Thermal Diffusivity Mapping of Solids by Scanning Photoacoustic Piezoelectric Technique

Quantitative thermal diffusivity mapping of solid samples was achieved using the scanning photoacoustic piezoelectric (PAPE) technique. Based on the frequency-domain PAPE theoretical model, the methodology of the scanning PAPE thermal diffusivity mapping is introduced. An experimental setup capable of spatial and frequency scanning was established. Thermal diffusivity mapping of homogeneous and inhomogeneous samples was carried out. The obtained thermal diffusivity images are consistent with the optical images in image contrast and consistent with the reference values in thermal diffusivity. Results show that the scanning PAPE technique is able to determine the thermal diffusivity distribution of solids, hence providing an effective method for thermal diffusivity mapping.     

A Modified Photoacoustic Piezoelectric Model for Thermal Diffusivity Determination of Solids

The conventional photoacoustic piezoelectric (PAPE) model did not take into account the influence of the piezoelectric transducer (PZT) on the vibrations of the sample, and this approximation brought certain error. In this article, a simple method has been proposed to investigate the vibrations of the sample–PZT combination, and the theory of the PAPE technique has been modified. By introducing an equivalent thickness parameter, the two-layered model has been simplified and an analytical expression for the phase of the PAPE output signal has been obtained. The experimental system has been set up, and the thermal diffusivities of several metal samples have been measured. The experimental results show that the modified model has a higher accuracy than the conventional model.     

应用光声技术测定薄型材料导温系数的研究

本文报导了用光声技术测试和研究薄型试样导温系数的结果,建立了该方法的理论模型,介绍了实验装置和数据处理的方法。用本装置对三种标准和亚标准试样的测试结果表明,实测值和文献推荐值相当吻合。本文的基本理论和实验方法同样也适用于其它有机、无机等薄型材料。     

用光声技术测量ZnO薄膜的压电系数

本文报导了用光声技术测量溅射 ZnO 薄膜的压电系数,介绍了用来测量 ZnO 薄膜压电系数的理论分析和实验方法。本实验所得压电系数 e_(33)、e_(31)的值分别为0.817C/m~2和-0.431C/m~2,与 ZnO 单晶的值相比是合理的。     

Non-destructive Imaging of Standard Cracks of Railway by Photoacoustic Piezoelectric Technology

The photoacoustic piezoelectric (PAPE) technique is an effective non-destructive testing technique for detecting defects in materials. In this paper, Chinese national standard railway cracks have been detected by thermal wave imaging based on the PAPE technique. First, the theory of the PAPE technique has been introduced and the corresponding imaging principle has been analyzed. Second, the corresponding experimental system has been setup, and the imaging tests have been carried out. Third, two kinds of standard cracks have been examined by the imaging system. The results show that thermal wave imaging based on the PAPE technique can effectively image and identify the cracks at different depths, which lays a foundation for practical application to the detection of rail cracks.     

改性凹凸棒石-不饱和聚酯复合材料的热性能研究

为研究改性凹凸棒石的掺入对不饱和聚酯热性能的影响,采用十八烷基三甲基氯化铵(OTAC)对凹凸棒石进行有机改性,然后制备改性凹凸棒石-不饱和聚酯复合材料,并用红外光谱(IR)和X射线衍射(XRD)等分析手段对改性效果进行表征,利用差热(DTA)、热重(TG)同步热分析仪研究复合材料的热性能,探究改性前后凹凸棒石的掺量对复合材料热起始温度的影响。结果表明:改性凹凸棒石-不饱和聚酯复合材料的热稳定性明显优于凹凸棒石-不饱和聚酯复合材料和纯不饱和聚酯,掺入改性凹凸棒石的最佳质量分数8.4%左右。     

用光声法测量陶瓷材料的热参量

以固体光声效应的RG理论为依据,用光声法测量了压电陶瓷材料PZT的热参量。实验结果表明:用此方法只需要测出一个量就能同时确定PZT的α、k和C的值,并且实验设备简单,速度快,是一种很有前途的测热参量方法。     

