Temperature Characteristics of Surface Acoustic Waves Propagating on La_3Ga_5SiO_4 Substrates

Langasite (LGS) is a novel piezoelectric crystal. The authors numerically analyses the temperature stability of surface acoustic waves (SAW) and the relation of SAW propagation with temperature on certain optimal cuts on LGS in this paper. The results show that LGS has better temperature stability than traditional piezo crystals. The results also demonstrate that the velocity of SAW decrease with temperature, the electro-mechanical coupling constant (k2) and temperature coefficient of frequency increases parabolically and the power flow angle increases linearly on certain optimal cuts of LGS. The calculation result compared with the experimental and show good agreement.

Surface Acoustic Wave Device with Reduced Insertion Loss by Electrospinning P(VDF–TrFE)/ZnO Nanocomposites

Surface acoustic wave(SAW) devices have been utilized for the sensing of chemical and biological phenomena in microscale for the past few decades. In this study, SAW device was fabricated by electrospinning poly(vinylidenefluoride-co-trifluoroethylene)(P(VDF-TrFE)) incorporated with zinc oxide(ZnO) nanoparticles over the delay line area of the SAW device. The morphology, composition, and crystallinity of P(VDF-TrFE)/ZnO nanocomposites were investigated. After measurement of SAW frequency response, it was found that the insertion loss of the SAW devices incorporated with ZnO nanoparticles was much less than that of the neat polymer-deposited device. The fabricated device was expected to be used in acoustic biosensors to detect and quantify the cell proliferation in cell culture systems.

Strain transfer mechanism of passive wireless surface acoustic wave torque sensors using shear lag theory

A shear-lag theory was developed to investigate the strain transfer from the metal substrate to the surface acoustic wave （SAW） resonator through a bonding layer. A three-layer model of host structure-adhesive layer-resonator layer was established. The strain transfer was theoretically analyzed, and the main factors impacting the SAW sensor measurement were studied. The relationship between the sensor response and the individual effect of all these factors under static loads was discussed. Results showed that better accuracy could be achieved with increase in the adhesive stiffness or resonator length, or decrease in the adhesive thickness. The values of the strain transfer rate calculated from the analytical model agreed well with that from the available experiment data.

Propagation Characteristics of Surface Acoustic Waves on LGT and Quartz Substrates

Langatate( LGT) is a novel piezoelectric crystal; its structure is similar to quartz. A numerical analysis of the most important propagation characteristics of surface acoustic waves( SAW) on LGT and quartz is presented in this paper. The results show that the phase velocity on LGT is slower than that on quartz.Similar to quartz,there are zero temperature cuts and pure module orientations on LGT. The electro-mechanical coupling constant( k2)of LGT is larger than that of quartz. The characteristics of SAW on LGT with different material constants are calculated and compared.The results show that there are somewhat deviations with different material constants. Especially, the temperature coefficient of frequency( TCF) shows a relatively high difference.

Application of PRO-ESPRIT algorithm in identification of surface acoustic wave identification-tags

The surface acoustic wave （SAW） identification （ID）-tags have great potential for application in radio frequency identification （RFID） due to their characteristics of wireless sensing and passive operation. In the measurements based on the frequency domain sampling （FDS）, to expand the range of detection and allow the system work in harsh environments, it is necessary to enhance the identification capability at low SNR. In addition, to identify the tags in real time, it is important to reduce identification time. Therefore, estimation of signal parameters based on the Procrustes rotations via the rotational invariance technique （PRO-ESPRIT） is adopted. Experimental results show that good identification capability is achieved with a relatively faster measurement speed.

