Proposed Design Methodology Research Articles

Highly Efficient Perfect Vortex Beams Generation Based on All-Dielectric Metasurface for Ultraviolet Light.

Featuring shorter wavelengths and high photon energy, ultraviolet (UV) light enables many exciting applications including photolithography, sensing, high-resolution imaging, and optical communication. The conventional methods of UV light manipulation through bulky optical components limit their integration in fast-growing on-chip systems. The advent of metasurfaces promised unprecedented control of electromagnetic waves from microwaves to visible spectrums. However, the availability of suitable and lossless dielectric material for the UV domain hindered the realization of highly efficient UV metasurfaces. Here, a bandgap-engineered silicon nitride (Si3N4) material is used as a best-suited candidate for all-dielectric highly efficient UV metasurfaces. To demonstrate the wavefront manipulation capability of the Si3N4 for the UV spectrum, we design and numerically simulate multiple all-dielectric metasurfaces for the perfect vortex beam generation by combing multiple phase profiles into a single device. For different numerical apertures (), it is concluded that the diffracted light from the metasurfaces with different topological charges results in an annular intensity profile with the same ring radius. It is believed that the presented Si3N4 materials and proposed design methodology for PV beam-generating metasurfaces will be applicable in various integrated optical and nanophotonic applications such as information processing, high-resolution spectroscopy, and on-chip optical communication.

Design of Virtual Inertia Controller for DC Microgrid Using Zero Placement Technique

With DC microgrids becoming popular, the concept of virtual inertia control (VIC) is gaining attention to minimize the DC bus voltage fluctuations caused by intermittent sources and loads. VIC scheme controls the power electronic converter (PEC) to achieve a smooth voltage profile. However, the intrinsic output impedance of the converter acts as an output disturbance and distorts the inertial response. An additional feed-forward controller has been used in previous works to mitigate this. However, the design proposed in this paper eliminates the additional controller while achieving a smooth voltage profile. This paper proposes a zero placement technique-based design of virtual inertia controller for a DC microgrid. Small-signal models for the system with the proposed controller designed using zero placement were developed to analyze the stability and the effect of parameter variation for optimal performance. Next, the application of the proposed design methodology is extended to a system employing two battery energy storage system units for analyzing parallel operation. Finally, the effectiveness of the controller designed using the zero placement technique was verified under different loading conditions through MATLAB/Simulink simulations and experiments carried out on the developed laboratory prototype.

Deformation‐based design of seismically isolated bridges

AbstractA performance‐based design procedure is proposed for seismically isolated bridges with/without supplemental energy dissipation devices. Considering multiple performance levels (PLs), the proposed method initially identifies the critical hazard level and “near‐optimal” alternatives of the isolation system. Both performance and economy are evaluated based on the inelastic response of reduced‐degree‐of‐freedom (RDOF) isolation and energy dissipation systems. Nonlinear response history analysis (NLRHA) of the multi‐degree‐of‐freedom (MDOF) system is employed in successive design steps, corresponding to different PLs, to refine the design solution through the control of a broad range of material strains and deformations. The above characteristics aim to deliver a rigorous and broadly applicable design method that reduces the high computational effort characterising complex design frameworks, while addressing identified deficiencies of alternative displacement‐based methods. The efficiency of the proposed design methodology is demonstrated by applying it to an actual bridge that was previously designed for ductile behaviour. Alternative isolation and energy dissipation schemes are investigated. Assessment of the design through NLRHA reveals in all cases enhanced seismic performance and cost reduction in the substructure design, thus rendering base‐isolation an appealing design alternative.

Analytical study and design approach of the axial and flexural response of reinforced masonry columns confined with FRP jackets

Using fiber-reinforced polymer (FRP) wraps has proven to be an effective and optimized confinement technique to upgrade the axial and flexural capacity of reinforced concrete (RC) and reinforced masonry (RM) columns. The axial capacity of FRP-confined masonry depends on both the compressive strength of masonry before strengthening and the confinement pressure provided by the FRP jacket. This study proposes a simplified methodology to design and analyze prismatic fully grouted reinforced masonry columns (RMCs) strengthened with FRP Jackets. The proposed design methodology included an analytical confinement model to predict the compressive strength gain in RMCs due to the effective confinement pressure provided by FRP jackets. The proposed procedure was also designed to predict the nominal capacity of RMCs for practical design applications, with columns subjected to both axial loading and bending moment. The essential parameters to perform detailed section analysis were established, and suggested expressions were proposed to obtain the parameter values. Practical values for the equivalent rectangular stress block parameters were proposed. The theoretical axial force-moment interaction diagrams obtained by the proposed procedure were compared with available experimental data. The experimental test results were in good agreement with the analytical predictions by a reasonable marginal error. Furthermore, the effect of five design variables on the axial-flexural interaction of FRP-wrapped RMCs was investigated. The variables considered in the parametric study were the number of FRP layers, radius of the corners, stiffness of the FRP composite, cross-sectional aspect ratio, and masonry compressive strength. The results showed that increasing the FRP layers, corner radius, and FRP jacket stiffness significantly enhanced the axial capacity of the FRP-confined RMCs. However, the increase in the masonry compressive strength and cross-sectional aspect ratio negatively affected the axial capacity gain ratio of FRP-strengthened RMCs.

