System-level Performance Modeling Research Articles

High-Performance Lithium-Sulfur Batteries with Atomic V- and Co-Modified Ketjen Black-Sulfur Composite Cathode

Lithium-sulfur (Li-S) batteries are potential alternatives to lithium-ion batteries, which are known to have certain drawbacks. This has drawn special technological attention. Sulfur’s low electrical conductivity, shuttling of the intermediate polysulfides, the slow conversion reaction kinetics of various lithium polysulfides (LiPS), and the major volume change of sulfur in the lithiation reaction are some of the main issues that still need to be resolved before Li-S batteries can be used in practical applications. Additionally, it is likely because there are not enough prognostic models determining energy densities at the cell and pack level based on materials and cell design, most of the articles do not report system-level metrics, specific energy (Wh kg-1), and energy density (Wh L-1).To overcome these problems, atomic vanadium (V) and cobalt (Co) modified ketjen black-sulfur composite (VCKBS) was prepared and used as a cathode in Li-S batteries. The synthesized composite was characterized by various techniques, e.g., XRD, Raman, SEM, HR-TEM, HAADF-STEM, and XPS spectra. The polysulfide adsorption test showed that V had increased the adsorption ability, and cyclic voltammetry displayed the increased catalytic activity resulting from Co, offering a large number of interfacial active sites and ensuring smooth electron transfer. Cycling performance tests showed an initial specific capacity of 1329 mAh g−1, maintained at 1249 mAh g−1 after 100 cycles. Under a higher sulfur loading (2.4 mg cm−2), at 0.2 C, Li-S cells demonstrated an initial specific capacity of 1201 mAh g−1 and retained 985 mAh g−1 after 300 cycles with a low fading rate of 0.059% per cycle. The rate performance tests showed that the prior capacity is nearly recovered, going from 1C back to 0.1C, demonstrating the superiority of the VCKBS material.In addition to the experimental characterization of the Li-S cell performance, energy densities were also predicted by a proposed system-level performance model. The 1st and 100th discharge capacities were used to forecast the system-level specific energies and energy densities. The system-level specific energies and energy densities based on the 100th discharge capacity of VCKBS cathodes had improvements of 1342 and 568%, respectively. This suggests that an easy route to construct the highly stable cathode material may pave the way for the development of highly efficient Li-S batteries. Acknowledgments Hira Fazal acknowledges support from the Türkiye Scholarship/Research Fellowship Program sponsored by the Prime Ministry of Turkey Presidency for Turks Abroad and Related Communities (21PK070917). Damla Eroglu acknowledges support from the Istanbul Development Agency (Award No: TR10/21/YEP/0001). We also thank the National Natural Science Foundation of China (22171180) and the Science and Technology Commission of Shanghai Municipality (20520710400).

Thermal Energy Storage With Horizontal Thermocline Tank for Sludge Drying Application

Solar thermal technologies can be an attractive option for the decarbonization of process heat applications; in particular, thermal energy storage is a high value proposition for continuous processes that may operate at a range of thermal conditions. A thermal-fluid model is developed to investigate the buoyant flow in a horizontal thermocline storage tank for a sludge-drying application. The process conditions and tank geometry considered are unique compared to the domestic water heating application typically considered in the literature and well suited for parabolic trough collectors. It was found that good separation of hot and cold fluids can be achieved with the long horizontal tank geometry depending on the inlet configuration. Uniform flow distribution along the length of the tank is required to establish a thermocline. Assuming desirable inlet conditions can be achieved, the tank outlet temperature predicted by the thermal-fluid model shows good agreement with the system-level performance model.

Energy-Accuracy Aware Finger Gesture Recognition for Wearable IoT Devices.

Wearable Internet of Things (IoT) devices can be used efficiently for gesture recognition applications. The nature of these applications requires high recognition accuracy with low energy consumption, which is not easy to solve at the same time. In this paper, we design a finger gesture recognition system using a wearable IoT device. The proposed recognition system uses a light-weight multi-layer perceptron (MLP) classifier which can be implemented even on a low-end micro controller unit (MCU), with a 2-axes flex sensor. To achieve high recognition accuracy with low energy consumption, we first design a framework for the finger gesture recognition system including its components, followed by system-level performance and energy models. Then, we analyze system-level accuracy and energy optimization issues, and explore the numerous design choices to finally achieve energy–accuracy aware finger gesture recognition, targeting four commonly used low-end MCUs. Our extensive simulation and measurements using prototypes demonstrate that the proposed design achieves up to 95.5% recognition accuracy with energy consumption under 2.74 mJ per gesture on a low-end embedded wearable IoT device. We also provide the Pareto-optimal designs among a total of 159 design choices to achieve energy–accuracy aware design points under given energy or accuracy constraints.

