Treatment of Thermal Gratings in the Time and Frequency Domain

Abstract

In this contribution we present the range of applicability on solids and surfaces of the photothermal displacement technique refined by using laser-induced thermal gratings. A suitable theoretical calculation has been performed showing the characteristic dependence of the absorption-induced surface deformation on optical and thermophysical parameters as well as on pulsed and amplitude-modulated laser excitation. The potential of the grating technique for thermal diffusivity measurements and for the study of heat diffusion in a preferential direction is clearly demonstrated. Moreover equivalence and convertibility of both dynamic approaches for thermal diffusivity measurements is found. However, in relation to other applications the selected operation form (pulsed or c.w.-modulated) presents specific advantages which justify its choice. The equivalent and complementary information obtained in the time and frequency domain is discussed using for this purpose experimentally limiting cases which are commonly applied. Useful analytical expressions have been derived interpreting both depth and laterally resolved photothermal measurements of homogeneous material parameters. Thus, the photothermal displacement grating technique is suggested as an alternative, contactless method, sensitive to surfaces, in the field of non-destructive evaluation.     

用光纤燃烧传感器测量汽油机的燃烧时间参数

介绍了一个光纤燃烧传感器＋（ＯＭＡ４光多通道分析仪组成的测量系统，用以测量汽油机燃烧火争光谱。光谱分析结果再次证实了燃烧火焰中ＣＨ（４３１．５ｎｍ），Ｃ２（５１６．ｎｍ），Ｈ２Ｏ３（５８９ｎｍ）等自由基的特征光谱同Ｃ粒子的热宫续光谱叠加在一起，构成了火焰光谱。根据光谱曲线中Ｈ２Ｏ光强峰值变化可以确定汽油机燃烧过程中重要的时间参数。着火延迟期和燃烧持续期。由于汽油机燃烧循环环变动大，与单色仪＋ＢＯＸ     

PLC和变频调速在热电厂灰渣泵系统中的应用

宏伟热电厂采用PLC和变频器实现灰渣泵的自动控制,取得了显著的经济效益。介绍了用PLC单片机控制的变频调速恒液位控制系统,该系统能根据灰渣池内的液位高低来调整灰渣泵的转速,实现池内液位的恒定,达到自动控制和高效节能的目的。     

GLONASS时间频率传递研究

分析了基于GNSS的时间频率传递方法的发展趋势和GLONASS发展现状及趋势。对GLONASS时间频率传递进行了研究,就其原理实现、误差补偿及数据处理进行了阐述,实现了GLONASS时间频率传递的基本方法,实施了GLONASS和GPS时间频率传递实验。将两种时间频率传递结果进行了对比,对GLONASS时间频率传递自身性能进行了分析,结果显示:GLONASS时间频率传递已达到了可与GPS时间频率传递相比较的水平。     

Method of Estimating Pulse Parameters by Frequency Comparison

A method is considered for increasing the accuracy and reliability of frequency comparisons which is based on the coincidence of the leading edges or cutoffs of pulses as a function of the result of a preliminary selection of these frequencies. The method makes it possible to lower the absolute pulse quantization error and to estimate the pulse parameters.     

Simultaneous Measurement of Local Magnetic and Thermal Parameters by Thermal Wave Scanning Microscopy

To characterize magnetic materials on nanoscales, a new technique has been developed which is based on the combination of two scanning thermal near-field techniques: the thermally modulated ferromagnetic resonance induced by the probe of a scanning thermal wave microscope and the detection of the 3?? signal from the same thermal probe. The simultaneous detection of the thermally modulated microwave absorption and of the 3?? response of the nanoprobe offers a means to control the thermal contact between probe and sample during scans across the sample. In this contribution, the experimental setup is described and results of measurements conducted on Fe-based structures deposited on a MgO substrate are presented.     

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。     

用状态方程计算多元混合工质的热导率

利用ＰＲ状态方程结合修正的Ｅｎｓｋｏｇ理论计算了氮烃类多元混合工持的热导率。在压力为０．０７２－５．７１５ＭＰａ，温度为１２２．１９０－３３５．５Ｋ范围内，总绝对平均偏差为４．９８％《     

Monitoring the Thermal Parameters of Different Edible Oils by Using Thermal Lens Spectrometry

Several vegetable edible oils (sunflower, canola, soya, and corn) were used to study the thermal diffusivity of edible oils. Thermal lens spectrometry (TLS) was applied to measure the thermal properties. The results showed that the obtained thermal diffusivities with this technique have good agreement when compared with literature values. In this technique an Ar⁺ laser and intensity stabilized He–Ne laser were used as the heating source and probe beam, respectively. These studies may contribute to a better understanding of the physical properties of edible oils and the quality of these important foodstuffs.     

电视信号中标准时间频率的应用

本文介绍了电视信号中标准时间、频率的应用 ,其中包括彩色副载波标准频率综合器、电视行同步标准频率综合器、采样保持鉴相器、电视标准时间数字钟等设备的研制。藉助这些设备 ,只要直接接收中央电视台 1、2或 4套节目的全电视信号 ,便可输出常用的标准频率和时间 ,可用于精密时间测量、计量和校频 ,也可作为标准频率信号源使用 ,其校频精度达 5× 10 - 12 / 30min ,时间同步精度在 1μs以下。     

复合材料缺陷的红外检测及处理方法

复合材料在制作、加工、使用的过程中，其内部有时会产生各种各样的缺陷，这将会影响其使用性能。红外热成像检测复合材料的缺陷是目前一种有效的方法。本文就红外热成像检测复合材料缺陷的机理、方法、技术关键及处理方法等方面做了简要的论述。     

一种频率/电压转换电路的设计

为了将电路中的频率信号转化为电压信号,本文提出了一种基于电荷平衡式原理的频率/电压转换电路,由微分器、电压比较器、带开关的单稳多谐振荡器、恒流源和有损积分器组成;根据电荷平衡式原理,使用电压频率转换芯片AD650的反向工作模式,设计了频率电压(F/V)转换电路,可以实现50～5 000 Hz频率到0.1～5 V电压的线性转换,线性度低至0.22%,并对所涉及的电路进行性能优化,提供了高精度的电源基准,精度可达0.02 V;并滤除了由电容放电所引起的纹波干扰.     

Measurement of Static AM-PM Conversion in Frequency Multipliers

The generation of very narrow spectral lines in the far-infrared by frequency synthesis from VHF precision sources requires very stringent specifications on the spectral purity of the source and on the phase noise introduced by the synthesizer. The dc measurements of the AM-PM conversion in different multiplier stages are presented in this paper: stages employing transistors, varactors and step-recovery diodes are examined. The results show that a few degrees per dB of input level variation are typical for the AM-PM conversion reported to the input in a simple, carefully built and well tuned multiplier stage employing any of the mentioned solid state devices. This value is shown to be unlikely to degrade more than the expected n2 factor the spectral purity of a signal with AM noise as low with respect to PM noise as it is in the output of a good quartz crystal controlled oscillator; however, such a conversion could become a source of phase noise, with degradation of the spectral purity, for a signal with a slightly worse AM noise.     

在时、频测量中的倍增器

本文阐述了倍增原理，详细分析了多级倍增器的噪声门限以及确定它们的测量上限，还介绍有关倍增器里的关键电路－倍频器及其影响和倍增器在时、频测量中的应用．