Fiber optic technology is making significant advances for use in a number of air and space applications, including communication networks, sensors, navigation and prognostics and health management. Many of these applications involve integration into systems which must operate in harsh environments, including extreme low to high temperatures, shock, vibration, radiation, corrosive conditions, high electromagnetic and high radio-frequency interference and pressure. Several current air and space platforms that use fiber optic systems include commercial and military aircraft, unmanned aircraft, the International Space Station and several NASA and international space exploration systems. Fiber optic technologies have demonstrated the ability to overcome resistance losses, provide revolutionary situational awareness to platforms and detect opens and shorts and other structural defects. These technologies do not require significant power and complex electronics while still allowing signal processing to be located close to the networked applications. There are many benefits of fiber optic systems for air and space applications, including minimal electromagnetic interference and environmental effects, lightweight and smaller diameter cables, greater bandwidth and the ability to be easily upgraded. This paper presents an overview of several fiber optic applications in harsh environments, including fiber optic components and standards, inertial measurement units, fiber optic sensor systems for prognostics, strain and temperature measurements, structural failure measurements, wavelength modulated fiber optic sensors for submersible testing and detection and fiber optics for space microwave imaging radiometers. As photonic link performance continues to improve, evolve and mature, it will yield high return on investment (ROI) by providing enabling capabilities and saving significant life-cycle costs.
Eutectic Bi/MnBi (97.8 a/o Bi) samples have been plane-front directionally solidified. The resultant microstructures consist of elongated, aligned particles of MnBi dispersed in a Bi-matrix. Magnetization as a function of temperature (4.2 to 300 K) and applied field (up to 220 kG) has been used to evaluate solidification parameters and magnetic properties. At room temperature, in addition to the diamagnetic contribution of Bi, one finds a superposition of the ferromagnetic, low temperature (LTP) MnBi phase and paramagnetic phases. At cryogenic temperatures, one of the room temperature paramagnetic phases is ferromagnetic with an intrinsic coercivity of 120 kOe while the other remains paramagnetic for low fields and orders ferromagnetically at high fields in a complicated way. Annealing of as-grown samples was found to produce significant changes in magnetic properties. The origins of the paramagnetic phases and their relation to the mechanisms which control the coercive field of the hard magnetic LTP MnBi phase are discussed.
Ferromagnetic films of the Sm–Co and Sm–Fe systems have been synthesized by sputtering onto substrates at temperatures above 600 °C so that the deposit is directly crystallized upon deposition. For the directly synthesized phases, high sputtering gas pressures were used so that the sputtered atoms transferred excess momentum to the sputtering gas atoms before arriving at the substrate. The object has been to promote the growth of possible metastable phases and to allow preferred orientation effects to be present in the films. Directly synthesized SmCo5 films grown by this method, showed a predominant (110) texture, for oxygen levels in the films of greater than about 6 at. %. As the oxygen incorporation level in the SmCo5 films was reduced to 1.4 at. % oxygen, only a (200) texture was observed. In Sm–Fe films with 6.5 at. % oxygen, a new metastable phase forms at the 1–5 composition. This oxygen stabilized metastable phase is not present in Sm–Fe films made with lower amounts of oxygen incorporation.
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