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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applications that existing PV solutions may not be able to address. Thus, a brief analysis of OPV physics is necessary to gauge its feasibility — and sustainability — for military applications. As shown in Figure 3, the organic semiconductors possess lower dielectric constants and lower charge mobility due to the screening of electrons and holes. Therefore, the primary optical excitation is a singlet exciton — a strongly bound electron-hole pair. The excitons are generated upon absorption of the electromagnetic wavelengths. These photogenerated excitons diffuse within the donor materials and dissociate at the interface with the acceptor material. The resulting polaron pair is then separated by the wide bandgaps of the electrodes. Thus, the charge separation occurs in the organic layer, and charge segregation occurs at the respective electrodes. Pyroelectricity Pyroelectricity is the ability of a certain class of materials to generate an electric charge when the materials experience temperature variations. The heating or cooling variation of the material slightly modifies the position of the atoms within the crystal structure, such that the polarization in the material changes. This change in polarization creates a voltage across the material, thus establishing thermal-electric converter properties. A typical energy-harvesting circuit is illustrated in Figure 4. The pyroelectric materials are capable of converting the majority of the electromagnetic radiation spectrum (e.g., ultraviolet, infrared, microwave, X-rays, terahertz) into electrical energy. Moreover, these materials have been exploited to convert thermal energy into electricity directly and, generally, can be used as uncooled wideband infrared detectors. Uncooled pyroelectric IR (PIR) imaging systems, such as night vision goggles, offer a multitude of strategic advantages in battlefield scenarios and reconnaissance surveys. Commercial PIR applications include fire rescue equipment, medical imaging technology, security surveillance systems, and imaging systems for cars, ships, and aircraft. In recent years, demand in the field of IR sensors has increasingly turned toward technologies with the potential to deliver lightweight, compact, low-power, and low-cost IR detectors and imaging heads, using thin- or thick-film elements integrated with silicon (Si) technology. PIR detectors also can be used for Earth-sensing applications, such as the detection of hot events (e.g., volcanic eruptions, fires, hot springs, etc.), detection and tracking of aircraft and missiles in flight, pollution monitoring, meteorology, and mineral exploration. Piezoelectricity Piezoelectricity is the process of converting pressure, or mechanical stress and strain, into electricity. Its commercial applications have touched numerous aspects of our day-to-day lives, harvesting energy from gym workouts, engine vibrations, heart beat vibrations (for pacemakers), and knee braces, to name a few. The piezoelectric effect is made possible by the electrical charge that accumulates in certain solid materials in response to mechanical stress. For most applications, crystals are used, and all crystals can be categorized into 32 different classes. These classes are point groups divided by using the following symmetry elements: (1) center of symmetry, (2) axes of rotation, Trends 42 Figure 4: A typical energy-harvesting circuit Figure 5: Typical charge mechanism in piezoelectric crystals Electronic Military & Defense Annual Resource, 5th Edition