Optical Strain Research Articles

Obtaining 20 μm Spatial Resolution with a 2940 nm Laser by IR-MALDESI Mass Spectrometry Imaging.

High spatial resolution is a key parameter in mass spectrometry imaging (MSI), enabling a greater understanding of system biology and cellular processes. Using a novel IR laser with good Gaussian beam quality (M2 = 4) coupled with spatial filtering and a reflective objective, 20 μm spatial resolution was obtained by IR-MALDESI. The optical train was optimized on burn paper before demonstrating feasibility for imaging of liver tissue. Finally, a mouse brain was analyzed using nested regions of interest at 20 and 140 μm spatial resolution, detecting neurotransmitters and lipids with high spatial resolution on the corpus callosum and surrounding brain tissue.

Study on Coal Seam Roof Failure Based on Optical Fiber Acoustic Sensing and the Parallel Electrical Method

As China enters the stage of deep coal mining, the accidents caused by roof failure pose increasingly serious threats. Current research on roof failure zones often use single methods, but single geophysical data may result in multisolution issues during interpretation. This paper employed similar simulation experiments, exploring the strain failure characteristics and the changes in apparent resistivity caused by stress variations, taking the 11-3106 working face of a mining area as the research object. Through optical fiber strain and apparent resistivity, the locations and degrees of fracture in postmining rock strata were identified. The feasibility of using distributed optical fiber sensing and the parallel electrical method for qualitative and quantitative analysis of mining-induced fractures was verified. The results showed that optical fiber strain increased significantly at the location of rock fracture, with apparent resistivity anomalies rising correspondingly. The peak strain region corresponded well with the region of apparent resistivity anomalies. In a similar simulation with a geometric ratio of 1:100, the height of the caving zone was measured to be 31.65 cm, with a caving-to-mining ratio of 6.33. In the field working face, the caving zone height was 29.47 m, with a caving-to-mining ratio of 6.01, consistent with the actual conditions of the 11-3106 working face.

A strain transmissibility-based analysis approach for operational modal of concrete dam under nonstationary excitation

The transmissibility-based operational modal analysis (TOMA) method is attracting more attentions due to its relaxation of assumptions about excitation properties, making accurately identifying the modes of actual engineering structures possible. However, in specific application on distributed vibration responses of huge hydraulic structures excited by broad-spectrum non-stationary earthquake, more proper selections of data segmentations on two dimensions (along time or spatial axis) are needed. Based on the concept of distributed vibration sensing optical fiber strain transmissibility, the operational modal analysis model based on single reference and poly references transmissibility under the strain format and the corresponding solutions of model and modal parameters are studied. A false mode elimination method combined with the continuity of spatial distribution of optical fiber measurements, a response sequence set optimization method that comprehensively consider amplitude/PSD non-stationarity, and the principle about how to select (non) reference points (sets) considering the spatial distribution of measurement signal-to-ratio are further developed. The case study shows that the proposed combined method could improve the modal parameter identification accuracy of concrete dams under broad-spectrum non-stationary excitation, and the distributed optical fiber vibration sensing technology can provide a rich (non) reference point (set) selection combination for this method.

Strain mode measurement of asphalt pavements using distributed fibre optic sensor data

This paper proposes a method for measuring strain modes in asphalt pavements using distributed fibre optic strain sensor data. A processing algorithm based on cross power spectral density (CPSD) was developed to utilize high spatial resolution strain data to determine the CPSD peak frequency and corresponding relative amplitude. The proposed method was applied in both laboratory and field settings, comparing the results of distributed fibre optic cables with those of accelerometers or theoretical solutions to validate accuracy. Local heating of asphalt structures was used to test the sensitivity of the measured strain modes to changes in material properties. The results demonstrate that different fibre optic cables can provide peak frequencies comparable to traditional accelerometers (±0.6 Hz). Additionally, they offer relative amplitude with a resolution of 1 cm, achieving a modal assurance criterion exceeding 0.95 when compared to theoretical strain mode shapes. The method also sensitively reflects material property changes at different positions within the asphalt structure. This indicates that the proposed approach can effectively measure strain modes in asphalt structures, offering a more detailed understanding of the distribution of structural properties compared to traditional methods.

