Non-contact Measurement Technique Research Articles

Noncontact speckle-based optical sensor for detection of glucose concentration using magneto-optic effect.

We experimentally verify a speckle-based technique for noncontact measurement of glucose concentration in the bloodstream. The final device is intended to be a single wristwatch-style device containing a laser, a camera, and an alternating current (ac) electromagnet generated by a solenoid. The experiments presented are performed in vitro as proof of the concept. When a glucose substance is inserted into a solenoid generating an ac magnetic field, it exhibits Faraday rotation, which affects the temporal changes of the secondary speckle pattern distributions. The temporal frequency resulting from the ac magnetic field was found to have a lock-in amplification role, which increased the observability of the relatively small magneto-optic effect. Experimental results to support the proposed concept are presented.

Development of experimental method for in situ distortion and temperature measurements during the laser powder bed fusion additive manufacturing process

Measurements of the temperature and distortion evolution during laser powder bed fusion (LPBF) are taken as a function of time. In situ measurements have proven vital to the development and validation of FE (finite element) models for alternate forms of additive manufacturing. Due to powder obscuring all but the top layer of the part in LPBF, many non-contact measurement techniques used for in situ measurement of additive manufacturing processes are impossible. Therefore, an enclosed instrumented system is designed to allow for the in situ measurement of temperature and distortion in an LPBF machine without the need for altering the machine or the build process. By instrumenting a substrate from underneath, the spread powder does not affect measurements. Default processing parameters for the EOS M280 machine prescribe a rotating scan pattern of 67° for each layer. One test is completed using the default rotating scan pattern and a second is completed using a constant scan pattern. Experimental observations for the build geometry tested showed that for Inconel® 718 and a constant scan pattern produce results in a 37.6% increase in distortion as compared with a rotated scan pattern. The in situ measurements also show that the thermal cycles caused by the processing of a layer can impact the distortion accumulated during the deposition of the previous layers. The amount of distortion built per layer between the rotating and constant scan pattern cases highlights inter-layer effects not previously discovered in LPBF. The demonstrated inter-layer effects in the LPBF process should be considered in the development of thermo-mechanical models of the LPBF process.

Photogrammetry and optical methods in structural dynamics – A review

In the last few decades, there has been a surge of research in the area of non-contact measurement techniques. Photogrammetry has received considerable attention due to its ability to achieve full-field measurement and its robustness to work in testing environments and on testing articles in which using other measurement techniques may not be practical. More recently, researchers have used this technique to study transient phenomena and to perform measurements on vibrating structures. The current paper reviews the most current trends in the photogrammetry technique (point tracking, digital image correlation, and target-less approaches) and compares the applications of photogrammetry to other measurement techniques used in structural dynamics (e.g. laser Doppler vibrometry and interferometry techniques). The paper does not present the theoretical background of the optical techniques, but instead presents the general principles of each approach and highlights the novel structural dynamic measurement concepts and applications that are enhanced by utilizing optical techniques.

Tension testing of silicone rubber at high strain rates

The effect of strain rate on the tension behavior of filled silicone rubber was investigated over a wide range of strain rates. A non-contact optical measurement technique was used to accurately capture the deformation information of the tensile specimen under quasi-static loading conditions. Experimental methodology to investigate the tension response of rubber-like materials at high strain rates is presented. Dynamic tensile tests were performed using a split Hopkinson tension bar (SHTB) system. Specific specimen geometry and grip connection were designed to meet the requirements of one-dimensional experimental principle in the Hopkinson bar tests. The dynamic tensile stress-strain response of silicone rubber at high strain rates up to 1400 s−1was obtained. Experiments reveal that the adopted experimental technique is reasonable for testing the tension response of soft materials at high strain rates, and the tensile behavior of silicone rubber is greatly dependent on the strain rate. The values of stiffness and nominal stress at a given elongation all increase with increased strain rate. According to the incompressible assumption, a phenomenological-based visco-hyperelastic constitutive model is proposed to describe the tensile behavior of silicone rubber over a wide range of strain rates.

