High-resolution Displacement Research Articles

Wireless Sensing in Complex Electromagnetic Media: Construction Materials and Structural Monitoring

In this paper, wireless sensing in the presence of complex electromagnetic media created by combinations of reinforcing bars and concrete is investigated. The wireless displacement sensing system, primarily designed for use in structural health monitoring (SHM), is composed of a comb-like nested split-ring resonator (NSRR) probe and a transceiver antenna. Although each complex medium scenario is predicted to have a detrimental effect on sensing in principle, it is demonstrated that the proposed sensor geometry is able to operate fairly well in all scenarios except one. In these scenarios that mimic real-life SHM, it is shown that this sensor exhibits a high displacement resolution of 1 $\mu \text{m}$ , a good sensitivity of 7 MHz/mm in average, and a high dynamic range extending over 20 mm. For the most disruptive scenario of placing concrete immediately behind NSRR, a solution based on employing a separator behind the probe is proposed to overcome the handicaps introduced by the medium. In order to obtain a one-to-one mapping from the measured frequency shift to the displacement, a numerical fit is proposed and used. The effects of several complex medium scenarios on this fit are discussed. These results indicate that the proposed sensing scheme works well in real-life SHM applications.

Skin microstructure deformation with displacement map convolution

We present a technique for synthesizing the effects of skin microstructure deformation by anisotropically convolving a high-resolution displacement map to match normal distribution changes in measured skin samples. We use a 10-micron resolution scanning technique to measure several in vivo skin samples as they are stretched and compressed in different directions, quantifying how stretching smooths the skin and compression makes it rougher. We tabulate the resulting surface normal distributions, and show that convolving a neutral skin microstructure displacement map with blurring and sharpening filters can mimic normal distribution changes and microstructure deformations. We implement the spatially-varying displacement map filtering on the GPU to interactively render the effects of dynamic microgeometry on animated faces obtained from high-resolution facial scans.

A Monolithic Self-Sensing Precision Stage: Design, Modeling, Calibration, and Hysteresis Compensation

This paper presents the design, modeling, calibration, and hysteresis compensation of a self-sensing precision stage used for active vibration isolation. The stage prototype is monolithically fabricated from the spring steel by wire electrical discharge machining process. Aiming to achieve an extremely compact structure, we design and fabricate a self-sensing actuator called smart piezo stack which is capable of not only generating high-resolution displacement but also monitoring the dynamic characteristics of the proposed stage. By means of the finite-element analysis and experimental measurements, we reveal and quantitatively analyze the crosstalk phenomenon in the smart piezo stack. After calibrating the sensitivity of the smart piezo stack experimentally, the dynamics model of the proposed stage is established. Furthermore, a nonlinear autoregressive moving average with exogenous inputs model based on backpropagation neural network is proposed to design a nonlinear controller based on adaptive inverse control. The intelligence of the developed controller allows the hysteresis in the stage which results from the embedded smart piezo stack to be directly compensated for without dynamics modeling in advance. Experimental validation of the adaptive inverse controller is conducted and the results demonstrate the effectiveness of the proposed mechanism and the developed control system.

Optical Cavity Interrogation for MEMS Accelerometers

MEMS accelerometers utilizing electrostatic, piezoelectric, and magnetic proof mass displacement readout approaches have achieved success in both commercial- and defense-related applications. However, there is a desire for improved acceleration resolution suitable for navigation-grade applications. Optical readout of mechanical displacements has demonstrated high levels of resolution in macro-scale applications including precision movement and placement systems. In addition, optical techniques are common in high performance inertial sensors such as fiber optic gyros and ring laser gyros. Incorporating optical readout approaches into MEMS acceleration devices may yield sufficient resolution to achieve navigation-grade performance. Therefore, the U.S. Army AMRDEC is developing MEMS accelerometers based on optical cavity resonance readout. In the device, an optical cavity is formed between a MEMS proof mass and a reference reflector. A tunable laser excites the cavity on the edge of its resonance peak. Small displacements of the cavity from its rest position are detected by frequency shifts of the resonance, leading to high-resolution proof mass displacement detection and therefore high acceleration resolutions. This paper will present modeling associated with the design concept, as well predictions of device geometries and performance with the goal of achieving less than 1 micro-g bias instability and a velocity random walk of better than 0.2 micro-g/rt.Hz.

