Robust Measurement Method Research Articles

Efficient and robust 3D reconstruction: Absolute phase extraction algorithm based on three gray images

The structured light three-dimensional (3D) measurement technology based on optical metrics has gained increasing applications, and there is a growing demand for capturing transient trajectory changes in dynamic scenes. Conventional temporal phase unwrapping (TPU) approaches often require multi-frequency fringe patterns for application. However, the inevitable conflict arises between the number of projected fringe patterns and the measurement speed. This paper proposes a highly accurate and robust 3D measurement method using only 3-step phase-shifting fringe patterns. To precisely reconstruct the 3D shape using the fewest fringe patterns, it is essential to extract as much information as possible from the available patterns. Therefore, we calculate the wrapped phase distribution using 3-step phase-shifting fringe patterns to ensure accuracy. Simultaneously, the trapezoidal phase-shifting method is employed to calculate the intensity ratio distribution. Through the proposed region-based indexing method, the intensity ratio map is transformed into an unwrapped phase map. Additionally, a novel self-correction method is introduced to correct the non-linear errors in the unwrapped phase map, which is then utilized for the calculation of the fringe order required for phase unwrapping. This high-speed measurement method utilizes only 3-step phase-shifting fringe patterns while retaining the advantages of TPU, meeting the requirements of high-speed and full-field measurements. Experimental results on both static and dynamic scenes validate the effectiveness and versatility of the proposed method, demonstrating its flexibility and simplicity in application. In our 3D measurement system, the method achieves 3D reconstruction of the dynamic object's trajectory at a measurement speed of 107 frames per second.

Sensor-Based Measurement Method to Support the Assessment of Robot-Assisted Radiofrequency Ablation.

Digital surgery technologies, such as interventional robotics and sensor systems, not only improve patient care but also aid in the development and optimization of traditional invasive treatments and methods. Atrial Fibrillation (AF) is the most common cardiac arrhythmia with critical clinical relevance today. Delayed intervention can lead to heart failure, stroke, or sudden cardiac death. Although many advances have been made in the field of radiofrequency (RF) catheter ablation (CA), it can be further developed by incorporating sensor technology to improve its efficacy and safety. Automation can be utilized to shorten the duration of RF ablation, provided that the interactions between the tissue and the RF tools are well understood and adequately modeled. Further research is needed to develop the optimal catheter design. This paper describes the systematic methodology developed to support robot-assisted RF CA characterization measurements. The article describes the custom instruments developed for the experiments, particularly the contact force limiter, the measurement procedure, and the evaluation of the results, as enablers for new results. The aim was to establish an objective, repeatable, robust measurement method and adjacent procedure.

Appropriate methods to analyse Power Conversion Harmonics

Nowadays, non-linear loads represent the majority of the residential electrical consumers. The limits on emission and immunity are imposed by IEC- standards, however there is a lack in the domain 2 – 150 kHz. Where power quality standards focus on the current, EMC standards use voltage limits. An appropriate method for measuring high frequency grid disturbances is explored. Measurement techniques described by the existing standards for power quality and EMC are investigated. The aim of this work is to find a robust measurement method for the considered frequency range 2 - 150 kHz. Experimental results are presented in order to validate the analyzed methods.

How Do Isothermal Calorimeters Age? Repeatability and Reproducibility Across Calorimeter Generations

