KEYWORDS: Ferroelectric polymers, Energy harvesting, Telecommunications, Electrodes, Medical devices, Resistors, Electronics, 3D modeling, Toxicity, Microelectromechanical systems
There is an increasing demand for powering on-person-devices (for communications, health-care purposes, and soldier protection) without the burden of the parasitic weight and toxicity of conventional batteries. This demand calls for an alternative power source from fibre-sized piezoelectric generators that can be integrated into garments. These piezopatches convert human movement induced mechanical strain on the fabric into electrical energy. In this paper, a dualfield computational analysis, combining harmonic and piezoelectric models, has been undertaken using the ANSYS Finite Element package. A Polyvinylidene Fluoride (PVDF) patch bonded to a material representative of a flexible fabric has been modeled in ANSYS. The electrodes are connected to a resistor that is matched to the piezo properties and loading conditions. The parametric variables used in this study include: surface area of the piezo-patches, aspect ratio, input force amplitude and the operational frequency. The complex interaction of these variables to the power output is explored and discussed in the context of the intended application. It is observed that the maximum output occurs at 5Hz for an optimal dimension of 400mm2 which makes it feasible as an energy harvesting system for low energy selfpowered electronics such as portable and wearable medical and communication devices.
Passive vibration shunt control using piezoelectric material (PZT) and an electrical network can remove considerable amount of vibration energy from flexible structures. In this paper, an analytical study of parallel passive resistor-inductor (R-L) piezoelectric vibration shunt control on a beam structure by using the Hamilton's principle, Galerkin's method is presented. However, the efficiency of such vibration control method relies on the optimization of vibration energy transfer between a structure and piezoelectric material. In this paper, the strain energy transfer within the composite material, which is made of two layers of different materials, is analyzed. It indicates that neutral axis of the composite material has some influence on the optimization of the strain energy transfer between the structure and PZT. The passive vibration shunt control is sensitive to frequency shift of structures. However, in reality, the natural frequencies of flexible structures often vary somewhat due to environment change, such as boundary conditions, temperature variation, etc. The effectiveness of the vibration shunt control will be significantly reduced when the frequency of the shunt circuit does not match the natural frequency of the structure. In this paper, a method of estimating the resonant frequencies of structures using adaptive IIR notch filter is presented. With online frequency detection, the inductor value is possible to be adjusted in real time by some kind of controllable capacitors and resistors to track the frequency change of structures.
This paper uses one category of Structural Health Monitoring (SHM) which uses strain variation across a structure as the key to damage detection. The structure used in this study was made from Glass Fibre Reinforced Plastic (GFRP). This paper discusses a technique developed called "Global Neural network Architecture Incorporating Sequential Processing of Internal sub Networks (GNAISPIN)" to predict the presence of multiple damage zones, determine their positions and also predict the extent of damage. Finite Element (FE) models of T-joints, used in ship structures, were created using MSC Patran(R) . These FE models were created with delaminations embedded at various locations across the bond-line of the structure. The resulting strain variation across the surface of the structure was observed. The validity of the Finite Element model was then verified experimentally. GNAISPIN was then used in tandem with the Damage Relativity Analysis Technique to predict and estimate the presence of multiple delaminations.
Vibration and resonance of plates are well known problems in designing and analysis of mechanical structures. While these problems are considered during the design process, significant amount of research has been directed to handle the unforeseen loading situations which may lead to catastrophic events. Different types of techniques (passive and active) were developed to prevent these events. Among these techniques, the implementation of the smart materials such as Shape Memory Alloys (SMAs) and piezoelectric ceramics gained importance for controlling the vibrations through damping or altering the resonant frequencies of the parent structures. Composite materials have become major players in building modern and advanced structures especially plates as a consequence; the development of smart composite structures emerged as an area of high interest. In this paper, the feasibility of SMA wires in controlling the vibration of composite plates through altering the strain energy and hence the natural frequency is investigated. The effect of placing the SMA wires in different directions (longitudinal and angularly transverse) over the composite plates will be studied. Computational and experimental work will be conducted to develop the control strategy to control combined vibration situations. Strain energy analysis of the composite panel using laminate theory considerations was used to relate the strain energy alteration in the panel as a result of the SMA actuation to its effect on the laminate stiffness.
Vibration control has been a subject of engineering research for the past few decades. Recently, the use of smart material-related components for vibration control has become an alternative to traditional vibration control techniques. Vibration control using such components has many advantages such as lighter overall weight and lower cost. They are especially suitable where traditional techniques cannot be applied due to weight and size restrictions. Passive vibration shunt control using piezoelectric ceramics (PZT) and an electrical network has been studied by many researchers both analytically and experimentally. In this paper, the modeling of a passive vibration shunt control on a cantilever beam using a finite element analysis software package -- ANSYS is presented. It is a useful alternative to an experimental approach that is costly as the PZT is useable only once in most instances. The simulation shows that the electrical shunt circuit can remove considerable vibration-based energy when properly tuned. The simulation reveals that the material property of the structure has a significant impact on the effectiveness of the vibration shunt circuit. This is postulated to be because of the mechanical impedance match between the structure and PZT transducer. The method provides a useful mechanism for selecting the material properties of a structure so that its vibration can be effectively absorbed by a piezoelectric vibration shunt network. Also shown in this paper is experimental verification of the computational results. This procedure has the potential for greatly increasing the flexibility in the design of such Mechatronic control devices especially when the mechanical and physical properties of synthetic materials such as polymeric composite materials can be varied to suit the application.
The use of glass-reinforced plastics (GFRP) as a structural material is widespread because of their high strength and stiffness, low mass, excellent durability and ability to be formed into complex shapes. However, GFRP composite structures are prone to delaminations which can lead to a significant degradation in structural integrity. A number of non-destructive inspection methods have been devised to inspect such structures. One class of SHM system relies on the examination of the strain distribution of the structure due to its operational loads. This paper considers the strain distribution in a GFRP structure subject to loading. The strain distribution due to delaminations of various sizes and locations along the bondline of the structure has been determined by finite element analysis (FEA). A technique called the Damage Relativity Assessment Technique (DRAT) has been developed and implemented to process the data in order to amplify the damage detection process. An Artificial Neural Network (ANN) has been trained to relate this strain distribution to damage size and location. This ANN has been shown to predict the size and location of damage for a number of simulated cases. The extension of this technique is to detect multiple cracks in a complex structure with multiple loading sets. These studies will also be carried over for structures subjected to impulse loading. A major aspect of this effort will include the pseudo-automated assessment of the criticality of the damage. Results from computational and experimental work, in this regard will be presented and used in conjunction with the DRAT and the ANN techniques described above.
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