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  • 1. Becher, Tobias H
    et al.
    Miedema, Martijn
    Kallio, Merja
    Papadouri, Thalia
    Karaoli, Christina
    Sophocleous, Louiza
    Rahtu, Marika
    van Leuteren, Ruud W
    Waldmann, Andreas D
    Strodthoff, Claas
    Yerworth, Rebecca
    Dupré, Antoine
    Benissa, Mohamed-Rida
    Nordebo, Sven
    Khodadad, Davood
    Department of Physics and Electrical Engineering, Linnaeus University, Vaxjö, Sweden.
    Bayford, Richard
    Vliegenthart, Roseanne
    Rimensberger, Peter C
    van Kaam, Anton H
    Frerichs, Inéz
    Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure2022Ingår i: Annals of the American Thoracic Society, ISSN 2329-6933, E-ISSN 2325-6621, Vol. 19, nr 6, s. 991-999Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet. Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure. Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of EIT measurements was 53 ± 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks. Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort. Clinical trial registered with www.clinicaltrials.gov (NCT02962505).

  • 2.
    Bergström, Per
    et al.
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Khodadad, Davood
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Hällstig, Emil
    Optronic Partner dp AB, Box 733, SE-931 27 Skellefteå, Sweden.
    Sjödahl, Mikael
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization2014Ingår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 53, nr 1, s. 123-31Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper discusses the possibility of evaluating the shape of a free-form object in comparison with its shape prescribed by a CAD model. Measurements are made based on a single-shot recording using dual-wavelength holography with a synthetic wavelength of 1.4 mm. Each hologram is numerically propagated to different focus planes and correlated. The result is a vector field of speckle displacements that is linearly dependent on the local distance between the measured surface and the focus plane. From these speckle displacements, a gradient field of the measured surface is extracted through a proportional relationship. The gradient field obtained from the measurement is then aligned to the shape of the CAD model using the iterative closest point (ICP) algorithm and regularization. Deviations between the measured shape and the CAD model are found from the phase difference field, giving a high precision shape evaluation. The phase differences and the CAD model are also used to find a representation of the measured shape. The standard deviation of the measured shape relative the CAD model varies between 7 and 19 μm, depending on the slope.

  • 3.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Advancing road safety assessment with digital holography: a study on skid resistance of asphalt pavements2023Ingår i: Proceedings of SPIE - The International Society for Optical Engineering / [ed] Thilo Erbertseder; Nektarios Chrysoulakis; Ying Zhang, SPIE - The International Society for Optics and Photonics, 2023, artikel-id 1273507Konferensbidrag (Refereegranskat)
    Abstract [en]

    Enhancing road safety through improved skid resistance is a critical endeavor in preventing accidents and promoting secure driving conditions. This study delves into the investigation of skid resistance in asphalt pavements using digital holography, focusing on macro and microtexture attributes. By employing off-axis digital holography, the paper presents a novel method to accurately measure surface profiles and assess friction properties. The experimental setup leverages single-shot dual-wavelength holography, providing precise 3D topographic information. The study demonstrates how the obtained phase information aids in deriving surface profiles and subsequently determining friction coefficients. The approach overcomes limitations of conventional methods, offering micron-level accuracy for surface roughness measurements. Through experimental results, the versatility of adjusting measurement accuracy and range based on requirements is showcased. The paper concludes by highlighting the interplay between surface features and friction characteristics, paving the way for improved road safety assessment.

  • 4.
    Khodadad, Davood
    Department of Mechanical Engineering, Örebro University, Örebro, Sweden; Experimental Mechanics, Lulea University of Technology, Luleå, Sweden.
    Combined Reduced Phase Dual-Directional Illumination Digital Holography and Speckle Displacements for Shape Measurement2019Ingår i: International Journal of Optics, ISSN 1687-9384, E-ISSN 1687-9392, Vol. 2019, artikel-id 4906109Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a digital holographic method to increase height range measurement with a reduced phase ambiguity using a dual-directional illumination. Small changes in the angle of incident illumination introduce phase differences between the recorded complex fields. We decrease relative phase difference between the recorded complex fields 279 and 139 times by changing the angle of incident 0.5° and 1°, respectively. A two cent Euro coin edge groove is used to measure the shape. The groove depth is measured as ≈300  . Further, numerical refocusing and analysis of speckle displacements in two different planes are used to measure the depth without a use of phase unwrapping process.