A review of terrestrial radar interferometry for measuring surface change in the geosciences

AbstractThis paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement. Different hardware‐types and acquisition concepts are described, which use either real or synthetic aperture for radar image formation. We present approaches for data processing procedures, paying special attention to the separation of high resolution displacement information from atmospheric phase variations. Recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection. Applications range from detection and quantification of very slow moving (millimeters to centimeters per year) displacements in rock walls from repeat monitoring, to rapid processes resulting in fast displacements (~50 m/yr) acquired during single measurement campaigns with durations of only a few hours. Fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes. A concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique, as well as in areas characterized by rapid decorrelation. Empirical data from a Ku‐band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock‐surfaces and after a few seconds to minutes in vegetated areas during windy conditions. The examples show that the displacement field can be measured for landslides in dense grassland, ice surfaces on flowing glaciers and snowpack creep. Copyright © 2014 John Wiley & Sons, Ltd.

Micrograting Displacement Sensor with Integrated Electrostatic Actuation

A high-resolution micro-grating displacement sensor with diffraction-based and integrated electrostatic actuation is proposed and experimentally demonstrated. The Al reflecting membrane is fabricated at the bottom of a silicon moving part and the Au micro-gratings are patterned on a transparent substrate. This structure forms a phase sensitive diffraction grating, providing the displacement sensitivity of the micro-grating interferometer. It shows sensitivity adjustment and self-calibration capabilities with electrostatic actuation. Additional system components include a coherent light source, photodiodes, and required electronics. Experimental results show that the displacement sensor has a sensitivity of about 1.8 mV/nm and a resolution of less than 1 nm in the linear region. This displacement sensor is very promising in the fields requiring high sensitivity, broad dynamic range, and immunity to electromagnetic interference.

Reinforcement Learning Fuzzy Neural Network Control for Magnetic Shape Memory Alloy Actuator

Magnetic shape memory alloy actuator is a new type of actuator that can offer big travel and high resolution of output displacement, which makes it suitable for driving task. However, its output displacement represents the hysteresis applied to input magnetic field. Hysteresis restricts its application in the high precision positioning. In order to eliminate the hysteresis of magnetic shape memory alloy actuator, a reinforcement learning fuzzy neural network controller is proposed. Network structure and special learning algorithm of reinforcement learning fuzzy neural network controller are introduced in detail. The proposed control system adopts the generalized approximate reasoning-based intelligent control architecture, which is mainly consisted of three parts: Action Selection Network, Action Evaluation Network and Stochastic Action Modifier. Finally, in order to verify the effectiveness of the proposed control method, the simulation experiment is researched. The experimental results show that the proposed control method can obtain the smaller tracking error, and the controller’s maximum tracking error is less than 0.95%, hysteresis loop is less than 2.66%.

Serial biomechanical comparison of edematous, normal, and collagen crosslinked human donor corneas using optical coherence elastography

To noninvasively evaluate the effects of corneal hydration and collagen crosslinking (CXL) on the mechanical behavior of the cornea. Cleveland Clinic Cole Eye Institute, Cleveland, Ohio, USA. Experimental study. An optical coherence elastography (OCE) technique was used to measure the displacement behavior of 5 pairs of debrided human donor globes in 3 serial states as follows: edematous, normal thickness, and after riboflavin-ultraviolet-A-mediated CXL. During micromotor-controlled axial displacements with a curved goniolens at physiologic intraocular pressure (IOP), serial optical coherence tomography scans were obtained to allow high-resolution intrastromal speckle tracking and displacement measurements over the central 4.0 mm of the cornea. With no imposed increase in IOP, the mean lateral to imposed axial displacement ratios were 0.035 μm/μm ± 0.037 (SD) in edematous corneas, 0.021 ± 0.02 μm/μm in normal thickness corneas, and 0.014 ± 0.009 μm/μm in post-CXL corneas. The differences were statistically significant (P<.05, analysis of variance) and indicated a 40% increase in lateral stromal resistance with deturgescence and a further 33% mean increase in relative stiffness with CXL. Serial perturbations of the corneal hydration state and CXL had significant effects on corneal biomechanical behavior. With an axially applied stress from a nonapplanating contact lens, displacements along the direction of the collagen lamellae were 2 orders of magnitude lower than axial deformations. These experiments show the ability of OCE to quantify clinically relevant mechanical property differences under physiologic conditions. Proprietary or commercial disclosures are listed after the references.

