| 1. |
- Adolfsson, Erik, et al.
(author)
-
Matrix crack induced stiffness reductions in [(0(m)/90(n)/+theta(p)/-theta(q))(s)](m) composite laminates
- 1995
-
In: Composites Engineering. - : Elsevier BV. - 0961-9526. ; 5:1, s. 107-123
-
Journal article (peer-reviewed)abstract
- Two- and three-dimensional linearly elastic glass/epoxy and carbon/epoxy laminates of the type [(0m/90n/ + theta(p)/ - theta(q))s]M containing periodically distributed matrix cracks have been analysed by aid of the finite element method. The presented finite element model enables modelling of several important thick and thin ply stacking sequences like cross-plies, angle plies and quasi-isotropic laminates. Due to periodicity it suffices to model a representative volume element of the laminate. The boundaries of this unit cell represent prospective crack surfaces. In this way varying crack configurations and crack densities could be simulated. By application of periodic boundary conditions the stiffness tensors for laminates containing different crack configurations were calculated. The results are presented in the form of reduced engineering stiffness parameters as functions of matrix crack densities for a thick quasi-isotropic [(0-degree/90-degrees/ + 45-degrees/ -45-degrees)s]M glass/epoxy laminate, a thick [(0-degree/90-degrees + 55-degrees/ - 55-degrees)s]M carbon/epoxy laminate and a thin (0-degree/ +45-degrees/ -45-degrees)s glass/epoxy laminate. Comparisons are made to an approximate analytic model developed previously. An excellent agreement between the analytic predictions and the finite element results was found for all cases under consideration.
|
|
| 2. |
- Adolfsson, Erik, et al.
(author)
-
Matrix crack initiation and progression in composite laminates subjected to bending and extension
- 1999
-
In: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 36:21, s. 3131-3169
-
Journal article (peer-reviewed)abstract
- An experimental investigation of matrix crack initiation and progression in glass/epoxy laminates of different stacking sequences is presented. The laminates have been loaded in extension and bending, and the degree of damage as function of the load has been recorded. The changes in certain elastic properties caused by the damage were also measured, and are compared to results from a previously developed approximate analytic model. An energy release rate resistance curve is adopted in an attempt to describe the initiation and progression of matrix cracks in the laminates. The amount of cracking is also viewed in relation to the strain transverse to the fibres in the ply under consideration, and the ply stresses at the onset of cracking are calculated. The different damage evolution criteria are compared to the experimental results, and their validity and reliability are discussed. By use of the ply strain transverse to the fibres as a critical parameter for damage evolution, the load-deformation curves of the tested laminates are simulated taking damage progression into account.
|
|
| 3. |
- Adolfsson, Erik, et al.
(author)
-
Thermoelastic properties in combined bending and extension of thin composite laminates with transverse matrix cracks
- 1997
-
In: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 34:16, s. 2035-2060
-
Journal article (peer-reviewed)abstract
- Approximate analytic expressions for the thermoelastic properties in combined bending and extension of composite laminates containing transverse matrix cracks are derived. The model covers two-dimensional laminates of arbitrary lay-up sequences. The derived expressions for the compliances and thermal expansion coefficients merely contain ply property data and crack distributions. In order to check the accuracy and reliability of the presented analytic method, some sample cracked geometries were examined by use of the finite element method. A good agreement was found between the numerically and analytically obtained results for all cases under consideration.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Barral, Joelle K., et al.
(author)
-
A Robust Methodology for In Vivo T1 Mapping
- 2010
-
In: Magnetic Resonance in Medicine. - : Wiley. - 0740-3194 .- 1522-2594. ; 64:4, s. 1057-1067
-
Journal article (peer-reviewed)abstract
- In this article, a robust methodology for in vivo T(1) mapping is presented. The approach combines a gold standard scanning procedure with a novel fitting procedure. Fitting complex data to a five-parameter model ensures accuracy and precision of the T(1) estimation. A reduced-dimension nonlinear least squares method is proposed. This method turns the complicated multi-parameter minimization into a straightforward one-dimensional search. As the range of possible T(1) values is known, a global grid search can be used, ensuring that a global optimal solution is found. When only magnitude data are available, the algorithm is adapted to concurrently restore polarity. The performance of the new algorithm is demonstrated in simulations and phantom experiments. The new algorithm is as accurate and precise as the conventionally used Levenberg-Marquardt algorithm but much faster. This gain in speed makes the use of the five-parameter model viable. In addition, the new algorithm does not require initialization of the search parameters. Finally, the methodology is applied in vivo to conventional brain imaging and to skin imaging. T(1) values are estimated for white matter and gray matter at 1.5T and for dermis, hypodermis, and muscle at 1.5T, 3T, and 7T. Magn Reson Med 64:1057-1067, 2010.
|
|
| 7. |
- Barral, Joelle K., et al.
