Research On Pulse Wave Detection Based On Optical Microfiber Coupler

With the development of optics,optical fiber sensing technology has also made great progress.As a kind of compact structure,low cost,high monitoring accuracy,fast response and easy-made sensors,optical fiber sensors are more and more applied in the fields of biological,military,aerospace and engineering detection.Now wearable devices in the field of human body because of its strong anti-electromagnetic interference ability has shown increasing application value.Aiming at the shortcomings of current mainstream pulse sensors,such as high production cost and weak anti-electromagnetic interference ability,based on fiber tapering technology and the strong evanescent field characteristic of micro-nano fiber coupler,this paper proposes a pulse detection sensor chip with a specially designed packaging structure and establishes a blood pressure monitoring system based on dual-channel pulse signals.The research contents of this paper are as follows:（1）The basic theory of micro-nano fiber coupler is elaborated,including geometric model,coupling mode theory and interference sensing principle.The interference mode field and output spectrum characteristics of the micro-nanofiber coupler are simulated and analyzed.The free spectrum range of the transmission spectrum of the micro-nanofiber coupler decreases with the increase of the interference length,and decreases first and then increases with the decrease of the waist region diameter.When the waist region diameter decreases to the range of 1.6-1.7μm,the dispersion inflection point appears in the C-L band of the incident light.（2）The micronano fiber coupler was prepared by hydrogen and oxygen flame fusion tapering method,and its axial strain and bending strain characteristics were investigated experimentally.When the waist region diameter is 3-10μm,the axial strain sensitivity is about-12 pm/με.When the waist region diameter is less than 3μm,the dispersion inflection point appears,and the axial strain sensitivity of the coupler can reach the highest of-35 pm/με.The bending strain sensitivity of the 5μm lumbar coupler can reach 0.087d B/m-1 in the range of 0-9 m^-1.（3）Using the prepared reflective micro-nano fiber coupler,a package structure based on polydimethylsiloxane（PDMS）was designed and manufactured to form a pulse detection sensor chip,and the mechanical simulation was carried out.The spherical design of the top of the structure in contact with the pulse surface can effectively alleviate the strict alignment of the sensor chip with the human artery,while the epoxy resin base with the perforated design can enhance the sensitivity of the sensor response.After performance test,pulse detection sensor in the range of 0-1 KPa,sensitivity can reach-0.682 KPa^-1,the response time is 35 ms,and it still has good pressure response after 2500 pressure cycles,which can effectively obtain human high-fidelity pulse signal.（4）The pulse detection sensor chip was embedded in the elastic wrist band to build a dual-channel pulse wave detection system,which could accurately and effectively obtain the dual-channel pulse signals of human radial and brachial arteries at the same time.Based on this,the support vector regression（SVR）human blood pressure prediction model was constructed.The mean deviation（MD）and standard deviation（SD）of the systolic blood pressure（SBP）prediction model were 0.08 and 1.13 mm Hg,respectively,and which the diastolic blood pressure（DBP）prediction model were-0.35 mm Hg and 1.25 mm Hg,all meeting the American Medical Device Association（AAMI）standard of 5±8 mm Hg.The continuity and stability of the blood pressure prediction model are tested,which can accurately reflect the change trend of blood pressure in a day and the blood pressure before and after exercise.