Power-Law Compensator Design for Plants with Uncertainties: Experimental Verification

A power-law compensator scheme for achieving robust frequency compensation in control systems including plants with an uncertain pole, is introduced in this work. This is achieved through an appropriate selection of the compensator parameters, which guarantee that the Nyquist diagram of the open-loop system compensator-plant crosses a fixed point independent of the plant pole variations. The implementation of the fractional-order compensator is performed through the utilization of a curve-fitting-based technique and the derived rational integer-order transfer function is realized on a Field-Programmable Analog Array device. The experimental results confirm that the the phase margin is well preserved, even for ±40% variation in the pole location of the plant.

Study on the corrosion resistance of sulfonated graphene/aluminum phosphate composites in waterborne polyurethane coatings

Sulfonated graphene/aluminum phosphate (SG/AlPO4) composites were synthesized by precipitation method, and composites with different mass ratios were added to water-based polyurethane (WPU) resins to prepare coatings. According to tests, composites with the addition of 2 wt% composite coating has good anticorrosion performance, and its protection efficiency is increased by 79.6% compared with pure resin. In the early stage of the corrosion, the SG layer forms the barrier. During the corrosion process, the SG layer was destroyed, the phosphate ions decomposed by the exposed spherical AlPO4 in the corrosive medium and the divalent iron ions on the iron-based surface form a stable precipitation protective layer to achieve the anticorrosion effect. From the EIS test, the coating with 2 wt% composite material has a larger radius of curvature in the Nyquist diagram at different time periods. According to the fitted circuit, it is further confirmed that the precipitation protection layer has a larger resistance value. After soaking for 24 h the resistance value is the largest, which is 1.231 × 104 Ω cm2.

Physico-Chemical Properties of a Hybrid Biomaterial (PVA/Chitosan) Reinforced with Conductive Fillers

In this study, a novel hybrid material based on Polyvinyl Alcohol-Chitosan (PVA-Chi) was made, reinforced with conductive fillers such as the polypyrrole (PPy), Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS), carbon black (CB), and multi-wall carbon nanotube (MWCNT). In order to observe the mechanical and electrical responses of this composite material, for obtaining composite materials, and to characterize them for the development of applications in engineering, FTIR analysis made clear the different functional groups present in the matrix and the fillers used. Using quaternary mixtures (4 fillers) increased the contact angle, which increased hydrophobicity of the biocomposite. The Nyquist diagram of the analyzed samples showed a decrease in resistance and energy diffusion; the latter because of transferring electrons caused by the conductive polymers CB and the MWCNT. In the mechanical tension tests, Young’s modulus values of 18.386 MPa were obtained, in contrast with the material matrix of PVA-Chi, which showed values of 11.628 MPa. Morphological analysis by SEM showed the materials got were homogeneous. The materials got showed higher electrical conductivity in the OH’s presence and NH2 groups, which could have possible applications in biopolymer electrodes.

Differential electrochemical impedance spectroscopy of the polymer proton electrolytes

A method of deriving standard electrochemical impedance spectroscopy (EIS) data such as Bode diagram, Nyquist diagram, and others from frequency dependence of the external impedance using numerical differentiation of the indicated dependence in quadratic coordinates is proposed, the method being named as the differential electrochemical impedance spectroscopy (DEIS). The method was tested experimentally on polyvinyl alcohol-based proton membranes doped with sulphated montmorillonite in granulated or dispersed states as an example. It is shown that DEIS data can be easier and with higher accuracy described by regular semicircles while leaving intact values of ohmic resistance. Very high values of dielectric permeability were obtained in the work enabling to develop condensers with high capacity based on highly conductive polymeric proton electrolytes.

Nondestructive Detection of the Gel State of Preserved Eggs Based on Dielectric Impedance

After completing the production of preserved eggs, traditionally, the degree of gelling is judged by allowing workers to tap the preserved eggs with their fingers and sense the resulting oscillations. The amount of oscillation is used for the quality classification. This traditional method produces varying results owing to the differences in the sensitivity of the individual workers, who are not objective. In this study, dielectric detection technology was used to classify the preserved eggs nondestructively. The impedance in the frequency range of 2–300 kHz was resolved into resistance and reactance, and was plotted on a Nyquist diagram. Next, the diagram curve was fitted in order to obtain the equivalent circuit, and the difference in the compositions of the equivalent circuits corresponding to gelled and non-gelled preserved eggs was analyzed. A preserved egg can be considered an RLC series circuit, and its decay rate is consistent with the decay rate given by mechanical vibration theory. The Nyquist diagrams for the resistance and reactance of preserved eggs clearly showed that the resistance and reactance of gelled and non-gelled eggs were quite different, and the classification of the eggs was performed using Bayesian network (BN). The results showed that a BN classifier with two variables, i.e., resistance and reactance, can be used to classify preserved eggs as gelled or non-gelled, with an accuracy of 81.0% and a kappa value of 0.62. Thus, a BN classifier based on resistance and reactance demonstrates the ability to classify the quality of preserved egg gel. This research provides a nondestructive method for the inspection of the quality of preserved egg gel, and provides a theoretical basis for the development of an automated preserved egg inspection system that can be used as the scientific basis for the determination of the quality of preserved eggs.

