An efficient iterative algorithm for computation of scattering from dielectric objects.

We have developed an efficient iterative algorithm for electromagnetic scattering of arbitrary but relatively smooth dielectric objects. The algorithm iteratively adapts the equivalent surface currents until the electromagnetic fields inside and outside the dielectric objects match the boundary conditions. Theoretical convergence is analyzed for two examples that solve scattering of plane waves incident upon air/dielectric slabs of semi-infinite and finite thicknesses. We applied the iterative algorithm for simulation of sinusoidally-perturbed dielectric slab on one side and the method converged for such unsmooth surfaces. We next simulated the shift in radiation pattern of a 6-inch dielectric lens for different offsets of the feed antenna on the focal plane. The result is compared to that of the Geometrical Optics (GO).

Millimeter wave detection of nuclear radiation: an alternative detection mechanism.

We present a nuclear radiation detection mechanism using millimeter waves as an alternative to conventional detection. It is based on the concept that nuclear radiation causes ionization of air and that if we place a dielectric material near the radiation source, it acts as a charge accumulator of the air ions. We have found that millimeter waves can interrogate the charge cloud on the dielectric material remotely. This concept was tested with a standoff millimeter wave system by monitoring the charge levels on a cardboard tube placed in an x-ray beam.

Emission of coherent THz radiation from superconductors.

Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to approximately 50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

Three-dimensional magnetic resonance microscopy of materials.

Several aspects of magnetic resonance microscopy are examined employing three-dimensional (3D) back-projection reconstruction techniques in combination with either simple Bloch-decay methods or MREV-8 multiple-pulse line narrowing techniques in the presence of static field gradients. Applications to the areas of ceramic processing, catalyst porosity measurements and the characterization of polymeric materials are presented. The focus of the discussion centers on issues of sensitivity and resolution using this approach compared with other methods. Advantages and limitations of 3D microscopy over more commonly employed slice selection protocols are discussed, as well as potential remedies to some of the inherent limitations of the technique.