Impact of Carbon-to-Sulfur and Electrolyte-to-Sulfur Ratios on the Energy Density of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been considered to be good candidates among rechargeable batteries due to their high theoretical specific capacity and specific energy of 1675 mAh/g S and 2567 Wh/kg, respectively. The performance of Li-S batteries can be impacted by various vital cell design parameters such as carbon-to-sulfur (C/S) ratio, electrolyte-to-sulfur (E/S), and sulfur loading. These critical design parameters should be carefully selected since they have a direct effect on the electrochemical and system-level performance of Li-S batteries 1,2. Therefore, in this work the effect of C/S and E/S ratios in the cathode on the system-level energy density of a Li-S battery was examined by developing a system-level performance model, which contains an electrochemical model predicting the current-voltage relationship. The system-level energy density and specific energy of the Li-S battery are calculated as a function of the C/S and E/S ratios in the cathode by modifying the publicly available Battery Performance and Cost (BatPac) model. The proposed system-level performance model contains a one-dimensional electrochemical model to calculate the area specific impedance (ASI) and overpotential for each cell component at rated power and energy. Cell design factors such as the C/S ratio, E/S ratio, carbon, sulfur and binder wt%, and sulfur loading are fed to the model along with the experimentally measured cell capacities. The experimental discharge capacities were measured for Li-S cells with varying C/S ratios of 3.5, 2, 1 and 0.5 at a constant E/S ratio of 35 µL/mg and cathode thickness of ≈ 90 µm and with varying E/S ratios of 35, 20, 13 and 6 µL/mg at a constant C/S ratio of 1 and cathode thickness of ≈ 90 µm. For the experimentally obtained capacities, the average of three replicates were taken and fed into the performance model. In the proposed cell-to-system design, the components of packaging and thermal management are also taken into consideration.Figure 1 presents the impact of C/S and E/S ratios on the system-level energy density of the Li-S battery. It can be seen in the figure that the system-level energy density decreases with increasing E/S ratios whereas it shows a slight increase with increasing C/S ratio. Increasing the carbon amount leads to an increase in the discharge capacity to some level due to higher electronic conductivity. Even though the discharge capacity increases with increasing C/S ratio, the energy density may be affected poorly due to an increase in the inactive materials amount in the cell. However, this behavior is less likely to be observed at high E/S ratios since significantly high pack mass and volume due to high amount of electrolyte dominates the performance. Furthermore, increasing E/S ratio worsens the energy density. This suggests that the increase in the cell volume with increasing E/S ratio is more significant than the enhancement in the discharge capacity.

Assessment of Li-S Battery Performance as a Function of Electrolyte-to-Sulfur Ratio

Lithium-Sulfur (Li-S) battery performance is greatly sensitive to cell design as a result of the highly complex reaction and shuttle mechanisms within the cathode. Electrolyte-to-sulfur (E/S) ratio is one of the key design parameters that have a great impact on the performance of Li-S batteries. Here, an integrated research methodology coupling experimental characterization and electrochemical modeling is applied to forecast the relation between the E/S ratio and the discharge capacity, cycling performance and cell- and system-level specific energy and energy density of the Li-S battery. The highest initial discharge capacity is achieved with an E/S ratio of 20 μl mg−1, whereas, the best capacity retention is observed for 13 μl mg−1. This experimentally obtained link between the E/S ratio and the discharge performance is taken into consideration in the proposed cell- and system-level performance models. Lower E/S ratios lead to higher battery performance at the cell and system level. Consequently, an E/S ratio of 13 μl mg−1 presents the best performance as the impact of E/S ratio not only on the peak discharge capacity and capacity retention but also on the specific energy and energy density at the cell and system level are all considered.

