A Large-Area PVDF Pyroelectric Sensor for CO 2 Laser Beam Alignment

We present the design of a large-area (50 mm times 50 mm) polyvynilidene fluoride (PVDF) pyroelectric sensor array for industrial CO₂ (lambda = 10.6 mum) laser beam positioning. The array dimensions were chosen to match the area typically monitored in the alignment procedure of external optics (beam steering moving arm system, for example) used to redirect the laser beam from the laser output window to a remote working station. The instrument is provided with a tilted, high reflection, ZnSe plate which partially transmits the laser beam onto the sensor array. From positioning simulations with a Gaussian laser intensity profile with a sigma = 3.2 mm standard deviation (equivalent spot size 3sigma cong 20 mm), the positional accuracy along the two orthogonal array dimensions was found to be better than 0.02 mm for an 8 times 8 array and one order of magnitude higher for a 16 times 16 array. The centroid position of a CO₂ industrial laser beam was evaluated by integrating the pyroelectric current for a time comparable to the time duration (100-200 ms) of the laser pulses used in the alignment procedure.     

Pressure-Change Detection by Infrared Sensors of Thermal Type, Thermistor Bolometer and Pyroelectric Sensor

The effect of a pressure change of air upon infrared sensors of thermal type, thermistor bolometer, and pyroelectric sensor, has been investigated. Experimental results indicate that the pressure dependence of the sensors is related to the temperature change of the sensor. The temperature change is caused by the pressure change of air surrounding the sensor. These results show that infrared sensors of the thermal type with high detectivity can be used as air-pressure change detectors.     

Pyroelectric Thermal-Wave Resonant Cavity: A Precision Thermal Diffusivity Sensor for Gases and Vapors

A novel thermal-wave resonant cavity (TWRC) was constructed and used for thermophysical measurements of gases and vapors, with an AC current-heated thin-film resistive element acting as a thermal-wave source. A thin-film pyroelectric element was used both as a cavity wall and as a signal transducer. A theoretical model of the cavity length-scanned thermal-wave field was developed to quantify the standing-wave resonance antinode patterns in the demodulated lock-in signal output in-phase and quadrature channels. These resonance extrema were used to measure precisely the thermal diffusivity of the intracavity gas or vapor. Seven high-purity gases (nitrogen, dry air, oxygen, methane, hydrogen in nitrogen, pure hydrogen, and helium) were measured using the cavity. Fourth-significant-figure precision was obtained for this parameter, with standard deviations less than 0.32% for the five measurements performed with each gas. Furthermore, three grades of gasoline vapors from Imperial Oil were studied with the cavity. The measured thermal diffusivities showed that the TWRC can monitor fundamental evaporation kinetics as an analytical quality-control instrument. These results, together with the simplicity of TWRC sensor fabrication, are indicative of its potential to become a new standard measurement instrument for the determination of gas thermal diffusivity with improved precision, and a new in situ monitor of chemical evaporation kinetics over conventional methodologies, such as gas chromatography and mass spectrometry.     

Pyroelectric PVDF sensor modeling of the temporal voltage response to arbitrarily modulated radiation

Our design of transducer arrays for custom pyroelectric sensors is mainly devoted to IR laser beam characterization and control. It benefits from some of the properties of PVDF film such as low cost, low weight, mechanical flexibility, chemical stability (inert), and compatibility of thick film interconnection technologies on metallized films. By using the temporal characteristics of the source intensity and starting from a standard equivalent one-dimensional model of a multilayer thick-film transducer in the frequency domain, we developed a computer model of the PVDF sensor that determines the temporal response to arbitrarily modulated radiation. The validation of the model accuracy has been carried out with a simulation procedure performed on a PVDF sensor designed for accurate beam alignment of low power laser beams. In this case, an iterative algorithm also was developed to estimate some thermal and physical properties of the front absorbing and the metallization layers that are generally barely known. We present a fitting procedure to determine these properties by using the temporal pyroelectric response to a square wave modulated laser diode that provides a reliable reference signal.     

