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This paper reports a fiber-optic displacement sensor based on a Michelson interferometer using the spectral demodulation method. The displacement information is sensed through the length variation of the sensing fiber following the deformation of the measured object. By deploying the relaxed reference arm along the sensing arm, the optical path difference variation introduced by temperature can be eliminated. A spectral demodulation method is employed to obtain the displacement from the interference spectrum by using the fast Fourier transform and the Buneman frequency estimation. The experimental results show that the proposed displacement sensor has a high resolution of 90 nm over a long span of 15.7 m and a large displacement measurement range of 7.5 mm. The theoretical displacement measurement range of the proposed sensor can be up to 10 cm. The proposed displacement sensor will be very useful and promising in large-scale civil infrastructure monitoring applications. [ABSTRACT FROM AUTHOR]

Power consumption is one of the major issues associated with deploying a wireless sensor to monitor natural environments in the real world. It is not practical to frequently replace the battery of a sensor that is located in a remote mountainous area. While considering to save valuable energy, the sensor must be able to detect a particular event in a timely manner and report data. To satisfy these requirements, in this paper, we present a wireless sensor system, termed SMARTCONE, which is designed to monitor the slope movement and minimize the standby power consumption, while remaining active to detect events. Multiple SMARTCONEs need to synchronously change their operation modes to collect the physical parameters and transmit raw vibration data simultaneously. SMARTCONE is consuming a power of only 0.05 mA at 3.6 V in standby mode, which is significantly less than that consumed by the previous design. As far as we know, SMARTCONE is an unprecedented instrument for the monitoring of slope movement; no other instruments can achieve such a low-energy consumption while being triggered by external vibration and managed remotely. These complicated issues are considered while designing the SMARTCONE, whose performance is then evaluated. In order to prevent redundant effort and to reduce the entry-level knowledge required by the users who wish to design a system, and to promote the use of this design for monitoring natural environments, we would like to open source the design of SMARTCONE for the public. It can be modified for use in other applications to satisfy their requirements without the need to build from scratch. [ABSTRACT FROM AUTHOR]