Thermal Image of Coffee-Seed Germ Obtained by Photoacoustic Microscopy

Photoacoustic microscopy (PAM) has been shown to be a suitable technique to obtain thermal images of a wide variety of samples from semiconductors to biological material. In PAM, the incidence of a modulated laser beam on a sample within a photoacoustic (PA) cell, hermetically sealed, produces a PA signal which depends on the thermal and optical properties of the studied sample. By making a sweep of the modulated laser beam on the sample surface, it is possible to obtain the PA signal as a function of their x?y coordinates, and from this signal, it is possible to reconstruct thermal images of the sample. In this study, thermal images of a coffee-seed germ were obtained, with a difference of 12 h between them, by using the PAM technique. Thermal differences observed between images give information which reflects degradation due to the fact that germ cells undergo changes as a function of time. The thermal images obtained by the PAM technique could be applied to biological materials that have a complex constitution (not homogeneous) in their structures, and thermal differences can be observed. PAM is a non-destructive technique, which is an important feature for this type of study. Other applications of this technique can be performed in the agricultural and biotechnological areas.     

热原子层沉积技术制备的TiAlC薄膜的性能

为了解以热原子层沉积技术制备的TiAlC薄膜的特性,在不同基底温度下,以硅和二氧化硅为基底材料制备了TiAlC薄膜;采用椭偏仪、分光光度计、X射线光电子能谱、原子力显微镜、X射线衍射仪对薄膜的性能进行了测试。结果表明:随着基底温度的升高,TiAlC薄膜平均透射率逐渐降低,吸收边产生红移,光学带隙由2.56eV降低到0.61 eV;薄膜的沉积速率由0.09 nm/cycle升高到0.20 nm/cycle,表面粗糙度由1.82 nm降低到0.49 nm;不同基底温度下生长的薄膜均为无定型结构;膜层中的氧源于空气的自然氧化,且膜层的氧化程度与膜层中TiC的含量及膜层的致密性有关;TiAlC薄膜的形成主要源于高温条件下TiC的形成及三甲基铝的分解。     

Thermal Buckling Analysis of Piezoelectric Functionally Graded Plates with Temperature-Dependent Properties

In this study, the thermal buckling analysis of hybrid laminated plates made of two-layered functionally graded materials (FGMs) that are integrated with surface-bonded piezoelectric actuators referred to as (P/FGM)_s are investigated. Material properties for both substrate FGM layers and piezoelectric layers are temperature-dependent. Uniform temperature rise as a thermal load and constant applied actuator voltage are considered for this analysis. By definition of four new analytic functions, the five coupled governing stability equations, which are derived based on the first-order shear deformation plate theory, are converted into fourth-order and second-order decoupled partial differential equations (PDEs). Considering a Levy-type solution, these two PDEs are reduced to two ordinary differential equations. One of these equations is solved using an accurate analytical solution, which is named as power series Frobenius method. The effects of parameters, such as the plate aspect ratio, ratio of piezoelectric layer thickness to thickness of FGM layer, gradient index, actuator voltage, and the temperature dependency on the critical buckling temperature difference, are illustrated and explained. The critical buckling temperatures of (P/FGM)_s with six various boundary conditions are reported for the first time and can be served as benchmark results for researchers to validate their numerical and analytical methods in the future.     

改性偏铌酸铅压电陶瓷高温特性及应用

文章分析了ＰＮＣ—３型改性偏铌酸铅压电陶瓷的高温特性，并就其可能的应用进行了试验．ＰＮＣ－３型陶瓷具有高居里温度（５６２℃）和低Ｑｍ特性，有强耦合系数和大的Ｋｔ／Ｋｐ比值．已成功地制成耐高温抗辐射的ＡＥ传感器和宽频带换能器等器件，并将其高温性能与美国Ｄ９２１５型高温ＡＥ传感器进行了比较．     

改性偏铌酸铅高温压电陶瓷材料的研究

偏铌酸铅是一种性能很有特色却又制备困难的高温压电陶瓷材料，而采用少量Ｍｅ＾２＋置换和微量稀有元素氧化物添杂方法，获得了压电性能和工艺性能均十分优良的改性偏铌酸铅高温压电陶瓷材料，并以热力学熵稳定原理，定性地解释了少量置换与微量添杂对稳定铁电相的作用，同时也对这种压电陶瓷材料的高温压电特性和高温下的应用进行了研究与试验，结果表明，这种材料是一种可以在４００℃下应用的高温压电陶瓷材料。     

Nodal Structure of Unconventional Superconductors Determined by Thermal Conductivity

