Modeling of Photoelectric Micro-Power Supply for Wireless Sensor Nodes

For the wireless sensor node integrated with photoelectric micro-power supply, the photoelectric micro-power supply (PMPS) determines their life time, stability and adaptability to the local environment. The design of PMPS involves the study related to incident light power, photoelectric conversion efficiency of solar cells, characterization of storage devices, energy management and operation state control of sensor nodes, etc. The design process of PMPS is complicated. In this study, in order to simplify the design process of the PMPS and optimize it, we analyze all of the power parameters for the PMPS for sensor nodes. According to the energy transmission modes of PMPS for sensor nodes, the design model of PMPS is established. The rationality of PMPS is verified by experiments and simulations based on wireless sensor node (Ginze3).     

Linearization of oscillation frequency for integrated LC-VCO with inversion-mode varactor

Metal-oxide semiconductor (MOS) varactors are widely used in voltage-controlled oscillators (VCOs) due to the need for a tunable capacitance. Two types of varactors that have been integrated on-chip include the inversion-mode and accumulation-mode types. The inversion-mode varactor offers immunity to latch-up, but suffers from a non-linear C(V) characteristic which directly leads to a nonlinear oscillation frequency tuning curve. This paper proposes an oscillation frequency linearization technique for LC-VCO with an inversion-mode varactor. The linearity of the frequency tuning curve is improved by linearization of C(V) characteristics of the inversion-mode varactor. A new varactor configuration consisting of varactor units and resistor divider network is proposed. The single-switch integrated LC-VCO with the proposed varactor configuration is fabricated in TSMC 0.18 μm CMOS technology. The improvement of linearity of the frequency tuning curve has been verified using mathematical models and measurement results.     

Study of the Formation Mechanism of Cu/Ge/Pd Ohmic Contact to <Emphasis Type="Italic">n</Emphasis>-Type InGaAs

This study investigates electrical characteristics and the formation mechanism of the Cu/Ge/Pd Ohmic contact to n-type InGaAs. After annealing the contact at 250°C for 20 min, Cu₃Ge and Pd₁₂Ga₅As₂ compounds formed and Ge diffused into the InGaAs layer, achieving a heavily doped InGaAs layer with a low contact resistivity of 1 × 10⁻⁶ Ω cm². Thermal stability tests were performed on the Cu/Ge/Pd Ohmic contact to InGaAs after Ohmic contact formation, showing no obvious degradation after a 72 h reliability test at 250°C. The results indicate excellent electrical characteristics and thermal stability using Cu/Ge/Pd as an Ohmic contact metal to an n-InGaAs layer.     

Achieving End-to-end Fairness in 802.11e Based Wireless Multi-Hop Mesh Networks Without Coordination

To mitigate the damaging impacts caused by interference and hidden terminals, it has been proposed to use orthogonal channels in wireless multi-hop mesh networks. We demonstrate however that even if these issues are completely eliminated with perfectly assigned channels, gross unfairness can still exist amongst competing flows which traverse multiple hops. We propose the use of 802.11e’s TXOP mechanism to restore/enforce fairness. The proposed scheme is simple, implementable using off-the-shelf devices and fully decentralised (requires no message passing).     

The case for SIMO random access in multi-antenna multi-hop wireless networks

In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Hence, we propose simple modifications to the widely deployed IEEE 802.11 Medium Access Control (MAC) to enable multiple non-spatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sense threshold, disable virtual carrier sensing, and enable message-in-message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks. We analytically compute the optimal carrier sense threshold based on different network performance objectives for a given node density and number of receive antennas.     

GEPON构建中小企业专用接入网的可行性探讨

中小企业(SME)是中国经济的生力军,也是各大电信运营商收入的重要贡献者.因此,构建有竞争力的宽带接入网是目前电信运营市场竞争的新焦点.但是随着SME客户需求的不断增长,传统接入解决方案存在诸多问题,无法满足要求.本文在分析需求、问题和GEPON(吉比特以太无源光网络)的技术优势的基础上,提出利用GEPON构建SME专用接入网的设想.     

