Showing papers in "Measurement Science and Technology in 2014"

Quantum cascade lasers: a versatile source for precise measurements in the mid/far-infrared range

Abstract: We provide an overview of recent developments of quantum cascade lasers (QCLs), from the mid-infrared (mid-IR) to the far-IR (THz) range, with a special focus on their metrological-grade applications in a number of fields. A special emphasis on the physics of the QCLs allows underlining peculiar effects and device features recently unveiled that pave the way to novel demanding photonics applications.

Review of the application of energy harvesting in buildings

Abstract: This review presents the state of the art of the application of energy harvesting in commercial and residential buildings. Electromagnetic (optical and radio frequency), kinetic, thermal and airflow-based energy sources are identified as potential energy sources within buildings and the available energy is measured in a range of buildings. Suitable energy harvesters are discussed and the available and the potential harvested energy calculated. Calculations based on these measurements, and the technical specifications of state-of-the-art harvesters, show that typical harvested powers are: (1) indoor solar cell (active area of 9 cm2, volume of 2.88 cm3): ~300 µW from a light intensity of 1000 lx; (2) thermoelectric harvester (volume of 1.4 cm3): 6 mW from a thermal gradient of 25 °C; (3) periodic kinetic energy harvester (volume of 0.15 cm3): 2 µW from a vibration acceleration of 0.25 m s−2 at 45 Hz; (4) electromagnetic wave harvester (13 cm antenna length and conversion efficiency of 0.7): 1 µW with an RF source power of −25 dBm; and (5) airflow harvester (wind turbine blade of 6 cm diameter and generator efficiency of 0.41): 140 mW from an airflow of 8 m s−1. These results highlight the high potential of energy harvesting technology in buildings and the relative attractions of various harvester technologies. The harvested power could either be used to replace batteries or to prolong the life of rechargeable batteries for low-power (~1 mW) electronic devices.

Kinetic and thermal energy harvesters for implantable medical devices and biomedical autonomous sensors

Abstract: Implantable medical devices usually require a battery to operate and this can represent a severe restriction. In most cases, the implantable medical devices must be surgically replaced because of the dead batteries; therefore, the longevity of the whole implantable medical device is determined by the battery lifespan. For this reason, researchers have been studying energy harvesting techniques from the human body in order to obtain batteryless implantable medical devices. The human body is a rich source of energy and this energy can be harvested from body heat, breathing, arm motion, leg motion or the motion of other body parts produced during walking or any other activity. In particular, the main human-body energy sources are kinetic energy and thermal energy. This paper reviews the state-of-art in kinetic and thermoelectric energy harvesters for powering implantable medical devices. Kinetic energy harvesters are based on electromagnetic, electrostatic and piezoelectric conversion. The different energy harvesters are analyzed highlighting their sizes, energy or power they produce and their relative applications. As they must be implanted, energy harvesting devices must be limited in size, typically about 1 cm 3 . The available energy depends on human-body positions; therefore, some positions are more advantageous than others. For example, favorable positions for piezoelectric harvesters are hip, knee and ankle where forces are significant. The energy harvesters here reported produce a power between 6 nW and 7.2 mW; these values are comparable with the supply requirements of the most common implantable medical devices; this demonstrates that energy harvesting techniques is a valid solution to design batteryless implantable medical devices.

A practical approach to optimizing the preparation of speckle patterns for digital-image correlation

