Uniaxially prestretched recast Nafion membranes exhibited an unusual combination of properties (a proton conductivity equal to that of commercial Nafion but with a lower methanol permeability) which make them ideal candidates for use in a direct liquid methanol fuel cell. To better understand the function and underlying morphology of the prestretched membranes, water uptake and mobility data were collected and analyzed for draw ratios ranging from 1 to 7. Macroscopic (gravimetric) water uptake and the water self-diffusion coefficient (measured by NMR) were found to be invariant with membrane elongation and essentially identical to those measured in a commercial Nafion 117 film (a similar behavior was observed for proton conductivity). The ratio of freezable/nonfreezable water in prestretched recast Nafion, the water electro-osmotic drag coefficient, and the spin-lattice relaxation time constant of deuterated water, however, decreased with increasing film elongation, up to a draw ratio of 4. The functional dependence of these properties on draw ratio was similar to that observed for methanol permeability. The combined water results indicated that there were a greater number of smaller ionic/ hydrophilic domains in prestretched recast Nafion as compared to commercial Nafion. Transmission electron microscopy of membrane cross sections confirmed this conclusion.
ABSTRACT:A linear open slot antenna with two open ends for the dual-wideband LTE/WWAN operation in the 698-960 and 1710-2690 MHz bands is presented for the smartphone application. The proposed antenna is referred to as a dual-opening slot (DOS) antenna and is especially suitable for the modern slim tablet device, such as a 5.5-inch smartphone. The DOS antenna has a slot length of 75 mm and a narrow slot width of 2 mm, and can be disposed with a short distance of 8 mm to the top or bottom edge of the smartphone. The DOS antenna will hence not overlap the display panel in the smartphone. This makes it promising and attractive for practical smartphone applications. As the DOS antenna has two open ends, two open slots [a first (longer) open slot and a second (shorter) open slot] can be created using a metal pad to short-circuit the DOS across its two parallel edges at a proper position. The first and second open slot antennas are then respectively excited by a first feed and a second feed. By further with the aid of wideband matching networks in the two feeds, the DOS antenna can provide two wide operating bands to cover the LTE/WWAN operation. Details of the DOS antenna are described in this study.
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