Research On Multi-channel Optical Fiber Acoustic Wave Sensing System And Noise Reduction Algorithm

Acoustic wave is an important carrier of information.Acoustic wave sensing technology has huge application requirements in various fields such as oil pipeline leakage,equipment health monitoring,and medical diagnosis.Traditional acoustic wave sensors are mostly electronic acoustic wave sensors.With the in-depth research on optical fiber sensing technology,various optical fiber acoustic wave sensors have developed rapidly.Compared with the electronic acoustic wave sensor,the optical fiber acoustic wave sensor is small in size,light in weight,high in detection sensitivity,strong in antielectromagnetic interference ability,and can be used in extremely harsh environments.Moreover,the smaller transmission loss of the optical fiber enables the optical fiber acoustic wave sensor to achieve high Quality telemetry remote sensing.In recent years,various principles and structures of optical fiber acoustic wave sensors have been reported.Among them,the optical fiber Fabry-Perot acoustic wave sensor is an interferometric optical fiber acoustic wave sensor,which has simple structure,small size,high sensitivity and bandwidth response.Advantages,it has broad application prospects in the field of acoustic signal sensing and detection.At present,the application of optical fiber FabryPerot acoustic wave sensors still has certain limitations: On the one hand,optical fiber Fabry-Perot acoustic wave sensors are difficult to meet the requirements of multi-point detection or large-scale networking due to their weak multiplexing ability.Application requirements;on the other hand,the optical fiber acoustic wave sensor demodulation system is often composed of a large number of electrical and optical devices,and there is a large amount of noise.In addition,due to the high sensitivity of the optical fiber acoustic wave sensor,the dynamic range of its response is small.Therefore,environmental noise is likely to cause interference to the sound wave detection effect of the system.In practical applications,the disturbance of the external air flow will also form a large impact noise,which makes the high-sensitivity optical fiber acoustic wave sensor appear saturated,which greatly affects the performance of the optical fiber acoustic wave sensor.The detection capability also greatly reduces the quality of the sensor's sound sensing and restoration.This thesis mainly focuses on the problems of noise interference filtering and effective speech signal extraction in different application scenarios faced by the multipoint detection fiber Fabry-Perot acoustic wave sensing system in practical applications.The main work content and results are as follows:(1)Introduced the main structure and working principle of the fiber Fabry-Perot acoustic wave sensor,including the standard Fabry-Perot cavity multi-beam interference theory and the double-beam interference theory,analyzed the optical fiber Fabry-Perot The principle and limitations of the traditional intensity demodulation scheme of the sensor.At the same time,the three-wavelength adaptive demodulation method of the multi-channel optical fiber Fabry-Perot acoustic wave sensor system used in this thesis is introduced.The three-wavelength adaptive demodulation method is used in the optical fiber Fabry-Perot sensor.The signal demodulation can overcome the influence of environmental changes on the operating point of the sensor,so that the sensor has better environmental adaptability.(2)Designed and built a multi-channel optical fiber acoustic wave sensing system and introduced two aspects of optical system construction and electrical demodulation system.The system can realize multiple optical fiber Fabry through space division multiplexing.The signal of the Perot acoustic wave sensor is demodulated at the same time.The thesis designs the optical and circuit system,builds the system prototype,and successfully realizes the signal acquisition and demodulation of the multi-channel optical fiber Fabry-Perot acoustic wave sensor.(3)Introduced the speech noise reduction algorithm based on digital signal processing,focusing on the spectral subtraction with low computational complexity and good real-time performance,aiming at the complex environmental noise of multi-channel optical fiber acoustic wave sensing system in multi-point detection Question,a new fusion algorithm combining spectral subtraction and wavelet packet threshold denoising is proposed.On the one hand,this algorithm can well solve the residual problem of "music noise" that is common in traditional spectral subtraction denoising.On the other hand,it can match the denoising algorithms with different wavelet basis functions to the optical fiber acoustic wave sensors used in different detection environments.,It can improve the anti-interference and de-noise ability of the sensor probe against a variety of specific environmental noises.(4)Aiming at the problem of high-energy impact noise caused by the strong background noise or strong airflow disturbance in the external detection environment of the acoustically sensitive vibrating film of the optical fiber Fabry-Perot acoustic wave sensor,the thesis proposed based on the Hilbert transform and Short-term energy analysis impulse noise removal algorithm,which combines the idea of median filtering in heart sound signal extraction and image processing.The filtering results of multiple sets of test samples show that the noise filtering algorithm proposed in the thesis can effectively filter the impulse noise in the detection signal,and at the same time,as much as possible to ensure the integrity of the audio information collected by the sensor.