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Sandwich panels with carbon fiber reinforced plastics (CFRP) have high flexural strength-to-weight and stiffness-to-weight ratios and are used in structures requiring good mechanical properties, such as aircrafts and marine vehicles. In this study, the overall displacement of a sandwich panel with CFRP faces and an aluminum honeycomb core was reconstructed using the inverse finite element method (iFEM). The full in-plane strain fields were input into the iFEM and reproduced from the measured strains and an interpolation technique. We propose an interpolation method to calculate the overall strain fields on the sandwich panel based on strain distributions measured by fiber-optic sensors and numerically showed that the fully distributed sensing yields accurate and robust results in both strain and displacement reconstructions. To validate the proposed method, fiber-optic sensors were embedded in the sandwich panel, and strain distributions were measured by the sensing system with optical frequency domain reflectometry. In these experiments, we successfully and accurately measured the strain distributions along the embedded fibers and reconstructed the overall strain fields and displacement of the sandwich panel under four load cases. Furthermore, the sandwich panel shape identified by the proposed method can be employed for structural health monitoring., QC 20230626

Minimally invasive catheter-based interventions normally take place under the guidance of fluoroscopy. However, fluoroscopy is harmful to both patients and clinicians. Moreover, it only offers 2-D shape visualization of flexible devices. To solve the problem of harmful radiation and offer 3-D pose and shape information, recent studies propose a combination of electromagnetic tracking (EMT) sensors and multicore fiber Bragg grating (FBG) fiber sensing. However, for robust localization, at least two EMT sensors are required to be attached to each multicore fiber. This may make the catheter overly complex and fragile. Furthermore, the inability of multicore FBG fibers to distinguish between twist-induced strain and bend-induced strain impacts shape sensing accuracy. This article proposes a new approach offering a precise shape sensing method that is robust against torsional twists and exploits symmetry and geometry to compensate for limited sensing information. The proposed approach originates from the observation that many interventional procedures employ a plurality of concentric instruments. By distributing sensors over these instruments, the complexity per instrument can be kept acceptable. The proposed sensor fusion approach ensures robust and superior shape reconstruction. Experiments in 3-D with ground truth generated by a stereo vision system have been done and yielded promising results. Compared to the state-of-the-art methods, the presented framework uses only half of the required EMT sensors per instrument resulting in significant spatial conservation while improving the catheter shape tracking accuracy by 57%., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Medical Instruments & Bio-Inspired Technology

Optical fiber-based shape sensing is gaining popularity in cardiac catheterization lately. Typically, these procedures are taking place under the guidance of fluoroscopy. However, fluoroscopy has several disadvantages. Thanks to fiber optic shape sensing and Electromagnetic Tracking (EMT), the 3D catheter shape can now be tracked in real-time without the need for fluoroscopy. Traditional optical fiber and EMT-based shape tracking methods have the drawback of the highest shape sensing error at the tip. The information offered by the EMT sensors is used mainly to localize the estimated shape in a fixed coordinate frame. In this letter, a novel approach for tracking the catheter is introduced to address the aforementioned problem. The catheter shape is directly reconstructed in the EMT coordinate frame by approximating the catheter shape by a number of Bézier curves while taking into account the curvatures measured by the optical fiber. Both 2D and 3D shape sensing experiments are conducted. The results of the 3D experiment show that the proposed method reduces the mean shape tracking error by approximately 38% (from 12.1 mm to 5.4 mm for a sensed length of 540 mm long) compared to the traditional method where the same number of sensors are used., Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Medical Instruments & Bio-Inspired Technology

In this paper, with the final aim of shape sensing for a morphing aircraft wing section, a developed multimodal shape sensing system is analysed. We utilise the method of interrogating a morphing wing section based on the principles of both hybrid interferometry and Fibre Bragg Grating (FBG) spectral sensing described in our previous work. The focus of this work is to assess the measurement performance and analyse the errors in the shape sensing system. This includes an estimation of the bending and torsional deformations of an aluminium mock-up section due to static loading that imitates the behaviour of a morphing wing trailing edge. The analysis involves using a detailed calibration procedure and a multimodal sensing algorithm to measure the deflection and shape. The method described In this paper, uses a standard single core optical fibre and two grating pairs on both the top and bottom surfaces of the morphing section. A study on the fibre placement and recommendations for efficient monitoring is also included. The analysis yielded a maximum deflection sensing error of 0.7 mm for a 347 × 350 mm wing section., Structural Integrity & Composites