AbstractReliable experimental data is essential for reproducible science. As our lab has access to five instruments of the isothermal (heat conduction) type of different age and product generations, we became interested in the quality of experimental data obtained from the different instruments. Each instrument consists of 8 individual calorimeters. An intralaboratory study of the first 72 hours of cement hydration was conducted with all five instruments. The objective was to determine the differences between the available instruments with respect to repeatability (precision of the 8 calorimeters within one instrument) and reproducibility (precision between the different instruments). The experimental program comprises 120 calorimetry runs in total (5 instruments each with 8 calorimeters, triple measurement performed). Results show that the oldest instrument version with its 8 calorimeters has a stronger higher standard deviation of the heat released after 72 hours compared to the latest state‐of‐the‐art instrument model (246.7 ± 2.7 vs. 232.3 ± 0.5 Jg–1). This is attributed to the technical design differences of the instruments and continuous use over time. In terms of reproducibility, an increasing standard deviation for the heat released from 1 day to 3 days (136.2 ± 2.6 and 236.4 ± 5.9 J g–1) is observed. From our point of view, this test study indicates that isothermal heat conduction calorimetry is a robust and precise measurement method to determine the heat of cement hydration for 72 hours.

Deep learning-based workflow for hip joint morphometric parameter measurement from CT images

Objective. Precise hip joint morphometry measurement from CT images is crucial for successful preoperative arthroplasty planning and biomechanical simulations. Although deep learning approaches have been applied to clinical bone surgery planning, there is still a lack of relevant research on quantifying hip joint morphometric parameters from CT images. Approach. This paper proposes a deep learning workflow for CT-based hip morphometry measurement. For the first step, a coarse-to-fine deep learning model is designed for accurate reconstruction of the hip geometry (3D bone models and key landmark points). Based on the geometric models, a robust measurement method is developed to calculate a full set of morphometric parameters, including the acetabular anteversion and inclination, the femoral neck shaft angle and the inclination, etc. Our methods were validated on two datasets with different imaging protocol parameters and further compared with the conventional 2D x-ray-based measurement method. Main results. The proposed method yields high bone segmentation accuracies (Dice coefficients of 98.18% and 97.85%, respectively) and low landmark prediction errors (1.55 mm and 1.65 mm) on both datasets. The automated measurements agree well with the radiologists’ manual measurements (Pearson correlation coefficients between 0.47 and 0.99 and intraclass correlation coefficients between 0.46 and 0.98). This method provides more accurate measurements than the conventional 2D x-ray-based measurement method, reducing the error of acetabular cup size from over 2 mm to less than 1 mm. Moreover, our morphometry measurement method is robust against the error of the previous bone segmentation step. As we tested different deep learning methods for the prerequisite bone segmentation, our method produced consistent final measurement results, with only a 0.37 mm maximum inter-method difference in the cup size. Significance. This study proposes a deep learning approach with improved robustness and accuracy for pelvis arthroplasty planning.

A wireless passive vibration sensing method for cryogenic applications

In this Letter, we developed a wireless passive vibration sensing method functional at cryogenic temperatures (−196 °C). Traditional vibration sensors are either inconvenient or complicated in cryogenic environments due to inaccessible working positions and weak low-temperature tolerances. We propose a vibration measurement method that transfers a mechanical vibration to a wirelessly obtained return loss. Passive wireless monitoring is performed using a backscattering tag antenna integrated with a tunnel magnetoresistor. We fabricate and evaluate our vibration sensor at room temperature (24 °C) and cryogenic temperature (−196 °C) to verify the proposed design. Experimental analysis identified different vibration amplitudes with sensitivities of 4.61 dB/mm at 24 °C and 1.13 dB/mm at −196 °C. Further analysis shows that the vibrational frequency can be extrapolated. Our sensor provides a low-cost, robust, wireless, and passive vibration measurement method that is desirable in cryogenic applications.

Fast and robust vision-based cable force monitoring method free from environmental disturbances

For long-term vision-based cable force monitoring, it is essential to fully consider different types of challenges, such as complex backgrounds in the field of view, illumination changes, occlusion, camera motion, and real-time realization. To address these challenges, this study proposes a vision-based, robust real-time cable force measurement method. In terms of innovation, three unique aspects were incorporated. First, to solve the difficulty of cable edge recognition caused by complex backgrounds, a linear feature detection operator called edge drawing lines was optimized by setting screening strategy based on the slope and line segments length. Second, the average of bilateral edge displacements was used as the final value to offset the displacement deviation caused by the illumination change. Third, to overcome obstacles to identifying the cable frequency caused by the camera motion, an interference frequency elimination method without reference targets or additional sensors was proposed. Furthermore, the integrated cable force calculation method was developed into a real-time measurement software. Finally, the proposed method was applied to a long-span cable-stayed bridge, where the camera was vibrated by the bridge deck or the wind significantly. The reliability of the proposed method was proved by comparing the results obtained with those achieved by accelerometers.

