声表面波压力遥测传感器的理论与设计

介绍了一种遥测声表面波压力传感器的原理与设计，其核心敏感部件是由声表面波谐振器组成的振荡器，文中给出了主要的测试结果。     

基于频域相位信息的声表面波谐振器回波频率估计

提出一种基于频域相位信息的频率估计算法,利用正弦信号傅里叶变换相位谱中相位与频率的关系实现对声表面波谐振器回波频率的估计,并采用自相关运算消除回波信号初相位对估计结果的影响。通过无线测试系统和仿真回波信号对该算法进行了验证,表明算法的频率估计精度不受激励信号频率变化的影响,并且在整个声表面波谐振器的谐振频率变化范围内都具有较高的精度和稳定性。     

规定高精度齐纳电压源性能参数的新方法

本文介绍规定高精度齐纳电压源噪声，稳定度及回归不确定度等性能参数的新方法。本方法特别适用于年稳定性优于３×１０＾－６的齐纳电压源及其用户。     

数字合成正弦信号

调幅式测量电路中，振荡器电路输出正弦信号幅值严重影响测量电路的优劣，现有的氏桥振荡电路幅值优于１０＾－４稳定度，但电路结构复杂，本提出了应用波形失真度小，精度高，稳定性好，结构简单的数字信号发生器方案和实施电路，并给通过大量实验获得的性能数据分析与幅值稳定性直接相关的因素。     

恒温槽温度补偿的晶体振荡器研制

本文主要介绍简易恒温晶体振荡器。由于加入了热敏电阻补偿网络，当温度从－１０℃－＋４５℃变化时，振荡器的频率稳定度得到了很大改进。     

弥漫激光抽运铯束频标实施研究

对本北京大学铯束频标实验室所提出的一种光抽运铯束频标的新结构弥漫激光抽运斜入射光检测铯束频标进行了首次实验。本论述了这种新抽运检测机制的工作原理及其主要特点，对弥漫激光场的光强分布作了计算和测量，并实验检测了弥漫激光场的光抽过性能。实现了弥漫激光抽运铯束频标实验系统的闭环工作，与ＨＰ－５０７１Ａ商品小铯钟比对，此频标实验系统频率短期稳定度为２＊１０＾－１１／√τ，天稳定度为３．５＊１０＾－１３。     

声表面波器件中叉指换能器及外电路引起的附加相移特性

一般的声表面波器件是由与外电路相联接的两个叉指换能器组成，其中所要处理的信号都要经受电 － 声和声 － 电两次转换。又指换能器的结构和外电路的特性对这些转换的效率和相位变化有着密切的联系。本文从声表面波又指换能器交叉场等效电路模型出发，较详细地讨论了声表面波器件中输入、输出又指换能器的设计参数（中心频率和叉指电极对数等）及外电路负载和匹配网络对信号的转换效率和相移（或延迟时间）的影响。本文还针对某些又指换能器的实际例子，给出了详细的计算数据。文中所给出的公式和计算结果，可作为设计声表面波延迟线和振荡器的参考。     

高精度SAW表面粗糙度传感器的研究与设计

提出了一种利用声表面波（ＳＡＷ）器件构成的新型高精度表面粗糙度传感器的设计方案，分析研究了它的工作原理１信号处理方法和动态静态特性。研究结果表明：它除了具有电感式表面粗糙度传感器的主要优点外，还具有灵敏度高、对外界温度和振动干扰不敏感、信号数字量输出等特点，当声表面波振荡器（ＳＡＷＯ）的中心频率为４０ＭＨＺ时，传感器可以得到１０ｋＨｚ／μｍ的位移灵敏度。     

采用双本振源激励的声表面波谐振器无线测量系统

在声表面波无线传感的实际应用中,针对以差动形式同时出现的两个声表面波谐振器设计了一种采用双本振源激励的阅读器,每次产生包括两个载波频率的激励信号,使两个谐振器同时响应。实际搭建了无线测量系统,对阅读器的发射和接收链路进行了测试,并通过上位机实时显示谐振频率,测量结果表明了系统的可靠性。最后,实验分析了系统在不同载波频率激励信号下的差动频率测量结果和最远测量距离。     

声发射测量系统的研制

介绍一种干涉式光纤声发射传感器,其分辨率高达１０＾－１０ｍ量级,频率范围为１００ｋＨｚ至１．４ＭＨｚ,响应时间小于１μｓ,具有很高的测量稳定性,且可用于状态监测和故障诊断。     

