Asymmetric Leakage Research Articles

Study of piston offset inhibition method based on the biased center port

The linear compressor is one of the main energy-consuming components in domestic and space refrigeration systems. Due to the asymmetric leakage in the clearance, the piston offset unavoidably causes the piston to deviate from its designed equilibrium position and worsens the compressor performance. In this paper, a new method is proposed to inhibit the piston offset. A biased center port is employed to direct gas from the back chamber to the front at the position close to the back chamber to balance the pressure on the two sides of the piston. To verify this method, a numerical simulation was performed to calculate the mass flow through the clearance and center port channel, and the average pressure difference across the piston. An experimental bench was established to compare the offset of the structures with no center port, unbiased center port and biased center port. Results show that the biased center port can almost eliminate the piston offset at the designed operating condition.

Asymmetric Early Leakage Failure in Bi-Directional SCR ESD Protection Device in BCD Technology

Asymmetric Early Leakage Failure in Bi-Directional SCR ESD Protection Device in BCD Technology

Asymmetric Environmental Regulation, Interfuel Substitution and Carbon Leakage

Asymmetric Environmental Regulation, Interfuel Substitution and Carbon Leakage

Fully-Integrated Transformer With Asymmetric Primary and Secondary Leakage Inductances for a Bidirectional Resonant Converter

Typically, inserted-shunt integrated transformers have symmetric primary and secondary leakage inductances. However, bidirectional resonant converters typically operate more efficiently with different primary and secondary series inductances. In this paper, a new topology for an inserted-shunt integrated transformer which can provide tunable, asymmetric leakage (series) inductances on the primary and secondary sides is presented. Two magnetic shunts, with appropriate air gaps, are inserted between two E-cores and the primary and secondary windings are separated by being placed at opposite sides of the shunts. The proposed transformer is analysed in detail and modelling and design guidelines are provided. It is shown that the magnetising inductance and the primary and secondary leakage inductances are decoupled from each other, and they can be determined separately. The design has the advantage of using planar E-cores and magnetically permeable sheets that are commercially available. The theoretical analysis is verified by simulation and experimental results. In addition, to demonstrate the performance of the proposed integrated transformer in practice, an exemplar bidirectional CLLLC resonant converter is designed, constructed and tested using the new integrated transformer.

Optimizing Multi-Objective Federated Learning on Non-IID Data with Improved NSGA-III and Hierarchical Clustering

Federated learning (FL) can tackle the problem of data silos of asymmetric information and privacy leakage; however, it still has shortcomings, such as data heterogeneity, high communication cost and uneven distribution of performance. To overcome these issues and achieve parameter optimization of FL on non-Independent Identically Distributed (non-IID) data, a multi-objective FL parameter optimization method based on hierarchical clustering and the third-generation non-dominated sorted genetic algorithm III (NSGA-III) algorithm is proposed, which aims to simultaneously minimize the global model error rate, global model accuracy distribution variance and communication cost. The introduction of a hierarchical clustering algorithm on non-IID data can accelerate convergence so that FL can employ an evolutionary algorithm with a low FL client participation ratio, reducing the overall communication cost of the NSGA-III algorithm. Meanwhile, the NSGA-III algorithm, with fast greedy initialization and a strategy of discarding low-quality individuals (named NSGA-III-FD), is proposed to improve the convergence efficiency and the quality of Pareto-optimal solutions. Under two non-IID data settings, the CNN experiments on both MNIST and CIFAR-10 datasets show that our approach can obtain better Pareto-optimal solutions than classical evolutionary algorithms, and the selected solutions with an optimized model can achieve better multi-objective equilibrium than the standard federated averaging (FedAvg) algorithm and the Clustering-based FedAvg algorithm.

