Polarity Effect in a Sn3Ag0.5Cu/Bismuth Telluride Thermoelectric System

This study investigates electromigration in Bi₂Te₃ thermoelectric (TE) material systems and the effectiveness of the diffusion barrier under current. The Peltier effect on the interfacial reaction was decoupled from the effect of electromigration. After connecting p- and n-type Bi₂Te₃ to Sn3Ag0.5Cu (SAC305) solders, different current densities were applied at varying temperatures. The Bi₂Te₃ samples were fabricated by the spark plasma sintering technique, and an electroless nickel-phosphorous (Ni-P) layer was deposited at the solder/TE interfaces. The experimental results confirm the importance of the Ni diffusion barrier in joint reliability. Intermetallic compound layers (Cu,Ni)₆Sn₅ and NiTe formed at the solder/Ni-P and Ni-P/substrate interfaces, respectively. The experimental results indicate that the mechanism of NiTe and (Cu,Ni)₆Sn₅ compound growth was dominated by the Peltier effect at high current density. When the current density was low, the growth of NiTe was affected by electromigration but the changes of thickness for (Cu,Ni)₆Sn₅ were not obvious.     

High performance BCB-bridged AlGaAs/InGaAs power HFETs

A novel low-k benzocyclobutene (BCB) bridged and passivated layer for AlGaAs/InGaAs doped-channel power field effect transistors (FETs) with high reliability and linearity has been developed and characterized. In this study, we applied a low-k BCB-bridged interlayer to replace the conventional air-bridged process and the SiN/sub x/ passivation technology of the 1 mm-wide power device fabrication. This novel and easy technique demonstrates a low power gain degradation under a high input power swing, and exhibits an improved adjacent channel power ratio (ACPR) than those of the air-bridged one, due to its lower gate leakage current. The power gain degradation ratio of BCB-bridged devices under a high input power operation (P/sub in/ = 5 /spl sim/ 10 dBm) is 0.51 dB/dBm, and this value is 0.65 dB/dBm of the conventional air-bridged device. Furthermore, this novel technology has been qualified by using the 85-85 industrial specification (temperature = 85 C, humidity = 85%) for 500 h. These results demonstrate a robust doped-channel HFET power device with a BCB passivation and bridged technology of future power device applications.     

Utilization of self-injection Fabry–Perot laser diode for long-reach WDM-PON

In this investigation we propose and demonstrate a wavelength widely tunable laser source employing a self-injected Fabry–Perot laser diode (FP-LD) for long-reach wavelength-division-multiplexed passive optical network (WDM-PON). By using a tunable bandpass filter and an optical circulator inside the gain cavity, a stable and single-longitudinal-mode (SLM) laser output is achieved. Besides, the proposed laser sources are directly modulated at 2.5 Gb/s for both downlink and uplink transmissions of 85 km single mode fiber (SMF) in PON without dispersion compensation.     

Experimental demonstration of CW light injection effect in upstream traffic TDM-PON

High capacity time-division-multiplexed passive optical network (TDM-PON) is an emerging fiber access network that deploys optical access lines between a carrier’s central office (CO) and a customer sites. In this investigation, we demonstrate and analyze the continuous wave (CW) upstream effect in TDM-PONs. Besides, we also propose and design a protection apparatus in each optical network unit (ONU) to avoid a CW upstream traffic in TDM-PONs due to sudden external environment change or ONU failure. When an upstream CW injection occurs in TDM access network, the protection scheme can stop the CW effect within a few ms to maintain the entire data traffic.     

Room-Temperature Preparation of High-Transparency Low-Resistivity ITO Films by Ion Beam Sputtering

Low-temperature preparation of transparent conducting electrodes is essential for flexible optoelectronic devices. Tin-doped In₂O₃ films with high transparency and low electrical resistance were prepared at room temperature using a radiofrequency ion beam sputtering system. Specimens with a low sheet resistivity of 10⁻⁴ Ω cm and a high visible-light transmittance of 85% to 90% were obtained. Hall measurements were used to determine mobility and carrier concentration, and the effects on resistivity are discussed.     

Numerical simulation for thin wall injection molding of fiber-reinforced thermoplastics

The thickness of product is less than 1mm and product compares flowing length to thickness (flow length ratio L/t) to be living above 150 of injection molding filling. This situation is called thin wall injection molding. This study uses MoldFlow software for material (PP), different processing parameters (injection time, melt temperature, mold temperature, injection pressure), various fiber (glass, long glass), different fiber ratio (40%, 50%) and different thickness (1mm, 0.9mm) to simulate the result on notebook computer. The result shows that the mold temperature is the important factor on processing. The mold temperature, melt temperature and injection pressure of thin wall injection molding are higher than convectional injection molding.     

Amplification of tunable, picosecond pulses from a single-mode, short cavity dye laser

The design and performance of an Nd⁺³:YAG pumped, short cavity dye laser-dye amplifier system is reported. This system produces narrow bandwidth, broadly tunable picosecond pulses with energies in the millijoule range.     

Effects of multiple scattering and Fresnel diffraction on random volume scattering

A wave incident on a volume of random fluctuations of medium parameters will be scattered in all directions. Two kinds of effects on random volume scattering are considered: 1) multiple scattering effect, and 2) Fresnel diffraction effect. The cumulative forward scattering is known to be responsible for the scintillation phenomenon. When strong, such cumulative or multiple scattering can drive the signal statistics into the saturated regime in which the complex amplitudes behave as a complex Gaussian process. These cumulative scattering effects on signals of a bistatic radar are investigated. Additionally, to allow for the possibility that the size of the irregularity is comparable or larger than the first Fresnel zone, Fresnel diffraction instead of Fraunhofer diffraction is considered. A generalized formula for calculating average scattered power, taking both multiple scattering and Fresnel diffraction into account, is derived. It shows that the Fresnel diffraction pattern appearing around the forward direction tends to be smeared out by multiple scattering. Also, both multiple scattering and Fresnel diffraction effects weaken and broaden the forward-scattered beam, and reduce the backscattered power when compared with the single scattering and Fraunhofer diffraction cases respectively. Under certain conditions, the enhancement effect of the backward scattered power is confirmed.     

Pummelos as Concept Generators for Biomimetically Inspired Low Weight Structures with Excellent Damping Properties

Natural materials often exhibit excellent mechanical properties. An example of outstanding impact resistance is the pummelo fruit (Citrus maxima) which can drop from heights of 10 m and more without showing significant outer damage. Our data suggest that this impact resistance is due to the hierarchical organization of the fruit peel, called pericarp. The project presented in the current paper aims at transferring structural features from the pummelo pericarp to engineering materials, in our case metal foams, produced by the investment casting process. The transfer necessitates a detailed structural and mechanical analysis of the biological model on the one hand, and the identification and development of adequate materials and processes on the other hand. Based on this analysis, engineering composite foam structures are developed and processed which show enhanced damping and impact properties. The modified investment casting process and the model alloy Bi57Sn43 proved to be excellent candidates to make these bio‐inspired structures. Mechanical testing of both the natural and the engineering structures has to consider the necessity to evaluate the impact of the different hierarchical features. Therefore, specimens of largely varying sizes have to be tested and size effects cannot be ignored, especially as the engineering structures might be upscaled in comparison with the natural role model. All in all, the present results are very promising: the basis for a transfer of bio‐inspired structural hierarchical levels has been set.