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The electromagnetic (EM) radiation problem for a prolate spheroidal antenna with a double-negative (DNG) metamaterial (MTM) radome is studied using the method of separation of the spheroidal scalar wave functions. The unknown expansion coefficients are found by applying the boundary conditions at each spheroidal surface. Numerical results show that the radiation pattern of a prolate spheroidal antenna coated with a half-wavelength confocal DNG MTM radome is practically the same as the uncoated antenna pattern, which can be intuitively explained by suggesting that the inductance introduced by the DNG MTM radome may cancel the capacitance introduced by the air layer between the antenna and the radome. This means that the DNG MTM radome can be electrically transparent to the antenna, and has almost no effect on the antenna's radiation pattern. Our results also show that this DNG MTM radome can be placed much closer to the antenna than a conventional dielectric one with a given system performance; therefore the size of the antenna system can be significantly reduced. [ABSTRACT FROM AUTHOR]

The possibility of using metamaterial covers to dramatically enhance the total scattering cross-sections (SCS) or drastically reduce total SCSs of spheroidal objects is presented. The scattering problem by a conducting spheroid with metamaterial coating at axial incidence is studied using an analytic solution by expanding the incident and scattered waves in terms of spheroidal vector wave functions and imposing the appropriate boundary conditions at each spheroidal surface. Numerical results show that the total SCSs of a conducting spheroid with different metamaterial coatings can be dramatically enhanced to achieve 'sub-wavelength resonant structures' or drastically reduced to achieve 'transparency' of objects. The results with different parameters, such as relative permittivity, the spheroidal geometry, and the ratio of semimajor axes of two layers, are provided and discussed. [ABSTRACT FROM AUTHOR]

This paper presents the theory and analysis of phase mode excitation of both prolate and oblate spheroidal antenna arrays in terms of spheroidal wave functions, which is an extension of the spherical counterparts reported in the literature. Theoretical and numerical results show that a spheroidal phase mode of the excitation function produces a far field radiation pattern with the same spheroidal phase mode form, and the elevation angle of that pattern increases (decreases) with the ratio of the interfocal distance of the prolate (oblate) spheroid antenna array to the wavenumber. [ABSTRACT FROM AUTHOR]

The efficacy of pest control of three different oil formulations in multiple low-concentration spray programmes on sweet orange and pummelo were compared with unsprayed and normal farmer-treatments over three years. Phytotoxicity of sprays was assessed in terms of fruit and leafdrop, fruityield and external fruitquality. Trees sprayed with any type of oil had lower pest numbers than unsprayed trees. On sweet orange, the heaviest oil was better than the normal farm practice at controlling chaff scale on fruit and red mite and whitefly on leaves. On pummelo it provided the best control of red mite on leaves. All three oils were as effective as the normal farm practice in control of rust mite on sweet orange fruit and leaves and red mite, rust mite and red scale on pummelo fruit. On sweet orange trees there was no evidence of phytotoxicity, and the external quality of fruit generally improved over time. On pummelo trees, oil sprays were unable to improve the external fruitquality. The number of pummelo per tree was reduced in three of the oil spray schedules in 1995 and one in 1996, but the total weight of fruit harvested per tree was unaffected. [ABSTRACT FROM AUTHOR]

The efficacy of petroleum spray oil against citrus psylla was tested in Guangzhou, China. As the oil concentration increased from 0.25% to 1.0% there was a linear decrease in the number of psylla of each stage present on foliar shoots after 8 days. When psylla infested shoots were sprayed with equivalent oil concentrations, survival was significantly different between oil treatments. Psylla survival was also stage-dependent, with 1st- 2nd instars being the most susceptible and eggs being the most tolerant to oil. Oil efficacy was compared to an organophosphate pesticide and an insect growth regulator, and all provided similarly effective controlofpsylla nymphs. Controlofeggs was not achieved by any of the treatments as application of sprays was not correctly timed. [ABSTRACT FROM AUTHOR]