Temperature Dependent Leakage Current Characteristics of an IrO <sub>2</sub>/TiO <sub>2</sub>/IrO <sub>2</sub> Redox Based Memristor and the Role of Aqueous Oxygen Evolution

Among materials that exhibit so-called memristive effects, high permittivity oxide-based capacitors are in the main focus in electronics research, as they tend to show a resistance that is dependent on the electrical history of the material. Since memristive effects were discovered in TiO2 thin films in the early 2000s there has been much effort to integrate memristive materials into next-generation resistive switching based random-access memories. In this study, we investigate the leakage current behaviour of high-k IrO2/TiO2/IrO2 capacitors with temperature dependent static current/voltage measurements and time dependent long-term leakage current measurements. We explain the highly complex leakage current characteristics of such high-k oxide capacitors with an existing leakage current model that incorporates redox processes between insulator and electrode. We conclude that due to the highly asymmetric leakage current behaviour of our symmetric IrO2/TiO2/IrO2 capacitors the oxygen vacancy density in the insulating TiO2 is most decisive and is dominated by the oxygen storage capacity of the electrode. There is strong evidence for an aqueous oxygen evolution of water incorporated in the IrO2 top electrode, which provides the oxygen that changes the vacancy density with temperature and bias condition. Finally, we expand the existing model with a qualitative description of how the redox processes influence the electrical performance of the capacitors as a function of time.

Atomic layer adhesion of ferroelectric nanoparticles: a new approach to dielectric composites

A thin film dielectric composite has been produced consisting of lead-free barium titanate nanoparticles bound by the conformal atomic layer deposition of hafnia. The materials were examined crystallographically, topologically, and structurally using a variety of techniques including scanning electron microscopy and high-resolution transmission electron microscopy. Electrical measurements of capacitors using the composite material revealed dielectric constant variations of 200–1200 depending on the bias direction, corresponding to asymmetric leakage mechanisms and contributions from interface defects. Piezoresponse force microscopy indicated accessible polarization within the nanoparticles. This work illustrates an approach for conformally depositing a dielectrically tunable composite thin film with novel electrical properties.

Thermodynamics and flow unsteadiness analysis of trans-critical CO2 in a scroll compressor for mobile heat pump air-conditioning system

Heat pump air-conditioning system operating with trans-critical CO2 is a promising technology on electric vehicles, and scroll compressor has played a vital role in micro heat pump air-conditioning system. In order to obtain a better performance of scroll compressor for CO2, internal flow characteristics should be investigated. In this paper, an unsteady Reynolds Average Navier-Stokes of working process in a scroll compressor operating with trans-critical CO2 was firstly carried out. The effect of CO2 properties tables resolution on numerical simulation was investigated in detail. Then, some phenomena including pre-compression and over-compression in the working process were presented. Finally, physical mechanisms of asymmetric leakage flow considering influence of aerodynamics and thermodynamics were revealed. The results indicated that CO2 properties tables resolution hardly affects simulation results considering fierce fluctuations of CO2 properties near critical point. Periodic pre-compression and over-compression was mainly induced by geometrical structure and operation mechanism of scroll compressor. Asymmetric flow fields in circumferential direction were also observed due to unilateral inlet and orbiting scroll rotation. Meanwhile, so-called “quasi-centrosymmetric” leakage flow was captured in compression chambers owing to the non-uniform distribution of flow field. The results provide an instrumental guidance for optimal design of trans-critical CO2 scroll compressor.

Backscattering-Immune Computing of Spatial Differentiation by Nonreciprocal Plasmonics

Using the excitation of surface plasmon polaritons (SPPs) for optical analog computing of spatial differentiation could find widespread application in $e.g.$ edge detection and image processing, but the inevitable backscattering of SPPs propagating around defects or discontinuities would in general introduce noise to the output signal. The authors design a backscattering-immune spatial differentiator based on a nonreciprocal plasmonic platform, where balance between the rates of asymmetric leakage and intrinsic absorption is required. Here a topologically protected, one-way leaky mode in the terahertz region is just the ticket.

