Coupled Acoustic / Vibration Fiber Optic Sensors

Measurement of acoustic/vibration signal is a very important part in a sensing system,acoustic/vibration sensors have experienced many kinds such as the piezoelectricity,the optic fiber interferometers (OFI),optic fiber F-P interferometers,optic fiber grating. Based on these types of acoustic / vibration sensor,a novel coupling acoustic / vibration optic fiber sensor has been developed. Based on local coupling mode theory of graded index optic fiber wave guide,the variation regularity of coupling output light has been deduced when sound wave acts on single mode optic fiber coupler. And a new idea has been proposed that a novel sensor can be applied on detection of acoustic/vibration. The sensing element of sensor is the melting area of single mode coupler in which the feasibility of the new-type optic fiber sensor has been proved in experiment.In the course of theory analyses,acoustic/vibration signal acts on the coupling area of a coupler. There are two different actions-horizontal operation and vertical operation and two different transmissions-traveling wave and standing wave. The responses of the sensor analyzed with MATLAB shows that the length of coupling and the frequency of acoustic/vibration signal will influence the sensitivity of the sensor. Besides,each factor of parameter M influencing coupling-out amplitude of sensor has been summarized.In experimental,static response and frequency response of coupling acoustic/vibration optic fiber sensor have been analyzed. The results indicate that the response of the sensor to static pressure has high sensitivity. Because the resonant frequency of different materials and structure is different,the sensor has maximum sensitivity in specific frequency. The special frequency varies according to different materials. This result offers very easy method for the material analysis. Application studies approve that the sensor has large application markets. The applications include the measurement of acoustic/vibration signal,intelligent material and intelligent structure,the measurement of hydro-acoustics,ultrasonic inspection and the measurement of current rate of fluid.