(author)
-
Skin T1 Mapping at 1.5T, 3T, and 7T
- 2009
-
In: Proceedings 17th Scientific Meeting, International Society for Magnetic Resonance in Medicine (2009).
-
Conference paper (peer-reviewed)abstract
- Increasing the field strength seems promising for high-resolution skin imaging but a legitimate concern is the increase in the spin-lattice relaxation parameter T1. Skin T1 maps at 1.5T, 3T, and 7T are compared and a novel non-linear least-square approach for fast and accurate T1-estimation is proposed.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Björk, Marcus, et al.
(author)
-
Parameter estimation approach to banding artifact reduction in balanced steady-state free precession
- 2014
-
In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 72:3, s. 880-892
-
Journal article (peer-reviewed)abstract
- Purpose: The balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest due to its high signal-to-noise ratio efficiency. However, bSSFP images often suffer from banding artifacts due to off-resonance effects, which we aim to minimize in this paper. Methods: We present a general and fast two-step algorithm for 1) estimating the unknowns in the bSSFP signal model from multiple phase-cycled acquisitions, and 2) reconstructing band-free images. The first step, Linearization for Off-Resonance Estimation (LORE), solves the nonlinear problem approximately by a robust linear approach. The second step applies a Gauss-Newton algorithm, initialized by LORE, to minimize the nonlinear least squares criterion. We name the full algorithm LORE-GN. Results: We derive the Cramér-Rao bound (CRB), a theoretical lower bound of the variance for any unbiased estimator, and show that LORE-GN is statistically efficient. Furthermore, we show that simultaneous estimation of T1 and T2 from phase-cycled bSSFP is difficult, since the CRB is high at common SNR. Using simulated, phantom, and in vivo data, we illustrate the band-reduction capabilities of LORE-GN compared to other techniques, such as sum-of-squares. Conclusion: Using LORE-GN we can successfully minimize banding artifacts in bSSFP.
|
|
| 11. |
- Björk, Marcus, 1985-, et al.
(author)
-
Signal Processing Algorithms for Removing Banding Artifacts in MRI
- 2011
-
In: Proceedings of the 19th European Signal Processing Conference (EUSIPCO-2011). ; , s. 1000-1004, s. 1000-1004
-
Conference paper (peer-reviewed)abstract
- In magnetic resonance imaging (MRI), the balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest, due to its relatively high signal-to-noise ratio in a short scan time. However, images acquired with this pulse sequence suffer from banding artifacts due to off-resonance effects. These artifacts typically appear as black bands covering parts of the image and they severely degrade the image quality. In this paper, we present a fast two-step algorithm for estimating the unknowns in the signal model and removing the banding artifacts. The first step consists of rewriting the model in such a way that it becomes linear in the unknowns (this step is named Linearization for Off-Resonance Estimation, or LORE). In the second step, we use a Gauss-Newton iterative optimization with the parameters obtained by LORE as initial guesses. We name the full algorithm LORE-GN. Using both simulated and in vivo data, we show the performance gain associated with using LORE-GN as compared to general methods commonly employed in similar cases.
|
|
| 12. |
- Butt, Naveed, et al.
(author)
-
An Overview of NQR Signal Detection Algorithms
- 2014
-
In: Magnetic Resonance Detection of Explosives and Illicit Materials. - Dordrecht : Springer Netherlands. - 9789400772656 - 9789400772649 ; part 1, s. 19-33
-
Book chapter (peer-reviewed)abstract
- Nuclear quadrupole resonance (NQR) is a solid-state radio frequency spectroscopic technique that can be used to detect the presence of quadrupolar nuclei, that are prevalent in many narcotics, drugs, and explosive materials. Similar to other modern spectroscopic techniques, such as nuclear magnetic resonance, and Raman spectroscopy, NQR also relies heavily on statistical signal processing systems for decision making and information extraction. This chapter provides an overview of the current state-of-the-art algorithms for detection, estimation, and classification of NQR signals. More specifically, the problem of NQR-based detection of illicit materials is considered in detail. Several single- and multi-sensor algorithms are reviewed that possess many features of practical importance, including (a) robustness to uncertainties in the assumed spectral amplitudes, (b) exploitation of the polymorphous nature of relevant compounds to improve detection, (c) ability to quantify mixtures, and (d) efficient estimation and cancellation of background noise and radio frequency interference.
|
|
| 13. |
- Gudmundson, Erik, et al.
(author)
-
An esprit-based parameter estimator for spectroscopic data
- 2012
-
In: 2012 IEEE Statistical Signal Processing Workshop, SSP 2012. - : IEEE conference proceedings. - 9781467301831 ; , s. 77-80
-
Conference paper (peer-reviewed)abstract
- The pulse spin-locking sequence is a common excitation sequence for magnetic resonance and nuclear quadrupole resonance signals, with the resulting measurement data being well modeled as a train of exponentially damped sinusoidals. In this paper, we derive an ESPRIT-based estimator for such signals, together with the corresponding Cramer-Rao lower bound. The proposed estimator is computationally efficient and only requires prior knowledge of the number of spectral lines, which is in general available in the considered applications. Numerical simulations indicate that the proposed method is close to statistically efficient, and that it offers an attractive approach for initialization of existing statistically efficient gradient or search based techniques.
|
|
| 14. |
|
|
| 15. |
- Gudmundson, Erik, et al.