Chromatic Dispersion Measurements of Single-Mode Fibers, Polarization-Maintaining Fibers, and Few-Mode Fibers Using a Frequency Domain Method

Chromatic dispersion is an important fiber attribute affecting transmission performance over optical fibers. Various chromatic dispersion measurement methods have been developed primarily for single-mode fibers. In the literature, measurement techniques were also developed to characterize few-mode fibers and multi-mode fibers. These methods are often subject to some limitations. In this paper, a simple and robust measurement method for chromatic dispersion measurement of single-mode fibers, polarization--maintaining fibers, and few-mode fibers is presented using a frequency domain instrument and a vector network analyzer. The method is applied to all three types of fibers through one measurement methodology uniformly. Using a vector network analyzer, the measurement instrument obtains the complex transfer function of fiber transmission. The inverse Fourier transform of the measured complex transfer function is used to determine the group delays for each mode of the fiber. Although the sampling is highly under-sampled for the whole fiber link, through proper treatment of the data, we can de-alias the signals and obtain accurate values of the group delays of each mode. By measuring the group delays over different wavelengths, the data can yield the chromatic dispersion of each mode over the wavelength window.

A Novel Measurement Method for Determining Geometric Errors of Rotary Tables by Using LaserTRACER and Reflectors

In this paper, a novel and robust measurement method is proposed for obtaining the geometric errors of rotary tables by using LaserTRACER and the reflectors mounted on the reflector standard fixture. For the machining accuracy, the six-degree-of-freedom (6-DOF) geometric errors of the rotary axes interactively influence the manufacturing quality of the precise workpieces. Therefore, this paper mainly aims to develop a measurement method for identifying the 6-DOF geometric errors of rotary tables without using the external linear axis. Furthermore, the set-up errors of the reflector standard fixture are also considered and identified to reduce the influence of the 6-DOF geometric error measurements. For each rotary table geometric error measurement, the positions of the LaserTRACER as well as the relative distance between the reflectors and the LaserTRACER are measured and obtained for determining the 6-DOF geometric errors of the rotary tables. In addition, the homogeneous transformation matrix (HTM), multilateration method, and least squares method are used for building the mathematical measurement algorithm. Moreover, the experimental verifications are implemented to demonstrate the accuracy of the proposed measurement method. Conclusively, the experiment and simulation verification results clearly delineate that the maximal relative differences in the linear errors and the angular errors of the 6-DOF geometric errors are, at most, 3.25% and 2.30%, respectively.

Associations of Personality, Physical and Mental Health with Voice Range Profiles

There is evidence in the literature that voice characteristics are linked to mental and physical health. The aim of this explorative study was to determine associations between voice parameters measured by a voice range profile (VRP) and personality, mental and physical health. Cross-sectional population-based study. As part of the LIFE-Adult-Study, 2639 individuals aged 18-80 years, randomly sampled from the general population, completed both speaking and singing voice tasks and answered questionnaires on depression, anxiety, life satisfaction, personality and quality of life. The voice parameters used were fundamental frequency, sound pressure level, their ranges and maximum phonation time. The associations were examined with the help of correlation and regression analyses. Wider ranges between the lowest and highest frequency, between the lowest and highest sound pressure level and longer maximum phonation time were significantly correlated with extraversion and quality of life in both sexes, as well as openness and agreeableness in women. Smaller ranges and shorter maximum phonation time were significantly correlated with depression. Neuroticism in men was inversely correlated with the maximum phonation time. In the speaking VRP, the associations for sound pressure level were more pronounced than for the fundamental frequency. The same was true in reverse for the singing VRP. Few associations were found for anxiety, life satisfaction and conscientiousness. Weak associations between voice parameters derived from the VRP and mental and physical health, as well as personality were seen in this exploratory study. The results indicate that the VRP measurements in a clinical context are not significantly affected by these parameters and thus are a robust measurement method for voice parameters.