Abstract: The quality of strain measurements by digital image correlation (DIC) strongly depends on the quality of the pattern on the specimen's surface. An ideal pattern should be highly contrasted, stochastic, and isotropic. In addition, the speckle pattern should have an average size that exceeds the image pixel size by a factor of 3–5. (Smaller speckles cause poor contrast, and larger speckles cause poor spatial resolution.) Finally, the ideal pattern should have a limited scatter in terms of speckle sizes.The aims of this study were: (i) to define the ideal speckle size in relation to the specimen size and acquisition system; (ii) provide practical guidelines to identify the optimal settings of an airbrush gun, in order to produce a pattern that is as close as possible to the desired one while minimizing the scatter of speckle sizes.Patterns of different sizes were produced using two different airbrush guns with different settings of the four most influential factors (dilution, airflow setting, spraying distance, and air pressure). A full-factorial DOE strategy was implemented to explore the four factors at two levels each: 36 specimens were analyzed for each of the 16 combinations.The images were acquired using the digital cameras of a DIC system. The distribution of speckle sizes was analyzed to calculate the average speckle size and the standard deviation of the corresponding truncated Gaussian distribution. A mathematical model was built to enable prediction of the average speckle size in relation to the airbrush gun settings.We showed that it is possible to obtain a pattern with a highly controlled average and a limited scatter of speckle sizes, so as to match the ideal distribution of speckle sizes for DIC. Although the settings identified here apply only to the specific equipment being used, this method can be adapted to any airbrush to produce a desired speckle pattern.

Particle image velocimetry correlation signal-to-noise ratio metrics and measurement uncertainty quantification

Abstract: In particle image velocimetry (PIV) the measurement signal is contained in the recorded intensity of the particle image pattern superimposed on a variety of noise sources. The signalto-noise-ratio (SNR) strength governs the resulting PIV cross correlation and ultimately the accuracy and uncertainty of the resulting PIV measurement. Hence we posit that correlation SNR metrics calculated from the correlation plane can be used to quantify the quality of the correlation and the resulting uncertainty of an individual measurement. In this paper we extend the original work by Charonko and Vlachos and present a framework for evaluating the correlation SNR using a set of different metrics, which in turn are used to develop models for uncertainty estimation. Several corrections have been applied in this work. The SNR metrics and corresponding models presented herein are expanded to be applicable to both standard and filtered correlations by applying a subtraction of the minimum correlation value to remove the effect of the background image noise. In addition, the notion of a ‘valid’ measurement is redefined with respect to the correlation peak width in order to be consistent with uncertainty quantification principles and distinct from an ‘outlier’ measurement. Finally the type and significance of the error distribution function is investigated. These advancements lead to more robust and reliable uncertainty estimation models compared with the original work by Charonko and Vlachos. The models are tested against both synthetic benchmark data as well as experimental measurements. In this work, U68.5 uncertainties are estimated at the 68.5% confidence level while U95 uncertainties are estimated at 95% confidence level. For all cases the resulting calculated coverage factors approximate the expected theoretical confidence intervals, thus demonstrating the applicability of these new models for estimation of uncertainty for individual PIV measurements.

Elimination of PIV light reflections via a temporal high pass filter

Abstract: A novel approach for PIV image pre-processing is proposed to deal with the undesired effect of laser light reflections from solid walls in wind tunnel experiments. The method can be applied for both stationary interfaces as well as when the image of the interface is moving due to vibration of either the model or the imaging system. The working hypothesis is that the motion of the interface is resolved temporally, which is typically the case when employing high-speed PIV systems. The method is based on the decomposition of the pixel intensity in the frequency domain. The high-frequency content of the signal is due to the transit of seeding particles, whereas undesired reflections will appear in the low-frequency range. Applying a high-pass filter on the light intensity time history retains only the contribution of the seeding particles and rejects the undesired light reflections. Two experiments show the application of the method. In the low-speed flow regime around a pitching airfoil, the trace of the laser impinging on the moving surface can be mostly eliminated, enabling cross correlation analysis of the flow closer to the wall. In the transonic regime, experiments are performed in an industrial wind tunnel around the base region of the ARIANE V launcher model. Here, the high-pass filter eliminates all secondary reflections and enhances the particles peak intensity relative to the reflections and the background light.

