| There is an increasing kind of materials not only relating to the air quality andindustrial and agricultural production but also affecting the public health andproperties.Based on a set of perfect legal system, a trace materials detection system withhigh sensitivity, selectivityand fast detection speed is an ideal strategy which is able todetect the suspicious substance comprehensively and deeply so as to improve air quality,reduce production safety accidents as well as prevent terrorist bombing activities.Laserinfrared spectroscopy with the ability to detect gas, liquid and solid, has become a newfocus on the material detection and a new development direction because of theadvantages with high sensitivity and precision, independent on the quantities or qualityof objects and capacity of detecting bulk quantities.On the basis of the analysis of laser infrared spectroscopy trace materials detectiontechnology, the photothermal spectroscopy system based on the micro-cantilevermodified by carbon nanotube film (CNF) was proposed.In this dissertation, the analysesof the basic principle and the feasibility of photothermal spectroscopy detection systemwere carried out. Antheoretical model for the description of randomly distributed CNFthermal conductivity was established. The physical model of the photothermal responseof themicro-cantilever modified by CNF was established and the expression of theabove photothermal signal was deduced. The composite cantilever was tested afterbeing optimized, designed and fabricated.The optical and soft-hardware designs of theoptical fiber Fabry-Perot non-scanning correlation demodulator were completed as wellas the experiential prototype was produced. Whereafter the properties of the vibrationsensor including the stability and resolution were measured. And then, the photothermalresponses of micro-cantilever to the infrared laser were measured. The materialspectrum detection experiments for water vapor were performed, and the feasibility andapplication prospect of the system were verified. The main jobs are shown as follows.1) The research on the thermal conductivity of CNF was performed systematicallyand the heat conduction equation was deduced. The description of the effects of CNTs’thermal conductivity, length, contract conductance, volume fraction and density on theCNF thermal conductivity were obtained.2) Research on the steady and transient responses to the photothermal excitationwas carried out systematically.The physical model of steady and transient response under continuous and pulsed laser excitation was established, thus the expressions weregained.The analysis of the thermal sensitivity excited by infrared laser excitationwasperformed, which provided the theoretical basis for subsequent micro-cantilever designand experimental researches. And furthermore the expression of photothermal signalwas developed based on the analysis referred, which provide d the theoretical supportfor subsequent materials detection.3) The CNF structure was optimized and designed on the basis of the theoreticalanalysis of CNF’s thermal conductivity and micro-cantilever’s photothermal response.The CNF was fabricated and tested. Moreover design and fabrication of Si-basedcomposite micro-cantilever was completed.And last the CNF was transferred to themicro-cantilever sucessfully.4) The non-scanning correlation demodulation theory for the fiber opticalFabry-Perot sensor was derived. The relationship between the output light intensity andFabry-Perot cavity length was acquired when thehalogen lamp was used as the systemlight source. The fiber optical Fabry-Perot sensor composed of the optical part and thesoft-hardware part was designed. The software system was designed and the flow chartwas given. At last, the prototype of Fabry-Perot sensor was processed and its propertieswere tested, including the stability and resolution.5) The dynamic photothermal response to the pulse laser was tested using the fiberoptical Fabry-Perot sensor. The dynamic response characteristics performed as afunction of the pulse frequency, duty cycle, laser power and illuminated zone weremeasured, and the resultsindicated that the theory modal was correct. The laserparameters used in the experiment for material detection were determined according tothe test results.6) The experimental system for materials detection was set up and thephotothermal spectrum of H2O was obtained by the system. The linear relationshipbetween the photothermal spectroscopy signal and the H2O concentration at range of0.5%to2.5%in open environment was gained, and the linear collection coefficient was upto0.9985. Under the same experimental conditions, the100sets of photothermal spectraof the H2O were gained, and the largest deviation of the signal intensity was less than0.83%. The experimental results indicated that the photothermal spectroscopy system isfeasible in the materials detection. |
PDF Full Text Request