Printed Sub‐2 V Gel‐Electrolyte‐Gated Polymer Transistors and Circuits

The fabrication and characterization of printed ion‐gel‐gated poly(3‐hexylthiophene) (P3HT) transistors and integrated circuits is reported, with emphasis on demonstrating both function and performance at supply voltages below 2 V. The key to achieving fast sub‐2 V operation is an unusual gel electrolyte based on an ionic liquid and a gelating block copolymer. This gel electrolyte serves as the gate dielectric and has both a short polarization response time (<1 ms) and a large specific capacitance (>10 µF cm^?2), which leads simultaneously to high output conductance (>2 mS mm^?1), low threshold voltage (<1 V) and high inverter switching frequencies (1–10 kHz). Aerosol‐jet‐printed inverters, ring oscillators, NAND gates, and flip‐flop circuits are demonstrated. The five‐stage ring oscillator operates at frequencies up to 150 Hz, corresponding to a propagation delay of 0.7 ms per stage. These printed gel electrolyte gated circuits compare favorably with other reported printed circuits that often require much larger operating voltages. Materials factors influencing the performance of the devices are discussed.     

Autonomic Self‐Repairing Glassy Materials

A new process that enables glassy materials to self‐repair from mechanical damage is presented in this paper. Contrary to intrinsic self‐healing, which involves overheating to enable crack healing by glass softening, this process is based on an extrinsic effect produced by vanadium boride (VB) particles dispersed within the glass matrix. Self‐repair is obtained through the oxidation of VB particles, and thus without the need to increase the operating temperature. The VB healing agent is selected for its capacity to oxidize at a lower temperature than the softening point of the glass. Thermogravimetric analyses indeed show that VB oxidation is rapid and occurs below the glass transition temperature. Solid‐state nuclear magnetic resonance spectroscopy indicates that VB is oxidized into V₂O₅ and B₂O₃, which enable the local formation of glass. The autonomic self‐healing effect is demonstrated by an in situ experiment visualized using an environmental scanning electron microscope. It is shown that a crack could be healed by the VB oxidation products.     

Novel transmit antenna selection strategy for massive MIMO downlink channel

In this paper, we deal with the problem of acquiring the channel state information (CSI) at the transmitter in large-scale multiple input multiple output (MIMO) systems, so-called massive MIMO systems. Clearly, obtaining CSI plays a central role to provide high system performance. Even though, in frequency-division duplexed systems, acquiring this information requires a prohibitive amount of feedback, since it increases with the number of transmit antenna. In this work, we design an efficient transmit antenna selection strategy aware of the amount of required CSI for a point-to-multipoint transmission in massive MIMO systems. The proposed strategy provides high sum-rate with limited CSI feedback and limited computational complexity. Innovatively, the antenna selection in our strategy is performed in a decentralized fashion successively at the receiving users. Two schemes are proposed in this work to perform the antenna selection at each user. Next, taking into consideration that the large-scale MIMO transmitter suffers from imperfect knowledge of CSI, we design a new performance criterion. Computer simulations validate that, when the CSI is perfectly known, the proposed strategy is able to achieve high performance in terms of system sum-rate while a significant reduction in both CSI feedback overhead and computational complexity is observed. Moreover, assuming imperfect CSI, the new proposed criterion achieves higher performance when the estimation accuracy is low and at high SNR regime.     

Study on the Effect of Mn,Zn, and Sb on Undercooling Behavior of Sn-Ag-Cu Alloys Using Differential Thermal Analysis

Differential thermal analysis (DTA) has been conducted on directionally solidified near-eutectic Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC), SAC \(+\) 0.2 wt.%Sb, SAC \(+\) 0.2 wt.%Mn, and SAC \(+\) 0.2 wt.%Zn. Laser ablation inductively coupled plasma mass spectroscopy was used to study element partitioning behavior and estimate DTA sample compositions. Mn and Zn additives reduced the undercooling of SAC from 20.4\(^\circ \hbox {C}\) to \(4.9^\circ \hbox {C}\) and \(2^\circ \hbox {C}\), respectively. Measurements were performed at cooling rate of \(10^\circ \hbox {C}\) per minute. After introducing 200 ppm \(\hbox {O}_2\) into the DTA, this undercooling reduction ceased for SAC \(+\) Mn but persisted for SAC \(+\) Zn.     

Bi-exponential edge-preserving smoother

Edge-preserving smoothers need not be taxed by a severe computational cost. We present, in this paper, a lean algorithm that is inspired by the bi-exponential filter and preserves its structure-a pair of one-tap recursions. By a careful but simple local adaptation of the filter weights to the data, we are able to design an edge-preserving smoother that has a very low memory and computational footprint while requiring a trivial coding effort. We demonstrate that our filter (a bi-exponential edge-preserving smoother, or BEEPS) has formal links with the traditional bilateral filter. On a practical side, we observe that the BEEPS also produces images that are similar to those that would result from the bilateral filter, but at a much-reduced computational cost. The cost per pixel is constant and depends neither on the data nor on the filter parameters, not even on the degree of smoothing.     

