Dynamic Surface Displacements Research Articles

Dynamic surface displacement measurement using carrier optical vortex interferometer: A numerical study

The measurement of dynamic surface displacement is crucial in understanding mechanical and thermophysical dynamics at nanometre to micrometer-scale. Interferometers using optical vortices are gaining attention due to their ability to demodulate fringe patterns with helical phase profiles. In this paper, we propose a novel carrier optical vortex interferometer (COVI) that overcomes the limitations of conventional pixelated morphological operations for demodulating fringe patterns. The COVI introduces a carrier frequency by placing a rotating chopper, a collecting lens and a point photodetector at the exit of the interferometer when there is no surface displacement. When the surface moves, the time-dependent total intensity of the chopped fringe pattern produces a Doppler frequency shift with respect to the carrier frequency. Moreover, a high-order Laguerre-Gaussian (LG) beam exhibiting multiple concentric rings is employed to extend the COVI to the dynamic measurement of non-uniform surface displacement with an axisymmetric profile. In this case, the Doppler frequency shift splits into multiple peaks corresponding to the radii of the rings of the LG beam. Locating the Doppler frequency peaks gives an immediate indication of the surface displacement velocities at those radii. Accordingly, the dynamic surface displacement can be retrieved by integrating the velocities over time. The basic principle and the performance of the COVI are theoretically analysed and numerically demonstrated. In addition, the effect of surface misalignment on the displacement measurement is studied thoroughly and the limitations of the measurable velocity are discussed. Although the proposed approach requires further development to make it more applicable in practice, our study provides a first insight into how to measure a dynamic surface displacement using the COVI.

Photothermal Radar Shearography: A Novel Transient-Based Speckle Pattern Interferometry for Depth-Tomographic Inspection

As an increasingly recognized optical interferometric technique for nondestructive testing and evaluation, shearography has attracted extensive interest in various industrial applications. However, it suffers from the ignorance of the whole process of dynamic surface deformation and the difficulty in determining the depth-resolved information of inhomogeneities. In this regard, a novel speckle pattern interferometric modality named photothermal radar shearography is proposed. Unlike the differential mode of conventional shearography, the present article focuses on the dynamic surface displacement field channel technique with more comprehensive understanding of the subsurface structural information. With the utilization of frequency modulated photothermal excitation, the depth-distributed information of subsurface structures and inhomogeneities is encoded into the induced dynamic surface deformation. Using Hilbert transform and least-square method solved by discrete cosine transform, the time-domain interference signal of each pixel from the recorded speckle patterns sequence is demodulated and unwrapped to obtain the transient full-field shearographic phase distribution which indicates the dynamic surface deformation. In the meanwhile, incrementally delayed cross-correlation matched filtering allows for the localization of axial energy distribution to generate depth-selective structural display for tomography. This proposed transient-based interferometric methodology thus enables depth-tomographic profiles and three-dimensional visualization of subsurface anomalies for the first time, which significantly improves the superiority and attractiveness of shearography in providing insight into the status, performance and reliability of industry.

Scattering of SH Waves by a Partially Debonded Cylindrical Inclusion in the Covering Layer

This article presents analytical solutions to the problem of dynamic stress concentration and the surface displacement of a partially debonded cylindrical inclusion in the covering layer under the action of a steady-state horizontally polarized shear wave (SH wave); these solutions are using the complex function method and wave function expansion method. By applying the large-arc assumption method, the straight line boundary of the half-space covering layer is transformed into a curved boundary. The wave field of the debonded inclusion is constructed utilizing a Fourier series and boundary conditions of continuity. The impact of debonding upon the dynamic stress concentration and surface displacement around the cylindrical concrete or steel inclusion is analyzed through numerical examples of the SH waves that are incident at normal angles, from a harder medium to a softer medium and from a softer medium to a harder medium. The examples show that various factors (including the medium parameters of the soil layers and the inclusion, the frequency of the incident waves, and the debonding situations) jointly affect the dynamic stress concentration factor and the surface displacement around the structure.

Quantification of surface displacements and electromechanical phenomena via dynamic atomic force microscopy

Detection of dynamic surface displacements associated with local changes in material strain provides access to a number of phenomena and material properties. Contact resonance-enhanced methods of atomic force microscopy (AFM) have been shown capable of detecting ∼1–3 pm-level surface displacements, an approach used in techniques such as piezoresponse force microscopy, atomic force acoustic microscopy, and ultrasonic force microscopy. Here, based on an analytical model of AFM cantilever vibrations, we demonstrate a guideline to quantify surface displacements with high accuracy by taking into account the cantilever shape at the first resonant contact mode, depending on the tip–sample contact stiffness. The approach has been experimentally verified and further developed for piezoresponse force microscopy (PFM) using well-defined ferroelectric materials. These results open up a way to accurate and precise measurements of surface displacement as well as piezoelectric constants at the pm-scale with nanometer spatial resolution and will allow avoiding erroneous data interpretations and measurement artifacts. This analysis is directly applicable to all cantilever-resonance-based scanning probe microscopy (SPM) techniques.