Adaptive design methodology of segmented non-uniform fin arrangements for trans-critical natural gas in the printed circuit heat exchanger

As the core heat transfer equipment of a floating storage regasification unit (FSRU), the printed circuit plate heat exchanger (PCHE) has a significant impact on the gasification performance of liquefied natural gas (LNG). During LNG regasification process, natural gas undergoes a trans-critical process and its thermal properties such as density, viscosity and specific heat capacity vary considerably especially near the pseudo-critical point, which will probably lead to more volatile flow heat transfer mechanism. The traditional design scheme of uniform finned channel is difficult to give full play to the efficiency and compactness of PCHE because of lacking considering the local fluid thermodynamic variation. Therefore, this paper provides a novel design method for optimizing the flow channel profile of PCHE by applying adaptive segmented non-uniform finned micro-channels. Firstly, the entire flow channels are segmented by qualifying the gradient of density with temperature ∂ρ/∂t of trans-critical natural gas. Subsequently, within the constraints of heat exchange requirements, maximum allowable pressure drop, existing manufacturing techniques and structural strength, a mathematical optimization design model considering non-uniform fin arrangements and interlinked thermal states among these segmented channels is established. Then, to comprehensively improve entropy generation number and volume, Pareto solutions covering local flow channel parameters are obtained based on multi-objective genetic algorithm. Finally, the actual performance differences between two optimization methods respectively derived from the conventional uniform fin channels and the proposed non-uniform fin arrangements are compared based on distributed parameter model. The results show that the deviation of the entropy generation number between the optimized and validated values for the non-uniform design is very small at 6.5%, much less than that of 31.4% in the uniform design. Moreover, under the premise of the similar heat transfer efficiency, the volume for the PCHE by the non-uniform design can be reduced by 9.3%. These indicate that the proposed design methodology of segmented non-uniform fin arrangements indeed makes the PCHE more compact and enables the thermal-hydraulic performance better. The current work will serve as a framework for the design and optimization of PCHEs with drastic changes in fluid physical properties.

Sub-Optimal Stabilizers of the Pendubot Using Various State Space Representations

This paper considers the issue of linear-quadratic regulator (LQR) design for nonlinear systems with the use of smooth state and input transformations. The proposed design methodology is considered in the stabilisation task of the Pendubot, which is based on the concept of feedback equivalent control systems. It turns out that it is possible to find a controller that ensures comparable dynamics of the closed-loop system in the vicinity of the set point regardless of the state-space representation adopted. In addition, the synthesis of suboptimal controllers according to the LQR strategy ensuring equal dynamics at the equilibrium point is presented. The properties of the studied controllers were investigated in a simulation environment and using experimental tests. The detailed forms of transformations and linear approximations given can be regarded as ready-made procedures that can be applied to stabilise similar mechanical systems in robotics.

Plug-in disturbance observer assisted DC link voltage control of grid-connected converters to improve transient performance without deteriorating grid current quality

Trade-off between DC link voltage dynamics and AC-side current quality in grid-interfacing power converters limits the attainable DC link voltage loop bandwidth for a given desired value of grid-side current total harmonic distortion (THD). It was recently shown that adding a notch filter in series with the typically employed DC link voltage controller of PI or type-II structure releases the above trade-off, yet requires full controller re-design. The paper proposes to replace the notch filter by a plug-in disturbance observer, allowing to increase attainable DC link voltage loop bandwidth for given grid-side current THD without any modification of the existing DC link voltage controller by utilizing a special frequency-selective filter. Simulations and experimental results validate the proposed design methodology.

