Viscoelastic Analysis of a Surface Acoustic Wave Gas Sensor Coated by a New Deposition Technique

An analysis of the response of surface acoustic wave sensors coated with polymer film based on new coating deposition （self-assemble and molecularly imprinted technology） is described and the response formulas are hence deduced. Using the real part of shear modulus, the polymer can be classified into three types： glassy film, glassy-rubbery film and rubbery film, Experimental results show that the attenuation response is in better consistence with the simulation than in Martin＇s theory, but the velocity response does not accord with the calculation exactly. Maybe it is influenced by the experimental methods and environment. In addition, simulations of gas sorption for polymer films are performed. As for glassy film, the SAW sensor response increases with increasing fihn thickness, and the relationship between the sensor response and the concentration of gas is pretty linear, while as for glassy-rubbery flint and rubbery film, the relationship between the sensor sensitivity anti concentration of gas is very complicated. The ultimately calculated results indicate that the relationship between the sensor response and frequency is not always linear due to the viscoelastic prooerties of the polymer.

Transparent ZnO/glass surface acoustic wave based high performance ultraviolet light sensors

Surface acoustic wave （SAW） resonators are a type of ultraviolet （UV） light sensors with high sensitivity, and they have been extensively studied. Transparent SAW devices are very useful and can be developed into various sensors and microfluidics for sensing/monitoring and lab-on-chip applications. We report the fabrication of high sensitivity SAW UV sensors based on piezoelectric （PE） ZnO thin films deposited on glass substrates. The sensors were fabricated and their performances against the post-deposition annealing condition were investigated. It was found that the UV-light sensitivity is improved by more than one order of magnitude after annealing. The frequency response increases significantly and the response becomes much faster. The optimized devices also show a small temperature coefficient of frequency and excellent repeatability and stability, demonstrating its potential for UV-light sensing application.

Surface Acoustic Wave Humidity Sensors Based on(1120) ZnO Piezoelectric Films Sputtered on R-Sapphire Substrates

ZnO films on R-sapphire substrates are prepared and characterized by x-ray diffraction and scanning electron microscopy, which indicate that the thin films are well crystallized with （1120） texture. Love wave and Rayleigh wave are used for fabrications of humidity sensors, which are excited in [1100] and [0001] directions of the （1120） ZnO piezoelectric films, respectively. The experimental results show that both kinds of sensors have good humidity response and repeatability, and the performances of the Love wave sensors are better than those of the Rayleigh wave sensors at room temperature. Moreover, the theoretical calculations of the mass sensitivity of the sensors are a/so carried out and the calculated results are in good agreement with the experimental measurements.

Development of A Surface Acoustic Wave LB Membrane Immunity Sensor

Summary: A new kind of biosensor for immunology was developed by ultrasonic technique and LB membrane. A double delay-line resonator was made by using ST-cut quartz crystal with working frequency of 149. 7 MHz. Then a layer of LB membrane was covered on it. When anti-IgM anti- body of various concentrations was added to it, the sensor can be used to detect IgM antigen. The biosensor was highly sensitive, small and light. The experimental results showed that the working frequency change of the sensor was proportional to the concentration of antibody with its dilution ratio between 1: 10000 and 1: 100. It was also first observed that the frequency curve of the sen- sor resulting from the reaction of IgM antigen and antibody undulated in the experiment.

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.

Influence of the anisotropy on the magneto-acoustic response of magnetic surface acoustic wave resonators

One-port magnetic surface acoustic wave(MSAW) resonators are fabricated by stacking multilayered(FeCoSiB/SiO2)n films directly on top of interdigital electrodes. It is shown that the magneto-acoustic response of the MSAW resonators critically depends the hysteresis of △E effect. For the magnetic multilayer without induced magnetic anisotropy, the resonance frequency( fR) exhibits a butterfly-like dependence on the external field, therefore, enabling bipolar detection of magnetic field smaller than its coercive field. However, for the magnetic multilayers with induced magnetic anisotropy, butterfly-like or loop-like fR–H curves are measured along the interdigtial electrode fingers or the SAW propagation direction, which can be attributed to the competition between the magnetic field-induced anisotropy and the stress-induced or shape anisotropy.

Surface acoustic wave devices for sensor applications

Surface acoustic wave （SAW） devices have been widely used in different fields and will continue to be of great importance in the foreseeable future. These devices are compact, cost efficient, easy to fabricate, and have a high performance, among other advantages. SAW devices can work as filters, signal processing units, sensors and actuators. They can even work without batteries and operate under harsh environments. In this review, the operating principles of SAW sensors, including temperature sensors, pressure sensors, humidity sensors and biosensors, will be discussed. Several examples and related issues will be presented. Technological trends and future developments will also be discussed.

