Low-complexity and MAI-robust wireless broadcasting system with return channel

A combination of orthogonal frequency division multiplexing (OFDM) with frequency-division multiple access (FDMA) called orthogonal frequency-division multiple access (OFDMA) is regarded as a promising solution for improving the performance of interactive wireless broadcasting systems. This paper deals with our investigations into improving the performance and reducing the complexity of a digital multimedia broadcasting (DMB) system with a return channel when OFDMA is used as an access scheme. To alleviate a multiple access interference (MAI) introduced by a symbol timing misalignment, the OFDMA-based DMB system adopts frequency diversity and cyclic suffix (CS) at the transmitter, namely FD-OFDMA DMB system with CS. When the system is fully loaded, in addition to low complexity at the transmitter, the performance of the FD-OFDMA DMB system with the CS comes close to that of a single-user FD-OFDMA system at the cost of a small loss of throughput.     

Millimeter Wave MMIC Low Noise Amplifiers Using a 0.15 µm Commercial pHEMT Process

This paper presents millimeter wave monolithic microwave integrated circuit (MMIC) low noise amplifiers using a 0.15 µm commercial pHEMT process. After carefully investigating design considerations for millimeter-wave applications, with emphasis on the active device model and electomagnetic (EM) simulation, we designed two singleended low noise amplifiers, one for Q-band and one for V-band. The Q-band two stage amplifier showed an average noise figure of 2.2 dB with an 18.3 dB average gain at 44 GHz. The V-band two stage amplifier showed an average noise figure of 2.9 dB with a 14.7 dB average gain at 65 GHz. Our design technique and model demonstrates good agreement between measured and predicted results. Compared with the published data, this work also presents state-of-the-art performance in terms of the gain and noise figure.     

Safe,Stable Cycling of Lithium Metal Batteries with Low‐Viscosity,Fire‐Retardant Locally Concentrated Ionic Liquid Electrolytes

Ionic liquid (IL) electrolytes with concentrated Li salt can ensure safe, high‐performance Li metal batteries (LMBs) but suffer from high viscosity and poor ionic transport. A locally concentrated IL (LCIL) electrolyte with a non‐solvating, fire‐retardant hydrofluoroether (HFE) is presented. This rationally designed electrolyte employs lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), 1‐methyl‐1‐propyl pyrrolidinium bis(fluorosulfonyl)imide (P13FSI) and 1,1,2,2‐tetrafluoroethyl 2,2,3,3‐tetrafluoropropyl ether (TTE) as the IL and HFE, respectively (1:2:2 by mol). Adding TTE enables a Li‐concentrated IL electrolyte with low viscosity and good separator wettability, facilitating Li‐ion transport to the Li metal anode. The non‐flammability of TTE contributes to excellent thermal stability. Furthermore, synergy between the dual (FSI/TFSI) anions in the LCIL electrolyte can help modify the solid electrolyte interphase, increasing Li Coulombic efficiency and decreasing dendritic Li deposition. LMBs (Li||LiCoO₂) employing the LCIL electrolyte exhibit good rate capability (≈89 mAh g^?1 at 1.8 mA cm^?2, room temperature) and long‐term cycling (≈80% retention after 400 cycles).     

Effect of Ta addition on magnetic properties of (Fe45Pt55)1−x-Tax thin films

It was studied that FePt-Ta thin films prepared on MgO (1 0 0) buffer-layer by DC/RF magnetron co-sputtering have shown better magnetic properties and micro structural improvement. The Ta-doped FePt-Ta films indicate somewhat differences in micro structural ordering and the aspect of grain growth after annealing. With respect to magnetic property, the sample having 30% increased coercivity was obtained after a heat treatment at 700 °C. In particular the addition of Ta (5.5%) enhances the L1₀ ordering of FePt at relatively high temperature (above 500 °C).     

A new a-Si:H thin-film transistor pixel circuit for active-matrix organic light-emitting diodes

We propose a new pixel circuit using hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs), composed of three switching and one driving TFT, for active-matrix organic light-emitting diodes (AMOLEDs) with a voltage source method. The circuit simulation results based on the measured threshold voltage shift of a-Si:H TFTs by gate-bias stress indicate that this circuit compensates for the threshold voltage shifts over 10000 h of operation.     