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  • 5.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Creating a supportive and effective learning environment for engineering students: Pedagogical strategies, engagement, and enhanced outcomes2023Ingår i: International Journal of Engineering Pedagogy, ISSN 2192-4880, Vol. 13, nr 8, s. 33-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Engineering education requires a strong emphasis on problem-solving, critical thinking, and practical application of knowledge. To achieve the highest quality of teaching, educators must create a trusting environment that allows students to feel comfortable asking questions and performing to the best of their abilities. This paper outlines the teaching philosophy and prac-tices of an engineering lecturer who has adapted his pedagogical approach across several universities in Sweden and abroad. The author emphasizes the importance of being flexible and responsive to student needs, offering early and constructive feedback, and providing students a safe and supportive learning environment with opportunities to develop program-ming skills. The paper also includes comments from students that reflect the author’s effec-tiveness as an educator in creating a supportive and challenging learning environment for engineering students.

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  • 6.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Digital holography for temperature investigations in space and transparent media2023Ingår i: Proceedings of SPIE - The International Society for Optical Engineering, SPIE , 2023Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper presents a method for investigating temperature fields in space and transparent media using off-axis digital holographic interferometry. This interferometric technique is particularly well-suited for measuring dynamically changing temperature fields due to its capability to automatically evaluate temperature from a single interferogram. The experimental validation of this technique involved measuring temperature variations within a burning candle's flame. To establish a reference point, an initial hologram was captured without a burning candle, followed by subsequent holograms during the burning process. This allowed the observation of changing refractive index gradient states in the surrounding air. The reconstruction of the complex amplitude facilitated the calculation of the distribution of phase changes. By establishing a relationship between phase changes, thermal coefficients of the air's refractive index, and temperature fluctuations, temperature measurements were achieved at these distinct states. The accuracy of the measurement was estimated to be less than 1 °C in our experimental setup, showing the high precision achievable with this technique. In summary, the paper offers analysis of digital holographic interferometry as a tool for temperature measurements in transparent media. Its potential applications extend to combustion studies, space exploration, atmospheric research, and various other scientific disciplines.

  • 7.
    Khodadad, Davood
    Experimental Mechanics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Phase-derivative-based estimation of a digital reference wave from a single off-axis digital hologram2016Ingår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 55, nr 7, s. 1663-1669Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a method to obtain an estimated digital reference wave from a single off-axis digital hologram that matches the actual experimental reference wave as closely as possible. The proposed method is independent of a reference flat plate and speckles. The digital reference wave parameters are estimated directly from the recorded phase information. The parameters include both the off-axis tilt angle and the curvature of the reference wave. Phase derivatives are used to extract the digital reference wave parameters without the need for a phase unwrapping process. Thus, problems associated with phase wrapping are avoided. Experimental results for the proposed method are provided. The simulated effect of the digital reference wave parameters on the reconstructed image phase distribution is shown. The pseudo phase gradient originating from incorrect estimation of the digital reference wave parameters and its effect on object reconstruction are discussed.

  • 8.
    Khodadad, Davood
    et al.
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Bergström, Per
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, SE-971 87 Luleå, Sweden.
    Hällstig, Emil
    Sjödahl, Mikael
    Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements2015Ingår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 54, nr 16, s. 5003-5010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.

  • 9.
    Khodadad, Davood
    et al.
    Luleå University of Technology, Luleå, Sweden.
    Hällstig, Emil
    Sjödahl, Mikael
    Shape reconstruction using dual wavelength digital holography and speckle movements2013Ingår i: Optical measurement systems for industrial inspection VIII / [ed] Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, SPIE - International Society for Optical Engineering, 2013, artikel-id 87880IKonferensbidrag (Refereegranskat)
    Abstract [en]

    A new technique to measure depth based on dual wavelength digital holography and image correlation of speckle movements is demonstrated. By numerical refocusing of the complex optical field to different focus planes and by measuring the speckle movements caused by a wavelength shift both the object surface position and its local slope can be determined. It is shown how the speckle movement varies linearly with the surface slope, the wavelength shift and the distance of the numerical propagation. This gives a possibility to measure the slope with approximately the same precision as from the interferometric phase maps. In addition, when the object surface is in focus there is no speckle movement so by estimating in what plane the speckle movement is zero the absolute surface position can be measured.

  • 10.
    Khodadad, Davood
    et al.
    Department of Physics and Electrical Engineering, Linnaeus University, Växjö, Sweden.
    Nordebo, S.
    Müller, B.
    Waldmann, A.
    Yerworth, R.
    Becher, T.
    Frerichs, I.
    Sophocleous, L.
    van Kaam, A.
    Miedema, M.
    Seifnaraghi, N.
    Bayford, R.
    Optimized breath detection algorithm in electrical impedance tomography2018Ingår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 39, nr 9, artikel-id 094001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    OBJECTIVE: This paper defines a method for optimizing the breath delineation algorithms used in electrical impedance tomography (EIT). In lung EIT the identification of the breath phases is central for generating tidal impedance variation images, subsequent data analysis and clinical evaluation. The optimisation of these algorithms is particularly important in neonatal care since the existing breath detectors developed for adults may give insufficient reliability in neonates due to their very irregular breathing pattern.

