Phase Based Sensing

• US 20100067018A1
• Filed: 03/10/2008
• Published: 03/18/2010
• Est. Priority Date: 03/14/2007
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Crickmore, Roger Ian, DeFreitas, Jolyon
• Granted Patent: US 8,564,786 B2
• Time in Patent Office: Days
• US Class Current: 356/477
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: G01D 5/35383 using multiple sensor devices using multiplexing techniques
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125

Abstract

Interrogation of a phase based transducer is performed by comparing the state of the transducer at two points in time to determine the rate of change with time of the measurand represented as a phase change. The rate of change, or derivative of the phase change typically has a much smaller amplitude than the signal itself, and the derivative measurement can therefore be thought of as a low sensitivity measurement to be used instead of or in combination with the normal signal measurement having higher sensitivity. In this way, large amplitude signals which might otherwise be subject to overscaling effects can be measured more effectively. For a signal with the majority of its energy centred at approximately 800 Hz, for example, the derivative of that signal will typically be attenuated by 60 dB with a period between the two measurement times of 200 ns.

Claims

1. A method of interrogating a phase based transducer, said transducer providing a change in phase of signal propagation in response to a sensed parameter, said method comprising:

receiving a signal propagated through said transducer,

comparing the signal at a point representing the state of the transducer at a first time, and at a point representing the state of the transducer at a second time, and

determining from said comparison a measure of the rate of change of phase with time of said signal.

2. A method according to claim 1, wherein comparing the signal comprises combining a delayed version and an undelayed version of the received signal.

3. A method according to claim 2, wherein the method comprises passing the signal through an output interferometer.

4. A method according to claim 1, wherein comparing the signal comprises sampling the signal at a plurality of different times, and comparing said sampled values.

5. A method according to claim 1, further comprising obtaining a value of phase based on said measured rate of change of phase.

6. A method according to claim 5, wherein obtaining a phase value comprises integrating said measured rate of change of phase.

7. A method according to claim 1, further comprising determining a measure of phase from said received signal.

8. A method according to claim 7, wherein said measure of phase and said measure of rate of change of phase are determined substantially simultaneously.

9. A method according to claim 7, comprising obtaining a phase value by combining the said measure of phase from said received signal, and the said measure of rate of change of phase.

10. A method according to claim 1, wherein the signal propagated through the transducer is a pulsed signal.

11. A method according to claim 10, wherein the signal includes at least two pulses having different frequencies.

25. A system or method according to claim 1, wherein the signal received from the transducer has a carrier frequency, and wherein the magnitude of the peak instantaneous frequency of said signal is greater than or equal to the magnitude of the carrier frequency.

27. A or method for interrogating a fibre optic seismic array according to claim 1.

28. A method according to claim 27, for recovering overscaled seismic signals returned from said array.

12-14. -14. (canceled)

15. A system for interrogating a phase based transducer, said transducer providing a change in phase of signal propagation in response to a sensed parameter, said system comprising:

a receiver for receiving the signal output from said transducer in response to an input signal,

and a phase detector including a delay for producing a delayed version of said output signal, and adapted to combine said output signal with said delayed output signal to determine a measure of the rate of change of phase of said output signal.

16. A system according to claim 15, further comprising a signal source for providing an input signal to said transducer.

17. A system according to claim 16, wherein said input signal comprises at least two pulses.

18. A system according to claim 17, wherein the delay between said two input pulses is equal to the delay of the phase detector.

26. A system according to claim 15, wherein the phase based transducer is one of a hydrophone, a geophone or an accelerometer.

19. A method for interrogating a phase based transducer, said transducer providing a change in phase of signal propagation in response to a sensed parameter, said method comprising:

receiving an output signal from said transducer in response to said input signal, and

sampling said received output signal at a plurality of different times and using said samples to determine a measure of the rate of change of phase.

20. A method according to claim 19, wherein said output signal is a pulsed signal, and wherein a plurality of samples are taken from each pulse.

21. A method according to claim 20, wherein at least three samples are taken from each pulse.

22. A method according to claim 20, wherein the duration of a sampled pulse is less than or equal to 200 ns.

23-24. -24. (canceled)

29. A method for recovering an overscaled signal returned from a fibre optic phase based sensor, the method comprising:

measuring the rate of change of phase of said overscaled signal, and

using said measure to re-construct the overscaled signal.

30. A method according to claim 29, further comprising measuring the phase of said overscaled signal

31. A method according to claim 30, wherein said measurement of phase and said measurement of rate of change of phase are performed substantially simultaneously.

32. A method according to claim 30, wherein re-constructing the overscaled signal comprises combining said measure of phase and said measure of rate of change of phase.

33. (canceled)