谐振式检测器指条厚度对质量型声表面波传感器灵敏度的影响

研究了谐振器指条厚度对质量型声表面波传感器灵敏度的影响.利用耦合模方程推导出耦合模参量与周期栅阵禁带边界频率的关系,结合有限元及P矩阵模型,获得了声表面波传感器灵敏度随指条厚度的变化关系。制备3种不同铝指条厚度(1600?,1900?,3100?)的声表面波谐振器,通过对其表面中心区域沉积SiO_2层验证了计算结果。结果表明:采用ST-X石英基底的声表面波谐振器对SiO_2负载检测时,传感器的灵敏度随铝指条厚度的增加先变大后减小,最优归一化指条厚度为1.9%。分析表明,指条厚度对传感器灵敏度的影响主要来自于传播速度和耦合系数的共同作用,通过优化指条厚度的方法可改善传感器的灵敏度.     

谐振式检测器谐振腔对声表面波气相色谱仪灵敏度的影响

研究了谐振式检测器谐振腔对声表面波气相色谱仪灵敏度的影响。构建无液膜负载和有液膜负载下压电基片和金属指条结构的三维有限元模型,利用有限元方法提取不同周期结构的耦合模参量,结合P矩阵级联技术,推导出传感器灵敏度随检测器腔体结构改变的变化关系。实验制备了两种三换能器结构的声表面波谐振器,其输入换能器与输出换能器间距离分别为22.25倍波长和1.25倍波长,通过测试甲基膦酸二甲酯气体,验证理论计算结果。结果表明:缩短谐振器的谐振腔长度使器件中心处能量更为集中,有效地提高了声表面波气相色谱仪灵敏度。      

声表面波介质表面受力条件下的波速变化研究

为了计算力负载直接作用在声表面波传播表面时波速的变化特性,通过有效材料系数将负载引入,并用广义Green函数计算声速,得到了数值计算的结果,并用声表面波谐振器进行了实验.实验结果表明,将力负载直接加载在声表面波的传播表面时,波速变化量和力负载大小近似为线性关系,该加载方式下,实验中声表面波谐振器的谐振频率对外加质量负载有较高的灵敏度,可达1900 Hz/g.     

应用于气体传感器的具有铝/金电极的单模式两端对声表面波谐振器

为改善气体传感器性能,通过器件优化设计获得了一种应用于气体传感器的具有低损耗、高品质因子(Q)的单模式两端对声表面波(SAW)谐振器。该谐振器由两个换能器、分置于换能器两边的短路栅反射器以及在换能器之间分布的用于敏感膜镀膜的约2.5mm金属薄层构成。谐振器采用铝/金双层电极以降低测试气体环境的腐蚀影响。利用经典耦合模(COM)理论对器件性能进行了仿真以提取优化的结构设计参数。基于仿真结果,实验研制了基于300MHz频率的新型铝/金电极SAW两端对谐振器,测试结果显示所研制器件具有较低损耗(〈7dB),较高Q值(-3000)以及单一谐振模式的特点,并且,以所研制的新型谐振器为频率控制单元的谐振器型振荡器表现出良好的频率稳定度(t15Hz/h),这对于改善气体传感器的检测下限及稳定性等性能指标具有重要意义。      

新型成膜法的SAW气体传感器聚合物膜的粘弹性分析

分析了一种基于自组装和分子印迹技术的声表面波气体传感器的响应模型。首先利用Martin理论和Auld的摄动方法分析金膜对于声表面波的扰动效应,然后将其扩展至覆盖于金膜上的聚合物膜对于声波的扰动分析。以剪切模量的实部为参量,可以将聚合物分为三种状态,即玻璃状膜、玻璃状-橡胶态膜和橡胶态膜。最后模拟分析了聚合物膜对于气体的吸附特性。结果表明由于聚合物膜的粘弹特性,传感器响应与其工作频率并不完全呈线性。通过实验获得了不同膜厚的采用新型成膜方法的聚合物对SAW的扰动效应并与理论计算结果进行对比,结果显示相对不考虑活性表面金膜的Martin理论,对于衰减扰动的分析与实验结果更加一致。但是对速度的扰动与实验结果有一定偏差。另外还模拟了基于新型成膜方式的气体传感器聚合物敏感膜对于气体的吸附效应,结果显示对于玻璃状膜,传感器的响应随着敏感膜厚的增加而递增,并与气体浓度呈现良好的线性特性,但是对于橡胶态膜,传感器灵敏度与膜厚之间的关系相对复杂。     