    APPROACH: Our approach is generic in the sense that it relies on the definition of a gold standard and the associated definition of detector sensitivity and specificity, an optimisation criterion and a set of detector parameters to be investigated. The gold standard has been defined by 11 clinicians with previous experience with EIT and the performance of our approach is described and validated using a neonatal EIT dataset acquired within the EU-funded CRADL project.

    MAIN RESULTS: Three different algorithms are proposed that improve the breath detector performance by adding conditions on (1) maximum tidal breath rate obtained from zero-crossings of the EIT breathing signal, (2) minimum tidal impedance amplitude and (3) minimum tidal breath rate obtained from time-frequency analysis. As a baseline a zero-crossing algorithm has been used with some default parameters based on the Swisstom EIT device.

    SIGNIFICANCE: Based on the gold standard, the most crucial parameters of the proposed algorithms are optimised by using a simple exhaustive search and a weighted metric defined in connection with the receiver operating characterics. This provides a practical way to achieve any desirable trade-off between the sensitivity and the specificity of the detectors.

  • 11.
    Khodadad, Davood
    et al.
    Department of Physics and Electrical Engineering, Linnaeus University, Växjö, Sweden.
    Nordebo, Sven
    Seifnaraghi, Nima
    Yerworth, Rebecca
    Waldmann, Andreas D.
    Müller, Beat
    Frerichs, Inéz
    van Kaam, Anton
    Miedema, Martijn
    Bayford, Richard
    The Value of Phase Angle in Electrical Impedance Tomography Breath Detection2018Ingår i: 2018 Progress in Electromagnetics Research Symposium (PIERS-Toyama), IEEE, 2018, s. 1040-1043Konferensbidrag (Refereegranskat)
    Abstract [en]

    The objective of this paper is to report our investigation demonstrating that the phase angle information of complex impedance could be a simple indicator of a breath cycle in chest Electrical Impedance Tomography (EIT). The study used clinical neonatal EIT data. The results show that measurement of the phase angle from complex EIT data can be used as a complementary information for improving the conventional breath detection algorithms.

  • 12.
    Khodadad, Davood
    et al.
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden; Institute of Applied Optics, University of Stuttgart, Stuttgart, Germany; Department of Physics and Electrical Engineering, Linnaeus University, Växjö, Sweden.
    Singh, Alok Kumar
    Pedrini, Giancarlo
    Sjödahl, Mikael
    Full-field 3D deformation measurement: comparison between speckle phase and displacement evaluation2016Ingår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 55, nr 27, s. 7735-7743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2×10-3 in the measurement of deformation gradients.

  • 13.
    Khodadad, Davood
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Tayebi, Behnam
    NYU Grossman School of Medicine, NY, New York, United States.
    Saremi, Amin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Paul, Satyam
    Gas Turbine and Transmissions Research Centre, University of Nottingham, Nottingham, United Kingdom.
    Temperature Sensing in Space and Transparent Media: Advancements in Off-Axis Digital Holography and the Temperature Coefficient of Refractive Index2023Ingår i: Applied Sciences, E-ISSN 2076-3417, Vol. 13, nr 14, artikel-id 8423Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An off-axis digital holographic interferometry technique integrated with a Mach–Zehnder interferometer based setup is demonstrated for measuring the temperature and temperature profile of a transparent medium. This technique offers several advantages: it does not require precise optomechanical adjustments or accurate definition of the frequency carrier mask, making it simple and cost-effective. Additionally, high-quality optics are not necessary. The methodology relies on measuring the phase difference between two digitally reconstructed complex wave fields and utilizing the temperature coefficient of the refractive index. In this way, we presented an equation of the temperature as a function of phase changes and the temperature coefficient of refractive index. This approach simplifies the calculation process and avoids the burden of complicated mathematical inversions, such as the inverse Abel transformation. It also eliminates the need for additional work with the Lorentz–Lorentz equation and Gladstone–Dale relation and can be extend for 3D measurements.

