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21.
In this report, a free space frequency‐time‐domain technique is presented for characterizing the electrical properties and thickness of the sample using multiple reflections and fabry‐perot resonance phenomenon. The retrieval of constitutive electromagnetic parameters of the sample has been carried out by comparing the measured reflection coefficient data from the sample at two different incident angles. The relative permittivity as well as relative permeability along with the thickness of different samples viz., beryllia, silicon, and plexiglass have been evaluated with high accuracy in the frequency range 1 to 15 GHz. The method is also experimentally validated by successfully reconstructing the unknown material properties of two different samples. The unique advantage of this method lies in non‐requirement of any prior knowledge of the sample's thickness for measuring the complex relative dielectric constant as well as relative permeability of the sample. To determine the electromagnetic properties of the sample, the sole knowledge of reflection coefficient data are needed. Moreover, the method does not involve any additional measurement for the reference calibration. The simple, cost‐effective proposed scheme is quite useful in many applications like accurate determination of signal strength in indoor wireless communication, through wall imaging, food industry, and so on. 相似文献
22.
An extensive study of the wire lag phenomenon in Wire-cut Electrical Discharge Machining (WEDM) has been carried out and the trend of variation of the geometrical inaccuracy caused due to wire lag with various machine control parameters has been established in this paper. In an extremely complicated machining process like Wire-cut EDM, which is governed by as many as ten control factors, it is very difficult to select the best parametric combination for a particular situation arising out of customer requirements. In the present research study, all the machine control parameters are considered simultaneously for the machining operation which comprised a rough cut followed by a trim cut. The objective of the study has been to carry out an experimental investigation based on the Taguchi method involving thirteen control factors with three levels for an orthogonal array L27 (313). The main influencing factors are determined for given machining criteria, such as: average cutting speed, surface finish characteristic and geometrical inaccuracy caused due to wire lag. Also, the optimum parametric settings for different machining situations have been found out and reported in the paper. 相似文献
23.
This paper investigates the exponential observer design problem for one‐sided Lipschitz nonlinear systems. A unified framework for designing both full‐order and reduced‐order exponential state observers is proposed. The developed design approach requires neither scaling of the one‐sided Lipschitz constant nor the additional quadratically inner‐bounded condition. It is shown that the synthesis conditions established include some known existing results as special cases and can reduce the intrinsic conservatism. For design purposes, we also formulate the observer synthesis conditions in a tractable LMI form or a Riccati‐type inequality with equality constraints. Simulation results on a numerical example are given to illustrate the advantages and effectiveness of the proposed design scheme. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
24.
A Measurement‐Based Approach for Designing Fixed‐Order Controllers for Unknown Closed‐Loop Architecture
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Sofiane Khadraoui Hazem N. Nounou Mohamed N. Nounou Aniruddha Datta Shankar P. Bhattacharyya 《Asian journal of control》2016,18(2):686-698
This paper presents a new technique to design fixed‐structure controllers for linear unknown systems using a set of measurements. In model‐based approaches, the measured data are used to identify a model of the plant for which a suitable controller can be designed. Due to the fact that real processes cannot be described perfectly by mathematical models, designing controllers using such models to guarantee some desired closed‐loop performance is a challenging task. Hence, a possible alternative to model‐based methods is to directly utilize the measured data in the design process. We propose an approach to designing structured controllers using a set of closed‐loop frequency‐domain data. The principle of such an approach is based on computing the parameters of a fixed‐order controller for which the closed‐loop frequency response fits a desired frequency response that describes some desired performance indices. This problem is formulated as an error minimization problem, which can be solved to find suitable values of the controller parameters. The main feature of the proposed control methodology is that it can be applied to stable and unstable plants. Additionally, the design process depends on a pre‐selected controller structure, which allows for the selection of low‐order controllers. An application of the proposed method to a DC servomotor system is presented to experimentally validate and demonstrate its efficacy. 相似文献
25.
The immobilization of strontium over titania was carried out by the method of coprecipitation. From a preliminary study, an appreciable uptake (52.8%) of90Sr was observed over preformed titania material. A weighable amount of strontium was coprecipitated with Ti(IV) hydroxide and a maximum of 34 wt% Sr was found to be adsorbed. The leachability of the mixed materials prepared by the addition of 250 and 400 mg Sr2+, calcined at 1000 °C, by soxhlet apparatus refluxing at 97 °C and repeated seven times at intervals of 24 h, was found to be of the order of 10–9 and 10–5 g cm–2 d–1, respectively. X-ray powder diffraction analysis revealed that strontium was immobilized in the crystalline matrix of rutile, which suffered some structural changes with the formation of new phases, SrTiO3+Sr2TiO4 and SrTiO3, respectively. 相似文献
26.