Effect of Water Adsorption on Conductivity in Epitaxial Sm0.1Ce0.9O2 -δ Thin Film for Micro Solid Oxide Fuel Cells Applications

The growing demand for miniaturized systems for energy conversion and storage has prompted extensive research aimed at fabricating electrochemical devices, such as solid oxide fuel cells for portable applications (μ-SOFCs). This goal requires reducing the operating temperature by producing components as thin films. Nowadays, there is a huge gap between macroscopic device-level electrochemical techniques and microscopic electrochemical techniques to study atomic-level diffusion and transport process. Recently, a new scanning probe microscopy technique, named electrochemical strain microscopy (ESM) has been developed in order to study the structure and physical properties on the microscopic level. After applying the dc bias to the tip, the oxygen vacancies and protons injection or annihilation can occur, depending on the working conditions and the material properties. The subsequent oxygen ion or proton movement results in localized strain under the tip, which can be detected through dynamic surface displacement.[1] This technique can be very useful to investigate the electrochemical activity at the nano-scale in ionic or proton conductors. In this presentation, I will discuss several examples of high-resolution studies of pure and Sm-doped CeO2 epitaxial thin films surfaces which allowed to understand water interaction and conductivity mechanisms on the nanoscale. In particular I will show: (1) The effect of the different doping concentrations on Sm1-xCexO2-a in terms of different transport mechanism and different type of charge carriers [2]. (2) The role of granularity and porosity on the oxygen ion or proton conduction 20% Sm doped CeO2 nanocrystalline films [3]. (3) The bias dependent mechanisms of irreversible cathodic and anodic processes on a pure CeO2 film.[4] [1] A. Kumar et al. Nature Chemistry, 2011, 3,707. [2] Nan Yang et al. ACS Nano DOI: 10.1021/nn505345c (2014) [3] S. Doria, Nan Yang, et al. Appl. Phys. Lett. 103, 171605 (2013) [4] Nan Yang et al. Nanotechnology 25, 075701 (2014).

Electrochemical strain microscopy with blocking electrodes: The role of electromigration and diffusion

Electrochemical strains are a ubiquitous feature of solid state ionic devices ranging from ion batteries and fuel cells to electroresistive and memristive memories. Recently, we proposed a scanning probe microscopy (SPM) based approach, referred as electrochemical strain microscopy (ESM), for probing local ionic flows and electrochemical reactions in solids based on bias-strain coupling. In ESM, the sharp SPM tip concentrates the electric field in a small (10–50 nm) region of material, inducing interfacial electrochemical processes and ionic flows. The resultant electrochemical strains are determined from dynamic surface displacement and provide information on local electrochemical functionality. Here, we analyze image formation mechanism in ESM for a special case of mixed electronic-ionic conductor with blocking tip electrode, and determine frequency dependence of response, role of diffusion and electromigration effects, and resolution and detection limits.

Defect detection and localization in orthotropic wood slabs by inversion of dynamic surface displacements

The nondestructive evaluation inversion and generalized force-mapping techniques developed and demonstrated for isotropic thin plates by Bucaro et al. [(2004). "Detection and localization of inclusions in plates using inversion of point actuated surface displacements," J. Acoust. Soc. Am. 115, 201-206] are extended to the case of orthotropic plates. The extended techniques are applied to a finite-element generated numerical database for point excited wooden slabs with and without an internal defect at 5 and 10 kHz. Operation of the original isotropic algorithms on the wood surface displacements is shown to fail in recovering the uniform elastic parameters or in detecting and locating the defect. The new algorithms based on the wave equation for a thin, orthotropic plate successfully convert the surface displacements on the uniform wooden slab to elastic parameter maps which serve to detect and localize the defect in the flawed plate. The results, particularly at the higher frequency, indicate that the onset of failure in the thin plate approximation impacts both the inversion and the generalized force-mapping accuracy. However, in this case use of the inversion algorithm to obtain modified wave equation coefficients followed by operation of the force-mapping algorithm with these new parameters inserted is shown to successfully mitigate this effect.

Detection and localization of rib detachment in thin metal and composite plates by inversion of laser Doppler vibrometry scans

The laboratory implementation of a fault detection and localization method based on inversion of dynamic surface displacements measured by a scanned laser Doppler vibrometer (SLDV) was investigated. The technique uses flexural wave and generalized force inversion algorithms which have previously been demonstrated using simulated noise-free vibration data generated for thick plates with a finite element model. Here these inversion algorithms to SLDV measurements made in the laboratory on a thin nickel plate and a thin carbon fiber composite plate, both having attached reinforcing ribs with intentional de-bonding of the rib/plate interface at a specific location on each structure are applied. The inverted displacement maps clearly detect and locate the detachment, whereas direct observation of the surface displacements does not. It is shown that the technique is relatively robust to the choice of frequency and to the presence of noise.

Fast four-channel fibre-optic displacement sensor for measuring impact waves at low cost

We have developed a fast four-channel fibre-optic sensor for measuring dynamic surface displacements caused by shock waves. Light from an LED emitter is sent through a plastic fibre and reflected from the surface back into the fibre. The intensity of the reflected light gives the distance to the surface unambigously. Based on simple principles and utilizing inexpensive components, micrometre and microsecond resolution is achieved at lower cost and with easier usage than for interferometric methods and with better reliability than an accelerometer. The sensor is comparatively easy to set up. It is battery operated for reduced sensitivity to electromagnetic interference. The design of the fibre probe facilitates access in narrow and hostile environments.