基于压电传感器获取任意边界板结构体积速度

介绍了一种设计体积速度传感器的新方法。设计策略为将PVDF压电薄膜黏结到结构表面上,两维振动结构的表面振速用Legendre多项式展开,利用两维分布式传感器压电方程,设计PVDF薄膜的形状,使传感器的输出电荷量正比于两维结构的体积速度。这样设计得到的传感器,其输出信号的实时性得到了保证,并且适用于任意边界条件,能测量振动结构的局部体积速度,拓宽了其应用范围。此外,还以简支板及其局部区域为例,通过数值计算,验证了设计方法的可行性。     

热激励硅谐振式微结构压力传感器若干关键参数设计

针对一种以方形硅膜片为一次敏感元件、硅梁为二次谐振敏感元件的热激励硅微结构压力传感器的实际结构,分析了其工作机理和产生热特性的机制.给出了考虑热特性情况时的传感器的被测压力与输出频率的特性方程;给出了传感器稳定可靠工作的条件;给出了梁谐振子的几何结构参数和激励、拾振电阻几何参数选择与位置设置的原则.     

PVDF压电传感器在模型化爆中的应用

本文利用PVDF压电薄膜的特性,根据模型化爆试验的特点,设计了实用的PVDF压电型压力传感器,测试结果和对比计算表明.压电型压力传感器设计合理,测力准确,应用性强.     

PZT和PT陶瓷的热释电效应与晶格参数的关系

测量了锆钛酸铅（PZT和钛酸铅（PT）陶瓷材料的热释电效应，利用X射线衍射测量了陶瓷材料在不同温度下晶格结构变化，研究了PZT和PT陶瓷材料的热释电效应与晶格参数之间的相互关系，实验表明，陶瓷材料的热释电系数的大小与晶格参数随温度变化的情形有关，c轴与c／a比随温度变化大的材料，其热释电系数较高．     

3-D Modeling of Pyroelectric Sensor Arrays Part II: Modulation Transfer Function

The modulation transfer function (MTF) for a pyroelectric infrared sensor array is determined from a finite-element simulation. Consideration of the full thermoelectromechanical coupling and use of a 3-D sensor model result in a good agreement between calculated and measured data.      

3-D Modeling of Pyroelectric Sensor Arrays Part I: Multiphysics Finite-Element Simulation

When modeling pyroelectric sensors, not all relevant and coupled physical phenomena could be considered contemporaneously up to now. We describe a method to examine problems with coupled thermal, electrical, and mechanical fields using finite-element software. Modeling the complex interaction between the physical fields is realized by implementing a two-step approach that takes advantage of the internal computational routines of finite-element programs. The method will be exemplified on a standard pyroelectric sensor array, whose efficient 3-D modeling and simulation is demonstrated using a public accessible commercial finite element software.      

Thermal conductivity and dielectric properties of Al/PVDF composites

Polymeric composites with relatively high thermal conductivity, high dielectric permittivity, and a low dissipation factor are obtained in the present study. Three types of core-shell-structured aluminum (Al) particles are incorporated in poly(vinylidene fluoride) (PVDF) by melt-mixing and hot-pressing processes. The morphological, thermal, and dielectric properties of the composites are characterized using thermal analysis, a scanning electron microscope, and a dielectric analyzer. The results indicate that the Al particles decrease the degree of crystallinity of PVDF, and that the particle size and shape of the filler affect the thermal conductivity and dielectric properties of Al/PVDF. No variation in the dissipation factor is observed up to 60 wt.% Al. Thermal conductivity and dielectric permittivity values as high as 1.65 W/m K and 230, respectively, as well as a low dissipation factor of 0.25 at 0.1 Hz, are realized for the composites with 80 wt.% spherical Al.     

PVDF传感器在火炮弹底撞击应力测试中的应用

在分析PVDF压电薄膜测压原理的基础上,提出了利用PVDF压电薄膜测量火炮发射过程中火药颗粒对弹底撞击应力方案,并论述了该方案的可行性.设计并试制了适合火炮膛内发射条件下测量火药颗粒对弹底撞击应力的弹载传感器,重点阐述了传感器结构设计、制作工艺以及PVDF压电薄膜的工程应用技术;设计完成了适合于弹上狭小空间使用的信号调理电路,并对电路进行了仿真及调试.最后初步探讨了影响测量精度的因素并提出改进措施.     