Suman Mukhopadhyay Goutam Mukhopadhyay Sandip Bhattacharyya 《Journal of Failure Analysis and Prevention》2017,17(4):624-631
Failure analysis of a steel chimney used in a lime plant was carried out. The chimney broke from two different locations during a storm. During the site visit, it was observed that the chimney was dislodged from weld joints. The chimney was made up of hot rolled mild steel plates. Investigations were carried out on the failed chimney plate and welding between plates. The investigation consists of visual observation, chemical analysis, characterization of macro- and microstructures, measurement of hardness, tensile property tests and energy-dispersive spectroscopy (EDS). Calculation of wind load at the location of breakage was also carried out. EDS analysis revealed entrapment of slag inside weld. Overall analysis suggested that the failure took place due to selection of improper reconditioning technique as well as poor workmanship in welding. 相似文献
27.
Karen M. Feigh Matthew J. Miller Raunak P. Bhattacharyya Minyue Ma Samantha Krening Yosef Razin 《Theoretical Issues in Ergonomics Science》2018,19(4):389-405
Human factors practitioners (HFPs) play many different roles in the design, creation, operation and maintenance of engineered systems. Less well known are the methods which are aimed at helping with the early stages of design, which are more systems-oriented and often involve questions of the concept of operation in which the engineered system will be fielded. Emerging from the field of cognitive engineering, these methods, including simulation, cognitive work analysis, cognitive task analyses and hierarchical task analysis, will be important as autonomous systems become increasingly capable. Even the most capable systems will continue to interact with humans, and it is at these interfaces between humans and engineered systems that HFP will continue to be needed. This paper describes recent work to leverage these methods to inform concepts of operation in aviation and space, machine learning algorithms and goal-oriented human–machine collaboration. 相似文献
28.
Kaushik Bhattacharyya Rakesh Biswas Anindya Sundar Dhar Swapna Banerjee 《Microprocessors and Microsystems》2010,34(2-4):96-101
A new scaled radix-4 CORDIC architecture that incorporates pipelining and parallelism is presented. The latency of the architecture is n/2 clock cycles and throughput rate is one valid result per n/2 clocks for n bit precision. A 16 bit radix-4 CORDIC architecture is implemented on the available FPGA platform. The corresponding latency of the architecture is eight clock cycles and throughput rate is one valid result per eight clock cycles. The entire scaled architecture operates at 56.96 MHz of clock rate with a power consumption of 380 mW. The speed can be enhanced with the upgraded version of FPGA device. A speed-area optimized processor is obtained through this architecture and is suitable for real time applications. 相似文献
29.
S. Chakraborty K. B. M. Swamy S. Sen T. K. Bhattacharyya 《Microsystem Technologies》2010,16(12):2131-2145
Micromechanical cantilevers are one of the most fundamental and widely studied structures in micro-electromechanical systems.
Dynamic response of such cantilevers has long been an interesting subject to researchers and different analytical and experimental
approaches have been reported to determine it. Theoretical estimation of different damping mechanisms have been reported over
years which are relevant particularly in studying the dynamics of the micro-mechanical structures. Most properties and functionalities
of the MEMS devices are invariably dependant on the dynamic response of the devices, which in turn depends on the quality
factor of the devices or in other words the overall damping present in the system. This paper presents a thorough experimental
analysis of vibration characteristics of micro-mechanical cantilevers of different dimensions. Arrays of polysilicon micro-cantilevers
of different dimensions have been designed and fabricated using surface micromachining process. The beams are resonated by
electrostatic actuation and their vibration characteristics have been observed using Laser Doppler Vibrometer. Also a thorough
analysis of modal behaviour of the beams is presented using analytical approach and finite element method based simulation.
Different damping mechanisms have been critically reviewed and a semi-analytical estimation of the overall damping is presented.
The results are compared with experimental values. 相似文献
30.
Raghunath P. Rana Swadesh K. Pratihar Santanu Bhattacharyya 《Journal of Materials Science》2006,41(21):7025-7032
Al2O3–ZrO2 composites containing nominally equal volume fraction of Al2O3 and ZrO2 have been synthesized through combined gel-precipitation technique. Subsequently the gels were subjected to three different post gel processing treatments like ultrasonication, ultrasonication followed by water washing and ultrasonication followed by alcohol washing. It was observed that while in unwashed samples crystallization took place at low temperature, crystallization was delayed in the washed gels. The phase transition of ZrO2 in the calcined gels followed the sequence; amorphous → cubic ZrO2 → tetragonal ZrO2 → monoclinic ZrO2. On the other hand, phase transition in alumina followed the sequence amorphous to γ-Al2O3, the transition taking place at 650 °C. No α-Al2O3 could be detected even after calcination at 950 °C. However, all the sintered samples had α-Al2O3. In spite of high linear shrinkage (19–21%) during sintering, the sintered sample had density of only above 70% for all the four varieties of the powders. However, in spite of the low sintered density of the pellets, 31% tetragonal zirconia could be retained after sintering at 1400 °C and it reduced to about 16% at 1600 °C. 相似文献