A multifrequency eletromagnetic applicator with an integrated AC magnetometer for magnetic hyperthermia experiments

Abstract: In the present paper, a lab-made electromagnetic applicator for magnetic hyperthermia experiments is described, fabricated and tested. The proposed device is able to measure the specific absorption rate (SAR) of nanoparticle samples at different magnetic field intensities and frequencies. Based on a variable parallel LCC resonant circuit fed by a linear power amplifier, the electromagnetic applicator is optimized to generate a controllable and homogeneous AC magnetic field in a 3.5 cm3 cylindrical volume, in a wide frequency range of 149–1030 kHz with high field intensities (up to 35 kA m−1 at low frequencies and up to 22 kA m−1 at high frequencies). In addition, a lab-made AC magnetometer is integrated in the electromagnetic applicator. The AC magnetometer is fully compensated to provide accurate measurements of the dynamic hysteresis cycle for nanoparticle powders or dispersions. From these dynamic hysteresis loops the SAR of the nanoparticle samples can be directly obtained. To show the capabilities of the proposed set-up, the AC hysteresis loops of two different magnetite nanoparticle samples with different sizes have been measured for various field intensities and frequencies. To our knowledge, no other work reports an electromagnetic applicator system with integrated AC magnetometer providing such characteristics in terms of frequency and intensity.

High-accuracy 2D digital image correlation measurements using low-cost imaging lenses: implementation of a generalized compensation method

Abstract: The ideal pinhole imaging model commonly assumed for an ordinary two-dimensional digital image correlation (2D-DIC) system is neither perfect nor stable because of the existence of small out-of-plane motion of the test sample surface that occurred after loading, small out-of-plane motion of the sensor target due to temperature variation of a camera and unavoidable geometric distortion of an imaging lens. In certain cases, these disadvantages can lead to significant errors in the measured displacements and strains. Although a high-quality bilateral telecentric lens has been strongly recommended to be used in the 2D-DIC system as an essential optical component to achieve high-accuracy measurement, it is not generally applicable due to its fixed field of view, limited depth of focus and high cost. To minimize the errors associated with the imperfectness and instability of a common 2D-DIC system using a low-cost imaging lens, a generalized compensation method using a non-deformable reference sample is proposed in this work. With the proposed method, the displacement of the reference sample rigidly attached behind the test sample is first measured using 2D-DIC, and then it is fitted using a parametric model. The fitted parametric model is then used to correct the displacements of the deformed sample to remove the influences of these unfavorable factors. The validity of the proposed compensation method is first verified using out-of-plane translation, out-of-plane rotation, in-plane translation tests and their combinations. Uniaxial tensile tests of an aluminum specimen were also performed to quantitatively examine the strain accuracy of the proposed compensation method. Experiments show that the proposed compensation method is an easy-to-implement yet effective technique for achieving high-accuracy deformation measurement using an ordinary 2D-DIC system.

Novel trends in affinity biosensors: current challenges and perspectives

Abstract: Molecular biorecognition processes facilitate physical and biochemical interactions between molecules in all crucial metabolic pathways Perhaps the target analyte and the biorecognition element interactions have the most impactful use in biosensing applications Traditional analytical sensing systems offer excellent biorecognition elements with the ability to detect and determine the presence of analytes High affinity antibodies and DNA play an important role in the development of affinity biosensors based on electrochemical, optical and mass sensitive approaches Advancements in this area routinely employ labels, label free, nanoparticles, multifunctional matrices, carbon nanotubes and other methods to meet the requirements of its own application However, despite increasing affinity ceilings for conventional biosensors, the field draws back in meeting specifically important demands, such as long-term stability, ultrasensitivity, rapid detection, extreme selectivity, strong biological base, calibration, in vivo measurements, regeneration, satisfactory performance and ease of production Nevertheless, recent efforts through this line have produced novel high-tech nanosensing systems such as ?aptamers? and ?phages? which exhibit high-throughput sensing Aptamers and phages are powerful tools that excel over antibodies in sensibility, stability, multi-detection, in vivo measurements and regeneration Phages are superior in stability, screening for affinity-based target molecules ranging from small to proteins and even cells, and easy production In this review, we focus mainly on recent developments in affinity-based biosensors such as immunosensors, DNA sensors, emphasizing aptasensors and phage-based biosensors basing on novel electrochemical, optical and mass sensitive detection techniques We also address enzyme inhibition-based biosensors and the current problems associated with the above sensors and their future perspectives

