Hendrik Bruns

Diffraction of a uniform complex source beam by a circular cone

The paper deals with the scalar (acoustic) diffraction of a uniform complex-source beam (Uniform CSB) by an acoustically soft or hard semi-infinite circular cone. The diffracted field is found by evaluating the bilinear modal form of the cones Greens function and by assigning suitable complex-valued source coordinates. The field expansion is valid everywhere in space including the waist of the beam and consists of a diverging as well as of a converging part. Results are shown for the scalar fields diffracted and scattered by the area around the tip of the circular cone.

Electromagnetic complex-source beam diffraction by the tip of a circular cone

The paper deals with the electromagnetic scattering and diffraction of a complex-source beam by a perfectly electrically conducting (PEC) semi-infinite circular cone. Particularly, we are interested in the diffraction by the tip of the circular cone as a function of various parameters (opening angle of the cone, angle of incidence, polarization). The results are important in the context of the application of asymptotic methods like GTD, UTD, or the complex-ray tracing (CRT) method.

Scattering and diffraction of an arbitrarily directed complex-source beam by a semi-infinite circular cone

The problem of an arbitrarily directed Gaussian beam (GB) illuminating an acoustically soft or hard semi-infinite circular cone is solved by using a complex source beam (CSB) whose waist and direction are defined by the real and imaginary parts of the source coordinate, respectively. The corresponding scalar boundary-value problem is solved by assigning a complex-valued source coordinate into the conventional spherical-multipole expression of the Greens function, thus converting it to the response to the incident CSB. The solution requires the calculation of the associated Legendre functions of the 1st kind for a complex-valued argument. Beside a numerical analysis of these calculations, we also present numerical results for the total near- and far-fields.

Obstacle-free particle measurement with a bistatic CW-radar

This paper compares two radar configurations with different antenna systems for measuring particle streams in the near field range. A complex source beam is employed to describe the field characteristics. This new approach is used to derive the associated antenna gain and power patterns and applied in the radar equation for particle streams. We demonstrate how indoor measurements benefit from a bistatic radar configuration and provide measurement results for streams with particles in the micron range.

Diverging and converging beam diffraction by wedges and cones

The complex source (CS) approach has long been used to obtain exact and approximate solutions for problems of beam-waves diffraction. However, the straightforward CS formulation may be applied only when the incident beam is diverging as it hits the scatterer, but not when it is converging. The present paper extends the CS method in the context of beam diffraction by wedges and cones, and present somewhat surprising rules for modifying the CS model so that it can addresses both the diverging incident beam (DIB) and the converging incident beam (CIB) cases. Using these models we demonstrate the different phenomenologies associated with each case.

Spherical-multipole expansion of an inhomogeneous electromagnetic plane wave in lossless media

The spherical-multipole expansion of an inhomogeneous electromagnetic plane wave is derived by extending the spherical source coordinates v to a complex number. The analytical results are successfully validated by comparing the numerical evaluation of the multipole expansion with the corresponding closed-form results. The paper also contains a first result for an inhomogeneous plane electromagnetic wave diffracted by a perfectly conducting semiinfinite circular cone.

Noninvasive Characterization of Solid Particle Streams Enclosed in a Dielectric Pipeline by a Bistatic Doppler Radar

This paper compares two radar configurations operating in the W-band with different antenna systems for measuring particle streams in the near-field range. A complex source beam is employed to describe the field characteristics. This new approach is used to derive the associated antenna gain and power patterns and applied in the radar equation for particle streams. We demonstrate how indoor measurements benefit from a bistatic radar configuration and provide measurement results for streams with particles in the micrometer size range. Owing to the bistatic configuration of the radar, the particle stream flowing through a plastic pipe has been detected showing the low interference caused by pipe walls, which enables nondestructive monitoring of particle streams through the dielectric pipe section.

Electromagnetic scattering of a complex-source beam by semi-infinite sectors and cones

A perfectly conducting semi-infinite elliptic cone is illuminated by an arbitrarily directed complex source beam (CSB). The boundary-value problem is solved by means of the corresponding spherical-multipole expansion of the electric field in sphero-conal coordinates. The CSB is realized by assigning a suitable complex value to the source coordinate of a Hertzian dipole. The CSB which asymptotically represents a Gaussian beam, that is a localized plane wave, can be used to probe any desired area of the elliptic cone. Besides, the resulting multipole expansion does not suffer from convergence problems as observed in case of an incident full plane wave.

Derivation of diffraction coefficients from complex-source beam solutions to canonical problems

The spherical-multipole analysis in sphero-conal coordinates in combination with a complex-source beam as the incident field has been utilized to derive the scattered electromagnetic far-field of a PEC plane angular sector. That canonical problem is of particular practical interest as many structures contain edge-like elements which cannot be treated by common asymptotic high-frequency techniques. The numerical evaluation yields exact and convergent spherical-multipole results which are ready for use in GTD/UTD frameworks.