Robust Pulse Rate Measurements from Facial Videos in Diverse Environments

Pulse wave and pulse rate are important indicators of cardiovascular health. Technologies that can check the pulse by contacting the skin with optical sensors built into smart devices have been developed. However, this may cause inconvenience, such as foreign body sensation. Accordingly, studies have been conducted on non-contact pulse rate measurements using facial videos focused on the indoors. Moreover, since the majority of studies are conducted indoors, the error in the pulse rate measurement in outdoor environments, such as an outdoor bench, car and drone, is high. In this paper, to deal with this issue, we focus on developing a robust pulse measurement method based on facial videos taken in diverse environments. The proposed method stably detects faces by removing high-frequency components of face coordinate signals derived from fine body tremors and illumination conditions. It optimizes for extracting skin color changes by reducing illumination-caused noise using the Cg color difference component. The robust pulse wave is extracted from the Cg signal using FFT-iFFT with zero-padding. It can eliminate signal-filtering distortion effectively. We demonstrate that the proposed method relieves pulse rate measurement problems, producing 3.36, 5.81, and 6.09 bpm RMSE for an outdoor bench, driving car, and flying drone, respectively.

Quantifying fluorescent nanoparticle uptake in mammalian cells using a plate reader

In keeping with the rapid expansion of nanoparticle applications, various tools are required to investigate how nanoparticles interact with biological entities. Many assays have been developed to measure the cellular uptake of nanoparticles, but so far most of the methods are laborious and often non-quantitative. Here we developed an easily accessible and robust quantitative measurement method of the level of cellular uptake of fluorescently labeled nanoparticles using a plate reader. In the experimental design, potential issues that could lead to measurement variation were identified and addressed. For example, the variation in fluorescence intensity of samples due to differences in cell number was normalized to optical density, which is a physical value corresponding to the cell number. Number of washings and sample handling temperature were optimized to minimize the interference by residual nanoparticles and possible efflux of nanoparticles from cells, respectively. The developed assay was demonstrated with the lymphocyte cell line Jurkat to measure the cellular uptake of fluorescently labeled 50 nm polystyrene beads, and its applicability was further confirmed with the lung carcinoma cell line A549 and another lymphocyte cell line RPMI8226.

An occupancy grid ruler based highly robust displacement measurement method and its application in brake wear assessment

The displacement of a multi-plate brake actuator provides insights into degradation. However, the displacement signal in a low sampling frequency is difficult to be assessed due to noise and outliers. This paper proposes an occupancy grid ruler (OGR) based displacement measurement method that sequentially implements displacement signal denoising and measurement value outlier removal and smoothing. The displacement and duration measurement values are extracted from the signal denoised by generalized Moreau envelope total variation. Next, the measurement values are assessed by the OGR, which has an updating function based on a binary Bayesian filter and inverse sensor model, and a time window with a specified observation length. Finally, the mass center of the grids with occupancy belief over the threshold is defined as the measurement result. A numerical simulation and experiments verified the proposed method is suitable for a quasi-static measurement with a given accuracy requirement, featuring dynamic performance and robustness.

