601 research outputs found
Microelectromechanical Maltese-cross metamaterial with tunable terahertz anisotropy
No full textDichroic polarizers and waveplates exploiting anisotropic materials have vast applications in displays and numerous optical components, such as filters, beamsplitters and isolators. Artificial anisotropic media were recently suggested for the realization of negative refraction, cloaking, hyperlenses, and controlling luminescence. However, extending these applications into the terahertz domain is hampered by a lack of natural anisotropic media, while artificial metamaterials offer a strong engineered anisotropic response. Here we demonstrate a terahertz metamaterial with anisotropy tunable from positive to negative values. It is based on the Maltese-cross pattern, where anisotropy is induced by breaking the four-fold symmetry of the cross by displacing one of its beams. The symmetry breaking permits the excitation of a Fano mode active for one of the polarization eigenstates controlled by actuators using microelectromechanical systems. The metamaterial offers new opportunities for the development of terahertz variable waveplates, tunable filters and polarimetry
Foldable 3D Wafer Level SSL Package Using Flexible Interconnect
No full textSolid State Lighting (SSL) is on track to replace conventional incandescent and fluorescent sources for general lighting. Even though it offers many benefits, the high initial device costs are still a major hindrance for many consumers. Packaging can account for up to half of the total device price, offering high potential for cost reduction. In this thesis, novel silicon wafer level packaging (WLP) concept and development platform are presented. The proposed packaging platform consists of silicon chips connected with neutral bending plane based flexible interconnect. Each chip contains an etched reflector cavity with wire bonded LED. The polyimide encapsulated flexible interconnects offer the benefit of folding the package into a 3D geometric shape. The space around the reflector cavity could be used to integrate active components and the backside { for passive components of the SSL driver circuit. The design, fabrication and characterization of the package is presented. A novel method to interconnect the front and backside of the chips is also incorporated into the process flow. After fabrication, packages are completed by adding LEDs, applying phosphor color conversion and release from substrate, followed by characterization of electrical, mechanical, thermal and optical performance. The developed packaging platform offers potential for future functional expansion by means of heterogeneous integration, possibly leading to a smart WLP package for SSL.ECTM Electronic Components, Technology and MaterialsMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Thermal management of solid state lighting module
No full textSolid-State Lighting (SSL), powered by Light-Emitting Diodes (LEDs), is an energy-efficient technology for lighting systems. In contrast to incandescent lights which obtain high efficiency at high temperatures, the highest efficiency of LEDs is reached at low temperatures. The thermal management in LED product is then a key design parameter as the high operation temperature directly affects the maximum light output, quality, reliability and life time. Solutions are sought in optimizing the thermal path, materials with better thermal conductivity and increasing the performance of convection and radiation. However, the apparent dilemma is to optimize light efficiency and effectively designing thermal management. In order to be able to optimize the LED temperature, an electrical-thermal-luminous-chromatic (E-T-L-C) model was developed that takes into account the thermal effect on the energy conversion rate from electric power (E) to primary blue light and from blue light into yellow light as a function of the in-situ temperature (T). As the conversion rates of the die and phosphor differ, the white light performance changes both in flux (L) and spectrum (C). The model was successfully verified using three commercially available LED packages. Furthermore, the model was also used to study the effect of layer thickness and particle density variations of the phosphorous layer on the thermal performance and light quality. As the temperature is both critical to light performance and thermal management, knowing the temperature in the LED is indispensable. The diode forward voltage method with pulsed currents has been widely used to monitor the junction temperature (Tj) of LEDs. However, this method suffers from a thermal transient effect (TTE) resulting in measurement errors. Using Thermoelectric (TE) physics this phenomenon was explained and a group of experiments was used to study the TTE in Tj measurements for high-voltage (HV) LEDs. The measurement uncertainty was more than ± 10 C which is not acceptable for accurate monitoring. Therefore, an improved Pulse-free Direct Junction Temperature Measurement (DJTM) method was applied to HV LEDs to reduce the errors and to achieve an accurate in situ Tj measurement using DC currents. This also resulted in a simpler setup and a simpler measurement sequence. Although the Tj is the most relevant temperature to know, the LED package or case temperature is much easier to measure and apply. A micro-electromechanical-system (MEMS) based, temperature triggered, switch was developed as a cost-effective solution for smart cooling control in SSL systems. The switch was embedded in a silicon substrate and fabricated with a single-mask 3D micromachining process. The device switched on at a designed temperature threshold with a small contact resistance, and switched off when the temperature drops below that limit. Through the embedded MEMS switch, an automatic temperature controller was obtained without adding electrical components to the package. As standard semiconductor manufacturing processes are used, integration and fabrication in future silicon based SSL systems is expected to be straight forward. The phase change from liquid to vapor can be used as a driving force to move the fluid in a cooling system. Based on this principle, a cooling solution based on micro-fluidics and MEMS technology was presented. A test vehicle was constructed consisting of a miniaturized evaporator with a fluid channel and an embedded bulk silicon temperature sensor. A commercial HP LED package was mounted on the evaporator, with the goal to achieve maximum light output using a very small coolant flow rate. Results showed that the package obtained high efficiency and correspondingly increased light output by the two-phase cooling. Additionally, via numerical simulation the phase change phenomenon and temperature distribution inside the evaporator was further investigated and optimized water flow rates for specific input powers of the package were calculated. Micro or micro-wick heat pipes (HPs) have received considerable attraction in the past decades especially for cooling of electronics in a limited volume. Among the HPs, the micro HP (MHP) and loop HP (LHP) with micro wicks are most preferred for their high efficiency, small dimension, and compatible process with semiconductor devices. Especially, the LHP possess all the main advantages of traditional HPs and next to that they can transfer heat over distances up to several meters at any orientation in the gravity field. Although silicon is one the most favorable materials for MHP and LHPs, polymer based MHP and LHPs are very attractive for further investigation. Therefore, a package, using a silicon substrate with temperature sensors and a polymer based LHP was designed, manufactured and assembled. This package was able to provide low and relatively stable temperature, enabling higher optical power, more luminous flux and less color shift. Last but not least, whatever cooling configuration is made, a constant element is the heat sink, which eventually dissipates the heat to the ambient environment. Thus, the heat sink design is essential but it needs a case by case approach. Using a thermal design of vertical fin arrays with HPs as passive cooling the design methodology was demonstrated. The HPs may be converted into active/passive liquid cooling as presented previously. As the natural convection and radiation dominate heat transfer in this case, the optimum vertical fin spacing, which is the critical parameter for natural convection, was calculated by the most used empirical correlations. In addition, the fin spacing was further numerical investigated and optimized using Computational Fluid Dynamics (CFD). The design was verified by building a prototype and the experimental and numerical results correlated well. The achieved results show the HPs supply good equivalent thermal conductivity with less weight and volume compared to copper or aluminum base. Furthermore, the HP (liquid cooling) enhanced the natural convection by high thermal conductivity and less obstruction to air flow.Electronic Components, Technology and MaterialsElectrical Engineering, Mathematics and Computer Scienc
