Metal-free super-wideband THz absorber for electromagnetic shielding

A technique is implemented for obtaining the high absorption over super-wideband (SWB) in a metal-free THz absorber. The multiple resonant modes with wide spectra are generated in a graphite-based resonator placed on a dielectric cavity merging of which provides the SWB response. The low permittivity dielectric slab sandwiched between the graphite sheet at its bottom and graphite resonator at its top acts as the Fabry–Perot cavity where absorption takes place. The high absorption rate of graphite in the THz regime can make it a suitable candidate for its utilization in implementing the broadband absorber. Thus, the molecular transition due to interaction of energy in graphite also provides the high absorption. The absorption bandwidth can further be enhanced by stacking of multiple layers in two different configurations of the proposed unit cell. The absorber maintains the polarization insensitivity due to symmetry and allows the high absorption for the electromagnetic wave incident up to the angle of more than 75 ° . The proposed absorber can be utilized in the THz electromagnetic shielding applications due to its SWB response.

New Thermal Design Strategy to Achieve an 80-kg-Class Lightweight X-Band Active SAR Small Satellite S-STEP

The main objective of the S-STEP (the Small Synthetic Aperture Radar (SAR) Technology Experimental Project (S-STEP)) mission is developing an 80-kg-class active X-band SAR observation small satellite. For lighter, smaller, better, and cheaper development of the S-STEP system, a new thermal design strategy is essential. Therefore, we proposed a new thermal design strategy in this study. The main features of the proposed thermal design involve the minimization of heater power consumption by optimizing environmental heat fluxes on the satellite, the provision of long-term SAR imaging duration in both right- and left-looking modes, and the use of a lightweight flexible graphite sheet as a thermal interface for some high-power instruments. These features contribute to minimizing the satellite’s mass budget through heater power minimization and achieving on-orbit system performance of S-STEP. The effectiveness of the proposed thermal design was numerically verified by on-orbit thermal analysis of the S-STEP system. In addition, the thermal design on a key payload component and the multifunctional transmit/receive module structure were verified through a space-simulated thermal vacuum test.

High Temperature Aged Leakage Relaxation Screening Tests on Confined Flexible Graphite Gaskets

Flexible graphite-based gaskets are used extensively in high-temperature applications as a replacement of asbestos based gaskets. The effect of aging and temperature exposure of flexible graphite sheet gaskets was the subject of a previous work [1,2], however, the effect when flexible graphite is in a confined gasket configuration is not known. This study outlines the performance evaluation of the elevated temperature behavior of flexible graphite-based gaskets under a confined configuration and exposed over a long period employing HALR (High temperature Aged Leakage Relaxation) fixture. This ARLA-like fixture can retain the mechanical feature of the ATRS/HATR while allowing the cold leakage rate and weight loss measurement. Four different confined gasket configurations, namely corrugated metal, spiral wound, kammprofile and double jacketed, are evaluated within a temperature range of (427 to 649 °C) 800 to 1200 °F and exposure time of 2500 hours. Graphite weight loss, gasket thickness change, leakage and tightness parameter, creep and relaxation measurements were taken at regular intervals for each gasket style. To better understand the aging process, these critical mechanical and leakage properties are scrutinized; the degradation process related to mainly graphite oxidation is further discussed, and a conclusion is drawn.