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Microscopic imaging in three dimensions enables numerous biological and clinical applications. However, high-resolution optical imaging preserved in a relatively large depth range is hampered by the rapid spread of tightly confined light due to diffraction. Here, we show that a particular disposition of light illumination and collection paths liberates optical imaging from the restrictions imposed by diffraction. This arrangement, realized by metasurfaces, decouples lateral resolution from depth-of-focus by establishing a one-to-one correspondence (bijection) along a focal line between the incident and collected light. Implementing this approach in optical coherence tomography, we demonstrate tissue imaging at 1.3 μm wavelength with ~ 3.2 μm lateral resolution, maintained nearly intact over 1.25 mm depth-of-focus, with no additional acquisition or computation burden. This method, termed bijective illumination collection imaging, is general and might be adapted across various existing imaging modalities.

Commercialization of organic solar cells (OSC) is imminent. Interlayers between the photoactive film and the electrodes are critical for high device efficiency and stability. Here, the applicability of SnO

This article presents a new nonisolated dc–dc converter with bidirectional power flow capability. The proposed converter operates in triangular conduction mode (TCM). Consequently, reverse-recovery losses are completely eliminated, zero voltage switching characteristics are obtained, and the inductor size can be reduced. However, in comparison with other converters in TCM that suffer from a large input-current-ripple, the proposed converter benefits from very low input-current-ripple. Furthermore, in the proposed converter, the voltage stress of the main switches is reduced, the converter voltage-gain is increased, the output current is nonpulsating, the input and output sources share a common ground, and only a single magnetic core is required. The proposed power circuit topology is theoretically analyzed and experimental results are provided to verify its feasibility and demonstrate its superior performance.

This article presents a three-port dc/dc converter along with a new control system to integrate solar panels and energy storage in a dc nanogrid. The proposed control system utilizes the duty cycle as well as the switching frequency to control the power flow between the three ports. The proposed converter offers a low number of components, low cost, and high reliability. Moreover, it is capable of providing bidirectional power flow for the energy storage system and the dc grid while having soft-switching for power semiconductors. The converter demonstrates high design flexibility in accommodating different applications. Theoretical analysis and experimental results verify the feasibility and demonstrate the superior performance of the proposed converter.

This article presents a novel isolated dc–dc converter circuit topology, which is able to offer high performance for a wide range of operating conditions. The prominent features of the proposed circuit topology include its direct power transfer (DPT) capability, quasi-rectangular waveform for the input current, and soft-switching performance for a wide range of operating conditions. The amount of power processed by the power switches and transformer is reduced through DPT. In addition, the quasi-rectangular waveform of the input current decreases its peak and root-mean-square values, leading to reduced conduction losses associated with the magnetics and power semiconductors. In the proposed structure, the power switches benefit from zero-voltage-switching characteristics, while the output diodes operate under zero-current-switching conditions. Thus, the proposed topology minimizes both the conduction and switching losses, thereby improving the overall efficiency. Extensive simulation and experimental results are provided to verify the feasibility of the proposed circuitry and demonstrate its superior performance.

This article presents a new droop-based supervisory-level controller for nanogrids (NGs) in the islanded mode of operation. The proposed control system is able to significantly improve the dynamics of power electronic interfaces in NGs. Unlike the existing techniques, the proposed controller takes into account the input-side (i.e., source-side) and the output-side (i.e., load-side) parameters as well as the dc-bus voltage dynamics. Theoretical analysis, simulation results, and experimental results confirm the feasibility of the proposed control system and demonstrate its superior performance.

