ZnO nanomaterials based surface acoustic wave ethanol gas sensor

ZnO nanomaterials based surface acoustic wave (SAW) gas sensor has been investigated in ethanol environment at room temperature. The ZnO nanomaterials have been prepared through thermal evaporation of high-purity zinc powder. The as-prepared ZnO nanomaterials have been characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray Diffraction (XRD) techniques. The results indicate that the obtained ZnO nanomaterials, including many types of nanostructures such as nanobelts, nanorods, nanowires as well as nanosheets, are wurtzite with hexagonal structure and well-crystallized. The SAW sensor coated with the nanostructured ZnO materials has been tested in ethanol gas of various concentrations at room temperature. A network analyzer is used to monitor the change of the insertion loss of the SAW sensor when exposed to ethanol gas. The insertion loss of the SAW sensor varies significantly with the change of ethanol concentration. The experimental results manifest that the ZnO nanomaterials based SAW ethanol gas sensor exhibits excellent sensitivity and good short-term reproducibility at room temperature.     

Surface acoustic wave properties of freestanding diamond films

"Ideal" diamond has the highest acoustic velocity of any material known, and is of great interest as a substrate material for high frequency surface acoustic wave (SAW) device structures. However, little is known of the acoustic wave propagation properties of polycrystalline diamond grown by chemical vapour deposition (CVD) techniques, the commercially accessible form of this material. We report on propagation of laser-generated SAW on three forms of freestanding CVD diamond samples, "white" polycrystalline, "black" polycrystalline, and "highly oriented" diamond. Despite differing sample nature, SAW waves propagating along the smooth (nucleation) side of the diamond showed similar velocities in the range 10600-11900 ms(-1). These results are discussed in terms of the potential of each form of CVD diamond for SAW device fabrication.     

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al₂O₃) films have been deposited on lithium niobate (LiNbO₃) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al₂O₃ films to LiNbO₃ substrates. As Al₂O₃ thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al₂O₃/LiNbO₃ structure was found to increase with the insertion of an Al₂O₃ film, which can be attributed to the stiffening effect of the Al₂O₃ layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al₂O₃ (9.7 μm)/LiNbO₃ sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO₃ structure, whose the velocity change ratio is 2%.     

基于WO3薄膜的双声路声表面波型SO2气体传感器

以金属钨粉,H2O2,CH3OH和PVP(聚乙烯吡咯烷酮)为原料,利用热喷射方法在双声路声表面波器件的测量声路上制作了细微多网孔状WO3薄膜,提出并实现了一种在常温下可以实现对二氧化硫(SO2)气体进行物理吸附和解吸附的基于WO3薄膜的双声路声表面波型SO2气体传感器.声表面波器件的双声路结构消除了由于外界测量条件改变引起的测量误差,也进一步提高了传感器的可靠性和准确性.实验结果表明,该传感器具有好的重复性,在测量范围内对各种浓度的SO2气体具有好的响应特性;传感器在0.5ppm到20ppm浓度范围内的线性灵敏度大约为6.8KHz/ppm.     

Surface acoustic wave properties of proton-exchanged LiNbO3 waveguides with SiO2 film

Surface acoustic wave (SAW) properties of proton-exchanged (PE) z-cut lithium niobate (LiNbO3) waveguides with silicon dioxide (SiO2) film layers were investigated using octanoic acid. The distribution of hydrogen measured by secondary ion mass spectrometry (SIMS) showed a step-like profile, which was assumed to be equal to the waveguide depth (d). The SiO2 film was deposited on z-cut LiNbO3 waveguide by radio frequency (rf) magnetron sputtering. We investigated the important parameters for the design of SAW devices such as phase velocity (Vp), insertion loss (IL) and temperature coefficient of frequency (TCF) by a network analyzer using thin-film aluminum interdigital transducer electrodes on the upper SiO2 film surface. The experimental results showed that the Vp of SAW decreased slightly with the increase of h/lambda, where h was the thickness of SiO2 films and lambda was the wavelength. The IL of SAW increased with increased h/lambda. The TCF of SAW calculated from the frequency change of the output of SAW delay line showed an evident decrease with the increase of h/lambda. The TCF for PE z-cut LiNbO3 was measured to be about -54.72 ppm/degreees C at h/lambda = 0.08. It revealed that the SiO2 films could compensate and improve the temperature stability as compared with the TCF of SAW on PE samples without SiO2 film.     

