Fabrication and characterization of one-port surface acoustic wave resonators on semi-insulating GaN substrates

One-port surface acoustic wave resonators(SAWRs) are fabricated on semi-insulating high-quality bulk GaN and GaN film substrates, respectively. The semi-insulating GaN substrates are grown by hydride vapor phase epitaxy(HVPE)and doped with Fe. The anisotropy of Rayleigh propagation and the electromechanical coupling coefficient in Fe-doped GaN are investigated. The difference in resonance frequency between the SAWs between [1120] GaN and [1100] GaN is about 0.25% for the Rayleigh propagation mode, which is smaller than that of non-intentionally doped GaN film(~1%)reported in the literature. The electromechanical coupling coefficient of Fe-doped GaN is about 3.03%, which is higher than that of non-intentionally doped GaN film. The one-port SAWR fabricated on an 8-μm Fe-doped GaN/sapphire substrate has a quality factor of 2050, and that fabricated on Fe-doped bulk GaN has a quality factor as high as 3650. All of our results indicate that high-quality bulk GaN is a very promising material for application in SAW devices.

Development of two-port surface acoustic wave resonator with Al/Au electrodes for gas sensing

Simple and efficient surface acoustic wave （SAW） two-port resonators with low insertion loss and high Q-values on ST-X quartz substrate using a corrosion-proof A1/Au-stripe electrode structure are developed for gas sensing. It was composed of two shorted grating reflectors and adjacent intedigital transducers （IDT）, and an active metal film in the cavity between the IDTs for the sensitive film coating. The devices are expected to provide good protection towards metal electrode for gas sensors application in chemically reactive environments. Excellent device performance as low insertion loss, high Q factor and single-mode are achieved by carefully selecting the metallic electrode thickness, cavity length and acoustic aperture. Prior to fabrication, the coupling of modes （COM） model was performed for device simulation to determine the optimal design parameters. The fabricated single-mode SAW resonator at operation frequency of 300 MHz range exhibits matched insertion loss of ~6.5 dB and loaded Q factor in the 3000 range. Using the fabricated resonator as the feedback element, a duaresonator-oscillator with excellent frequency stability （0.1 ppm） was developed and evaluated experimentally, and it is significant for performance improvement of SAW gas sensor.

Design and fabrication of an surface acoustic wave resonator based on AlN/4H-SiC material for harsh environments

Surface acoustic wave （SAW） sensors and micro-electromechanical system （MEMS） technology provide a promising solution for measurement in harsh environments such as gas turbines. In this paper, a SAW resonator （size： 1107μm× 721 μm） based on the AlN/4H-SiC multilayer structure is designed and simulated. A MEMS-compatible fabrication process is employed to fabricate the resonator. The results show that highly c-axis-oriented AlN thin films deposited on the 4H-SiC substrate are obtained, with that the diffraction peak of AlN is 36.10° and the lowest full width at half maximum （FWHM） value is only 1.19°. The test results of the network analyzer are consistent with the simulation curve, which is very encouraging and indicates that our work is a significant attempt to solve the measurement problems mainly including high temperature stability of sensitive structures and the heat transmission of leads in harsh environments. It is essential to get the best performance of SAW resonator, optimize and characterize the behaviors in high temperatures in future research.

Bulk GaN-based SAW resonators with high quality factors for wireless temperature sensor

Surface acoustic wave(SAW)resonator with outstanding quality factors of 4829/6775 at the resonant/anti-resonant frequencies has been demonstrated on C-doped semi-insulating bulk GaN.The impact of device parameters including aspect ratio of length to width of resonators,number of interdigital transducers,and acoustic propagation direction on resonator performance have been studied.For the first time,we demonstrate wireless temperature sensing from 21.6 to 120℃ with a stable temperature coefficient of frequency of–24.3 ppm/℃ on bulk GaN-based SAW resonators.