Quantum efficiency and spatial noise tradeoffs for III–V focal plane arrays

Recent advances in quantum well detector materials such as SLS, QWIP, and QDIP photodetectors have made the performance of those technologies competitive with traditional MCT and InSb detectors while offering the potential of lower unit costs. Some III–V focal plane arrays operating in the MWIR spectral region have already achieved similar quantum efficiency performance as MCT and InSb devices, and are therefore, highly competitive for those applications. In the LWIR spectral region, quantum efficiency performance for III–V FPAs still lags MCT devices by a significant margin, but recent improvements have begun to close this gap. In addition, the improved spatial noise and operability typically associated with III–V devices can mitigate some of the shortfall in quantum efficiency when assessing overall system level performance. This paper will seek to quantify this tradeoff based on the most recent reported results for both III–V and MCT devices in order to help focus future research.This paper will first seek to quantify the current state of MCT and III–V (primarily SLS) FPAs in both MWIR and LWIR using a detailed literature survey to assess recent results, particularly in terms of reported quantum efficiency and spatial noise (quantified as residual fixed pattern noise). This data is then used to bound system-level performance modeling using the US Army’s Night Vision Integrated Performance Model (NV-IPM), which calculates image contrast and spatial frequency content using data from the target/background, intervening atmosphere, and system components. The modeling analyzes various tradeoffs in quantum efficiency and spatial noise under relevant operating conditions, including scenarios with both high and low target photon fluxes, and using realistic constraints for integration time (based on both frame rate and ROIC parameters). The results of this analysis are then compared to the current state of the art performance for both III–V and MCT FPAs to determine relative performance between the material systems and to recommend areas of improvement for each. This will provide insights to the FPA development community regarding the most pressing needs for improvements to each material system.

A blueprint for system-level performance modeling of software-intensive embedded systems

Exploration of design alternatives and estimation of their key performance metrics such as latency and energy consumption is essential for making the proper design decisions in the early phases of system development. Often, high-level models of the dynamic behavior of the system are used for the analysis of design alternatives. Our work presents a blueprint for building efficient and re-usable models for this purpose. It builds on the well-known Y-chart pattern in that it gives more structure for the proper modeling of interaction on shared resources that plays a prominent role in software-intensive embedded systems. We show how the blueprint can be used to model a small yet illustrative example system with the Uppaal tool, and with the Java general-purpose programming language, and reflect on their respective strengths and weaknesses. The Java-based approach has resulted in a very flexible and fast discrete-event simulator with many re-usable components. It currently is used by TNO-ESI and Oce-Technologies B.V. for early model-based performance analysis that supports the design process for professional printing systems.

Optimization of an Integrated SOFC-Fuel Processing System for Aircraft Propulsion

As fuel cells continue to improve in performance and power densities levels rise, potential applications ensue. System-level performance modeling tools are needed to further the investigation of future applications. One such application is small-scale aircraft propulsion. Both piloted and unmanned fuel cell aircrafts have been successfully demonstrated suggesting the near-term viability of revolutionizing small-scale aviation. Nearly all of the flight demonstrations and modeling efforts are conducted with low temperature fuel cells; however, the solid oxide fuel cell (SOFC) should not be overlooked. Attributing to their durability and popularity in stationary applications, which require continuous operation, SOFCs are attractive options for long endurance flights. This study presents the optimization of an integrated solid oxide fuel cell-fuel processing system model for performance evaluation in aircraft propulsion. System parameters corresponding to maximum steady state thermal efficiencies for various flight phase power levels were obtained through implementation of the particle swarm optimization (PSO) algorithm. Optimal values for fuel utilization, air stoichiometric ratio, air bypass ratio, and burner ratio, a four-dimensional optimization problem, were obtained while constraining the SOFC operating temperature to 650–1000 °C. The PSO swarm size was set to 35 particles, and the number of iterations performed for each case flight power level was set at 40. Results indicate the maximum thermal efficiency of the integrated fuel cell-fuel processing system remains in the range of 44–46% throughout descend, loitering, and cruise conditions. This paper discusses a system-level model of an integrated fuel cell-fuel processing system, and presents a methodology for system optimization through the particle swarm algorithm.

Stochastic Flow Model using Kalman Filters for parameter estimation

Attaining high quality from manufacturing systems requires utilizing appropriate system-level quality performance modeling and analysis tools. This paper describes the application of the stochastic-flow-modeling (SFM) approach to represent the quality output behavior of a manufacturing system. To do this, a basic one-product type SFM is extended to that of a multiple-product manufacturing system. This work also provides a novel addition to the SFM approach through the use of a Kalman filter to estimate quality parameters. After a presentation of the reference manufacturing system, results are given for different examples and the effectiveness of the SFM model is examined in terms of accuracy and convergence.

