Reduce Measurement Uncertainty Research Articles

Characterization of Dynamic and Nanoscale Materials and Metamaterials with Continuously Referenced Interferometry

AbstractThe development of new optical materials and metamaterials has seen a natural progression toward both nanoscale geometries and dynamic performance. The development of these materials, such as optical metasurfaces which impart discrete, spatially dependent phase shifts on incident light, often benefits from the measurement of transmitted or reflected phase. Careful measurement of phase typically proves difficult to implement, due to high measurement sensitivity to practically unavoidable environmental sources of noise and drift. To date, no characterization technique has yet emerged as a frontrunner for these applications. This challenge is addressed using a custom‐designed three‐beam Mach–Zehnder interferometer capable of continuously referenced measurement of both phase and transmittance, resulting in a 10× reduction of noise and drift and phase measurement standard deviation over 10 min of 0.56° and over 16 h of 2.8°. High measurement stability provided by this method enables samples to be easily characterized under dynamic conditions. Temperature‐dependent measurements are demonstrated with phase‐change material vanadium dioxide (VO2), and with wavelength‐dependent measurements of a dielectric Huygens metasurface supporting a characteristic resonant reflection peak. A Fourier‐based signal filtering technique is applied, reducing measurement uncertainty to 0.13° and enabling discernment of monolayer thickness variations in 2D material MoS2.

A laser scanning posture optimization method to reduce the measurement uncertainty of large complex surface parts

Non-contact laser scanning is widely used in aircraft parts inspection and components assembly, especially for the dimensional error of complex structural parts. Careful scan path planning can greatly improve the measurement accuracy and efficiency of scanning. This paper presents a methodology to solve the design and optimization problems of scanning posture. The scanning quality is improved by reducing measurement uncertainty to obtain the optimum posture angle and spatial position for scanning. A posture coordinate system is established to obtain the posture angle deviation between the current scanning posture and the principal direction of all points in the corresponding measuring area, which quantifies the measurement uncertainty of the scanning area. The posture adjustment interval is defined according to the limit scanning envelope to search for the feasible direction and position of the scanner, and the measurement uncertainty of the scanning area is reduced by optimizing the posture angles iteratively. We demonstrate the effectiveness of the proposed method by comparing it with other posture planning algorithms.

Investigation of the effect of microstructural changes on thermal transport in semicrystalline polymer semiconductors

Great progress in the development of new semiconducting polymers over the last two decades alongside improved understanding of electron transport mechanisms have resulted in a dramatic increase in the electron mobility of these materials making them promising candidates for electronic and thermoelectric applications. Heat transport phenomena, on the other hand—which govern thermal conductivity—have not received as much attention up to date. In spite of the simplicity of the principle behind the measurement of thermoelectric properties, the combined uncertainty in thermoelectric figure of merit zT could easily reach 50% with the largest uncertainty coming from thermal conductivity measurements. Such a high measurement uncertainty, often comparable to relative variations in zT encountered when optimizing within a given class of materials, prevents the study of structure-thermal property relationships. Here we present a protocol for the measurement of the thermal conductivity of thin films with reduced measurement uncertainty, which allowed us to investigate the effect of microstructural changes on the thermal conductivity of the conjugated polymer P(NDI2OD-T2). We show that the enhancement of the thermal conductivity upon annealing is much less pronounced than the corresponding increase in the electron mobility that has been reported under the same annealing conditions in the literature. This suggests that semicrystalline conjugated polymers in which thermal transport remains limited by the amorphous domain boundaries in between crystalline grains could be a suitable system for realizing the electron-crystal phonon glass concept and enable higher performance thermoelectric materials.

Twenty-Five-Fold Reduction in Measurement Uncertainty for a Molecular Line Intensity.

To accurately attribute sources and sinks of molecules like CO_{2}, remote sensing missions require line intensities (S) with relative uncertainties u_{r}(S)<0.1%. However, discrepancies in S of ≈1% are common when comparing different experiments, thus limiting their potential impact. Here we report a cavity ring-down spectroscopy multi-instrument comparison which revealed that the hardware used to digitize analog ring-down signals caused variability in spectral integrals which yield S. Our refined approach improved measurement accuracy 25-fold, resulting in u_{r}(S)=0.06%.