Impact of Substrate Bias Polarity on Buffer-Related Current Collapse in AlGaN/GaN-on-Si Power Devices

Bulk traps in the high-resistivity buffer stack underneath the 2-dimensional electron gas (2DEG), which can interact with the high vertical electric field at OFF state, impose a critical challenge to the dynamic ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}})$ of AlGaN/GaN-on-Si power devices. In this paper, the impact of substrate bias polarity on carrier injection/transport and buffer-induced current collapse has been investigated by using ramped and transient back-gating characterizations as well as TCAD simulations. High voltage applied to the conductive Si substrate can modulate 2DEG conductivity through the back-gate effect, whereby the dynamics of both acceptor and donor buffer traps are identified. Distinct buffer trapping and asymmetric vertical leakage under opposite top-to-substrate bias polarities have been observed, which are attributed to the fundamentally different carrier injection/transport mechanisms. It is suggested that the energy barrier at the nucleation-layer/Si interface can limit the electron injection from Si substrate into the buffer stack and consequently influence the buffer-related current collapse.

SU‐F‐T‐540: Comprehensive Fluence Delivery Optimization with Multileaf Collimation

Purpose:Multileaf collimator (MLC) leaf sequencing is performed via commercial black‐box implementations, on which a user has limited to no access. We have developed an explicit, generic MLC sequencing model to serve as a tool for future investigations of fluence map optimization, fluence delivery optimization, and rotational collimator delivery methods.Methods:We have developed a novel, comprehensive model to effectively account for a variety of transmission and penumbra effects previously treated on an ad hoc basis in the literature. As the model is capable of quantifying a variety of effects, we utilize the asymmetric leakage intensity across each leaf to deliver fluence maps with pixel size smaller than the narrowest leaf width. Developed using linear programming and mixed integer programming formulations, the model is implemented using state of the art open‐source solvers. To demonstrate the versatility of the algorithm, a graphical user interface (GUI) was developed in MATLAB capable of accepting custom leaf specifications and transmission parameters. As a preliminary proof‐ofconcept, we have sequenced the leaves of a Varian 120 Leaf Millennium MLC for five prostate cancer patient fields and one head and neck field. Predetermined fluence maps have been processed by data smoothing methods to obtain pixel sizes of 2.5 cm2. The quality of output was analyzed using computer simulations.Results:For the prostate fields, an average root mean squared error (RMSE) of 0.82 and gamma (0.5mm/0.5%) of 91.4% were observed compared to RMSE and gamma (0.5mm/0.5%) values of 7.04 and 34.0% when the leakage considerations were omitted. Similar results were observed for the head and neck case.Conclusion:A model to sequence MLC leaves to optimality has been proposed. Future work will involve extensive testing and evaluation of the method on clinical MLCs and comparison with black‐box leaf sequencing algorithms currently used by commercial treatment planning systems.

An Asymmetric Highly Efficient Multistage Depressed Collector for Space TWTs

Asymmetric multistage depressed collectors (MDCs) are preferred in traveling wave tubes due to their high performance in terms of high collector efficiency and low back-streaming current. However, the main drawbacks associated with these asymmetric MDCs are due to their difficulty in fabrication and often bulkier size, as it generally requires an additional magnet or pole piece. Here, we have designed and developed an asymmetric MDC, where asymmetry in electric field has been achieved by suitable electrode geometry modification. Furthermore, the modification in the material of collector envelope has also been done to allow asymmetric leakage of magnetic field within the MDC, without requiring any magnet or pole piece. This MDC offers: 1) high collector performance (with a simulated collector efficiency of 95% in zero drive and zero back-streaming current); 2) ease of fabrication; 3) no increase in size and weight; 4) nonrequirement of additional magnet or pole piece; 5) no high-voltage breakdown issues; and 6) no thermal management issues. Therefore, due to these aforementioned advantages, the MDC stands as a potential candidate for use in space applications.

