A lateral field excited liquid acoustic wave sensor

Lateral field excited (LFE) AT-cut quartz acoustic wave sensors in which the electrodes are located on the reference surface have been fabricated and tested in liquid environments. The sensing surface, which is opposite to the reference surface, is free allowing the electric field of the thickness shear mode (TSM) to penetrate into the liquid. This results in increased sensitivity to both mechanical and electrical property changes of the liquid. In the present paper, several 5-MHz LFE sensors with a range of electrode spacings were exposed to liquid environments in which the viscosity, relative permittivity, and conductivity were varied. The LFE sensors demonstrate sensitivity to viscosity that is more than twice that obtained for the standard quartz crystal microbalance (QCM), and sensitivity to relative permittivity and conductivity about 1.5 times that of the QCM sensors with modified electrodes. The present results clearly indicate that the LFE sensors may have a wide range of liquid phase applications in which sensitivity is crucial.     

Semiconductor liquid helium level sensor

An all purpose liquid helium level detector utilizing a silicon transistor is described. The small size, low power dissipation, fast response time and tolerance of high magnetic fields combine to make this sensor suitable for the majority of helium level detection applications.     

Simple liquid nitrogen level monitor using copper wire as a sensor

A simple, compact and reliable liquid nitrogen level monitor is described which uses fine copper wire for continuous monitoring of liquid nitrogen levels in a dewar. The monitor has an analogue meter and light emitting diodes as indicators. A level of resolution better than ± 10 mm has been achieved. Sensor construction and the sensing electronic circuit are presented. The monitor incorporates an automatic liquid nitrogen refill system and remote shut-down of high voltage bias supply to the detector. Also built into the system is an alarm which sounds when the liquid nitrogen level is unacceptably low or the supply is exhausted.     

磁性液体水平传感器的研究

利用磁性液体既具有磁体磁性又具有液体流动性的特性设计出一种新型的一维磁性液体水平传感器.推导了水平传感器输出电压的表达式.对影响传感器灵敏度的各因素(激励信号频率、峰值电流、磁性液体磁化系数)进行了分析,并进行了相应的实验研究.理论计算结果与实验结果相符合.这种传感器具有高灵敏度的特性.     

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.

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新型液位传感器和电动阀在液位控制中的应用

电子液位控制系统可以很好地实现对液位的控制,保证系统的平稳运行并提高效率。但是电子液位系统中的关键部件,如液位传感器,依然面临某些问题,例如液位传感器和执行机构的准确性/控制精度以及可维护性问题。本文尝试采用新型液位传感技术——导向雷达液位测试技术配合电动阀作为执行机构,确保工业制冷系统安全运行可靠的同时,提高系统效率、增强系统的可维护性。     

Differential absorption sensor applied for liquid oxygen measurements

Differential laser absorption was investigated for its merit in liquid oxygen (LOX) sensing. Whereas previous researchers have used differential absorption to detect trace concentrations of a substance, we use differential absorption to monitor small changes in large amounts of a substance. Two lasers of different wavelengths were intensity modulated 180 deg out of phase from each other and multiplexed into a single beam. After probing the LOX, the total transmitted signal was demodulated by a lock-in amplifier. Our experiment simulated rapid changes in LOX number density by varying the length of an approximately 73 mm path through pure LOX. In this experiment, we demonstrated the ability to monitor LOX number density with an uncertainty of approximately 1% with a time constant of 3 micros. The uncertainty could be halved by doubling the path length, and this improvement could be repeated as long as the relative intensity noise of the lasers is the dominating factor. We discuss the benefits of differential absorption for problems requiring an extended dynamic range.     