Molecular modeling in design of polyaniline for polymer-based carbon dioxide sensor
No full textConducting polymers are attractive chemical sensing materials due to their outstanding characteristics including low cost, room-temperature operations, easy device fabrication, high sensitivity and short response time. The new nanowires architecture, with high surface-to-volume ratio, makes possible the conducting polymers an ultra fast detection of chemical at low concentrations. Polymer-coated nanowires are thus the potential cost effective solution for the new generation gas sensors. As a sensing material, the molecular design of the conducting polymer is utterly important. The conductive polymers can be tailored to fulfill the sensing requirement by its modifying functional groups in accordance to the applications. Molecular modeling which predicts the material properties of conductive polymers helps in the design of the sensor material. In this thesis, I present a molecular modeling approach to design and evaluate conducting polymer as chemical sensing material for polymer nanowire or polymer-coated nanowire carbon dioxide (CO2) sensors in greenhouse application. In order to provide an overview of the rapid progress in the application of chemical sensing materials with nanowire architecture, literature study on nanowire gas sensors has been presented in the Chapter 2. A comparison between the two basic approaches (top-down and bottom-up) in the nanowire synthesis is given. The sensing principles and configurations of nanowire gas sensors with their relevant assembly technologies are summarized. Based on the review work, a polyaniline-coated nanowire field-effect transistor (NanoFET) is proposed for CO2 sensing system in greenhouse. This sensor set combines the advantages of nanowire architecture, FET sensor configuration and conducting polymers. A crucial part of any molecular simulation study is the choice of forcefields. In Chapter 3, we evaluate the validity of COMPASS and PCFF forcefields in predicting the physical and thermophysical properties of amorphous polymer emeraldine based polyaniline (EB–PANI). A combination of molecular mechanics (MM) and molecular dynamics (MD) analysis is employed to determine the polymer’s properties, including density (?) and solubility parameter (?). The temperature dependence of specific volume (?), non-bond energy (Enon-bond) and solubility parameters are used to estimate the glass transition temperature (Tg). Comparing the simulation results with experimental data, the accuracy of forcefields (COMPASS and PCFF) is elucidated. The COMPASS forcefield has been demonstrated as a better forcefield which provides a closer agreement with experiment data than the PCFF. Thus, the molecular modeling design of PANI for CO2 sensing is conducted by using the COMPASS forcefield. For effective sensing, the dissolution of an analyte, as quantified as the solubility parameter ?, in the sensing materials is crucial. Understanding of the temperature dependence of solubility parameter can provide adequate information for the sensitivity issue induced as the temperature changes. In Chapter 4, I have developed a compact model to describe the solubility parameter change due to the temperature impacts. It is showing that in the working temperature range of greenhouse, the temperature impact on the solubility parameter is limited and can be neglected. To verify the accuracy of our calculation, two kind of analysis has been are performed: (i) the ? value at 298 K for EB–PANI is predicted and compared with the literature reported data; (ii) the Tg of the polymer is determined from the ?–T curve and compared with the experimental value. The temperature dependence of solubility parameter of the EB-PANI has been determined by molecular modeling approach. The sensing mechanism of the PANI for CO2 materials is based on protonic acid doping. Molecular modeling of the sensing mechanism can offer useful information for the sensitivity and the selectivity of PANI. In Chapter 5, a compact model has been developed to describe the protonic acid doping of PANI with reasonable accuracy. The atomistic model is developed by using a statistical thermodynamic analysis method. The molecular modeling method is comprised of three key steps: (i) developing the atomistic models; (ii) defining the doing criteria; and (iii) simulating the protonic acid doping. By using the molecular model, the relationships including pKa/pH and doping percentage/pH are established. The computed results compare favorably with the reported experimental data. The change of charge carrier