Abstract: This work reports fabrication details of heterojunction diodes and solar cells obtained by sputter deposition of amorphous GaAs on p-doped single crystalline Si. The effects of two additional process steps were investigated: A hydrofluoric acid (HF) etching treatment of the Si substrate prior to the GaAs sputter deposition and a subsequent annealing treatment of the complete layered system. A transmission electron microscopy (TEM) exploration of the interface reveals the formation of a few nanometer thick SiO2 interface layer and some crystallinity degree of the GaAs layer close to the interface. It was shown that an additional HF etching treatment of the Si substrate improves the short circuit current and degrades the open circuit voltage of the solar cells. Furthermore, an additional thermal annealing step was performed on some selected samples before and after the deposition of an indium tin oxide (ITO) film on top of the a-GaAs layer. It was found that the occurrence of surface related defects is reduced in case of a heat treatment performed after the deposition of the ITO layer, which also results in a reduction of the dark saturation current density and resistive losses.
Abstract: Dual active bridge (DAB) converters have been popular in high voltage, low and medium power DC-DC applications, as well as an intermediate high frequency link in solid state transformers. In this paper, a multilevel DAB (ML-DAB) has been proposed in which two active bridges produce two-level (2L)-5L, 5L-2L and 3L-5L voltage waveforms across the high frequency transformer. The proposed ML-DAB has the advantage of being used in high step-up/down converters, which deal with higher voltages, as compared to conventional two-level DABs. A three-level neutral point diode clamped (NPC) topology has been used in the high voltage bridge, which enables the semiconductor switches to be operated within a higher voltage range without the need for cascaded bridges or multiple two-level DAB converters. A symmetric modulation scheme, based on the least number of angular parameters rather than the duty-ratio, has been proposed for a different combination of bridge voltages. This ML-DAB is also suitable for maximum power point tracking (MPPT) control in photovoltaic applications. Steady-state analysis of the converter with symmetric phase-shift modulation is presented and verified using simulation and hardware experiments.
Abstract: We propose the data mining-informed cognitive radio, which uses non-traditional data sources and data-mining techniques for decision making and improving the performance of a wireless network. To date, the application of information other than wireless channel data in cognitive radios has not been significantly studied. We use a novel dataset (Twitter traffic) as an indicator of network load in a wireless channel. Using this dataset, we present and test a series of predictive algorithms that show an improvement in wireless channel utilization over traditional collision-detection algorithms. Our results demonstrate the viability of using these novel datasets to inform and create more efficient cognitive radio networks.
Abstract: The authors present a large area collision detection sensor utilizing the piezoelectric effect of polyvinylidene fluoride film. The proposed sensor system provides high dynamic range for touch sensation, as well as robust adaptability to achieve collision detection on complex-shaped surfaces. The design allows for cohabitation of humans and robots in cooperative environments that require advanced and robust collision detection systems. Data presented in the paper are from sensors successfully retrofitted onto an existing commercial robotic manipulator.
Abstract: Electronic textiles have potential for many practical uses in clinical rehabilitation. This scoping review appraises recent and emerging developments of textile-based sensors with applications to rehabilitation. Contributions published from 2009 to 2013 are appraised with a specific focus on the measured physiological or biomechanical phenomenon, current measurement practices, textile innovations, and their merits and limitations. While fabric-based signal quality and sensor integration have advanced considerably, overall system integration (including circuitry and power) has not been fully realized. Validation against clinical gold standards is inconsistent at best, and feasibility with clinical populations remains to be demonstrated. The overwhelming focus of research and development has been on remote sensing but the opportunity for textile-mediated feedback to the wearer remains unexplored. Recommendations for future research are provided.
Abstract: With CMOS technology aggressively scaling towards the 22-nm node, modern FPGA devices face tremendous aging-induced reliability challenges due to bias temperature instability (BTI) and hot carrier injection (HCI). This paper presents a novel anti-aging technique at the logic level that is both scalable and applicable for VLSI digital circuits implemented with FPGA devices. The key idea is to prolong the lifetime of FPGA-mapped designs by strategically elevating the VDD values of some LUTs based on their modular criticality values. Although the idea of scaling VDD in order to improve either energy efficiency or circuit reliability has been explored extensively, our study distinguishes itself by approaching this challenge through an analytical procedure, therefore being able to maximize the overall reliability of the target FPGA design by rigorously modeling the BTI-induced device reliability and optimally solving the VDD assignment problem. Specifically, we first develop a systematic framework to analytically model the reliability of an FPGA LUT (look-up table), which consists of both RAM memory bits and associated switching circuit. We also, for the first time, establish the relationship between signal transition density and a LUT’s reliability in an analytical way. This key observation further motivates us to define the modular criticality as the product of signal transition density and the logic observability of each LUT. Finally, we analytically prove, for the first time, that the optimal way to improve the overall reliability of a whole FPGA device is to fortify individual LUTs according to their modular criticality. To the best of our knowledge, this work is the first to draw such a conclusion.