Devices and systems for transmitting information within a body are disclosed. An example system includes a signal generator configured for transmitting an acoustic interrogation signal, a sensor for sensing at least one parameter within the body and generating an electrical sensor signal, an acoustic transducer configured to convert a received acoustic interrogation signal into an electrical signal, and a switching element adapted to modulate a reflected acoustic wave from the acoustic transducer. The switching element is configured to controllably change the mechanical impedance of the acoustic transducer.