Patent ID: 7994932

Claim:
An acoustic telemetry apparatus for communicating digital data from a down-hole location through a borehole to the surface comprising: an acoustic channel terminated at a down-hole end by a reflecting terminal; an acoustic wave generator located at the surface and providing an acoustic wave carrier signal within said acoustic channel, wherein said signal is continuous; a modulator which is configured to encode said digital data as phase modulation of the reflected carrier wave, and which comprises a resonator located in the vicinity of the reflecting terminal point at said down-hole location and a valve to open and close access to the resonator to modulate phase of said carrier wave in response to a digital signal, wherein the modulator and the reflecting terminal form a phase shifting reflector for the carrier wave, switchable between a first state in which the valve closes access to the resonator and closes the downhole end of the acoustic channel and reflects the carrier wave and a second state in which the valve opens access to the resonator which closes the downhole end of the acoustic channel and reflects the carrier wave with a shift in phase relative to reflection by said first state; and one or more sensors located at the surface adapted to detect information encoded as phase modulation of acoustic waves traveling within said acoustic channel and connected to a decoding unit adapted to convert the detected information into a digital signal.