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.

Surface acoustic wave sensor system applied to the kinetic study of urease in plant seeds

A new type of the surface acoustic wave (SAW) sensor system was delivered. Urease from several kinds of plant seeds was extracted with different extracting solvents. The urease activity, Michaelis constant and other kinetic parameters were estimated for the first time by means of the new device-SAW sensor system. Some factors such as pH, temperature, activators and inhibitors are also discussed. The method can be applied to the determination of urea content in human urine and the experimental results consist with those reported.

Development of a surface acoustic wave wireless and passive temperature sensor incorporating reflective delay line

based on optimal design on the core element of the sensor,a wireless and passive surface acoustic wave（SAW）temperature sensor integrated with ID Tag was presented.A reflective delay line,which consists of a transducer and eight reflectors on YZ LiNbO3 substrate.Was fabricated as the sensor element,in which,three reflectors were used for temperature sensing,and the other five were for the ID Tag using phase encoding.Single phase unidirectional transducers（SPUDTs）and shorted grating were used to structure the sAW device,leading to excellent signal to noise ratio（SNR）.The performance of the SAW device was simulated by the coupling of modes（COM）prior to fabrication.Using the network analyzer,the response in time domain of the fabricated 434 MHz SAW sensor was characterized,the measured S11 agrees well with the simulated one,sharp reflection peaks,high signal/noise,and low spurious noise between the reflection peaks were observed.Using the radar system based on FSCW as the reader unit.the developed SAW temperature sensors were evaluated wirelessly.Excellent1 inearity and good resolution of士1℃ were observed.

Controlling the properties of surface acoustic waves using graphene

Surface acoustic waves （SAWs） are elastic waves that propagate on the surface of a solid, much like waves on the ocean, with SAW devices used widely in communication and sensing. The ability to dynamically control the properties of SAWs would allow the creation of devices with improved performance or new functionality. However, so far it has proved extremely difficult to develop a practical way of achieving this control. In this paper we demonstrate voltage control of SAWs in a hybrid graphene-lithium niobate device. The velocity shift of the SAWs was measured as the conductivity of the graphene was modulated using an ion-gel gate, with a 0.1% velocity shift achieved for a bias of approximately 1 V. This velocity shift is comparable to that previously achieved in much more complicated hybrid semiconductor devices, and optimization of this approach could therefore lead to a practical, cost-effective voltage-controlled velocity shifter. In addition, the piezoelectric fields associated with the SAW can also be used to trap and transport the charge carriers within the graphene. Uniquely to graphene, we show that the acoustoelectric current in the same device can be reversed, and switched off, using the gate voltage.

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.

Effect of Fluid Electrical Property Changes on Surface Transverse Wave Sensors

A fluid sensor based on the surface transverse wave (STW) delay line on ST-cut quartz has been developed and tested in a large number of fluids with different viscosity and permittivity levels.Influence of fluid mechanical and electrical properties on the sensor's response has been determined and the sensor's performance has been compared with a bulk acoustic wave (BAW) viscosity sensor.The result shows that the viscosity sensitivity of the developed STW sensor represented by the signal to noise ratio is lower than that of a 5 MHz BAW sensor.Applications of the sensor in detecting the quality of industrial fluids are discussed.

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.

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.

Integrated sensor based on acoustics-electricity-mechanics coupling effect for wireless passive gas detection

Integrated sensor combines multiple sensor functions into a single unit,which has the advantages of miniaturization and better application potential.However,limited by the sensing platforms of the sensor and the selectivity of the sensitive film,there are still challenges to realize multi-component gas detection in one unit.Herein,a principle integration method is proposed to achieve the multi-component gas detection based on the acoustics-electricity-mechanics coupling effect.The electrical and mechanical properties of the Bi_(2)S_(3)nanobelts materials in different atmospheres indicate the possibility of realizing the principle integration.At the same time,the surface acoustic wave(SAW)sensor as a multivariable physical transducer can sense both electrical and mechanical properties.Upon exposure to 10 ppm NO_(2),NH_(3),and their mixtures,the integrated SAW gas sensor shows a 4.5 kHz positive frequency shift(acoustoelectric effect),an 11 kHz negative frequency shift(mechanics effects),and a reduced 4 kHz negative frequency shift(acoustics-electricity-mechanics coupling effect),respectively.Moreover,we realize wireless passive detection of NO_(2)and NH_(3)based on the SAW sensor.Our work provides valuable insights that can serve as a guide to the design and fabrication of single sensors offering multi-component gas detection via different gas sensing mechanisms.

