An experimental study on time delay control of actuation system of tilt rotor unmanned aerial vehicle

This paper presents an actuation control system for the Smart Unmanned Aerial Vehicle (SUAV), a tilt rotor aircraft that is being developed by the Korea Aerospace Research Institute. The actuation system, which consists of flaperon, rotor, and nacelle tilt, should be controlled to track the position command sent from the flight controller. However, substantial variations in the aerodynamic load on the actuation system make it difficult to achieve the desired level of control performance. In this study, the actuation system was controlled using the Time Delay Control (TDC) law. The experimental results show that the following control performance specifications are completely satisfied under load variation from 0 to 455 kgf: bandwidth of 4 Hz, overshoot of 2.5%, and steady state error of 1% for flaperon and rotor actuation system. Especially, the accuracy was within the noise level of the steady state position error over broad ranges of the load. In addition, the command filter was applied to the TDC command to mitigate the effects of the phase delay that occurs when a sinusoidal command is applied. Furthermore, an actual flight test was performed, which clearly showed the effectiveness of the proposed control scheme. This promising control performance shows that TDC is an effective alternative for controlling the actuation system of the SUAV with substantial load variation.     

Enhanced efficiency of organic light emitting devices (OLEDs) by control of laser imaging condition

Laser Induced Thermal Imaging (LITI) is a laser addressed thermal patterning technology with unique advantages such as excellent uniformity of transfer film thickness, capability of multilayer stack transfer, high resolution and scalability to large-size mother glass. However, the deterioration of the device performance during imaging process has been an obstacle to use it as a commercial technology. To investigate a possibility of thermal deformation of organic materials as a transfer layer and a receptor layer during imaging process, we executed a preliminary annealing test by using standard green devices at various temperatures. By comparison of these results with those obtained from LITI devices, we found that the main reason of device deterioration could be originated from the mobility change of the organic layers. Hence, we developed the dwell time control technology to suppress the thermal impact during LITI process and we finally obtained current efficiency which is quite equivalent to that obtained from the standard evaporation devices.     

Power law behavior of magnetoresistance in tris(8-hydroxyquinolinato)aluminum-based organic light-emitting diodes

Long-term current drift and dielectric relaxation in organic thin films of a single-layer structure pose a serious problem for the accurate measurement of magnetoresistance at low magnetic fields. A new measurement scheme was devised to minimize errors and to report that the magnetoresistance in tris(8-hydroxyquinolinato)aluminum obeys a power law on the magnetic field at 300, 100, and 4.2 K in an entire range from 1 to 140 mT. The exponent of the power increases gradually from 0.47 for a bias voltage of 3 V to 0.58 for a bias voltage of 8 V. The magnetoresistance was observable above the threshold voltage only and its sign was always negative.     

Effect of hydroxyl density on condensation behaviors of self-assembled monolayers and performance of pentacene-base organic thin-film transistors

A series of self-assembled monolayers (SAMs), comprising octadecyltrichlorosilane (ODTS), dodecyltrichlorosilane (DDTS), and hexamethyldisilazane (HMDS), were prepared to examine the effects of phase states and condensation behaviors of SAMs on the morphologies and performance of pentacene-based organic field-effect transistors (OFETs) by means of Fourier Transform Infrared (FT-IR) spectrometer, atomic force microscope (AFM), X-ray diffraction (XRD), and semiconductor parameter analyzer. Experimental results reveal that the treatment of SiO₂ substrates with O₂ plasma (denoted as O₂-SiO₂) and the preparation temperature of SAMs dramatically influence the morphologies of SAMs and the performance of corresponding pentacene-based (no purification) OFETs. When the SAMs were prepared at 30 °C, the OFET based on ODTS-treated O₂-SiO₂ substrate had the highest hole mobility, reaching as large as 1.15 cm² V^?1 s^?1, and an on/off current ratio in excess of 10⁵; these values are both much larger than those of a device based on ODTS-modified SiO₂ substrates without O₂ plasma treatment and O₂-SiO₂ substrates modified by ODTS SAMs prepared at other temperatures. OFETs based on O₂-SiO₂ substrates that were modified by DDTS and HMDS SAMs prepared at 4 °C performed best.     

