基于半导体激光器的乙炔气体光声光谱检测及其定量分析

油中溶解乙炔是变压器等油浸式电气设备早期放电性故障的重要特征气体。基于半导体激光器的光声光谱传感技术具有灵敏度高,选择性好等优点,能很好地应用于微弱气体检测中。论文构建了基于分布反馈半导体激光器光声光谱检测装置,并分析了光声池的特性参数;实验研究了光声信号与激光功率、乙炔气体浓度之间的关系;并借助激光器的波长调制特性,研究了乙炔分子在近红外区第一泛音带1.5μm附近的光声光谱;提出了一种基于最小二乘回归的光声光谱定量分析方法。理论和实验结果为乙炔的光声光谱在线检测及高灵敏度可调谐光声光谱仪的设计提供了参考。     

PROCESSING OF WEAK PHOTOTHERMAL SIGNALS FROM THE OPTOTHERMAL WINDOW (OW) CELL; APPLICATION TO THE DETERMINATION OF AMMONIUM ION IN WATER

Abstract

The optothermal window (OW) cell is a compact photothermal device similar to an open photoacoustic cell. Using the c.w. He-Ne laser for excitation, and a piezoelectric transducer, the concentrations of ammonium ion (range 2 to 400 mmol/m³) in water were determined via the measurement of the amplitude of the OW signal. Although theoretical signal phase saturates in case of weak absorption, it was demonstrated here that at specific modulation frequencies the uncorrected signal phase carries spectrophotometric information as well. This is due to the fact that the phase of the background signal is shifted relative to that of the absorption signal. Simpler calibration procedure is an advantage in phase measurements.     

New photoacoustic cell design for studying aqueous solutions and gels

A new photoacoustic (PA) cell design, which is particularly suitable for investigations of liquids, gels, and outgassing samples is presented. The setup is based on a PA cell of only 78.5 mm(3) volume, which is sealed on the sample side with either a 163 μm thick chemical vapor deposition diamond window or a 3.91 μm thin diamond membrane. This design offers great advantages compared to traditionally used open-ended PA cells especially when investigating volatile compounds. The new PA cell design is particularly interesting in the studies of biological samples characterized by a high water content. The performance was demonstrated with mid-infrared PA measurements of glucose in aqueous solutions using a tunable quantum-cascade laser as a light source. A detection limit of 100?mg/dl (SNR = 3) has been achieved. Furthermore, the spectral changes of glucose dissolved in water caused by mutorotation have been monitored time-resolved.     

Nonlinear behavior of micro bubbles under ultrasound due to heat transfer

We investigated the nonlinear behavior of a microbubble under ultrasound, taking into account the heat transfer inside the bubble and through the bubble wall. The polytropic relation, which has been used for the process of pressure change depending on the volume variation of ideal gases, cannot properly treat heat transfer involving the oscillating bubble under ultrasound. In this study, a set of solutions of the Navier-Stokes equations for the gas inside the bubble along with an analytical treatment of the Navier-Stokes equations for the liquid adjacent to the bubble wall was used to treat properly the heat transfer process for the oscillating bubble under ultrasound. Entropy generation due to finite heat transfer, which induces the lost work during bubble evolution, reduces the collapsing process and considerably affects the nonlinear behavior of the bubble.     

Highly depth-resolved chirped pulse photothermal radar for bone diagnostics

A novel chirped pulse photothermal (PT) radiometric radar with improved sensitivity over the conventional harmonically modulated thermal-wave radar technique and alternative pulsed laser photothermal radiometry is introduced for the diagnosis of biological samples, especially bones with tissue and skin overlayers. The constraints imposed by the laser safety (maximum permissible exposure) ceiling on pump laser energy and the strong attenuation of thermal-wave signals in tissues significantly limit the photothermally active depth in most biological specimens to a level which is normally insufficient for practical applications (a few mm below the skin surface). A theoretical approach for improvement of signal-to-noise ratio (SNR), minimizing the static (dc) component of the photothermal signal and making use of the photothermal radiometric nonlinearity has been introduced and verified by comparing the SNR of four distinct excitation wave forms (sine-wave, square-wave, constant-width and constant duty-cycle pulses) for chirping the pump laser, under constant exposure energy. At low frequencies fixed-pulsewidth chirps of large peak power were found to be superior to all other equal-energy modalities, with an SNR improvement up to two orders of magnitude. Distinct thickness-dependent characteristic delay times in a goat bone were obtained, establishing an active depth resolution range of ~2.8 mm in a layered skin-fat-bone structure, a favorable result compared to the maximum reported pulsed photothermal radiometric depth resolution <1 mm in turbid biological media.     