Full-field linear and nonlinear measurements using Continuous-Scan Laser Doppler Vibrometry and high speed Three-Dimensional Digital Image Correlation

Spatially detailed dynamic measurements of thin, lightweight structures can be difficult to obtain due to the structure׳s low mass and complicated deformations under certain loading conditions. If traditional contacting sensors, such as accelerometers, strain gauges, displacement transducers, etc., are used, the total number of measurement locations available is limited by the weight added and the effect each sensor has on the local stiffness of the contact area. Other non-contacting sensors, such as Laser Doppler Vibrometers (LDV), laser triangulation sensors, proximity sensors, etc., do not affect the dynamics of a structure, but are limited to single point measurements. In contrast, a few recently developed non-contacting measurement techniques have been shown to be capable of simultaneously measuring the response over a wide measurement field. Two techniques are considered here: Continuous-Scan Laser Doppler Vibrometry (CSLDV) and high speed Three-Dimensional Digital Image Correlation (3D DIC). With the use of these techniques, unprecedented measurement resolution can be achieved. In this work, the linear and nonlinear deformations of a clamped, nominally flat beam and plate under steady state sinusoidal loading will be measured using both techniques. In order to assess their relative merits, the linear natural frequencies, mode shapes, and nonlinear deformation shapes measured with each method are compared. Both measurement systems give comparable results in many cases, although 3D DIC is more accurate for spatially complex deformations at large amplitudes and CSLDV is more accurate at low amplitudes and when the spatial deformation pattern is simpler.

Noncontact Measurement of Complex Permittivity and Thickness by Using Planar Resonators

This paper presents a novel noncontact measurement technique that entails using a single-compound triple complementary split-ring resonator (SC-TCSRR) to determine the complex permittivity and thickness of a material under test (MUT). The proposed technique overcomes the problem engendered by the existence of air gaps between the sensor ground plane and the MUT. In the proposed approach, a derived governing equation of the resonance frequencies is used to estimate the thickness and complex permittivity of the MUT by calculating the resonant frequency $(f_{{ r}})$ and magnitude response in a single-step noncontact measurement process. This study theoretically analyzed and experimentally verified a simple and low-cost SC-TCSRR measurement method for assessing materials in a noncontact method. For a 0.2-mm air gap, the experiments yielded average measurement errors of 4.32% and 5.05% for the thickness and permittivity, respectively. The proposed SC-TCSRR technique provides excellent solutions for reducing the effect of air-gap conditions on permittivity, thickness, and loss tangent in noncontact measurements.

Silicon Micromachined Device Testing by Infrared Low-Coherence Reflectometry

With the development of silicon micromachining technologies, non-contact measurement techniques for in-depth non-destructive inspection of layered and microstructured samples are becoming increasingly relevant. In this paper, we apply optical low-coherence reflectometry (OLCR) to detect the optical path between the interfaces of several silicon devices with characteristic distance in the range 3–17 $\mu \text{m}$ . The implemented configuration is based on a fiberoptic Michelson interferometer that exploits infrared broadband radiation in the wavelength range of 1.2–1.7 $\mu \text{m}$ , with coherence length shorter than 2 $\mu \text{m}$ , for performing spot tomographic measurements. OLCR enabled out-of-plane measurements on a MEMS linear accelerometer and in-plane measurements on vertical periodic silicon/air microstructures. The optical distance between hidden interfaces was found well in agreement with the design parameters. [2015-0108]

Design and Implementation of Real-Time Flow Measurement System Using Hall Probe Sensor and PC-Based SCADA

