Central-fed hemispherical helical antenna
The characteristics of a hemispherical helical antenna with central-fed are investigated by experiment. Results for a 3-turn hemispherical helix indicate that circular polarization can be obtained over a wide angular range with relatively high gain of about 8 dB. The frequency bandwidth for a 3-dB axial ratio criterion is /spl sim/11%, with a nearly resistive input impedance of 163 /spl Omega/.
A Self-matching Hemispherical Helical Antenna
This paper presents the design of self-matching hemispherical helical antenna. The obtained experimental and simulated results show that adding the copper strip can both match the antenna and maintain its circularly polarized (CP) performance. This technique makes the proposed hemispherical helical antenna more attractable in satellite communication
Experimental energy barriers to anions transporting through nanofiltration membranes.
Environmentally relevant contaminants fluoride, chloride, nitrate, and nitrite face Arrhenius energy barriers during transport through nanofiltration (NF) membranes. The energy barriers were quantified using crossflow filtration experiments and were in the range of 7-17 kcal·mol(-1), according to ion type and membrane type (Filmtec NF90 and NF270). Fluoride faced a comparatively high energy barrier for both membranes. This can be explained by the strong hydration energy of fluoride rather than other ion properties such as bare ion radius, fully hydrated radius, Stokes radius, diffusion coefficient, or ion charge. The energy barrier for fluoride decreased with pressure, indicating an impact of directional force on energy barriers. The influence of temperature-induced pore radius variability and viscosity on energy barriers was considered. The novel link between energy barriers and ion properties emphasizes the importance of ion hydration and/or partial dehydration mechanisms in determining transport in NF.