Ultra-wideband Luneburg lens with high performance based on gradient metamaterials

Based on the perspective of a wide scanning range and ultra-broad bandwidth, Luneburg lenses are highly anticipated to be an outstanding option for multibeam radiation. However, owing to the lack of low-loss continuously varying permittivity materials, the practical application of Luneburg lenses is far below the expected level. In this paper, an ultra-wideband planar Luneburg lens (PLL) is proposed. Due to the novel design of an all dielectric lightweight radially symmetric periodic gradient metamaterial, the presented lens is able to yield highly directional emission with side lobes all below −8 dB and achromatic sub-diffraction focusing with full width at half maximum about 0.4λ from 4 GHz to 22 GHz. The prototype of the lens is manufactured by computer-numerical controlled machining. The measured data of the near field and far field agree well with that of the simulated data, verifying the effectiveness of the proposed design methodology. The superiority of the presented approach to design a Luneburg lens is demonstrated. Therefore, the PLL has the advantages of being lightweight, with a compact structure, low profile, ultrabroadband function, high resolution, and convenient fabrication, giving it great potential to be practically deployed.

Robust invariance-based explicit reference control for constrained linear systems

In the linear system control, the traditional invariance-based explicit reference governor (ERG) method provides a solution to the control of a class of systems subject to state and control constraints, while there still exist some limitations on the form of system models, which hinders its wider application. In response to this situation, we propose the invariance-based explicit reference control (IERC) which is composed of double-invariance-based explicit reference governor (DIERG) and anti-windup controller (AWC). Specifically, the DIERG forces the system states at the intersection of two invariant sets including the constraint-based invariant set and performance-based invariant set; the AWC adopts amplified artificial amplitudes in control constraints to make the obtained two invariant sets tolerant to some degree of saturation. The advantages of the proposed design methodology are illustrated through the simulation studies.

Delay-Dependent Stability Analysis and Design of Input-delayed Systems by Smooth Sliding Mode Control: Lagrange Theorem Approach

A new smooth sliding mode control design methodology based on Lagrange mean value theorem is proposed for stabilization of single input delayed systems. The Lagrange mean value theorem as a basic theorem of calculus is used for the design of linear sliding mode time-delay controller for the first time. This controller satisfies the sliding condition using a Zhou and Fisher type continuous control law eliminating the chattering effect. The constructive delay-dependent asymptotically stable sliding conditions are obtained by using the augmented Lyapunov-Krasovskii functionals and formulated in terms of simple (4x4)-matrix inequality with scalar elements. Developed design approach can be extended to robust stabilization of sliding system with unknown but bounded input delay. The maximum upper bounds of delay size can be found by using simple optimization algorithms. Helicopter hover control is considered as a design example for illustrating the usefulness of smooth sliding mode approach. Unstable helicopter dynamics are successfully stabilized by using linear sliding mode time-delay controller. For example, settling time is about 20 sec. Therefore, simulation results confirmed the effectiveness of proposed design methodology. Apparently, the proposed method has a great potential in design of time-delayed controllers.

A novel compact asymmetric Doherty PA design using symmetric transistors

AbstractA novel 7.2 dB output power back off Doherty power amplifier (DPA) based on asymmetrical load is proposed using two same transistors in this paper. To get maximum efficiency at back‐off output power and the largest saturate output power level simultaneously, the carrier power amplifier (PA) is matched to the maximum efficiency region when peaking PA is almost off, and both of the two PAs are matched to maximum power region to get largest output power. According to the proposed design methodology, high efficiency at back‐off power and high peak power DPA is designed and fabricated with two Cree's GaN HEMT CGH40010F devices. Measurements results show that the saturated output power of the DPA is over 44.5 dBm, the drain efficiency when 7.2 dB output power back off and saturate power are above 42% and 53%, respectively, in the range of 3.4–3.8 GHz. Meanwhile, better than −47.8 dBc adjacent channel leak power ratio can be achieved with digital predistortion under 20 MHz LTE signal testing at 3.4 GHz, the final design size is only 14 × 12 cm2.

Two-Step Robust Design of LLC Converter With Corner Judgment and Greedy Algorithm

Negative effects caused by parameter fluctuation (PF) of resonant elements have not been thoroughly considered in the current design methodologies of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters. In this letter, typical negative PF effects are revealed as restriction violation and optimization degradation. Then, a novel two-step robust design methodology is proposed for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters. The first step is to effectively establish more reliable solving domain considering PF effects on all the restrictions by the proposed corner judgment method. In the second step, the lowest fluctuation efficiency as the novel concept is proposed and taken as the global optimization goal of efficiency due to optimization degradation, with a greedy algorithm proposed for simplicity and effectiveness. Simulation and experimental results have proved the validity and superiority of the proposed design methodology.

