## 1 Introduction
In recent years, with the rapid development of bionic science, materials and computer science, researchers began to use different kinds of sensors to simulate the lateral-line system of fish to perceive the function of water-flow information [14; 15], as is shown in Table 1. The artificial lateral-line system can be used as a scientific bionic experiment to study the interaction mechanism between the biological lateral line and surrounding water flow [16]. It can also be used as a sensor for underwater robots to perceive the environment, and obtain information on the robot's own state and its surrounding water environment. Research of the artificial lateral-line system has attracted more and more attention since 2006, and it is still in its infancy [17]. Sensors based on different kinds of sensing mechanisms, such as piezo-resistive, piezoelectric and optical-detection schemes have been designed by researchers [18; 19; 20]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Author** & **Achievements** \\ \hline [PERSON] et al. [14] & An ALL system based on IPMC sensors was presented to localize the dipole source (vlbrating sphere) underwater. \\ \hline [PERSON] et al. [16] & The locations with the largest pressure change were concentrated, and a simulation was presented to mimic the flows encountered during swimming. \\ \hline [PERSON] et al. [17] & An ALL system with a distributed linear array was presented, which can successfully perform dipole-source localization and hydrodynamic wake detection. \\ \hline [PERSON] et al. [21] & A dynamic model was developed for the IPMC beam under the flow to estimate fluid properties and flow parameters. \\ \hline [PERSON] et al. [22] & An ALL system equipped with optical-flow sensors was presented to detect water motions, vortices or water (air) movement. \\ \hline [PERSON] et al. [23] & To detect and navigate turbulent flows and sense fluid interactions for underwater vehicles, a total of 33 pressure sensors were used under Karman vortex streets at different parameters. \\ \hline [PERSON] et al. [24] & To sense the underwater environment better, 20 pressure sensors were used to distinguish the Karman vortex streets and uniform flow. \\ \hline [PERSON] et al. [25] & A fish robot with ALL system was presented to detect the beating frequency of its neighboring robot and the distance between the robots. \\ \hline [PERSON] et al. [26] & Theoretically justified nonlinear estimation strategies were presented to perceive the environment using 4 pressure sensors, and to use the strategies to construct a feedback-control system. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Previous works about artificial lateral line. Most of the existing artificial lateral-line systems are composed of multiple water-flow sensors distributed on a cylinder or streamlined shell; the research contents focus on dipole-oscillation source location [21], obstacle identification and tracking [22], flow velocity and Karman vortex-street frequency detection [23], steady and unsteady flow analysis [24] and so on. In the paper [25], the artificial lateral-line system is composed of pressure-sensor arrays distributed on both sides of the body to study the various characteristics of the Karman vortex street. In paper [26], the problem of water-flow perception of the artificial lateral-line system when moving longitudinally and laterally is studied. However, most of the existing work focuses on the research of sensors with different principles and the observation of water-fluid information such as the Karman vortex street, vibration source and water-flow velocity. Research on force and water-flow disturbance of robots has not been studied. In this paper, the bionic-sensing theory and method of water environment based on the artificial lateral system is used to design an artificial lateral system with a reasonable bionic mechanism and full fluid-sensing function for underwater robots.