The reconstruction of the elastic deformed shape of a structure from strain measurements is a field which has received considerable attention over the years. This work aims to suggest some improvements for wing-like structures trying to limit as much as possible the amount of strain measurements needed. In particular, a simple beam model is proposed based on the framework of the inverse Finite Element Method (iFEM). Then, the performances of iFEM using shell elements will be enhanced pre-extrapolating the strain field and the results will be compared with another shape sensing method, the so-called Modal Method (MM). In the final part of the work the external loads under the form of a pressure field are recovered using both the reconstructed displacements and directly the strain measurements. Both static and dynamic analyses will be carried out, so recovering the load both in space and in time. The results obtained show that the beam model developed allows to obtain a satisfactory bending reconstruction of the structure, while the twist is not always accurate. Computing the full displacement field with iFEM brings to a relatively good representation, even though not as satisfactory as the one delivered by the Modal Method. Finally, recovering the static external loads directly from the strain measurements seems to perform better compared to the reconstruction from the full displacement field, but it is significantly affected by noise and uncertainties. The dynamic load reconstruction is in general much more challenging and the results obtained often show a significant error compared to the reference solution., Aerospace Engineering

Abstract: Optical fibre sensors and in particular fibre Bragg gratings (FBG) have received a lot of interest for Structural Health Monitoring in different application fields, such as aerospace, pipeline and civil engineering. FBGs are conventionally used to monitor strain and sometimes temperature. In this paper, we propose a new method for load monitoring of a cantilever plate subjected to point loading. The bending of plate is complex due to the interaction between the axial and transverse bending stiffnesses of the material. We use a novel algorithm for interrogating fibre Bragg grating sensors based on both hybrid interferometry and FBG spectral sensing. The method is demonstrated in this paper using a single-mode optical fibre containing four FBG sensors to estimate both the point loading position and the loading magnitude at an arbitrary location on a 1 m2 cantilever plate. The algorithm first utilizes point strain information through spectral sensing as well as strain from interferometric sensing over a long path. The gratings are interrogated using Wavelength Division Multiplexing (WDM). We calibrated the system using an experimental model. This model was then verified by using single point static loading tests and comparing the calculated sensing position with the actual position. The method achieved a good estimation of loading position achieving a measurement error of about 9% in a 2D plane. The analysis discusses the possible sources of inaccuracies. This study forms the basis of our future work involving morphing smart-wing sections for the purpose of load monitoring. Article highlights: A new optical sensing configuration is demonstrated for load and structuralhealth monitoring of cantilever structures.The algorithm successfully estimates the position of an arbitrary load on acantilever plate, with an error of 9%.This methodology will be extended to monitor more complex structures, in-cluding morphing aircraft wing sections., Structural Integrity & Composites

This paper presents a study on trailing edge deflection estimation for the SmartX camber morphing wing demonstrator. This demonstrator integrates the technologies of smart sensing, smart actuation and smart controls using a six module distributed morphing concept. The morphing sequence is brought about by two actuators present at both ends of each of the morphing modules. The deflection estimation is carried out by interrogating optical fibers that are bonded on to the wing’s inner surface. A novel application is demonstrated using this method that utilizes the least amount of sensors for load monitoring purposes. The fiber optic sensor data is used to measure the deflections of the modules in the wind tunnel using a multi-modal fiber optic sensing approach and is compared to the deflections estimated by the actuators. Each module is probed by single-mode optical fibers that contain just four grating sensors and consider both bending and torsional deformations. The fiber optic method in this work combines the principles of hybrid interferometry and FBG spectral sensing. The analysis involves an initial calibration procedure outside the wind tunnel followed by experimental testing in the wind tunnel. This method is shown to experimentally achieve an accuracy of 2.8 mm deflection with an error of 9%. The error sources, including actuator dynamics, random errors, and nonlinear mechanical backlash, are identified and discussed., Structural Integrity & Composites, Aerospace Structures & Computational Mechanics

The inherent flexibility, the small dimensions as well as the curvilinear shape of continuum robots makes it challenging to precisely measure their shape. Optical fibers with Bragg gratings (FBGs) provide a powerful tool to reconstruct the centerline of continuum robots. We present a theoretical model to determine the shape of such a sensor array based on longitudinal strain measurements and incorporating bending, twisting, and elongation. To validate our approach, we conduct several simulations by calculating arbitrary shapes based on the Cosserat rod theory. Our algorithm showed a maximum mean relative shape deviation of 0.04%, although the sensor array was twisted up to 78°. Because we derive a closed-form solution for the strain curvature twist model, we also give analytical sensitivity values for the model, which can be used in the calculation of error propagation.

