field at the metal-electrolyte interface is demonstrated for pyridine on silver.

H-polarization induction in two thin half-sheets

The Wiener—Hopf technique is used to solve the problem of electromagnetic induction in two adjacent half-sheets underlain by a uniform conducting half-space. The H-polarization mode is considered in which the inducing magnetic field is assumed to be uniform and horizontal in space and directed parallel to the boundary between the two sheets. The solution, which complements one for E-polarization induction in two half-sheets obtained previously by Weidelt, is of geophysical interest in describing the change in apparent resistivity across a conductivity discontinuity near the Earth's surface and also in explaining the coast effect on geomagnetic variations recorded on the ocean-floor. The analysis shows that the horizontal electric field has a finite jump discontinuity where the two sheets meet and that the vertical electric field on the underside of the sheets has a logarithmic singularity there. Algebraic singularities occur in both components of the electric field when only one half-sheet is present. The surface electromagnetic field is calculated for two specific models, one of which represents a coastal region, and the results are compared with those obtained by a recently published numerical method. The pattern of induced current-flow associated with the coast effect is illustrated.

Surface electromagnetic wave mode and field analysis in a metal-metal-oxide-air system with damping

An explanation is provided for the surface electromagnetic wave (SEW) energy ejection from a thin film at the longitudinal and transverse optical-phonon frequencies of the film material. Field ratio calculations identify previously discussed metal-metal-oxide-air SEW modes as those expected from the Berreman configuration, and it is shown that Greenler technique high-incidence-angle-reflectance data on the same system may be similarly interpreted.

Surface differential operator and electromagnetic field tensor

In view of the recent work of Ross (see ibid, vol.7, p.705 (1974)) concerning Mandelstam's formulation of gauge-independent quantum electrodynamics, and involving the additional assumption of path independence, the use of a surface differential operator for the electromagnetic field quantities is suggested and some of the results so obtained are discussed.

The theory of Raman scattering by surface polaritons

AbstractThe fluctuation–dissipation theory of spontaneous Raman scattering (RS) by surface polaritons (SP) is carried out. The appearance of scattering emission is treated as the result of mixing of the pump emission and the fluctuating surface electromagnetic field. A calculation is made of the surface electromagnetic fluctuations near the interface between the two dissipative media and in the absorbing layer surrounded by transparent dielectrics. Expressions are found and analysed describing the frequency–angular distribution of the scattering emission intensity in the layer, taking into account the interference of SP localized near different surfaces (and near the interface of two absorbing media). The RS intensities are expressed by the phenomenological parameters of the media. It is also shown that the RS intensity decreases essentially with increasing scattering angle θ (when the scattering frequency approaches the frequency of the surface phonon) due to the increasing localization of SP. Various essential physical features of the phenomenon are analysed in detail: scattering line shape and its angular dependence; the Fermi resonance of SP and its display in the RS; mixing of SP of different media and RS by appearing mixed modes; RS by SP connected genetically with the linear medium which borders with the transparent nonlinear medium; evolution of RS in a layer by decreasing its thickness, and others.

Magnetotelluric response of a two-dimensional sloping contact by the finite element method

The finite element method, with triangular elements, is used to study the effect of a two-dimensional sloping contact on the surface electromagnetic fields. It is found in the case ofH-polarization and small slopes that the electric field and the apparent resistivity near the contact, on the conductive side, are higher than their asymptotic values. In the case ofE-polarization the apparent resistivity and phase values on the conductive side fall off less rapidly to their asymptotic values with decreasing slope resulting in higher apparent resistivity and phase values on the conductive side, than those expected for a vertical contact. The peak in the amplitude and phase of the normalized vertical magnetic field shifts from the resistive side for a vertical contact to the conductive side for a sloping contact. Far from the sloping contact, on the conductive side, higher values are observed for the normalized vertical magnetic field than in the case of a vertical contact.

The Effect of a Sloping Sea Floor on the Surface Electromagnetic Field

Plane electromagnetic waves are assumed to be incident normally on an ocean surface, overlying a sea floor of uniform slope. Berdichevskii's method of images is used to extend the computations of surface fields for a basement with non-zero conductivity, at sites remote from the coastline. The vertical magnetic field is enhanced over shallower depths while the horizontal electric field shows a transition from the polarization behaviour on the landward side of a continental shore to that on the seaward side. The fields are computed for slopes of 3° and 10° and compared with those over an ocean with a horizontal floor. The calculations are applied to three sets of measurements on iceislands in the Arctic Ocean; no disagreement is found, although quantitative explanation cannot be made owing to the difficulties of controlling the experimental conditions, or of simulating them precisely in a mathematical analysis.