Heeralal Gargama

Criticality Assessment Models for Failure Mode Effects and Criticality Analysis Using Fuzzy Logic

Traditional Failure Mode and Effects Analysis (FMEA) has shown its effectiveness in defining, identifying, and eliminating known and/or potential failures or problems in products, process, designs, and services to help ensure the safety and reliability of systems applied in a wide range of industries. However, its approach to prioritize failure modes through a crisp risk priority number (RPN) has been highly controversial. This paper proposes two models for prioritizing failures modes, specifically intended to overcome such limitations of traditional FMEA. The first proposed model treats the three risk factors as fuzzy linguistic variables, and employs alpha level sets to provide a fuzzy RPN. The second model employs an approach based on the degree of match and fuzzy rule-base. This second model considers the diversity and uncertainty in the opinions of FMEA team members, and converts the assessed information into a convex normalized fuzzy number. The degree of match (DM) is used thereafter to estimate the matching between the assessed information and the fuzzy number characterizing the linguistic terms. The proposed models are suitably supplemented by illustrative examples.

Fuzzy arithmetic based reliability allocation approach during early design and development

A fuzzy arithmetic based reliability allocation method at early system design stage.Linguistic variables are used to assess the ratings of allocation factors in an intuitive and easy manner.Use of trapezoidal fuzzy division linear programming method to reduce the fuzziness.More flexible to combine diversified opinions of multiple domain experts. During early design and development stages, every engineering system has to meet its specific reliability goals. The target reliability of the system is achieved through application of an effective reliability apportionment technique to its subsystems. There are various traditional methods exist to perform the reliability allocation based on engineering factors that are assessed in a subjective manner. The conventional reliability allocation approach requires the assessment of factors like complexity, cost, and maintenance. This may not be realistic in real applications if they are assessed in a crisp manner by the domain experts of their varied expertise and background.In this paper, we treat allocation factors as fuzzy numbers, which are evaluated in fuzzy linguistic terms. As a result, fuzzy proportionality factor scales are proposed for the subsystems. In order to accomplish fuzzy division to evaluate the fuzzy proportionality factor, an approximation method based on linear programming for trapezoidal fuzzy numbers is also proposed in this paper. For the evaluation of weighting factors from fuzzy proportionality factors, centroid method of defuzzification is being employed. The allocated reliability of each subsystem is computed with the help of weighting factor thereafter. An example is provided to illustrate the potential application of the proposed fuzzy based reliability allocation approach.

Polyvinylidene fluoride/nickel composite materials for charge storing, electromagnetic interference absorption, and shielding applications

In this paper, the composites of polyvinylidene fluoride (PVDF)/nickel (Ni) prepared through simple blending and hot-molding process have been investigated for dielectric, electromagnetic shielding, and radar absorbing properties. In order to study complex permittivity of the composites in 40 Hz–20 MHz frequency range, impedance spectroscopy (IS) technique is used. Besides, the complex permittivity and permeability in addition to shielding effectiveness (SE), reflection coefficient (backed by air), and loss factor are calculated using scattering parameters measured in X-band (8.2–12.4 GHz) by waveguide method. Further, in X-band, a theoretical analysis of single layer absorbing structure backed by perfect electrical conductor is then performed. A flanged coaxial holder has also been designed, fabricated, calibrated, and tested for electromagnetic interference SE measurement in the broad frequency range (50 MHz–18 GHz). The IS results indicate large enhancement in dielectric constant as a function of Ni lo...

Design and Optimization of Multilayered Electromagnetic Shield Using a Real-Coded Genetic Algorithm

We report optimized design of multilayered electromag- netic shield using real coded genetic algorithm. It is observed that the shielding efiectiveness in multilayer design is higher than single layered counterpart of equal thickness. An efiort has been made to develop an alternative approach to achieve speciflc objective of identifying the design characteristics of each layer in the multilayered shielding con- flguration. The proposed approach incorporates interrelated factors, such as absorption and re∞ection in the design optimization as per speciflc shielding requirements. The design problem has been solved using shielding efiectiveness theory based on transmission line (TL) modeling and real-coded genetic algorithm (GA) with simulated bi- nary crossover (SBX) and parameter-based mutation. The advantage of real-coded GA lies in e-cient solution for electromagnetic interfer- ence (EMI) shielding design due to its strength in solving constraint optimization problems of continuous variables with many parameters without any gradient information. Additionally, the role of material parameters, such as permittivity and permeability on re∞ection char- acteristics and shielding efiectiveness, has also been investigated and optimized using the proposed models and real-coded GA. Theoretical optimization of electromagnetic parameters has been carried out for SE » 40dB for many industrial/commercial applications and SE » 80dB for military applications.