Scanning tomographic acoustic microscopy using shear waves

We propose to use shear waves instead of longitudinal waves in a novel scanning tomographic acoustic microscope (STAM) in which the specimens are solid. When a specimen with a shear modulus is immersed in the microscope's water bath, mode conversion takes place at the water-solid interface. The shear wave energy is detectable and can be used for image reconstruction. Although wave transmission in most solid specimens is limited to about 20 degrees for longitudinal waves, it is about twice that for shear waves. Also, velocities of shear waves are lower than those of longitudinal waves and hence the wavelengths at the same frequency are smaller. For these and other reasons we can expect that for many specimens the resolution of a shear-wave STAM to be substantially better than that of a longitudinal-wave STAM. We use computer simulation in order to compare the operation of a shear-wave STAM with that of the conventional longitudinal-wave STAM. We have simulated tomographic reconstruction for each. The corresponding critical angles of incidence are computed and tomographic reconstructions of a particular solid specimen is obtained by using the back-and-forth propagation algorithm (BFP). Our simulation results show that shear-wave STAM has better resolution than longitudinal-wave STAM.     

Multi-technique approach for non destructive diagnostic of structural composite materials using bulk ultrasonic waves,guided waves,acoustic emission and infrared thermography

The damage phenomenon occurring in glass fiber reinforced polymer (GFRP) laminate is very complex; it is inherently an anisotropic, multi-source and multi-scale process. In the present work, a new non destructive testing (NDT) approach is suggested using, simultaneously, multiple techniques. These are bulk and guided ultrasonic waves, acoustic emission, passive and active infrared thermography, for evaluating mechanical damage occurring in GFRP laminate under uniaxial tensile tests. The principal result of this work, other than the success of each applied technique to evaluate the created damage in the material, is the possibility to effectively combine multiple NDT techniques in order to validate or to complete the diagnosis of the structural health of the materials.     

Ultrasonic linear motor using surface acoustic waves

The first success in the operation of an ultrasonic linear motor at HF band driving frequency using the Rayleigh wave is described. The substrate material is a 127.8° Y-cut LiNbO₃ wafer whose diameter is three inches. Four interdigital transducers (IDT's) are arranged to excite x- and y-propagation waves in both directions. The dimensions of the IDT are 25 mm aperture size, 400 μm pitch, 100 μm strip width, and 10 pairs. The operation area is about 25 mm square, The driving frequency is about 9.6 MHz in the x direction and about 9.1 MHz in the y direction. The most important point of the success is the shape of the contact surface and slider materials. For the contact materials, small balls about 1 mm in diameter are introduced to obtain sufficient contact pressure around 100 MPa. The use of ruby balls, steel balls, and tungsten carbide balls is investigated. Each slider has three balls to enable stable contact at three points. The maximum transfer speed is about 20 cm/s. The transfer speed is controllable by changing the driving voltage     

Noninvasive assessment of human jawbone using ultrasonic guided waves

The problem of detecting defects in jawbones is an important problem. Existing methods based on Xrays are invasive and constrain the achievable image quality. They also may carry known risks of cancer generation or may be limited in accurate diagnosis scope. This work is motivated by the lack of current imaging modalities to accurately predict the mechanical properties and defects in jawbone. Ultrasonic guided waves are sensitive to changes in microstructural properties and thus have been widely used for noninvasive material characterization. Using these waves may provide means for early diagnosis of marrow ischemic disorders via detecting focal osteoporotic marrow defect, chronic nonsuppurative osteomyelitis, and cavitations in the mandible (jawbone). Guided waves propagating along the mandibles may exhibit dispersion behavior that depends on material properties, geometry, and embedded cavities. In this work, we present the first study in the theoretical and experimental analysis of guided wave propagation in jawbone. Semianalytical, finite-element (SAFE) method is used to analyze dispersion behavior of guided waves propagating in human mandibles. The geometry of the cross section is obtained by segmenting the computed tomography (CT) images of the jawbone. The cross section of the mandible is divided in two regions representing the cortical and trabecular bones. Each region is modeled as a linear Hookean material. The material properties for both regions are adopted from the literature. The experimental setup for the guided waves experiment is described. The results from both numerical analysis and guided waves experiment exhibit variations in the group velocity of the first arrival signal and in the dispersion behavior of healthy and defected mandibles. These results shall provide a means to noninvasively characterize the jawbone and accurately assess the bone mechanical properties. Our study is not aimed at characterizing the bone density in human mandibles. Rather, it is aimed to assess bone mechanical properties and defects that cannot be diagnosed by X-ray or other imaging modalities. This work may pave the way to the development of inexpensive noninvasive devices to detect small defects in human mandibles.     