density causes the changes in the conductivity of the gas-sensitive conducting polymers. Thus, the relationship between macroscopic conductivity and charge carrier density is very useful in the design and evaluation of PANI as chemical sensing materials. In Chapter 6, by using the molecular model derived from Chapter 5, the relationships include the charge carrier density/pH and the conductivity/charge carrier density of EB-PANI are established properly. It is to find that the conductivity has an exponential function relationship with the charge carrier density [? = (A*n)a] in PANI. Using the computing relationship of conductivity/charge carrier density, the sensitivity of EB-PANI and its derivative K-SPANI for the detection of HCl is evaluated. The finding shows that by introducing function groups (–SO3K), the sensitivity of K-SPANI is greatly improved by two times. Thus the conducting polymer K-SPANI is a good candidate for acidic gas sensing, such as HCl, H2S, or CO2 in high humidity conditions. With the fundamental knowledge established in Chapters 3-6, the molecular design of PANI for greenhouse CO2 gas sensing can be achieved. Chapter 7 investigates the effect of functional group on the working range of polyaniline sensors for CO2 in agriculture industry. The humidity, temprature and the concentration of CO2 in the tightly clad greenhouses have been considered in the molecular model. The work compares the response of the pure EB, the polymer mixture of EB-PANI and undoped sodium sulfonated polyaniline (NaSPANI) with sulfur to nitrogen ratio (S/N) of 0.6, 0.5 and 0.4 to CO2. Under the working condition in a greenhouse, the working range of NaSPANI has been estimated as ~ [102- 104] ppm which demonstrates it is a good candidate for CO2 detection in agricultural industry. In considering the synthetic difficulty, I propose the conducting polymer NaSPANI (S/N = 0.5) is a good candidate for agricultural CO2 sensing. In summary, a molecular modeling method which helps in the design and evaluation of conductive polymers for carbon dioxide sensing in greenhouses has been established. This thesis work contributes at use of computational approaches in designing and optimizing chemical sensing materials for various applications.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
A Systematic Approach to Address the Reliability of Solid State Lighting Drivers
No full textSolid State Lighting (SSL) technology is a new technology based on light emitting diodes as light sources. This technology due to its several outstanding characteristics such as lower energy consumption, longer lifetime, and higher design flexibility with respect to the conventional lighting technology has become very attractive to both manufacturers and consumers. It is applied in variety of applications such as in-door, out-door, automotive, and agriculture lighting. Like any other new and fast evolving technology, SSL technology reliability requires special attention, and its long lifetime brings extra challenges to this study. This research focuses on reliability of SSL devices electrical driver (SSL driver). In this thesis, a systematic approach to address the reliability of SSL drivers is introduced. There are many design variations for SSL drivers due to the application field criteria. It means SSL driver as one term refers to a wide range of devices. The systematic approach tries to provide guidelines suitable to be applied to different types of SSL drivers. In order to predict the SSL driver's thermal / electrical behavior and consequently to define its lifetime, a multi-physics reliability assessment methodology is introduced.Microelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
Megalotomus acutulus G. Q. Liu & Q. Liu 1998
No full text<i>Megalotomus acutulus</i> Liu & Liu, 1998 <p>(Figs. 20–22, 38–40)</p> <p> <i>Megalotomus acutulus</i> G.Q. Liu & Q. Liu, 1998: 41. Holotype: ♂, China (North), Inner Mongolia, Hailar (49.2°N / 119.7°E); NKUM. Dolling, 2006: 38.</p> <p> <b>Diagnosis.</b> This species is recognized within the genus <i>Megalotomus</i> by a combination of the following characters: body size relatively moderate, 12.5–14.0 mm in length, yellowish brown to black, with black punctures; head and pronotum with long, dense pilosity; vertex black, with pale yellow midline and macula on both sides; posterior angle of pronotum slightly upward, not sharp; forewings with small, light-coloured spots, and anterolateral margin pale; meta-femora with 3–5 spines on the inner margin of the terminal half, becoming gradually longer from proximal to terminal; surcapsular spines of the genital capsule acute and straight, extending without any projection or bifurcation; parameres strongly curved upward, elongate and slender, tapering gradually towards apex, and each with one or two prominent acute projections in the middle on the inner side.