Epicenter and magnitude of large earthquake determined from high-rate GPS observations: A case study of the 2008 M8.0 Wenchuan earthquake

For earthquake and tsunami early warning and emergency response, the earthquake epicenter and magnitude should be determined rapidly and correctly. Using high-rate GPS observations, we can readily obtain precise and high resolution displacement time series and the seismic waveforms during the earthquake. In this paper, a new algorithm is proposed for estimating the earthquake epicenter and magnitude with the seismic waveforms derived from high-rate GPS data during the earthquake. A case study of the 2008 Wenchuan earthquake is conducted from 1 Hz GPS data and the epicenter and magnitude are determined. Compared with the results issued by the China Seismological Bureau, the estimation error of the epicenter and the magnitude is about 12 km and 0.1 magnitude unit, respectively. It has shown that high-rate GPS could be a new tool feasible for estimating the earthquake epicenter and magnitude, independent of or combined with seismometers.

Eye-Specific IOP-Induced Displacements and Deformations of Human Lamina Cribrosa

To measure high-resolution eye-specific displacements and deformations induced within the human LC microstructure by an acute increase in IOP. Six eyes from donors aged 23 to 82 were scanned using second harmonic-generated (SHG) imaging at various levels of IOP from 10 to 50 mm Hg. An image registration technique was developed, tested, and used to find the deformation mapping between maximum intensity projection images acquired at low and elevated IOP. The mappings were analyzed to determine the magnitude and distribution of the IOP-induced displacements and deformations and contralateral similarity. Images of the LC were obtained and the registration technique was successful. IOP increases produced substantial, and potentially biologically significant, levels of in-plane LC stretch and compression (reaching 10%-25% medians and 20%-30% 75th percentiles). Deformations were sometimes highly focal and concentrated in regions as small as a few pores. Regions of largest displacement, stretch, compression, and shear did not colocalize. Displacements and strains were not normally distributed. Contralateral eyes did not always have more similar responses to IOP than unrelated eyes. Under elevated IOP, some LC regions were under bi-axial stretch, others under bi-axial compression. We obtained eye-specific measurements of the complex effects of IOP on the LC with unprecedented resolution in uncut and unfixed human eyes. Our technique was robust to electronic and speckle noise. Elevated IOP produced substantial in-plane LC stretch and compression. Further research will explore the effects of IOP on the LC in a three-dimensional framework.

Accelerated cine DENSE MRI using compressed sensing and parallel imaging

Background Cine DENSE (Displacement Encoding with Stimulated Echoes) provides accurate and high-resolution displacement and strain imaging of the heart; however, image acquisition times are relatively long and, due to properties inherent to stimulated echoes, signal-to-noise ratio (SNR) is relatively low. Accelerated cine DENSE could substantially shorten scan times and/or provide improved spatial and/or temporal resolution; however, the low SNR, requirement to preserve phase information, and cardiac motion present technical challenges. We aimed to develop acceleration methods that overcome these challenges.

Quantitative dielectrophoretic tracking for characterization and separation of persistent subpopulations of Cryptosporidium parvum

Microbial persistence to antibiotics is attributed to subpopulations with phenotypic variations that cause a spread of susceptibility levels, leading to the recurrence of infections and stability of biofilms. Herein, persistent oocyst subpopulations identified by animal infectivity and excystation assays during the disinfection of Cryptosporidium parvum, a water-borne pathogen capable of causing enteric infections at ultra-low doses, are separated and characterized by quantitative dielectrophoretic tracking over a wide frequency range (10 kHz-10 MHz). To enable the simultaneous and facile dielectrophoretic tracking of individual oocysts, insulator constrictions in a microfluidic channel are utilized to spatially modulate the localized field over the extent needed for defining oocyst trajectories and for obtaining high-resolution displacement versus time measurements under both, positive and negative dielectrophoresis. In this manner, by obviating the need for averaging dielectrophoretic data over a large collection region, the force response is more sensitive to differences in electrophysiology from sub-population fractions. Hence, the electrophysiology of sensitive and persistent oocysts after heat and silver nanoparticle treatments can be quantified by correlating the force response at low frequencies (<100 kHz) to the integrity of the oocyst wall and at high frequencies (0.4-1 MHz) to the sporozoites in the oocyst. This label-free method can characterize heterogeneous microbial samples with subpopulations of phenotypically different alterations, for quantifying the intensity of alteration and fraction with a particular alteration type.

