This paper presents the developed orthogonal frequency division multiplexing (OFDM) baseband processor employing adaptive modulations to grouped subcarriers, and its demonstration in millimeter-wave wireless indoor links. Channel measurements and characterizations are performed in line-of-sight (LOS) office environments where the developed OFDM system is supposed to be used. The OFDM baseband processor utilizes 192 data subcarriers among 256 FFT numbers. To minimize bit-error-rate (BER) performance in frequency selective channels of millimeter-wave wireless indoor links, these 192 data subcarriers are grouped into 24 subcarrier groups and independently modulated according to channel characteristics in each subcarrier group. We demonstrate it incorporating with the developed 70 GHz self-heterodyne transceiver. BER measurements and maximum TCP throughput test are performed in practical millimeterwave indoor environments. The results verify the advantages of the proposed adaptive modulation in OFDM and show better BER performance as well as higher throughput performance than a typical OFDM system.
With increasing hydrogen demand, the development of a low-cost and high-performance anion-exchange membrane water electrolysis (AEMWE) stack is crucial. Here, two AEMWE models using all non-noble metal-based components were developed. Three components of the membrane electrode assembly─a porous transport layer (PTL), an oxygen evolution reaction (OER) catalyst, and a hydrogen evolution reaction (HER) catalyst─were examined to be substituted for a non-noble metal. The results revealed that stainless steel felt and carbon paper were the anode and cathode PTLs, respectively, exhibiting the highest and most durable performance. Additionally, nickel–iron (NiFe) was selected as the most applicable OER catalyst. Further, low-loading platinum and nickel–iron oxide (NiFeOx) were optimized as suitable HER catalysts. For a single cell, the resulting AEMWEs showed outstanding performance of 4633 and 1231 mA cm–2 at 2.1 V, with stable performance for 500 h. Further, they exhibited a higher performance relative to their cost than all noble metal AEMWEs. High performances were also observed for 5-layer stacks, in addition to stable durability and energy conversion efficiency. This work supports the commercialization of a low-cost, high-performance, and durable AEMWE stack.
Asymmetric supercapacitors are receiving much research interests due to their wide operating potential window and high energy density. In this study, we report the fabrication of asymmetrically configured yarn based supercapacitor by using liquid-state biscrolling technology. High loading amounts of reduced graphene oxide anode guest (90.1 wt%) and MnO
We developed a flexible two-ply piezoelectric yarn-type generator using an electrospun polyvinylidenefluorideco- trifluoroethylene (PVDF–TrFE) mat and a commercially available silver-coated nylon fiber. By rolling the silvercoated nylon fiber into the electrospun PVDF–TrFE mat as the inner electrode, the two-dimensional piezoelectric PVDF– TrFE mat was easily transformed into a one-dimensional fiber. Then silver-coated nylon fiber rolled in PVDF–TrFE was plied with another similar fiber to make a flexible two-ply piezoelectric yarn. The overall fabrication processes of the flexible two-ply piezoelectric yarn are simple and have a high application potential. The flexible two-ply piezoelectric yarn can generate up to 0.7 V in compression and 0.55 V in tension. The yarn retained the piezoelectric performance in various shapes, such as a sewn structure. In addition, the piezoelectric performance was sensitive to velocity and pressure. The flexible two-ply piezoelectric yarn has potential applications as a human motion sensor, as a building block of energy- harvesting textiles, and in self-powered biomedical applications. Keywords: Energy harvester, Flexible, Piezoelectric, Two-ply, Wearable, Yarn.
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