What is the vibration response frequency of fiber optic acoustic sensing (DAS)?
The vibration response frequency of fiber optic acoustic sensing (DAS) is determined by the repetition frequency of the laser.The actual vibration response frequency of DAS has a theoretical value of half the repetition frequency. For example, if you set the repetition frequency to 20kHz, then the actual vibration frequency response will be 10kHz in theory.
Can the repeat frequency be set arbitrarily?
Certainly not to be set at random. The re-frequency rate is limited by the actual length of the fiber optic cable. The DAS system requires that after a pulse is sent out and until it is received back, no more pulses can be sent out within this time period, or it will lead to data errors.
Therefore, the maximum number of times the re-frequency rate can be set is limited by the length of the fiber optic cable, if the length of the fiber optic cable is short, the re-frequency rate can be set to a large number of times, if the length of the fiber optic cable is very long, then the repetition frequency has to be set to a small number of times. The maximum repetition frequency = 10^8/length of the fiber optic cable is evaluated by this equation.
What is the low frequency response?
We tested with the PZT and were able to respond as low as 1Hz, which is sufficient for use in common vibration monitoring scenarios. The response frequency of low frequency is limited by the laser. If the laser performance is good enough, then theoretically it can be lower. Of course, such a laser may be very, very expensive.
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