Study On Acoustic Sensing Characteristics Of Microfiber Knot Resonator

With the widespread application of acoustic sensors in military applications,national defense security,medical diagnosis,aviation detection,industrial manufacturing,daily life and other fields,acoustic sensors have become an indispensable part of modern social development.By using fiber optic acoustic sensors,multi-point acoustic measurements can be carried out in complex electromagnetic fields.The fiber optic acoustic sensor has the advantages of high sensitivity,compact structure,and electromagnetic interference resistance.It also has the potential of embedded measurement in narrow space.The microfiber ring resonator,which combines optical fiber and nanotechnology and is made of the micro-nano optical fiber knotted rings,has the advantages of small size,low cost and strong evanescent field,optical resonance plays an important role in resonator.It can sense the deformation of resonator,so microfiber knot resonator can be used as acoustic sensor.In this paper,a covered PDMS composite microfiber knot resonator acoustic sensor with sandwich structure is proposed.The sensor uses a flat glass with a square hole in the middle as the substrate structure,and the microfiber knot resonator is prepared and packaged with two layers of PDMS film.Firstly,the research of the microfiber ring resonator is introduced,and the research of the microfiber knot resonator in acoustic sensing is emphasized.Secondly,the basic optical transmission theory of the micro-nano optical fiber is introduced.And the simulation model of micro-nano optical fiber with different diameter and different refractive index cladding is built by using simulation software,the effective mode refractive index and core energy ratio are analyzed.Then the basic transmission theory and performance index of the microfiber knot resonator and the sound pressure sensing principle of the microfiber knot resonator are introduced.Then,the heating melt taper method of micro-nano optical fiber is introduced,and the hydrogen-oxygen flame heating taper platform used in this paper is also introduced.The microfiber knot resonator is prepared by drawing the uniform diameter micro-nano optical fiber using the built taper platform,knotting and continuously reducing the ring diameter,then we design and package the structure of PDMS-based micro-and the microfiber knot resonator to form a sandwich structure of PDMS-based composite the microfiber knot resonator acoustic sensor.Finally,an optical testing system and an air-acoustic and underwater-acoustic testing system are set up,and the performance of the microfiber knot resonator is tested and analyzed.The results show that the Q value of the cavity is 10~4and the full width of the cavity is 0.13 nm.The sensor has good response at 100Hz-10 k Hz air sound frequency,and the sensitivity reaches 0.92 m V/Pa at 1 k Hz air sound frequency,and the minimum detectable sound pressure is 48.7 d B.The underwater acoustic frequency response range is 10 Hz-1 k Hz,and the underwater acoustic signal sensitivity is better than-185 dB.