An efficient omnidirectional vision system for soccer robots: From calibration to object detection

Robotic soccer is nowadays a popular research domain in the area of multi-robot systems. In the context of RoboCup, the Middle Size League is one of the most challenging. This paper presents an efficient omnidirectional vision system for real-time object detection, developed for the robotic soccer team of the University of Aveiro, CAMBADA. The vision system is used to find the ball and white lines, which are used for self-localization, as well as to find the presence of obstacles. Algorithms for detecting these objects and also for calibrating most of the parameters of the vision system are presented in this paper. We also propose an efficient approach for detecting arbitrary FIFA balls, which is an important topic of research in the Middle Size League. The experimental results that we present show the effectiveness of our algorithms, both in terms of accuracy and processing time, as well as the results that the team has been achieving: 1st place in RoboCup 2008, 3rd place in 2009 and 1st place in the mandatory technical challenge in RoboCup 2009, where the robots have to play with an arbitrary standard FIFA ball.     

New Alternatives to the Estimation Problem in Hardware-Software Codesign of Complex Embedded Systems: The H.261 Video Co-dec Case Study

As Codesign problems become larger and more realistic, the required time to estimate their solutions turns into an important bottleneck. This paper presents a new approach to improve the traditional estimation techniques, in order to avoid this drawback. The presented method has been successfully tested on a large experimental benchmark, attaining quality levels close to those provided by the Synopsys Behavioral Compiler. Finally, a case study based on the standard H.261 video co-dec is described, proving the convenience of the technique on real-life situations. The obtained results show a significant improvement in the process time, while keeping the good precision and fidelity levels that the traditional estimation models usually offer.     

Interdigitated back‐contact heterojunction solar cell concept for liquid phase crystallized thin‐film silicon on glass

We present an interdigitated back‐contact silicon heterojunction system designed for liquid‐phase crystallized thin‐film (~10 µm) silicon on glass. The preparation of the interdigitated emitter (a‐Si:H(p)) and absorber (a‐Si:H(n)) contact layers relies on the etch selectivity of doped amorphous silicon layers in alkaline solutions. The etch rates of a‐Si:H(n) and a‐Si:H(p) in 0.6% NaOH were determined and interdigitated back‐contact silicon heterojunction solar cells with two different metallizations, namely Al and ITO/Ag electrodes, were evaluated regarding electrical and optical properties. An additional random pyramid texture on the back side provides short‐circuit current density (j_SC) of up to 30.3 mA/cm² using the ITO/Ag metallization. The maximum efficiency of 10.5% is mainly limited by a low of fill factor of 57%. However, the high j_SC, as well as V_OC values of 633 mV and pseudo‐fill factors of 77%, underline the high potential of this approach. Copyright © 2015 John Wiley & Sons, Ltd.     

Compact Modules for Wireless Communication Systems in the E-Band (71–76 GHz)

The millimeter-wave spectrum above 70 GHz provides a cost-effective solution to increase the wireless communications data rates by increasing the carrier wave frequencies. We report on the development of two key components of a wireless transmission system, a high-speed photodiode (HS-PD) and a Schottky Barrier Diode (SBD). Both components operate uncooled, a key issue in the development of compact modules. On the transmitter side, an improved design of the HS-PD allows it to deliver an output RF power exceeding 0 dBm (1 mW). On the receiver side, we present the design process and achieved results on the development of a compact direct envelope detection receiver based on a quasi-optical SDB module. Different resonant (meander dipole) and broadband (Log-Spiral and Log-Periodic) planar antenna solutions are designed, matching the antenna and Schottky diode impedances at high frequency. Impedance matching at baseband is also provided by means of an impedance transition to a 50 Ohm output. From this comparison, we demonstrate the excellent performance of the broadband antennas over the entire E-band by setting up a short-range wireless link transmitting a 1 Gbps data signal.     

Crystallization-Directed Anisotropic Electroactuation in Selectively Solvated Olefinic Thermoplastic Elastomers: A Thermal and (Electro)Mechanical Property Study

Dielectric elastomers (DEs), a class of soft electroactive polymers that change size upon exposure to an external electric field, constitute an increasingly important class of stimuli-responsive polymers due primarily to their large actuation strains, facile and low-cost fabrication, scalability, and mechanical robustness. Unless purposefully constrained, most DEs exhibit isotropic actuation wherein size changes are the same in all actuation directions. Previous studies of DEs containing oriented, stiff fibers have demonstrated, however, that anisotropic actuation along a designated direction is more electromechanically efficient since this design eliminates energy expended in nonessential directions. To identify an alternative, supramolecular-level route to anisotropic electroactuation, we investigate the thermal and mechanical properties of novel thermoplastic elastomer gels composed of a selectively solvated olefinic block copolymer that not only microphase-separates but also crystallizes upon cooling from the solution state. While these materials possess remarkable mechanical attributes (e.g., giant strains in excess of 4000%), their ability to be strain-conditioned enables huge anisotropic actuation levels, measured to be greater than 30 from the ratio of orthogonal actuation strains. This work establishes that crystallization-induced anisotropic actuation can be achieved with these DEs.