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。

基于IDT/ZnO/AlN/Diamond结构的混合SAW/BAW压力敏感元件特性研究

利用有限元方法分析了基于IDT/ZnO/AlN/Diamond不同结构混合SAW/BAW器件的声学特性,包括层状薄膜结构、ZnO薄膜刻蚀结构和填充结构。结果表明,当h_(ZnO)/λ=0.3、h_(AlN)/λ=0.5,且ZnO被完全刻蚀(d/h_(ZnO)=1)时,刻蚀结构混合SAW/BAW(准西沙瓦波)的机电耦合系数(K^(2))取得最大值6.54%,比层状结构(d/h_(ZnO)=0)提升了近一倍。刻蚀结构中,SiO_(2)和Diamond填充物的引入不仅提高了准西沙瓦波的K_(2),而且改善了其压力传感特性。当d/h_(ZnO)=1时,SiO_(2)和Diamond填充结构准西沙瓦波的压力频移分别为81.2 kHz/MPa和207.4 kHz/MPa,比刻蚀结构分别提高了58.7%和300%;同时,Diamond填充物的引入使准西沙瓦波的频率压力系数(PCF)达到最大值297×10^(-6)/MPa,比d/h_(ZnO)=0时提高了约30%。由此可知,通过引入不同的填充物可以开发不同的功能传感器,在压力、温度和气敏等传感领域将具有极大的应用前景。

离子束刻蚀技术在SAW滤波器频率修整上的应用

随着声表面波(SAW)滤波器的应用向高频、窄带方向延伸,在制造过程中准确地控制其中心频率及一致性变得越来越困难,需要对SAW滤波器的频率进行微调。重点介绍了一种在SAW滤波器上可实现目标频率修整的离子束刻蚀修频工艺,通过实验发现刻蚀厚度不同对滤波器表面的影响程度不同,一次离子束刻蚀厚度为50 nm时,铝膜表面出现微结构变化。分析了对晶圆、器件进行离子刻蚀工艺引起热损伤的机理,表征了不同刻蚀厚度对SAW滤波器粘接芯片的剪切力和硅铝丝键合力的影响。根据实验现象及结果提出了分梯度多次刻蚀的优化方案,给出了不同刻蚀厚度的刻蚀精度,对实验结果进行拟合,得到中心频率与刻蚀厚度的关系方程,从频率、插入损耗和通带方面分析了离子束刻蚀工艺对SAW滤波器电学性能的影响。经离子束刻蚀修频后,滤波器中心频率提高2 MHz,中心频率标准差由0.4 MHz减少为0.15 MHz,中心频率的均一性由0.29%改善至0.11%,频率一致性变好。

Using coupling slabs to tailor surface-acoustic-wave band structures in phononic crystals consisting of pillars attached to elastic substrates

The propagation of surface acoustic waves(SAWs) in two-dimensional phononic crystals(PnCs) with and without coupling-enhancement slabs was theoretically investigated using a three-dimensional finite element method.Different piezoelectric substrates,for example,lithium niobate(LiNbO_3),gallium nitride(GaN),and aluminium nitride(A1N),were taken into account.Compared to the PnCs without coupling-enhancement slabs,the coupling between each pillar and its nearest neighbor was largely enhanced in the presence of slabs.The bandwidth of the first directional band gap increased markedly compared with its initial value for the PnCs without a slab(within square symmetry).In addition,with increasing thicknesses of the slabs bonded between neighboring pillars,the first directional band-gap and second directional band gap of the PnCs tend to merge.Therefore,the structure with coupling-enhancement slabs can be used as an excellent electrical band elimination filter for most electro-SAW devices,offering a new strategy to realize chip-scale applications in electroacoustic signal processing,optoacoustic modulation,and even SAW microfluidic devices.

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.

Peculiarities of surface acoustic waves,propagation in structures with functionally graded piezoelectric materials,coating from different ceramics on the basis of PZT

A model of a piezoelectric structure with an inhomogeneous coating is considered.The structure is a homogeneous half-space made of PZT-5H ferroelectric ceramics with a functionally graded coating.The properties of coating vary continuously in thickness from parameters of one material to parameters of another material in a continuously nonmonotonic or piecewise-continuous manner.As coating materials,various combinations of ceramics of different stiffness based on PZT are considered.Using the example of the problem of the propagation of sh-waves in a piezoelectric structure,we studied the influence of the ratio of the physical parameters of the coating materials,the localization region,and the size of the transition zone of one material to another on the propagation features of surface acoustic waves(SAWs)and the structure of the wave field.

