I forgot to say that the reason that confuses me is that this is supossed to be a transducer.. not an emitter or receiver.
A
transducer is "any electronic device that changes one form of energy into another, such as a microphone, which changes sound waves into electrical signals".
A
transceiver is "a device that has both a transmitter and a receiver which are combined and share common circuitry or a single housing. If no circuitry is common between transmit and receive functions, the device is a transmitter-receiver".
An ultrasonic transmitter is a "transducer" it converts electrical energy into ultrasound.
An ultrasonic receiver is a "transducer" it converts ultrasound into electrical energy.
Are you sure the "sensor" device you purchased is not just a "detector" or "receiver" i.e. you also need a transmitter.
The "ping" unit mentioned by AWOL is an ultrasonic range finder it has both a transmitter and a receiver, its range is 2cm to 3m.
Before you purchase anything you might want to consider the environment it will work in e.g. if on a vehicle will it survive a car wash.