Influence of pattern gradation on the design of piezocomposite energy harvesting devices using topology optimization

Piezoelectric materials can be used to convert oscillatory mechanical energy into electrical energy. Energy harvesting devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The design of energy harvesting devices is not obvious, requiring optimization procedures. This paper investigates the influence of pattern gradation using topology optimization on the design of piezocomposite energy harvesting devices based on bending behavior. The objective function consists of maximizing the electric power generated in a load resistor. A projection scheme is employed to compute the element densities from design variables and control the length scale of the material density. Examples of two-dimensional piezocomposite energy harvesting devices are presented and discussed using the proposed method. The numerical results illustrate that pattern gradation constraints help to increase the electric power generated in a load resistor and guides the problem toward a more stable solution. (C) 2012 Elsevier Ltd. All rights reserved.

Analysis, manufacture and characterization of Ni/Cu functionally graded structures

In this work, an experimental and numerical analysis and characterization of functionally graded structures (FGSs) is developed. Nickel (Ni) and copper (Cu) materials are used as basic materials in the numerical modeling and experimental characterization. For modeling, a MATLAB finite element code is developed, which allows simulation of harmonic and modal analysis considering the graded finite element formulation. For experimental characterization, Ni-Cu FGSs are manufactured by using spark plasma sintering technique. Hardness and Young's modulus are found by using microindentation and ultrasonic measurements, respectively. The effective gradation of Ni/Cu FGS is addressed by means of optical microscopy, energy dispersive spectrometry, scanning electron microscopy and hardness testing. For the purpose of comparing modeling and experimental results, the hardness curve, along the gradation direction, is used for identifying the gradation profile; accordingly, the experimental hardness curve is used for approximating the Young's modulus variation and the graded finite element modeling is used for verification. For the first two resonance frequency values, a difference smaller than 1% between simulated and experimental results is obtained. (C) 2012 Elsevier Ltd. All rights reserved.

The meristematic activity of the endodermis and the pericycle and its role in the primary thickening of stems in monocotyledonous plants

Background: It had long been thought that a lateral meristem, the so-called primary thickening meristem (PTM) was responsible for stem thickening in monocotyledons. Recent work has shown that primary thickening in the stems of monocotyledons is due to the meristematic activity of both the endodermis and the pericycle. Aims: The aim of this work is to answer a set of questions about the developmental anatomy of monocotyledonous plants: (1) Do the stem apices of monocots have a special meristematic tissue, the PTM? (2) Are the primary tissues of the stem the same as those of the root? (3) Is there good evidence for the formation of both the cortex and the vascular tissue from a single meristem, the PTM, in the shoot and from two distinguishable meristems in the root? (4) If the PTM forms only the cortex, what kind of meristem forms the vascular tissue? Methods: Light microscopy was used to examine stem and root anatomy in 16 species from 10 monocotyledonous families. Results: It was observed that radially aligned cortical cells extend outwards from endodermal initial cells in the cortex of the roots and the stems in all the species. The radial gradation in size observed indicates that the cortical cells are derivatives of a meristematic endodermis. In addition, perfect continuity was observed between the endodermis of the root and that of the stem. Meristematic activity in the pericycle gives rise to cauline vascular bundles composed of metaxylem and metaphloem. Conclusion: No evidence was obtained for the existence in monocotyledons of a PTM. Monocotyledons appear to resemble other vascular plants in this respect.