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  • 14. M.Haghighi, Alireza
    et al.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Department of Mechanical Engineering, Örebro University, Örebro, Sweden.
    Automated AISI 317L SS thin section image porosity recognition and semi-automated prioritization for predicting the yielding position by means of image processing2021Ingår i: Acta Mechanica Malaysia, E-ISSN 2616-4302, Vol. 4, nr 2, s. 34-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Porosity is a common phenomenon in fabricated parts, which cause stress concentration and leads to yielding, brittle fraction and fatigue of structures which makes porosity recognition and analyzing very important to increase efficiency and decrease the defects of manufactured parts. Many researches have been done in order to detecting and recognizing pores of material by different numerical and experimental methods. In this paper, an algorithm is developed in order to detect the porosity of thin section images automatically and prioritize them for a semi-automatically prediction of yielding position. The algorithm results is the following parameters in a porous material: number of pores, position and size of pores, maximum and minimum distances of pores both from each other and from boundaries. The algorithm shows an accuracy of 83% in the prediction of the results for simulated finite element method (FEM) tensile tests, which makes the algorithm creditable to be used as a non-destructive testing method.

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  • 15.
    Mohammadi, Younes
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Palstev, Aleksey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Polajžer, Boštjan
    Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia.
    Miraftabzadeh, Seyed Mahdi
    Department of Energy, Politecnico di Milano, Via Lambruschini 4, Milano, Italy.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Investigating Winter Temperatures in Sweden and Norway: Potential Relationships with Climatic Indices and Effects on Electrical Power and Energy Systems2023Ingår i: Energies, E-ISSN 1996-1073, Vol. 16, nr 14, artikel-id 5575Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents a comprehensive study of winter temperatures in Norway and northern Sweden, covering a period of 50 to 70 years. The analysis utilizes Singular Spectrum Analysis (SSA) to investigate temperature trends at six selected locations. The results demonstrate an overall long-term rise in temperatures, which can be attributed to global warming. However, when investigating variations in highest, lowest, and average temperatures for December, January, and February, 50% of the cases exhibit a significant decrease in recent years, indicating colder winters, especially in December. The study also explores the variations in Atlantic Meridional Overturning Circulation (AMOC) variations as a crucial climate factor over the last 15 years, estimating a possible 20% decrease/slowdown within the first half of the 21st century. Subsequently, the study investigates potential similarities between winter AMOC and winter temperatures in the mid to high latitudes over the chosen locations. Additionally, the study examines another important climatic index, the North Atlantic Oscillation (NAO), and explores possible similarities between the winter NAO index and winter temperatures. The findings reveal a moderate observed lagged correlation for AMOC-smoothed temperatures, particularly in December, along the coastal areas of Norway. Conversely, a stronger lagged correlation is observed between the winter NAO index and temperatures in northwest Sweden and coastal areas of Norway. Thus, NAO may influence both AMOC and winter temperatures (NAO drives both AMOC and temperatures). Furthermore, the paper investigates the impact of colder winters, whether caused by AMOC, NAO, or other factors like winds or sea ice changes, on electrical power and energy systems, highlighting potential challenges such as reduced electricity generation, increased electricity consumption, and the vulnerability of power grids to winter storms. The study concludes by emphasizing the importance of enhancing the knowledge of electrical engineering researchers regarding important climate indices, AMOC and NAO, the possible associations between them and winter temperatures, and addressing the challenges posed by the likelihood of colder winters in power systems.

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  • 16.
    Mohammadi, Younes
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Polajžer, Boštjan
    Leborgne, Roberto Chouhy
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Most influential feature form for supervised learning in voltage sag source localization2024Ingår i: Engineering applications of artificial intelligence, ISSN 0952-1976, E-ISSN 1873-6769, Vol. 133, nr Part D, artikel-id 108331Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The paper investigates the application of machine learning (ML) for voltage sag source localization (VSSL) in electrical power systems. To overcome feature-selection challenges for traditional ML methods and provide more meaningful sequential features for deep learning methods, the paper proposes three time-sample-based feature forms, and evaluates an existing feature form. The effectiveness of these feature forms is assessed using k-means clustering with k = 2 referred to as downstream and upstream classes, according to the direction of voltage sag origins. Through extensive voltage sag simulations, including noises in a regional electrical power network, k-means identifies a sequence involving the multiplication of positive-sequence current magnitude with the sine of its angle as the most prominent feature form. The study develops further traditional ML methods such as decision trees (DT), support vector machine (SVM), random forest (RF), k-nearest neighbor (KNN), an ensemble learning (EL), and a designed one-dimensional convolutional neural network (1D-CNN). The results found that the combination of 1D-CNN or SVM with the most prominent feature achieved the highest accuracies of 99.37% and 99.13%, respectively, with acceptable/fast prediction times, enhancing VSSL. The exceptional performance of the CNN was also approved by field measurements in a real power network. However, selecting the best ML methods for deployment requires a trade-off between accuracy and real-time implementation requirements. The research findings benefit network operators, large factory owners, and renewable energy park producers. They enable preventive maintenance, reduce equipment downtime/damage in industry and electrical power systems, mitigate financial losses, and facilitate the assignment of power-quality penalties to responsible parties.

