934 research outputs found
Effect of micro-Si<sub>3</sub>N<sub>4</sub>–nano-Al<sub>2</sub>O<sub>3</sub> co-filled particles on thermal conductivity, dielectric and mechanical properties of silicone rubber composites
No full textSilicone rubber (SR) is widely used on the distribution and transmission lines of power systems owing to its excellent insulating properties, extraordinary hydrophobicity and high tensile strength. However, the thermal conductivity of pure silicone rubber is very low which restricts its application for long time due to heat formation under electric field. This research focuses on the effect of micro- and nano-sized filler mixture on thermal conductivity, dielectric and mechanical properties of the SR composites. The micro-Si3N4 and nano-Al2O3 cofilled SR composites (MNCSR) with different volume ratios of Si3N4 and Al2O3 were fabricated by simple blending and subsequently hot-molding technique. With the addition of micro-Si3N4-nano-Al2O3 mixture at 30 vol. % (Si3N4/Al2O3=26/4), the composites showed high thermal conductivity of ~1.6 W m-1 k-1, low relative dielectric permittivity of ~5.3 and high breakdown strength of ~85 MV/m. Meanwhile, the introduction of micro-nano-sized particles resulted in improved elongation at beak and tensile strength. Besides, the MNCSR composites demonstrated good hydrophobicity with the static contact angle over 110°. The combination of these outstanding performances makes the MNCSR composites attractive in the field of insulating materials
RF MEMS Switches for Smart Antenna
No full textThe adoption of smart antenna techniques in future wireless systems is expected to have a significant impact on the efficient use of the spectrum and the minimisation of the cost of establishing new wireless networks. RF MEMS devices are the potential candidates to revolutionise RF and microwave system implementation for next generation wireless applications. Despite having excellent performances, there are some drawbacks associated with RF MEMS switches. The main challenges with RF MEMS switches are their high actuation voltage, limited reliability and low power handling capability. This thesis presents novel RF MEMS switches which can overcome these issues. To achieve zero power consumption, we have fabricated latching RF MEMS switches. In addition, we have combined thermal actuation and electrostatic actuation mechanisms to achieve lower actuation voltage. We have also developed a novel contactless RF MEMS switch to increase the reliability of the switch. The switch is free from unavoidable stiction and micro-welding problems in other contact types, which in return guarantees high reliability and long lifetime. The proposed device is based on variable capacitance between signal lines and movable grounded electrodes controlled by electrostatic actuator. The movable grounded electrode has the capability to move bi- directionally, therefore the switch can change among ON, OFF and deep-OFF states. Thus, additional isolation can be achieved in the deep-OFF state. The switch shows excellent RF performances. To increase the power handling capability of switch, we have developed a multi-contact Single Pole Single Throw (SPST). The switch achieves uniform current distribution through each contact, thereby increasing power handling capability. The switch is actuated with separate electrodes to control the current density and direction.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)Griffith School of EngineeringScience, Environment, Engineering and TechnologyFull Tex
The influence of TiO<sub>2</sub> nanoparticle incorporation on surface potential decay of corona-resistant polyimide nanocomposite films
No full textPI nanocomposite films containing surface modified nanoparticles by employing silane coupling agent were prepared using in-situ dispersion polymerization process. The surface potential decay measurements on films were investigated over the different negative corona-charged voltages and times in a controlled environment where temperature and relative humidity were kept at 21 ºC and 45%, respectively. There is a significant change in the surface potential decay characteristics after nano-fillers were introduced into polyimide. The surface potential decay pattern depends also on the amount of nano-fillers. The possible surface potential decay and corona resistance mechanisms responsible for the observed phenomena were discussed
The Electromagnetic Compatibility Problems of Integrated Circuits
No full textWith the constant speed of growth in semiconductor technology, integrated
circuit (IC) has taken a considerable position in an electronic system. The
integrated circuit is working in a low supply voltage with high operation
frequency. The internal complexity and chip density are also increased
dramatically. Modern microelectronic technology in wafer fabrication
easily allows component densities to exceed one million transistors per
die. So far, integrated circuits are suering from various and complicated
electromagnetic environments. Being the heart of an electronic system,
stability and reliability of the integrated circuit are of the most important
requirement along with the techniques development. The demands of high
electromagnetic compatibility (EMC) performance for integrated circuits are
therefore broadly spread among semiconductor manufacturers and product
users.
Traditionally, EMC for IC is only considered at the post-design stage.
Once built, it is only then that equipment is tested to see whether or
not it conforms to the relevant standards. This can prove very expensive
in terms of time, cost, and the potential need for retrot modications.
Simulating a piece of equipment is potentially much faster and cheaper than
taking a prototype or existing piece of equipment to a test-house. More
importantly, it allows the engineer to \look into" the equipment and see
where currents and elds are largest; this is almost impossible with physical
testing. Recently, computational electromagnetics (CEM) technique has
moved from pure mathematical analysis into design in engineering practice.