(author)
-
Automatic Smoothing of Periodograms
- 2006
-
In: Proceedings of the 2006 IEEE International Conference on Acoustics, Speech, and Signal Processing: May 14-19, 2006, Toulouse, France. ; , s. III-504-III-507
-
Conference paper (peer-reviewed)abstract
- Thresholding the cepstrum associated with the periodogram is a smoothing technique that appears to be very useful for variance reduction. Here the thresholding is performed via the methods SThresh and EbayesThresh. They both work fine in the broadband spectra case, even if some of the data is missing. The SThresh method appears to be more efficient as it shows a smaller variance and is faster computationally. The smoothing methods are also shown to perform well on a real-life broadband signal.
|
|
| 16. |
- Gudmundson, Erik, et al.
(author)
-
Blood velocity estimation using ultrasound and spectral iterative adaptive approaches
- 2011
-
In: Signal Processing. - : Elsevier BV. - 0165-1684 .- 1872-7557. ; 91:5, s. 1275-1283
-
Journal article (peer-reviewed)abstract
- This paper proposes two novel iterative data-adaptive spectral estimation techniques for blood velocity estimation using medical ultrasound scanners. The techniques make no assumption on the sampling pattern of the emissions or the depth samples, allowing for duplex mode transmissions where B-mode images are interleaved with the Doppler emissions. Furthermore, the techniques are shown, using both simplified and more realistic Field II simulations as well as in vivo data, to outperform current state-of-the-art techniques, allowing for accurate estimation of the blood velocity spectrum using only 30% of the transmissions, thereby allowing for the examination of two separate vessel regions while retaining an adequate updating rate of the B-mode images. In addition, the proposed methods also allow for more flexible transmission patterns, as well as exhibit fewer spectral artifacts as compared to earlier techniques.
|
|
| 17. |
- Gudmundson, Erik, et al.
(author)
-
Detection and Classification of Liquid Explosives Using NMR
- 2009
-
In: 2009 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH, AND SIGNAL PROCESSING. - 9781424423538 ; , s. 3053-3056, s. 3053-3056
-
Conference paper (peer-reviewed)abstract
- In this work, we present a novel method for non-invasive identification of liquids, for instance to allow for the detection of liquid explosives at airports or border controls. The approach is based on a nuclear magnetic resonance technique with an inhomogeneous magnetic field, forming estimates of the liquid's spin-spin relaxation time, T(2), and diffusion constant, D, thereby allowing for a unique classification of the liquid. The proposed detectors are evaluated using both simulated and measured data sets.
|
|
| 18. |
- Gudmundson, Erik, et al.
(author)
-
Efficient Algorithms for Computing the Capon and APES Filters
- 2007
-
In: CONFERENCE RECORD OF THE FORTY-FIRST ASILOMAR CONFERENCE ON SIGNALS, SYSTEMS & COMPUTERS, VOLS 1-5. - 9781424421091 ; , s. 427-430
-
Conference paper (peer-reviewed)abstract
- The computation of the Capon and the amplitude and phase estimation (APES) filters can be very time consuming. The burden lies not only in the inversion of the sample covariance matrix, but also in the matrix multiplications. In this paper, we propose an efficient algorithm for the computation of the above mentioned filters, using Cholesky Factorization and fast Fourier transforms. Furthermore, we discuss and illustrate the benefits of using the proposed algorithms in the spectral analysis of data with missing samples.
|
|
| 19. |
|
|
| 20. |
- Gudmundson, Erik, et al.
(author)
-
NQR-Based Explosives Detection—An Overview
- 2009
-
In: ISSCS 2009. - 9781424437849 ; , s. 9-12
-
Conference paper (peer-reviewed)abstract
- Nuclear quadrupole resonance (NQR) is a radio frequency spectroscopic technique that can be used to detect solid-state compounds containing quadrupolar nuclei, a requirement fulfflled by most high explosives (and narcotics). In this paper, we present an overview of recent research in the detection of explosives using this technique. We also present mathematical models for the data for different acquistion techniques and discuss different state of the art detection algorithms. Finally, we evaluate various algorithms on measured and simulated NQR data.
|
|
| 21. |
- Gudmundson, Erik, et al.