A two-dimensional analysis of surface acoustic waves in finite elastic plates with eigensolutions

It is generally known that surface acoustic waves, or Rayleigh waves, have different mode shapes in infinite plates. To be precise, there are both exponentially decaying and growing components in plates appearing in pairs, representing symmetric and antisymmentric modes in a plate. As the plate thickness increases, the combined modes will approach the Rayleigh mode in a semi-infinite solid, exhibiting surface acoustic wave deformation and velocity. In this study, the two-dimensional theory for surface acoustic waves in finite plates is extended to include the exponentially growing modes in the expansion function. With these extra equations, we study the surface acoustic waves in a plate with different thickness to examine the coupling of the exponentially decaying and growing modes. It is found that for small thick- ness, the two groups of waves are strongly coupled, showing the significance of including the effect of thickness in analysis. As the thickness increases to certain values, such as more than five wavelengths, the exponentially decaying modes alone will be able to predict vibrations of surface acoustic wave modes accurately, thus simplifying the equations and solutions significantly.

Adaptive Lagrange finite element methods for high precision vibrations and piezoelectric acoustic wave computations in SMT structures and plates with nano interfaces

This paper discusses the validity of (adaptive) Lagrange generalized plain finite element method (FEM) and plate element method for accurate analysis of acoustic waves in multi-layered piezoelectric structures with tiny interfaces between metal electrodes and surface mounted piezoelectric substrates. We have come to conclusion that the quantitative relationships between the acoustic and electric fields in a piezoelectric structure can be accurately determined through the proposed finite element methods. The higher-order Lagrange FEM proposed for dynamic piezoelectric computation is proved to be very accurate (prescribed relative error 0.02% - 0.04% ) and a great improvement in convergence accuracy over the higher order Mindlin plate element method for piezoelectric structural analysis due to the assumptions and corrections in the plate theories.The converged lagrange finite element methods are compared with the plate element methods and the computedresults are in good agreement with available exact and experimental data. The adaptive Lagrange finite elementmethods and a new FEA computer program developed for macro- and micro-scale analyses are reviewed, and recently extended with great potential to high-precision nano-scale analysis in this paper and the similarities between piezoelectric and seismic wave propagations in layered structures and plates are stressed.

Investigation of Acoustomagnetoelectric Effect in Bandgap Graphene by the Boltzmann Transport Equation

We study the acoustomagnetoelectric (AME) effect in two-dimensional graphene with an energy bandgap using the semiclassical Boltzmann transport equation within the hypersound regime, (where represents the acoustic wavenumber and is the mean free path of the electron). The Boltzmann transport equation and other relevant equations were solved analytically to obtain an expression for the AME current density, consisting of longitudinal and Hall components. Our numerical results indicate that both components of the AME current densities display oscillatory behaviour. Furthermore, geometric resonances and Weiss oscillations were each defined using the relationship between the current density and Surface Acoustic Wave (SAW) frequency and the inverse of the applied magnetic field, respectively. Our results show that the AME current density of bandgap graphene, which can be controlled to suit a particular electronic device application, is smaller than that of (gapless) graphene and is therefore, more suited for nanophotonic device applications.

基于声表面波传感器的转子叶片应变无线测量研究

声表面波传感器可以实现无线无源工作,该特性使其在高速旋转部件测试中有重要的应用前景。利用硅酸镓镧压电晶体设计并制备了谐振型SAW传感器,研究了其应变敏感特性,并成功应用于转子叶片应变的无线测试试验。结果表明,所制备的SAW传感器的谐振频率为217.794 MHz,品质因子达到5807,应变灵敏度为-317 Hz/με。在3000~15000 r/min转速下,无线测试了转子叶片应变,测试结果与电阻应变计测量结果及有限元仿真计算结果基本一致。研究结果可以为SAW传感器在高速旋转设备的无线测试工程应用提供参考。