Compositional Dependence of Normal Spectral Emissivity of Molten Cu-Fe Alloy

Normal spectral emissivity of molten Cu-Fe alloy with different compositions was measured at the wavelength of 807 nm using an electromagnetic levitator superimposed with a static magnetic field, which is capable of producing accurate normal spectral emissivity data because the applied static magnetic field suppresses translational and surface oscillations of a levitated sample to consequently reduce measurement uncertainties. Cu-Fe alloy samples used in this study were Cu97Fe3, Cu93Fe7, Cu92Fe8, Cu90Fe10, Cu80Fe20, and Cu70Fe30. The strength of the static magnetic field and temperature ranged from 3.0 to 3.5 T and 1350 to 1750 K, respectively. The measured normal spectral emissivity indicated negligible temperature dependence in a wide temperature range. In contrast, the compositional dependence indicated a distinct tendency in which the emissivity increased markedly with the composition of Fe up to 10 at pct.

Measurement uncertainty in stream nutrient uptake: Detecting land-use impacts on tropical streams

Abstract Stream nutrient uptake is an important ecosystem service, because it supplies human needs such as water purification. Uncertainty in nutrient uptake measurement determines, in combination with effect magnitude, whether effects of land use, stream restoration or climate change can be detected by this method. However, measurement uncertainty for nutrient uptake metrics is rarely reported. Here, we compared whole-stream phosphate and nitrate uptake among three pristine and three agricultural tropical Cerrado streams. We quantified uncertainty in uptake metrics estimated by kinetic nutrient-addition experiments and evaluated their potential to detect land-use effects. Ambient phosphate and nitrate uptake lengths (SW) ranged from 11 to 106 m and from 29 to 357 m, respectively, in pristine streams and from 41 to 586 m and from 76 to 1372 m in agricultural streams. Moderate measurement uncertainty in SW allowed for the detection of land-use impacts with this metric. However, derived nutrient uptake metrics, such as ambient uptake rates and uptake velocities, as well as parameters of whole-stream saturation kinetics, were associated with high measurement uncertainties that prevented the detection of potential land-use effects. Sensitivity analyses suggested that avoiding high enrichment levels in kinetic addition experiments and increasing sampling effort for plateau nutrient and tracer concentration at the first and last sampling stations of investigated stream reaches are the most promising strategies to reduce measurement uncertainty. Analyzing nutrient uptake without considering measurement uncertainty might lead to poor interpretation in case studies and meta-analyses, such as incorrect evaluations of human impacts or comparisons among systems.

An in-house software program for quantitative image quality evaluation of linac cone-beam CT system

The study presents application of an in-house software program to calculate image quality parameters of kV cone-beam CT (CBCT) system in radiotherapy. The parameters include uniformity, noise, contrast-to-noise ratio, CT number linearity, spatial resolution and geometric distortion as recommended in AAPM TG142 and TG179 quality assurance (QA) programme for image quality performance of kV CBCT. The computer algorithm packaged in the software program is developed using MATLAB (MathWorks, Natick, MA). The algorithm was optimised for two CT image quality phantoms, Catphan 600 (The Phantom Laboratory, Salem, NY) and CIRS 062QA (CIRS, Norfolk, VA). The phantoms were scanned with XVI CBCT system (Elekta AB, Stockholm, Sweden) using an optimised CT imaging protocol. The algorithm measures the image quality metrices from the corresponding image quality test patterns in the reconstructed CT images. The algorithm provides image quality parameters from both phantoms quantitatively. The software program allows the results to be exported and recorded in MS Excel for monitoring the performance trend of the image quality parameters. The software reduces measurement uncertainties from qualitative human observation of the test patterns.

Simultaneous measurement uncertainty reduction and proppant bank height control of hydraulic fracturing

In hydraulic fracturing, higher fracturing fluid injection rates can trigger increased stress, thereby creating more microseismic events; particularly, simultaneously occurring multiple microseismic events can reduce measurement errors. This suggests a new state and output estimation scheme that utilizes the dependence between the fracturing fluid injection rate (i.e., manipulated input) and measurement errors. Motivated by this, we propose a novel control framework for measurement uncertainty reduction while achieving the original control task of proppant bank height control in hydraulic fracturing. Initially, using the simulation data from the high-fidelity model of hydraulic fracturing, a reduced-order model is constructed to design a Kalman filter. Then, a model-based feedback control system is proposed to regulate the uniformity of proppant bank height along the optimal fracture length and achieve accurate state and output estimation by manipulating the fracturing fluid pumping schedule that includes the fracturing fluid injection rate and proppant concentration at the wellbore.

Can the Sperm Class Analyser (SCA) CASA-Mot system for human sperm motility analysis reduce imprecision and operator subjectivity and improve semen analysis?

