What is the difference between ultrasonic transmitter sensor and ultrasonic receiver sensor? Can an ultrasonic receiver sensor be used as an ultrasonic transmitter sensor or vice versa?
A transmitter is optimized for, or might be optimized for transmitting.
A receiver is optimized for, or might be optimized for receiving.
Some transmitters can also receive.
Some receivers can also transmit.
There are also many transceivers (transmitter and receiver), you find these in the bumpers of many cars (park assist) for example.
Basic difference is that an ultrasonic transmitter is a speaker while an ultrasonic receiver is a microphone. Both are tuned to ultrasonic range.
So in transmitter case its your controller (or something else) that makes the membrane of the transmitter vibrate, while in receiver case the membrane of the sensor is vibrated by direct or reflected ultrasonic waves coming from ultrasonic transmitter.