(author)
-
On Denoising via Penalized Least-Squares Rules
- 2008
-
In: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - Piscataway, NJ : IEEE. - 9781424414833 ; , s. 3705-3708
-
Conference paper (peer-reviewed)abstract
- Penalized least-squares (PELS) rules for signal denoising can be obtained via the use of various information criteria (AIC, BIC, etc.) or various minmax LS approaches. Let S denote the set of "significant" parameters in the denoising problem (which is to be determined), let n(S) be the dimension of S, and let n(S)rho denote the penalty term of a PELS criterion. We show that, depending on the expression for rho, the following cases can occur: type-1) If rho does not depend on S, then denoising via the corresponding PELS rule is equivalent to simple thresholding; and type-2) If rho depends on n(S) only, then the equivalence to thresholding no longer holds but the PELS rule can still be implemented quite efficiently. We also show that the use of BIC leads to an existing PELS rule of type-1 when the noise variance in the denoising problem is known, and to a novel PELS rule of type-2 when the noise variance is unknown.
|
|
| 22. |
- Gudmundson, Erik, et al.
(author)
-
On the Reconstruction of Gapped Sinusoidal Data
- 2008
-
In: 2008 IEEE INTERNATIONAL CONFERENCE ON ACOUSTICS, SPEECH AND SIGNAL PROCESSING. - Piscataway, NJ : IEEE. - 9781424414833 ; , s. 3513-3516
-
Conference paper (peer-reviewed)abstract
- The problem of estimating a spectral representation of damped sinusoidal signals from a gapped data set is of considerable interest in several applications. In this paper, we propose a filterbank approach to provide such an estimate, by first reconstructing the missing data samples assuming that the spectral content of the missing data is similar to that of the available samples, and then forming a spectral representation of the reconstruced data set as a function of frequency and damping. Numerical examples illustrate the benefits of the proposed estimator as compared to currently available methods.
|
|
| 23. |
- Gudmundson, Erik, et al.
(author)
-
Overcoming the Nyquist Limit in Blood Flow Velocity Estimation
- 2012
-
In: 2012 IEEE International Ultrasonics Symposium (IUS'12), Proceedings of. - 1948-5719. ; , s. 1615-1618
-
Conference paper (peer-reviewed)abstract
- Spectral Doppler ultrasound imaging typically consists of a spectrogram, showing the velocity distribution of the blood, and a brightness (B-) mode image allowing the operator to navigate. It is desirable to have both high spectral and velocity resolution, so that details in the blood flow can be traced, as well as a high B-mode frame rate to allow for tracking of movements and to adjust the position of the transducer. The blood flow signal is often sampled 1) using alternating transmissions for blood flow estimation and for B-mode imaging, or, 2) by acquiring a full Doppler spectrum and then parts of the B-mode image. The former has the disadvantage that it halves the sampling rate, making it likely that aliasing will occur when imaging fast moving blood or deeply positioned vessels; the latter that gaps appears in the spectrogram, and that if the frame rate of the B-mode images is slow, it will be difficult to track movements. Adaptive methods have been implemented to circumvent such problems, but even so, to get an acceptable frame rate of the B- mode images, the number of transmissions for Doppler estimation will be limited, restricting the spectral resolution. Alternatively, one may use an irregularly spaced emission pattern, but existing work on the topic is limited and generally suffers from poor resolution and spurious velocity components resulting from the irregular sampling pattern. In this paper, we examine the BIAA algorithm, showing that this approach allows for an accurate velocity estimate even from irregularly sampled measurements. Using an irregular emission pattern, with half the emissions used to form the B-mode image, the remaining emissions are found to yield accurate velocity estimates without reducing the maximally measurable velocity and without the spurious velocity components. Moreover, we show that the approach will allow for the same maximal velocity without aliasing as if all emissions would have been used for the velocity estimation.
|
|
| 24. |
- Gudmundson, Erik, 1976-
(author)
-
Signal Processing for Spectroscopic Applications
- 2010
-
Doctoral thesis (other academic/artistic)abstract
- Spectroscopic techniques allow for studies of materials and organisms on the atomic and molecular level. Examples of such techniques are nuclear magnetic resonance (NMR) spectroscopy—one of the principal techniques to obtain physical, chemical, electronic and structural information about molecules—and magnetic resonance imaging (MRI)—an important medical imaging technique for, e.g., visualization of the internal structure of the human body. The less well-known spectroscopic technique of nuclear quadrupole resonance (NQR) is related to NMR and MRI but with the difference that no external magnetic field is needed. NQR has found applications in, e.g., detection of explosives and narcotics. The first part of this thesis is focused on detection and identification of solid and liquid explosives using both NQR and NMR data. Methods allowing for uncertainties in the assumed signal amplitudes are proposed, as well as methods for estimation of model parameters that allow for non-uniform sampling of the data. The second part treats two medical applications. Firstly, new, fast methods for parameter estimation in MRI data are presented. MRI can be used for, e.g., the diagnosis of anomalies in the skin or in the brain. The presented methods allow for a significant decrease in computational complexity without loss in performance. Secondly, the estimation of blood flow velo-city using medical ultrasound scanners is addressed. Information about anomalies in the blood flow dynamics is an important tool for the diagnosis of, for example, stenosis and atherosclerosis. The presented methods make no assumption on the sampling schemes, allowing for duplex mode transmissions where B-mode images are interleaved with the Doppler emissions.
|
|
| 25. |
- Gudmundson, Erik, et al.