Differential interference contrast‐photothermal microscopy in nanospace: impacts of systematic parameters

Differential interference contrast‐photothermal microscopy (DIC‐PTM), as a promising tool for trace analysis of nonfluorescent compounds, suffered low sensitivity in nanospace especially for aqueous samples, due to the poor thermophysical property of water and the unoptimised configuration. To improve its performance, a five‐layer DIC‐PTM model is built and influences of different parameters on the photothermal signal are investigated. The initial phase shift φ₀ between two branches of the probe beam is found to be a key factor determining the detection sensitivity and response linearity: at a large φ₀ (≤π/2) both a high sensitivity and a good linearity can be achieved, while a high signal‐to‐noise ratio occurs at a small φ₀. The steady‐state photothermal phase shift φ_dc has little impact on the linearity, which, however, is greatly influenced by the range of periodic photothermal phase shift φ_ac. By introducing two coatings into a nanospace to confine the photothermal effect within and around the sample, the sensitivity can be enhanced from a few times to over 100 times. On an optimised DIC‐PTM configuration and chip structure, detection limit down to 10^?3 cm^?1 (or 40 molecules in a detection volume of 0.2 fL) was achieved in a 300‐nm‐thick nanospace. This work paves a way for optimising the DIC‐PTM and chip structure for sensitive detection of analytes in nanospaces.     

Photothermal microscopy: a step from thermal wave visualization to spatially localized thermal analysis

The calculation of photothermal response detected by a photothermal microscope is presented. By using a technique based on Green's functions and integral transforms, a model for laser‐induced temperature distribution functions has been derived. The mathematical method for solution of inverse problem is proposed. It suggests that photothermal microscopy, besides imaging subsurface of solids, has the potential for quantitative thermal analysis of varioussamples.     

高精度光声成像技术在脑成像中应用

光声成像技术可以提供深层组织的高分辨率和高对比度的组织断层图像,是进行脑成像的有力潜在工具之一。本文开展此项研究,搭建一套光声成像实验系统,在此基础上,获得10mm的混浊介质深度下的血管模拟样品图像,直径0.07mm的模拟血管能清晰地成像;活体研究中,成功进行活体白鼠脑部的血管分布的成像研究,重建图像中的各血管位置和形状与实际情况很好的吻合。     

Modal analysis of conical shell filled with fluid

As a basic study on the fluid-structure interaction of the shell structure, a theoretical formulation has been suggested on the free vibration of a thin-walled conical frustum shell filled with an ideal fluid, where the shell is assumed to be fixed at both ends. The motion of fluid coupled with the shell is determined by means of the velocity potential flow theory. In order to calculate the normalized natural frequencies that represent the fluid effect on a fluid-coupled system, finite element analyses for a fluid-filled conical frustum shell are carried out. Also, the effect of apex angle on the frequencies is investigated.     

PHOTOSYNTHETIC ENERGY STORAGE AND OXYGEN EVOLUTION DETERMINED THROUGH AN OPEN PHOTOACOUSTIC CELL TECHNIQUE

Abstract

Recently, a new open photoacoustic cell (OPC) has been developed for the determination of both optical and thermal properties of the sample. The OPC can also be applied for the determination of photosynthetic parameters as energy storage and oxygen evolution for in vivo and in situ plant leaves. However, the membrane of the microphone used in this cell inserts a spurious component in the photoacoustic signal of non-opaque samples such as plant leaves. The membrane signal is added to the sample signal, making the analysis more complicated. In the present work, we discuss this problem and propose a simple method to eliminate it.     

Device for characterization of thermal effusivity of liquids using photothermal beam deflection

We propose and study a novel optoelectronic device for thermal characterization of materials. It is based on monitoring the photothermal deflection of a laser beam within a slab of a thermo-optic material in thermal contact with the sample under study. An optical angle sensor is used to measure the laser deflection providing a simple and experimental arrangement. We demonstrate its principle and a simple procedure to measure thermal effusivity of liquids. The proposed device could be implemented into a compact sensor head for remote measurements using electrical and fiber optic links.     

