光声效应及光声检测系统

七十年代以来,一门以光声效应为基础的光声检测技术得到了迅速发展, 正在形成一门新的光声学学科,光声效应是物质吸收了调制光能而产生声信号的一种由光能转变成热能、由热能转变成声能的一种效应,它早在1880年就为美国著名科学家A.G.贝尔发现[1]。然而,随着近年来激光技术,弱信号检测技术以及换能器制造技术的发展,又使这一古老的发现焕发了青春。 七十年代初,由于大气污染检测需要一种灵敏的检测器,促使人们对气体光声效应进行了大量的研究。由于激光技术为光声检测提供了单色、大功率、可调谐及准直的光源,使光声检测技术对气体的浓度(…     

基于光声技术的火灾气体探测系统设计

近年来，针对标识性气体的探测成为火灾探测技术中发展最活跃的领域之一。将可检测极低浓度的某一气体的光声检测技术应用于极早期火灾气体产物的检测是一个新的尝试，将可能实现高灵敏度、高可靠性的火灾探测。但常规光声气体检测设备结构复杂、价格昂贵，必须恰当的重新设计才能应用到火灾探测系统中。分析了该技术在火灾探测中应用的关键问题,并提出了一种利用光声腔和光源间的“自由吸收路径”进行测量的光声气体探测系统，避免了对光源的窄带滤波要求，实现了在线式的气体检测。起始状态下，光声腔密封有纯CO气体，吸收光源中4.6 μm的辐射，产生一定强度的初始光声信号；当火灾气体产物流经吸收路径时，其中的CO气体吸收使到达光声腔的光辐射在4.6 μm波长上发生衰减，导致光声信号减弱，这个信号的变化量就反映了吸收路径中的CO气体浓度。     

光腔衰荡光谱法在痕量气体检测中的应用

气体检测有气相色谱法、非色散红外法、电化学电极法、光声光谱法、半导体气敏电极法、催化燃烧法、热导法、光离子化法等。光腔衰荡光谱法(CRDS)是一种新型的气体检测方法。它从原理上不需要标准气体标定,是极具潜力的痕量气体参考级测量方法。CRDS又叫光腔衰荡激光吸收光谱法,是一种高     

基于长度可调T形光声腔和掺铒光纤激光器的光声光谱气体浓度测量系统

应用光声光谱原理设计了气体浓度测量系统。针对C2H2气体运用了掺铒光纤激光器作为光源。光声腔为新型长度可调T形一阶纵向共振式光声腔,调制频率为1099 Hz。将成熟的二次谐波检测技术作为信号处理的基本原理,采用三角波调制并得到受调制后光源输出信号曲线。将二次谐波系数与一次谐波系数的比值作为系统输出,并得到影响其因素的曲线关系。对不同浓度的乙炔气体的实验结果表明,该系统的检测灵敏度为9.634×10^-6,信噪比为41.52 dB。     

一种高灵敏度光声光纤SO2气体传感器的研究

基于气体光声效应原理，研究了一种高灵敏度光纤SO2气体浓度传感器。用染料激光器作为激励源，激励出光声信号，采用光纤位移传感器测量光声信号。设计了光学长程装置以提高光声腔的灵敏度。用此装置测量SO2气体浓度，给出了实验数据并对结果作了分析。     

液体光声效应及光纤水声探测技术的研究

利用液体的光声效应可以实现对液体成分含量的检测.将光纤水声探测技术与液体的声光效应相结合,是一项新的研究内容.本文介绍了液体光声效应产生的三种主要的机制,论述了液体光声效应的研究现状和在科研和生产中的应用.分析了光纤水声传感器用于光声效应中声信号检测的可行性.对各种光纤水听器的结构和原理进行了详细的介绍,对不同类型的光纤水声探测技术进行了讨论和比较,并预测了光纤水听器的发展前景.     

激光发声及其发声的机理

宽带调制的相关光声检测技术是兼有单频和脉冲光声检测特点的一种新的光声检测技术。在时域,它可以获得不同深度的信息,在频域,它可以得到很宽频率范围内的响应。 目前宽带调制技术主要有伪随机编码调制和线性调频两种。我们在实现了Lagrange序列伪随机编码调制的光声检测后,又进行线性调频技术的研究。理论和实验上均已证明线性调频信号的自相关函数比伪随机编码调制信号的自相关函数更逼近δ函数。本文将简要地介绍线性调频技术的原理及在薄膜热扩散率测定中的一些实验结果。线性调频技术在光声检测薄膜热扩散率中的应用@钱梦騄$同济大学…     

不同厚度样品的表面光洁度对光声信号的影响

采用光声室和压电陶瓷两种检测方式,研究了不同厚度的单晶硅表面光洁度变化对光声信号的影响。结果表明,样品越薄,随着样品表面光洁度变差,光声信号增加得越迅速。     

光声显微镜技术的研究进展

光声显微镜技术具有新兴的一种非侵害性的显微成像技术,具有高分辨率、高对比度、穿透深度高的优点。简要介绍光声成像技术机理,总结报道了国内外几种典型的光声显微成像方法和光声显微图像重建算法的发展历程及其最新进展,指出该技术是一种很有应用前景的医学检测方法。     