封装材料对PVDF薄膜传感器激波响应的影响

PVDF(聚偏氟乙烯)及其共聚物压电薄膜具有响应快、灵敏度高、测压范围宽等特点,为冲击波压力测试传感器提供了新的敏感材料.本文详细的介绍了PVDF薄膜传感器的制作过程,并对封装用的粘结剂以及外保护层进行了激波管的对比试验,考察封装材料对PVDF薄膜传感器动态性能的影响.通过对试验数据的判读,确定了较为合适的封装粘结剂及保护层材料.     

坐标测量机结构热特性参数的估计

本文提出了一种通过热位移时间序列分析对坐标测量机结构热特性参数进行估计的计算机辅助实验方法。     

LEC法GaAs单晶生长中热应力分布研究

采用有限元法对LEC法生长的3英寸GaAs单晶中的热应力进行求解.假设晶体为轴对称的各向同性线弹性体.主要讨论了不同液封厚度、轴向磁场强度以及晶体转速下的流动和传热所对应的晶体中的热应力分布,同时也考察了界面形状对应力的影响.     

Analysis of the Thermal Performance of SODI Instrument for DCMIX Configuration

There exists an instrument SODI (Selected Optical Diagnostic Instrument) on the ISS where series of the DCMIX (Diffusion Coefficients in Mixtures) experiments are conducted by members of the ESA Topical Team. The study is addressed to the performance of thermal design of SODI instrument for DCMIX configuration. We report the results on the temperature fields which were measured interferometrically both in two ground setups (one thermally optimized; the other one, the engineering model of the ISS SODI-DCMIX experiment: non optimized) and in the ISS experiment itself with the respective numerical simulations. Even though monitoring of the cell with binary mixture $THN-nC_{12}$ employs only an interferometer with one wave length instead of two for other cells with ternary mixtures, it gives valuable information about the instrument performance. Temperature and concentration fields observed during the tests in the engineering model are compared with those obtained in laboratory experiments with the same liquid, with numerical simulations and with first results from the ISS in Run #16. The thermal design of the microgravity cell, being not optimized for ground experiments, exhibits a promising performance in the weightlessness condition.     

Unexpected Thermal Fracture of a Ceramic Sensor

A ceramic substrate bonded to an electronic sensor was reported to crack during thermal testing between −46 and +71 °C. Initially, this was assumed to occur at high temperature because of the thermal expansion of a polymer pad under the sensor. However, further investigations indicated that fracture was also occurring at low temperature. This was surprising since the suspected cause of fracture was pressure exerted by the polymer pad under the ceramic. This polymer pad has a coefficient of thermal expansion much greater than any other component. Conventional wisdom suggests that this failure would happen only during expansion of the pad during high temperature phases of temperature cycling. Subsequent dynamic thermal analysis revealed that differential contraction of the steel clamp fasteners was causing pressure to be exerted on the ceramic during the initial phase of the cold cycle. In addition, lateral constraint of the polymer pad caused pressure to rise to counterintuitive levels. An alteration of the geometry of the pad proved to be the simplest and most economical solution. This was confirmed by subsequent testing.     

Apparatus for Investigating the Electrical and Optical Parameters of Pulsed Spark Discharges

A circuit and the structural features of apparatus for the synchronous recording of the electrical and optical characteristics of spark discharges, which occur between two electrodes at low voltages, are described. The parameters are recorded in digital form with a discreteness of 4 sec.     

Thermal Fluctuations of Order Parameters in Two-Gap Superconductors

The thermodynamics of a finite two-band superconductor has been studied by means of the Hubbard–Stratonovich representation of partition function in the static approximation. The temperature behavior of heat capacity depends substantially on interband interaction and volume. Interband coupling controls the distribution of thermal gap fluctuations on the temperature scale according to the changes in superconducting ordering.