A rotameter is a variable-area-type flow rate measuring instrument in which the position of a metallic float in a transparent conical tube is taken as a flow rate indicator. It has the disadvantage that it is a local indicating type instrument and special type of transducer is used for its remote indication. In this paper, a noncontact flow rate measurement technique using Hall probe sensor and rotameter is designed, developed, and tested. In this design, a float carrying a thin circular permanent magnet is used, and a Hall probe sensor placed outside the rotameter tube has been used to sense the variation of magnetic field of the magnet with the variation of float position. A signal conditioner unit has been used to convert the Hall probe sensor output into 1–5 V dc signal. This dc signal output of the signal conditioner has been sent to a PC-based flow indicator through optoisolator and analog input channel of a data acquisition system (DAS) card. The PC-based flow indicator has been designed using the Lab Tech Note Book Pro software and the PC-based supervisory control and DAS. A theoretical equation has been derived to explain the operation of the system. The performance of the system has been tested experimentally, and the experimental results are reported in this paper. A very good repeatability and linearity of results has been observed.

Single-lens 3D digital image correlation system based on a bilateral telecentric lens and a bi-prism: validation and application.

By using the principle of stereovision, 3D digital image correlation (3D-DIC) can determine the 3D morphology and deformation of a target and has been widely used in experimental mechanics as a noncontact 3D measurement technique. To eliminate the limitations of the conventional 3D-DIC system, this study proposes a calibration-free single-lens 3D-DIC system based on a bilateral telecentric lens and a bi-prism. The performance of the proposed system is verified by tests of rigid-body translation along the out-of-plane direction. As a comparison, the same rigid-body translations are measured using a single-entocentric-lens 3D-DIC system. The results show that the measurement accuracy of the proposed system is higher than that of the entocentric-lens-based one. As an application, the proposed system is used to measure the thermal linear expansion of a ceramic plate at elevated temperatures. The reasonable measurement results verify its applicability in deformation measurements, even in high-temperature environments.

Noncontact Thickness Measurement of Metal Films Using Eddy-Current Sensors Immune to Distance Variation

A simple method for measuring the thickness of metal films based on eddy-current sensors (ECSs) immune to distance variation is proposed. The slope of the lift-off curve (LOC) in the RL impedance plane is a good feature for characterizing target thickness independent of lift-off distance variation. A simple equivalent model was built to deal with the ECS problem, and the essential relationship between the slope of LOC (SLOC) and target properties was obtained. Full finite element analysis was conducted to analyze the relationship between SLOC feature and target thickness, and the results matched the modeling results very well. A sensor coil probe was then manufactured and used to measure the thickness of copper films with high performance, and the capability of this technique for online noncontact thickness measurement was verified. The basic characteristics and performances of this thickness measurement technique were tested and discussed. The SLOC feature for thickness measurement had significant advantages, such as simplicity, reliability, immunity to the lift-off effect (most important), high speed, simple signal processing, and negligible design limitation of the sensor probe. The results of this paper revealed that online thickness measurement systems could be developed for various advanced industrial applications.

Non-contact measurement technique for dimensional metrology using optical comb

This paper proposes a non-contact pulsed interferometer for dimensional metrology using the repetition frequency of an optical frequency comb. A compact absolute-length measuring system is established for practical non-contact measurement based on a single-mode fiber interferometer. The stability and accuracy of the measurements are compared with those from a commercial incremental laser interferometer. The drifts of both systems have the same tendency and a maximum difference is approximately 0.1μm. Subsequently, preliminary absolute-length measurements up to 1.5m were measured. The signal-to-noise ratios of the small signals are improved by a frequency-selective amplifier. It is apparent that the noise is rejected, and the intensity of the interference fringes is amplified, achieving a maximum standard deviation of measurement approximately 1μm. The proposed technique can provide sufficient accuracy for non-contact measurement in applications such as a simple laser-pulse tracking system.

Blood Pulsation Measurement Using Linearly Polarized Light

Blood molecules are optically active molecules. They have the ability to alter the polarization properties of light. This paper investigates the effect of blood pulsation variation on the polarization properties of linearly polarized light. This paper presents a new noninvasive noncontact blood pulsation measurement technique. Linearly polarized light has been allowed to transmit through the fingertips of a person and degree of linear polarization for transmitted part of the light has been calculated using polarized images. Experimental results show a strong correlation between the blood pulsation rate and the measured degree of linear polarization. The standard correlation coefficient value for the experiment with laser light source and two polarizers in the light path is 0.9484. Similarly for dc light source the correlation coefficient values are 0.9410 and 0.92 with two polarizers and one polarizer, respectively. Statistical analysis of the collected data has been done to measure the accuracy of the method. It shows that an accurate, low cost, and simple polarization-based blood pulsation measurement device can be developed by following the experiment performed with laser light source which could offer significant benefits to primary healthcare.