用光声信号飞越时间法对纯铜脉冲激光烧蚀的研究

利用脉冲激光束轰击金属样品表面时在周围空气中激发的光声信号研究了纯铜的激光烧蚀。实验中,用He-Ne探测光束偏转方法检测光声信号,并根据光声信号飞越时间随激光能量密度的变化测定了纯铜的脉冲激光烧蚀阈值。文中还给出了一种理论估计脉冲激光烧蚀阈值的较为实用的方法。纯铜的脉冲激光烧蚀阈值的实测值约为3.0 J/cm2,理论估计值为3.2 J/cm2。两者符合较好。结果表明,光声信号方法是测定纯铜的脉冲激光烧蚀阈值的一种简单可行的方法。     

Photothermal gas analyzer for simultaneous measurements of thermal diffusivity and thermal effusivity

In this paper, we describe a new, simple, and fast photothermal method for simultaneous measurements of two important gas thermal properties: thermal diffusivity and thermal effusivity. The method consists essentially in combining a photoacoustic cell and a thermal wave pyroelectric cell enclosed in a single compact gas analyzer. The photoacoustic cell is kept filled with synthetic air and sealed. The pyroelectric cell is also filled with synthetic air, and after some warm up time, the synthetic air is exchanged to the gas of interest. It is shown that the analysis of the transient and saturation signals of both photoacoustic and pyroelectric cells is capable of measuring the thermal properties with an accuracy of 3%. This particular capability of performing simultaneously the measurements of thermal diffusivity and thermal effusivity allows us to carry on the complete characterization of the thermal properties of gases.     

Generation of a Photoacoustic Signal in Two-Layer Transparent Samples on an Absorbing Substrate

Technical Physics Letters - A theory of generation of a photoacoustic signal in a two-layer transparent sample on an absorbing substrate to a buffer gas of a photoacoustic cell has been developed....     

Improved Open Photoacoustic Helmholtz Cell

This paper presents the design of an open photoacoustic Helmholtz cell in which high acoustic volumes with quarter-wave ducts act as high-impedance separators between the main Helmholtz cell structure and the exterior. As a result, penetration of the external acoustic noise into the cell was substantially reduced in comparison to earlier open Helmholtz cell designs. Although the presented cell is not windowless, the photoacoustic background signal resulting from the absorption of the light by the windows is significantly lower in comparison to standard Helmholtz cells. Such an effect was obtained by locating the windows not at the relatively small sample cavity, but at the acoustic buffers, for which the volumes are two orders of magnitude higher. The proposed cell is dedicated for gas or liquid measurements, and its design allows for constant flow of the fluid. Hence, it can be used in continuous, real-time photoacoustic measurements.     

Berührungslose Prüfung von Kunststoffen mittels photothermischer Wärmewellenanalyse

Remote Testing of Polymers with Photothermal Analysis of Thermal Waves After an introduction to thermal waves a comparison is made of photoacoustic detection methods (gas cell, piezoceramic) and photothermal detection arrangements (front surface and rear surface methods). Previously only photoacoustic methods have been applied to polymer related problems, while the advantages of photothermal measurements – remote and nondestructive evaluation – have been demonstrated on metals. The experimental part of this paper presents first steps to apply photothermal analysis of thermal waves to some problems of polymers: thickness measurement of thin layers; on-surface and subsurface defects; delamination of bonding and coating curing reactions; glass fibre content; orientation of fibres and molecules; aging processes. The present results indicate that the method can be used for nondestructive remote quality assurance of thin layers and foils. Further development is required to apply the method to nondestructive testing of thick walled components.     

Measurement of Thermal Effusivity of Human Skin Using the Photoacoustic Method

In order to understand heat transfer in the human body, information regarding the thermophysical properties of biological materials is required. It is preferable that these properties are evaluated by in vivo measurements. The photoacoustic method is a non-contact, non-destructive method of measuring the thermophysical properties of various materials. In this study, the photoacoustic method was applied to human skin, and an open-type cell for on-site measurements was used instead of the previously used closed-type cell. Measurements of the thermophysical properties of human skin were carried out, and reasonable values of the thermal effusivity of the skin were obtained. Differences between different body parts and individual variations in thermal effusivity were investigated.     

Photoacoustic Spectroscopy Analysis of Traditional Chinese Medicine

Chinese medicine is a historic cultural legacy of China. It has made a significant contribution to medicine and healthcare for generations. The development of Chinese herbal medicine analysis is emphasized by the Chinese pharmaceutical industry. This study has carried out the experimental analysis of ten kinds of Chinese herbal powder including Fritillaria powder, etc., based on the photoacoustic spectroscopy (PAS) method. First, a photoacoustic spectroscopy system was designed and constructed, especially a highly sensitive solid photoacoustic cell was established. Second, the experimental setup was verified through the characteristic emission spectrum of the light source, obtained by using carbon as a sample in the photoacoustic cell. Finally, as the photoacoustic spectroscopy analysis of Fritillaria, etc., was completed, the specificity of the Chinese herb medicine analysis was verified. This study shows that the PAS can provide a valid, highly sensitive analytical method for the specificity of Chinese herb medicine without preparing and damaging samples.     

In situ photoacoustic spectroscopic studies on heterogeneous catalysts under conditions of gas flow

An all-glass open photoacoustic cell through which gases can be passed without affecting the signal has been described. The cell has been characterized for various chopping frequencies and temperatures. Several heterogeneous catalytic reactions have been studied under conditions of gas flow at elevated temperatures and the potential application of this method in the field of heterogeneous catalysis has been pointed out. Communication No. 428 from the Solid State and Structural Chemistry Unit.