Velazquez-Rizo, Martin; Iida, Daisuke; Ohkawa, Kazuhiro(Japanese Journal of Applied Physics, Institute of Physics Publishinghelen.email@example.com, 2019-01-01)[Article]
We report the fabrication of a GaN-based photoelectrode with CoO x as a cocatalyst for the photoelectrochemical H2 generation from water. We confirmed that the cocatalyst prevented the GaN photocorrosion partially during the water photoelectrolysis reaction and that it has a superior performance when it is deposited as particles instead of as a thin film. We demonstrated that the CoO x /GaN photoelectrode is capable of generating H2 at a quasi-stable rate for at least 20 h. Scanning and transmission electron microscopy analyses of the cocatalyst confirmed that the CoO x particles agglomerate in sparse polycrystalline clusters, which were formed mainly by spinel Co3O4.
Almansouri, Abdullah S.; Alsharif, Nouf; Khan, Mohammed Asadullah; Swanepoel, Liam; Kaidarova, Altynay; Salama, Khaled N.; Kosel, Jürgen(Advanced Materials Technologies, Wiley-Blackwellinfo@wiley.com, 2019-01-01)[Article]
Flexible and wearable magnetoelectronics add intriguing new functionalities to natural perception. Of particular interest regarding these artificial skins are wireless sensing and touchless interactions. Biocompatibility and imperceptibility are the most significant features of devices attached to the bodies. A biocompatible magnetic skin is introduced. It offers extreme flexibility, stretchability (>300%), and is lightweight, while maintaining a remanent magnetization up to 360 mT. It is comfortable to wear, can be realized in any desired shape or color, and adds tunable permanent magnetic properties to the surface it is applied to. It provides remote control functions and is combined with magnetic sensors; it implements a complete wearable magnetic system. For example, eye tracking is realized by attaching the magnetic skin to the eyelid. The advantage that it does not require any wiring makes it an extremely viable solution for soft robotics and human–machine interactions. Wearing the magnetic skin on a finger or integrated into a glove allows for remote gesture control. This type of application opens the door to new control concepts, relevant for people with disabilities, sterile environments, or the consumer industry.
Efficient carrier extraction is essential for high performance optoelectronic devices, such as solar cells and photodetectors. Conventional strategies to separate photogenerated carriers typically involve the fabrication of a p-n junction by doping and the use of carrier selective charge transport layers. However, these techniques often require high temperature processes or costly materials. In this work, we demonstrate an innovative and simple approach of extracting photogenerated carriers from organometallic halide perovskites utilizing triboelectricity. The triboelectric device can be easily fabricated at low temperature using inexpensive materials on plastic substrates, enabling it to be readily integrated into self-powered optoelectronic devices. As a proof-of-concept, we fabricated a triboelectrics-assisted perovskite photodetector, which enabled us to study the surface charges generated using different electrical contacts and bending conditions performed by the device. With the assistance of a triboelectric charge-induced electric field, the photocurrent and transient photoresponses were significantly enhanced. Furthermore, we integrated the plastic triboelectric device with a flexible photodetector to demonstrate this carrier collection approach in flexible/wearable electronics. To the best of our knowledge, this work is the first report of carrier extraction in organometallic halide perovskite photodetector by triboelectric charges, demonstrating a potential use for carrier extraction in other semiconductor-based optoeletronic devices.
Karimi, Muhammad Akram; Zhang, Qingle; Kuo, Yen Hung; Shaikh, Sohail F.; Kaidarova, Altynay; Geraldi, Nathan; Hussain, Muhammad Mustafa; Kosel, Jürgen; Duarte, Carlos M.; Shamim, Atif(Flexible and Printed Electronics, IOP Publishing, 2019-09-06)[Article]
Acquisition of sensor data from tagged marine animals has always been a challenge. Presently, we come across two extreme mechanisms to acquire marine data. For continuous data acquisition, hundreds of kilometers of optical fiber links are used which in addition to being expensive, are impractical in certain circumstances. On the other extreme, data is retrieved in an offline and invasive manner after removing the sensor tag from the animal's skin. This paper presents a semi-continuous method of acquiring marine data without requiring tags to be removed from the sea animal. Marine data is temporarily stored in the tag's memory, which is then automatically synced to floating receivers as soon as the animal rises to the water surface. To ensure effective wireless communication in an unpredictable environment, a quasi-isotropic antenna has been designed which works equally well irrespective of the orientation of the tagged animal. In contrast to existing rigid wireless devices, the tag presented in this work is flexible and thus convenient for mounting on marine animals. The tag has been initially tested in air as a standalone unit with a communication range of 120m. During tests in water, with the tag mounted on the skin of a crab, a range of 12m has been observed. In a system-level test, the muscle activity of a small giant clam (Tridacna maxima) has been recorded in real time via the non-invasive wireless tag.
