High precision structural displacement monitoring is challenging, but an effective method for structural health monitoring and particularly damage evaluation. In this paper, a high precision fiber Bragg grating (FBG) displacement sensor with embedded spring is developed to monitor structural displacement variation even at very small ranges. The principle of such monitoring is based on the central wavelength shifts in accordance with the displacement between measuring points. Calibration experiments are conducted to examine the performance of the innovative displacement sensor. The result indicates that the sensor has excellent linearity and repeatability, with the sensitivity coefficient being 23.96[Formula: see text]pm/mm, and the static relative error is 4.94% after three loading and unloading cycles. The displacement sensor therefore shows an excellent sensitivity and high precision for application. Moreover, it has been verified that this sensor is suitable and applicable for displacement monitoring in quasi-static experiment of structures.
Target localization, which aims to estimate the location of an unknown target, is one of the key issues in applications of underwater acoustic sensor networks (UASNs). However, the resource-constrained property of an underwater environment such as noise makes target localization a challenging problem. This paper considers a consensus estimation-based approach to the target localization problem in UASNs. To detect and acquire the position of the target, a hybrid architecture is applied to UASNs, where autonomous underwater vehicles provide self-location and clock synchronization for sensor nodes. Built on this architecture, a trilateration method coupled with a regional optimal solution is provided to estimate the rough localization of a target. Furthermore, a consensus estimation-based algorithm is designed for the regional optimal solution, such that localization accuracy is improved. In the presence of measurement and communication noises, localization error and asymptotic unbiasedness for the estimation algorithm are also investigated. Finally, simulation results show that the proposed localization approach can avoid the occurrence of nosolution while improving the localization accuracy. In addition, the hybrid communication architecture can reduce the number of transmissions compared with egalitarian decentralized networks. . 1608 J. YAN ET AL.error accumulation problem is the principal issue to be addressed in this paper. Subsequently, sensing sensors are required to achieve the underwater target localization task. To address this problem, a variety of localization schemes have been proposed. Generally speaking, these schemes can be classified into two categories: range-based schemes and range-free schemes. Range-based schemes rely on various mechanisms such as time of arrival, time difference of arrival, angle of arrival, or received signal strength indicator to measure the distances and then convert these distance measurements to position information. For instance, a time difference of arrival-based localization algorithm was proposed in [6] to localize swarms of autonomous underwater vehicles (AUVs). In [7], an energyaware localization algorithm was presented to collaboratively localize an underwater target with minimum energy consumption. In addition, sonar arrays towed by ships or submersibles were also used to achieve the target localization task [8,9]. These range-based results are well framed without considering the measurement errors. As we know, the noises are ignored in the general localization problem, because of the good communication conditions in terrestrial environment. However, the communication conditions underwater are always rough, and the man-made (or ambient) noises cannot be ignored [10]. As it is pointed in [11], the localization errors for the range-based schemes are closely related to the precision of distance measurements, and the existence of even a small measurement error may result in no-solution for the trilateration methods [7,12]. On the other hand, range-free based schemes d...
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