| As a non-contact measurement,optical sensing measurement has the advantages of good stability,anti-interference and high precision,and plays an important role in the field of sensing measurement.Laser interferometry is widely used in many optical detection and sensing methods.In recent years,the rapid development of optical sensing measurement technology based on laser self-mixing interference(SMI)has attracted wide attention of scholars at home and abroad.The main advantages of this technique are compact structure,simple system and easy alignment.This paper builds a medical signal sensing system based on SMI,the system can realize non-contact detection of human pulse wave.Meanwhile,ELM was introduced to construct mathematical model to predict human blood pressure.Firstly,this paper reviewed the research background of laser self-mixing effect,summarized the historical development process of theory research and current status of application research.Secondly,this paper expounded the mechanism of laser self-mixing interference based on F-P three-mirror cavity model,established the mathematical model of the system by detailed formula derivation and analyzed the parameters and their influence on SMI system by numerical simulation.Thirdly,a new detection scheme for self-mixing interferometry using two photodiodes for implementing a differential acquisition is introduced.Meanwhile,this paper introduces the principle of Extreme Learning Machine and expounds the concrete process of the realization of ELM algorithm.The physiological basis of pulse wave and blood pressure is analyzed,and the feasibility of predicting blood pressure through pulse wave is explained.Then build the hardware platform of self-mixing detection.Finally,the algorithm flow of the system is described in detail,and the prediction error is given.The experimental results show that this method has a high prediction accuracy for the blood pressure value of human body. |
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