面内传播方向对SAW滤波器性能的影响研究

为了满足窄带声表面波滤波器对品质因数Q值和带外抑制日益增长的需求,提出了一种窄带滤波器设计方法。在基于新型POI结构谐振器的基础上,通过旋转谐振器达到改变波传播角度的目的,并利用二维全模型得到准确的实验数据,与原结构谐振器分别代入滤波器设计中进行比较。实验结果表明,该方法在一定程度上能够有效地增加带外抑制,对过渡带抑制能力有2~4 dB的提升,且具有设计简便,占用空间小等优点。

具有片上电感的改进型梯形声表面波滤波器

针对小体积声表面波(SAW)滤波器性能受封装影响较大的问题,提出了一种新型SAW梯形滤波器电路拓扑结构。通过分析滤波器高频受封装影响造成的远端抑制上翘的现象,从电路结构出发,改变版图设计,实现了片上电感。采用传统梯形滤波器结构和利用纵向耦合双模谐振器型滤波器(DMS)特殊接地结构相结合的电路拓扑结构,有助于提高带外抑制和设计灵活性。在标准的42°Y-X钽酸锂(LiTaO_(3))基板上制作滤波器,通过仿真分析得到中心频率2580 MHz、带宽50 MHz、插入损耗小于2.5 dB的高阶梯形射频SAW滤波器的最优拓扑结构。测试结果表明,通过改变电路拓扑结构关键参数和引入新的传输零点,可改善在高频段内的带外抑制特性。

基于软件无线电方案无线无源SAW温度阅读器设计

目前谐振型声表面波(SAW)阅读器射频电路大多采取分立器件设计,针对系统整体工作频段受限,硬件设计繁琐的问题,该文提出了一种软件无线电方案。软件无线电系统主体由ZYNQ和AD9361组成,射频收发端口添加LNA、PA进行信号功率放大,使用射频开关隔离收发。通过发射步进频率5 kHz、带宽1 MHz扫频信号,并对回波进行频谱分析求取最大值,最终得到谐振频率。针对SAW传感器回波持续时间较短而导致FFT计算分辨率的不足,使用重复采集增加数据长度,将阅读器的分辨率提高到468.75 Hz。实验结果表明,该阅读器能够正确探测传感器温度变化。

新型波浪加权式高性能声表面波滤波器设计

射频滤波器是移动通信中信号传输频率选择、噪声滤除干扰的不可或缺的关键器件。压电薄膜多层衬底结构的声表面波滤波器因具有高矩形度、低损耗等优点在近年来被广泛应用,但其谐振器固有的横向模式会极大影响滤波器性能。为此提出了一种新型的波浪加权式叉指设计的声表面波谐振器,该谐振器通过使用正弦函数作为交叠长度加权包络曲线,能够在不恶化谐振器性能的前提下有效抑制谐振器中的横向模式。将波浪加权式叉指设计的谐振器按照梯形拓扑结构级联,设计并制备了一款尺寸为1.1 mm×0.9 mm×0.55 mm的高性能滤波器。该滤波器中心频率为2.593 GHz,相对带宽为8.8%,插入损耗为0.52 dB。实物测试结果与仿真基本一致。

面向曲面应变监测的SAW应变传感单元的设计

高端装备的内部性能参数,如应变等的实时监测,对评估装备在各状态、各阶段的性能变化尤为重要。基于高端装备的应变无源无线监测需求,根据待测表面的曲面特性,设计了面向曲面应变传感的SAW传感芯片,并通过有限元方法对设计参数进行了仿真分析和优化设计,采用特殊结构设计以增加曲面应变监测效果及提升应变芯片灵敏度。采用MEMS加工方法制作了应变芯片样品,并使用矢量网络分析仪测量了芯片的工作频率。测试结果表明,所设计的应变传感芯片中心频率与仿真结果接近。最后搭建应变测试平台进行实验研究,结果表明,所设计的应变芯片灵敏度达到1500 Hz/με,并且在模拟曲面构建应用场景的实验装置中表现出良好的适用性,上述研究为SAW器件在曲面构件应变监测上的应用提供了参考。