Asymmetric Leakage from Multiplier and Collision-Based Single-Shot Side-Channel Attack

Asymmetric Leakage from Multiplier and Collision-Based Single-Shot Side-Channel Attack

SU‐E‐T‐344: Dynamic Electron Beam Therapy Using Multiple Apertures in a Single Cut‐Out

Purpose:Few leaf electron collimators (FLEC) or electron MLCs (eMLC) are highly desirable for dynamic electron beam therapies as they produce multiple apertures within a single delivery to achieve conformal dose distributions. However, their clinical implementation has been challenging. Alternatively, multiple small apertures in a single cut‐out with variable jaw sizes could be utilized in a single dynamic delivery. In this study, we investigate dosimetric characteristics of such arrangement.Methods:Monte Carlo (EGSnrc/BEAMnrc/DOSXYnrc) simulations utilized validated Varian TrueBeam phase spaces. Investigated quantities included: Energy (6 MeV), jaw size (1×1 to 22×22 cm 2; centered to aperture), applicator/cut‐out (15×15 cm2), aperture (1×1, 2×2, 3×3, 4×4 cm2), and aperture placement (on/off central axis). Three configurations were assessed: (1) single aperture on‐axis, (2) single aperture off‐axis, and (3) multiple apertures. Reference was configuration (1) with standard jaw size. Aperture placement and jaw size were optimized to maintain reference dosimetry and minimize leakage through unused apertures to <5%. Comparison metrics included depth dose and orthogonal profiles.Results:Configuration (1) and (2): Jaw openings were reduced to 10×10 cm2 without affecting dosimetry (gamma 2%/1mm) regardless of on‐ or off‐axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1×1 cm2 aperture) and increased Bremsstrahlung (<2%, 10% for 1×1 cm2 aperture) dose was observed. Configuration (3): Optimal aperture placement was in the corners (order: 1×1, 4×4, 2×2, 3×3 cm2) and jaw sizes were 4×4, 4×4, 7×7, and 5×5 cm2 (apertures: 1×1, 2×2, 3×3, 4×4 cm2 ). Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1×1 cm2 aperture irradiation.Conclusion:Multiple apertures in a single cut‐out with variable jaw size can be used in a single dynamic delivery, providing a practical alternative to FLEC or eMLC. Future simulations will expand on all variables.

Highly resolved pulsatile flows through prosthetic heart valves using the entropic lattice-Boltzmann method

AbstractProsthetic heart valves have been widely used to replace diseased or defective native heart valves. Flow through bileaflet mechanical heart valves (BMHVs) have previously demonstrated complex phenomena in the vicinity of the valve owing to the presence of two rigid leaflets. This study aims to accurately capture the complex flow dynamics for pulsatile flow through a 23 mm St Jude Medical (SJM) Regent™ BMHV. The lattice-Boltzmann method (LBM) is used to simulate pulsatile flow through the valve with the inclusion of reverse leakage flow at very high spatiotemporal resolution that can capture fine details in the pulsatile BMHV flow field. For higher-Reynolds-number flows, this high spatiotemporal resolution captures features that have not been observed in previous coarse resolution studies. In addition, the simulations are able to capture with detail the features of leaflet closing and the asymmetric b-datum leakage jet during mid-diastole. Novel flow physics are visualized and discussed along with quantification of turbulent features of this flow, which is made possible by this parallelized numerical method.

Dynamic and Balanced Control of Three-Phase High-Power Dual-Active Bridge DC–DC Converters in DC-Grid Applications

The three-phase dual-active bridge (DAB) is a dc–dc converter, which provides galvanic isolation, inherent soft-switching capability, and small filter size. In this study, the dynamic behavior of three-phase DAB is analyzed and a dynamic control strategy is developed. Furthermore, a compensation technique is implemented to compensate unbalanced transformer phase currents. The latter is often caused by asymmetric leakage inductances. State space averaging and first harmonic approximation models, both for the steady state and transient analysis, are developed to describe the dynamic behavior of the three-phase DAB. The accuracy of the models is compared with a detailed circuit simulation and the benefits of each model are identified. When the transferred power of the DAB changes fast, the transformer currents can become unbalanced, leading to oscillations in the output current. A unique control method is presented, which allows settling of the transformer currents within one-third of the switching period. Additionally, the transformer currents stay symmetrical and oscillations are avoided. Based on this fast current control, an outer voltage controller is designed. The comparison of the control system using the fast current control and the conventional quasi-steady-state control demonstrates the potential advantages of the new approach under dynamic conditions. In practice, it is difficult to achieve completely symmetrical short-circuit impedances in a high-power medium-voltage transformer. Asymmetric leakage inductances, however, result in unbalanced phase currents and higher dc current ripple in a three-phase DAB. The new control scheme that is developed here can be extended to compensate any unbalances in the transformer. This approach enables effectively the balancing of the three-phase currents. The new control schemes are experimentally verified.

