Hydrogen Sensor Based On Surface Plasmon Polaritons

With the rise of the third energy revolution,hydrogen energy is developing rapidly as a clean,efficient and renewable new energy.However,due to the explosive limits of hydrogen in air range from about 4.65-74.5%,the safety of hydrogen has become an urgent problem to be solved before the large-scale use of hydrogen energy.In order to be able to detect possible hydrogen leakage in time during hydrogen storage and transportation,and avoid safety accidents caused by hydrogen explosions,the hydrogen energy industry has a huge demand for hydrogen sensors with high sensitivity,good selectivity,and rapid response.Hydrogen sensors can be classified into catalytic,electrochemical,optical and other types depending on their operating principle.Currently,the mainstream type of hydrogen sensors in use is the electrochemical hydrogen sensor,which has high sensitivity and low power consumption.The optical hydrogen sensor is an intrinsically safe sensor because it does not rely on electrical signals,does not release high heat during the sensing process,and has no safety risk in a hydrogen environment.Compared with traditional hydrogen sensors,optical hydrogen sensor is considered to have broad application prospects in the future.The hydrogen sensor based on surface plasmons(SPs)is an optical sensor that uses surface plasmon resonance(SPR)to detect hydrogen,and has many advantages such as high sensitivity.The essence of SPs is a phenomenon in which free electrons in a metal oscillate collectively under the action of an external electromagnetic field.SPs usually exists at the interface between the noble metal and the dielectric,and is a localized surface electromagnetic wave mode caused by the SPR phenomenon,which decays exponentially with depth in the direction perpendicular to the interface.Since the SPR phenomenon is highly sensitive to small changes on the metal surface,the refractive index of the dielectric and the optical properties of the metal will affect its resonance absorption,so highsensitivity sensing of hydrogen can be achieved by using the palladiumbased hydrogen sensitive film(PHF).This thesis mainly studies the basic principle of hydrogen sensor based on SPs,then discusses the cross-sensitivity caused by the volume expansion of PHF in hydrogen and the difficulty of integration and miniaturization of conventional angle scanning hydrogen sensors.In order to solve the above problems,this thesis designs and optimizes a highsensitivity hydrogen sensor based on fiber-optic surface plasmon resonance(FO-SPR)and a highly integrated hydrogen sensor based on inverse surface plasmon polaritons(ISPPs).The main content and research of this thesis are as follows:1.Design a high-sensitivity hydrogen sensor based on FO-SPR.When the palladium film is exposed to the hydrogen environment,hydrogen molecules will adsorb and move to the surface of the palladium film and split into hydrogen atoms to enter the palladium lattice,and the optical properties of the palladium film will change with the hydrogen absorption reaction.This characteristic makes PHF an important hydrogensensing material,but in addition,the palladium lattice expansion also causes the volume expansion of PHF,which is generally regarded as a disadvantageous factor that brings cross-sensitivity.In this thesis,a high-sensitivity hydrogen sensor based on FO-SPR is proposed.The optical property change and volume expansion of PHF are both considered in the structural design and parameter optimization,and the cross-sensitivity caused by the volume expansion of PHF is avoided.The sensitivity of the sensor is 4.67 nm/%in the concentration range of 03%.In addition,the sensor is exceptionally sensitive at low concentrations(less than 1%)of hydrogen gas and can reach a sensitivity of 7 nm/%.2.Design a highly integrated hydrogen sensor based on ISPPs.At present,the existing ISPPs hydrogen sensors are all angle scanning sensors.Since the angle scanning sensor needs to change its incident angle in real time within a detection period,it generally has a mechanical movable device,which makes it difficult to achieve integration and miniaturization.In addition,the response time of the angle scanning sensor is also affected by the scanning period.This thesis proposes an angular scanning sensor structure that does not require motors or other movable structures.The sensor integrates the grating used to excite surface plasmon polaritons(SPPs)on the palladium film.SPPs excited by grating coupling is decoupled by the Kretschmann configuration,and the corresponding hydrogen concentration can be obtained by monitoring the deflection angle of the outgoing light.According to the simulation results,within the concentration range of 04.6%,the emission angle of the sensor will change by 2.33° for every 1%increase in the hydrogen concentration,and the intensity of the emitted light at a fixed angle will decrease by 1.55%.