Reactive Sintering of Copper Nanoparticles Using Intense Pulsed Light for Printed Electronics

Most commercial copper nanoparticles are covered with an oxide shell and cannot be sintered into conducting lines/films by conventional thermal sintering. To address this issue, past efforts have utilized complex reduction schemes and sophisticated chambers to prevent oxidation, thereby rendering the process cost ineffective. To alleviate these problems, we demonstrate a reactive sintering process using intense pulsed light (IPL) in the present study. The IPL process successfully removed the oxide shells of copper nanoparticles, leaving a conductive, pure copper film in a short period of time (2 ms) under ambient conditions. The in situ copper oxide reduction mechanism was studied using several different experiments and analyses. We observed instant copper oxide reduction and sintering through poly(N-vinylpyrrolidone) functionalization of copper nanoparticles, followed by IPL irradiation. This phenomenon may be explained by oxide reduction either via an intermediate acid created by ultraviolet (UV) light irradiation or by hydroxyl (-OH) end groups, which act like long-chain alcohol reductants.     

Thin-Film Thermoelectric Module for Power Generator Applications Using a Screen-Printing Method

A new process for fabricating a low-cost thermoelectric module using a screen-printing method has been developed. Thermoelectric properties of screen-printed ZnSb films were investigated in an effort to develop a thermoelectric module with low cost per watt. The screen-printed Zn _x Sb_1−x films showed a low carrier concentration and high Seebeck coefficient when x was in the range of 0.5 to 0.57 and the annealing temperature was kept below 550°C. When the annealing temperature was higher than 550°C, the carrier concentration of the Zn _x Sb_1−x films reached that of a metal, leading to a decrease of the Seebeck coefficient. In the present experiment, the optimized carrier concentration of screen-printed ZnSb was 7 × 10¹⁸/cm³. The output voltage and power density of the ZnSb film were 10 mV and 0.17 mW/cm², respectively, at ΔT = 50 K. A thermoelectric module was produced using the proposed screen-printing approach with ZnSb and CoSb₃ as p-type and n-type thermoelectric materials, respectively, and copper as the pad metal.     

Effects of Double Substitution with Ge and Te on Thermoelectric Properties of a Skutterudite Compound

Studies have shown that the thermoelectric properties of CoSb₃ could be improved by the substitution of group IVB or VIB elements for Sb. However, the substitution volume is limited. To get a better picture of the substitution volume in view of thermoelectric properties, Ge and Te double-substituted skutterudite materials were prepared with the nominal composition of Co₄Sb _x Ge_5.9−0.5x Te_6.1−0.5x (x = 11, 10, 9, 8) by the traditional solid-state reaction method and spark plasma sintering, and Rietveld analysis was employed to refine the crystal structure. The results showed that the lattice parameter decreased linearly and the solubility limitations of group IVB and VIB elements were greatly alleviated by the Ge and Te codoping. Besides, the thermoelectric properties were analyzed through measurements of electrical and thermal conductivities as well as room-temperature electrical transport properties. The results showed that the substitution volume of Ge and Te could play an important role in the thermoelectric properties, and a minimum lattice thermal conductivity value of 1.56 W m⁻¹ K⁻¹ was obtained at around 673 K for Co₄Sb₈Ge_1.9Te_2.1. Co₄Sb₁₁Ge_0.4Te_0.6 achieved the best figure of merit of 0.89 at around 773 K, which was remarkably improved over that of untreated CoSb₃.     

A 1.44-mW, 1-MHz bandwidth continuous-time Σ∆ modulator with 10-bit ENOB in 130-nm CMOS

A low-power, low-pass continuous-time sigma-delta A/D modulator with 1-MHz bandwidth is implemented in a 130-nm CMOS process. The circuit is targeted for an IEEE 802.15.4 direct conversion receiver operating in the 2.4-GHz band. It has a third-order feedforward single-loop filter and a 1-bit quantizer to minimize power consumption. Non-return-to-zero DAC pulse shaping is used to reduce sensitivity to clock jitter. Clocked at 64 MHz, the prototype chip achieves 62-dB peak SNR, −70-dB peak THD, 63-dB dynamic range with an oversampling ratio of 32. The built-in anti-alias filter provides alias attenuation greater than 57 dB, which improves coexistence of the receiver with other devices that operate in the 2.4-GHz band. The circuit dissipates 1.44 mW from the 1.2-V supply and the active die area is 0.1 mm².