Research on transmission performance of a surface acoustic wave sensing system used in manufacturing environment monitoring

Surface acoustic wave （SAW） sensors show great promise in monitoring fast-rotating or moving machinery in manufacturing environments, and have several advantages in the measurement of temperature, torque, pressure, and strain because of their passive and wireless capability. However, very few studies have systematically attempted to evaluate the characteristics of SAW sensors in a metal environment and rotating structures, both of which are common in machine tools. Simulation of the influence of the metal using CST software and a series of experiments with an SAW temperature sensor in real environments were designed to investigate the factors that affect transmission pertbrmance, including antenna angles, orientations, rotation speeds, and a metallic plate, along with the interrogator antenna-SAW sensor antenna separation distance. Our experimental measure- ments show that the sensor＇s optimal placement in manufacturing environments should take into account all these factors in order to maintain system measurement and data transmission capability. As the first attempt to systematically investigate the transmis- sion characteristics of the SAW sensor used in manufacturing environment, this study aims to guide users of SAW sensor appli- cations and encourage more research in the field of wireless passive SAW sensors in monitoring applications.

Tunable patterning of microscale particles using a surface acoustic wave device with slanted-finger interdigital transducers

Polymer-based materials with patterned functional particles have been used to develop smart devices with multiple functionalities.This paper presents a novel method to pattern microscale particles into biocompatible polyethylene glycol diacrylate(PEGDA)fluid through a designed surface acoustic wave(SAW)device with slanted-finger interdigital transducers(SFITs).By applying signals of different frequencies,the SFITs can excite SAWs with various wavelengths to pattern the microscale particles.The structural design and working principle of the SAW device with SFITs are firstly presented.To investigate the generation of standing SAWs and pressure field distributions of the SAW device with SFITs,a numerical model was developed.Simulation results showed that different strip-shape patterned pressure fields can be generated,and the period and width of adjacent strips can be adjusted by changing the frequencies of the excitation signals.Experiments were performed to verify that the microscale particles in the PEGDA solution can be successfully patterned into strip-shape patterns with various positions,periods,and widths.The results obtained in this study demonstrate that the developed method of using an SAW device with SFITs can be used for tunable patterning of microscale particles in solutions,and shows great potential for biomedical and microfluidic applications.

Walsh Threshold Matched-Filtering Based Anti-collision for Surface Acoustic Wave Tags

Surface acoustic wave(SAW) tags are truly passive devices and do not contain any intelligence,so the question of multiple read in the reading range comes up.The paper suggests a Walsh matched-filtering method in Walsh field to distinguish the collision tags with a threshold.In advance,the code states with special sequency are selected from large possible states and the sequency variables of these tags are saved in a database.When a few tags are read simultaneously in read range,the received signal is filtered by the known sequency of single tag in database,and then these tags can be distinguished by the filtered result.Proper threshold selection improves operation speed.Experiment proves that this method is useful and reliable.

碳纳米管聚苯胺薄膜SAWSO2传感器的实验研究

以128°YX-LiNbO3晶体上实现的双声路声表面波(SAW)器件为载体,在器件的测量声路上制作了对SO2气体具有敏感作用的碳纳米管聚苯胺薄膜,提出了一种基于碳纳米管聚苯胺薄膜的SAW SO2气体传感器。该传感器中的双声路结构消除了因外界测量条件改变引起的测量误差,提高了传感器的可靠性和准确性。利用原位法制备的碳纳米管聚苯胺增加了SO2气体的吸附面积,提高了传感器的灵敏度。实验结果表明,基于碳纳米管聚苯胺薄膜的SAW SO2气体传感器在测量范围内对各种浓度的SO2气体具有好的响应特性;当输入体积分数为1×10-6时,传感器的响应灵敏度约为8.3 kHz,比单一聚苯胺薄膜高1.8 kHz。此外,该传感器也具有更好的线性特性。

一种可同时测量温度和压力的新型SAW传感器

针对汽车轮胎压力监测系统（TPMS）的典型应用,提出了一种基于声表面波（SAW）的新型传感器.这用SAW延迟线理论,温度和压力对于传感器的影响能够通过射频回波信号的变化反映出来.通过在数据处理中引入权重因子,实现对于温度和压力的准确测量.在一定压力（0-200 kPa）和温度（20-100℃）范围内的测试结果表明,该传感器能够同时准确测量温度和压力.SAW传感器对温度的测量精度可以达到0.05℃,对压力的测量精度可以达到7.2 kPa.在对于可靠性和耐久性具有特殊要求的汽车轮胎压力监测等领域,该传感器简单的结构和无线无源的测量方式,进一步提高了其实用性和推广价值.