It can provide a much easier, faster and more economical solution of
prediction in EMC characteristics than conventional methods. Thus, EMC
computer modelling and simulation of IC is going to play an important role
in scientic research and industrial applications.Thesis (PhD Doctorate)Doctor of Philosophy (PhD)Griffith School of EngineeringScience, Environment, Engineering and TechnologyFull Tex
Electron-Transport-Layer-Assisted Crystallization of Perovskite Films for High-Efficiency Planar Heterojunction Solar Cells
No full textCrystal engineering of CH3NH3PbI3 perovskite materials through template-directed nucleation and growth on PbI2 nuclei dispersed in a polar fullerene (C-60 pyrrolidine tris-acid, CPTA) electron transport layer (ETL) (CPTA:PbI2) is proposed as a route for controlling crystallization kinetics and grain sizes. Chemical analysis of the CPTA:PbI2 template confirms that CPTA carboxylic acid groups can form a monodentate or bidentate chelate with Pb(II), resulting in a lower nucleation barrier that promotes rapid formation of the tetragonal perovskite phase. Moreover, it is demonstrated that a uniform CH3NH3PbI3 film with highly crystalline and large domain sizes can be realized by increasing the spacing between nuclei to retard perovskite crystal growth via careful control of the preferred nucleation site distribution in the CPTA:PbI2 layer. The improved perovskite morphology possesses a long photoluminescence lifetime and efficient photocarrier transport/separation properties to eliminate the hysteresis effect. The corresponding planar heterojunction photovoltaic yields a high power conversion efficiency (PCE) of 20.20%, with a high fill factor (FF) of 81.13%. The average PCE and FF values for 30 devices are 19.03% +/- 0.57% and 78.67% +/- 2.13%, respectively. The results indicate that this ETL template-assisted crystallization strategy can be applied to other organometal halide perovskite-based systems
Promotion of Ni2+ Removal by Masking Toxicity to Sulfate-Reducing Bacteria: Addition of Citrate
No full textThe sulfate-reducing bioprocess is a promising technology for the treatment of heavy metal-containing wastewater. This work was conducted to investigate the possibility of promoting heavy metal removal by the addition of citrate to mask Ni2+ toxicity to sulfate-reducing bacteria (SRB) in batch reactors. SRB growth was completely inhibited in Ni2+-containing medium (1 mM) when lactate served as the sole carbon resource, leading to no sulfate reduction and Ni2+ removal. However, after the addition of citrate, SRB grew well, and sulfate was quickly reduced to sulfide. Simultaneously, the Ni-citrate complex was biodegraded to Ni2+ and acetate. The NiS precipitate was then formed, and Ni2+ was completely removed from the solution. It was suggested that the addition of citrate greatly alleviates Ni2+ toxicity to SRB and improves the removal of Ni2+, which was confirmed by quantitative real-time PCR targeting dissimilatory sulfite reductase (dsrAB) genes. Analysis of the carbon metabolism indicated that lactate instead of acetate served as the electron donor for sulfate reduction. This study offers a potential approach to increase the removal of heavy metals from wastewater in the single stage SRB-based bioprocess
Leveraging Smart Lights for Passive Localization
No full textLocalization based on visible light is gaining significant attention. But most existing studies rely on a key requirement: the object of interest needs to carry an optical receiver (camera or photodiode). We remove this requirement and investigate the possibility of achieving accurate localization in a passive manner, that is, without requiring objects to carry any optical receiver. To achieve this goal, we exploit the reflective surfaces of objects and the unique propagation properties of LED luminaires. We present geometric models, a testbed implementation, and empirical evaluations to showcase the opportunities and challenges posed by this new type of localization. Overall, we show that our method can track with high accuracy (few centimeters) a subset of an object’s trajectory and it can also identify passively the object’s ID.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Embedded System
Infochemical-tritrophic Interactions of Soybean Aphids-host Plants-natural Enemies and Their Practical Applications in Pest Management
No full textThe soybean aphid, Aphis glycines Matsumura, is a newly invasive insect species that seriously threatens U.S. soybean production. This aphid pest has kept haunting many soybean growers by developing large colonies on soybeans in North America since 2000. Since its first appearance inWisconsin, it has spread to over half of US states and southern provinces in Canada. The heavy infestation of this pest whittles soybean growers’ profits and causes hundreds of million dollar losses. The present chapter will mainly describe efforts in studying aphid chemical ecology and sensory physiology for understanding how male aphids find their mates and host plants. It will also cover research efforts to understand host plant associated volatiles being used as cues for overwintering host plant location. In addition, findings on how soybean plant defensive system works against aphid infestation, as well as how those induced plant volatiles are used by aphid’s natural enemies for prey location will be presented. Finally, the use the basic understandings for developing useful tools for soybean aphid practical control will be discussed
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