Trefftz-Based Methods for Time-Harmonic Acoustics

Over the last decade, Computer Aided Engineering (CAE) tools have become essential in the assessment and optimization of the acoustic characteristics of products and processes. The possibility of evaluating these characteristics on virtual prototypes at almost any stage of the design process reduces the need for very expensive and time consuming physical prototype testing. However, despite their steady improvements and extensions, CAE techniques are still primarily used by analysis specialists. In order to turn them into easy-to-use, versatile tools that are also easily accessible for designers, several bottlenecks have to be resolved. The latter include, amongst others, the lack of efficient numerical techniques for solving system-level functional performance models in a wide frequency range. This paper reviews the CAE modelling techniques which can be used for the analysis of time-harmonic acoustic problems and focusses on techniques which have the Trefftz approach as baseline methodology. The basic properties of the different methods are highlighted and their strengths and limitations are discussed. Furthermore, an overview is given of the state-of-the-art of the extensions and the enhancements which have been recently investigated to enlarge the application range of the different techniques. Specific attention is paid to one very promising Trefftz-based technique, which is the so-called wave based method. This method has all the necessary attributes for putting a next step in the evolution towards truly virtual product design.

Calibration of Abstract Performance Models for System-Level Design Space Exploration

High-level performance modeling and simulation have become a key ingredient of system-level design as they facilitate early architectural design space exploration. An important precondition for such high-level modeling and simulation methods is that they should yield trustworthy performance estimations. This requires validation (if possible) and calibration of the simulation models, which are two aspects that have not yet been widely addressed in the system-level community. This article presents a number of mechanisms for both calibrating isolated model components as well as a system-level performance model as a whole. We discuss these model calibration mechanisms in the context of our Sesame system-level simulation framework. Two illustrative case studies will also be presented to indicate the merits of model calibration.

Performance modeling of optical refrigerators

Optical refrigeration using anti-Stokes fluorescence in solids has several advantages over more conventional techniques including low mass, low volume, low cost and no vibration. It also has the potential of allowing miniature cryocoolers on the scale of a few cubic centimeters. It has been the topic of analysis and experimental work by several organizations. In 2003, we demonstrated the first optical refrigerator. We have developed a comprehensive system-level performance model of optical refrigerators. Our current version models the refrigeration cycle based on the fluorescent material emission and absorption data at ambient and reduced temperature for the Ytterbium–ZBLAN glass (Yb:ZBLAN) cooling material. It also includes the heat transfer into the refrigerator cooling assembly due to radiation and conduction. In this paper, we report on modeling results which reveal the interplay between size, power input, and cooling load. This interplay results in practical size limitations using Yb:ZBLAN.

Analytical modeling and characterization of deep-submicrometer interconnect

This work addresses two fundamental concepts regarding deep-submicrometer interconnect. First, characterization of on-chip interconnect is considered with particular attention to ultrasmall capacitance measurement and in-situ noise evaluation techniques. An approach to measuring femto-Farad level wiring capacitances is presented that is based on the concept of supplying and removing charge with active devices. The method, called the charge-based capacitance measurement (CBCM) technique, has the advantages of being compact, having high-resolution, and being very simple. We also present a novel time-domain measurement scheme for on-chip crosstalk noise that is based on the use of cascaded high-speed differential pairs to compare a user-defined reference voltage to the unknown noise peak value. The noise measurement technique complements a delay measurement to directly evaluate the impact of capacitive coupling on delay for various victim and aggressor driver sizes as well as arbitrary waveform timing and phase alignments. The second area of emphasis in this work is analytical interconnect modeling. Several important effects are modeled, including a rigorous crosstalk noise model that also includes a timing-level model. Results from this noise model show it to provide accuracy within 10% of SPICE for a wide range of input parameters. The noise model can also be calibrated and verified with comparison to the noise measurement scheme described in this work. A fast Monte Carlo approach to modeling the circuit impact of back-end process variation is presented providing a better depiction of real 3-/spl sigma/ performance spreads compared to the traditional skew-corner approach. Finally. A comprehensive system-level performance model called Berkeley Advanced Chip Performance Calculator (BACPAC) is developed that accounts for a number of relevant deep-submicrometer system design issues. BACPAC has been implemented online and is useful in exploring the capabilities of future very large scale integration systems as well as determining trends and tradeoffs inherent in the design process.