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  • 17.
    Mohammadi, Younes
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Polajžer, Boštjan
    Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor 2000, Slovenia.
    Leborgne, Roberto Chouhy
    Universidade Federal do Rio Grande do Sul, Osvaldo Aranha, 99, Porto Alegre RS-90035-190, Brazil .
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Quantifying power system frequency quality and extracting typical patterns within short time scales below one hour2024Ingår i: Sustainable Energy, Grids and Networks, E-ISSN 2352-4677, Vol. 38, artikel-id 101359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper addresses the lack of consideration of short time scales, below one hour, such as sub-15-min and sub-1-hr, in grid codes for frequency quality analysis. These time scales are becoming increasingly important due to the flexible market-based operation of power systems as well as the rising penetration of renewable energy sources and battery energy storage systems. For this, firstly, a set of frequency-quality indices is considered, complementing established statistical indices commonly used in power-quality standards. These indices provide valuable insights for quantifying variations, events, fluctuations, and outliers specific to the discussed time scales. Among all the implemented indices, the proposed indices are based on over/under frequency events (6 indices), fast frequency rise/drop events (6 indices), and summation of positive and negative peaks (1 index), of which the 5 with the lowest thresholds are identified as the most dominant. Secondly, k-means and k-medoids clustering methods in a learning scheme are employed to identify typical patterns within the discussed time windows, in which the number of clusters is determined based on prior knowledge linked to reality. In order to clarify the frequency variations and patterns, three frequency case studies are analyzed: case 1 (sub-15-min scale, 10-s values, 6 months), case 2 (sub-1-hr scale, 10-s values, 6 months), and case 3 (sub-1-hr, 3-min values, the year 2021). Results obtained from the indices and learning methods demonstrate a full picture of the information within the windows. The maximum value of the highest frequency value minus the lowest one over the windows is about 0.35 Hz for cases 1 and 2 and 0.25 Hz for case 3. Over-frequency values (with a typical 0.1% threshold) slightly dominates under-frequency values in cases 1 and 2, while the opposite is observed in case 3. Medium fluctuations occur in 35% of windows for cases 1 and 2 and 41% for case 3. Outlier values are detected using the quartile method in 70% of windows for case 2, surpassing the other two cases. About six or seven typical patterns are also extracted using the presented learning scheme, revealing the frequency trends within the short time windows. The proposed approaches offer a simpler alternative than tracking frequency single values and also capture more comprehensive information than existing approaches that analyze the aggregated frequency values at the end of the specific time windows without considering the frequency trends. In this way, the network operators have the possibility to monitor the frequency quality and trends within short time scales using the most dominant indices and typical patterns.

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  • 18.
    Moradi, Mahmoud
    et al.
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Karamimoghadam, Mojtaba
    Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Via Orabona 4, Bari, Italy.
    Meiabadi, Saleh
    Department of Mechanical Engineering, École de Technologie Supérieure, 1100 Notre-Dame West, QC, Montreal, Canada.
    Casalino, Giuseppe
    Department of Mechanics, Mathematics and Management, Polytechnic University of Bari, Via Orabona 4, Bari, Italy.
    Ghaleeh, Mohammad
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Baby, Bobymon
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Ganapathi, Harikrishna
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Jose, Jomal
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Abdulla, Muhammed Shahzad
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Tallon, Paul
    Faculty of Arts, Science and Technology, University of Northampton, Northampton, United Kingdom.
    Shamsborhan, Mahmoud
    Department of Mechanical Engineering, University of Zakho, Dahouk, Iraq.
    Rezayat, Mohammad
    Center for Structural Integrity, Micromechanics, and Reliability of Materials (CIEFMA), Department of Materials Science and Engineering, Universitat Politècnica de Catalunya-BarcelonaTECH, Barcelona, Spain.
    Paul, Satyam
    Gas Turbine and Transmissions Research Centre, University of Nottingham, Northampton, United Kingdom.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Mathematical modelling of fused deposition modeling (FDM) 3D printing of poly vinyl alcohol parts through statistical design of experiments approach2023Ingår i: Mathematics, E-ISSN 2227-7390, Vol. 11, nr 13, artikel-id 3022Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper explores the 3D printing of poly vinyl alcohol (PVA) using the fused deposition modeling (FDM) process by conducting statistical modeling and optimization. This study focuses on varying the infill percentage (10–50%) and patterns (Cubic, Gyroid, tri-hexagon and triangle, Grid) as input parameters for the response surface methodology (DOE) while measuring modulus, elongation at break, and weight as experimental responses. To determine the optimal parameters, a regression equation analysis was conducted to identify the most significant parameters. The results indicate that both input parameters significantly impact the output responses. The Design Expert software was utilized to create surface and residual plots, and the interaction between the two input parameters shows that increasing the infill percentage (IP) leads to printing heavier samples, while the patterns do not affect the weight of the parts due to close printing structures. On the contrary, the discrepancy between the predicted and actual responses for the optimal samples is below 15%. This level of error is deemed acceptable for the DOE experiments.

