A diaphragm-based interferometric fiber optical microelectromechanical system sensor with high sensitivity is designed and tested for on-line detection of the acoustic waves generated by partial discharges (PD) inside high-voltage power transformers. In principle, the sensor is made according to Fabry Perot interference, which is placed on a micro-machined rectangular silicon membrane as a pressure-sensitive element. A fiber-optic readout scheme has been used to monitor sensor membrane deflection. Sensor design, fabrication, characterization, and application in PD acoustic detection are described. Test results indicate that the fiber optical sensor is capable of detecting PD acoustic signals propagating inside transformer oil with high sensitivity.

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We report on the study of large two-level, low-frequency resistance fluctuations in l-//m^ metaloxide-silicon tunnel diodes, which are due to the strongly correlated emptying and filling of ensembles or clusters of interacting localized states in the oxide. The interaction mechanism is attributed to ionic forces in the strained oxide. It can give rise to complex structure in the switching noise and, under strong electrical stress, can result in the breaking of oxide bonds by the collective action of localized states.

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