OLEDs have become prominent in commercial display and lighting applications, mainly for television and smartphone screens, and in many electronic gadgets due to superior features over other display technologies such as Liquid Crystal Displays (LCDs). In the evolution of OLED fabrication, roll-to-roll (R2R) solution-based techniques, which are low-cost and high throughput, have emerged as next-generation manufacturing methods for OLED production. Researchers and scientists all over the world are investigating R2R upscaling methods. Thus far, the existing R2R fabrication methods for manufacturing high performance OLEDs have had limited success due to film thickness variations, aggregation in films, challenges in forming the multi-layer structure, and scarcity of efficient interlayers. Slot-die coating is a very promising fabrication technique that can facilitate R2R manufacturing of OLEDs and address some of the aforementioned challenges. In this review, a summary of the developments in OLED fabrication using slot-die coating methods is presented. First, we highlight the research work on the slot-die coating of single and multi-layer OLEDs, and then we present various modifications of slot-die heads to fabricate micro-sized OLEDs for high-resolution display applications. Lastly, we present a qualitative comparison between the performance of OLEDs fabricated by slot-die coating and the ones fabricated by other R2R techniques. While many review articles have been published on OLED materials and devices, there is not one collection of reports detailing the slot-die coating, an additive manufacturing method, of OLEDs.

We have designed and synthesized three N-annulated perylene diimide (PDI) compounds containing sterically bulky alkyl-substituted benzyl moieties (PDI-X, where X = 1, 2, 3) with photoluminescence quantum yield (PLQY) in the solid-state >20%. The PDI molecules show PLQY of ∼0.8 in solution and ∼0.2 as neat films. Organic light-emitting diodes (OLEDs) have been fabricated using these new PDI molecules as light emitters with the active layer being solution processed from non-halogenated solvents. The OLED devices had brightness of ∼2000 cd m−2 and low turn-on voltage of ∼3 V, among the best for PDI based red colored OLEDs.

This article presents a novel sensorless control system for a solar tile microinverter employing the flyback topology. The elimination of current sensors from the circuit lowers the overall cost and reduces measurement noise introduced into the control system. The proposed control system eliminates both the high frequency inductor current measurement as well as the photovoltaic (PV) module current measurement. Additionally, an inductance observer is combined with the proposed technique to increase the accuracy of the high frequency inductor current estimation. A stability analysis proves the system to be stable. The proposed control system is experimentally validated on a microinverter prototype. Simulation and experimental results affirm the feasibility and performance of the control system. The experimental setup includes a grid simulator and a PV module simulator to test the system at varying irradiance levels. The proposed control system is also compared to methods presented in previous literature to demonstrate its superior characteristics.

In this article, a new control system is introduced for use in uninterruptible power supply (UPS) systems. The proposed control system is able to improve the dynamic performance of UPS systems, facilitating their integration into smart grids. The proposed control system isolates the battery from the double-frequency ripple both in the normal mode (charging) and in the backup mode (discharging). The new UPS control system is tailored for single-phase systems utilizing lithium-ion battery storage systems, where current ripple must be limited. Simulation and experimental results verify the feasibility of the proposed control system and demonstrate its superior performance.

This article presents a new digital control system for dual active bridge dc/dc converters. The proposed control system includes a novel compensator with asymmetric half-cycle modulation. The proposed compensator is based on a novel geometric-sequence-control algorithm, which is a model-based predictive current control. The proposed control system provides fast and seamless tracking of the reference current and ensures zero dc current in the transformer windings (prevents transformer saturation). Moreover, it offers high robustness against perturbations and uncertainties in the converter. It also allows symmetric growth of transformer current during transients, thereby eliminating potential temporary saturation issues. Analysis, simulation, and experimental results are provided to demonstrate the superior performance of the proposed control in achieving high precision output regulation, fast and seamless transient response, and high robustness.

Power electronic converters for electric vehicles (EVs) have been the subject of great interest over the last several decades. This article presents a thorough review of different EV power electronic converters on which the authors have worked for more than one decade. The readers will find this review interesting to design current products and to devise/invent new converters for emerging applications in EV.

In this article, a novel dual-switch discontinuous current-source gate driver (CSD) suitable for driving the high-side mosfet (HS mosfet ) of buck voltage regulator module (VRM) is presented. The proposed gate driver completely solves the gate current diversion problem, which most of the previous CSDs suffer from, during turn- off transition. Thus, in comparison to most of the previous CSDs, the proposed gate driver achieves to turn- off the power mosfet considerably faster and with much higher effective gate current, which leads to significant reduction of turn- off losses. Whereas, turn- on losses of buck VRM HS mosfet driven by the proposed CSD and the previous CSDs are equal. Furthermore, the introduced gate driver consists of the minimum number of control switches and circuit elements, compared to previous CSDs. The proposed gate driver is analyzed and a prototype of the driver operating at 1 MHz is implemented in order to validate the theoretical analysis.

