Hi Niyas,
The emitting surface is a cone with an angle of 15 degrees, When it hits the objects, the beam will return to echo sensor. If the beam can enter into echi sensor, the distance can be measured. Or else, it can not. Here is the datasheet of the 2 sensors, trig and echo.
<LINK_TEXT text=“https://github.com/SeeedDocument/Grove_ … 6T-R-1.pdf”>https://github.com/SeeedDocument/Grove_Ultrasonic_Ranger/blob/master/res/NU40C16T-R-1.pdf</LINK_TEXT>
Thanksbest rgdsBill