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  • 19. Nordebo, Sven
    et al.
    Dalarsson, Mariana
    Khodadad, Davood
    Department of Physics and Electrical Engineering, Linnæus University, Växjö, Sweden.
    Müller, Beat
    Waldmann, Andreas D.
    Becher, Tobias
    Frerichs, Inez
    Sophocleous, Louiza
    Sjöberg, Daniel
    Seifnaraghi, Nima
    Bayford, Richard
    A parametric model for the changes in the complex valued conductivity of a lung during tidal breathing2018Ingår i: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, nr 20, artikel-id 205401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Classical homogenization theory based on the Hashin–Shtrikman coated ellipsoids is used to model the changes in the complex valued conductivity (or admittivity) of a lung during tidal breathing. Here, the lung is modeled as a two-phase composite material where the alveolar air-filling corresponds to the inclusion phase. The theory predicts a linear relationship between the real and the imaginary parts of the change in the complex valued conductivity of a lung during tidal breathing, and where the loss cotangent of the change is approximately the same as of the effective background conductivity and hence easy to estimate. The theory is illustrated with numerical examples based on realistic parameter values and frequency ranges used with electrical impedance tomography (EIT). The theory may be potentially useful for imaging and clinical evaluations in connection with lung EIT for respiratory management and control.

  • 20.
    Paul, Satyam
    et al.
    Department of Engineering Design and Mathematics, University of the West of England, Bristol, United Kingdom.
    Arunachalam, Ajay
    Centre for Applied Autonomous Sensor Systems (AASS), Örebro University, Örebro, Sweden.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Andreasson, Henrik
    Centre for Applied Autonomous Sensor Systems (AASS), Örebro University, Örebro, Sweden.
    Rubanenko, Olena
    Regional Innovational Center for Electrical Engineering, Faculty of Electrical Engineering, University of West Bohemia, Pilsen, Czech Republic.
    Fuzzy Tuned PID Controller for Envisioned Agricultural Manipulator2021Ingår i: International Journal of Automation and Computing, ISSN 1476-8186, E-ISSN 1751-8520, Vol. 18, nr 4, s. 568-580Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The implementation of image-based phenotyping systems has become an important aspect of crop and plant science research which has shown tremendous growth over the years. Accurate determination of features using images requires stable imaging and very precise processing. By installing a camera on a mechanical arm driven by motor, the maintenance of accuracy and stability becomes non-trivial. As per the state-of-the-art, the issue of external camera shake incurred due to vibration is a great concern in capturing accurate images, which may be induced by the driving motor of the manipulator. So, there is a requirement for a stable active controller for sufficient vibration attenuation of the manipulator. However, there are very few reports in agricultural practices which use control algorithms. Although, many control strategies have been utilized to control the vibration in manipulators associated to various applications, no control strategy with validated stability has been provided to control the vibration in such envisioned agricultural manipulator with simple low-cost hardware devices with the compensation of non-linearities. So, in this work, the combination of proportional-integral-differential (PID) control with type-2 fuzzy logic (T2-F-PID) is implemented for vibration control. The validation of the controller stability using Lyapunov analysis is established. A torsional actuator (TA) is applied for mitigating torsional vibration, which is a new contribution in the area of agricultural manipulators. Also, to prove the effectiveness of the controller, the vibration attenuation results with T2-F-PID is compared with conventional PD/PID controllers, and a type-1 fuzzy PID (T1-F-PID) controller.