This paper presents a new harmonic compensation system along with a hybrid load observer used for micro-grids in the islanded mode. The proposed control system includes an online hybrid load observer, which is able to precisely estimate the harmonic contents of the load as well as the equivalent load impedance in the islanded mode. One of the main features of the proposed control system is its capability to deal with unknown load harmonics, which is a big challenge in micro-grids. Basically, the proposed control system is able to detect, estimate, and compensate various load disturbances and harmonics (e.g., synchronous and asynchronous harmonics, and dc components). Theoretical analysis, simulation results, and experimental results verify the feasibility and performance of the proposed control system.

In this contribution we report on solution processed red OLEDs based upon an N-annulated perylene diimide dimer, namely tPDI2N-EH, a red-light emitting molecule. OLED devices with the architecture of glass/ITO/PEDOT:PSS/EML/LiF/Ag (EML = emitting layer) were fabricated with EMLs comprised of tPDI2N-EH neat and blended with poly(9,9-dioctylfluorene, PFO), all solution processed from non-halogenated solvents. The photophysical and electrophysical performance of PFO:tPDI2N-EH-blend films with different composition ratios were investigated. The PFO : tPDI2N-EH-based OLEDs with a 2 : 18 ratio exhibited the best performance. The PFO:tPDI2N-EH-based OLEDs gave red electroluminescence with the emission wavelength of 635 nm and the CIE (international commission on illumination) coordinates of (x = 0.672, y = 0.321). OLEDs with EMLs fabricated using roll-to-roll compatible methods are also demonstrated.

The series LC-parallel LC (LCLC) resonant converter with capacitive output filter is an emerging favorite for high frequency, high output voltage applications. Existing literature utilizes conventional fundamental harmonic approximation (FHA) based techniques for steady-state analysis due to its simplicity. However, FHA results in limited accuracy when applied on low-quality factor (Q

Three-phase resonant converters are preferred for high power applications as they provide several advantages such as reduced component stress, small filter size requirement, and high power density. The analysis of these converters is generally performed in frequency-domain using a single-phase equivalent circuit which provides approximate results and may lead to the erroneous design of the converter. This paper presents a time-domain modeling technique for the analysis of a low Q three-phase series resonant converter operating under asymmetric pulse width and variable frequency modulation. This method can also be applied to analyze converters with different resonant tank and transformer configurations without compromising accuracy.

This article proposes a real-time dynamic maximum efficiency tracking algorithm for wireless power transfer (WPT) systems with multiple receivers. The algorithm sequentially varies the net reactance of each of the receivers using switched capacitor circuits (SCCs) to reach the maximum efficiency point (MEP). The MEP in multiple-receiver systems varies in the presence of cross-coupling. This article provides an in-depth analysis of the effects of cross-coupling and proves that cross-coupling could be beneficial or detrimental to efficiency, depending on circuit conditions such as the load resistances and coupling factors among the coils. Hence, unlike previous research, this article emphasizes the improvement of the link efficiency in the presence of cross-coupling rather than the complete elimination of its effects. Experimental results have been included for a single-transmitter and two-receiver system to validate the feasibility of the proposed algorithm.

Flexible red OLEDs based on a quadruple-layer stack, in between electrodes, with 160 mm2 active area were fabricated in ambient air on PET via slot-die-coating. For the OLED structure PET/ITO/PEDOT...

This paper presents a novel resonant power converter for transcutaneous power transmission in retinal prosthesis applications. In retinal prosthetic applications, the frequency and power of the transmitted signal must be limited to a specific range such that the living tissue is not harmed. The design goal is to transmit power with maximum efficiency, and minimum sensitivity to the nonideal power transfer link. The proposed wireless power-transfer circuit offers significant advantages over conventional ones, which usually use Class E converters. The proposed approach has very low sensitivity to coupling factor/load variations in the inductive link and demonstrates very fast dynamic response. In addition, the proposed approach does not require a dc–dc converter to control the output power. Soft switching is achieved for the proposed circuitry despite the variations in the coupling coefficient. Thus, superior efficiency can be obtained using the proposed approach. Theoretical analysis and various simulations validate the superior performance of the proposed approach. In addition, a 1-MHz experimental prototype has been prepared to verify the feasibility of the proposed wireless power-transfer circuit.