Microbubble ultrasound contrast agents: a review

The superior scattering properties of gas bubbles compared with blood cells have made microbubble ultrasound contrast agents important tools in ultrasound diagnosis. Over the past 2 years they have become the focus of a wide and rapidly expanding field of research, with their benefits being repeatedly demonstrated, both in ultrasound image enhancement, and more recently in drug and gene delivery applications. However, despite considerable investigation, their behaviour is by no means fully understood and, while no definite evidence of harmful effects has been obtained, there remain some concerns as to their safety. In this review the existing theoretical and experimental evidence is examined in order to clarify the extent to which contrast agents are currently understood and to identify areas for future research. In particular the disparity between the conditions considered in theoretical models and those encountered both in vitro, and more importantly in vivo is discussed, together with the controversy regarding the risk of harmful bio-effects.     

IR780 loaded hollow MnO₂ nanoparticles for dual-mode imaging and enhanced photodynamic therapy of oral squamous cell carcinoma

Photodynamic therapy (PDT) has emerged as a novel therapeutic modality for cancer treatment, but its therapeutic efficacy is severely limited by the hypoxic tumor microenvironment (TME). Here we designed an innovative multifunctional nano-platform which consists of a hollow MnO₂ shell and internal photosensitizer IR780. It is not only used for multimodal imaging of oral squamous cell carcinoma (OSCC), but also for adjustment hypoxic TME to enhance cancer treatment. Hollow MnO₂ can promote decomposition of tumor endogenous H₂O₂ to relieve tumor hypoxia, thereby enhancing the effect of photodynamic therapy. Photosensitizer IR780 generates singlet oxygen under laser irradiation to kill tumor cells, playing photodynamic effect, can also act as the contrast agents for photoacoustic and fluorescence multiple imaging, providing potential imaging capability for cancer therapeutic guidance and monitoring. Our research results in this article show that HMnO₂-IR780 nanocomposite exhibits good biocompatibility and nontoxicity, strong PA/FL imaging contrast, excellent oxygen production capacity and outstanding photodynamic therapy effect. This finding provides a new idea for multimodal imaging-guided nanotherapy for OSCC.     

湿度和SF_6在石英增强光声光谱中对CO分子弛豫率的影响

为了研究六氟化硫(SF_6)气体分子和水汽(H_2O)对一氧化碳(CO)气体分子的弛豫率的影响,建立了一个基于石英增强光声光谱(QEPAS)技术的痕量气体传感器系统。采用1.57μm的近红外分布式反馈二极管激光器作为激励光源,并对不同SF_6和H_2O气体浓度下的CO的光声信号进行对比研究。首先用CO传感器系统探测CO与N_2的气体混合物中CO的光声信号,然后在CO与N_2气体混合物中加入不同浓度的SF_6气体,分别探测不同浓度SF_6气体下的CO光声信号强度。最后在CO与N_2的气体混合物中加入不同浓度H_2O,探测加入H_2O后的CO的光声信号强度。实验结果表明随着CO和N_2气体混合物中SF_6气体浓度的增加,CO的光声信号幅值几乎没有变化,而在混合物中加入2.5%的H_2O后,发现CO的光声信号提高了约5倍。因此,SF_6对CO气体的弛豫率没有明显的影响,然而H_2O的添加能够有效缩短CO气体的弛豫时间。     

Tool Chatter Monitoring in Turning Operations Using Wavelet Analysis of Ultrasound Waves

This paper presents a new method for tool chatter monitoring using the wavelet analysis of ultrasound waves. Ultrasound waves are pulsed through the cutting tool towards the nose and are reflected back off the cutting edge. Fluctuating states of contact and non-contact between the tool insert and the workpiece, which are generated as a result of tool chatter, affect the amount of the transmitted ultrasound energy into the workpiece material and, in turn, the amount of the reflected energy. The change in the energy of the echo signals can be related directly to the severity and frequency of tool chatter. Wavelet packet analysis was used to filter the ultrasound signals. A three-layer multilayer perceptron (MLP) artificial neural network (ANN) was used to correlate the response of the ultrasound sensor to the accelerometer measurement of tool chatter. The main advantage of the ultrasound sensor is its ability to monitor other parameters such as the first contact of the tool and workpiece tool chipping and flank gradual tool wear. Experimental results show that the severity of tool chatter can be successfully monitored using the proposed ultrasound system. The system response to various frequency levels of tool chatter was investigated, however, the measurement of the chatter frequency is beyond the system capability at the current time.     

