| In the field of sensing,people have been devoted to obtaining high-precision measurement results.With the improvement of photoelectric technology,laser sensing technology has become more and more important in this field with the advantages of non-contact,high accuracy,good stability,anti-interference and others.In recent years,there has been a laser self-mixing interference effect that modulates the output characteristics by feedback light,which not only has the half-wavelength accuracy of the traditional dual-optical path interference technique,but also has the advantages of compact structure,easy collimation and not requiring laser type which are widely used in the field of vibration,displacement,speed,medical sensing,etc.The paper first describes the concept and theoretical research progress of laser selfmixing interference effect,as well as its application progress in the field of sensing.Secondly,based on the FP three-mirror cavity model,the phase and power equations of the self-mixing interference system are derived.Based on this,a mathematical model is established,and on the basis of this model,the effects of different parameters on the output characteristics of the system are discussed through simulation.Then the principle of self-mixing interference to detect the acoustic wave is analyzed.According to the characteristics of the introduction of frequency doubling on the frequency spectrum after the self-mixing interference of acoustic wave vibration,the fundamental frequency of the self-mixed signal is extracted using equal interval fundamental frequency extraction algorithm.At the same time,due to the effect of noise in the actual self-mixed signal on the extraction of the fundamental frequency,the spectral subtraction method was introduced to reduce the noise.Based on the above principles,the feasibility is verified by simulation and experiment.A real-time acoustic wave sensor system based on laser self-mixing interference is designed,including hardware design and software design.The hardware design part is composed of a signal acquisition module and an analog-to-digital conversion module.The software part uses a virtual instrument platform,and MATLAB and LabVIEW mixed programming performs data processing and real-time display on the signals passed by the hardware part.The partially transmitted signals are used for data processing and real-time display.The system can measure the fundamental frequency of the target acoustic source in real time and the maximum error is not greater than 1 Hz,while the maximum error of traditional electronic sensing equipment is 2.5 Hz.The acoustic wave measurement method proposed in this paper has lower measurement error than traditional electronic measurement methods.Compared with professional spectrum analyzer measurement methods,this method has lower cost and more practicality while ensuring high accuracy.Meanwhile,the built-in structure that encapsulates the semiconductor laser and the photodetector provides the convenience and miniaturization of the system.Therefore,this method can become one of the important means to develop industrial abnormal acoustic detection and musical instrument tuning in the future. |