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  • 21.
    Paul, Satyam
    et al.
    Department of Engineering Design and Mathematics, University of the West of England, Bristol, United Kingdom.
    Arunachalam, Ajay
    Centre for Applied Autonomous Sensor Systems (AASS), Örebro University, Örebro, Sweden.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Rubanenko, Olena
    Regional Innovational Center for Electrical Engineering Faculty of Electrical Engineering, University of West Bohemia, Pilsen, Czech Republic.
    Fuzzy Tuned PID Controller for Vibration Control of Agricultural Manipulator2020Ingår i: 2nd International Congress on Human-Computer Interaction, Optimization and Robotic Applications (HORA 2020), IEEE, 2020, s. 166-170Konferensbidrag (Refereegranskat)
    Abstract [en]

    Image-based phenotyping systems have evolved over the years, and become an integral part of crop and plant science research. Phenotyping systems provide great potential to deliver critical insights, than the conventional destructive field methods. Stable image acquisition and processing is very important to accurately determine the characteristics in general, which further becomes very challenging and non-trivial when mounted over an motor mechanised arm. To address the near associated problems, we investigate on the possibility of applying the Proportional-Integral-Derivative (PID) control algorithm to the present manual setup with an aim to reduce vibration. This study focused towards investigating the active control and stabilization of the external camera shake, that may be induced by the driving motor. Nonetheless, very few researchers have focused on application of control algorithms for agriculture related practices. We validate the active control, and justify the need for the same.Type-2 fuzzy logic is combined with the PID control for better effectiveness. The non-linearity associated with the system is compensated by the type-2 fuzzy logic. The results shows that the active control has been achieved, and the vibration is minimized.

  • 22.
    Paul, Satyam
    et al.
    Gas Turbine and Transmission Research Centre, Faculty of Engineering, University of Nottingham, Nottingham, UK.
    Turnbull, Rob
    Gas Turbine and Transmission Research Centre, Faculty of Engineering, University of Nottingham, Nottingham, UK.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Löfstrand, Magnus
    School of Science and Technology, Örebro University, Örebro, Sweden.
    A Vibration Based Automatic Fault Detection Scheme for Drilling Process Using Type-2 Fuzzy Logic2022Ingår i: Algorithms, E-ISSN 1999-4893, Vol. 15, nr 8, artikel-id 284Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fault detection system using automated concepts is a crucial aspect of the industrial process. The automated system can contribute efficiently in minimizing equipment downtime therefore improving the production process cost. This paper highlights a novel model based fault detection (FD) approach combined with an interval type-2 (IT2) Takagi–Sugeno (T–S) fuzzy system for fault detection in the drilling process. The system uncertainty is considered prevailing during the process, and type-2 fuzzy methodology is utilized to deal with these uncertainties in an effective way. Two theorems are developed; Theorem 1, which proves the stability of the fuzzy modeling, and Theorem 2, which establishes the fault detector algorithm stability. A Lyapunov stabilty analysis is implemented for validating the stability criterion for Theorem 1 and Theorem 2. In order to validate the effective implementation of the complex theoretical approach, a numerical analysis is carried out at the end. The proposed methodology can be implemented in real time to detect faults in the drilling tool maintaining the stability of the proposed fault detection estimator. This is critical for increasing the productivity and quality of the machining process, and it also helps improve the surface finish of the work piece satisfying the customer needs and expectations.

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  • 23.
    Saremi, Amin
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Khodadad, Davood
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    The timing of the cochlear wave propagation: a comparative study of computational models2024Ingår i: AIP Conference Proceedings, ISSN 0094-243X, E-ISSN 1551-7616, Vol. 3062, nr 1, artikel-id 020009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is believed that the phase of the cochlear wave propagation might play a crucial role in binaural perceptionand sound localization by generating cochlear disparities. Experimental data demonstrate that, while a tone is being played,an excitation pattern is formed extending from the base to the apex of the cochlea. The phase of the excitation patterndecays along the cochlear length until the slope of the phase curve (i.e. group delay) reaches its maximum at a locationwith the characteristic frequency (CF) that matches the frequency of the input tone. Thereafter, the phase stays almostconstant (group delay equals zero) until the apex. Computational models have been devised to simulate the cochlearresponses and thereby illuminate the underlying electromechanics of the human inner ear. These computational models canbe divided, according to their topology, into two groups: Parallel filterbanks that model the cochlea as several independentdecoupled filters versus cascade filterbanks (including transmission lines) which assume that the filters are coupled inseries. Due to their modeling principles, cascade filterbanks intrinsically include the longitudinal traveling wavepropagation whereas the parallel filterbank models lack this intrinsic feature since there is no longitudinal relation betweenthe filter stages in these models. The objective of this study is to verify if cascade filterbanks are actually more successfulin simulating the phase responses than parallel filterbanks. The excitation patterns generated by seven cochlear models(four parallel filterbanks, two cascade filterbanks and a transmission-line model) in response to 4 and 9 kHz tones wereestimated using an impulse, and the results were compared with corresponding experimental data recorded at comparablelengths in living mammalian cochleae. The accuracy of the model predictions was reported in mean absolute error (MAE)relative to the experimental data. The results show that cascade filterbank models are remarkably more successful withCARFAC and VERHULST models reproducing the experimental data most closely. However, DRNL model (a parallelfilterbank) also produces outcomes that are comparable in accuracy with those generated by cascade filterbank models.Further investigations showed that this specific parallel filterbank model externally incorporated correct phase delays inthe impulse responses of its filter stages. The results indicate that, if parallel filterbanks incorporate the phase delays intheir impulse responses according to the proposed method, they could successfully simulate the timing of the longitudinalwave propagation along the cochlea within the same accuracy range as cascade filterbank models do.