High-bandwidth scanned-wavelength-modulation spectroscopy sensors for temperature and H2O in a rotating detonation engine

Abstract: The design and use of two-color tunable diode laser (TDL) absorption sensors for measurements of temperature and H2O in a rotating detonation engine (RDE) are presented Both sensors used first-harmonic-normalized scanned-wavelength-modulation spectroscopy with second-harmonic detection (scanned-WMS-2f/1f) to account for non-absorbing transmission losses and emission encountered in the harsh combustion environment One sensor used two near-infrared (NIR) TDLs near 13917 nm and 14693 nm that were modulated at 225 kHz and 285 kHz, respectively, and sinusoidally scanned across the peak of their respective H2O absorption transitions to provide a measurement rate of 50 kHz and a detection limit in the RDE of 02% H2O by mole The other sensor used two mid-infrared (MIR) TDLs near 2551 nm and 2482 nm that were modulated at 90 kHz and 112 kHz, respectively, and sinusoidally scanned across the peak of their respective H2O transitions to provide a measurement rate of 10 kHz and a detection limit in the RDE of 002% H2O by mole Four H2O absorption transitions with different lower-state energies were used to assess the homogeneity of temperature in the measurement plane Experimentally derived spectroscopic parameters that enable temperature and H2O sensing to within 15–35% of known values are reported The sensor design enabling the high-bandwidth scanned-WMS-2f/1f measurements is presented The two sensors were deployed across two orthogonal and coplanar lines-of-sight (LOS) located in the throat of a converging-diverging nozzle at the RDE combustor exit Measurements in the non-premixed H2-fueled RDE indicate that the temperature and H2O oscillate at the detonation frequency (≈325 kHz) and that production of H2O is a weak function of global equivalence ratio

Extending the flash method to measure the thermal diffusivity of semitransparent solids

Abstract: In this work, we extend the classical flash method to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of semitransparent plates. A complete theoretical model that allows calculating the rear surface temperature rise of the sample has been developed. It takes into consideration additional effects such as multiple reflections of the heating light beam inside the sample, heat losses by convection and radiation, transparency of the sample to infrared wavelengths and finite duration of the heating pulse. Measurements performed on calibrated solids, covering a wide range of absorption coefficients from transparent to opaque, validate the proposed method.

A calibration technique to correct sensor drift issues in hot-wire anemometry

Abstract: Accurate calibration is imperative to obtain reliable flow measurements using hot-wire anemometry. Calibration errors owing to temperature drift, wire degradation, changes in ambient conditions etc can lead to substantial uncertainties in hot-wire measurements. A new calibration procedure is implemented here to account for most forms of drift that are typically encountered during high quality flow measurements using hot-wires. The method involves obtaining single point recalibrations of the hot-wire (in the free-stream) at regular intervals during the course of an actual experiment, and using these during post-processing to correct for any drift encountered. Unlike many other existing schemes, this proposed calibration correction method is not solely restricted to correcting temperature drift.

Spatially resolved acoustic spectroscopy for rapid imaging of material microstructure and grain orientation

Abstract: Measuring the grain structure of aerospace materials is very important to understand their mechanical properties and in-service performance. Spatially resolved acoustic spectroscopy is an acoustic technique utilizing surface acoustic waves to map the grain structure of a material. When combined with measurements in multiple acoustic propagation directions, the grain orientation can be obtained by fitting the velocity surface to a model. The new instrument presented here can take thousands of acoustic velocity measurements per second. The spatial and velocity resolution can be adjusted by simple modification to the system; this is discussed in detail by comparison of theoretical expectations with experimental data.