声表面波梁式加速度传感器的优化设计

为获得传感器的优化设计,对一种声表面波梁式加速度传感器敏感机理进行了研究。从声波波动方程出发,结合有限元分析以及微扰理论对加速度作用力作用下声表面波传播特性进行分析,以此构建梁式声表面波加速度传感器敏感机理的理论模型,特别分析了压电梁材料及几何结构、振子质量对传感响应的贡献以确定传感器优化的几何参数。为验证理论分析结果,实验研制了基于ST-X石英悬臂梁结构的差分振荡式声表面波加速度传感器,并利用精密振动台对所研制传感器性能进行评价。实验结果显示,在给定加速度测试范围内,采用ST-X石英梁并延长梁长度、降低梁厚度以及采用较大的阵子质量将有效的改善传感器检测灵敏度,在±2 g范围内加速度灵敏度可达27 k Hz/g,且实验结果很好的验证了理论模型。     

声表面波气体传感器研究进展*

基于声表面波技术的气体传感器包括采用敏感膜和结合气相色谱两种方式。比较而言,采用敏感膜的声表面波气体传感器体积小、功耗低,适应小型化毒气报警器的发展要求,但可检测的气体种类少、灵敏度低、存在交叉干扰问题;声表面波与气相色谱联用的气体分析仪灵敏度高、可检测气体种类多、很好地解决交叉干扰问题,特别适合于复杂大气背景条件下的气体成分分析。本文从传感器响应机理分析与物理功能结构两方面出发介绍了两类声表面波气体传感器的研究进展情况。     

声表面横波压力传感器的电极质量负载效应分析方法

针对声表面横波(Surface Transverse Wave,STW)压力传感器,提出了一种考虑叉指电极质量负载的有限元和微扰理论结合分析方法。首先构建包含叉指电极的有限元模型,通过计算电极表面的面电荷得到器件的等效输入导纳,由导纳谐振点处提取STW传播声场,然后根据微扰理论,由STW传播声场以及压力引起的传感器结构的应力应变,得到包含电极质量负载影响的STW传感器的灵敏度。以一种基于ST-90°X石英材料的点压式STW压力传感器为例进行了理论计算,电极厚度为0.17 μm和0.21 μm时,计算灵敏度分别为-54.9 kHz/bar和-21.7 kHz/bar,说明电极质量负载对于传感器有较大影响。制作电极厚度为0.17 μm的传感器进行测试,得到-57 kHz/bar的压力灵敏度,实验结果和理论结果吻合,证明计算方法的有效性。      

超小型声表面波谐振器

传统声表面波谐振器中的指条反射阵占据了器件的大部分尺寸。由于剪切横波(SH wave)在材料基片的自由端面反射时不产生模式转换,因此可望利用自由端面来代替SH型声表面波谐振器中的指条反射阵,实现超小型低损耗的新型声表面波谐振器。本文首先用COM理论对新结构的谐振器进行了讨论,并且在实验上实现了120MHz至440MHz的几个单端谐振器(ST36°石英基片),其插入损耗从0.87dB至1.29dB,面积缩小到传统谐振器的50％至25％。     

用于电流传感的声表面波磁致伸缩效应

利用声表面波(SAW)磁致伸缩效应可以实现一种快速、高灵敏度的电流检测方法,但磁致伸缩薄膜内部矫顽力导致了明显的磁滞误差。磁致伸缩薄膜的栅阵化设计可以减小磁致伸缩时薄膜内部矫顽力,抑制磁滞现象,从而实现高灵敏和低迟滞误差的SAW电流检测。结合有限元和耦合模理论对沉积铁钴(FeCo)薄膜栅阵的声表面波电流传感器中的磁致伸缩效应进行分析,对传感响应进行仿真,确定优化的传感结构参数。为验证理论分析,实验研制了频率为150 MHz的声表面波电流传感器件,并结合差分振荡电路及亥姆霍兹线圈,建立传感器测试系统.实验结果表明,磁致伸缩薄膜的栅阵设计大幅降低了迟滞误差,并显著提升了传感器灵敏度。      

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

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.     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.