用于甲胎蛋白检测的表面波免疫传感器的研制

文章设计了以声表面波为振动模式的压电免疫传感器，用于检测溶液中甲胎蛋白(AFP)的含量。实验采用双通道系统进行频率变化的测定，并采用蛋白A在晶体固定AFP抗体。实验结果得到了频率变化和质量附着的定量关系，并与理论分析相比较。试验表明该免疫传感器具有较好的重复性、选择性和敏感性。     

Steric factors affecting the discrimination of isomeric and structurally related olefin gases and vapors with a reagent-coated surface acoustic wave sensor.

An investigation of steric factors affecting the olefin-olefin selectivity of a surface acoustic wave (SAW) sensor coated with reagents of the general formula trans-PtCl2(ethylene)-(substituted-pyridine) is described. Detection is based on the mass increase accompanying replacement of ethylene by other gas-phase olefins to form the corresponding olefin-substituted products. Selectivity depends on the relative reaction rates of the different olefins. Within series of structurally similar butenes, acrylates, and aromatic olefins, unusually high selectivity is observed for the less hindered olefins and complete discrimination of isomers is achieved in certain cases. Replacing pyridine by 2-methylpyridine and 2,6-dimethylpyridine in the reagent complex progressively reduces the sensor response. Sensitivities increase with increasing temperature and limits of detection ranging from about 2 to 70 micrograms/L are achieved with modest heating (30-40 degrees C) using a 30-MHz SAW oscillator. Initial results with a 52-MHz sensor shows a 3.4-fold increase in sensitivity compared to the 30-MHz sensor in rough agreement with theory.     

一种新型氨敏配合物的合成和气敏特性

以无水NiCl2和2，2‘-联吡啶-1，1‘-二氧化物为原料，在DMF溶剂中合成了一种新型氨敏配合物。经元素分析、摩尔电导、红外光谱和紫外光谱表征．该配合物的组成为Ni(bipyO2)Cl2。气敏性研究表明,配合物对氨气有好的敏感性和选择性。可用它制作氨气泄漏报警和涉氨化工生产中氨气浓度自动控制方面的传感器。     

A microfluidic surface acoustic wave sensor platform: Application to high viscosity measurements

Acoustic Love wave oscillators offer a great potentiality to integrated viscosity measurements thanks to a high sensitivity and the lack of moving parts. The main limitation is insertion losses that increase with viscosity. To overcome this limitation, this paper reports the use of microfluidic techniques with a poly(dimethylsiloxane) (PDMS) chip bonded on the Love wave device. Liquid flows of aqueous glycerol solutions up to 0.939 Pa s (939cP, 98% glycerol) have been tested in oscillator mode. These results are promising for the viscoelastic study of viscous liquids. Modelisation using the classical perturbation theory is discussed.     

Surface acoustic wave characterization of PECVD films on galliumarsenide

Surface-acoustic-wave (SAW) measurement techniques can be effectively used to determine the acoustic properties of dielectric and piezoelectric films. Such films can be used for the development of semiconductor-integrated microwave-frequency surface and bulk acoustic wave devices. The acoustic properties of silicon nitride, silicon oxynitride, silicon carbide, and TEOS glass, deposited by plasma-enhanced chemical-vapor-deposition (PECVD) on GaAs, have been characterized using linear arrays of SAW interdigital electrodes operating in the harmonic mode over the frequency region from 30 MHz to above 1.0 GHz. The elastic constants of these amorphous films have been determined by fitting theoretical dispersion curves to the measured SAW velocity characteristics. Frequency-dependent SAW propagation-loss values have been determined from the observed linear change in loss as a function of transducer separation. Preliminary measurements of the temperature coefficient of frequency (TCF) for SAW propagation of the films on GaAs are also given     