  • 24. Shiraz, A.
    et al.
    Khodadad, Davood
    Department of Mechanical Engineering, Örebro University, Örebro, Sweden.
    Nordebo, S.
    Yerworth, R.
    Frerichs, I.
    van Kaam, A.
    Kallio, M.
    Papadouri, T.
    Bayford, R.
    Demosthenous, A.
    Compressive sensing in electrical impedance tomography for breathing monitoring2019Ingår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 40, nr 3, artikel-id 034010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    OBJECTIVE: Electrical impedance tomography (EIT) is a functional imaging technique in which cross-sectional images of structures are reconstructed based on boundary trans-impedance measurements. Continuous functional thorax monitoring using EIT has been extensively researched. Increasing the number of electrodes, number of planes and frame rate may improve clinical decision making. Thus, a limiting factor in high temporal resolution, 3D and fast EIT is the handling of the volume of raw impedance data produced for transmission and its subsequent storage. Owing to the periodicity (i.e. sparsity in frequency domain) of breathing and other physiological variations that may be reflected in EIT boundary measurements, data dimensionality may be reduced efficiently at the time of sampling using compressed sensing techniques. This way, a fewer number of samples may be taken.

    APPROACH: Measurements using a 32-electrode, 48-frames-per-second EIT system from 30 neonates were post-processed to simulate random demodulation acquisition method on 2000 frames (each consisting of 544 measurements) for compression ratios (CRs) ranging from 2 to 100. Sparse reconstruction was performed by solving the basis pursuit problem using SPGL1 package. The global impedance data (i.e. sum of all 544 measurements in each frame) was used in the subsequent studies. The signal to noise ratio (SNR) for the entire frequency band (0 Hz-24 Hz) and three local frequency bands were analysed. A breath detection algorithm was applied to traces and the subsequent error-rates were calculated while considering the outcome of the algorithm applied to a down-sampled and linearly interpolated version of the traces as the baseline.

    MAIN RESULTS: SNR degradation was generally proportional with CR. The mean degradation for 0 Hz-8 Hz (of interest for the target physiological variations) was below ~15 dB for all CRs. The error-rates in the outcome of the breath detection algorithm in the case of decompressed traces were lower than those associated with the corresponding down-sampled traces for CR  ⩾  25, corresponding to sub-Nyquist rate for breathing frequency. For instance, the mean error-rate associated with CR  =  50 was ~60% lower than that of the corresponding down-sampled traces.

    SIGNIFICANCE: To the best of our knowledge, no other study has evaluated the applicability of compressive sensing techniques on raw boundary impedance data in EIT. While further research should be directed at optimising the acquisition and decompression techniques for this application, this contribution serves as the baseline for future efforts.

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  • 25. Tjörnhammar, Staffan
    et al.
    Eklöf, Finn Klemming
    Yu, Zhangwei
    Khodadad, Davood
    Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden.
    Hällstig, Emil
    Sjödahl, Mikael
    Laurell, Fredrik
    Multiwavelength laser designed for single-frame digital holography2016Ingår i: Applied Optics, ISSN 0003-6935, E-ISSN 1539-4522, Vol. 55, nr 27, s. 7517-7521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present a tailored multiwavelength Yb-fiber laser source in the 1.03 μm spectral region for spatially multiplexed digital holographic acquisitions. The wavelengths with bandwidths below 0.1 nm were spectrally separated by approximately 1 nm by employing fiber Bragg gratings for spectral control. As a proof of concept, the shape of a cylindrically shaped object with a diameter of 48 mm was measured. The holographic acquisition was performed in single-shot dual-wavelength mode with a synthetic wavelength of 1.1 mm, and the accuracy was estimated to be 3% of the synthetic wavelength.

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