RESUMO
The excitation efficiencies for coupling surface electromagnetic waves onto aluminum at a microwave frequency (f = 8.445 GHz, lambda = 3.55 cm) were studied experimentally for several different standard microwave techniques as well as two optical techniques (prism and grating) applied to the microwave frequency region and two new techniques (hump and valley). The peak measured efficiencies found were: for the standard rectangular waveguide, 92%; for the horn antenna, 73%; for the right angle prism properly gapped above the metal, 60%; for the hump of 10-wavelength radius of curvature, 35%; for the thin grating strips on polystyrene coated metal, 30%; for the grating bars gapped (1/2) wavelength above the metal, 26%; and, for the valley of 10-wavelength radius, 12%. The measurement of the excitation efficiencies for prism and grating coupling techniques sometimes required that the prism or grating be in the near field of the antenna. In addition to measuring peak efficiencies, the efficiencies were measured as functions of the gap heights, the angular orientations, the different diffraction modes, the shapes, and the materials of the grating bars. The coupling efficiencies for both prism and grating couplers show a strong dependence on gap height above the metal. Dielectric grating bars were found to be inefficient compared to solid or hollow metallic bars, or thin metallic strips. The distance between the target point of the center line of the microwave horn antenna and the corner of the prism was found to be about 1 wavelength for maximum prism coupling efficiency.
RESUMO
Excitation of surface electromagnetic waves (SEW) on water was studied using optical coupling techniques at microwave frequencies. Excitation of SEW was also achieved using direct horn antenna coupling. The transmitted SEW power was increased by adding acid and salt to water. The horn antenna gave the maximum excitation efficiency 70%. It was increased to 75% by collimating the electromagnetic beam in the vertical direction. Excitation efficiency for the prism (0 degrees pitch angle) and grating couplers were 15.2% and 10.5% respectively. By changing the prism coupler pitch angle to +36 degrees , its excitation efficiency was increased to 82%.
RESUMO
Two-dimensional optical effects were observed for surface electromagnetic waves (SEW) on metals at lambda = 3.55 cm. Refractive processes with prisms and lenses established Snell's law experimentally. Reflection with prisms and metal sheets established the law of reflection and indicated that radiative losses were small and that Fresnel's equations hold to a good approximation for the reflectivities of SEW. A two-dimensional SEW grating was made and first-order diffraction observed. Although the experiments were performed at microwave frequencies, the principles are usable for two-dimensional SEW optics at least as far as the near ir. It was shown that the propagation constant of the SEW with an overlayer material is as though the SEW propagates entirely in the overlayer material. That is, losses in the metal substrate were negligible.
RESUMO
The first measurements of the absorption coefficient of materials via surface electromagnetic wave (SEW) techniques are reported. By simply laying samples on a metal sheet on which SEW were passing, the transmittances and absorption coefficients of the sample have been determined. These measurements were made at microwave frequencies, but the general techniques are applicable over the entire frequency range from microwaves into the near ir. Solid samples were used in these measurements, but liquid or gases could also be studied by this new easy-to-use technique. Comments about the applicability of the technique to very thin samples are made. Another result reported is the existence of different propagating SEW modes as a function of the height of a sample (film thickness) measured from the metal-sample interface to the top of the sample at the sample-vacuum interface above.