AppAxO : Designing App lication-specific A ppro x imate O perators for FPGA-based Embedded Systems

Approximate arithmetic operators, such as adders and multipliers, are increasingly used to satisfy the energy and performance requirements of resource-constrained embedded systems. However, most of the available approximate operators have an application-agnostic design methodology, and the efficacy of these operators can only be evaluated by employing them in the applications. Furthermore, the various available libraries of approximate operators do not share any standard approximation-induction policy to design new operators according to an application’s accuracy and performance constraints. These limitations also hinder the utilization of machine learning models to explore and determine approximate operators according to an application’s requirements. In this work, we present a generic design methodology for implementing FPGA-based application-specific approximate arithmetic operators. Our proposed technique utilizes lookup tables and carry-chains of FPGAs to implement approximate operators according to the input configurations. For instance, for an \( \text{M}\times \text{N} \) accurate multiplier utilizing K lookup tables, our methodology utilizes K -bit configurations to design \( 2^K \) approximate multipliers. We then utilize various machine learning models to evaluate and select configurations satisfying application accuracy and performance constraints. We have evaluated our proposed methodology for three benchmark applications, i.e., biomedical signal processing, image processing, and ANNs. We report more non-dominated approximate multipliers with better hypervolume contribution than state-of-the-art designs for these benchmark applications with the proposed design methodology.

Analysis and design of laminated composite beams based on a refined higher-order theory

In this work, a new analysis and design methodology of laminated composite beams is presented. The problem is formulated for both symmetric and antisymmetric ply-stacking configurations, based on a refined higher-order shear deformation theory. The solution is obtained using the Analog Equation Method (AEM) while the design process is based on the Differential Evolution (DE) metaheuristic optimization algorithm, using both displacement and strength-related objective functions. Numerical examples are presented, demonstrating the applicability and effectiveness of the proposed analysis and design methodology. The results indicate that to minimize the deflection of an orthotropic laminated beam the principal material orientation must coincide with the longitudinal axis of the beam. Moreover, for the strength optimization problem, the Tsai-Wu failure criterion proved to be numerically unstable, returning very large negative values for seemingly indifferent configurations. Conversely, Hashin’s criterion manifests robustness during the optimization process ensuring efficacious design.

Gain-scheduled output-feedback control of uncertain input-delay LPV systems with saturation via polytopic differential inclusion

This paper examines the control design for parameter-dependent input-delay linear parameter-varying (LPV) systems with saturation constraints. A linear differential inclusion approach is implemented to formulate the saturation nonlinearity. Subsequently, a gain-scheduled dynamic output-feedback controller is structured to conform to the saturation representation. By means of a Lyapunov–Krasovskii functional, sufficient delay-dependent conditions are derived for the analysis and feedback control synthesis of the closed-loop system in the presence of uncertainties and exogenous disturbances. Disturbance rejection objectives following an induced -norm and an norm formulation are examined. Estimation of the domain of attraction with the parametrisation of the admissible LPV controllers is presented. Three different optimisation objectives with respect to disturbance rejection, disturbance tolerance, and domain of attraction expansion are formulated. The proposed design methodology is examined in the context of the air-fuel ratio (AFR) regulation in a spark ignition (SI) engine with a speed-dependent delay and model parameters in the presence of canister purge disturbances and AFR dynamics uncertainty. The injector is restricted in the amount of fuel it can deliver to the cylinder. The three-way catalytic converter's performance in terms of oxygen storage and emission reduction is taken into consideration. Closed-loop simulation results are provided to validate the methodology.

Command‐filter‐based adaptive output feedback quantized tracking control for switched stochastic nonlinear time‐delay systems with actuator saturation

AbstractThis work addresses the adaptive output feedback quantized control for a class of switched stochastic nonstrict‐feedback nonlinear time‐delay systems with input and output quantization and actuator saturation under arbitrary switching. A novel state observer including the quantized output signal and the saturated input signal is designed to estimate the unknown system states. Then, the command‐filtered backstepping method is introduced to avoid the “explosion of complexity” in the adaptive backstepping recursive design. Moreover, the design challenges from input and output quantization errors and actuator saturation are overcome by combining the auxiliary variable approach and some special techniques. Instead of the traditional quartic Lyapunov–Krasovskii functional, the common quadratic Lyapunov–Krasovskii functional is constructed to develop the adaptive quantized tracking control scheme for such systems. By means of the proposed common controller independent of switching signal, all closed‐loop signals are mean‐square semi‐globally uniformly ultimately bounded, while the tracking error will remain in a small neighborhood of the origin. Finally, stability analysis and simulation results are provided to show the effectiveness and performance of the proposed design methodology.