Machine-learning-based automatic small-angle measurement between planar surfaces in interferometer images: A 2D multilayer Laue lenses case

We report a new machine-learning-based approach to automatically measure the small angle between multiple planar surfaces characterized by white light interferometers. By applying an unsupervised clustering algorithm, DBSCAN (Density-Based Spatial Clustering of Applications with Noise), the multiple surfaces in an interferometer image are automatically identified as distinct surfaces. The angles between every two surfaces are then calculated through the surface fitting. This method can be applied to multiple surfaces regardless of their shapes and locations and significantly simplifies the angle measurement procedure. Using the developed method, we have demonstrated a quick and precise angle measurement for the alignment of 2D Multilayer Laue Lenses (MLLs) for the development of high-resolution x-ray microscopy. This automatic, accurate, and robust small-angle measurement method is compatible with widely used white light interferometers and can be further applied to other metrology applications of interferometer results.

Photothermal determination of thermal properties of concrete - a method evaluation

The evaluation of thermal properties is probably an underrated tool for the onsite health monitoring of concrete structures. While the influence of water content on the thermal behaviour is obviously, a specific correlation with microcrack-density or carbonization state can be suspected. For further investigations, a robust measurement method is needed to characterize the thermal behaviour of concrete – under lab conditions as well as onsite. The photothermal approach offers a possibility to realize a real onsite measurement. Here, the surface to be investigated is heated shortly by a laser pulse and the cooling down is contactless recorded by an infrared camera or pyrometer. The obtained temperature transient allows the calculation of the thermal effusivity of the heated material. Especially this parameter - the thermal effusivity - is very sensitive to characteristic material modifications because it is the simple product of density, thermal conductivity and specific heat capacity. This contribution presents the application of the photothermal approach on three different concrete types. The obtained results were compared with those of a commercial device for laboratory investigations. Both agreed well within the estimated uncertainty ranges and therefore demonstrate the applicability of the photothermal method for this kind of investigations. First results of a concrete sample with different water contents support the potential of this method for the characterization of concrete in general.

Precise wide-band electrical impedance spectroscopy measurement via an ADC operated below the Nyquist sampling rate

Usually, an analog-to-digital converter (ADC) used for electrical impedance measurement is required to operate above the Nyquist sampling rate of excitation signals to ensure the accurate discretization. This paper proposed a robust impedance measurement method in wide-band spectrum via using compressive sensing to eliminate this requirement. The excitation signals were compressed by a random-modulator and a low-pass filter with bandwidth below the excitation frequency, then impedance is recovered by the reconstruction algorithm with the filter parameter identified on-line and the data recorded by the ADC operated just above the Nyquist rate of the filter bandwidth. In the simulations and experiments, a sparse wide-band impedance spectroscopy from 0.01 to 1.05 MHz was sampled by an ADC operated with fixed sampling rate 400 kHz, and the results is comparable to the impedance analyzer. Impedance imaging experiment results demonstrated that the impedance measurement could be precisely achieved for both single- and multi- frequencies.

Developing a robust, fast and reliable measurement method for the analysis of methylarginine derivatives and related metabolites

BackgroundNitric oxide (NO) plays an important role in endothelial homeostasis. Asymmetric dimethyl arginine (ADMA), L-N monomethyl arginine (L-NMMA) and symmetric dimethyl arginine (SDMA), which are derivatives of methylarginine, directly or indirectly reduce NO production. Therefore, these metabolites are an important risk factor for various diseases, including cardiovascular diseases. Numerous methods have been developed for the measurement of methylarginine derivatives, but various difficulties have been encountered. This study aimed to develop a reliable, fast and cost-effective method for the analysis and measurement of methylarginine derivatives (ADMA, SDMA, L-NMMA) and related metabolites (arginine, citrulline, homoarginine, ornithine), and to validate this method according to Clinical and Laboratory Standards Institute (CLSI) protocols. MethodsFor the analysis of ADMA, SDMA, L-NMMA, arginine, homoarginine, citrulline, ornithine, 200 µl of serum were precipitated with methanol, and subsequently derivatized with a butanol solution containing 5% acetyl chloride. Butyl derivatives were separated using a C18 reverse phase column with a 5 min run time. Detection of analytes was achieved by utilising the specific fragmentation patterns identified through tandem mass spectrometry. ResultsThe method was linear for ADMA, SDMA, L-NMMA, ornithine, arginine, homoarginine and citrulline in the ranges of 0.023–6.0, 0.021–5.5, 0.019–5.0, 0.015–250, 0.015–250, 0.019–5 and 0.015–250 µM, respectively. The inter-assay CV% values for all analytes was less than 9.8%. ConclusionsData obtained from method validation studies shows that the developed method is highly sensitive, precise and accurate. Short analysis time, cost-effectiveness, and multiplexed analysis of these metabolites, with the same pretreatment steps, are the main advantages of the method.