</p> <p> <b>Material examined.</b> <b>China: Hebei Province:</b> 1 ♂, Xiaowutaishan National Nature Reserve, Donglingshan, 1700 m, 21-August-2005, Xin Yu leg. (NKUM); <b>Inner Mongolia:</b> 3 ♂♂, 1 ♀, Chifeng City, Keshiketeng Banner, Daerhansumu, 1240 m, 9-August-2008, Xueqin Shi leg. (NKUM); <b>Shanxi Province:</b> 4 ♂♂, 1 ♀, Xinzhou City, Wutai County, Taihuai Town, Wutaishan National Nature Reserve, Xinyinsi Temple, 39.01°N, 113.63°E, 1844 m, 13-August-2020, Wenbo Yi leg. (XZTU); 9 ♂♂, 4♀♀, Xinzhou City, Wutai County, Taihuai Town, Wutaishan National Nature Reserve, Loushang Village, 39.00°N, 113.65°E, 1924 m, 13-August-2020, Wenbo Yi leg. (XZTU); 8 ♂♂, 3 ♀♀, Xinzhou City, Wutai County, Taihuai Town, Wutaishan National Nature Reserve, Muwagou, 39.03°N, 113.62°E, 1849 m, 14-August-2020, Wenbo Yi leg. (XZTU).</p> <p> <b>Distribution.</b> China (Hebei, Inner Mongolia, Shanxi).</p> <p> <b>Remarks.</b> This species is readily recognized within the genus <i>Megalotomus</i> by its diagnostic characters, as thoroughly described and illustrated in Liu & Liu (1998). During field work in Wutaishan National Nature Reserve, Shanxi Province, China, large amounts of adults of this species were found on <i>Melilotus officinalis</i>, a common herbaceous plant of Leguminosae, which is highly suspected to be the host plant of this species, since there are no previous host records.</p>Published as part of <i>Yi, Wenbo, Wang, Shijun, Zhang, Hufang & Bu, Wenjun, 2022, Notes on Megalotomus Fieber, 1860 in the Palaearctic Region (Hemiptera, Heteroptera, Alydidae), pp. 211-224 in Zootaxa 5128 (2)</i> on page 219, DOI: 10.11646/zootaxa.5128.2.3, <a href="http://zenodo.org/record/6479798">http://zenodo.org/record/6479798</a>
Organic Materials Degradation in Solid State Lighting Applications
No full textIn this thesis the degradation and failure mechanisms of organic materials in the optical part of LED-based products are studied. The main causes of discoloration of substrate/lens in remote phosphor of LED-based products are also comprehensively investigated. Solid State Lighting (SSL) technology is a new technology based on light emitting diodes as light sources. This technology, due to its several exceptional characteristics such as lower energy consumption, longer lifetime, and higher design flexibility with respect to the conventional lighting technology, has become very attractive to both manufacturers and consumers. It is applied in a variety of applications such as general lighting for in-door and out-door applications, and for automotive. Reliability in the highly demanding and fast growing SSL market is a key challenge, which requires special attention. A SSL system is typically composed of an LED engine with an electronic driver(s), integrated in a housing that also provides optical functions, thermal management, sensing and/or other functions. Knowledge of (system) reliability is crucial for not only the business success of today!s SSL products and applications, but also to gain deeper scientific understanding which will enable improved product and application design in the future. A malfunction of the system may be induced by the failure and/or degradation of any subsystem or interface. A comprehensive and in-depth understanding of failure and degradation behaviors of different SSL system components would obviously result in a more effective and reliable design as well as a proper selection of materials and anufacturing techniques. Package-related failure mechanisms. that result in an optical degradation, colour change, and severe discoloration of the encapsulant are listed as carbonization of the encapsulant, encapsulant yellowing, and phosphor thermal quenching. Among different materials used as an encapsulant or substrate for the phosphor in remote phosphor design, PolyCarbonate (BPA-PC) is chosen in this research. In order to study the main reason(s) of discoloration and consequently to define lifetime, a series of experiments are performed under different external stresses (temperature range of 100 to 140 ºC and radiation of blue light with 450 nm wavelength). A highly accelerated test set-up was designed to control these stresses and monitor light output of the system at the same time. Evaluating and analyzing of chemical and optical characteristics