Boukhedimi, Ikram; Kammoun, Abla; Alouini, Mohamed-Slim(IEEE Wireless Communications Letters, Institute of Electrical and Electronics Engineers (IEEE), 2019-09-04)[Article]
This work investigates the uplink of massive MIMO systems using multi-cell MMSE (M-MMSE) combining that was shown to yield unbounded capacity in Rayleigh fading. All intra and inter-cell channels are correlated with distinct per-user Rician factors and channel correlation matrices, pilot contamination and imperfect channel estimation. First, a closed-form approximation of the spectral efficiency (SE) is derived thus enabling to demonstrate that, under certain conditions on the correlation matrices, M-MMSE generates unbounded SE in Rician fading. Second, the impact of inter-cell LoS components is examined in favorable propagation conditions, and, interestingly, shown to be more beneficial in terms of SE than when these interfering links are entirely scattered.
Saeed, Nasir; Alouini, Mohamed-Slim; Al-Naffouri, Tareq Y.(IEEE Access, Institute of Electrical and Electronics Engineers (IEEE), 2019-08-27)[Article]
Magnetic Induction (MI) is an efficient wireless communication method to deploy operational internet of underground things (IoUT) for oil and gas reservoirs. The IoUT consists of underground things which are capable of sensing the underground environment and communicating with the surface. The MI-based IoUT enable many applications, such as monitoring of the oil rigs, optimized fracturing, and optimized extraction. Most of these applications are dependent on the location of the underground things and therefore require accurate localization techniques. The existing localization techniques for MI-based underground sensing networks are two-dimensional and do not characterize the achievable accuracy of the developed methods, which are both crucial and challenging tasks. Therefore, this paper proposes a novel three-dimensional (3D) localization technique based on Isometric scaling (Isomap) for future IoUT. Moreover, this paper also presents the closed-form expression of the Cramer Rao lower bound (CRLB) for the proposed technique, which takes into account the channel parameters of the underground magnetic-induction. The derived CRLB provides the suggestions for an MI-based underground localization system by associating the system parameters with the error trend. Numerical results demonstrate that localization accuracy is affected by different channel and networks parameters such as the number of underground things, ranging error variance, size of the coils, and the transmitting power. The root mean square error performance of the proposed technique shows that increase in the number of turns of the coils, transmitting power, and the number of anchors improves the performance. Results also show that the proposed technique is robust to the ranging error variance in the range of 10 to 30 %; however, a further increase in the ranging error variance does not allow to achieve acceptable accuracy. Also, the results show that the proposed technique achieves an average of 30 % better localization accuracy compare to the traditional methods.
Obeed, Mohanad; Dahrouj, Hayssam; Salhab, Anas M.; Zummo, Salam A.; Alouini, Mohamed-Slim(IEEE Transactions on Wireless Communications, Institute of Electrical and Electronics Engineers (IEEE), 2019-08-27)[Article]
Visible light communications (VLC) have emerged as a strong candidate for meeting the escalating demand for high data rates. In this paper, we consider a VLC network, where multiple access points (APs) serve both energy-harvesting users (EHUs), i.e., users who harvest energy from light emitted by diodes and information users (IUs), i.e., users who gather data information. In order to jointly balance the achievable sum rate at the IUs and the energy harvested by the EHUs, the paper considers maximizing a network-wide utility, which consists of a weighted sum of the IUs sum rate and the EHUs harvested energy, subject to individual IU rate constraint, individual EHU harvested-energy constraint, and AP power constraints, so as to jointly determine the direct current (DC) bias value at each AP, and the power of the alternating-current (AC) signals of the users. A difficult non-convex optimization problem is solved using an iterative approach which relies on inner convex approximations, and compensates for the used approximations using proper outer-loop updates. The paper further considers solving the special cases of the problem, i.e., maximizing the sum rate, and maximizing the total harvested-energy, both subject to the same constraints. Numerical results highlight the significant performance improvement of the proposed algorithms, and illustrate the impacts of the network parameters on the performance trade-off between the sum rate and harvested-energy.