Semen analysis (SA) is considered mandatory for suspected male infertility although its clinical value has recently become questionable. Sperm motility is an essential parameter for SA, but is limited by high measurement uncertainty, which includes operator subjectivity. Computer-assisted sperm analysis (CASA) can reduce measurement uncertainty compared with manual SA. The objective of this study was to determine whether the Sperm Class Analyser (SCA) CASA-Mot system could reduce specific components of sperm motility measurement uncertainty compared with the World Health Organization (WHO) manual method in a single laboratory undertaking routine diagnostic SA. The study examined: (i) operator subjectivity; (ii) precision, (iii) accuracy against internal and external quality standards; and (iv) a pilot sub-study examining the potential to predict an IVF fertilisation rate. Compared with the manual WHO method of SA on 4000 semen samples, SCA reduces but does not completely eliminate operator subjectivity. Study SCA and CASA-Mot are useful tools for well-trained staff that allow rapid, high-number sperm motility categorization with less analytical variance than the manual equivalent. Our initial data suggest that SCA motility may have superior predictive potential compared with the WHO manual method for predicating IVF fertilization.

Effect of iterative sparse-view CT reconstruction with task-specific projection angles on dimensional measurements

X-ray computed tomography based on a small number of radiographic projections (sparse-view CT) is relevant for several application cases in industry, where reducing the measurement time plays a major role (e.g. for in-line CT). Because of low data quality of sparse-view CT scans due to insufficient sampling, new concepts are needed to reduce measurement uncertainties for dimensional metrology. Iterative image reconstruction techniques provide a promising opportunity for this purpose as they are in principle able to handle limited data or noise well and give the possibility to select specific projection angles (i.e. perspective views) for circular scan trajectories. In this paper, the influence of task-specific projection angles on dimensional measurements is discussed using algebraic and statistical iterative reconstruction of simulated and experimentally obtained sparse-view scans. It is shown that measurement deviations for specific dimensional measurands can be reduced by selecting projection angles which are expected to have a high contribution to a good imaging of relevant geometric features.

Development of an absorption-corrected method for 3D computed tomography of chemiluminescence

The computed tomography of chemiluminescence (CTC) technique is an advanced volumetric imaging technique that can resolve the internal structure of a flame and has found extensive applications in spatiotemporally resolved measurements of complex combustion phenomena. Despite its extensive application, certain improvements are still long-desired to further enhance its performance and reduce measurement uncertainties. Based on the Beer–Lambert law, this work introduces absorption correction into the CTC technique to account for the impact of signal attenuation in the tomographic algorithm. A reverse ray tracing method with distortion correction is proposed to calculate the absorption length within each cubic voxel and the corresponding absorption term, which has been ignored by previous works. To mathematically resolve the coupling process between chemiluminescence attenuation and accumulation during the signal trapping, an alternating-iteration reconstruction algorithm is developed. The results from a proof-of-concept experiment prove the good fidelity of the absorption-corrected CTC technique in solving the 3D distribution of chemiluminescence.

Validation of three-component wind lidar sensor for traceable highly resolved wind vector measurements

Abstract. Conventional monostatic wind lidar (light detection and ranging) systems are well-established wind speed remote sensing devices in the field of wind energy that provide reliable measurement results for flat terrain and homogeneous wind fields. These conventional wind lidar systems use a common transmitting and receiving unit and become unacceptably inaccurate as the wind fields become increasingly inhomogeneous due to their spatial and temporal averaging procedure (large measurement volume) that is inherent to the monostatic measurement principle. The new three-component fiber laser-based wind lidar sensor developed by the Physikalisch-Technische Bundesanstalt (PTB) uses one transmitting unit (fiber laser) and three receiving units to measure the velocity vector of single aerosols in a spatially highly resolved measurement volume (with diameter d and length l) in heights from 5 m (d=300 µm, l=2 mm) to 250 m (d=14 mm, l=4 m) with a resolution of about 0.1 m s−1. Detailed comparison measurements with a 135 m high wind met mast and a conventional lidar system have proven that the high spatial and temporal resolution of the new, so-called bistatic lidar leads to a reduced measurement uncertainty compared to conventional lidar systems. Furthermore, the comparison demonstrates that the deviation between the bistatic lidar and the wind met mast lies well within the measurement uncertainty of the cup anemometers of the wind met mast for both homogeneous and inhomogeneous wind fields. At PTB, the aim is to use the bistatic wind lidar as a traceable reference standard to calibrate other remote sensing devices, necessitating an in-depth validation of the bistatic lidar system and its measurement uncertainty. To this end, a new, specially designed wind tunnel with a laser Doppler anemometer (LDA) as flow velocity reference has been erected on a platform at a height of 8 m; this allows the new wind lidar to be positioned below the wind tunnel test section to be validated for wind vector measurements that are traceable to the SI units. A first validation measurement within the wind tunnel test section is presented, showing a deviation between the bistatic lidar system and the LDA clearly below 0.1 %.