A Novel Wireless PassiveTemperature-Pressure SAW-based Sensor

A novel wireless and passive surface acoustic wave(SAW)sensor is developed for measuring temperature and pressure.The sensor has two single-port resonators on a substrate.One resonator,acting as the temperature sensor,is located at the fixed end without pressure deformation,and the other one,acting as the pressure sensor,is located at the free end to detect pressure changes due to substrate deformation.Pressure at the free end bends the cantilever,causing a relative change in the acoustic propagation characteristics of the SAW traveling along the surface of the substrate and a relative change in the resonant frequency of the resulting signal.The temperature acts on the entire substrate,affecting the propagation speed of the SAW on the substrate and directly affecting the resonant frequency characteristic parameters.The temperature and pressure performance of this new antenna-connected sensor is tested by using a network analyzer,a constant temperature heating station,and a force gauge.A temperature sensitivity of 1.5015 kHz/℃and a pressure sensitivity of 10.6 kHz/gf at the ambient temperature have been observed by wireless measurements.This work should result in practical engineering applications for high-temperature devices.

Langasite-based SAW high-temperature vibration sensor with temperature decoupling

Monitoring high-temperature vibrations is critical in aerospace engineering,industrial manufacturing,and energy production,where harsh conditions necessitate robust vibration sensors for detecting anomalous signals.However,the accuracy of such sensors is often compromised by crosstalk between temperature and vibration signals.This study introduces a high-temperature vibration sensor based on langasite(LGS)surface acoustic wave(SAW)technology,designed to withstand temperatures up to 500℃.The sensor demonstrates high sensitivity,ranging from 12.54 kHz/g at 25℃ to 15.63 k Hz/g at 500℃.A comprehensive mechanical and electrical coupling model for the SAW vibration sensor was developed by integrating theoretical equations with numerical simulations to optimize the sensor's performance.Additionally,a novel decoupling algorithm for temperature and vibration was established,achieving thermomechanical decoupling with precise vibration parameters.Experimental results indicated a maximum relative deviation of 4.67%for the algorithm.In conclusion,the proposed LGS SAW vibration sensor emerges as a promising solution for the accurate detection of multiple parameters in high-temperature vibration monitoring.

混凝土结构钢筋锈蚀无损检测方法研究进展

钢筋混凝土结构性能优良并且成本低廉,广泛应用于基础设施建设和工业民用建筑中。在外部荷载和环境侵蚀等因素的作用下,结构中的钢筋不可避免地出现锈蚀情况,降低了结构的安全性和耐久性,导致高昂的维修费用。对混凝土结构钢筋锈蚀情况进行定期检测,对于确定锈蚀出现后结构的承载力、预测结构剩余寿命等有直接意义。经过多年发展,融合了多学科理论,钢筋锈蚀无损检测技术已经应用在一些实际工程上。但是现代工程建设对锈蚀检测技术提出了更高的要求,尤其是在大数据和机器学习等新一代信息技术的推动下,钢筋检测方法面临着向数字化、自动化和智能化的产业变革和技术升级。为了推动钢筋混凝土结构检测技术和评价体系的进步,本文对钢筋锈蚀无损检测的主要方法进行了总结评述,重点探讨新兴智能感知技术在钢筋锈蚀检测方面的应用和研究成果,提出现有技术面临的挑战,展望其未来发展方向。

表面波相控变频电磁声传感器的研制

电磁声传感器(EMAT)因其具有非接触、可设计性强等优势,在无损检测领域得到了广泛的应用。目前,大多数EMAT只能在固定频率下激发超声波,限制了传感器的应用范围,为此,提出了一种新型相控变频电磁超声传感器(PC-FC-EMAT),通过调控传感器激励信号的相控时延,可达到变频激励的目的。首先,提出了PC-FC-EMAT的设计方案,建立了PC-FC-EMAT的频域响应模型,揭示了洛伦兹力空间响应下相控时延对频域响应的作用机理;其次,建立了PC-FC-EMAT多物理场耦合仿真模型,研究了相控时延对PC-FC-EMAT时域及频域响应的作用规律,仿真验证了相控时延对PC-FC-EMAT频率响应的调控作用;最后,研制了PC-FC-EMAT,并开展实验研究。实验结果表明,所研制的的PC-FC-EMAT可实现4~12 mm的波长调控,频带范围覆盖252~687 kHz,满足设计要求。