Vapor Phase Growth of Functional Pentacene Films at Atmospheric Pressure

Compared to traditional vacuum evaporation techniques for small organic molecules, organic vapor phase deposition (OVPD) possesses a extra processing parameter: the pressure of process gas P_ch. Here, the influence of large P_ch variations (from 0.1 mbar to atmospheric pressure) on pentacene thin film growth is explored. OVPD operation at higher P_ch is characterized by lower carrier gas velocities and lower organic diffusivities. These result in an invariance of the material utilization efficiency over the entire pressure span and in an advantageous equilibrium evaporation regime in the source. An increase in P_ch yields rough pentacene layers. Classical nucleation theory is applied to demonstrate how the pressure rise triggers homogeneous nucleation in the gas phase, causing the observed roughening. The use of lower deposition rates, higher dilution flow rates, and higher substrate temperatures result in the suppression of gas phase nucleation and the growth of smooth pentacene films at atmospheric pressure. Using these optimized conditions, state‐of‐the‐art pentacene thin film transistors with saturation mobilities above 0.9 cm²/Vs are reproducibly fabricated. p‐Type circuits are also made and a 19‐stage ring oscillator with a stage delay of 51 μs at a supply voltage of 15 V is demonstrated.     

改革模拟实验教学和考试方法的尝试

模拟电子线路实验课对于电子线路教学改革和提高学生的工程实践能力具有重要作用。本文阐述了模拟实验课单独设课后教学及考试方法的改革尝试以及教学体会和教学效果。     

A 640 by 480 Pixels Readout Circuit for IR Imaging

A readout circuit for a 640 × 480 pixels FPA (focal plane array) has been successfully designed, fabricated and tested. The circuit solution is based on a per pixel source-follower direct injection (SFDI) pre-amplifier. Signal multiplexing is performed in both X and Y direction. The pixel size is 25 m × 25m. The chip is optimized for a QWIP (quantum well infrared photodetector) operating at a temperature of 70 K. The circuit has been realized in a standard 0.8 m CMOS process.     

Fully Integrated Low Phase-Noise VCOs: From Special Processing to Standard CMOS

An overview is given on the several options for and problems associated with creating high-quality integrated inductors for VCOs. Special processing techniques are reported that can enhance the performance of a normal planar inductor coil. Bonding Wire inductors are presented as an alternative, that allows state-of-the-art phase noise performance at no extra cost. Finally, it is shown that by thorough analysis of standard planar inductors with finite-element simulations, performances can be achieved that are even better than structures requiring extra processing cost. This is done despite a low-ohmic substrate with only two metal layers.     

Realization of an active inductance for a low power high bandwidth DC power line communication network transceiver

An active inductor based on an improved gyrator circuit is proposed. The active inductor is developed to be implemented in a high impedance transceiver for a wearable DC power line communication network where requirements such as low power consumption, high bandwidth and numerous nodes support are prioritized. A load isolation step is introduced to ensure the stability of the active inductance's size on different load currents. The proposed gyrator circuit is analyzed and optimized by means of theoretical calculations. The theoretical results are then verified by simulations and experiments in the frequency range up to 10 MHz.     

Insights in wind turbine drive train dynamics gathered by validating advanced models on a newly developed 13.2 MW dynamically controlled test-rig

Guaranteeing reliable and cost-effective wind turbine drive trains requires expert insights in dynamics during operation. A combination of advanced modeling techniques and detailed measurements are suggested to realize this goal. The flexible multibody modeling technique enables the simulation of dynamic loads on all drive train components. Moreover it facilitates estimation of structural component deformation caused by dynamic loading. This paper gives a detailed overview of the assumptions made in this modeling approach. Furthermore the influence of the different structural component flexibilities is investigated in detail. To gain confidence in the models created, model validation by means of a comparison with measurements is necessary. To overcome issues concerning test repeatability experienced in field testing, test-rig testing is suggested as a valid alternative. In order to be representative, dedicated dynamic load cases, which represent specific dynamic behavior of the gearbox in a wind turbine need to be realized on the test-rig. However a highly dynamic test-rig complying with the specifications was not commercially available. Therefore Hansen developed a high dynamic test-rig with a nominal power of 13.2 MW and a peak power capacity of 16.8 MW. A back-to-back gearbox configuration was used. The complexity of controlling dynamics of the test-rig was solved by identifying dedicated load cases which represent specific wind turbine behavior. This paper describes the development process of the project consisting of four phases. During two phases a scaled set-up was used, which enabled iterative optimization of the complex interaction between the mechanical dynamics and the electrical controller of the test-rig. In the final part of the paper the two previously discussed approaches are combined, as it discusses results from the validation of simulation models using measurements performed on the 13.2 MW test-rig.     