UV light driven high-performance room temperature surface acoustic wave NH_(3) gas sensor using sulfur-doped g-C_(3)N_(4) quantum dots

Nanomaterials integrated surface acoustic wave(SAW)gas sensing technology has emerged as a promising candidate for realtime toxic gas sensing applications for environmental and human health safety.However,the development of novel chemical interface based on two-dimensional(2D)sensing materials for SAW sensors for the rapid and sensitive detection of NH_(3)gas at room temperature(RT)still remains challenging.Herein,we report a highly selective RT NH_(3)gas sensor based on sulfur-doped graphitic carbon nitride quantum dots(S@g-C_(3)N_(4)QD)coated langasite(LGS)SAW sensor with enhanced sensitivity and recovery rate under ultraviolet(UV)illumination.Fascinatingly,the sensitivity of the S@g-C_(3)N_(4)QD/LGS SAW sensor to NH_(3)(500 ppb)at RT is dramatically enhanced by~4.5-fold with a low detection limit(~85 ppb),high selectivity,excellent reproducibility,fast response/recovery time(70 s/79 s)under UV activation(365 nm)as compared to dark condition.Additionally,the proposed sensor exhibited augmented NH_(3)detection capability across the broad range of relative humidity(20%–80%).Such remarkable gas sensing performances of the as-prepared sensor to NH_(3)are attributed to the high surface area,enhanced functional groups,sulfur defects,UV photogenerated charge carriers,facile charge transfer in the S@g-C_(3)N_(4)QD sensing layer,which further helps to improve the gas molecules adsorption that causes the increase in conductivity,resulting in larger frequency responses.The gas sensing mechanism of S@g-C_(3)N_(4)QD/LGS SAW sensor is ascribed to the enhanced electroacoustic effect,which is supported by the correlation of resistive type and COMSOL Multiphysics simulation studies.We envisage that the present work paves a promising strategy to develop the next generation 2D g-C_(3)N_(4)based high responsive RT SAW gas sensors.

剥离工艺制作SAW滤波器IDT的研究

研究了用于声表面波滤波器的微米尺度的叉指换能器的制作工艺。利用剥离工艺,分别采用铝和铬金两种金属制作了叉指换能器的电极,分析了剥离工艺制作叉指电极时的工艺特性。对加工样品的测量分析结果表明,利用剥离工艺制备的叉指换能器电极线条光滑、陡直、清晰,但是成品率较低。对比分析了采用铝和铬金制作的叉指换能器样品结构,结果表明两种金属材料在剥离液中的腐蚀时间不同,铝材料需要较长的剥离时间;两种材料制作的电极图形质量也有差异,铝材料制作的电极更为陡直、精细。

QCM和SAW传感器的原理及其在现场检测中的应用

压电化学传感器是一类重要的质量敏感型检测器,由于具有体积小、灵敏度高、响应时间快等优越性而具有极好的应用前景。本文介绍了体声波化学传感器(QCM)和表面声波化学传感器(SAW)的原理,概述了最近几年的应用情况及提高灵敏度的方法,并对其发展趋势进行了展望。

SAW氢传感器的研究进展

对声表面波(SAW)氢传感器的研究目前主要集中在改善其敏感性、加快响应速度、增强稳定性以及消除温度的影响。要实现这些目标,一是改善SAW氢传感器的关键部件——敏感薄膜的性能;二是改进传感器的结构。对主要研究机构在这些方面的研究进行了系统的综述,并提出了发展方向。