Research On Flexible Self-Mixing Microfiber Sensor And Wearable Bio-Signal Detection

A flexible wearable sensor is a new sensor technology that can be worn on the surface of the human body to carry out the real-time monitoring of human physiological parameters,or the detection of motion state.The technology is biocompatible,non-invasive and skinapplicable.It is also able to adjust to various body forms and patterns of motion,and it has been extensively researched and applied in the fields of medical health monitoring and humanmachine interaction control.In order to overcome the problems of insufficient insulation,electromagnetic interference and parasitic effects of electrical sensors,many optical wearable sensors have been proposed by researchers in recent years,but there are still some challenges in terms of sensitivity,stability and reliability due to the limitations of sensing mechanism and fiber fragility,etc.Therefore,this paper proposes a flexible wearable sensing scheme based on microfiber self-mixing interference according to the characteristic demand and development trend during wearable,and takes human bio-signal as the research object,conducts a full-scale study of human bio-signals.The following describes the specific study and results:Firstly,this paper delves into the fundamental concept of optical waveguide based on microfiber,examining Maxwell’s system of equations to determine the distribution of the microfiber mode field.Subsequently,the electric field and energy distribution characteristics of the bending microfiber are examined,as well as the refractive index distribution and radiation mode conversion conditions.Then,the intrinsic mechanism of the self-mixing interference effect is comprehensively described from the three-mirror cavity model and the elastodynamic model.Theoretically,deriving the optical power output equation of the sensor to provide the theoretical foundation for subsequent measurement experiments,the detection principle based on self-mixed interference of the microfiber is finally examined.Secondly,a flexible wearable optical sensor based on micro and nano optical fiber selfmixing interference is proposed to meet the demand of human health management for real-time monitoring of cardiovascular and cerebrovascular information.Firstly,the pulse transit time(PTT)based blood pressure detection algorithm is investigated,and the relationship between PTT and blood pressure,i.e.,Systolic blood pressure(SBP)and Diastolic blood pressure(DBP),is modeled.The properties of the microfiber were simulated by commercial finite element simulation software,and the fabrication process of the microfiber was described in detail.Then the microfiber was sensitized and encapsulated with polydimethylsiloxane(PDMS)to make a flexible wearable sensor.Verification of the feasibility of the scheme through experiments was achieved by constructing and applying an experimental platform to the investigation of physiological signal detection.The results of this experiment fulfilled the error requirements of the American Association for the Advancement of Medical Instrumentation(AAMI)for noninvasive blood pressure monitors,with only one exception,and only use one sensing fiber can achieve multiparameter monitoring of pulse,heart rate and blood pressure,and,due to its high sensitivity,it can also obtain high-fidelity pulse wave signals at the fingertips.Finally,in order to further extend the flexible wearable optical sensing based on selfmixing interference of microfiber and apply it successfully in human wearable sensing detection system,this paper proposes a way to arrange the micro-nano-fiber in PDMS film with wave-like embedding,which results in a larger dynamic range and stronger bending sensing characteristics.The preparation process of the flexible wearable sensing film is further optimized and studied to make a soft and stretchable optical sensor.The flexible wave-like microfiber self-mixing interference of the evil wearable sensor can achieve static and dynamic haptic responses such as feathers,water drops and breeze,as well as human motion recognition of joint bending and grasping movements.The sensor not only further expands the application range in human bio-signals,but also provides new ideas and perspectives for the advancement of intelligent healthcare.Moreover,it presents a promising prospect for future wearable optical devices and haptic sensors for dexterous manipulators.