(author)
-
Spectral Estimation of Damped Sinusoids in the Case of Irregularly Sampled Data
- 2009
-
In: ISSCS 2009. - 9781424437849 ; , s. 97-100
-
Conference paper (peer-reviewed)abstract
- The problem of estimating a spectral representation of damped sinusoidal signals from a gapped data set is of considerable interest in several applications. In this paper, we propose a new iterative adaptive approach, named dIAA, that provides such an estimate also in the case of irregularly sampled data, a common scenario in, for instance, spectroscopical data measurements. Numerical examples illustrate the benefits of the proposed estimator as compared to typically used methods.
|
|
| 26. |
|
|
| 27. |
- Gudmundson, Erik, 1976-, et al.
(author)
-
Spectral Estimation of Irregularly Sampled Exponentially Decaying Signals with Applications to RF Spectroscopy
- 2010
-
In: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 203:1, s. 167-176
-
Journal article (peer-reviewed)abstract
- The problem of estimating the spectral content of exponentially decaying signals from a set of irregularly sampled data is of considerable interest in several applications, for example in various forms of radio frequency spectroscopy. In this paper, we propose a new nonparametric iterative adaptive approach that provides a solution to this estimation problem. As opposed to commonly used methods in the field, the damping coefficient, or linewidth, is explicitly modeled, which allows for an improved estimation performance. Numerical examples using both simulated data and data from NQR experiments illustrate the benefits of the proposed estimator as compared to currently available nonparametric methods.
|
|
| 28. |
- Gupta, Priyank, et al.
(author)
-
Characterization of the Constitutive Behavior of a Cathode ActiveLayer in Lithium-Ion Batteries Using a Bending Test Method
- 2020
-
In: Experimental mechanics. - : Springer. - 0014-4851 .- 1741-2765. ; 60, s. 847-860
-
Journal article (peer-reviewed)abstract
- Presently used experimental techniques for the characterization of tensile and compressive behavior of active layers in lithiumionbatteries have limitations of different kinds. This is particularly true for measurements of compressive properties.Furthermore, the characterizations of time-dependent stress-strain behavior are largely missing. In order to characterize thestress-strain relationship for a dry cathode active layer in lithium-ion batteries, a mechanical testing method is presented thatpreviously has been applied to the testing of optical fibers. The method is based on U-shaped bending of single-side coatedaluminum foils, which enables separate measurements of tensile and compressive properties. In particular, the method has clearadvantages for measurements of compressive properties in comparison to previously reported techniques. Relaxation experimentsare also conducted in order to characterize the time-dependent properties of the dry active layer and to check if these effectscould explain the measured hysteresis. It is found that the elastic modulus in compression is significantly larger than the elasticmodulus in tension and that the compressive modulus increases with strain level. Contrary, the tensile modulus is approximatelyindependent of strain. Furthermore, hysteresis effects are present at loading-unloading measurements, both for tension andcompression. The low values of the measured elastic moduli show that the electrode properties are largely controlled by thebinder and carbon additives. It is concluded that the development of particle-particle contacts most likely is the reason for thehigher modulus in compression in comparison to tension. The time-dependent effects are significant, primarily for shorter timescales, which explains the relaxation behavior, but they cannot fully explain the hysteresis effects. Most likely non-linear micromechanismsdo contribute as well.
