Electronic Military & Defense Annual Resource

5th Edition

Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.

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(3) mirror planes, and (4) combinations of the previous symmetry elements. The 32 point groups themselves are subdivisions of seven basic crystal systems that are, in order of ascending symmetry: triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral (trigonal), hexagonal, and cubic. Of the 32 point groups, 21 classes are noncentrosymmetric — a necessary condition for piezoelectricity to exist — and 20 of them are piezoelectric. Of the 20 piezoelectric crystal classes, 10 crystals also have pyroelectric properties. All dielectric materials (crystals, in this case) under- go a change in dimensions when subjected to an external force. This is due to the dis- placement of positive and negative charges within the mate- rial. When an external electric field is applied to such a mate- rial, the cations are displaced in the direction of the electric field, and anions are displaced toward the positive direction, result- ing in net defor- mation of the material. The change in dimension can vary from quite small to very large, depending upon the crystal class to which the material belongs. Depending on the struc- ture of the material, such a small change in dimension might result in a change in an electric polarization (dipole moment per unit volume), thereby giving rise to the piezoelectric effect, as demonstrated in Figure 5. Still, in order to successfully and efficiently use an energy-harvesting system, that system must be paired with a structure that optimally converts the input light, thermal energy, or mechanical energy to useful energy. While progress has been made with energy harvesting in military applications — including sensing technology, microelectronics, and wireless communications — it will be of great benefit to military personnel to develop an integrated power storage system, to accompany the renewable power sources, that adds little or no weight to a soldier's pack. Printing Methodology The potential of energy harvesters based on flexible and printed electronics has captured the attention of researchers and entrepreneurs alike, but that potential has not yet translated into commercial viability. However, the advent of wearable devices and electronic gadgets has opened the door to and created demand for printing methodologies that are both viable and durable. Printing meth- ods like screen printing, inkjet printing, flexo- graphic printing, gravure printing, nanoimprinting (or embossing), slot die, and other alterna- tives are feasi- ble solutions to develop flexible, printed electron- ic devices. These printing tech- nologies could allow develop- ers to improve current military and defense electronics and to create ener- g y - h a r v e s t i n g versions of as-yet-untapped military electronics. Furthermore, an automated or robotic version of such printing equipment could benefit a multitude of mili- tary applications. Dr. Ashwith Chilvery is an avid material scientist and assistant professor in the Department of Applied Physics at Xavier University of Louisiana. His research interests are in the fields of photovoltaics, energy harvesting, and computational physics. Silpika Karampuri is an M.S. student in the Department of Computer Science and Engineering at Alabama A&M; University. Her research focuses on the numerical analysis of piezoelectric materials for energy harvesting. Technology Materials Efficiency Printability Characteristics Photovoltaic Conductive polymers, p-type and n-type organic semiconduc- tor 22-38% Screen print- ing, inkjet, brush, and spray coating Outdoor Indoor Piezoelectric Ferroelectric materi- als (PZT, BaTiO3, etc.) 15-28% Gravure, screen print- ing, etc. Human and machines Pyroelectric Ferroelectric ceramics, polymers, and composites 0.1-3% Gravure, paint, screen printing, etc. Human and machines Figure 6: Comparison of various technologies feasible for printed electronics Trends Electronic Military & Defense Annual Resource, 5th Edition 44

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