How to model a certain Ultrasonic sensor?

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Hi, I am a newbie of Gazebo and ROS. I want to model a robot with 4 Ultrasonic sensors. While according to the user manual of my sensors, the detected region is not a sector with certain radius. Thus, could someone tell me if there is some tutorial or files about building such a Ultrasonic sensor, that can only detect a irregular region?

I have seen that there is a Plug-In tutorial about construct Velodyne HDL-32 LiDAR, while seems different from my sensor in property, as the beams are in a sector.

Thank you for your help!