Mercuric ion sensing by a film bulk acoustic resonator

This paper describes a film bulk acoustic resonator (FBAR) mass sensor for detecting Hg2+ ion in water with excellent sensitivity and selectivity. When a thin Au film was deposited on the surface of an FBAR, the resonant frequency shifted to a lower value when the film was exposed to Hg2+ in aqueous solution. The FBAR sensor detected as low as 10(-9) M Hg2+ (0.2 ppb Hg2+) in water. Other ions such as K+, Ca2+, Mg2+, Zn2+, and Ni2+ had little or no effect on the resonant frequency of the FBAR. Coating of the FBAR Au surface with a self-assembled monolayer (SAM) of 4-mercaptobenzoic acid decreased the Hg2+ response.     

Atomic diffusion from liquid to solid phase during contact melting

It is shown that atomic diffusion from liquid to solid phase during contact melting influences the kinetics of liquid interlayer growth only at temperatures close to the eutectic melting temperature.     

Nanoscale mapping of contact stiffness and damping by contact resonance atomic force microscopy

In this work, a new procedure is demonstrated to retrieve the conservative and dissipative contributions to contact resonance atomic force microscopy (CR-AFM) measurements from the contact resonance frequency and resonance amplitude. By simultaneously tracking the CR-AFM frequency and amplitude during contact AFM scanning, the contact stiffness and damping were mapped with nanoscale resolution on copper (Cu) interconnects and low-k dielectric materials. A detailed surface mechanical characterization of the two materials and their interfaces was performed in terms of elastic moduli and contact damping coefficients by considering the system dynamics and included contact mechanics. Using Cu as a reference material, the CR-AFM measurements on the patterned structures showed a significant increase in the elastic modulus of the low-k dielectric material compared with that of a blanket pristine film. Such an increase in the elastic modulus suggests an enhancement in the densification of low-k dielectric films during patterning. In addition, the subsurface response of the materials was investigated in load-dependent CR-AFM point measurements and in this way a depth dimension was added to the common CR-AFM surface characterization. With the new proposed measurement procedure and analysis, the present investigation provides new insights into characterization of surface and subsurface mechanical responses of nanoscale structures and the integrity of their interfaces.     

Distortion of acoustic emission signals by a change of gain in the sensing device

A semi-theoretical model of an acoustic emission (AE) signal is used to predict the effects of changes of amplification and threshold level in the recording device. Predictions are confirmed by experiments on simulated AE signals. The progress of real AE tests on cracks in welds is analysed statistically to predict the effect of the same variations in the sensitivity of the recording device. Once again the predictions are confirmed by experiment and it is shown how to convert an AE/time curve from one set of recording conditions to another.It is concluded that compensation for distortion of AE signals by changes of sensitivity of the recording device presents no great difficulty.     

Analysis of the process of onset and growth of a liquid phase in contact of dissimilar crystals

Based on the concepts of percolation theory (leakage theory), an attempt is made to explain the initial stage of contact melting. Using the fluctuation-dissipation theorem, an equation is obtained for the kinetic and diffusion stages of the contact-melting process. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 4, pp. 875–879, July–August, 2000.     

Crack tip shielding by asperity contact as determined by acoustic measurements

Asperity contact along the fracture surface of a crack is one of the mechanisms of crack closure. This contact shields the crack tip, in part, from the externally applied driving force. We have now succeeded in using information from acoustic transmission and diffraction experiments, obtained under plane strain conditions, to determine the size and density of the contacting asperities in the closure region. We have also succeeded in estimating values for the static stress across a partially closed crack as well as the stress intensity factor,K_I (local), which shields the crack tip below the stress intensity factor K_Iclosure at which the first contact during unloading occurs. It is suggested that when crack closure has an important influence on crack propagation, the shielding stress intensity factor provides information that can be used to estimate the fatigue crack propagation rate.     

Relationship between contact stiffness ratio and structural stiffness coefficient of a rectangular granular sample: a numerical analysis

In this study, the relationship between contact stiffness ratio and stiffness coefficient of a rectangular sample of granular material is investigated using the granular element method (GEM). Randomly packed granular samples are studied with different contact force models and particle size distributions in numerical simulation using the GEM. Initial arrangements of particles in the granular samples are generated using different algorithms such as inwards packing method, iterative growth method and compression method. It is demonstrated that the relationship between the stiffness coefficient of the granular sample and the contact stiffness ratio is basically logarithmic (Eq. 6). For granular samples generated by inwards packing method, the deviation for logarithmic relationship is relatively small. For granular samples generated by iterative growth method and compressive method, the deviation for logarithmic relationship is relatively large.     