|
|
| 29. |
- Gupta, Priyank, 1991-
(author)
-
Experimental Characterization of Electrodes and Multi-Scale Modeling of Swelling Induced Stresses in Lithium-ion Batteries
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Over the last few decades, rechargeable lithium-ion batteries have been extensively used in portable instruments due to their high energy density and low self-discharge rate. Recently, lithium-ion batteries have emerged as the most promising candidate for electric vehicles and stationary energy storage. However, the maximum energy that lithium-ion batteries store decreases as they are used because of various irreversible degradation mechanisms. The mechanical properties of the electrode layers inside the battery highly influence the battery's performance. There is, however, a fundamental lack of understanding of the mechanical properties of electrodes and how they evolve during electrochemical cycling, which makes it a necessity to characterize their mechanical behavior for mesoscopic and macroscopic level modeling. Lithium-ion batteries are complex systems to understand, and various processes and their interactions make battery modeling challenging. This thesis contributes to understanding the mechanical behavior of electrodes in lithium-ion batteries and provides methods for the design and efficient modeling of battery systems. In Paper A and Paper B, the macroscopic mechanical behavior of active layers in the electrodes is investigated using U-shape bending tests. The active layers are porous and a different tensile and compressive behavior is captured by performing tests on single side coated dry electrodes. The experiments reveal that the active layer is stiffer in compression as compared to tension. The compressive stiffness increases with bending strain whereas the tensile stiffness is almost independent of the bending strain. A very low value of modulus of the active layer (1-5 GPa) is measured in comparison to the metal foils (70-110 GPa) and the active particles (50-200 GPa) which shows that the electrode properties are governed majorly by the binders present in the active layers. The time-dependent and hysteresis effects are also captured by the method which circumvents the flaws of many other test methods presented in the literature. Paper C focuses on characterizing the layer-level evolution of mechanical and electrochemical properties of a Ni-rich positive electrode during early-stage electrochemical cycling, along with complementary cross-section analyses to understand the relationship between macroscopic and microscopic changes. Macroscopic constitutive properties were measured using the U-shaped bending test method developed in papers A and B, which revealed that the compressive modulus was primarily influenced by the porous structure and binder properties. It decreased notably with electrolyte wetting but increased with cycling and aging. Electrochemical impedance spectra showed an increase in local resistance near the particle-electrolyte interface with early-stage aging, which was likely due to secondary particle grain separation and carbon black redistribution. Cross-section analyses reveal significant variations in particle properties between pristine and cycled samples, including particle swelling, compression of the binder phase, and increased particle contact, contributing to the rise in the elastic modulus of the porous layer during cycling. In Paper D and Paper E, we present a multiscale homogenization method that couples mechanics and electrochemistry at the particle, electrode, and battery scales. The active materials of lithium-ion battery electrodes exhibit volume change during lithium intercalation or deintercalation. A lithium concentration gradient develops inside particles, as well as inside the active layer. The developed stress due to deformations further affects solid diffusion. We utilized models that have already been developed to couple particle and electrode layer levels. Electric vehicle battery packs consist of numerous battery modules, each of which includes multiple battery cells composed of electrode, separator, and current collector layers. A finite element model capable of capturing stresses at the layer level would need to be very large to account for all the details. The mechanical coupling between the electrode and the battery level is achieved by homogenization of the layered battery using three-dimensional laminate theory, which greatly reduces the number of finite elements required for stress simulations in batteries. After obtaining a homogenized solution, layer-level stresses can be determined in a post-processing step. The method accurately predicts stresses on various scales and captures the effects of external battery loadings, cycling rates, and mechanical parameters. The efficiency of the method is demonstrated by comparing it to detailed finite element computations. The simulations indicate that layer-wise stresses, such as pressure, can be predicted as functions of position and time, providing insights into the inhomogeneous aging state of the battery.
|
|
| 30. |
|
|
| 31. |
- Jakobsson, Andreas, et al.
(author)
-
Computationally Efficient Time-Recursive IAA-Based Blood Velocity Estimation
- 2012
-
In: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 60:7, s. 3853-3858
-
Journal article (peer-reviewed)abstract
- High-resolution spectral Doppler is an important and powerful noninvasive tool for estimation of velocities in blood vessels using medical ultrasound scanners. Such estimates are typically formed using an averaged periodogram technique, resulting in well-known limitations in the resulting spectral resolution. Recently, we have proposed techniques to instead form high-resolution data-adaptive estimates exploiting measurements along both depth and emission. The resulting estimates gives noticeably superior velocity estimates as compared to the standard technique, but suffers from a high computational complexity, making it interesting to formulate computationally efficient implementations of the estimators. In this work, by exploiting the rich structure of the iterative adaptive approach (IAA) based estimator, we examine how these estimates can be efficiently implemented in a time-recursive manner using both exact and approximate formulations of the method. The resulting algorithms are shown to reduce the necessary computational load with several orders of magnitude without noticeable loss of performance.
|
|
| 32. |
- Kyriakidou, Georgia, et al.
(author)
-
Improved modeling and bounds for NQR spectroscopy signals
- 2014
-
In: European Signal Processing Conference. - 2219-5491.
-
Conference paper (peer-reviewed)abstract
- Nuclear Quadrupole Resonance (NQR) is a method of de- tection and unique characterization of compounds containing quadrupolar nuclei, commonly found in many forms of ex- plosives, narcotics, and medicines. Typically, multi-pulse sequences are used to acquire the NQR signal, allowing the resulting signal to be well modeled as a sum of exponentially damped sinusoidal echoes. In this paper, we improve upon the earlier used NQR signal model, introducing an observed amplitude modulation of the spectral lines as a function of the sample temperature. This dependency noticeably af- fects the achievable identification performance in the typical case when the substance temperature is not perfectly known. We further extend the recently presented Cramér-Rao lower bound to the more detailed model, allowing one to determine suitable experimental conditions to optimize the detection and identifiability of the resulting signal. The theoretical results are carefully motivated using extensive NQR measurements.
|
|
| 33. |
- Lundgren, Jan-Erik, et al.
