High-sensitivity FBG microphone with static pressure equalization and optimized response

We present a high-sensitivity fiber Bragg grating(FBG)-based microphone with a flat response and static pressure equalization. A very high dynamic sensitivity of the microphone is achieved by a pressure sensing structure based on a carbon fiber diaphragm. Static pressure equalization is realized by a balance structure with a capillary glass tube. The resonances of the sensor are suppressed by air damping structures, and a broadened flat response is achieved. An acoustic-solid interaction model was used to analyze the response characteristics of the microphone. An experimental prototype was produced and tested, and the results are well consistent with the design.The tested sensitivity was-10 d B re 1 pm/Pa from 10 Hz to 2.5 kHz with a fluctuation of less than ±1.5 dB.Combined with the phase-generated-carrier-based coherent detection scheme, the microphone can achieve a sound resolution of the milli-pascal level. The static pressure sensitivity is measured to be-0.27 pm/atm, which is 100 dB lower than the dynamic sensitivity.     

FP cavity and FBG cascaded optical fiber temperature and pressure sensor

A fiber Bragg grating(FBG) and Fabry–Perot(FP) cavity cascaded fiber sensing system was manufactured for temperature and pressure sensing. Temperature sensing as high as 175°C was performed by an FBG for the linear variation of an FBG wavelength with temperature. After the temperature was sensed, the demodulation system can find the original FP cavity length and its pressure and cavity length correlation coefficient; thus, the ambient pressure would be calculated. The sensing pressure can be as high as 100 MPa with a repeatability of 1/10,000 and high stability. This kind of fiber sensor has been used in the Shengli Oil Field.