带声学放大器的行波热声发动机声阻抗特性

通过分析带有声学放大器的行波热声发电系统中直线发电机的电-力-声类比图，发现直线发电机的最佳工作状态与行波热声发动机的输出声阻抗特性相关。采用DeltaEC软件计算带有声学放大器的行波热声发动机（以下简称系统）的输出声阻抗特性。计算结果发现，输出声阻抗虚部X_a为-1×10⁷ Pa·s·m^-3时，系统的最大输出声功率545.47 W，最大热声转换效率为7.2%；当输出声阻抗虚部X_a在-3.9×10⁶~-1×10⁷ Pa·s·m^-3之间变化，实部R_a在1.37×10⁶~2.31×10⁷ Pa·s·m^-3之间时，等效位移在1.89~6 mm之间变化，符合直线发电机的位移要求；结合输出声阻抗对压力与体积流率的相位差及系统工作频率的影响，发现声阻抗实部R_a应在1.37×10⁶~2.31×10⁷ Pa·s·m^-3之间，声阻抗虚部X_a在-7.5×10⁶~-1.0×107 Pa·s·m^-3之间时，系统具有较好的工作状态。     

Nonlinear Second Sound Waves and Acoustic Turbulence in Superfluid 4He

The preliminary results of an investigation of nonlinear second sound waves in a high quality resonator filled with superfluid ⁴He are presented and discussed. It is found that, for a sufficiently strong periodic driving force, a cascade of second sound waves is formed at multiple harmonics of the driving frequency over the extremely wide frequency range 1–100 kHz. It can be described by a power law A _ω =const.×ω ^−m , where the scaling index m≈1. These observation can be attributed to the formation of a Kolmogorov-like turbulent cascade in the system of second sound waves, accompanied by directed energy flux through the frequency scales. It manifests itself as a limiting of the amplitude of a standing wave, a distortion of the shape of the initially harmonic waves, and a reduction of the effective quality factor Q of the resonator.     

A heterodyne laser system to study frequency stabilized Zeeman 633 nm He-Ne lasers deficient in temperature steadiness

A heterodyne laser system is constructed to study the effect of external transverse magnetic field on the dynamic instability of internal mirror TEM_00q He-Ne lasers having temperature instability. The system could provide precise detailed knowledge about the roles of both the temperature and the applied magnetic field separately. Two different internal mirror 633 nm TEM_00q He-Ne lasers with frequency stability of 10⁻⁶ are studied. The applied transverse magnetic field on He-Ne lasers increased the frequency stability to be in the order of ∼10⁻¹⁰, in spite of temperature instability. In the same time, a single-mode operation with an enhanced laser output power is obtained. The sensitivity of the method showed that the laser exhibits a short-term frequency stability of 4.7×10⁻¹⁰, which after one minute, when mode collapse starts, decreased to 2.6×10⁻⁸, over the next four minutes. This increase in the frequency difference of the inter-mode beat signal that affect the stability is attributed to the uncontrolled temperature of the laser tube. The results revealed that the magnetic field plays the dominant role to achieve the maximum frequency stability, while the unsteadiness of temperature of the laser tubes limits the long term single-mode laser operation.     

High-temperature electrical conductivity and thermal expansion of SmBa2(Cu1-xFex 3O6+δ (x = 0–0.2)

The electrical conductivity and thermal expansion of SmBa₂(Cu_1-xFe_{x 3}O_6+δ (x = 0-0.2) were measured in air in the temperature range from 20 to 900°C. The linear thermal expansion coefficient was determined to be (12.8–13.5) × 10^-6 K^-1 in the temperature range from 20 to 350°C and (16.2–17.8) × 10^-6 K^-1 in the range from 350 to 800°C. Between 400 and 900°C, the conductivity of SmBa₂(Cu_1-xFe_x)₃O_6+δ was found to decrease with increasingx, mainly in the rangex = 0–0.1. This finding was interpreted in terms of the Fe occupancies on the Cu(1) and Cu(2) sites.     

Spectral parameters of Nd3+ ion in Nd:KLa(WO4)2 crystal

The spectral parameters of Nd³⁺ ions in Nd:KLa(WO₄)₂ crystal have been investigated based on Judd-Ofelt theory. The spectral parameters were obtained: the parameters of oscillator strengths are Ω₂=3.0887×10^–20 cm², Ω₄=1.0375×10^–20 cm², Ω₆=1.0422×10^–20 cm², the radiative lifetime is 685 μs, the quantum efficiency is 30.7%, and the fluorescence branch ratios were calculated: β₁=0.432, β₂=0.475, β₃=0.089, β₄=0.004. Electronic Publication     