The influence of nitrogen and oxygen additions on the thermal characteristics of aluminium-based thin films

The ternary aluminium oxynitride (AlNxOy) system offers the possibility to obtain a wide range of properties by tailoring the ratio between pure Al, AlNx and AlOy and therefore opening a significant number of possible applications. In this work the thermal behaviour of AlNxOy thin films was analysed by modulated infrared radiometry (MIRR), taking as reference the binary AlOy and AlNx systems. MIRR is a non-contact and non-destructive thermal wave measurement technique based on the excitation, propagation and detection of temperature oscillations of very small amplitudes. The intended change of the partial pressure of the reactive gas (N2 and/or O2) influenced the target condition and hence the deposition characteristics which, altogether, affected the composition and microstructure of the films. Based on the MIRR measurements and their qualitative and quantitative interpretation, some correlations between the thermal transport properties of the films and their chemical/physical properties have been found. Furthermore, the potential of such technique applied in this oxynitride system, which present a wide range of different physical responses, is also discussed. The experimental results obtained are consistent with those reported in previous works and show a high potential to fulfil the demands needed for the possible applications of the systems studied. They are clearly indicative of an adequate thermal response if this particular thin film system is aimed to be applied in small sensor devices or in electrodes for biosignal acquisition, such as those for electroencephalography or electromyography as it is the case of the main research area that is being developed in the group.

Temperature sensing of micron scale polymer fibers using fiber Bragg gratings

Highly conductive polymer fibers are key components in the design of multifunctional textiles. Measuring the voltage/temperature relationships of these fibers is very challenging due to their very small diameters, making it impossible to rely on classical temperature sensing techniques. These fibers are also so fragile that they cannot withstand any perturbation from external measurement systems. We propose here, a non-contact temperature measurement technique based on fiber Bragg gratings (FBGs). The heat exchange is carefully controlled between the probed fibers and the sensing FBG by promoting radiation and convective heat transfer rather than conduction, which is known to be poorly controlled. We demonstrate our technique on a highly conductive Poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based fiber. A non-phenomenological model of the sensing system based on meaningful physical parameters is validated towards experimental observations. The technique reliably measures the temperature of the polymer fibers when subjected to electrical loading.

Accurate three-dimensional shape and deformation measurement at microscale using digital image correlation.

Based on stereomicroscope and three-dimensional (3D) digital image correlation (DIC) method, a non-contact measurement technique is presented to measure the 3D shape and deformation data on miniature specimens and the corresponding microscopic measurement system is developed. A pair of cameras is mounted on a binocular stereo light microscope to acquire pairing micrographs from two different optical paths of a specimen surface spraying with speckle pattern. Considering complex optical paths and high magnification, an accurate equivalent relative calibration method, combining a priori warping functions, is proposed to correct image distortions and optimize the intrinsic and extrinsic parameters of stereomicroscope. Then, a fast one-dimensional synchronous stereo matching method, based on the DIC method and image rectification technique, is proposed to search for discontinuous corresponding points in the pairing micrographs. Finally, the 3D shape is reconstructed from the corresponding points, while the temporal micrographs acquired before and after deformation are employed to determine the full-field deformation. The effectiveness and accuracy of the presented microscale measurement technique are verified by a series of experiments.

