Incoming Electromagnetic Wave Research Articles

High-resolution angular and displacement sensing based on the excitation of surface plasma waves

The possibility of building angular and displacement sensors based on the phenomenon of attenuated total reflection (ATR) is explored both numerically and experimentally. ATR occurs when a surface wave is excited by an incoming TM electromagnetic wave through a resonant phase-matching process, as in the Kretschmann coupling scheme. The reflected intensity strongly depends on the angle of incidence of the beam. We first show some computations of the sensitivity and the linearity of an ATR-based sensor, then proceed to the experiment, illustrating how an angular resolution of the order of 0.1 arc sec can be obtained with moderate effort. Finally we show how the sensor, combined with a simple optical arrangement, can be used to detect and measure nanometric displacements, as those provided by piezoelectric actuators.

Angular momentum photon drag in a mesoscopic ring

It is predicted that an incoming electromagnetic wave possessing a net angular momentum may generate a steady-state current in a mesoscopic metallic (or semiconducting) ring by means of its nonlinear electrodynamic interaction with the conduction electrons of the ring. In a sense this phenomenon is analogous to the classical photon-drag effect which originates in a nonlinear exchange of linear momentum between the photon and electron fields. In the wake of the establishment of the basic theory, a numerical calculation and an analysis of the angular-momentum photon drag in a mesoscopic Au ring are presented. Particular attention is paid to a study of the photon-drag current as a function of the photon energy, and it is shown that the drag current provides a detailed fingerprint of the allowed angular electronic transitions of the ring if the collision frequency of the conduction electrons is sufficiently low.

Application of spectral domain Prony's method to the FDTD analysis of planar microstrip circuits

Residual reflection from absorbing boundaries that truncate the computational mesh in the finite-difference time-domain (FDTD) method introduces significant error in the characterization of transmission lines and discontinuities employed in microwave and millimeter-wave integrated circuits. We apply the least squares Prony's method to accurately estimate the complex reflection coefficient (at Mur's absorbing boundary) in the frequency domain by representing the sampled voltages along a microstrip transmission line as a plane wave superposition of incoming and outgoing transverse electromagnetic (TEM) waves at each reference port. Prony's method is used to compute the frequency-dependent effective dielectric constant of a microstrip line and the scattering parameters of microstrip circuit elements, which corroborate well with published and measured results. A new method is discussed to reduce the computer memory required to store the temporal samples which are employed in the spectral processing of the FDTD data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The propagation of electromagnetic waves in magnetoelectric crystals: The discrete dipole approach

Abstract The propagation of an electromagnetic wave through a crystal consisting of atoms which display electric, magnetic and magnetoelectric interactions is described. The incoming electromagnetic wave induces electric and magnetic dipoles in this system, which will generate, through their polarizabilities, electric and magnetic dipole fields. By a self-consistency procedure we arrive at a secular determinant equation, which yields the normal mode wavevectors in the bulk. A computer program is generated to find these wavevectors and the accompanying dipole strengths. Some model calculations are performed. A comparison with classical continuum approaches is made and small differences are found.

Optical Properties of Cometary Dust

AbstractCometary dust is observed in a variety of ways: scattered light, thermal emission, stellar occultations, coma and tail morphology, radar echoes, and meteors associated with comets. To interpret these observations with respect to the physical parameters of the dust (size, shape, and composition) and the properties of the dust-emitting region, the physics of how electromagnetic radiation interacts with small particles must be understood.The interaction between electromagnetic radiation and a small particle depends on the size, shape, and composition of the particle. The composition determines the optical constants of the material. Classically, a solid can be approximated by a collection of bound charges with a number of resonant frequencies. The optical constants (the index of refraction or dielectric constant) are a measure of the ability of the material to vibrate in response to an incoming electromagnetic wave. The laboratory measurement of optical constants is very difficult, and many published optical constants may be in error. Care must also be taken in choosing the optical constants that best represent the assumed composition of the cometary dust.Scattering theory is usually synonymous with Mie theory, although Mie theory pertains only to spherical particles. In many cases, homogeneous spheres may be good approximations of the dust in the coma, but an understanding of the effects of non-sphericity and heterogeneity is essential to determine the limitations of the spherical approximation. A variety of methods exist that, although computationally intensive, do provide insight into shape effects.