Gas mixing apparatus for automated gas sensor characterization

Abstract: We developed a computer-controlled gas mixing system that provides automated test procedures for the characterization of gas sensors. The focus is the generation of trace gases (e.g. VOCs like benzene or naphthalene) using permeation furnaces and pre-dilution of test gases. With these methods, the sensor reaction can be analyzed at very low gas concentrations in the ppb range (parts per billion) and even lower. The pre-dilution setup enables to cover a high concentration range (1:62?500) within one test procedure. Up to six test gases, humidity, oxygen content, total flow and their variation over time can be controlled via a LabVIEW-based user-interface.

Wavelength-modulation spectroscopy near 1.4 µm for measurements of H2O and temperature in high-pressure and -temperature gases

Abstract: The development, validation and demonstration of a two-color tunable diode laser (TDL) absorption sensor for measurements of temperature and H2O in high-pressure and high-temperature gases are presented. This sensor uses first-harmonic-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f/1f) to account for non-absorbing transmission losses and emission encountered in harsh, high-pressure environments. Two telecommunications-grade TDLs were used to probe H2O absorption transitions near 1391.7 and 1469.3 nm. The lasers were frequency-multiplexed and modulated at 160 and 200 kHz to enable a measurement bandwidth up to 30 kHz along a single line-of-sight. In addition, accurate measurements are enabled at extreme conditions via an experimentally derived spectroscopic database. This sensor was validated under low-absorbance (<0.05) conditions in shock-heated H2O–N2 mixtures at temperatures and pressures from 700 to 2400 K and 2 to 25 atm. There, this sensor recovered the known temperature and H2O mole fraction with a nominal accuracy of 2.8% and 4.7% RMS, respectively. Lastly, this sensor resolved expected transients with high bandwidth and high precision in a reactive shock tube experiment and a pulse detonation combustor.

Video-based measurements for wireless capsule endoscope tracking

Abstract: The wireless capsule endoscope is a swallowable medical device equipped with a miniature camera enabling the visual examination of the gastrointestinal (GI) tract. It wirelessly transmits thousands of images to an external video recording system, while its location and orientation are being tracked approximately by external sensor arrays. In this paper we investigate a video-based approach to tracking the capsule endoscope without requiring any external equipment. The proposed method involves extraction of speeded up robust features from video frames, registration of consecutive frames based on the random sample consensus algorithm, and estimation of the displacement and rotation of interest points within these frames. The results obtained by the application of this method on wireless capsule endoscopy videos indicate its effectiveness and improved performance over the state of the art. The findings of this research pave the way for a cost-effective localization and travel distance measurement of capsule endoscopes in the GI tract, which could contribute in the planning of more accurate surgical interventions.

A fast response temperature sensor based on fiber Bragg grating

Abstract: Aimed at the requirement for a fast-response expendable ocean temperature sensor, this paper presents a new design scheme for an optic fiber sensor. Ocean temperature sensors require high sensitivity and high response speed, which must be up to milliseconds. The fiber Bragg grating (FBG) temperature sensor with high sensitivity has been declared in the last decade, but its response speed has been rarely reported. In this paper, a method is proposed which is to package an FBG with a metal tube. The response time of this sensor is 48.6 ms, which is an order of magnitude greater than that of an ordinary optical fiber temperature sensor. Temperature sensitivity is 27.6 pm/°C and the linearity is up to 0.9999. In addition, the sensor can be less than 15 mm. It offers a new way to detect ocean temperature.

Accurate 3D shape measurement of multiple separate objects with stereo vision

Abstract: D shape measurement has emerged as a very useful tool in numerous fields because of its wide and ever-increasing applications. In this paper, we present a passive, fast and accurate 3D shape measurement technique using stereo vision approach. The technique first employs a scale-invariant feature transform algorithm to detect point matches at a number of discrete locations despite the discontinuities in the images. Then an automated image registration algorithm is applied to find full-field point matches with subpixel accuracy. After that, the 3D shapes of the objects can be reconstructed according to the obtained point matching and the camera information. The proposed technique is capable of performing a full-field 3D shape measurement with high accuracy even in the presence of discontinuities and multiple separate regions. The validity is verified by experiments.