Cooperative diagnostics for combinations of large-volume metrology systems

Recent studies show that the combined use of large-volume metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic theodolites, photogrammetric systems, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. The objective of this paper is to present some diagnostic tests for combinations of LVM systems that are equipped with distance and/or angular sensors. Two are the tests presented: a global test to detect the presence of potential anomalies during measurement and a local test to isolate any faulty sensor(s). This diagnostics is based on the cooperation of sensors of different nature, which merge their local measurement data, and it can be implemented in real-time, without interrupting or slowing down the measurement process. The description of the tests is supported by several experimental examples. [Submitted 28 March 2017; Accepted 27 December 2017]

Cooperative diagnostics for combinations of large volume metrology systems

Recent studies show that the combined use of large-volume metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic theodolites, photogrammetric systems, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. The objective of this paper is to present some diagnostic tests for combinations of LVM systems that are equipped with distance and/or angular sensors. Two are the tests presented: a global test to detect the presence of potential anomalies during measurement and a local test to isolate any faulty sensor(s). This diagnostics is based on the cooperation of sensors of different nature, which merge their local measurement data, and it can be implemented in real-time, without interrupting or slowing down the measurement process. The description of the tests is supported by several experimental examples. [Submitted 28 March 2017; Accepted 27 December 2017]

Advances in age-dating of individual uranium particles by large geometry secondary ion mass spectrometry.

We present the ability to conduct single micrometer-sized uranium particle age-dating measurements on particles that are younger, smaller, and less enriched in 235U content than previously reported. Specifically, we use large geometry secondary ion mass spectrometry (LG-SIMS) to precisely measure the 230Th/234U radiochronometer, combined with a systematic treatment of relevant parameters such as particle size, enrichment, and age, to achieve this development. We describe the necessary requirements for instrument background, interference rejection, abundance sensitivity, and other instrumental conditions that allow for this advance in single-particle uranium age-dating. We introduce the use of statistics developed by Feldman and Cousins to generate 95% confidence intervals in particle age, even when 230Th daughter ions are not detected. For particles where counts are limited and are of identical isotopic signatures, we provide an option for aggregating individual measurements of single particles to reduce measurement uncertainty, as if the measurement had been performed on one larger particle. The methodology is validated on a range of certified reference materials and 'real-world' samples, ranging in age from 15 to 60 years, and on individual particles ranging in equivalent size from 0.6 to 6.8 micrometers. Additionally, we provide model age calculations for particles ranging in size from 1.0 to 3.0 micrometers across enrichments ranging from natural uranium to highly-enriched uranium and on ages ranging from 0 to 60 years. Experimental results compare well with the predicted model ages, providing realistic guidance for expectations of single micrometer-sized uranium particle age-dating measurements. The age-dating capabilities described herein are directly relevant to the International Atomic Energy Agency (IAEA) and its mission to safeguard nuclear materials and monitor member state nuclear programs.

Essential considerations for accurate evaluation of photoneutron contamination in Radiotherapy

Nowadays, high-energy X-rays produced by medical linear accelerators (LINACs) are widely used in many Radiation Therapy (RT) centers. High-energy photons (> 8 MeV) produce undesired neutrons in the LINAC head which raise concerns about unwanted neutron dose to the patients and RT personnel. Regarding the significance of radiation protection in RT, it is important to evaluate photoneutron contamination inside the RT room. Unfortunately, neutron dosimeters used for this purpose have limitations that can under the best conditions cause to > 10% uncertainty. In addition to this uncertainty, the present Monte Carlo (MC) study introduces another uncertainty in measurements (nearly up to 20%) when neutron ambient dose equivalent (Hn*(10)) is measured at the patient table or inside the maze and the change in neutron energy is ignored. This type of uncertainty can even reach 35% if Hn*(10) is measured by dosimeters covered by a layer of 10B as converter. So, in these cases, neglecting the change in neutron energy can threaten the credibility of measured data and one should attend to this energy change in order to reduce measurement uncertainty to the possible minimum. This study also discusses the change in neutron spectra and Hn*(10) at the patient table caused by removing a typical RT room from MC simulations. Under such conditions, neutron mean energy (Ēn) overestimated by 0.2–0.4 MeV at the patient table. Neutron fluence (φn) at the isocenter (IC) was underestimated by 23–54% for different field sizes that caused Hn*(10) to be miscalculated up to 24%. This finding informs researchers that for accurate evaluation of Hn*(10) at the patient table, simulating the RT room is an effective parameter in MC studies.

