Highly Stretchable and Sensitive Strain Sensors Using Fragmentized Graphene Foam

Stretchable electronics have recently been extensively investigated for the development of highly advanced human‐interactive devices. Here, a highly stretchable and sensitive strain sensor is fabricated based on the composite of fragmentized graphene foam (FGF) and polydimethylsiloxane (PDMS). A graphene foam (GF) is disintegrated into 200–300 μm sized fragments while maintaining its 3D structure by using a vortex mixer, forming a percolation network of the FGFs. The strain sensor shows high sensitivity with a gauge factor of 15 to 29, which is much higher compared to the GF/PDMS strain sensor with a gauge factor of 2.2. It is attributed to the great change in the contact resistance between FGFs over the large contact area, when stretched. In addition to the high sensitivity, the FGF/PDMS strain sensor exhibits high stretchability over 70% and high durability over 10 000 stretching‐releasing cycles. When the sensor is attached to the human body, it functions as a health‐monitoring device by detecting various human motions such as the bending of elbows and fingers in addition to the pulse of radial artery. Finally, by using the FGF, PDMS, and μ‐LEDs, a stretchable touch sensor array is fabricated, thus demonstrating its potential application as an artificial skin.     

Reversible Conversion Reactions and Small First Cycle Irreversible Capacity Loss in Metal Sulfide‐Based Electrodes Enabled by Solid Electrolytes

Solid‐state batteries can potentially enable new classes of electrode materials which are unstable against liquid electrolytes. Here, SnS nanocrystals, synthesized by a wet chemical method, are used to fabricate a Li‐ion electrode, and the electrochemical properties of this electrode are examined in both solid and liquid electrolyte designs. The SnS‐based solid‐state cell delivers a capacity of 629 mAh g^?1 after 100 cycles and exhibits an unprecedentedly small irreversible capacity in the first cycle (8.2%), while the SnS‐based liquid cell shows a rapid capacity decay and large first cycle irreversible capacity (44.6%). Cyclic voltammetry (CV) experiments show significant solid electrolyte interphase (SEI) formation in the liquid cell during the first discharge while SEI formation by electrolyte reduction in the solid‐state cell appears negligible. Along with CV, X‐ray photoelectron spectroscopy and energy dispersive spectroscopy are used to investigate the differences between the solid‐state and liquid cells. The reaction chemistry of SnS in solid‐state cells is also studied in detail by ex situ X‐ray diffraction and X‐ray absorption spectroscopy. The overarching findings are that use of a solid electrolyte suppresses materials degradation and electrolyte reduction which leads to a small first cycle irreversible capacity and stable cycling.     

Designing a Stable Cathode with Multiple Layers to Improve the Operational Lifetime of Polymer Light‐Emitting Diodes

The short device lifetime of blue polymer light‐emitting diodes (PLEDs) is still a bottleneck for commercialization of self‐emissive full‐color displays. Since the cathode in the device has a dominant influence on the device lifetime, a systematic design of the cathode structure is necessary. The operational lifetime of blue PLEDs can be greatly improved by introducing a three‐layer (BaF₂/Ca/Al) cathode compared with conventional two‐layer cathodes (BaF₂/Al and Ba/Al). Therefore, the roles of the BaF₂ and Ca layers in terms of electron injection, luminous efficiency, and device lifetime are here investigated. For efficient electron injection, the BaF₂ layer should be deposited to the thickness of at least one monolayer (～3 nm). However, it is found that the device lifetime does not show a strong relation with the electron injection or luminous efficiency. In order to prolong the device lifetime, sufficient reaction between BaF₂ and the overlying Ca layer should take place during the deposition where the thickness of each layer is around that of a monolayer.     

NCl(α)/I全气相碘激光与氧碘化学激光能量提取的分析比较

利用连续流光腔动力学模型,对氧碘化学激光(COIL)和基于NCl(α)-I传能的全气相碘激光(AGIL)的能量提取进行了分析和公式推导,得到了连续流光腔的光子通量解析表达式以及氧碘化学激光光子通量沿流动方向的分布和输出功率的简化计算公式.AGIL的体系较为复杂,不能得到光子通量沿流动方向分布和输出功率的简化计算公式.从能量提取和体积重量效率角度,对氧碘化学激光和基于NCl(α)-I传能的全气相碘激光进行了对比评价.     

Performance of DS SS system under on-off wideband jamming

A performance analysis of a direct sequence spread spectrum (DS SS) system under a periodic on-off wideband jammer is presented. Closed-form results of system bit error rate (BER) are derived for all possible cases of jammer duty cycle     

Performance of Efficient Signal Detection for LED-ID Systems

In this paper, effects of reader-to-reader interference are investigated for LED identification (LED-ID) system in a multi-reader environment. The LED-ID readers typically use different channels to avoid collision between readers. However, in-channel collision usually happens in terms of interrogation range. A reader-to-reader interference scenario is proposed, and nominal interrogation range of a desired reader is derived from this model. In order to evaluate the LED-ID reader-to-reader interference quantitatively, an efficient detection scheme is proposed and simulated by employing spreading sequence. The spreading sequence is inserted between each user’s frame formats. In the receiver, the desired signal is detected by using correlation among inserted spreading sequences. From simulation results, it is confirmed that the proposed scheme is very effective to enhance reliability of LED-ID communication systems.     

A Discrete‐Amplitude Pulse Width Modulation for a High‐Efficiency Linear Power Amplifier

A new discrete‐amplitude pulse width modulation (DAPWM) scheme for a high‐efficiency linear power amplifier is proposed. A radio frequency (RF) input signal is divided into an envelope and a phase modulated carrier. The low‐frequency envelope is modulated so that it can be represented by a pulse whose area is proportional to its amplitude. The modulated pulse has at least two different pulse amplitude levels in order that the duty ratios of the pulse are kept large for small input. Then, an RF pulse train is generated by mixing the modulated envelope with the phase modulated carrier. The RF pulse train is amplified by a switching‐mode power amplifier, and the original RF input signal is restored by a band pass filter. Because duty ratios of the RF pulse train are kept large in spite of a small input envelope, the DAPWM technique can reduce loss from harmonic components. Furthermore, it reduces filtering efforts required to suppress harmonic components. Simulations show that the overall efficiency of the pulsed power amplifier with DAPWM is about 60.3% for a mobile WiMax signal. This is approximately a 73% increase compared to a pulsed power amplifier with PWM.     

Examining the factors that influence early adopters’ smartphone adoption: The case of college students

The influence of early adopters on potential adopters’ decisions of whether or not to adopt a product is known to be critical. In this paper, we examine the factors that influence the adoption behavior of smartphone early adopters by looking at smartphone adoption behavior of college students, because a large portion of the early adopters of smartphones are college students. Our focus is on the effect of normative peer influence on a college student’s smartphone adoption. We also examine the influence of other factors such as self-innovativeness, self-efficacy, the decision maker’s attitudes towards a product, financial burden of using the product, familial influence, and other demographic factors (e.g., age and gender). College students’ adoption behavior is studied using logit and probit choice models developed based on random utility theory. The discrete choice models are empirically estimated using survey data. We find important influence of friends, financial burden, and other family members on the smartphone adoption of college students who adopted smartphones earlier than other students.