Passive Transducer
A passive transducer requires energy to be put into it for the transducer to produce the required transduction.
They utilize the principle of controlling a dc excitation voltage or an ac carrier signal.
For example: a variable resistance placed in a Wheatstone bridge in which the voltage at the output of the circuit reflects the physical variable.
Here, the actual transducer is a passive circuit element but needs to be powered by an ac or dc excitation signal.