On the Efficiency Enhancement of an Actively Tunable MEMS Energy Harvesting Device

In this paper, we propose an active control method to adjust the resonance frequency of a capacitive energy harvester. To this end, the resonance frequency of the harvester is tuned using an electrostatic force, which is actively controlled by a voltage source. The spring softening effect of the electrostatic force is used to accommodate the dominant frequency of the ambient mechanical vibration within the bandwidth of the resonance region. A single degree of freedom is considered, and the nonlinear equation of motion is numerically integrated over time. Using a conventional proportional–integral–derivative (PID) control mechanism, the results demonstrated that our controller could shift the resonance frequency leftward on the frequency domain and, as a result, improve the efficiency of the energy harvester, provided that the excitation frequency is lower than the resonance frequency of the energy harvester. Application of the PID controller in the resonance zone resulted in pull-in instability, adversely affecting the harvester’s performance. To tackle this problem, we embedded a saturation mechanism in the path of the control signal to prevent a sudden change in motion amplitude. Outside the pull-in band, the saturation of the control signal resulted in the reduction of harvested power compared to the non-saturated signal; this is a promising improvement in the design and analysis of energy harvesting devices

A seismic vulnerability index method for masonry schools in the province of Yazd

School facilities in Iran, in particular masonry schools, have shown poor performance during past earthquakes and can be identified as the most vulnerable buildings to the earthquakes. Hence, in this paper a method to perform observational-based damage assessment for brick masonry schools located in the province of Yazd, the central region of Iran, using a comprehensive database of schools is proposed. The database was obtained from the field survey forms applied for each observed school to collect the seismic influential parameters. The results of a vulnerability index method developed in Iran are employed to use in a correlation procedure as input data, aiming at obtaining the empirical fragility curves for each school inventory. The macroseismic model and GNDT II level method are two empirical methods that are combined in this procedure. The procedure is verified using damage survey data after earthquakes occurred in Iran

Applied mechatronics: Designing a sliding mode controller for active suspension system

The suspension system is referred to as the set of springs, shock absorbers, and linkages that connect the car to the wheel system. The main purpose of the suspension system is to provide comfort for the passengers, which is created by reducing the effects of road bumpiness. It is worth noting that reducing the effects of such vibrations also diminishes the noise and undesirable sound as well as the effects of fatigue on mechanical parts of the vehicle. Due to the importance of the abovementioned issues, the objective of this article is to reduce such vibrations on the car by implementing an active control method on the suspension system. For this purpose, a conventional first-order sliding mode controller has been designed for stochastic control of the quarter-car model. It is noteworthy that this controller has a significant ability to overcome the stochastic effects, uncertainty, and deal with nonlinear factors. To design a controller, the governing dynamical equation of the quarter-car system has been presented by considering the nonlinear terms in the springs and shock absorber, as well as taking into account the uncertainty factors in the system and the actuator. The design process of the sliding mode controller has been presented and its stability has been investigated in terms of the Lyapunov stability. In the current research, road surface variations are considered as Gaussian white noise. The dynamical system behavior for controlled and uncontrolled situations has been simulated and the extracted results have been presented. Besides, the effects of existing uncertainty in the suspension system and actuator have been evaluated and controller robustness has been checked. Also, the obtained quantitative and qualitative compressions have been presented. Moreover, the effect of controller parameters on the basin of attraction set and its extensiveness has been assessed. The achieved results have indicated the good performance and significant robustness of the designed controller to stabilize the suspension system and mitigate the effects of road bumpiness in the presence of uncertainty and noise factors

A new approach in compatibilization of the poly(lactic acid)/thermoplastic starch (PLA/TPS) blends

tIn this study, a new compatibilizer was synthesized to improve the compatibility of the poly(lacticacid)/thermoplastic starch blends. The compatibilizer was based on maleic anhydride grafted poly-ethylene glycol grafted starch (mPEG-g-St), and was characterized using Fourier transform infraredspectroscopy (FTIR), dynamic mechanical thermal analysis (DMTA) and back titration techniques. Theresults indicated successful accomplishment of the designed reactions and formation of a starch coredstructure with many connections to m-PEG chains. To assess the performance of synthesized compati-bilizer, several PLA/TPS blends were prepared using an internal mixer. Consequently, their morphology,dynamic-mechanical behavior, crystallization and mechanical properties were studied. The compatibi-lizer enhanced interfacial adhesion, possibly due to interaction between free end carboxylic acid groupsof compatibilizer and active groups of TPS and PLA phases. In addition, biodegradability of the sampleswas evaluated by various methods consisting of weight loss, FTIR-ATR analysis and morphology. Theresults revealed no considerable effect of compatibilizer on biodegradability of samples

On the nonlinear dynamics of a piezoresistive based mass switch based on catastrophic bifurcation