Temperature controlled tensile testing of individual nanowires

We present a novel experimental method for quantitatively characterizing the temperature-dependent mechanical behavior of individual nanostructures during uniaxial straining. By combining a microelectromechanical tensile testing device with a low thermal mass and digital image correlation providing nm-level displacement resolution, we show successful incorporation of a testing platform in a vacuum cryostat system with an integrated heater and temperature control. Characterization of the local sample temperature and time-dependent response at both low and high temperature demonstrates a testing range of ∼90-475 K and steady-state drift rates less than 0.04 K/min. In situ operation of the tensile testing device employing resistively heated thermal actuators while imaging with an optical microscope enables high-resolution displacement measurements, from which stress-strain behavior of the nanoscale specimens is deduced. We demonstrate the efficacy of our approach in measuring the temperature dependence of tensile strength in nominally defect-free ⟨110⟩ Pd nanowhiskers. We uncover a pronounced sensitivity of the plastic response to testing temperature over a range of ∼300 K, with an ultimate strength in excess of 6 GPa at low temperature. The results are discussed in the context of thermally activated deformation mechanisms and defect nucleation in defect-free metallic nanostructures.

High resolution measurement of internal full-field displacements and strains using global spectral digital volume correlation

Thanks to its ability to non-destructively access internal strains in materials, Digital Volume Correlation (DVC) is gaining growing interest from both experimental and theoretical mechanics communities. One important issue in the implementation of DVC is the considerable computational costs associated with the huge amount of data, which hinders the applications of the technique, especially for high-resolution displacement and strain measurements. In this paper, we propose an accurate global DVC approach based on a Fourier decomposition for the kinematic basis of the sought displacement field. The approach, referred to as IS-DVC, leads to an algorithm whose computational complexity is not considerably increased by increasing the number of Degrees of Freedom (DOF) of the kinematic basis, thus being computationally efficient using the Fast Fourier Transform (FFT). Artificial experiments have been used to evaluate the uncertainties of IS-DVC at high resolutions. Especially, displacement fields of 3D composites with spherical and non-aligned ellipsoidal particles at small scales were reconstructed. Resulting measurements revealed close similarities in terms of strain heterogeneities throughout the volume with the benchmark strains. Furthermore, it was shown that, in the presence of a discontinuity, the measurement uncertainties are not significantly affected, except for regions surrounding the discontinuity, hence validating the robustness of the reconstructed displacement field at a large number of DOF.

Geoelectrical monitoring: an innovative method to supplement landslide surveillance and early warning

ABSTRACTPermanent geoelectrical monitoring, using the GEOMON4D instrumentation in combination with high resolution displacement monitoring by means of the D.M.S. system, was performed at two active landslide areas: Ampflwang/Hausruck in Austria, and Bagnaschino in Italy. These sites are part of the Austrian geoelectrical monitoring network, which currently comprises six permanently monitored landslides in Europe. Within the observation intervals, several displacement events, triggered by intense precipitation, were monitored and analysed. All of these events were preceded by a decrease of electric resistivity. The application of an innovative 4D inversion algorithm made it possible to investigate the potential processes which led to the triggering of these events. We conclude that resistivity monitoring can significantly help in the investigation of the causes of landslide reactivation. Since the results also contribute to the extrapolation of local displacement monitoring data to a larger scale, resistivity monitoring can definitely support decision‐finding in emergencies.

