共查询到20条相似文献,搜索用时 575 毫秒
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弛豫铁电单晶PMNT具有优异的压电性能,它可以替代传统的压电陶瓷,在声呐探测,超声成像,高应变驱动器等方面得到广泛的应用。我们已经成功地生长地了尺寸为φ40&;#215;80mm的PMNT单晶,其主要性能为,压电系数d33&;gt;3000pC/N,介电常数ε-5000,损耗tanδ&;lt;0.9%,纵向长度伸缩机电耦合k33-94%,厚度伸缩机电耦合kt-62%,我们成功地制备出了在电声成像系统中的PMNT单晶压电换能器,使探测器的电声信号幅度有显著提高,充分显示了新型压电单晶在电声换能技术中具有巨大的应用前景。 相似文献
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本文简要介绍了用TDK-36单晶炉拉制的较大直径(φ=25mm)、低位错(<100cm ̄(-2))的锑化铟单晶的理论和实践。通过对晶体生长室内温场,特别是内外坩埚尺寸的调整及对循环水流量的控制,成功地拉制出较大直径、低位错的锑化铟单晶。 相似文献
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以55%PbO(摩尔分数)作熔剂,BaTiO3为成核剂,采用高温熔剂法加底部冷却技术成功生长了PZNT91/9单晶,其最大晶体尺寸达15 mm×13 mm。X-射线衍射(XRD)分析表明晶体为纯钙钛矿相,其显露面为立方晶形(100)面族。热释电研究表明单晶在69℃发生三方-四方相变,在174℃发生四方-立方相变。单晶的压电性能测试结果为:平面和厚度机电耦合系数分别为0.69、0.49;压电常数d33为1 330 pC/N;在13.6 kV/cm电场下应变达0.312%。 相似文献
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(YbTbBi)_3Fe_5O_(12)块状单晶生长及其磁光性能 总被引:2,自引:2,他引:0
用助熔剂法生长出(YbTbBi)3Fe5O12块状单晶,测量了该单晶在1.0~1.7μm范围的Faraday旋转谱及透射谱.当温度为10~80℃,λ=1.55μm时,测得该单晶的Faraday旋转温度系数为2.0×10-2.(°)·mm-1·K-1.所得结果表明:(YbTbBi)3Fe5O12单晶既有较大的Faraday旋转角,又有很小的温度系数 相似文献
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铁电钛酸铋超微粉及陶瓷的研究 总被引:13,自引:4,他引:9
采用类溶胶-凝胶方法制备了铁电Bi4Ti3O12超微粉,分别用X射线衍射、透射电子显微镜、激光散射粒度仪和差热分析仪对其结构、形貌、粒度和相变特性进行了测试分析。结果表明,超微粉形成了正交晶系Bi4Ti3O12结构,晶粒尺寸为10~50nm。由微粉制备了Bi4Ti3O12陶瓷,其介电常数和损耗角正切分别为ε=105.6和tgδ=0.052(100Hz)及ε=97.2和tgδ=0.00036(4MHz),铁电参数矫顽电场Ec为2.91×106V/m,剩余极化强度Pr为7×10-3C/m2。 相似文献
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准分子激光扫描淀积PZT/YBCO结构铁电薄膜 总被引:2,自引:1,他引:1
利用脉冲准分子激光(工作气体XeCl,波长308nm,脉宽28ns)在外延YBCO/LaAlO3(100)单晶基片上淀积了Pb(Zr0.55Ti0.45)O3铁电薄膜,YBCO薄膜既为生长高取向PZT薄膜提供了晶体匹配条件,同时也为PZT铁电薄膜提供了下电极。讨论了工艺参数对晶相结构和表面形貌的影响。用X射线衍射表征了该多层膜的晶相结构,扫描电镜观察其表面形貌。PZT铁电薄膜的剩余极化为21μC/cm2,矫顽场为65kV/cm。 相似文献
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In 1948, Geronimus discovered that the inverse of the sum of the (modulus squared) orthogonal polynomials corresponding to a Toeplitz matrix converges to the point spectrum as the matrix order goes to infinity. In 1969, Capon independently generalized part of Geronimus' result to the random field setting as a fixed-order point spectrum estimator. Within signal processing, this Geronimus-Capon result is known as the maximum likelihood spectral estimator or alternatively, the minimum variance estimator. A simple proof that the Geronimus-Capon spectra estimator converges to the point spectrum in the multichannel setting is presented 相似文献
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利用调制引入循环平稳的CDMA盲信道估计 总被引:5,自引:0,他引:5
针对CDMA系统给出了一种新颖的盲辨识方法.它利用了恒模复序列调制产生的循环平稳性,其特色是,在接收机上可以根据循环统计量的支撑的不同,将各个用户的二阶循环统计量分离开来,每个用户形成自己的小规模子空间.采用已成熟的子空间方法,可以识别出不同的用户各自的片率传输信道,以便于均衡和检测.文中给出了自己的信道可辨识性的条件和证明,提出了辨识算法,并对算法进行了模拟.方法简单明了,适合于CDMA上行链路信道. 相似文献
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In this paper, a new low-power versatile current-mode rectifier is proposed. As a salient feature, the proposed rectifier provides two positive half-wave, two inverting negative half-wave or two full-wave outputs from the same configuration. The proposed circuit employs only a dual-output second-generation current conveyor (DO-CCII) and a core rectifying circuit consisting of twelve MOS transistors. The input and output signals are current. Favorably, by adding two additional transistors, the proposed rectifier can also rectify voltage signals with electronic tuning capability. The simple and MOS only structure of the proposed circuit is highly attractive from integration point of view. In spite of providing multiple outputs at the same time, the proposed rectifier enjoys low power consumption. PSPICE simulations using 0.18 μm CMOS parameters and supply voltage of ±0.9 V demonstrate a precise operation and good temperature stability. 相似文献
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用前馈补偿法对双输入双输出系统(TITO)时滞系统进行解耦,有些系统的补偿器往往会含有超前环节,无法用器件实现。针对这一问题,该文提出了一种近似方法:把超前环节展开成泰勒级数,根据精度要求取前几项。该文通过Simulink软件对实例进行了仿真分析,证实了用这种方法设计的补偿器非常简单,能很好地实现解耦。这种近似的补偿器也可以用硬件和软件实现,所以这种方法是有实用价值的解耦法。 相似文献
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《Photonics Technology Letters, IEEE》2008,20(19):1618-1620
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Enhanced group velocity dispersion (GVD) due to coupled-waveguide modes (supermodes) has been experimentally observed, for the first time, using an InGaAsP-InP semiconductor coupled waveguide structure. The observed waveguide dispersion, which was due to supermodes, was about 10 3 times as large as that due to single-waveguide modes. Preliminary experimental results on the compression of a chirped pulse using coupled-waveguide structures is also presented, and shows its potential for use in a simple, compact, and transmissive dispersion compensator or pulse compressor 相似文献
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This paper presents an analysis of the blocking phenomenon in circuit-switched routing policies with alternate routing and trunk reservation. From the usual assumptions on the offered traffic (Poisson) and the service time (exponential distribution), a classical Markov chain model is derived. Some approximate formulas are given to compute the blocking probabilities for first- and second-choice traffic. The accuracy of the proposed estimates is evaluated by direct comparison with already known results in simple cases and with the exact solution of the state equations. 相似文献