CAJ | 학술논문

光声光谱法是基于红外吸收光谱原理的一种高灵敏度的微量气体探测技术.它使用声共振腔来实现微弱声信号的共振放大.通过调节激光的调制频率,当它等于腔的某个共振频率时,在腔内形成声驻波,而腔本身的作用相当于一声放大器.共振腔的放大作用取决于当前被激活的共振模式、腔的品质因素、声传感器的状态以及电磁辐射与腔共振模式的耦合作用.值得关注的是,红外激光相对于声共振腔的入射方位不同则激励产生的光声信号幅值也不同.采用理论推导与数值计算相结合的方法,以圆柱形光声池为例,研究了径向共振模式下耦合系数受激光入射方位的影响.研究表明,激光入射角在O～π/2范围变化时耦合系数存在2个零点和2个极大值:入射角为0或tan~(-1)(0.859 2×2R/L)时,耦合系数为零而径向共振失效;入射角为tan~(-1)(0.556 8×2R/L)或tan~(-1)(2R/L)时,耦合系数极大而径向共振最强.此处R为池径而L为池长.结果呵用于指导光声池结构优化设计与安装调试,增强光声法检测微量气体的信号幅值,提高检测灵敏度.
광성광보법시기우홍외흡수광보원리적일충고령민도적미량기체탐측기술.타사용성공진강래실현미약성신호적공진방대.통과조절격광적조제빈솔,당타등우강적모개공진빈솔시,재강내형성성주파,이강본신적작용상당우일성방대기.공진강적방대작용취결우당전피격활적공진모식、강적품질인소、성전감기적상태이급전자복사여강공진모식적우합작용.치득관주적시,홍외격광상대우성공진강적입사방위불동칙격려산생적광성신호폭치야불동.채용이론추도여수치계산상결합적방법,이원주형광성지위례,연구료경향공진모식하우합계수수격광입사방위적영향.연구표명,격광입사각재O～π/2범위변화시우합계수존재2개영점화2개겁대치:입사각위0혹tan~(-1)(0.859 2×2R/L)시,우합계수위령이경향공진실효;입사각위tan~(-1)(0.556 8×2R/L)혹tan~(-1)(2R/L)시,우합계수겁대이경향공진최강.차처R위지경이L위지장.결과가용우지도광성지결구우화설계여안장조시,증강광성법검측미량기체적신호폭치,제고검측령민도.
Photoacoustic detection of trace concentrations of gases is one of the most sensitive techniques of infrared absorption spectroscopy. High-sensitivity photnacoustic detectors apply an acoustic resonator for the amplification of the weak photoacoustic signal If the modulation frequency coincides with one of the resonance frequencies of the chamber, a standing acoustic wave is excited and the system works as an acoustic amplifier. The amplification of the resonator relies on the acting mode, quality fac-tor, nature of microphone, and the coupling between electromagnetic radiation and the stand wave resonance mode. With differ-ent incidence orientation of the modulated IR laser relative to acoustic chamber, the sound pressure magnitude of resonance mode varies. The influence of different laser incidence orientation on the coupling coefficients of radial resonance mode of cylindrical photoacoustic cells was investigated by both theoretical deduction and numerical computation method. It is concluded that the coupling coefficients have two zeros and two maximums when the laser incidence angle varies from 0 to π/2. When the incidence angle is 0 or tan~(-1) (0. 859 2 × 2R/L), the coupling coefficients are zeros and the radial resonance is invalid. When the incidence angle is tan~(-1) (0. 556 8×2R/L) or tan~(-1) (2R/L), the coupling coefficients are the maximums and the radial resonance is the strongest. Here R is the radius and L the length of the cell. The results therein before give some theoretical guidelines for photo-acoustic cell designing, optimizing, installing and adjusting, and for improvement of detection sensitivity in trace gas detectors through maximal excitement of radial modes in cylindrical acoustic cells.