This research investigates the feasibility of mass sensing in piezoresistive MEMS devices based on catastrophic bifurcation and sensitivity enhancement due to the orientation adjustment of the device with respect to the crystallographic orientation of the silicon wafer. The model studied is a cantilever microbeam at the end of which an electrostatically actuated tip mass is attached. The piezoresistive layers are bonded to the vicinity of the clamped end of the cantilever and the device is set to operate in the resonance regime by means of harmonic electrostatic excitation. The nonlinearities due to curvature, shortening and electrostatic excitation have been considered in the modelling process. It is shown that once the mass is deposited on the tip mass, the system undergoes a cyclic fold bifurcation in the frequency domain, which yields a sudden jump in the output voltage of the piezoresistive layers; this bifurcation is attributed to the nonlinearities governing the dynamics of the response. The partial differential equations of the motion are derived and discretized to give a finite degree of freedom model based on the Galerkin method, and the limit cycles are captured in the frequency domain by using the shooting method. The effect of the orientation of the device with respect to the crystallographic coordinates of the silicon and the effect of the orientation of the piezoresistive layers with respect to the microbeam length on the sensitivity of the device is also investigated. Thanks to the nonlinearity and the orientation adjustment of the device and piezoresistive layers, a twofold sensitivity enhancement due to the added mass was achieved. This achievement is due to the combined amplification of the sensitivity in the vicinity of the bifurcation point, which is attributed to the nonlinearity and maximizing the sensitivity by orientation adjustment of the anisotropic piezoresistive coefficients

DESIGNING AN EFFICIENT OBSERVER FOR THE NON-LINEAR LIPSCHITZ SYSTEM TO TROUBLESHOOT AND DETECT SECONDARY FAULTS CONSIDERING LINEARIZING THE DYNAMIC ERROR

The presence of faults in a system leads to a lower value for efficiency, accuracy and speed, and, in some cases, even a complete breakdown. Thus, early fault detection is a major factor in efficiency and productivity of the procedure. In recent decades, many research studies have been conducted on troubleshooting and secondary fault detection. The current work presents an efficient and novel observer design capable of stabilizing the residue and dynamic error for the nonlinear Lipschitz systems with faults as well as a troubleshooting analysis and determining the formation of secondary faults in defective systems. The observer is designed based on linearizing dynamic error considering uncertainty, disturbance, and defects by employing non-linear gain factors instead of using state transformation. The dynamic error and residue stabilization of a non-linear faulty system have been discussed as well as the likelihood of secondary fault generation. The results indicate that the observer is able to determine fault-emergence, fault-disappearance and secondary fault formation well and quite fast

Preventive conservation of vernacular adobe heritage located in seismic-prone regions

In general, relevant actions to retrofit heritage should be considered before the occurrence of earthquakes. This proactive approach is preferred, rather than a reactive approach in an emergency situation, following the earthquake. These preventive actions are known as disaster mitigation, risk mitigation, disaster risk management, seismic upgrading and preventive conservation. In the case of vernacular heritage, poor workmanship, lack of financial support, vast number of buildings, and the use of weak material lead to the need to conduct efforts to develop preventive conservation methods with relevant criteria. All these actions were directed to protecting vernacular heritage from multiple potential damages that could threaten this architecture in the future. In recent years, records of casualty and losses due to earthquakes reveal that seismic events can be one of the most destructive potential damages for building, especially if constructed with a weak material, such as adobe. There is little literature concerning preventive conservation of vernacular adobe buildings, which are at risk from earthquakes. Vernacular architecture needs more consideration due to the high number of vernacular dwellings worldwide but especially due to the inhabitants’ safety. Failure to recall the effects of destructive earthquakes with a large recurrent period of seismic actions, but also economic reasons lead to the neglect of these important preventive solutions. The main objective of this paper is to emphasize that a comprehensive conservation procedure related to prevention of casualties and damage of vernacular adobe heritage located in seismic-prone regions, should consider relevant principles and criteria for the conservation of cultural heritage. In the field of preventive conservation of adobe vernacular heritage located in seismic-prone regions, there is some confusion concerning the relation between the conservation process and the seismic protection process; the importance and need of conservation principles in seismic protection procedures; and also the role of the architect and of the engineer in these processes. These matters will be discussed in the current paper.(undefined

A comparative analysis of policy frameworks and admission procedures in the teacher education system of England, Finland, Iran and Japan

The purpose of research was to compare the characteristics of teacher education system with an emphasis on the policy making process and admission procedures in Finland, England, Japan and Iran. The research method was a qualitatively comparative approach using four-stage regional model of Bereday. Scientific documents and reports related to the teacher education system in the four selected countries were used to collect data. The findings showed that, in terms of policy frameworks, the teacher education system in Iran, unlike the other three countries, follows a centralized structure that originates from ideological thought. The structural and administrative concentration and vital role of supranational institutions in the policy-making and decision-making processes have caused the teacher education system in Iran to lack institutional independence and academic freedom. Contrary to England and Finland, in Iran and Japan, obtaining legal obligations from student-teachers is considered an important precondition for continued work in the educational system. Also, the results reveal the similarity of Iran's teacher education system with England, Finland and Japan regarding the necessity of participation of candidates in a national exam, while in terms of educational qualifications and degree of discretion and freedom of action of universities in the admission process, there is a difference between Iran and other countries