This paper presents a new dc/ac inverter for low-power applications (i.e., high-voltage, low-current applications), which offers soft switching of the power semiconductors and low output current ripple. In the proposed power circuitry, a novel ripple steering approach is used that can provide soft switching for the power semiconductors and significantly attenuate the high-frequency current ripple of the inverter. The proposed ripple steering technique utilizes the switching frequency and the duty cycle in order to perform the aforementioned tasks. Basically, the ripple steering technique steers the energy of the ripple to the output capacitances of the power semiconductors in order to provide the soft-switching condition. Theoretical analysis, simulation results, and experimental results verify the feasibility of the proposed technique and demonstrate the superior performance of the proposed inverter.

This letter presents an active dc-eliminating method for dc/dc converters in order to prevent the transformer saturation. The proposed method is based on the asymmetry in the voltage ripple waveform caused by the dc component of the transformer current. The proposed dc-eliminating technique is able to quickly eliminate the dc component of the transformer current during transients as well as steady-state operation. The main advantage of the proposed method is that it avoids transformer saturation without the need for dc blocking capacitor or any use of current sensors and their additional circuitry. Also, since the proposed method is implemented in the control system, it does not create any power losses or distortions in the waveforms. The simulation and experimental results show the feasibility of the proposed technique.

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. These batteries have a relatively low energy density; however, they offer important advantages, including: long life-time; decoupled energy (arbitrarily large electrolyte volume) and power (electrode area); high round-trip efficiency; scalability and design flexibility; fast response; and low environmental impacts. These advantages make them superior to many energy storage technologies for stationary applications [1-4]. Among the various types of RFBs, vanadium RFBs (VRFBs) are an emerging technology for grid scale energy storage and the integration of renewable energy generation [5]. The membrane is a key component of a VRFB that separates the two half-cell electrolytes and prevents cross-mixing, while allowing the transport of ions during charge-discharge cycles [6]. The VRFB membrane should exhibit low vanadium ion permeability to minimize self-discharge, low cost, and long‐term chemical stability under normal operating conditions. A high proton conductivity and low vanadium ion crossover are known to improve the efficiency of VRFBs [6-7]. In this study, we present a novel composite Nafion based membrane that results in a significant increase in the VRFB performance. The composite membrane has been characterized for its chemical, structural, and thermal properties using appropriate analytical techniques. The battery performance was evaluated in a flow cell using a ‘zero-gap’ design with an electrode area of 5 cm2. The electrolytic solution, 1.6 M VOSO4 in 3 M H2SO4, was circulated through the cell. Thermally treated carbon papers were used as the cathode and anode electrodes. For charge-discharge experiments, a constant current density (10 to 80 mA cm−2) was applied with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. The stability of the battery using the composite membrane was evaluated over 100 cycles. Figures 1 and 2 show the energy efficiency and capacity retention during 100 charge-discharge cycles. The results reveal that the energy efficiency was improved from 51% to 63% by using the composite membrane. In addition, the charge-discharge capacity and capacity retention improved by around 200% and 25%, respectively. This improvement can be attributed to a higher proton conductivity and lower vanadium permeability of the composite membrane. References: [1] M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, Vanadium Electrolyte Studies for the Vanadium Redox Battery-A Review, ChemSusChem. 9 (2016) 1521–1543. [2] A.K. Singh, M. Pahlevaninezhad, N. Yasri, E. Roberts, Degradation of Carbon Electrodes in the All-Vanadium Redox Flow Battery, ChemSusChem. (2021). [3] K.E. Rodby, T.J. Carney, Y. Ashraf Gandomi, J.L. Barton, R.M. Darling, F.R. Brushett, Assessing the levelized cost of vanadium redox flow batteries with capacity fade and rebalancing, J. Power Sources. 460 (2020) 227958. [4] M. Pahlevaninezhad, P. Leung, M. Pahlevani, F. C. Walsh, C. Ponce de Leon, and E. P. L. Roberts, Experimental and Computational Studies of Disperse Blue-1 in Organic Non-Aqueous Redox Flow Batteries, J. Power Sources, Volume 500, 15 July 2021, 229942. [5] X.Z. Yuan, C. Song, A. Platt, N. Zhao, H. Wang, H. Li, K. Fatih, D. Jang, A review of all-vanadium redox flow battery durability: Degradation mechanisms and mitigation strategies, Int. J. Energy Res. (2019). https://doi.org/10.1002/er.4607. [6] X. Li, H. Zhang, Zh. Mai, H. Zhang, I. Vankelecom, Ion exchange membranes for vanadium redox flow battery (VRB) applications, Energy Environ. Sci., 2011, 4, 1147. [7] L. Yu, F. Lin, L. Xua, J. Xi, A recast Nafion/graphene oxide composite membrane for advanced vanadium redox flow batteries, RSC Adv., 2016, 6, 3756. Figure 1