Image segmentation is an important first step of many image processing, computer graphics, and computer vision pipelines. Unfortunately, it remains difficult to automatically and robustly segment cluttered scenes, or scenes in which multiple objects have similar color and texture. In these scenarios, light fields offer much richer cues that can be used efficiently to drastically improve the quality and robustness of segmentations. In this paper we introduce a new light field segmentation method that respectstextureappearance,depthconsistency,aswellasocclusion,andcreates well-shaped segments that are robust under view point changes. Furthermore, our segmentation is hierarchical, i.e. with a single optimization, a whole hierarchy of segmentations with different numbers of regions is available. All this is achieved with a submodular objective function that allows for efficient greedy optimization. Finally, we introduce a new tree-array type data structure, i.e. a disjoint tree, to efficiently perform submodular optimization on very large graphs. This approach is of interest beyond our specific application of light field segmentation. We demonstrate the efficacy of our method on a number of synthetic and real data sets, and show how the obtained segmentations can be used for applications in image processing and graphics.
Liao, Hanguang; Zhang, Qingle; Karimi, Muhammad Akram; Kuo, Yen Hung; Mishra, Nidhi; Shamim, Atif(IEEE Antennas and Wireless Propagation Letters, Institute of Electrical and Electronics Engineers (IEEE), 2019-08-26)[Article]
A low-cost and additively manufactured 3D Antenna-in-Package (AiP) with quasi-isotropic radiation is proposed for a marine animals monitoring system. The antenna is based on a meandered dipole folded as a split ring resonator (SRR) structure, which can generate simultaneously a pair of orthogonal electric and magnetic dipoles, thus providing a quasi-isotropic radiation pattern. The antenna (integrated with a balun) has been inkjet-printed on a 3D-printed buoyant cone structure, which acts also as the system package to house the electronics and the battery. The antenna designed at 2.4 GHz is electrically small, with a ka = 0.49, and has a bandwidth of 70 MHz (2.9%). The measured gain deviation of the antenna (maximum to minimum) is near 3 dB in bandwidth, thus qualifying it as a quasi-isotropic antenna. Field tests of the antenna in the active state (integrated with the electronics) confirm a reliable communication range of 240 m in any direction in the azimuthal plane.
Elserougi, Ahmed; Massoud, Ahmed; Ahmed, Shehab(IET Generation, Transmission & Distribution, Institution of Engineering and Technology (IET), 2019-06-19)[Article]
In this study, a cost-effective HVDC shunt tap with low-number of relatively low-voltage semiconductor devices and small-sized passive components is proposed. The proposed architecture is based on employing three single-phase half-bridge Modular Multilevel Converters (MMCs), where the DC sides of MMCs are connected in series across the total DC-link voltage. The MMCs are adopted instead of conventional Two-Level Voltage Source Converters (2L-VSCs) to avoid the complications of series connection of Insulated Gate Bipolar Transistors (IGBTs). The involved MMCs in the suggested architecture are operated with the conventional 2L modulation, which results in insignificant arm inductors and Sub-Modules (SMs) capacitances (in range of µH and µF, respectively). This, in turn, affects positively the converter cost and footprint. Each arm of the involved MMCs can be considered as a high-voltage valve of a 2L-VSC. To maintain the balance of SMs capacitors, each arm of the involved (N + 1)-level MMC has an extra SM (a balancing SM) to select N out of N + 1 SMs during the turn-off condition. The operational concept, design, and assessment of the proposed architecture are presented in this study. Simulation results are provided for substantiation of the proposed concept. Finally, a scaled down single-phase prototype is used for experimental validation.
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