An investigation into the durability of screen-printed conductive tracks on textiles

Abstract: This paper examines the durability of screen-printed conductive tracks on textiles These tracks are composed of a silver polymer paste as a conductive layer, which is fully encapsulated with polyurethane The polyurethane materials and layer structures used to encapsulate the textile are varied and each structure is tested in a cyclic mandrel machine to simulate the effects of normal wear and tear These results are compared to a MATLAB model of the strain in the conductive track, relating the predicted strain on the conductive layer to the measured resistance change From these results, a batch of structures with high durability are fabricated and these are machine washed It was found that 971% of the conductive tracks remained conductive after ten domestic machine washes with a 1 kg load at 40 °C and 1000 rpm spin speed This compares with 89% which remained conductive before optimization This optimization process has therefore led to over ten times improvement in durability for screen-printed conductive tracks on textiles

Simultaneous two-phase flow measurement of spray mixing process by means of high-speed two-color PIV

Abstract: In this article, a novel high-speed two-color PIV optical diagnostic technique has been developed and applied to simultaneously measure the velocity flow-fields of a multi-hole spark-ignition direct injection (SIDI) fuel injector spray and its ambient gas in a high-pressure constant volume chamber. To allow for the phase discrimination between the fuel droplets and ambient gas, a special tracer-filter system was designed. Fluorescent seeding particles with Sauter mean diameter (SMD) of 4.8 µm were used to trace the gas inside the chamber. With a single high-speed Nd:YLF laser sheet (527 nm) as the incident light source, the Mie-scattering signal marked the phase of the fuel spray, while the fluorescent signal generated from the seeding particles tracked the phase of ambient gas. A high-speed camera, with an image-doubler (mounted in front of the camera lens) that divided the camera pixels into two parts focusing on the same field of view, was used to collect the Mie-scattering signal and LIF (laser induced fluorescence) signal simultaneously with two carefully selected optical filters. To accommodate the large dynamic range of velocities in the two phases (1–2 orders of magnitude difference), two separation times (dt) were introduced. This technique was successfully applied to the liquid spray and ambient gas two-phase flow measurement. The measurement accuracy was compared with those from LDV (laser Doppler velocimetry) measurement and good agreement was obtained. Ambient gas motion surrounding the fuel spray was investigated and characterized into three zones. The momentum transfer process between the fuel spray and ambient gas in each zone was analyzed. The two-phase flow interaction under various superheated conditions was investigated. A strengthened momentum transfer from the liquid spray to the ambient was observed with increased superheat degree.

Measurement and calculation of the viscosity of metals—a review of the current status and developing trends

Abstract: Viscosity is an important rheological property of metals in casting because it controls the rate of transport of liquid metals, which may lead to casting defects such as hot tearing and porosity. The measurement methods and numerical models of the viscosity of liquid and semi-solid state metals that have been published to date are reviewed in this paper. Most experimental measurements have been performed with rotational and oscillatory viscometers, which offer advantages at low viscosities in particular. Besides these two traditional methods for measuring viscosities, a couple of studies also introduced the technique of isothermal compression for alloys in the semi-solid state, and even an optical basicity method for the viscosity of slags. As to numerical models, most published results show that the viscosity of liquid and semi-solid state metals can be described by the Arrhenius, Andrade, Kaptay or Budai–Bemkő–Kaptay equations. In addition, there are some alternative models, such as the power model and the isothermal stress–strain model.