of samples during ageing in this specially designed highly accelerated test set-up are performed using a wide range of techniques including UV-Vis, FTIR-ATR, and X-ray photoelectron spectroscopy (XPS), Lambda spectroscopy and Integrated Sphere. The results show that increasing the thermal ageing time leads to yellowing, loss of optical properties, and decrease of the light transmission of the relative radiant power value of both pure and commercial BPA-PC plates. Thermally induced oxidation reactions of BPA-PC are found to be the major reason of the yellowing and discoloration. The major effect of light intensity in remote phosphor is believed to be increasing the temperature of the phosphor, and therefore enhancing the kinetics of thermal ageing. Photo-fries products are found in photo-thermally aged BPA-PC plates, aged under blue light radiation at elevated temperature of 140 ºC, and believed to have a contribution to the discoloration. The XPS analyses of aged samples confirm that discoloration is associated with surface oxidation. A significant increase in the signal ratio O1s /C1s in the XPS spectra of degraded specimens is observed. During thermal ageing, the C-H concentration decreases and new oxide features C=O and O-C=O form, with the latter being a support for oxidation at the surface being a major reaction during discoloration. Results also show that irradiation with blue light during thermal ageing accelerates the kinetics of discoloration and the increases O1s /C1s ratio in XPS spectra. The accelerated optical degradation and reliability of two different commercial BPA-PC plates under elevated temperature stress are studied as well. The reliability model, explained in this thesis, is indeed a useful framework to incorporate kinetics of (photo)-thermal ageing of BPA-PC and YAG:Ce phosphor into the life-time prediction models. It is shown that increasing the exposure time leads to degradation of BPA-PC optical properties, i.e. decrease of light transmission and increase in the yellowing index (YI). By increasing the temperature, the rate increases, meaning that lumen depreciation takes place at shorter time. The reaction rate follows the Arrhenius acceleration law. The thermal stability and life time of remote phosphor lens plates are also studied. The photometric properties of thermally-aged plates, monitored during the stress thermal ageing tests, show a significant change both in the correlated color temperature (CCT) and in the chromaticity coordinates (CIE x,y). It is also observed that there is a significant decay both in the phosphor yellow emission and in the blue peak intensity, with yellow emission being more affected, inferring that the main reason for the optical degradation of thermally-aged BPA-PC plates could be ascribed to yellow conversion of blue light. As final conclusions, among different existing stresses including light intensity, humidity and heat, thermal stress has a more pronounced influence on the ageing of encapsulants in optical parts in LED-based products. Also it is shown that the rate of lumen depreciation is highly dependent on temperature; the higher the temperature the faster the kinetics of color shifting and lumen depreciation is. The effect of light intensity is increasing the temperature in phosphor plates. Reliability of optical components in LED-based products can be well described by the Arrhenius equation and generalized Eyeing equation. Coating the BPA-PC by a graphene monolayer can significantly enhance the optical properties and stability of BPA-PC, used as substrate in remote phosphor plates. Graphene decreases the oxidation kinetics of BPA-PC and acts as a barrier for moisture and oxygen diffusion.DIMESElectrical Engineering, Mathematics and Computer Scienc
Theory of electrochemical cells and its application to plastic-encapsulated IC reliability
No full textMicroelectronicsElectrical Engineering, Mathematics and Computer Scienc
Wireless control of LED display lighting system using Bluetooth and Android
No full textThis thesis will describe our research and process during the Bachelor project "Wireless control of LED lighting system using Bluetooth and Android". Our team was a 4 man team, where we, the authors, worked on the Android app development, the PCB design and the Power Supply. For work done on an FPGA and the flexible LEDs, see thesis written by P. Omidi and D. Lew - http://resolver.tudelft.nl/uuid:8150a6c6-ff15-4ad3-bcb5-2df6b1a7df54Bachelor ProgrammeMicroelectronics & Computer EngineeringElectrical Engineering, Mathematics and Computer Scienc
- …