Human-robot synchrony: flexible assistance using adaptive oscillators

We propose a novel method for movement assistance that is based on adaptive oscillators, i.e., mathematical tools that are capable of extracting the high-level features (amplitude, frequency, and offset) of a periodic signal. Such an oscillator acts like a filter on these features, but keeps its output in phase with respect to the input signal. Using a simple inverse model, we predicted the torque produced by human participants during rhythmic flexion-extension of the elbow. Feeding back a fraction of this estimated torque to the participant through an elbow exoskeleton, we were able to prove the assistance efficiency through a marked decrease of the biceps and triceps electromyography. Importantly, since the oscillator adapted to the movement imposed by the user, the method flexibly allowed us to change the movement pattern and was still efficient during the nonstationary epochs. This method holds promise for the development of new robot-assisted rehabilitation protocols because it does not require prespecifying a reference trajectory and does not require complex signal sensing or single-user calibration: the only signal that is measured is the position of the augmented joint. In this paper, we further demonstrate that this assistance was very intuitive for the participants who adapted almost instantaneously.     

Rotation moment invariants for recognition of symmetric objects.

In this paper, a new set of moment invariants with respect to rotation, translation, and scaling suitable for recognition of objects having N-fold rotation symmetry are presented. Moment invariants described earlier cannot be used for this purpose because most moments of symmetric objects vanish. The invariants proposed here are based on complex moments. Their independence and completeness are proven theoretically and their performance is demonstrated by experiments.     

Friction Compensation of an $XY$ Feed Table Using Friction-Model-Based Feedforward and an Inverse-Model-Based Disturbance Observer

Uncompensated friction forces compromise the positioning and tracking accuracy of motion systems. A unique tracking error known as quadrant glitch is the result of complex nonlinear friction behavior at motion reversal or near-zero velocity. Linear-feedback control strategies such as PID, cascade P/PI, or state-feedback control have to be extended with model- and nonmodel-based friction-compensation strategies to acquire sufficiently high path and tracking accuracy. This paper analyzes and validates experimentally three different friction-compensation strategies for a linear motor-based xy feed drive of a high-speed milling machine: (1) friction-model-based feedforward; (2) an inverse-model-based disturbance observer; and (3) the combination of both techniques. The friction models considered are as follows: a simple static-friction model and the recently developed generalized Maxwell-slip (GMS) model. GMS friction-model-based feedforward combined with disturbance observer almost completely eliminates the radial tracking error and quadrant glitches.     

Ester-functionalized poly(3-alkylthiophene) copolymers: Synthesis,physicochemical characterization and performance in bulk heterojunction organic solar cells

The introduction of functional moieties in the donor polymer (side chains) offers a potential pathway toward selective modification of the nanomorphology of conjugated polymer:fullerene active layer blends applied in bulk heterojunction organic photovoltaics, pursuing morphology control and solar cell stability. For this purpose, two types of poly(3-alkylthiophene) random copolymers, incorporating different amounts (10/30/50%) of ester-functionalized side chains, were efficiently synthesized using the Rieke method. The solar cell performance of the functionalized copolymers was evaluated and compared to the pristine P3HT:PCBM system. It was observed that the physicochemical and opto-electronic characteristics of the polythiophene donor material can be modified to a certain extent via copolymerization without (too much) jeopardizing the OPV efficiency, as far as the functionalized side chains are introduced in a moderate ratio (<30%) and that preference is given to side chains with a small molar volume. A range of complementary techniques – UV–Vis spectroscopy, (modulated temperature) differential scanning calorimetry, transmission electron microscopy and X-ray diffraction analysis – indicated that variations in polymer crystallinity, while maintaining a high level of regioregularity, are probably the main factor responsible for the observed differences.