Wei-Hsin Liao

Sensitivity Analysis and Energy Harvesting for a Self-Powered Piezoelectric Sensor:

Sensors play a crucial role in structural systems with concern over reliability/ failure issues. The development of wireless monitoring systems has been of great interest because wireless transmission has been proven as a convenient means to transmit signals while minimizing the use of many long wires. However, the wireless transmission systems need sufficient power to function properly. Conventionally, batteries are used as the power sources for the remote sensing systems. However, due to their limited lifetime, replacement of batteries has to be carried out periodically, which is inconvenient. In recent years, piezoelectric materials have been developed as sensing and actuating devices mostly, and power generators in some cases. In this article, a self-powered piezoelectric sensor is studied, in which one piece of piezoelectric element is simultaneously used as a sensor and a power generator under vibration environment. Concurrent design with piezoelectric materials in sensor and power generator is integrated with energy storage device. We evaluate sensing and power generating abilities individually and then energy harvesting performances. The potential of the piezoelectric sensor to power wireless transmission systems is discussed. Experimental efforts are carried out to study the feasibility of the self-powered piezoelectric sensor system.

Magnetorheological fluid dampers: a review of parametric modelling

Due to the inherent nonlinear nature of magnetorheological (MR) dampers, one of the challenging aspects for developing and utilizing these devices to achieve high performance is the development of models that can accurately describe their unique characteristics. In this review, the characteristics of MR dampers are summarized according to the measured responses under different conditions. On these bases, the considerations and methods of the parametric dynamic modelling for MR dampers are given and the state-of-the-art parametric dynamic modelling, identification and validation techniques for MR dampers are reviewed. In the past two decades, the models for MR dampers have been focused on how to improve the modelling accuracy. Although the force–displacement behaviour is well represented by most of the proposed dynamic models for MR dampers, no simple parametric models with high accuracy for MR dampers can be found. In addition, the parametric dynamic models for MR dampers with on-line updating ability and the inverse parametric models for MR dampers are scarcely explored. Moreover, whether one dynamic model for MR dampers can portray the force–displacement and force–velocity behaviour is not only determined by the dynamic model itself but also determined by the identification method.

Vibration Control of a Suspension System via a Magnetorheological Fluid Damper

Semi-active control systems are becoming more popular because they offer both the reliability of passive systems and the versatility of active control without imposing heavy power demands. It has been found that magneto-rheological (MR) fluids can be designed to be very effective vibration control actuators. The MR fluid damper is a semi-active control device that uses MR fluids to produce a controllable damping force. The objective of this paper is to study a single-degree-of-freedom suspension system with an MR fluid damper for the purpose of vibration control. A mathematical model for the MR fluid damper is adopted. The model is compared with experimental results for a prototype damper through finding suitable model parameters. In this study, a sliding mode controller is developed by considering loading uncertainty to result in a robust control system. Two kinds of excitations are inputted in order to investigate the performance of the suspension system. The vibration responses are evaluated in both time and frequency domains. Compared to the passive system, the acceleration of the sprung mass is significantly reduced for the system with a controlled MR damper. Under random excitation, the ability of the MR fluid damper to reduce both peak response and root-mean-square response is also shown.

Modeling and control of magnetorheological fluid dampers using neural networks

Due to the inherent nonlinear nature of magnetorheological (MR) fluid dampers, one of the challenging aspects for utilizing these devices to achieve high system performance is the development of accurate models and control algorithms that can take advantage of their unique characteristics. In this paper, the direct identification and inverse dynamic modeling for MR fluid dampers using feedforward and recurrent neural networks are studied. The trained direct identification neural network model can be used to predict the damping force of the MR fluid damper on line, on the basis of the dynamic responses across the MR fluid damper and the command voltage, and the inverse dynamic neural network model can be used to generate the command voltage according to the desired damping force through supervised learning. The architectures and the learning methods of the dynamic neural network models and inverse neural network models for MR fluid dampers are presented, and some simulation results are discussed. Finally, the trained neural network models are applied to predict and control the damping force of the MR fluid damper. Moreover, validation methods for the neural network models developed are proposed and used to evaluate their performance. Validation results with different data sets indicate that the proposed direct identification dynamic model using the recurrent neural network can be used to predict the damping force accurately and the inverse identification dynamic model using the recurrent neural network can act as a damper controller to generate the command voltage when the MR fluid damper is used in a semi-active mode.

On the efficiencies of piezoelectric energy harvesting circuits towards storage device voltages

Using piezoelectric elements to harvest energy from ambient vibrations has been of great interest over the past few years. Due to the relatively low power output of piezoelectric materials, energy storage devices are used to accumulate harvested energy for intermittent use. Piezoelectric energy harvesting circuits have two schemes: one-stage and two-stage energy harvesting. A one-stage energy harvesting scheme includes a conventional diode bridge rectifier and an energy storage device. In recent years, two-stage energy harvesting circuits have been explored. While the results shown in previous research and development are promising, there are still some issues that need to be studied. Energy storage devices such as rechargeable batteries and supercapacitors have different cell voltages. Moreover, the storage cells can be connected in series to increase the voltage range. The storage device voltage is an important factor that influences the energy harvesting efficiency. This paper will study the efficiencies of the energy harvesting circuits considering the storage device voltages. For one-stage energy harvesting, expressions are derived to calculate the efficiencies towards different storage device voltages and verified by experiments. For two-stage energy harvesting circuits, theoretical efficiency expressions are derived and verified by PSPICE simulations. These two energy harvesting schemes are also compared. The results show that a one-stage energy harvesting scheme can achieve higher efficiency than the two-stage scheme towards a range of energy storage voltages.