Some aspects of recording an acoustic wave in a liquid by a fiber-mounted piezoelectric transducer

The main characteristics of a piezoelectric transducer mounted on an optical fiber and used to measure the acoustic signals induced by interaction between the radiation and the material are described. Results of an investigation of a laser-induced acoustic signal in a liquid are presented. Pis’ma Zh. Tekh. Fiz. 23, 54–58 (February 12, 1997)     

Electrical surface perturbation of a piezoelectric acoustic plate mode by a conductive liquid loading

Surface loading of a piezoelectric crystal supporting acoustic plate modes (APMs) by a dilute conductive liquid is analyzed using a perturbation theory. The formulation of the problem is such that only the electrical loading is relevant, and the mass loading and viscous entrainment caused by the solute are ignored. The perturbation in the propagation characteristics is then obtained relative to the solvent and is described in terms of the coupling coefficient, the capacitive loading, and the conductivity of the liquid. The results are compared to measurements made on Z-cut X-propagating LiNbO(3 ) APM device loaded with various conductive liquids of different concentrations. While an interpretation of the results can be given on the use of the APM device as a detector of the liquid properties, it is shown that a conductive liquid loading of the piezoelectric surface can be used as a means of assessing the electromechanical coupling coefficient of APMs.     

Dynamic calibration of contact thermometers in a liquid stream

Results are presented for the dynamic calibration of temperature converters in a liquid stream using thermal heterogeneities produced in the water by pulses of infrared radiation of a neodymium laser.     

机械结合面接触刚度超声波检测方法研究

针对检查机械产品结合部接触刚度特性的需要,进行超声波测量结合面接触刚度与超声波检测频率相关性的研究,基于简单弹簧模型设计一种用超声波测量两钢块结合部接触刚度的实验方案。实验结果表明:超声波反射系数随超声波频率增大而增大;作用于结合面的压力较小时,超声波测量接触刚度随频率没有明显变化;作用于结合面的压力较大时,超声波测量接触刚度随频率有一定波动。在结合面上加入润滑油,模拟工程实践中结合面状态,实验结果表明:因结合面上油膜的存在,在同样大小压力作用下超声波测量的接触刚度相对无油膜时增大。通过以上分析可知简单弹簧模型是有效的,机械结合面处的相互作用可用一个刚度可变的弹簧等效。     

Combustion of a liquid fuel droplet in an acoustic field

The rate of combustion of a liquid fuel droplet in an acoustic field is investigated analytically for certain limiting values of the dimensionless numbers characterizing the process. An expression relating the burning rate and the acoustic parameters is derived.     

Practical issues in wave-front sensing by use of phase diversity

We present the results of the phase-diversity algorithm applied to simulated and laboratory data. We show that the exact amount of defocus distance does not need to be known exactly for the phase-diversity algorithm on extended scene imaging. We determine, through computer simulation, the optimum diversity distance for various scene types. Using laboratory data, we compare the aberrations recovered with the phase-diversity algorithm and those measured with a Fizeau interferometer that uses a He-Ne laser. The two aberration sets agree with a Strehl ratio of over 0.9. The contrast of the recovered object is found to be ten times that of the raw image.     

A stereoscopic technique for seafloor statistical characterization by acoustic remote sensing

The authors present a new method for performing statistical characterization of underwater surfaces by acoustic remote sensing. A wideband technique is outlined that, by exploiting stereoscopic observation, estimates the roughness height of underwater surfaces however oriented with respect to the instrument. The surface is ensonified by a wideband signal and simultaneously viewed from two or more slightly different directions of view. The corresponding echoes are compared in the frequency domain, and a roughness estimate is obtained. Once the instrument centerband frequency has been fixed, the scale factor in the estimation can be adjusted by varying the differences between the view directions. This permits a wide estimation interval, ranging from a small fraction to many times the wavelength corresponding to the centerband frequency. Preliminary experiments have been carried out in a water tank, and the estimated roughness values are in agreement with the theory.     