Shear-horizontal acoustic waves in piezoelectric plates bordered with conductive liquid

The influence of a conductive liquid on the characteristics of shear-horizontal acoustic waves of zeroth order (SH0 mode) propagating in thin piezoelectric plates of lithium tantalate, lithium niobate, and potassium niobate was investigated. Experimental results obtained for SH0 mode devices fabricated on lithium niobate plates are found to be in good agreement with theory. The data presented in this paper is useful for a proper design of various acoustic wave sensors operating in contact with conductive liquids.     

Finite-amplitude acoustic waves in liquid3He and4He

Finite-amplitude acoustic waves have been propagated in liquid³He and⁴He. The acoustic cell has been operated at 83, 250, and 420 MHz and down to 17 mK. Our measurements of the anharmonic effects are in agreement with theoretical predictions and with previous experimental work that investigated a restricted temperature range.     

水声传感网中的高效调制解调器的设计

为适应水声传感网络节点密集、规模大、工作时间长的特点,提出了一种具有小体积、低成本、低功耗等特点的水声调制解调器。采用数字幅度调制2ASK调制解调方式,硬件使用低功耗设计方案,电池供电,使用市场上量产的收发一体式小型水声换能器,使功耗和成本得到大幅度降低。经实际测试,整机最大功耗为90 mW,数据传输速率为2kbps,具备代替市场上昂贵水声调制解调器的潜力,在水声传感网技术中有良好的应用前景。     

Kapitza conductance model using loaded acoustic surface waves

An investigation is presented of the heat transfer between liquid helium and solids associated with surface impurities or faults. The solid is described as a linear chain which is terminated by a matched dissipating element, formed by an impurity, which excites loaded acoustic surface waves (loaded Rayleigh waves). Using established theoretical and experimental results on the behavior of acoustic surface waves on a solid-to-helium interface, a heat transfer coefficient is calculated. Suggestions are made on the interpretation of some outstanding problems in Kapitza work in the light of the present model.Supported by the SRC in the form of research grants.     

Sensitive acoustic vibration sensor using single-mode fiber tapers

Optical fiber sensors are a good alternative to piezoelectric devices in electromagnetic sensitive environments. In this study, we reported a fiber acoustic sensor based on single-mode fiber (SMF) tapers. The fiber taper is used as the sensing arm in a Mach-Zehnder interferometer. Benefiting from their micrometer dimensions, fiber tapers have shown higher sensitivities to the acoustic vibrations than SMFs. Under the same conditions, the thinnest fiber taper in this report, with a diameter of 1.7 μm, shows a 20 dB improvement in the signal to noise ratio as compared to that of an SMF. This acoustic vibration sensor can detect the acoustic waves over the frequencies of 30 Hz-40 kHz, which is limited by the acoustic wave generator in experiments. We also discussed the phase changes of fiber tapers with different diameters under acoustic vibrations.     

Thin-film characterization using a scanning laser acoustic microscope with surface acoustic waves

The use of surface acoustic waves in a scanning laser acoustic microscope for the characterization of the mechanical or acoustic properties of thin films deposited on piezoelectric substrates is demonstrated. Quantitative measurements of mass loading effects of 5000-A-thick tungsten films deposited on lithium niobate substrates were obtained using 100-MHz surface acoustic waves. No information about the tungsten film could be obtained using 100-MHz compressional waves. Methods of generating surface waves on nonpiezoelectric materials so that this technique could be used on arbitrary substrates are discussed.