Physico-Chemical Properties of a Hybrid Biomaterial (Pva/Chitosan) Reinforced With Conductive Fillers

A novel hybrid material based on Polyvinyl alcohol-Chitosan (PVA-Cs) was made, reinforced with conductive polymer fillers such as polypyrrole (PPy), Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS), carbon black (CB) and multi-wall carbon nanotubes (MW CNT). Our proposal is to use these fillers, which have not been studied in this context before, for obtaining composite materials, and to characterize them for the development of applications in microelectronics. FTIR analysis made evident the different func-tional groups present in the matrix and the fillers used. The use of quaternary mixtures (4 fillers) increased the contact angle, which increased the degree of hydrophobicity of the biocomposite. The Nyquist diagram of the analyzed samples showed a decrease in resistance and energy diffu-sion; the latter due to the transfer of electrons caused by the conductive polymers CB and the MWCNT. In the mechanical tension tests, Young's modulus values of 18.386 MPa were obtained, in contrast with the material matrix of PVA-Cs, which showed values of 11.628 MPa. Further-more, morphological analysis by SEM showed that the materials obtained were homogeneous, with no phase formation. The materials obtained showed higher electrical conductivity in the presence of the OH and NH2 groups, which could have possible applications in biopolymer elec-trodes.

Fixed-order data-driven H∞ controller synthesis for flexible mechanical systems: Two-stage approach

In this paper, a two-stage method is introduced to design fixed-order data-driven [Formula: see text] controller for flexible mechanical systems. In the first stage of the proposed method, unknown parameters of anti-resonance filter that is added to the forward path of the control loop of the system to minimize resonant peaks, are calculated using frequency domain data obtained from open-loop system identification tests. In the second stage, a fixed-order data-driven [Formula: see text] controller is calculated by solving an optimization problem under convex [Formula: see text] constraints obtained based on the Nyquist diagram. With the proposed method, lower order controllers that meets the performance constraints of classical model-based [Formula: see text] problems can be synthesized without need of a parametric plant model. The method developed in this study is tested experimentally on a military stabilized platform and its performance is compared with a model-based [Formula: see text] controller design method.

Effect of Bi2O3-B2O3 as a Sintering aid in Microstructure and Dielectric Properties of Fe2Mo3O12 Electroceramic.

Molybdates from A2Mo3O12 family have been widely investigated due to its low sintering temperature, low thermal expansion coefficient, and low dielectric loss. Fe2Mo3O12 (FMO) is an oxide from this family and widely used in the catalytic field. The aim of this work is to evaluate the influence of the Bi2O3-B2O3 as a sintering aid in the microstructure and dielectric properties of FMO. The diffraction results showed that the FMO with the monoclinic structure phase was obtained after the calcination process (650 °C). Mössbauer spectroscopy showed the formation of Fe2O3 after the sintering process at 800 °C. The scanning electron-microscopic demonstrates an increase of the grain as a function of sintering aid concentration. The samples were analyzed by using the impedance spectroscopy at radiofrequency with temperature variation. The Nyquist diagram obtained in this temperature range was fitted from an equivalent circuit with three R-CPE associations, corresponding to the morphology of the electroceramics. For dielectric properties in the microwave, all the samples showed values of εr lower than 10. Values of Q x f above 14132.35 GHz were achieved. The thermal stability was evaluated by the temperature coefficient of resonant frequency (τf). The lowest τf values of -6.55 ppm/°C and -4.35 ppm/°C (near-zero) were measured to FMO and FMO mixed with 7.5 wt% Bi2O3-B2O3, respectively. Based on these results, FMO can be used to low permittivity ceramic for low temperature co-fired ceramics (LTCC) applications, antenna substrate, and millimeter-wave range.

Development of Adaptive Feed-Forward Cancellation With Frequency Estimation Algorithm for Compensation of Periodic Disturbance at Arbitrary Frequency

In this study, an adaptive feed-forward cancellation (AFC) with frequency estimation algorithm has been developed to compensate for periodic disturbance at an arbitrary frequency. Conventional AFC was developed to compensate for periodic disturbance at a fixed frequency and cannot compensate for the disturbance in which the frequency varies in real-time. The proposed method can estimate the frequency of the disturbance in real-time by using the input and output signals of the AFC. It can compensate for the periodic disturbance at an arbitrary frequency. In addition, the stability of the feedback control system with the proposed AFC can be optimized at any frequency based on the vector locus of the open-loop characteristic on the Nyquist diagram. The effectiveness of the proposed AFC was confirmed in experiments compensating for whirling vibration, whose frequency varies in real-time in rotating machinery. The proposed AFC can estimate the frequency of the disturbance automatically and compensate for this adequately.

Electrochemical Study of a Hybrid Polymethyl Methacrylate Coating using SiO2 Nanoparticles toward the Mitigation of the Corrosion in Marine Environments

The demand for hydrophobic polymer-based protective coatings to impart high corrosion resistance has increased recently. The increase of the hydrophobicity in a hybrid coating is a new challenge, for that reason and in order to protect a metallic surface of oxidant agents, a poly (methyl methacrylate) (PMMA) coating with the addition of a different amount of silicon dioxide (SiO2) was developed. The hybrid coating was applied on a sample of stainless steel AISI 304 by the dip-coating method. The characterization of the coatings was determined by electrochemical impedance spectroscopy and with a scanning electrochemical microscopy. The best coatings were PMMA and PMMA + SiO2 0.01% that exhibits a real impedance in the Nyquist diagram of 760 and 427,800 MΩ⋅cm2, respectively, and the modulus of the real impedance in the Bode diagram present values of 2.2 × 108 and 3.3 × 108 Ω⋅cm2. Moreover, the phase angle presents constant values around 75° to 85° and 85° for the PMMA and PMMA + SiO2 0.01%, respectively. Moreover, the values of the real resistance for the PMMA + SiO2 0.01% coating present values in the order of Mega-ohms despite the coating exhibits an artificial defect in their surface. The contact angle test showed that the hydrophobicity of the hybrid PMMA + SiO2 0.01% coating is higher than that of the pure PMMA coatings. The hybrid PMMA + SiO2 coatings developed in this work are a very interesting and promising area of study in order to develop efficient products to protect metallic surfaces from corrosion phenomenon.