QoS‐aware routing and power control algorithm for multimedia service over multi‐hop mobile ad hoc network

This paper presents a QoS (quality of service) aware routing and power control algorithm consuming low transmission power for multimedia service over mobile ad hoc network. Generally, multimedia services need stringent QoS over the network. However, it is not easy to guarantee the QoS over mobile ad hoc network since its network resources are very limited and time‐varying. Furthermore, only a limited amount of power is available at mobile nodes, which makes the problem more challenging. We propose an effective routing and power control algorithm for multimedia services that satisfies end‐to‐end delay constraint with low transmission power consumption. The proposed algorithm supports the required bandwidth by controlling each link channel quality over route in a tolerable range. In addition, a simple but effective route maintenance mechanism is implemented to avoid link failures that may significantly degrade streaming video quality. Finally, performance comparison with existing algorithms is presented in respect to traditional routing performance metrics, and an achievable video quality comparison is provided to demonstrate the superiority of the proposed algorithm for multimedia services over mobile ad hoc network. Copyright © 2010 John Wiley & Sons, Ltd.     

无铅BGA封装可靠性的力学试验与分析

着重研究了机械冲击和应力对无铅BGA封装焊点可靠性的影响,介绍了BGA封装的可靠性力学试验(跌落、弯曲试验)及其分析方法.通过对力学试验中失效焊点的分析以及借助ANSYS模拟工具,找出引起失效的根本原因,为开发性能更好、高可靠性的无铅材料、改进无铅工艺提供依据.     

Mechanical bending of flexible complementary inverters based on organic and oxide thin film transistors

Flexible complementary inverters composed of p-channel pentacene thin-film transistors (TFTs) and n-channel amorphous indium gallium zinc oxide TFTs were fabricated on polymer substrates. The characteristics of the TFTs and inverters were evaluated at different bending radii. Throughout the bending experiments, the relationship between the performances of the inverters and the characteristics of the TFTs under mechanical deformation was analyzed. The mechanically applied strain led to a change in the voltage transfer characteristics of the complementary inverters, as well as the source–drain saturation current, field-effect mobility and threshold voltage of the TFTs. The switching threshold voltage of the fabricated inverters decreased with decreasing bending radius, which was related to changes in the field-effect mobility and the threshold voltage of the TFTs.     

Determination of the interface energy level alignment of a doped organic hetero-junction using capacitance–voltage measurements

A simple method based on capacitance–voltage (C–V) measurements is reported to determine the interface energy level alignment at the junction of 15 mol% Cs₂CO₃ doped 4,7-diphenyl-1,10-phenanthroline (BPhen) and 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HATCN) fabricated under high vacuum. The junction properties, such as the depletion layer thickness, built-in potentials and vacuum level shift were calculated with simple Mott–Schottky and Poisson’s equations with the boundary condition of a continuous electric flux density using the information from the C–V data. The interface energy level alignment determined by this method is well matched with the one determined using the in situ ultraviolet photoemission spectroscopy (UPS) and X-ray photoemission spectroscopy (XPS) experiments performed under ultra-high vacuum. This method can be applied to other semiconductor junctions such as the organic p–n homojunctions and heterojunctions with known energy levels, as long as the metal/semiconductor contact is Ohmic without referring to the photoemission spectroscopies. Moreover, the energy level alignment determined by the C–V measurement gives a more realistic result since the films for the measurements are formed under high vacuum which is a normal device fabrication environment rather than under ultra high vacuum.     

Improving the R-score of an adaptive VoIP codec in IEEE 802.16 networks

Worldwide Interoperability for Microwave Access (WiMAX) technology, which is based on the IEEE 802.16 standard, supports different quality of service (QoS) for different services. WiMAX is expected to support QoS in real-time applications such as Voice over Internet Protocol (VoIP). When network congestion occurs, the VoIP bit rate needs to be adjusted to achieve the best speech quality. In this study, we propose a new scheme called Adaptive VoIP Level Coding (AVLC). This scheme takes into consideration network conditions (packet delay and packet loss) and a connection’s modulation scheme. The amount of data that can be transmitted increases with the speed of the modulation scheme. When network congestion occurs, AVLC scheme prioritizes reducing the bit rate of a connection that has a slower modulation scheme to mitigate congestion. Depending on network conditions, such as modulation scheme, packet delay, packet loss, and residual time slot, we use the G.722.2 codec to adjust each connection’s bit rate. Simulations are conducted to test the performance (network delay, packet loss, number of modulation symbols, and R-score) of the proposed scheme. The simulation results indicate that speech quality is improved by the use of AVLC.     

Name‐Based Autoconfiguration for Mobile Ad hoc Networks

In a mobile ad hoc network, difficulties exist in supporting address autoconfiguration and naming resolution due to the lack of centralized servers. This letter presents a novel approach, called name‐based autoconfiguration (NBA), which uses host names to determine IP addresses and provides address autoconfiguration and name resolution as a single protocol.