[EN] This paper describes a study of the influence of strain measurement uncertainty on sensing curvature and bending direction, considering one of the most widely used fiber geometries for sensing applications (7-core Multicore Fiber) with different core spacings (distance between outer cores and fiber axis). The Monte Carlo method was proposed to simulate the real measurement process and 33 simulations with 106 iterations were performed to determine the laws of propagation of strain measurement uncertainty in calculating curvature and bending direction. The outcomes, which show the strong influence of strain uncertainty and core spacing on the precision of Multicore Fiber sensors, can be used to support the design of new sensors or new fiber geometry and to predict their achievable performance.

Over the years, many shape sensing methods have been developed with technologies including optical fibre, PZT and fringe projection. Among them, optical fibres have gained a lot of attention due to their unobtrusive nature when either surface mounted or embedded in the structure. Optical fibre Bragg gratings (FBG) are currently employed for structural health monitoring in civil and aerospace systems and their shape sensing capabilities have been previously reported. In this paper, we propose a novel fibre optic based shape sensor of an isotropic cantilever beam based on the principles of interferometry and FBG sensing. The method described in this paper uses a standard single core single-mode optical fibre and the least number of sensors to estimate the shape, making it comparatively an inexpensive sensing method. On displacing the beam with an unknown magnitude and at an unknown location along the beam, we are able to demonstrate that we can measure the shape of the displaced beam and the magnitude and location of the force applied. The analysis involves using a calibration method and an iterative calculation to measure the two unknowns. An analytical model based on the known beam theories was used to assess the accuracy of the measurements. The preliminary analysis yielded an accuracy of ±1 mm and ±50 mm for the displacement and location, respectively., Structural Integrity & Composites

This paper extends the approach for determining the three-dimensional global displaced shape of slender structures from a limited set of scalar surface strain measurements. It is an exhaustive approach that captures the effect of curvature, shear, torsion, and elongation. The theory developed provides both a determination of the uniaxial strain (in a given direction) anywhere in the structure and the deformed shape, given a set of strain values. The approach utilizes Cosserat rod theory and exploits a localized linearization approach that helps to obtain a local basis function set for the displacement solution in the Cosserat frame. For the assumed deformed shape (both the midcurve and the cross-sectional orientation), the uniaxial value of strain in any given direction is obtained analytically, and this strain model is the basis used to predict the shape via an approximate local linearized solution strategy. Error analysis due to noise in measured strain values and in uncertainty in the proximal boundary condition is performed showing uniform convergence with increased sensor count.

The development of advanced needles for diagnostic and therapeutic purposes such as ablation and brachytherapy in the liver has offered minimally invasive therapies to patients that were previously untreatable. This thesis focuses on accurate placement of such needles guided by magnetic resonance imaging (MRI) to maximize the effect of the treatment and to minimize unwanted side-effects. To this end, an MRI-compatible steerable needle is developed which consists of a cable-actuated tip and a passively flexible shaft. The trajectory of this needle can be adjusted after the needle has been inserted. In addition, shape sensing based on optical strain sensors (fiber Bragg gratings or FBGs) is investigated aiming at feeding back information about the position and orientation of the needle tip in real-time. This is essential for accurate targeting, particularly when the needle trajectory is curved. Finally, steerability and shape sensing are integrated in a robotic system for needle steering in MRI-guided percutaneous interventions in the liver. The master-slave system comprises a steerable needle equipped with FBGs for tracking and a piezoelectric actuator unit. Needle insertion and steering is controlled by the physician through a master device, while FBG-based visual feedback of the needle shape is provided., BioMechanical Engineering, Mechanical, Maritime and Materials Engineering