First‐order Wiener‐Hermite expansion in the electromagnetic scattering by dielectric rough interfaces

The electric and magnetic currents induced by an incoming electromagnetic wave on a rough surface which separates free space from a lossy dielectric medium are calculated as expansions to first‐order in Wiener‐Hermite functionals. The diffuse scattered intensity resulting from this approach is compared with the classical results following from the use of perturbation theory or the Kirchhoff approximation.

Colliding plane gravitational and electromagnetic waves

A new class of type-II Einstein-Maxwell fields is presented. These describe the space-time subsequent to a collision of a gravitational wave with an electromagnetic wave. The gravitational wave is an arbitrary pp wave with generally non-constant polarisation. The incoming electromagnetic wave is also an arbitrary pp wave, and it is shown that this is partially reflected by the gravitational wave.

On the dielectric theory of a molecular crystalline slab with complex polarisability

Expressions for the transmission, reflection and absorption coefficients of a crystalline slab of polarisable molecules are obtained. The results are applied to one and two oscillator models with dissipation and with parameter values suggested by experimental data for the rare gas solids. The usual macroscopic, point equation of state D= ϵE, is found to give a satisfactory description of the dielectric response except near the molecular resonance frequencies. The deviations from the macroscopic theory depend on the strength of the dissipation and vary with the orientation of the slab faces with respect to the lattice and possibly the polarisation of incoming electromagnetic wave.

Resonant absorption due to dc magnetic fields parallel to the density gradient

A new resonant absorption mechanism of an electromagnetic wave incident on a magnetized plasma is investigated. A dc magnetic field along the density gradient couples the incoming electromagnetic wave to electromagnetic waves in other directions. These electromagnetic waves drive electrostatic waves which results in resonant absorption of the incident electromagnetic wave. This indirect process can be well separated from the direct process in the s polarization case in which a maximum absorption of 90% is obtained. For completeness, the total directly and indirectly driven absorptions due to perpendicular, parallel, and azimuthal magnetic fields are obtained.

Newman-Penrose Constants and Their Invariant Transformations

The origin and significance of the Newman-Penrose (N-P) constants of the motion are examined from the point of view that constants of the motion generate invariant transformations. Here the calculation makes use of a generalization of Green's theorem to a situation applicable to the coupled Einstein-Maxwell fields in general relativity. One finds strictly electromagnetic constants generated by an incoming electromagnetic shock wave, with dipole symmetry, at future null infinity. The gravitational constants contain an admixture from the electromagnetic field. They are generated by an incident quadrupole gravitational shock wave at future null infinity (J+). Both the electromagnetic dipole field and the gravitational quadrupole field behave like linearized fields at J+. All higher-multipole fields do not uncouple from the nonlinear corrections induced by the self-coupling of the gravitational field and its coupling with the electromagnetic field. It is shown that the gravitational constants are related to the rate of shear of the null rays near J+ a result which suggests a connection with sources. Finally, the supertranslation invariance of the result is discussed.

Tensor Scattering Matrix for the Electromagnetic Field

The scattering of an arbitrary incoming electromagnetic wave by an unrestricted scattering object is described in terms of a tensor scattering matrix. General reciprocity relations and the cross-section theorem, including an interesting extension, are established using this representation. The results are related to the special case of plane-wave scattering and the scattering matrix is explicitly exhibited in terms of the plane-wave scattering amplitude for two mutually perpendicular directions of polarization.

Ultra-High-Frequency Radiosonde Direction Finding

A simple radio direction finder, operating at 183 megacycles, for observing the flight of meteorological balloons is described. An Adcock antenna and a single-dipole antenna system, including a corner-type reflector as shield against ground-reflected waves, were used for measuring the azimuthal and the elevation angles of an incoming electromagnetic wave. Shielding characteristics of the corner-type reflector for various wire spacings, focal lengths, and wire lengths are given. The direction finder has an accuracy of ¼ degree in the determination of the azimuthal angles. An accuracy of ½ degree is easily obtained in the determination of the elevation angles when a stationary transmitter is used as target on top of Mt. Wilson at a distance of seven miles. Larger errors in the elevation angles were observed when the target transmitter was sent aloft on balloons.