ON THE DESIGN AND RELIABILITY ANALYSIS OF ELECTROMAGNETIC ABSORBERS USING REAL- CODED GENETIC ALGORITHM AND MONTE CARLO SIMULATION

In this paper, we propose an approach for designing and quantitatively assessing the performance of the multilayered radar- absorbing structure. In our proposed approach, a flve layered radar- absorbing materials design is optimized from the predeflned materials database. But to determine the optimal choice of the material and thickness of each layer, a combined binary and real-coded genetic algorithm (GA) is used to handle the integer and real variables involved in such designs. Further, the proposed approach employs the Latin hypercube sampling with Monte Carlo Simulation to carry out the performance based reliability analysis of the design. Absorber synthesized results are compared with the published work using other algorithms. The outcomes of our approach show that the combined GA works quite well, and most prominently the reliability analysis provides the decision maker a means to select among the several design alternatives available before him.

Reliability-based design optimization of broadband microwave absorbers

This paper proposes a reliability-based design optimization approach to handle variability/uncertainties involved in the design variables/parameters of microwave absorber. The proposed approach uses hybrid genetic algorithm for optimization and Monte Carlo simulation with Latin hypercube sampling technique for probabilistic analysis to identify the optimal design of absorbing structure under probabilistic constraints. The proposed approach is illustrated with examples considering broadband absorbing coatings in the frequency range of 0.2–2, 2–8, and 0.5–8 GHz, respectively.

Reliability-based design optimization scheme for designing electromagnetic shielding structures

This article, presents a reliability-based design optimization (RBDO) study for designing electromagnetic shielding structures. The existing deterministic design approaches do not integrate the uncertainty involved in the design variables or problem parameters of such shielding structures thereby, the ignorance of uncertainty provides variation in the expected shielding effectiveness (SE) in the optimized design solution. The application of RBDO allows determining the best design solution, while explicitly considering the inevitable effects of uncertainty in the design variables and problem parameters. The proposed approach employs a nested optimization approach for solving the RBDO formulation for the shielding structure under uncertainty. The real-coded genetic algorithm is being used to handle deterministic constraints (outer loop) whereas hybrid mean-value method is employed to evaluate probabilistic constraints in the RBDO formulation (inner loops). The approach is illustrated with an example considering three-layered shielding structures’ design for the SE requirement of ~80 dB in 8–12.5 GHz frequency range.

Reliability-based design optimization of electromagnetic shielding structure using neural networks and real-coded genetic algorithm

The conventional approaches for electromagnetic shielding structures’ design, lack the incorporation of uncertainty in the design variables/parameters. In this paper, a reliability-based design optimization approach for designing electromagnetic shielding structure is proposed. The uncertainties/variability in the design variables/parameters are dealt with using the probabilistic sufficiency factor, which is a factor of safety relative to a target probability of failure. Estimation of probabilistic sufficiency factor requires performance function evaluation at every design point, which is extremely computationally intensive. The computational burden is reduced greatly by evaluating design responses only at the selected design points from the whole design space and employing artificial neural networks to approximate probabilistic sufficiency factor as a function of design variables. Subsequently, the trained artificial neural networks are used for the probabilistic sufficiency factor evaluation in the reliability-based design optimization, where optimization part is processed with the real-coded genetic algorithm. The proposed reliability-based design optimization approach is applied to design a three-layered shielding structure for a shielding effectiveness requirement of ∼40 dB, used in many industrial/commercial applications, and for ∼80 dB used in the military applications.

Electromagnetic Interference Shielding Design Using Real-Coded Genetic Algorithm and Reliability Evaluation in X-Band

The increased deployment of various electrical and electronic equipments/devices for the commercial, industrial, and military systems has created a number of sources and receptors of electromagnetic interference that can degrade the system performance or affect safety operation of intelligence/secrecy between the various services. To avoid the interference problems from the adverse effects of electromagnetic waves, there is a greater need for shielding of these equipments/devices. In this paper, a design approach to meet the military requirement shielding for multi-layer electromagnetic shield is described. This design problem is solved by using shielding effectiveness theory based on transmission line modeling and real-coded genetic algorithm with simulated binary crossover and parameter-based mutation. Further, it is shown that by using Monte Carlo simulation, the performance of electromagnetic shielding under the uncertain operating conditions can be evaluated in terms of reliability.

Experimental validation of reliability-based design optimization models for designing EMI shielding and absorbing structures

Abstract This paper aims to comprehend and demonstrate the validity of the theoretical models proposed recently for designing electromagnetic interference (EMI) shielding [Gargama H, Chaturvedi SK, Thakur AK. Reliability-based design optimization scheme for designing electromagnetic shielding structures. J. Electromagn. Waves Appl. 2014;28(6):765–776] and absorbing structures [Gargama H, Chaturvedi SK, Thakur AK. Reliability-based design optimization of broadband microwave absorbers. J. Electromagn. Waves Appl. 2013;27:1407–1418]. Initially, the composites of polyvinylidene fluoride comprising varying concentration of nickel, iron, iron oxide, and activated carbon are prepared through compression hot-molding technique. Subsequently, the number of composite layers and the desirable material parameters for each of the layers are optimized using the composite’s database for a three layered EMI shielding and absorbing structures. The structures are fabricated and evaluated for the performance as an EMI shield and absorber for electromagnetic waves considering their state of polarization and angle of incidence on the designed structures. A comparison and a close agreement within an acceptable error of the theoretically optimized and experimentally realized parameters are the real strength of this work.