Development of noncontact measurement methods using multiple laser displacement sensors for bending and torsional vibration stresses in piping systems

In this study, two methods to measure bending and torsional vibration stresses of piping systems conveniently and quickly are proposed. The proposed methods are composed of a modeling approach of piping vibration and noncontact measurement techniques. The methods assume the vibration modes as a primary mode within the measuring range without the mode-identification and then estimate the vibration stress by approximating the vibration displacements measured in a noncontact manner as a primary mode. This paper presents the principles and calculation formulas of both methods and shows the measurement techniques for the bending and torsional vibration stresses using laser displacement sensors. Finally the applicability of one method is discussed based on the results of a vibration experiment.

Viscoplastic tearing of polyethylene thin film

Recent advances in noncontact strain measurement techniques and large-strain constitutive modeling of the linear low-density polyethylene film used in NASA superpressure balloons StratoFilm 420 are combined to provide a novel measurement technique for the tear propagation critical value of the J-integral. Previously these measurements required complex test configurations and procedures. It is found that the critical value of the J-integral increases by approximately 50 % when the strain rate is decreased from 1.33×10−4 s−1 to 1.33×10−5 s−1. It is shown that there is good correlation between measurements made on uniaxially loaded dogbone samples and circular diaphragms loaded by pressure, both with a 2-mm-wide slit in the middle. This result indicates that more extensive studies of strain-rate dependence may be made with the simpler, uniaxial test configuration.

Progressive damage assessment of centrally notched composite specimens in fatigue

The aim of this study is to assess the residual properties and the corresponding damage states within centrally notched quasi-isotropic [0/−45/+45/90]S T650/F584 (Hexcel) carbon-fiber/epoxy composites subjected to fatigue loading using Digital Image Correlation (DIC), radiography, and a non-contact vibration measurement technique. Quasi-static tests were performed on virgin samples using DIC to determine the full-field in-plane strains at different applied load levels. Fatigue tests were interrupted during the fatigue lifetimes in order to perform quasi-static tests with DIC measurements. Non-contact vibration measurements were performed to investigate the effect of fatigue damage on residual frequency responses. X-ray computed tomography was used to determine the type, location, and extent of fatigue damage development. The results provide an important step in the validation of DIC and vibration response as a powerful combined non-destructive evaluation tool for monitoring the development of fatigue damage as well as predicting the damage level of notched composite materials.

Influence of bonding technique on bond behavior of CFRP-to-clay brick masonry joints: Experimental study using particle image velocimetry (PIV)

This paper presents a comparative study on the performance of three different techniques for bonding carbon fiber reinforced polymer (CFRP) sheets to masonry substrate. To do so, eight CFRP-to-clay brick masonry joints were prepared using conventional externally bonded reinforcement (EBR) technique, with and without surface preparation. Moreover, for the first time, grooving method (GM) in the form of externally bonded reinforcement on grooves (EBROG) technique was used for bonding CFRP sheets to masonry substrate in six other joints. The specimens were tested under single lap-shear loading and the influence of bonding technique as well as effect of fiber reinforced polymer (FRP) bond length were comprehensively investigated and discussed based on the experimental results. A non-contact full field deformation measurement technique, i.e. particle image velocimetry (PIV), was used to obtain the load–slip diagrams, strain profiles along the bonded length, and strain fields of all tested specimens. Experimental results and PIV measurements demonstrated that bond behavior of CFRP sheets attached to masonry substrate was significantly improved by using EBROG technique. Consequently, the technique can be used as an alternative to conventional EBR method to more efficiently utilize the tensile capacity of FRPs used for external strengthening of unreinforced masonry (URM) structures.

<b>Development of an Aerial Survey System and Numerical Analysis Modeling Software for Unstable Rock Blocks</b>

The authors have been studying a method for evaluating rock slope stability by applying a non-contact vibration measurement technique. Consideration of the size of the rock block, its shape and conditions supporting it are indispensable for improving the accuracy of the evaluation method. Accordingly, an aerial survey system to observe the shape of the rock block was built. Next, software was developed to automatically generate a three dimensional finite element analysis model from the data collected relating to the shape of the block. Finally, a rockfall risk evaluation technique was proposed using the parametrical analysis results of the FE analysis model regarding loads exerted on and conditions supporting the block.