Scanning magnetic tunnel junction microscope for high-resolution imaging of remanent magnetization fields

Abstract: Scanning magnetic microscopy is a new methodology for mapping magnetic fields with high spatial resolution and field sensitivity. An important goal has been to develop high-performance instruments that do not require cryogenic technology due to its high cost, complexity, and limitation on sensor-to-sample distance. Here we report the development of a low-cost scanning magnetic microscope based on commercial room-temperature magnetic tunnel junction (MTJ) sensors that typically achieves spatial resolution better than 7 µm. By comparing different bias and detection schemes, optimal performance was obtained when biasing the MTJ sensor with a modulated current at 1.0 kHz in a Wheatstone bridge configuration while using a lock-in amplifier in conjunction with a low-noise custom-made preamplifier. A precision horizontal (x–y) scanning stage comprising two coupled nanopositioners controls the position of the sample and a linear actuator adjusts the sensor-to-sample distance. We obtained magnetic field sensitivities better than 150 nT/Hz1/2 between 0.1 and 10 Hz, which is a critical frequency range for scanning magnetic microscopy. This corresponds to a magnetic moment sensitivity of 10–14 A m2, a factor of 100 better than achievable with typical commercial superconducting moment magnetometers. It also represents an improvement in sensitivity by a factor between 10 and 30 compared to similar scanning MTJ microscopes based on conventional bias-detection schemes. To demonstrate the capabilities of the instrument, two polished thin sections of representative geological samples were scanned along with a synthetic sample containing magnetic microparticles. The instrument is usable for a diversity of applications that require mapping of samples at room temperature to preserve magnetic properties or viability, including paleomagnetism and rock magnetism, nondestructive evaluation of materials, and biological assays.

Sensing sheet: the sensitivity of thin-film full-bridge strain sensors for crack detection and characterization

Abstract: Increasing concerns regarding the conditions of civil structures and infrastructure give rise to the need for efficient strategies to identify and repair structural anomalies. ‘Sensing sheets’ based on large-area electronics consist of a dense array of unit strain sensors. These are an effective and affordable structural health monitoring tool that can identify and continuously monitor the growth of cracks in structures. This paper presents a study on the quantitative relationship between crack width and strain, the latter measured by an individual sensor that would be part of a sensing sheet. We investigate the sensitivity of thin-film full-bridge strain sensors to concrete cracks by conducting laboratory experiments in temperature-controlled settings. The results show a distribution of near-linear relationships with an average sensitivity of 31 μe μm −1 . Experiments were also conducted to investigate the effect of crack position and orientation with respect to the sensor, and it appears that both variables affect the sensitivity of strain sensors to cracks. Overall, this study confirms that full-bridge resistive strain sensors can successfully detect and quantify cracks in structural materials and are therefore appropriate as part of a dense array of sensors on a sensing sheet.

Determination of gas composition in a biogas plant using a Raman-based sensor?system

Abstract: We propose a gas sensor, based on spontaneous Raman scattering, for the compositional analysis of typical biogas mixtures and present a description of the sensor, as well as of the calibration procedure, which allows the quantification of condensable gases. Moreover, we carry out a comprehensive characterization of the system, in order to determine the measurement uncertainty, as well as influences of temperature and pressure fluctuation. Finally, the sensor is applied at different locations inside a plant in which biogas is produced from renewable raw materials. The composition is monitored after fermenting, after purification and after the final conditioning, where natural gas is added. The Raman sensor is able to detect all the relevant gas components, i.e. CH4, CO2, N2 and H2O, and report their individual concentrations over time. The results were compared to reference data from a conventional gas analyzer and good agreement was obtained.

Adaptive robust Kalman filtering for precise point positioning

Abstract: The optimality of precise point postioning (PPP) solution using a Kalman filter is closely connected to the quality of the a priori information about the process noise and the updated mesurement noise, which are sometimes difficult to obtain. Also, the estimation enviroment in the case of dynamic or kinematic applications is not always fixed but is subject to change. To overcome these problems, an adaptive robust Kalman filtering algorithm, the main feature of which introduces an equivalent covariance matrix to resist the unexpected outliers and an adaptive factor to balance the contribution of observational information and predicted information from the system dynamic model, is applied for PPP processing. The basic models of PPP including the observation model, dynamic model and stochastic model are provided first. Then an adaptive robust Kalmam filter is developed for PPP. Compared with the conventional robust estimator, only the observation with largest standardized residual will be operated by the IGG III function in each iteration to avoid reducing the contribution of the normal observations or even filter divergence. Finally, tests carried out in both static and kinematic modes have confirmed that the adaptive robust Kalman filter outperforms the classic Kalman filter by turning either the equivalent variance matrix or the adaptive factor or both of them. This becomes evident when analyzing the positioning errors in flight tests at the turns due to the target maneuvering and unknown process/measurement noises.