SEMI-ACTIVE CONTROL OF AUTOMOTIVE SUSPENSION SYSTEMS WITH MAGNETO- RHEOLOGICAL DAMPERS.

This paper is aimed to develop semi-active control for automotive suspension systems with magneto-rheological (MR) fluid dampers. A two degree-of-freedom quarter car model is considered. A mathematical model of MR fluid damper is adopted. In this study, there are two nested controllers including system controller and damper controller. For the system controller, a model-reference sliding mode controller is developed for considering loading uncertainty to result in a robust control system. In order to choose a good reference model, the single-degree-of-freedom skyhook system is analysed. For the damper controller, the continuous-state control is used to track the actual damping force to the desired damping force. The transmissibilities of the MR suspension system are investigated. The performances of the MR suspension systems are evaluated by computer simulation with bump and random excitations. The effectiveness of the MR suspension system is also demonstrated via hardware-in-the-loop simulation (HILS) with sinusoidal excitation.

Improved Design and Analysis of Self-Powered Synchronized Switch Interface Circuit for Piezoelectric Energy Harvesting Systems

In piezoelectric energy harvesting (PEH), with the use of the technique named synchronized switch harvesting on inductor (SSHI), the harvesting efficiency can be greatly enhanced. Furthermore, the introduction of its self-powered feature makes this technique more applicable for stand-alone systems. In this paper, a modified circuit and an improved analysis for the self-powered SSHI (SP-SSHI) are proposed. With the modified circuit, direct peak detection and better isolation among different units within the circuit are achieved, both of which result in the further removal on the dissipative components. In the improved analysis, details in the open circuit voltage, switching phase lag, and intermediate voltages among different phases are discussed, all of which lead to a better understanding on the working principle of SP-SSHI. The total power dissipation from the piezoelectric source is also investigated. It is of concern but has not been considered in the previous literatures. Both analyses and experiments show that, in terms of the harvested power, the higher the excitation level, the closer between SP-SSHI and ideal (externally powered) SSHI; at the same time, the more beneficial the adoption of SP-SSHI treatment in PEH, compared to the standard energy harvesting (SEH) technique. Under the four excitation levels investigated, the SP-SSHI can harvest up to 200% more power than the SEH interface circuit.

Semiactive Vibration Control of Train Suspension Systems via Magnetorheological Dampers

This paper is aimed to show the feasibility for improving the ride quality of railway vehicles with semiactive secondary suspension systems using magnetorheological (MR) dampers. A nine degree-of-freedom railway vehicle model, which includes a car body, two trucks and four wheelsets, is proposed to cope with vertical, pitch and roll motions of the car body and trucks. The governing equations of the railway vehicle suspension systems integrated with MR dampers are developed. To illustrate the feasibility and effectiveness of the controlled MR dampers on railway vehicle suspension systems, the LQG control law using the acceleration feedback is adopted as the system controller, in which the state variables are estimated from the measurable accelerations with the Kalman estimator. In order to make the MR dampers track the optimal damping forces, a damper controller to command the voltage to the current drivers for the MR dampers is proposed. The acceleration responses of the car body of the train vehicle with semiactive secondary suspension system integrated with MR dampers are evaluated under random and periodical track irregularities. This semiactive controlled system is also compared to the conventional passive suspension system using viscous dampers without MR dampers, and the secondary suspension system integrated with MR dampers in passive on and passive off modes. The simulation results show that the vibration control of the train suspension system with semiactive controlled MR dampers is feasible and effective.

Impedance Modeling and Analysis for Piezoelectric Energy Harvesting Systems

In a piezoelectric energy harvesting (PEH) system, the dynamics and harvested power vary with different interface circuits connected. The impedance matching theory was regarded as the theoretical base for the harvested power optimization in the harmonically excited PEH systems. The previous literature started the impedance analyses based on the proposition that the harvested power is maximized when the output impedance of the piezoelectric transducer is matched by the input impedance of the harvesting circuit. Yet, retrospecting to the origin of the impedance matching theory, a philosophical problem is found with this proposition. Moreover, the definition, constraint, and composition of the equivalent impedance in the real (nonlinear) harvesting circuits were not clear as well. This paper clarifies these concepts and provides the impedance modeling and analysis for the PEH systems with different interface circuits, including standard energy harvesting, parallel synchronized switch harvesting on inductor, and series synchronized switch harvesting on inductor. The equivalent impedance network and corresponding mechanical schematics of a general PEH system are proposed. The difference between the PEH equivalent impedance network and the conventional impedance network is discussed. The harvested power is investigated based on this impedance analysis. The analytical results show good agreement with the experiments carried out on a base excited PEH device.

A self-sensing magnetorheological damper with power generation

Magnetorheological (MR) dampers are promising for semi-active vibration control of various dynamic systems. In the current MR damper systems, a separate power supply and dynamic sensor are required. To enable the MR damper to be self-powered and self-sensing in the future, in this paper we propose and investigate a self-sensing MR damper with power generation, which integrates energy harvesting, dynamic sensing and MR damping technologies into one device. This MR damper has self-contained power generation and velocity sensing capabilities, and is applicable to various dynamic systems. It combines the advantages of energy harvesting—reusing wasted energy, MR damping—controllable damping force, and sensing—providing dynamic information for controlling system dynamics. This multifunctional integration would bring great benefits such as energy saving, size and weight reduction, lower cost, high reliability, and less maintenance for the MR damper systems. In this paper, a prototype of the self-sensing MR damper with power generation was designed, fabricated, and tested. Theoretical analyses and experimental studies on power generation were performed. A velocity-sensing method was proposed and experimentally validated. The magnetic-field interference among three functions was prevented by a combined magnetic-field isolation method. Modeling, analysis, and experimental results on damping forces are also presented.