Temporal speckle pattern interferometry for measuring micron-order surface motion of a liquid bridge

This paper presents a technique based on temporal speckle pattern interferometry (TSPI), a new version of electronic speckle pattern interferometry (ESPI), for measuring micron-order motion of a deformable surface of a quasi-cylindrical liquid bridge. The time sequence phase method (TSPM) proposed recently has been extended to develop automated and robust procedures for temporal phase recovering of specklegrams. The performance of the procedures is verified through computer simulations made in a range of parameters involved. The technique is implemented into a TSPI system utilizing a ground glass for generating speckles from non-speckled reference and object wavefronts. The validity and accuracy of the technique are examined in the measurement of dynamic displacement of both a flat mirror and a cylindrical glass rod, where detailed comparison is made with the simultaneous measurement taken with the laser focusing displacement meter. The capability of the present technique is demonstrated by some experimental results obtained from dynamic surface displacement of a liquid bridge of silicone oil.

USE OF HOLOGRAPHIC INTERFEROMETRY AND ELECTRONIC SPECKLE PATTERN INTERFEROMETRY FOR MEASUREMENTS OF DYNAMIC DISPLACEMENTS

The paper presents the use of Holographic Interferometry and Electronic Speckle Pattern Interferometry for the measurement of dynamic surface displacements. A concise theoretical background of the optical phenomena on which the two techniques are based is given. Analysis of holographic and speckle fringe patterns due to dynamic displacements is introduced as a generalisation of the case of fringe patterns due to static displacements. Experimental results obtained on a turbine blade, an aluminium panel and a microsatellite sandwich structure are reported.

Dynamic surface displacement measurement in 1-3 and 1-1-3 piezocomposites

The sensitivity of 1-3 piezocomposites can be improved by the addition of a third phase or interlayer around the piezoceramic rods which results in a composite with 1-1-3 connectivity. In the current investigation, dynamic surface displacements of both 1-3 and 1-1-3 piezocomposites were measured using a laser Doppler heterodyne interferometer. Dynamic displacement profiles showing the nonuniform deformation of the piezoelectric rod and the nonpiezoelectric polymer were obtained at 10 Hz, 100 Hz, and 1.0 kHz. Measurements of the displacement at the center of the piezoelectric rod were performed over the frequency range from 10 Hz to 27 kHz. Three different interlayer conditions were considered. The experimental measurements demonstrated that both the surface displacement profile and the maximum rod displacement varied with frequency and interlayer properties. The dynamic displacement profiles were also compared with previously measured static displacement profiles.

Theoretical noise-limited sensitivity of classical interferometry

The signal-to-noise ratios for the path-stabilized, the active-heterodyne, the Sag, and the Fabry-Perot interferometers are calculated for cases in which dynamic surface displacements are detected. Expressions for the minimum-detectable displacements are given for the sensitivity limit of each interferometer. It is found that the ultimate sensitivities of the interferometers considered are nearly equal for similar conditions of use. Sensitivity values are shown to be about 10−15 m Hz−1/2 for systems that use typical laboratory instruments.

ESPI—The ultimate holographic tool for vibration analysis?

Holographic interferometry opened new worlds of research by making possible accurate, global mapping of small dynamic surface displacements in a two-step process. A technique, called Electronic Speckle Pattern Interferometry or ESPI, has been developed in various forms to provide similar results instantly. ESPI’s principal capabilities, and some practical applications in industry, biomedicine, and acoustical research are described in an overview in the hope of encouraging its use by researchers who were deterred by the relatively cumbersome process of holography. In various forms, ESPI is shown to be capable of measuring phase and amplitude of dynamic displacements between 0.01 nm and 10 μm over an area of up to 1 m2.

Thermodisplacement imaging of current in thin-film circuits

We present initial results on a novel scheme for measuring current distribution in thin-film circuits. When an AC current passes through a thin-film circuit, the resulting periodic heating sets up a dynamic surface displacement which can be detected using a phase-sensitive laser probe. Results indicate that the present system has a sensitivity of 4 × 10−3 Å for displacement and 2.7 × 10−2°C for temperature in a 1 Hz bandwidth. The spatial resolution can be as small as an optical wavelength and is currently limited to 2 μm by the optics used. As the surface displacement amplitude depends on the thermal properties of the substrate material, the technique can also be used to detect defects beneath the metallisation in integrated-circuit structures.

Use Of Electronic Speckle Pattern Interferometry (ESPI) In The Measurement Of Static And Dynamic Surface Displacements

Electronic speckle pattern interferometry (ESPI) enables static and dynamic surface displacements to be measured in real time to an accuracy of the order of a wavelength of light. The principles of the technique are outlined and the different configurations of interferometers described. Some applications of the technique are discussed.

A note on dynamic surface displacements in an elastic half-space

A note on dynamic surface displacements in an elastic half-space