Polyacrylonitrile Nanofibers: Formation Mechanism and Applications as a Photoluminescent Material and Carbon‐Nanofiber Precursor

The facile synthesis of polyacrylonitrile (PAN) nanofibers is achieved using a microemulsion polymerization. The detailed formation mechanism of polymer nanofibers is examined using electron microscopy and UV‐vis and Fourier transform infrared spectroscopies, and the optoelectronic properties are studied by confocal laser scanning microscopy. The effects of surfactant properties, such as concentration, chain length, and ionic character, as well as monomer structure and polymerization temperature, on the structure of the resulting polymer nanofibers are also investigated extensively. Importantly, PAN nanofibers exhibited novel photoluminescence (PL), which is observed for the first time. The PL of PAN nanofibers is significantly different from that of PAN nanoparticles. The PAN nanofibers are also used as a precursor for carbon nanofibers. The carbonization temperature has a dominant effect on the degree of crystallinity of the resulting carbon nanofibers. This study is the first demonstration of the fabrication of polymer and carbon nanofibers using a convenient polymerization technique.     

Achieving Narrow FWHM and High EQE Over 38% in Blue OLEDs Using Rigid Heteroatom-Based Deep Blue TADF Sensitized Host

Simultaneously obtaining high efficiency and deep blue emission in organic light emitting diodes (OLEDs) remains a challenge. To overcome the demands associated with deep blue thermally activated delayed fluorescence (TADF) emitters, two deep blue TADF materials namely, DBA–BFICz and DBA–BTICz, are designed and synthesized by incorporating oxygen-bridged boron (DBA) acceptor with heteroatoms, oxygen and sulphur-based donors, BFICz and BTICz, respectively. Both TADF materials show deep blue photoluminescence emissions below 450 nm by enhancing the optical band gap over 2.8 eV through deeper highest occupied molecular orbital (HOMO) level of heteroatom based donor moieties. At the same time, the photoluminescence quantum yields (PLQYs) of both TADF materials remain over 94%. The TADF device with DBA–BFICz as an emitter exhibits a good external quantum efficiency (EQE) of 33.2%. Since both new TADF materials show deep blue emissions and high efficiencies, hyperfluorescence (HF) OLED devices are fabricated using ν-DABNA as a fluorescence dopant. DBA–BFICz as a TADF sensitized host in HF–OLED reveals an outstanding EQE of 38.8% along with narrow full width at half maximum of 19 nm in the bottom emission pure blue OLEDs. This study provides an approach to develop deep blue TADF emitters for highly efficient OLEDs.     

Indicator Sensor Development and Fuel Cell Degradation Imaging

Although extensive research has been conducted, understanding the exact phenomena occurring during the operation of polymer electrolyte fuel cells (PEFCs) remains difficult. This research attempted to identify new reasons for the reduced performance of PEFC using an imaging technique. To begin with, H⁺ and OH⁻ indicator sensors, which display red, blue, and green values (RGB) using digital microscopes, are developed and attached to each electrode of a membrane electrode assembly to enable quantitative analysis of ion generation. The proposed reaction in the fuel cell can be confirmed, and various reactions occurring in the electrode can be examined using this approach. In particular, H⁺ is generated at the anode and cathode of the anion exchange membrane fuel cell, which is found to be a major cause of performance deterioration.     

A process simplification scheme for fabricating CMOS polycrystalline-Si thin film transistors

A process simplification scheme for fabricating CMOS poly-Si thin-film transistors (TFTs) has been pro-posed, which employs large-angle-tilt-implantation of dopant through a gate sidewall spacer (LATITS). By this LATITS scheme, a lightly doped drain region under the oxide spacer is formed by low-dose tilt implantation of phosphorus (orboron) dopant through the spacer, and then the n+-source/drain (n+-S/D) (or p+-S/D) region is formed via using the same photo-mask layer during CMOS integration. For both n-TFT and p-TFT devices, as compared to the sample with conventional single n+-S/D (or p+-S/D) structure, the LATITS scheme can cause an obviously smaller leakage current, due to more gradual dopant distribution and thus smaller electric field. In addition, the resultant on-state currents only show slight degradation for the LATITS scheme, As a result, by the LATITS scheme, CMOS poly-Si TFT devices with an on/off current ratio well above 8 orders may be achieved without needing extra photo-mask layers during CMOS integration.     

Realization of 2-D Variable IIR Digital Filter Structures with a Small Amount of Calculations for Coefficient Update

This paper proposes 2-D variable IIR digital filter structures with a small amount of calculations for coefficient update. The proposed realization method uses the 2-D parallel allpass structure derived from the separable denominator 2-D filter as the prototype structure for 2-D variable digital filters. In order to reduce the amount of calculations, all the redundant first-order complex allpass sections are combined by modularization of the variable structure. Furthermore, we can realize a very compact variable structure with a minimal number of first-order complex allpass sections by combining complex allpass sections with their complex conjugate allpass sections. Comparison of the calculation loads of the variable structures is presented to demonstrate that the amount of calculations for coefficient update of the proposed variable structure is far less than that of the original and the modular variable structure.