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Damage index sensor for smart structures
Mita, Akira,Takahira, Shinpei Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.3
A new sensor system is proposed for measuring damage indexes. The damage index is a physical value that is well correlated to a critical damage in a device or a structure. The mechanism proposed here utilizes elastic buckling of a thin wire and does not require any external power supply for memorizing the index. The mechanisms to detect peak strain, peak displacement, peak acceleration and cumulative deformation as examples of damage indexes are presented. Furthermore, passive and active wireless data retrieval mechanisms using electromagnetic induction are proposed. The passive wireless system is achieved by forming a closed LC circuit to oscillate at its natural frequency. The active wireless sensor can transmit the data much further than the passive system at the sacrifice of slightly complicated electric circuit for the sensor. For wireless data retrieval, no wire is needed for the sensor to supply electrical power. For the active system, electrical power is supplied to the sensor by radio waves emitted from the retrieval system. Thus, external power supply is only needed for the retrieval system when the retrieval becomes necessary. Theoretical and experimental studies to show excellent performance of the proposed sensor are presented. Finally, a prototype damage index sensor installed into a 7 storey base-isolated building is explained.
27R-SiAlON Reinforced AlN Composite: Synthesis, Sintering and Characterization
Mita Biswas,Siddhartha Bandyopadhyay 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
Synthesis of powder containing a dual phase mixture of 27R-SiAlON and AlN has been successfully carried out throughcarbothermal reduction and nitridation route. The probable reaction sequences of formation have been identified through theanalysis of transient appearances of intermediate phases associated with parameters like loss of carbon, oxygen and weightas well as nitrogen uptake. Formation of 27R-SiAlON takes place through further reaction of a primary polytype phase,Si3Al7O3N9. FTIR spectra provide supplementary evidence for supporting the revealed model of reaction sequences. Particlesare agglomerative in nature consisting of fine grains, as low as below 50 nm in size. Spark plasma sintering was applied foran initial densification trial of this bi-phasic powder without externally added sintering aid. The densified samples exhibitedelongated grain-reinforced composite microstructure with improved properties over monolithic AlN.
Y. Mita,T. Kagayama,G. M. Abramova,G. A. Petrakovskii,V. V. Sokolov 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3
A pressure-induced phase transition in the colossal magnetoresistance (CMR) materialFe0.18Mn0.82S was studied by using infrared (IR) reflection and X-ray diffraction (XRD) at pressuresup to 40 GPa at room temperature. XRD shows that the crystal structure of this sample is aNaCl-type structure at ambient pressure, that a structural change starts around 17 GPa, and thata mixed phase mixed between the NaCl-type low-pressure phase and an unknown structure highpressure phase continues up to around 25 GPa. On the other hand, the IR reflectivity increaseswith increasing pressure from 15 GPa and becomes remarkably high around 20 GPa. The spectrado not show any changes from 30 GPa. From these results, we conclude that the phase transitionof Fe0.18Mn0.82S at room temperature starts around 15 GPa and is completed around