弛豫铁电单晶弯曲梁矢量水听器研究

研制了一种弛豫铁电单晶(PMNT)二维矢量水听器,矢量通道和声压通道分别由两个正交压电单晶复合弯曲梁振子和PZT-5压电陶瓷圆管组成。基于弹性力学理论和水下质点振速测量原理对弯曲梁矢量水听器进行建模,推导给出了接收电压灵敏度表达式,分析了弯曲梁应力分布对矢量水听器接收性能的影响以及PMNT压电单晶材料与弯曲梁结构的匹配问题。在理论分析的基础上,研制了PMNT压电单晶和PZT、-5压电陶瓷矢量水听器样品并进行测试。测试结果表明:压电单晶矢量水听器与压电陶瓷矢量水听器相比,接收电压灵敏度提高11 dB,自噪声降低3 dB,测试结果与理论结果相符。      

中频小型矢量水听器设计研究

中频小型同振式矢量水听器采用低密度复合材料作为矢量通道外壳、压电加速度计作为内部振动传感器，以拾取水下声场中的矢量信息。与以往同振式矢量水听器设计不同的是每个矢量通道中只放置一只压电加速度计，这样，不仅减小了矢量水听器的体积，降低了水听器的整体平均密度，而且消除了以往同振式矢量水听器设计中矢量通道采用两只配对传感器而引起的相位不一致给矢量水听器定向带来的影响。而声压通道采用PVDF压电薄膜作为敏感元件，以拾取水下声场中的标量信息。     

二维同振柱形组合矢量水听器

介绍一种采用两只压电加速度计作为敏感元件的二维同振型组合矢量水听器。叙述了该矢量 水听器的设计方法,给出了相应的灵敏度和指向性测试结果。     

MEMS压电水听器和矢量水听器研究进展*

基于微电子机械系统制造技术的MEMS压电水听器和矢量水听器具有小型化、低功耗、低成本、易成阵、无源、噪音低等优点。对基于ZnO薄膜的MEMS水听器和矢量水听器进行了研究,测试结果表明,硅微压电水听器的灵敏度为-192 d B(ref.1 V/μPa),基本达到实用化的要求。MEMS压电矢量水听器等效声压灵敏度为-229.5 d B(ref.1 V/μPa),比同类型压阻式MEMS矢量水听器的灵敏度高17 d B,但还未达到实用化要求。为了进一步提高MEMS矢量水听器的灵敏度,设计了具有U形槽的压电复合悬臂梁结构和电极串联结构,采用具有更高压电系数的掺钒ZnO薄膜作为压电层,并对MEMS制备工艺进行了改进,有望显著提高MEMS矢量水听器的灵敏度。     

采用双迭片压电敏感元件的同振柱型矢量水听器

介绍一种采用双选片作为压电敏感元件的同振柱型矢量水听器。描述了该矢量水听器的设计方法，并给出所研制该类型水听器的灵敏度和指向性测试结果。     

用于矢量水听器的低频高灵敏度层合梁加速度传感器

压电加速度传感器是同振型矢量水听器的核心部件。为了满足低频高灵敏度矢量水听器的应用需求,提出并研究一种具有层合梁结构的低频高灵敏度加速度传感器。结合弹性力学和压电方程推导层合梁加速度传感器的加速度灵敏度解析解表达式,通过有限元仿真对层合梁加速度传感器尺寸进行优化,给出优化后的尺寸范围。从优化的尺寸范围中选取两种不同尺寸进行加速度传感器振动特性的仿真分析及实物制作(其中压电材料为PZT-5)与性能测试。仿真与测试结果均表明,相比已有的同尺寸金属梁加速度传感器,层合梁加速度传感器可以有效降低谐振频率并提升加速度灵敏度。当压电层厚度为0.5 mm时,加速度灵敏度最大提升3.9 dB,谐振频率下降23%。测试结果与理论分析相符。      

新型MEMS压电矢量水听器

对一种具有U形槽或双U形槽结构的MEMS压电式矢量水听器进行了仿真分析与优化,采用微机械加工技术研制出水听器芯片,并对芯片进行了封装与性能测试。提出了理论灵敏度和能量综合分析的方法,在考虑杂散电容的情况下,对敏感结构进行了更加精确的优化。从实验结果可以看出,所提出的优化方法比仅考虑理论灵敏度的传统优化方法具有更高的准确度。此外,具有双U形槽结构的矢量水听器的灵敏度比传统的单臂悬臂梁结构的灵敏度高约5.9 dB,并且具有良好的指向性。     

ZnO薄膜硅微压电矢量水听器

提出了一种基于ZnO压电薄膜的硅微压电矢量水听器,其核心部件是利用微电子机械系统(MEMS)技术制作的悬臂梁结构压电加速度计。由近似解析和有限元分析,得出加速度计的灵敏度和谐振频率,并在此基础上对其进行了优化设计。研制了MEMS压电加速度计,并装配后构成MEMS矢量水听器。测试结果表明:加速度灵敏度在20~1,200 Hz范围内约为0.83 mV/(m/s2)。经过液柱法测量,在1 kHz时,MEMS矢量水听器等效声压灵敏度为-229.5 dB (ref.1V/μPa),比同类型压阻式MEMS矢量水听器的灵敏度高17 dB以上。      

开缝压电圆环深海水听器

利用能量法得到了开缝压电圆环水中的谐振频率方程与电导纳曲线;通过构建开缝压电圆环低频接收状态等效电路图,推导了开缝压电圆环低频开路电压灵敏度;比较开缝压电圆环和整体圆环低频接收灵敏度,提出了利用开缝压电陶瓷圆环与溢流结构相结合设计深海水听器的思路;通过建立溢流式开缝压电圆环有限元仿真模型,探讨了开缝压电圆环的低频开路电压灵敏度与圆环结构参数的关系。经过仿真优化,研制了水中谐振频率600 Hz的开缝压电圆环深海水听器。水池声学测试与耐压测试结果表明,溢流式开缝压电圆环水听器在100~300 Hz频段内低频开路电压灵敏度最大值为-193.2 dB,最小值-197.9 dB,起伏-4.7 dB,耐静水压30 MPa;与采用相同尺寸压电元件的溢流圆环水听器相比,溢流式开缝压电圆环水听器的低频开路电压灵敏度提高20 dB;验证了本文提出的采用开缝压电圆环构建深海水听器的实用性。      

同振球型声压梯度水听器的研究

介绍一种采用压电加速度计作敏感元件的球形声压梯度水听器。从理论上分析了球体直径及重量对水听器灵敏度频率响应和指向性的影响；描述了该水听器的设计细节；给出作者所研制水听器的性能测试结果。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.