Characterization of SEM speckle pattern marking and imaging distortion by digital image correlation

Abstract: Surface patterning by e-beam lithography and scanning electron microscope (SEM) imaging distortions are studied via digital image correlation. The global distortions from the reference pattern, which has been numerically generated, are first quantified from a digital image correlation procedure between the (virtual) reference pattern and the actual SEM image both in secondary and backscattered electron imaging modes. These distortions result from both patterning and imaging techniques. These two contributions can be separated (without resorting to an external caliper) based on the images of the same patterned surface acquired at different orientations. Patterning distortions are much smaller than those due to imaging on wide field images.

Current state of standardization in the field of dimensional computed tomography

Abstract: Industrial x-ray computed tomography (CT) is a well-established non-destructive testing (NDT) technology and has been in use for decades. Moreover, CT has also started to become an important technology for dimensional metrology. But the requirements on dimensional CTs, i.e., on performing coordinate measurements with CT, are different from NDT. For dimensional measurements, the position of interfaces or surfaces is of importance, while this is often less critical in NDT. Standardization plays an important role here as it can create trust in new measurement technologies as is the case for dimensional CT. At the international standardization level, the ISO TC 213 WG 10 is working on specifications for dimensional CT. This paper highlights the demands on international standards in the field of dimensional CT and describes the current developments from the viewpoint of representatives of national and international standardization committees. Key aspects of the discussion are the material influence on the length measurement error E and how E can best be measured. A respective study was performed on hole plates as new reference standards for error testing of length measurements incorporating the material influence. We performed corresponding measurement data analysis and present a further elaborated hole plate design. The authors also comment on different approaches currently pursued and give an outlook on upcoming developments as far as they can be foreseen.

Robust condition monitoring and fault diagnosis of rolling element bearings using improved EEMD and statistical features

Abstract: Condition monitoring and fault diagnosis play an important role in the health management of mechanical equipment. However, the robust performance of data-driven-based methods with unknown fault inputs remains to be further improved. In this paper, a novel approach of condition monitoring and fault diagnosis is proposed for rolling element bearings based on an improved ensemble empirical mode decomposition (IEEMD), which is able to solve the non-intrinsic mode function problem of EEMD. In this method, IEEMD is applied to process the primordial vibration signals collected from rolling element bearings at first. Then the correlation analysis and data fusion technology are introduced to extract statistical features from these decomposition results of IEEMD. Finally, a complete self-zero space model is constructed for the condition monitoring and fault diagnosis of rolling element bearings. Experiments are implemented on a mechanical fault simulator to demonstrate the reliability and effectiveness of the proposed method. The experimental results show that the proposed method can not only diagnose known faults but also monitor unknown faults with strong robust performance.

Capabilities and limitations of the self-calibration of angle encoders

Abstract: At the Physikalisch-Technische Bundesanstalt (PTB), a self-calibration method for the fast and precise in situ calibration of angle encoders without recourse to external reference standards has been developed. It relies on a suitable geometric arrangement of multiple reading heads which read out the radial grating of the angle encoder at different angular positions. Fourier-based algorithms are used to analyse the measurement differences of pairs of heads to recover the graduation error of the grating. A comprehensive overview, both theoretical and experimental, of the capabilities and limitations of the self-calibration method is presented, including experimental data obtained with the high-precision primary angle standard of PTB. The evaluation and, where it is possible, correction of error influences due to lateral shifts of the centre of the encoder's grating during its rotation, including its eccentricity, the reading heads' angular positions, and their non-uniform response, are discussed in detail, as well as the resulting uncertainty budget.