High resolution displacement monitoring of a slow velocity landslide using ground based radar interferometry

Ground-based interferometric radar (GBIR) monitoring was conducted on a slow-moving, translational failure landslide in Granby, Grand County, Colorado, USA. Radar monitoring was completed over two separate surveys in 2011 using a tripod mounted real aperture sensor. The purpose of this work is to evaluate GBIR as a temporally dense monitoring technique for monitoring landslide displacement and compare the monitoring results to ongoing GPS based surveying methods to verify measured displacements. We discuss the strengths and limitations of GBIR displacement monitoring with a variety of available sensors, and place this monitoring platform, sensor, and workflow into context of previous slope stability monitoring with GBIR. For both surveys, displacement time series were created through a small temporal baseline stacking to reduce noise and maintain high temporal resolution. The results of the displacement time series were compared to average displacement rates derived from GPS based surveying. An overall verification of radar and GPS derived displacement rates was achieved, and identifies important differences relating to the precision and uncertainty of the two techniques. This work demonstrates GBIR monitoring capability of establishing high temporal resolution on tracking variable rates of landslide movements. Spatial modeling of total observed displacements was completed for both surveys verifying a conceptual model of uniform translational landslide movement, providing greater confidence for mitigation planning.

Study on the Method of the Compensation for the Hysteresis Nonlinear Characteristics of Piezoelectric Actuator

Piezoelectric actuator has the characteristics of high displacement resolution, fast dynamic response, miniature size and etc. But its inherent hysteresis nonlinear affects its positioning accuracy. This paper analysis the hysteresis nonlinear characteristics of piezoelectric actuator, verifies the effect of hysteresis nonlinear on piezoelectric actuator, and compensate the hysteresis nonlinear characteristics by using the integrated control algorithm of feed-forward control and PI control, which can improve the control precision of the piezoelectric actuator.

A procedure for extracting primary and secondary creep parameters from nanoindentation data

A methodology is presented for the extraction of creep parameters from nanoindentation data – i.e. data obtained from an indentation system with a high resolution displacement measuring capability. The procedure involves consideration of both primary and secondary creep regimes. The sensitivities inherent in the methodology are explored and it is concluded that, provided certain conditions are satisfied, it should be reasonably robust and reliable. In contrast to this, it is also shown that the methodology commonly used at present to obtain (steady state) creep parameters is in general highly unreliable; the effects responsible for this are identified.

Experiment and design of a high-resolution optical encoder

An optical mechanism proposed in this paper is composed of a movable part and a fixed part for the increment high-resolution optical displacement encoders. A parallel light source is set on the moving part and a double-concave lens, a specially designed optical grating and a phototransistor array receiver are set on the fixed part. The parallel light emitted from the movable part passes through the double-concave lens and the specially designed optical grating; it is then projected onto the phototransistor array receiver to indicate the displacement of the movable part. The relationship equation of the lens is developed to design an optical mechanism, which can enlarge the displacement so that it becomes observable. Based on the simulation results, three different radii in the curvature of the double-concave lens were proposed. The simulation results indicated that the optical mechanism with 50 times magnification could make the 10 nm movement intervals of a light source be about 500 nm movement intervals in the detecting surface. Furthermore, considering the limitation of the precision of existing tools, an experimental system with a 200 nm resolution was established to verify the possibility of the proposed structure. The experimental result indicates the possibility of using the proposed theorem to achieve the desired results.

Precision tracking of a piezo-driven stage by charge feedback control

Abstract This paper presents a novel approach for precisely controlling the motion of a piezo actuator embedded in a mechanical stage without using a displacement sensor. A piezo actuator has a high displacement resolution, but the positioning performance is degraded by hysteresis between the applied voltage and resultant displacement. However, an electromechanical model of a piezo actuator suggests that the charge flowing in the actuator is directly related to the dynamic response of the piezo displacement. Therefore, this study directly measured the charge stored in a piezo actuator, and achieved dynamic reference tracking of the actuator's displacement by regulating the charge flowing through the actuator to follow a predefined trajectory. This novel approach requires neither specially designed charge amplifier circuits nor implementation of an inverse hysteresis model. The complete model identification and the digital controller design procedure for a piezo-driven mechanical stage are presented. The charge feedback controller is designed according to the dynamic characteristics of both the actuator and the stage, so that instability is minimized relative to using a charge amplifier. The experimental results confirm satisfactory tracking performance, and reveal the influence of model uncertainties on the system performance.