(author)
-
A model for moisture absorption in cross-ply composite laminates with matrix cracks
- 1998
-
In: Journal of composite materials. - : SAGE Publications. - 0021-9983 .- 1530-793X. ; 32:24, s. 2226-2253
-
Journal article (peer-reviewed)abstract
- A homogenized analytic model for average moisture uptake in composite laminates containing periodically distributed matrix-cracks is presented. It is shown that the model, compared to FE-calculations, well decribes moisture absorption in a cross-ply composite laminate containing periodically distributed transverse matrix cracks in the 90 degrees plies. The homogenized model is based on a two-phase model consisting of the crack channels and the composite material respectively. An analytic solution to the two-phase model for moisture uptake in composite laminates is presented. The model can be used to judge whether micro cracks are of importance or not concerning moisture absorption.
|
|
| 34. |
- Lundgren, Jan-Erik, et al.
(author)
-
Moisture absorption in glass-fibre/epoxy laminates with transverse matrix cracks
- 1999
-
In: Composites Science And Technology. - 0266-3538 .- 1879-1050. ; 59:13, s. 1983-1991
-
Journal article (peer-reviewed)abstract
- Moisture uptake in cross-ply glass-fibre/epoxy laminates containing matrix cracks in transverse plies has been investigated. Experimental results are compared to finite-element calculations and an approximate analytical model. The experimental results show that crack closure may occur early in the absorption process. This is confirmed by finite-element calculations which indicate that even small amounts of absorbed moisture (average moisture concentration < 10% of saturation level) may result in crack closure. As a result of crack closure, moisture penetration through the crack channels is prevented. The experimentally observed small differences in moisture uptake between cracked and uncracked laminates thus support the crack-closure hypothesis. Direct microscopic observations of crack closure versus time furthermore confirm the mechanism. A previously developed analytical model has been extended to include the case of crack-closure effects. The model compares favourably with experimental observations.
|
|
| 35. |
- Pirnia, Elham, et al.
(author)
-
Data Adaptive Estimation of Transversal Blood Flow Velocities
- 2014
-
In: [Host publication title missing]. - 1520-6149.
-
Conference paper (peer-reviewed)abstract
- The examination of blood flow inside the body may yield important information about vascular anomalies, such as possible indications of, for example, stenosis. Current medical ultrasound systems suffer from only allowing for measuring the blood flow velocity along the direction of irradiation, posing natural difficulties due to the complex behaviour of blood flow, and due to the natural orientation of most blood vessels. Recently, a transversal modulation scheme was introduced to induce also an oscillation along the transversal direction, thereby allowing for the measurement of also the transversal blood flow. In this paper, we propose a novel data-adaptive blood flow estimator exploiting this modulation scheme. Using realistic Field II simulations, the proposed estimator is shown to achieve a notable performance improvement as compared to current state-of-the-art techniques.
|
|
| 36. |
|
|
| 37. |
- Selén, Yngve, et al.
(author)
-
An approach to sparse model selection and averaging
- 2006
-
In: Conference Record of the 2006 IEEE Instrumentation and Measurement Technology Conference (IMTC 2006).
-
Conference paper (peer-reviewed)abstract
- Parameter estimation when the true model structure is unknown is a commonly occurring task in measurement problems. In a sparse modeling scenario, the number of possible models grows exponentially with the total number of parameters. The full set of models therefore becomes computationally infeasible to handle. We propose a method, based on successive model reduction, for finding a sound and computationally feasible set of sparse linear regression models. Once this set of models has been found, standard model selection or model averaging techniques can be applied. We demonstrate the performance of our method by some numerical examples.
|
|
| 38. |
- Skog, Isaac, et al.
(author)
-
Signals of Opportunity based Geometry Calibration of Hydrophone Arrays
- 2019
-
In: OCEANS 2019 MTS/IEEE SEATTLE. - : IEEE. - 9780578576183
-
Conference paper (peer-reviewed)abstract
- A method to calibrate the geometries of hydrophone arrays using the sound emitted from nearby ships, is presented. The calibration problem is formulated as a simultaneous localization and mapping (SLAM) estimation problem, where the locations and geometries of the arrays are viewed as unknown map states and the position of the source is viewed as the unknown dynamic state. Two models for the geometry of the arrays are presented. The first model does not impose any constraint on array geometry, whereas the second model takes into account the known maximum distance between the hydrophones. The performance of the proposed calibration method is evaluated using data from two PASS-2447 Omnitech Electronics Inc. 56-element hydrophone arrays. Tests with three data sets show that array geometries in the north-east plane can be consistently estimated. Only the second model provides consistent results in the depth direction. The calibration of the array geometries is shown to increase source localization accuracy significantly.
|
|
| 39. |
- Somasundaram, Samuel D., et al.