Performance-based seismic design and assessment of multi-storey CFS strap-braced frames

Cold-formed steel (CFS) structures typically rely on diagonally braced stud walls to withstand lateral forces. While the response of CFS single-wall panels has been extensively investigated, limited studies focused on the seismic performance of multi-storey CFS strap-braced frames. Previous research highlighted that the presence of vertical loading can significantly reduce the lateral load and ductility capacity of strap-braced walls by amplifying the secondary moments due to P-Δ effects. While this effect is generally ignored in current design practice, it may lead to premature failures and poor seismic performance. This study aims to investigate the efficiency of a new design methodology to take into account the vertical load effects on the performance of multi-storey CFS strap-braced frames. Detailed experimentally validated FE models of CFS panels were developed in ABAQUS and used to obtain equivalent hysteretic models in OpenSees. The seismic performance of 6-storey strap-braced frames designed based on the Eurocode 8 and the proposed design methodology were then investigated under a set of artificial spectrum-compatible records. While the code-base design did not satisfy the ASCE/SEI 41–17 Life Safety (LS) and Collapse Prevention (CP) ductility limits, all performance targets were met using the proposed design methodology. The results of Incremental Dynamic Analyses (IDA) also indicated that meeting the code capacity requirements could not prevent extensive global damage in the strap-braced frames, due to soft-storey failure modes associated with the premature buckling of chord studs. Finally, the efficiency of the proposed design compared to its code-compliant counterpart was demonstrated under a set of 20 real spectrum compatible records, showing higher ductility capacity and considerably lower damage levels.

Ultracompact High‐Extinction‐Ratio Nonvolatile On‐Chip Switches Based on Structured Phase Change Materials

AbstractAdopting phase change material (PCM) in constructing nonvolatile on‐chip photonic switches has received intensive attention recently. Usually, a large‐area thin PCM film is directly used to construct a switch. Here, subwavelength structured PCM supporting localized resonance are adopted to efficiently improve the switching performance in a moderate bandwidth to obtain an optimal switch of higher switching contrast, smaller footprint, lower energy consumption, and better structure stability. Such a switch consisting of three cascaded Ge2Sb2Te nanodisks with a total volume of only 0.229 µm 35 nm on top of a single mode strip silicon waveguide is demonstrated. In the experimental verification, a high extinction ratio up to 27 dB is supported by the fabricated device as a high performance switch. The proposed design methodology will find its great potential in various large‐scale integration in optical interconnection and optical computing with new architectures or applications.

Design Optimization of Ultra-Wideband Vivaldi Antenna using Artificial Intelligence

In this work, computationally efficient design optimization of frequency selective surface (FSS)-loaded ultra-wideband Vivaldi antenna via the use of data-driven surrogate model is studied. The proposed design methodology consists of a multi-layer FSS structure aimed for performance improvement of the Vivaldi design, which makes the design a multi-objective multi-dimensional optimization problem. For having a fast and accurate optimization process, a data-driven surrogate model alongside the metaheuristic optimizer honeybee mating optimization (HBMO) had been used. The optimally designed antenna had been prototyped and its performance characteristics had been measured. The obtained experimental results are compared with the simulated results of the proposed method. Results show that the obtained FSS-loaded structure has enhanced directivity compared with the design without FSS structure, without any performance losses in the return loss characteristics. The FSS-loaded Vivaldi antenna operates at 2–12 GHz band with a maximum gain of 10 dBi at 10 GHz which makes the design a good solution for RADAR applications.

Passive hydraulic prosthetic foot to improve the push-off during walking

Passive prosthetic feet struggle to reproduce the human biological ankle range of motion and push-off. We propose the Hybrid-Hydraulic Ankle Prosthesis (H2AP), a prosthetic foot that provides a greater range of motion and push-off support compared to regular carbon feet. This novel prosthesis comprises a carbon foot and a hydraulic unit that includes a plantar flexion damper, a dorsiflexion damper, and a unidirectional spring that engage at specific phases of the gait cycle. The dampers are designed to enable an increased range of motion, and the unidirectional spring is used to store and release increased energy in late dorsiflexion and push-off. This paper focuses on the details of the mechanical design of the H2AP, its working principles, and the parameter tuning process. The design target is to replicate human ankle behavior in unimpaired walking, which is optimized using mathematical analyses and a simulation model. Pilot walking experiments with one transtibial amputee subject on level ground and a treadmill demonstrate the usability of the developed device and its acceptance in providing the intended functionality. The proposed design methodology can be used in the development and parameterization of the other assistive devices.