Surface acoustic wave thermogravimetric measurements of thin polymer films

The increased use of thin film polymers in microelectronic applications has resulted in the need to better understand their chemical, thermal, mechanical, and electrical properties. Of particular interest are changes in mass and viscoelasticity during curing of new high temperature polymers. A highly sensitive technique that can monitor mass and viscoelastic changes in thin polymer films during curing to high temperature is needed. In this work a surface acoustic wave (SAW) based system was developed that was capable of measuring the mass loss due to water outgassing during cure of thin polymer films in a temperature range of 20 to 400 degrees C. It also could measure the apparent glass transition temperature of acoustically thin films, and film resonance for acoustically thick films. The principle limitations of the system are the limited accuracy of temperature compensation and the limited ability to separate mass loss effects from viscoelastic effects.     

Surface acoustic wave measurements of surface cracks in ceramics

An investigation of scattering from surface cracks has been conducted. In particular, the change in the reflection coefficient of a Rayleigh wave incident on a surface indentation crack has been measured as the sample is stressed to fracture. The acoustic measurements have been correlated with the stable crack extension that precedes final failure. The crack extension behavior of as-indented specimens was found to differ appreciably from that of annealed specimens. Cracks in the annealed samples exhibited partial crack tip closure, but little stable extension, whereas cracks in the as-indented samples displayed both crack closure and irreversible crack growth. This behavior has been rationalized by invoking concepts based upon the residual stresses created by indentation.     

Measurement of evanescent wave properties of a bulk acoustic wave resonator

Acoustic wave fields in a thin-film bulk acoustic wave resonator are studied using a heterodyne laser interferometer. The measurement area is extended outside the active electrode region of the resonator, so that wave fields in both the active and surrounding regions can be characterized. At frequencies at which the region surrounding the resonator does not support laterally propagating acoustic waves, the analysis of the measurement data shows exponentially decaying amplitude fields outside the active resonator area, as suggested by theory. The magnitude of the imaginary wave vectors is determined by fitting an exponential function to the measured amplitude data, and thereby the experimentally determined dispersion diagram is extended into the region of imaginary wave numbers.     

ZnO基氯气传感元件的制备及其气敏性能

以硝酸锌和氨水为反应物,采用沉淀法制备ZnO纳米粉体.通过X射线衍射仪和透射电镜对其进行分析,结果表明,制得的ZnO颗粒为球形,粒径较小,在20nm左右,为六方形纤锌矿结构.通过掺杂In2O3,大大提高元件对氯气的气敏特性.实验表明,该元件对体积分数为20×10-6的氯气,灵敏度可达301,响应时间2秒,恢复时间在110秒左右,具有高选择性.     

Surface acoustic wave properties of (100) AIN films on diamond with different IDT positions

(100)AlN films have better surface acoustic wave (SAW) properties than (002) AlN films. In this research, (100) AlN films were combined with diamonds as a new composite SAW substrate. The SAW properties of (100) AlN films on diamonds were analyzed with 4 composite structures: interdigital transducer (IDT)/(100)AlN/diamond, (100)AlN/IDT/diamond, IDT/(100)AlN/metal/diamond, and metal/IDT/(100) AlN/diamond, and they exhibited some excellent SAW properties. Our research results provide a predictable and theoretical basis for further application on high-velocity SAW devices.     

Theoretical and experimental studies of a surface acoustic wave flow sensor

A novel SAW flow sensor is proposed based on pressure measurement. The relationship between the flow rate and the pressure difference along the flow path is evaluated. The results show a linear relationship between the flow rate and pressure difference, which agrees with the past research results. Strain analysis and FEM simulation show that phase delay depends linearly on the flow rate passing the SAW sensor, whereas SAW frequency decreases linearly upon the increase of flow rate. Phase delay experiment results agree with analysis and simulation, and the frequency change falls in a reasonable range around the predicted curve.     

