​Abstract: This article describes the research and development directed toward an autonomous time-synchronized sensor device equipped with a chip scale atomic clock (CSAC) that records highly accurate time information. The R & D project presented herein aims to achieve earthquake observation to prepare for disasters and structural health monitoring to improve the efficiency of maintenance and management of buildings and civil engineering structures. For these reasons, it is necessary to install sensors in a wide area at a high density and to measure the data with accurately synchronized time information. It is recommended that the sensor device itself maintains accurate time information without relying on the network or a Global Positioning System (GPS) signal. Therefore, in this study, a sensor device that autonomously maintains accurate time information using an ultra-high precision, ultra- low power consuming, and ultra-small (and therefore, loadable on a board) atomic clock, known as CSAC, was developed. In this article, first, the concepts of autonomous time synchronization and CSACs are described, and the mechanism for assigning ultra- high precision time information to the sensor data by using a CSAC is explained. Next, the performance of the improved sensor device is demonstrated and the results of the vibration table test, which was conducted to examine the performance, are presented. Finally, the developed sensor devices were applied to an actual pedestrian bridge and acceleration measurement was carried out at several points on the bridge. The vibration characteristics of the bridge were obtained from a frequency analysis of the acceleration data.

Keywords: Time synchronization, Chip scale atomic clock, Earthquake observation, Structural health monitoring, MEMS.

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