Distributed optical fiber sensing using point sensors
View Patent ↗Aspects of the present disclosure describe distributed optical fiber sensing systems, methods, and structures that advantageously employ point sensors that send sensory data/information over an attached, distributed optical fiber sensor without using a separate network or communications facility.
1. A distributed optical fiber sensing (DOFS) system comprising:
a length optical fiber cable;
a DOFS interrogator system in optical communication with the optical fiber cable; and
one or more point sensor systems in mechanical communication with the length of optical fiber cable;
wherein the one or more point sensor systems include: a sensor, an acoustic modulator, an acoustic vibration generator, and two timers configured such that a fixed time-interval transmission period is realized and one of the two timers triggers regular operations including data collection and the second timer triggers data transmission and a sum of the two timer's values is a constant value.
2. The DOFS system of claim 1 wherein the sensor is one selected from the group consisting of temperature sensor, vibration sensor, and strain sensor.
3. The DOFS system of claim 1 wherein the acoustic modulator converts digital data representative of an environmental condition sensed by the sensor into an acoustic-modulated signal.
4. The DOFS system of claim 1 wherein the acoustic vibration generator converts the acoustic-modulated signal to a mechanical vibration applied to the optical fiber.
5. The DOFS system of claim 4 wherein acoustic modulated signal is a frequency modulated signal.
6. The DOFS system of claim 5 wherein the frequency modulated signal incudes two frequencies f 0 and f 1 (waveform cos(2πf 0 t) and cos (2πf 1 t) used to represent binary ‘0’ and ‘1’ respectively.
7. The DOFS system of claim 6 wherein frequencies f 0 and f 1 are selected within Nyquist bandwidth, which is below ½ of the interrogator's optical pulse repetition rate.
8. The DOFS system of claim 7 wherein f 0 and f 1 are sufficiently spaced away from each other's harmonic frequencies and be selected to avoid field interference.
9. The DOFS system of claim 7 wherein each frequency-bit lasts for fixed time period T b , and the acoustic modulator uses 2{circumflex over ( )}n frequencies f 0 , f 1 , . . . f n-1 , to represent a symbol of n-bit.
10. The DOFS system of claim 9 wherein each frequency-bit is windowed.
11. The DOFS system of claim 5 wherein the frequency modulated signal included information encapsulated in frames, each frame having a preamble wherein the preamble is encoded at a fixed frequency.
12. The DOFS system of claim 11 wherein the preamble includes data indicative of a quiet period representing no mechanical vibrations.
13. The DOFS system of claim 12 wherein the frame is a fixed length.
14. The DOFS system of claim 12 wherein the frame is of variable length from one frame to another, including duplicate information.