CONSTRUCTION
The No. 1/No. 2/No. 4 ultrasonic sensors consist of a microphone and a circuit portion that transmits and receives ultrasonic waves.
The circuit portion is filled with urethane to prevent water from entering.
Figure 1. No. 1 Ultrasonic Sensor (Front Side)
Figure 2. No. 2/No. 4 Ultrasonic Sensor (Front Corner/Front Center/Rear Corner/Rear Center)