Redox flow batteries (RFBs) are a promising technology for grid scale stationary energy storage to complement renewable energy systems. Although RFBs have a relatively low energy density, they offer important benefits such as long lifetime, decoupled energy and power, high round-trip efficiency, scalability and design flexibility, fast response and low environmental impacts. These benefits make them superior to many other stationary energy storage technologies [1-3]. The vanadium RFB (VRFB) is the most widely used RFB in industry for grid scale energy storage and for integration of renewable energy generation systems [4]. However, due to their slow redox reaction rates, their performance and stability are limited and VRFBs would thus benefit from enhancement of the electrode kinetics [5]. Various catalysts have been employed to improve the redox reaction rates [5-6]. Bismuth is considered a suitable candidate due to its good reactivity with oxygen, low toxicity, relatively low cost and comparable catalytic properties to other metal competitors [5, 7-8]. In this study, we present a novel modified VRFB electrode composed of carbonized bismuth-polyaniline (Bi-PANI) on a thermally-treated carbon paper substrate. The battery performance was evaluated in a 5 cm2 flow cell using a ‘zero-gap’ design with a 1.6 M VOSO4 in 3 M H2SO4 electrolyte. Charge-discharge of the VRFB was performed at a constant current density (ranging from 10 to 80 mA cm−2) with upper and lower voltage cut-offs of 1.65 and 0.8 V, respectively. Thermally treated carbon paper electrodes were tested as a comparison, and it was found that the VRFB efficiency was significantly enhanced, from 51% to 68% at a current density of 80 mA cm− 2, due to the modification of the electrodes with Bi-PANI. The charge-discharge capacity was also improved by around 17.2%. In addition, the stability of the battery using the modified electrodes was evaluated for over 200 cycles. The improved battery performance was attributed to the catalytic effect of the Bi particles on the VO2+/VO2 + and V2+/V3+ redox reactions leading to a significant increase in capacity, voltage, and energy efficiency. References: [1] M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, ChemSusChem. 9 (2016) 1521–1543. [2] A.K. Singh, M. Pahlevaninezhad, N. Yasri, E. Roberts, ChemSusChem. (2021). [3] M. Pahlevaninezhad, P. Leung, M. Pahlevani, F. C. Walsh, C. Ponce de Leon, and E. P. L. Roberts, Experimental and Computational Studies of Disperse Blue-1 in Organic Non-Aqueous Redox Flow Batteries, J. Power Sources, Volume 500, 15 July 2021, 229942. [4] X.Z. Yuan, C. Song, A. Platt, N. Zhao, H. Wang, H. Li, K. Fatih, D. Jang, Int. J. Energy Res. (2019). [5] S. Moon, B.W. Kwon, Y. Chung, Y. Kwon, Journal of The Electrochemical Society, 166 (12) A2602-A2609 (2019) [6] W. Lee, C. Jo, S. Youk, H. Y. Shin, J. Lee, Y. Chung, and Y. Kwon, Appl. Surf. Sci., 429, 187 (2018) [7] Z González, A. Sánchez, C. Blanco, M. Granda, R. Menéndez, and R. Santamaria, Electrochem. Commun., 13, 1379 (2011). [8] B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, and W. Wang, Nano Lett., 13, 1330 (2013).