Reducing measurement uncertainties of high-pressure gas flow calibrations by using reference values based on multiple independent traceability chains

Abstract This paper describes the recently updated realization of the harmonized cubic metre for natural gas. It is a procedure based on an intercomparison, that combines the mutually independent traceability chains of four primary laboratories in the field of high-pressure gas flow measurement. The reference value, also called harmonized cubic metre, is the weighted average of at least two laboratories with weighing factors that are inversely proportional to the squared uncertainties of the calibration results. This results in lower uncertainties for the laboratories as long as the stochastic contributions (Type A) to the overall measurement uncertainties are significantly smaller than the uncertainties arising from the traceability chain (Type B). This condition is fulfilled in practice as traceability uncertainties are at least a factor ten greater than the other uncertainty sources. When evaluating the data of intercomparisons, curve fitting is used for the representation of the calibration data. A polynomial equation of maximum four degrees, expressed in the logarithm of the flow Reynolds number, proves to be the optimum choice for fitting the calibration curve of the turbine gasmeters.

Model and Simulation Studies of the Method for Optimization of Dynamic Properties of Tachometric Anemometers.

Mechanical tachometric anemometers, based on the phenomenon of the exchange of momentum between the flow and rotating measuring element, represent an important class of instruments used in flow metrology. In particular, they are used in meteorological and ventilation measurements. Mechanical anemometers with rotating measuring element are, however, known for their drawback related to their poor dynamic properties resulting from relatively large dimensions and mechanical inertia of the measuring element. In these instruments, the phenomenon of overestimating the measured average velocity caused by the inertia of the rotor takes place. Optimization of the dynamics of the measurement process, as well as the estimation and minimization of the measurement uncertainty, can be performed based on mathematical model of anemometer. In this study, a new, original concept of optimization of dynamic properties of tachometric anemometers is proposed, and the results of model and simulation studies are presented. The new concept of measuring instrument is based on the use of feedback and active control of the rotor. The new method was tested using model research, where two types of flow velocity excitations were applied: sinusoidal and rectangular. The tests carried out showed that the developed method allows for minimization of the dynamic uncertainty of the measurement and minimizes the phenomenon of average flow velocity overestimation occurring in time-varying flows. It has been shown that the use of optimization system allows for approximately tenfold reduction of the error of average velocity measurement in the case of pulsating flows. In addition, the optimization systems allow for anemometer’s transmission bandwidth to be extended about a hundred times. This creates new application possibilities for these instruments and allows for a large reduction of measurement uncertainty.

Application for optical thermometers calibration based on virtual instruments

In this paper we present a new developed application for calibration of optical thermometers which is implemented in the Serbian Metrology Institute. The method for calibration of optical thermometer–pyrometer is based on measuring blackbody temperature via thermocouple standards and measuring voltage on pyrometer in temperature range from 550 to 1650 °C. The objective is to precisely determinate calibration curve of pyrometer—transfer function. The metrology traceability was realized through thermocouples standard which has traceability to the international standard. A developed application has a role to control and supervise calibration process. Based on virtual instruments (VI), application offers monitoring measurement parameters in real time on three charts. The main advantage of the developed VI application is reduction of measurement uncertainty of type A by increased accuracy with multi—temperature measurement up to 3 thermocouples on temperature equilibrium in the measurement system and automatic data processing by converting voltage to temperature, calculating the mean value and standard deviation of the mean value. Advantage is also reflected in permanent data logging while application is running and low cost and user friendly interface One of the goals is to improve quality of metrological services through this application and support the establishment of a traceability chain to SI.

Sensor system optimization to meet reliability targets

In this work, we show the influence of sensor system measurement uncertainties to sensor system reliability and ways to meet reliability targets. A general model to handle measurement uncertainties is defined and the according influence to reliability is presented, which is defined as probability of meeting specification requirements. Initial step is to optimize sensor systems concerning lowest influences of sensor system parameter fluctuations to the measurement uncertainty using statistical optimization methodologies. In case the influence of unknown nuisance parameters cannot be sufficiently suppressed, such parameters may be additionally measured in order to further reduce measurement uncertainties. The remaining uncertainties are again addressed using statistical optimization methodologies. Finally, measurement uncertainty also affects the reliability of such a system. For sensor systems in safety critical applications it may thus be required to include measures such as redundancy. This is also included in the investigations. Further examples for explained optimization methodologies of measurement uncertainty reduction are presented.