To identify the gap structure of unconventional superconductors, spin-triplet Sr₂RuO₄, heavy fermion CeCoIn₅, organic -(BEDT-TTF)₂Cu(NCS)₂ and borocarbide YNi₂B₂C, we measured the thermal conductivity in magnetic field rotated within the 2D plane with very high precision. On the basis of these results, we show that the gap functions of Sr₂RuO₄, CeCoIn₅ and -(BEDT-TTF)₂Cu(NCS)₂ are most likely to be d(k)=₀ ^z(k _x+ik _y)(cos ck _z+), d_x ^{2-y 2} and d _xy, respectively. We also demonstrate the presence of point nodes along the a- and b-axes in YNi₂B₂C.     

Photoacoustic Microscopy of Vickers Indentations in Metals with Piezoelectric Detection

The effect of mechanical stress influence on the thermoelastic photoacoustic signals inside Vickers indents in steel and nanonickel has been experimentally demonstrated. It has been shown that photoacoustic signal changes due to external stresses can be reversible or irreversible, depending on the indent orientation and the stress applied to the sample. Reversible changes in the photoacoustic signal can reach significant values at the level of tens percent of the average signal amplitude from the sample. Relative changes in the photoacoustic signal amplitudes have been theoretically evaluated for Vickers-indented and non-indented areas, taking into account the dependence of the elastic modulus of metals on temperature. It has been shown that this theoretical consideration provides qualitative explanation of differences in the behavior of photoacoustic signals under stress in indented and non-indented areas in metals.     

Analysis of Maize Seed Germs by Photoacoustic Microscopy and Photopyroelectric Technique

A knowledge about thermal parameters of structural components of maize seed is of great relevance in the seed technology practice. The objective of the present study was to determine the thermal effusivity of germs of maize (Zea mays L.) of different genotypes by means of the photopyroelectric technique (PPE) in the inverse configuration and obtaining the thermal imaging of these samples by photoacoustic microscopy (PAM). Germs from crystalline maize (white pigment), semi-crystalline maize (yellow pigment), and floury maize (blue pigment) were used in this investigation. The results show differences between germs of maize seeds mainly in the values of their thermal effusivities. The thermal images showed minimum inhomogeneity of these seed germs. Characterizations of thermal parameters in seeds are important in agriculture and food production and could be particularly useful to define their quality and determine their utility. PPE and PAM can be considered as potential diagnostic tools for the characterization of agriculture seeds.     

Analog Front-End Circuitry in Piezoelectric and Microphone Detection of Photoacoustic Signals

This paper is a review of analog front-end circuitry used in photoacoustic equipment with microphone or piezoelectric detection. A block structure of the front end as well as detailed circuit diagrams of preamplifiers dedicated for piezoelectric sensors and measurement condenser and electret microphones are described. The presented circuits are optimized toward low-noise operation. Practical remarks regarding the design of the remaining analog blocks are also given. The analysis shows that it is possible to design an analog front end for which specifications will be comparable with the best commercial solutions.     

Influence of Thermal Memory on Thermal Piston Model of Photoacoustic Response

In this study, a model of thermoconducting components of the transmission photoacoustic response is analyzed, which includes thermal memory properties of both the examined solid sample and its fluid environment. It is shown that, at low modulation frequencies, lower than minimum among the inverse thermal relaxation time of air, the inverse thermal relaxation time of the sample, and the certain frequency at which the sample is thinner than one-quarter of the wavelength of time-varying temperature perturbation, thermal memory does not affect the photoacoustic response, while, at high frequencies, noticeable effects are observed. These results indicate the possibility of evaluating thermal memory properties of solid samples using classical, transmission, high frequency photoacoustic measurements.     

液化改性型超支化聚氨酯相变材料的热性能

以液化改性4,4′-二苯基甲烷二异氰酸酯(L-MDI)、聚乙二醇(PEG)为原料,超支化聚酯为扩链剂,合成一系列不同软段含量的超支化聚氨酯固-固相变储能材料.用差示扫描量热法(DSC)、热失重分析(TGA)等方法对这些聚合物的热性能进行了研究.结果表明,采用L-MDI为原料,可得到具有优异相变储能性质的液化改性型超支化聚氨酯,此外由于L-MDI在贮存和使用上优于普通MDI,能为生产带来便利.