In regards to this Teardown Tuesday article:

http://www.allaboutcircuits.com/news/teardown-tuesday-backup-sensors/

The piezo transducer both sends the initial signal and receives the reflection using only 2 wires. So the output signal generator, and the reflection processing circuitry must be directly connected. On the signal processing side of things; how is this device separating the initial signal from the reflection, so that only the reflection is amplified and evaluated? Is there some clock based synchronization, or is it all level based?

Edit --> The more I think about it, it must send a signal then pause and listen for x-time for a reflection to come back, then repeat. My question stemmed from a past request to help someone make these sensors wireless while keeping the sensing hardware intact, and I stumbled on how to make that possible.

 

The sensor is wired directly to a driver and receiver circuit. When in the send mode, the driver output is enabled. After transmission the driver is disable (switched to high impedance state) and the receiver is enabled.

 

A couple of subtlties. The received signal must not overload the receiver with any near echoes. If the transmit signal is large (which it probably is) Then the receiver circuit must be protected against this voltage without loading the transmitter.

If it helps, imagine a transmit pulse of of over one hundred volts and a receiver with a voltage gain of more than 10,000. (This is an example from a diagnostic ultrasound machine.)