Electrical properties of Sb2O3–CaO–V2O5 glasses and glass-ceramics

The d.c. conductivity (σ) of (a) glasses prepared by the press-quenching method and (b) glass-ceramics (crystallized glass) produced by post-heat treatment was investigated in the system Sb₂O₃–CaO–V₂O₅ and their conduction mechanism was studied. The glasses were n-type semiconductors with σ = 2.6 × 10^-6 ∼ 2.8 × 10^-5 S cm^-1 at 333 K for varying glass compositions. The conduction was attributed to small polaron hopping in the adiabatic regime. The estimated carrier density was 1.7 ∼ 3.8 × 10²¹ cm^-3 for V₂O₅ = 70 ∼ 80 mol% and the mobility was 3.5 × 10^-9 to 6.9 × 10^-8 cm² V^-1 s^-1. Crystallization raised the conductivity by a factor of 10³. The crystalline product in the glass-ceramics was Ca_0.17V₂O₅. The glass-ceramics were n-type semiconductors, and the conduction was interpreted by a superposition of the small polaron hopping in the crystalline and glassy phases. This revised version was published online in November 2006 with corrections to the Cover Date.     

Preparation, characterization and conductivity studies of Li3?2xAl2?xSbx(PO4)3

New NASICON type materials of composition, Li_3−2x Al_2−x Sb _x (PO₄)₃ (x = 0·6 to 1·4), have been prepared and characterized by powder XRD and IR. D.C. conductivities were measured in the temperature range 300–573 K by a two-probe method. Impedance studies were carried out in the frequency region 10²−10⁶ Hz as a function of temperature (300–573 K). An Arrhenius behaviour is observed for all compositions by d.c. conductivity and the Cole-Cole plots obtained from impedance data do not show any spikes on the lower frequency side indicating negligible electrode effects. A maximum conductivity of 4·5 × 10⁻⁶ S cm⁻¹ at 573 K was obtained for x = 0·8 of the Li_3−2x Al_2−x Sb _x (PO₄)₃ system.     

Frequency-dependent dielectric properties and electrical conductivity of CdIn<Subscript>2</Subscript>S<Subscript>4</Subscript> single crystals

The real (ɛ) and imaginary (ɛ″) parts of complex dielectric permittivity and ac conductivity (σ_ac) of CdIn₂S₄ single crystals (cubic structure) have been measured in the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz. The results demonstrate that the dielectric dispersion in the crystals has a relaxation nature. In the frequency range f = 5 × 10⁴ to 3.5 × 10⁷ Hz, the ac conductivity of single-crystal CdIn₂S₄ follows the relation σ_ac ∼ f ^0.8, characteristic of hopping conduction through localized states near the Fermi level.     

Physical Properties of AZ91D Measured Using the Draining Crucible Method: Effect of SF<Subscript>6</Subscript>

The draining crucible (DC) technique was used for measurements on AZ91D under Ar and SF₆. The DC technique is a new method developed to simultaneously measure the physical properties of fluids, the density, surface tension, and viscosity. Based on the relationship between the height of a metal in a crucible and the outgoing flow rate, a multi-variable regression is used to calculate the values of these fluid properties. Experiments performed with AZ91D at temperatures from 923 K to 1173 K indicate that under argon, the surface tension (N · m⁻¹) and density (kg · m⁻³) are [0.63 − 2.13 × 10⁻⁴ (T − T _L)] and [1656 − 0.158 (T − T _L)], respectively. The viscosity (Pa · s) has been determined to be [1.455 × 10⁻³ − 1.209 × 10⁻⁵ (T − T _L)] over the temperature range from 921 K to 967 K superheat. Above 967 K, the viscosity of the alloy under argon seems to be constant at (2.66 × 10⁻⁴ ± 8.67 × 10⁻⁵) Pa · s. SF₆ reduces the surface tension of AZ91D.     

Structure and properties of the layered oxide GdBaFeNiO<Subscript>5 + δ</Subscript>

GdBaFeNiO_5+δ has been synthesized, and its crystal structure, thermal expansion, and electrical properties have been studied. It has a tetragonal structure (sp. gr. P4/mmm) with unit-cell parameters a = 0.3910(2) nm, c = 0.7582(6) nm, and V = 115.9(2) × 10⁻³ nm³ (δ = 0.53) and is a p-type semiconductor. The linear thermal expansion coefficient of GdBaFeNiO_5+δ is 1.32 × 10⁻⁵, 1.72 × 10⁻⁵, and 1.37 × 10⁻⁵ K⁻¹ in the temperature ranges 340–655, 655–870, and 870–1080 K, respectively.