Ferroic phase boundaries investigations by the acoustic emission method

 By the acoustic emission, dilatometric and optic methods the phase transitions have been investigated in PbTiO₃, PbZrO₃ and PbHfO₃ ferroelectric crystals. By the quantities of the acoustic emission activity the related coherence of the phase boundaries have been appraised. In general case the distribution on the transitions by coherence of the boundaries between the transforming phases in perovskite-type crystals are following: paraelectric-ferroelectric, paraelectric-antiferroelectric, ferroelectric-antiferroelectric, antiferroelectric-antiferroelectric. The received results have been discussed generalized in order of the similarity between the ferroelectric and martensitic phase transitions. It is shown, that acoustic emission method would be to apply for identification of the phase transition type in the multiaxial ferroic crystals fruitful. Received: 22 July 1998 / Reviewed and accepted: 25 September 1998     

Incorporating contact sensing in virtual environment for roboticapplications

Many robotic tasks involve dynamic interaction between the work piece and handling device, in which sensory information constitutes an indispensable part of the task. It is therefore of practical interest to incorporate sensor modules in the simulation stage to provide a more realistic preview of the operation and predict the behavior of the components prior to the implementation on a real work cell. Most of the current virtual reality (VR) systems use geometric models and sensorless robots for simulation, which cannot provide the insight into the real behavior of the work cell components. In this paper, we report our work in studying the issues related to simulated sensors for dynamic interaction in virtual environment (VE) using physics based models. Based on previous development, a simplified force sensor is modeled and simulated. The current implementation was carried out on a PC based VR platform, with the low-level programs developed using C via the systems development interface (SDK)     

Microstructural investigation of a Co-base alloy processed by liquid phase sintering

The microstructure of samples processed by liquid phase sintering of prealloyed atomized powders is investigated by microprobe analysis, X-ray and electron diffraction. Materials obtained from thin powders are shown to consist of a dispersion of M₇C₃ in a Co matrix; the composition of the phases corresponds to the thermodynamic equilibria. A coarser powder provides a cellular structure containing islands of very thin spheroidal structure as well as M₇C₃ and a Co matrix. The W level is very high in these islands (star phase). A comparison of compositions indicates these islands correspond to the massive solidification of the undercooled liquid phase strongly saturated in W, Cr and C. For all the samples, during ageing, intense precipitation of M₂₃C₆ occurs in coherency with the Co matrix. The structure of the star phase coarsens and the W level decreases. After long ageing the star phase consists of only M₇C₃ and a Co matrix.     

Controlling the contact line behavior by introduction of artificial perturbations in a nonisothermal liquid film

The effect of periodic artificial perturbations on a heated liquid film at small Reynolds numbers is studied experimentally using a high-speed infrared camera. It is shown that the development of thermocapillary perturbations leads to movement of rivulets and affects contact line that outlines dry spot in a vertically falling heated film. It has been established that at sufficiently intense heat fluxes the artificial perturbations exert a significant effect on the structure of the flow and on the repeated wetting of dry zones.     

Dissolution of a hot body in contact with a free liquid surface

The effect of capillary forces on the dissolution of a hot body in contact with a free liquid surface is examined.     

Gas sensing properties of Langmuir-Blodgett polypyrrole film investigated by surface acoustic waves

The gas sensing properties of organic polypyrrole (PPS) film, deposited onto LiNbO(3) substrate by Langmuir-Blodgett (LB) technique, have been monitored by surface acoustic wave (SAW) delay lines and studied with respect to sensitivity, selectivity, response time, stability, repeatability, and aging. The SAW PPy elements demonstrate high sensitivity toward NH(3) gas with high selectivity against CH(4), CO, H(2), and O(2). The detectable threshold concentration has been estimated as 20 ppm NH(3) in air; the response time is in the 10s range, and the recovery time is about 15 min; the repeatability of the SAW response toward eight sequential NH(3) gas exposures is within 6%; the aging of the PPy film is within 4% over a month; and the effect of humidity on SAW NH(3) gas response is negligible for the typical conditions at room ambient air. Partially reversible SAW response recognizing NH(3) gas as one component of an interfering gases-mixture has been observed. Simultaneous chemoresponses of SAW phase and insertion loss have been performed in order to investigate the sensing mechanisms. By merging with electrical conductivity gas response, the dominant SAW sensing effects for NH(3 ) gas detection are defined as elastic loading.