一种新型双振子声子晶体带隙特性研究

为获得较宽频率范围弹性波耗散性能,并有效控制减振降噪频率带宽,提出一种新型双振子声子晶体结构,研究其能带和传输特性,并利用COMSOL Multiphysics软件计算该声子晶体结构起始频率、截止频率以及相应的振动模态,分析该结构带隙形成机理,以及散射体密度和尺寸对该声子晶体带隙的影响规律。研究表明:双振子声子晶体结构带隙打开是基体中长波行波与振子的谐振相互耦合作用产生的结果。研究结果可为工业装备的噪声与振动控制提供一种新方法。

飞机结冰探测技术

飞机结冰探测对于保障飞机飞行安全具有重要的意义,目前国外飞机结冰传感技术发展已较为成熟。文中根据结冰传感器不同的工作原理,分别按光学法、热学法、电学法、机械法、波导法等进行分类,对国内外已成型的结冰传感器或正在研发的新技术作了一个概述,介绍了各自的工作原理、性能特点及研究现状。

研究激光激发的声表面波与材料近表面缺陷的振荡效应

根据激光激发声表面波的热弹运动方程及热传导方程,采取有限元技术对方程进行求解,得到声表面波传播波形图.当声表面波经过近表面缺陷时,声表面波与近表面缺陷之间产生一种振荡效应,通过近表面缺陷的振荡波形幅值存在一个逐渐增加后又逐渐减小的过程.当声表面波经过不同深度的近表面缺陷时,振荡信号中心频率存在一定的变化规律.数值仿真结果表明:当近表面缺陷深度从0.1 mm到0.5 mm变化时,振荡效应产生的振荡信号中心频率从0.4 MHz到0.76 MHz变化,振荡信号中心频率与近表面缺陷深度呈近似线性关系,这为近表面缺陷的定量检测提供了一种理论基础.

声表面波谐振器的时域响应特性研究

由于电磁波的速度比声表面波的速度快得多,叉指换能器在进行电声转换的同时,也降低了信号能量流的速度,在一定时间内蓄积了电磁能量,所以当电磁激励结束后的一定时间内,声表面波器件仍然有瞬态输出,这是声表器件实现无源无线传感的物理基础。该文通过推导声表面波谐振器各部分的冲激响应函数,得到谐振器的冲激响应,据此分析研究声表面波谐振器在各种激励下的响应波形和特征。分析表明声表面波谐振器的瞬态响应完全反映了器件的性能参数。

高接收信噪比的远距离SAW传感系统研究

远距离的声表面波传感系统具有广泛的应用前景。为增加查询距离,需提高接收通道回波信噪比。针对接收通道干扰信号与传感响应信号频率一致且难以消除等问题,提出了一种能够在接收期间通过调节发射信号频率改变干扰信号与响应信号频率差,以频率不同抑制干扰信号,进而提高信噪比的方法。设计并测试了实验系统。实验结果表明,该方法能有效提高回波信号信噪比10.68 dB,实测查询距离大于16 m。该方法为远程无源无线传感测量提供了保证,具有实际应用价值。

智能PKE系统设计

随着汽车越来越向智能化和人性化发展,PKE系统将会成为汽车门禁系统的主流。本文介绍了一种新的汽车智能无匙门控系统设计方案,给出具体的软、硬件设计,并对设计中的关键技术进行详细的描述。该系统功耗低、收发距离远、可靠性及安全性高,具有很好的应用前景。

基于COMSOL的声表面波标签仿真

以有限元法为基础,利用有限元软件COMSOL对声表面波标签进行仿真。声表面波标签的基片材料为铌酸锂压电单晶,叉指换能器与反射栅采用金属铝电极。通过频率特性仿真,提取了标签的谐振频率和反谐振频率,分析了叉指换能器金属电极对谐振频率的影响,获得了标签的幅频特性曲线。通过回波特性仿真,研究了不同反射栅编码对应的回波脉冲,分析了反射栅金属电极对回波脉冲的影响。