Single-channel shear horizontal surface acoustic wave sensor for the identification of liquid-phase substances

The principal possibility of liquid-phase substances recognition with the aid of a single-channel sensor operating on a shear horizontal surface acoustic wave (SH-SAW) delay line has been experimentally demonstrated. The SH-SAW sensor was manufactured as a SAW delay line based on a layered structure on 36°YX LiTaO₃ crystal substrate. The response signal is related to the analyt-induced change in a pulse characteristic obtained by the frequency-to-time domain transformation of one of the measured S-parameters.     

Surface acoustic wave sensors of delay lines based on MEMS

A high frequency Surface Acoustic Wave (SAW) filter which is the key point of the SAW sensor is made by MEMS technology. The SAW filter used for sensors needs to have the factors of high frequency, low loss and high quality factor. In order to satisfy the performance of the factors, the SAW delay lines of Electrode Wave Control Single Phase Unidirectional Transducer (EWC/SPUDT) are used in the filter. This transducer can be considered as the networks of connection of some units of IDTs and the loss of device can be effectively reduced. Based on the Coupling of Modes (COM) theory and equivalent circuit modal, the mixed matrix (P matrix) of the transducers can be deduced, and further, the response of the delay lines can be obtained. According to the calculated results, a mask layout is made. Then the SAW delay line is completed and found to agree with the theoretical simulation. Its center frequency is 503 MHz and insertion loss is low enough for use of sensors.     

Mass sensitivity of the thin-rod acoustic wave sensor operated in flexural and extensional modes

The mass sensitivities of the thin-rod acoustic wave sensor in both flexural and extensional acoustic modes are presented. These are based on experiments involving the electrodeposition of a test loading material onto a thin metal fiber (the thin rod) in a delay line configuration. Only small changes in acoustic loss occur when the device is immersed in an electrolyte, particularly in the flexural mode. Copper and lead have been used as test materials to confirm that the effects of elasticity can give rise to positive and negative mass sensitivities, respectively. The experimental and theoretical values all agree in sign and are of the same order of magnitude. This result confirms a refined theoretical model that includes incorporation of the effects of elasticity and inertia. An increase in experimental mass sensitivity with decrease in fiber radius is one of the advantages for the construction of a sensitive chemical sensor based on the thin-rod device. The sensor can be operated with facility in both gas and liquid phases and offers a new technique for the study of interfacial electrochemistry on metal surfaces. The phenomenon of mechanical resonance was observed during a number of experiments.     

First-principles calculations of adsorption sensitivity of Au-doped MoS2 gas sensor to main characteristic gases in oil

Detecting oil-dissolved gases in transformer is crucial for internal discharge fault diagnosis. Methane (CH₄), acetylene (C₂H₂), ethylene (C₂H₄), ethane (C₂H₆) are some of the important fault characteristic gases in oil-immersed transformer discharge faults. The concentration and production rate can effectively reflect the insulation performance of oil-paper power transformer. In order to realize the effective detection of gases in the oil, the Au atom-doped MoS₂ (Au-MoS₂) monolayer was proposed. To study adsorption properties of different gases, the density functional theory (DFT) was used to study applicability of Au-MoS₂ two-dimensional (2D) nanomaterials for gas sensor. Meanwhile, the adsorption properties, sensitivity and electronic behavior were calculated. The results show that the doped systems have a better sensing performance for C₂H₂, C₂H₄ and C₂H₆. And Au-MoS₂ monolayer has a unique response to C₂H₂ with appropriate adsorption energy (??1.056 eV) and charge transfer (0.252 e), which are far more than CH₄ (??0.065 eV, 0.037 e). Based on the above data, Au-MoS₂ monolayer has selectivity for different oil-dissolved gases.

Graphical abstract