(author)
-
Enhancing Signals
- 2008
-
Patent (pop. science, debate, etc.)abstract
- A method of testing a sample comprising the steps of: applying an excitation to the sample; detecting a response signal from the sample; processing a first part and a second part of the response signal; and determining from the second part of the response signal information with which to enhance the first part of the response signal.
|
|
| 40. |
- Somasundaram, Samuel D., et al.
(author)
-
Enhancing Signals
- 2008
-
Patent (pop. science, debate, etc.)
|
|
| 41. |
- Somasundaram, Samuel D., et al.
(author)
-
Robust NQR Signal Detection
- 2007
-
In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, Vol III, Pts 1-3.
-
Conference paper (peer-reviewed)
|
|
| 42. |
- Somasundaram, Samuel Dilshan, et al.
(author)
-
Robust NQR Signal Detection
- 2007
-
In: Proceedings of the 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing: April 15-20, 2007, Honolulu, Hawaii, USA.
-
Conference paper (peer-reviewed)abstract
- Nuclear quadrupole resonance (NQR) is a spectroscopic technique that can be used to detect many high explosives and narcotics. Unfortunately, the measured signals are weak, thereby inhibiting the widespread use of the technique. Current state-of-the-art detectors, which exploit realistic NQR data models, assume that the complex amplitudes of the NQR signal components are known, to within a multiplicative constant. However, these amplitudes are typically prone to some level of uncertainty, thus leading to performance loss in these algorithms. Herein, we develop a frequency selective algorithm, robust to uncertainties in the assumed amplitudes, that offers a significant performance gain over current state-of-the art techniques.
|
|
| 43. |
- Somasundaram, Samuel D., et al.
(author)
-
Robust Nuclear Quadrupole Resonance Signal Detection Allowing for Amplitude Uncertainties
- 2008
-
In: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 56:3, s. 887-894
-
Journal article (peer-reviewed)abstract
- Nuclear quadrupole resonance (NQR) is a solid-state radio frequency spectroscopic technique that can be used to detect compounds which contain quadrupolar nuclei, a requirement fulfilled by many high explosives and narcotics. Unfortunately, the low signal-to-noise ratio (SNR) of the observed signals currently inhibits the widespread use of the technique, thus highlighting the need for intelligent processing algorithms. In earlier work, we proposed a set of maximum likelihood-based algorithms enabling detection of even very weak NQR signals. These algorithms are based on derived realistic NQR data models, assuming that the (complex) amplitudes of the NQR signal components are known to within a multiplicative constant. However, these amplitudes, which are obtained from experimental measurements, are typically prone to some level of uncertainty. For such-cases, these algorithms will experience a loss in performance. Herein, we develop a set of robust algorithms, allowing for uncertainties in the assumed amplitudes, showing that these offer a significant performance gain over the current state-of-the art techniques.
|
|
| 44. |
- Wahlström, Johan
(author)
-
Sensor Fusion for Smartphone-based Vehicle Telematics
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- The fields of navigation and motion inference have rapidly been transformed by advances in computing, connectivity, and sensor design. As a result, unprecedented amounts of data are today being collected by cheap and small navigation sensors residing in our surroundings. Often, these sensors will be embedded into personal mobile devices such as smartphones and tablets. To transform the collected data into valuable information, one must typically formulate and solve a statistical inference problem.This thesis is concerned with inference problems that arise when trying to use smartphone sensors to extract information on driving behavior and traffic conditions. One of the fundamental differences between smartphone-based driver behavior profiling and traditional analysis based on vehicle-fixed sensors is that the former is based on measurements from sensors that are mobile with respect to the vehicle. Thus, the utility of data from smartphone-embedded sensors is diminished by not knowing the relative orientation and position of the smartphone and the vehicle.The problem of estimating the relative smartphone-to-vehicle orientation is solved by extending the state-space model of a global navigation satellite system-aided inertial navigation system. Specifically, the state vector is augmented to include the relative orientation, and the measurement vector is augmented with pseudo observations describing well-known characteristics of car dynamics. To estimate the relative positions of multiple smartphones, we exploit the kinematic relation between the accelerometer measurements from different smartphones. The characteristics of the estimation problem are examined using the Cramér-Rao bound, and the positioning method is evaluated in a field study using concurrent measurements from seven smartphones.The characteristics of smartphone data vary with the smartphone's placement in the vehicle. To investigate this, a large set of vehicle trip segments are clustered based on measurements from smartphone-embedded sensors and vehicle-fixed accelerometers. The clusters are interpreted as representing the smartphone being rigidly mounted on a cradle, placed on the passenger seat, held by hand, etc. Finally, the problem of fusing speed measurements from the on-board diagnostics system and a global navigation satellite system receiver is considered. Estimators of the vehicle’s speed and the scale factor of the wheel speed sensors are derived under the assumptions of synchronous and asynchronous samples.
|
|