基于CO2激光单点加热的微泡腔制备及其性能研究

为了简化微泡腔的制备工艺,在传统CO_2激光双向加热方案的基础上,采用CO_2激光单点加热毛细管。通过精确控制加热温度和气体流速,制备出半球形的微泡腔,进而通过调节激光光斑,增加加热面积的方式制备出球形的微泡腔。使用光学显微镜和原子力显微镜(AFM)对制备的球形微泡腔进行表征,并通过COMSOL仿真验证了所制备微泡腔的性能。所制备的微泡腔表面光滑,壁厚最薄处可达到亚微米量级。研究结果表明,通过CO_2激光单点加热制备的微泡腔的壁厚存在轻微的不均匀性,但其谐振Q值仍然较高,可广泛应用于传感领域。     

A high-order shear element for nonlinear vibration analysis of composite layered plates and shells

This paper introduces a family of high-order facetted shell elements for linear and nonlinear stress and vibration analysis of composite layered plate and shell structures. Engineering slope angles are employed in element equations, and transverse stresses are expanded over the thickness. The lateral deflection is modelled by conforming or non-conforming Hermitian shape functions, within rectangular or paralellogrammic and triangular elements. Nonlinear terms associated with geometrical nonlinearity are also derived using a practical approach based upon the actual components of strain. A finite element programming package was designed employing the newly developed elements. Several case studies have been investigated and package results were compared with existing theoretical and/or experimental results. It has been proved that the developed elements can lead to accurate estimations of natural frequencies. The effect of fibre angles on natural frequencies has also been investigated with some case studies, and the results proved that the package can be a useful tool for the design optimization of composite layered plate and shell structures.     

Photoacoustic detection of CO2 based on LABVIEW at 10.303 μm

A detailed study on a photoacoustic carbon dioxide detection system, through sound card based on virtual instrument, is presented in this paper. In this system, the CO(2) concentration was measured with the non-resonant photoacoustic cell technique through measuring the photoacoustic signal caused by the CO(2). In order to obtain small photoacoustic signals buried in noise, a measurement software was designed with LABVIEW. It has functions of Lock-in Amplifier, digital filter, and signal generator; can also be used to achieve spectrum analysis and signal recovery; has been provided with powerful function for data processing and communication with other measuring instrument. The test results show that the entire system has an outstanding measuring performance with the sensitivity of 10 μv between 10-44 KHz. The non-resonance test of the trace gas analyte CO(2) conducted at 100 Hz demonstrated large signals (15.89 mV) for CO(2) concentrations at 600 ppm and high signal-to-noise values (～85:1).     

非共振光声红外气体传感器结构参量分析

非共振光声红外气体传感器在气体检测领域有很好的应用前景。对基于MEMS红外光源的非共振光声红外气体传感器进行了一维模拟,分析了光声腔及红外吸收光路结构对传感器性能的影响;计算了吸收腔气体压强变化量与吸收腔长度及调制频率的关系,研究了光路内壁反射率、样品气室长度对样品气体红外吸收效率的影响。简化的理论分析和计算结果,可以为非共振光声红外气体传感器的结构设计提供参考。     

基于负折射率声透镜的亚波长分辨率光声实时成像方法

基于负折射率材料的信号处理技术为光声图像的研究提供了新的思路。光声成像是一种全新的非破坏性生物光子技术,是一种基于生物组织内光吸收差异的成像方法。然而,当前的光声成像方法主要依靠传感器扫描工作,而传感器阵列有其固有的缺点,导致实时性较差,因此,普通的光声成像方式具有一定的局限性。但是,利用具有负折射率的声透镜特性(如聚焦、滤波、定向等)构成的成像方式可以解决普通光声成像中的这些局限性问题。本文在对负折射率声透镜的负质量响应和负折射率成像进行优势分析后,提出了利用声透镜改变当前扫描成像的方法。模拟分析实验结果表明,所设计的声透镜直接成像方案达到了预期效果,透镜成像后像点的声压分布与吸收体原始的声压分布基本一致。此外,0.6倍波长的实验图像结果说明本文实现了亚波长的光声成像效果。