RETRACTED: Studies of Asymmetric Hysteresis Loops and Leakage Current Behaviors in Pt/Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub>/Si /PZT/Au Structures Prepared by MOCVD Method

The polarization-voltage (P-V) and leakage currents density (J-V) characteristics were investigated on the ferroelectric PZT films deposited on Pt/Al2O3/SiO2/Si substrate with a vapor-deposited gold top electrode. The P-V hysteresis loops and the J-V characteristics were measured after performing a rapid thermal annealing (RTA) process. A ferroelectric test system (Precision LC Radiant Technology) was used to measure their electrical properties with a 90-nm PZT thickness and an area of 7.85 x10-5 cm2. The measurements were taken by connecting a Pt bottom electrode to the drive of the precision LC and the Au top electrode to the drive of the precision LC. The P-V hysteresis and J-V characteristics of PZT samples showed the asymmetry for both measurements. The asymmetric hysteresis loops and leakage current behavior were shifted in the positive direction when the drive was applied to the Pt electrode, while being negatively shifted in the converse case. The asymmetric behavior of the polarized state in the hysteresis loops due to the electrode configuration resulted from different work function between the Pt and Au electrodes, further influencing the leakage current behavior.

Asymmetric Hysteresis Loops, Leakage Current and Capacitance Voltage Behaviors in Ferroelectric PZT Films Deposited on a Pt/Al2O3/SiO2/Si Substrate by MOCVD method with a vapor-deposited Gold Top Electrode

Asymmetric Hysteresis Loops, Leakage Current and Capacitance Voltage Behaviors in Ferroelectric PZT Films Deposited on a Pt/Al2O3/SiO2/Si Substrate by MOCVD method with a vapor-deposited Gold Top Electrode

Maxwell–Wagner instability in bilayer dielectric stacks

The Maxwell–Wagner effect, the enhanced charge migration to the interface of a stack of two dielectrics with different conductances, is shown to cause asymmetric leakage current and electrical breakdown behavior for different electrode polarities. For this purpose, metal-insulator-silicon capacitors were fabricated consisting of bilayered silicon dioxide–lanthanum zirconate dielectric stacks. Maxwell–Wagner instability and Debye polarization can be distinguished upon comparing electron injection from both sides of the stack. The Maxwell–Wagner charges have relaxation times that are nearly five orders of magnitude larger than the Debye polarization, suggesting the long-lasting influence of these trapped charges in nanolaminated dielectric systems.

Development of pyroelectric ceramics for high-temperature applications

Ceramics based on Bi 3NbTiO 9 (BNT) were investigated for their high-temperature pyroelectric properties. Doping BNT with 0.05 atoms of W 6+ donor ions decreased its DC conductivity, enhanced its dielectric strength and remnant polarization. Thick films of BNT produced by airflow deposition show preferential grain orientation and enhanced sinterability, giving improved polarizability and higher dielectric strength than the comparable ceramic. Further improvements in grain orientation and enhanced remnant polarization are derived by sintering under an applied electric field. Airflow deposition was also used to prepare graded films of Ba (1− x) Sr x TiO 3 (BST), showing temperature dependent hysteresis offsets that originate from asymmetric leakage currents and are not related to the pyroelectric properties. These graded films show an enhanced conventional pyroelectric coefficient over a wide temperature range. These results predict that a graded structure of BaBi 2Ta 2O 9 and Bi 3NbTi 0.95W 0.05O 9 should show enhanced high-temperature pyroelectric properties.