Heat-assisted magnetic recording (HAMR), also known as hybrid recording, has been proposed to enable storage densities greater than 1 Tb/in 2 in hard disc drives while circumventing the superparamagnetic limit. Light is delivered in the near field to the recording medium to heat just the spot which is to be recorded. Techniques based on apertures, antennas, waveguides, and solid immersion lenses have been suggested for delivering substantial amounts of optical power into subwavelength spots in the near field. A practical transducer for HAMR may require a combination of techniques.

Using the scattered field finite difference time domain (FDTD) formalism, equations for a plane wave incident from a dense medium onto lossy media are derived. The Richards-Wolf vector field equations are introduced into the scattered field FDTD formalism to model an incident focused beam. The results are compared to Mie theory scattering from spherical lossy dielectric and metallic spheres.

Three-dimensional thermal and radiometric models have been developed to study the passive IR signature of a land mine buried under a rough soil surface. A Þnite element model is used to describe the thermal phenomena, including temporal variations, the spatial structure of the signature, and enviromental effects. The Crank-Nicholson algorithm is used for time-stepping the simulation. The mine and the surroundings are approximated by pentahedral elements having linear interpolation functions. The FEM grid for the soil includes a random rough surface having a normal probability density and speciÞed covariance function. The mine is modeled as a homogeneous body of deterministic shape having the thermal properties of TNT. Natural solar insolation (both direct and atmosphericscattered components) and the effects of convective heat transfer are represented by linearized boundary conditions. The behavior over a periodic diurnal cycle is studied by running the simulation to steady state. Finite element solutions for the thermal emissions are combined with reßected radiometric components to predict the signatures seen by an IR camera. Numerical simulations are presented for a representative target, a 25 cm anti-tank mine simulant developed by the US Army. The temporal evolution of the temperature distribution and IR signature are presented for both smooth and rough surfaces.

Abstract.Basis functions that are used to model surface electric current densities in the electric field integral equations of computational electromagnetics are analyzed with respect to how well they model the charge distribution, in addition to the current. This analysis is carried out with the help of the topological properties of open and closed surfaces meshed into networks of triangles and quadrangles. The need for current basis functions to properly model the charge distribution is demonstrated by several examples. In some of these examples, the basis functions seem to be perfectly legitimate when only the current distribution is considered, but they fail to deliver a correct solution of the electromagnetic problem, since they are not capable of properly modeling the charge distribution on some surfaces. Although the idea of proper modeling of the charge distribution by the current basis functions is easy to accept and can even be claimed well known, the contrary uses encountered in the literature have been the motivation behind the investigation reported in this paper.

We describe sensor-based and signal-processing-based techniques for improving the detection of buried land mines in thermal infrared imagery. Results of experimental studies using MWIR (2.2-4.6 µm) and LWIR (8-12 µm) imaging systems are reported. Thermal clutter due to surface reßected sunlight and skylight are investigated and shown to be the dominant clutter component for both MWIR and LWIR imagery collected during daylight hours. A sensorbased clutter reduction technique, spectral differencing, was considered and found to provide some beneÞt. The temporal evolution of thermal signatures was investigated. The imagery are found to have near-Gaussian statistics, and therefore the deßection coefficient is a valid measure of detectability. The deßection coefficient for some buried mines was found to improve with time after sunset. In addition, the LWIR band appears to offer some advantages in detection. Clutter mitigation via signal processing is also explored using an "estimator-classiÞer" technique in which target-related parameters (features) are estimated from the data and detected with a classiÞer. The theoretical basis of the method is discussed. MWIR and LWIR imagery are used to illustrate both the sensor-based and signalprocessing-based techniques.