Abstract-A low-loss passive metamaterial exhibiting negative refractive index or "double negative" electromagnetic properties at microwave frequencies is proposed. The metamaterial is a lattice of spherical particles made up of multiple dielectric materials in concentric layers. Because no magnetic constituents (that tend to have higher losses) are involved, the negative-index behavior is possible with very low values of attenuation. A negative-index metamaterial based on dielectric-coated metal spheres is also proposed, and is predicted to have lower attenuation than other structures based on metallic scatterers. Numerical results and design principles are given.

Phase resonances in transmission compound structures with subwavelength slits produce sharp dips in the transmission response. For all equal slits, the wavelengths of these sharp transmission minima can be varied by changing the width or the length of all the slits. In this paper we show that the width of the dip, i.e., the frequency range of minimum transmittance, can be controlled by making at least one slit different from the rest within a compound unit cell. In particular, we investigate the effect that a change in the dielectric filling, or in the length of a single slit, produces in the transmission response. We also analyze the scan angle behavior of these structures by means of band diagrams and compare them with previous results for all-equal slit structures.

The Total Irradiance Monitor (TIM) is a total solar irradiance (TSI) instrument designed to achieve a relative standard uncertainty (1 σ accuracy) of 100 parts per million (ppm) and a precision and long-term uncertainty of 10 ppm/year. This instrument is one of four on the Solar Radiation and Climate Experiment (SORCE), a NASA/EOS satellite mission scheduled for launch in Nov. 2002. The TIM will report four TSI measurements d aily throughout SORCE's goal 5-year mission life. Instrument DescriptionElectrical Substitution Radiometers (ESRs) measure incident radi ant power. The four ambienttemperature TIM ESRs operate in pairs, with a DSP-controlled servo system continually balancing the temperature of an active ESR to its paired reference ESR. Incident sunlight passing through an open shutter and a precision aperture radiatively heats the active ESR. The replacement electrical heater power required by this ESR to maintain thermal balance as the shutter is cycled determines the incident solar irradiance.The relative standard uncertainty of this primary instrument is 100 ppm (1 σ) with 2 ppm noise.

In recent years, increasing deployment of large wind-turbine farms has become an issue of growing concern for the radar community. The large radar cross section (RCS) presented by wind turbines interferes with radar operation, and the Doppler shift caused by blade rotation causes problems identifying and tracking moving targets. Each new wind-turbine farm installation must be carefully evaluated for potential disruption of radar operation for air defense, air traffic control, weather sensing, and other applications. Several approaches currently exist to minimize conflict between wind-turbine farms and radar installations, including procedural adjustroents, radar upgrades, and proper choice of low-impact wind-farm sites, but each has problems with limited effectiveness or prohibitive cost. An alternative approach, heretofore not techoically feasible, is to reduce the RCS of wind turbines to the extent that they can be installed near existing radar installations. This report summarizes efforts to reduce wind-turbine RCS, with a particular emphasis on the blades. The report begins with a survey of the wind-turbine RCS-reduction literature to establish a baseline for comparison. The following topics are then addressed: electromagnetic model development and validation, novel material development, integration into wind-turbine fabrication processes, integrated-absorber design, and wind-turbine RCS modeling. Related topics of interest, including alternative mitigation techoiques (procedural, at-the-radar, etc.), an introduction to RCS and electromagnetic scattering, and RCS-reduction modeling techniques, can be found in a previous report.

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