Development of a rigid suspended micro-island device and robust measurement method for thermal transport measurements.

One of the most versatile techniques to study thermal transport in low dimensional materials utilizes a suspended micro-island device integrated with resistance thermometers. Advancements in experimental techniques with suspended micro-island devices resulted in increasing capabilities such as enhancing temperature resolution and expanding a measurable range of sample thermal conductance. In this work, we further improve the suspended micro-island based technique. Specifically, we present a rigid structure of the suspended micro-island device and robust measurement method for sequential heating. The rigid structure enabled by T-shaped beams prevents the displacement of suspended micro-islands, thus increasing the success rates of sample transfer especially for samples with a large cross-sectional area and short length. Besides, thermal isolation of micro-islands is maintained at a similar level through the T-shaped beams compared to conventional flat beams. Next, we introduce an advanced experimental approach that enables sequential heating to measure sample thermal conductance. Sequential heating in micro-islands can be used either to measure accurate sample thermal conductance even under unexpected asymmetric supporting beam configuration or to study thermal transport dependence on heat flow directions. Using a switch matrix for sequential heating eliminates the need for experimental reconfigurations during the experiment. We demonstrate the experimental method with thermal conductivity measurements of the Si nanowire under both the ideal symmetric beam configuration and replicated asymmetric beam configuration scenarios. The results show that the developed experimental method effectively eliminates potential experimental errors that can arise from the asymmetry in beam configurations.

A camera-based ballistocardiogram heart rate measurement method.

Recent studies have shown that head movements associated with cardiac activity contain a heart rate (HR) signal. In most previous studies, subjects were required to remain stationary in a specific environment during HR measurements, and measurement accuracy depended on the choice of target in the scene, i.e., the specified region of the face. In this paper, we proposed a robust HR measurement method based on ballistocardiogram (BCG) technology. This method requires only a camera and does not require that users establish a complex measurement environment. In addition, a bidirectional optical flow algorithm is designed to select and track valid feature points in the video captured by using the camera. Experiments with 11 subjects show that the HR values measured using the proposed method differ slightly from the reference values, and the average error is only 1.09%. Overall, this method can improve the accuracy of BCG without limitations related to skin tone, illumination, the state of the subject, or the test location.

Robust Azimuth Measurement Method Based on Polarimetric Imaging for Bionic Polarization Navigation

Azimuth information obtained from a polarization pattern in the sky provides many organisms like insects and birds, with the ability to navigate. The aim of this article is to investigate the azimuth method to measure the solar meridian from the pattern of the Angle of E (AOE) vector when it is partially obscured and disturbed. The model of the sky polarization pattern projected onto an imaging sensor is analyzed. The projection characteristic of the solar meridian is proved to be a straight line passing through the principal point, which is composed of pixels with the E-vector orientation 90° in the AOE map. Based on the mutation feature of the gradient amplitude of E-vector orientation 90° and occlusion without mutation on the solar meridian, a robust gradient amplitude and binary integration (GABI) azimuth method for a polarization imaging sensor is proposed. Then, the feasibility and robustness of this method are verified via numerical simulation and outdoor experiments, and the results show that when branches and buildings shield more than 80% of the AOE map, the azimuth measurement method remains effective. The accuracy of azimuth is 0.417° ( $\sigma$ ). This indicates that the azimuth can be effectively measured, even in the presence of occlusion and interference.