Ultrasensitive strain sensor of dual parallel FPIs utilizing femtosecond laser processing and Vernier effect

This study proposes and develops a highly sensitive fiber optic strain sensor utilizing femtosecond laser processing and the Vernier effect. The sensor features two parallel Fabry-Pérot interferometers (FPI), with each FPI consisting of an air bubble and a tapered fiber optic cascade. FPI 2 serves as the sensing cavity, while FPI 1 acts as the reference cavity. The strain sensing capability of a single FPI 2 is measured at 6.67 p.m./με, while the parallel configuration of FPI 2 with FPI 1 achieves a sensitivity of 68.3 p.m./με, resulting in an amplification of 10.24. Furthermore, the proposed sensor demonstrates excellent repeatability, low-temperature cross-sensitivity, simple fabrication, and cost-effectiveness, making it a promising tool for strain measurement applications.

Field monitoring and prediction of the thermal response of an in-service curved continuous welded rail using distributed fiber optic strain measurements

Field monitoring and prediction of the thermal response of an in-service curved continuous welded rail using distributed fiber optic strain measurements

Absolute Quantification of Glutathione Using Top-Hat Optics for IR-MALDESI Mass Spectrometry Imaging.

Infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) uses an infrared laser to desorb neutral biomolecules with postionization via ESI at atmospheric pressure. The Gaussian profile of the laser with conventional optics results in the heating of adjacent nonablated tissue due to the energy profile being circular. A diffractive optical element (DOE) was incorporated into the optical train to correct for this disadvantage. The DOE produces a top-hat beam profile and square ablation spots, which have uniform energy distributions. Although beneficial to mass spectrometry imaging (MSI), it is unknown how the DOE affects the ability to perform quantitative MSI (qMSI). In this work, we evaluate the performance of the DOE optical train against our conventional optics to define the potential advantages of the top-hat beam profile. Absolute quantification of glutathione (GSH) was achieved by normalizing the analyte of interest to homoglutathione (hGSH), spotting a dilution series of stable isotope labeled glutathione (SIL-GSH), and analyzing by IR-MALDESI MSI with either the conventional optical train or with the DOE incorporated. Statistical comparison indicates that there was no significant difference between the quantification of GSH by the two optical trains as evidenced by similar calibration curves. Results support that both optical trains can be used for qMSI without a change in the ability to carry out absolute quantification but providing the benefits of the top-hat optical train (i.e., flat energy profile and square ablation spots)-for future qMSI studies.

Stretchable Distributed Bragg Reflectors as Strain-Responsive Mechanochromic Sensors.

Mechanochromic materials exhibit color changes upon external mechanical stimuli, finding wide-ranging applications in colorimetric sensing, display technology, and anticounterfeiting measures. Many of these materials rely on fluorescence properties and therefore necessitate external optical or electrical excitation. However, for broader applicability, the detection of color changes by the naked eye only or without complicated detection instrumentation is highly desirable. Photonic crystals offer a promising avenue for attaining such performances. In this work, we present elastomeric distributed Bragg reflectors (DBRs) characterized by a series of photonic bandgaps exhibiting mechanochromic response from the near-infrared to the visible wavelengths. To achieve this, we engineered alternating thin films of a thermoplastic fluoropolymer and a styrene-butadiene copolymer using different elastomeric substrates to attain different behaviors. The reported system demonstrates a reversible and instantaneous shift of the photonic bandgaps in response to 100% strain in multiple deformation cycles. Comparing the DBR stress-strain response with the optical strain response confirms a mechanochromic sensitivity of ∼1.7-6.9 nm/% and ∼80 nm/MPa, with an optical Poisson's ratio in the range 0.3-0.7. All these properties are spectrally dependent, as demonstrated by exploiting the properties of different diffraction order photonic band gaps.

Measuring strain distributions in an asphalt pavement using fibre optic sensors under static loading by test vehicles

Understanding the in-situ structural behaviour of pavements plays an important role in road engineering. Hence, various measurement methods were developed in the past to get an insight into the response of roads to traffic loading. In the present study, distributed fibre optic strain sensors were embedded into a hot mix asphalt pavement. The sensors were used for strain measurements with high spatial resolution in order to assess its feasibility to gain the continuous strain distribution in the pavement under short-term static loading. In addition, the loading process was measured with high temporal resolution, indicating that – using shorter sensor lengths – vehicle passages could also be studied. The strain distributions gathered with this type of sensor were compared to the results of a simple finite element model and the effect of applying various sensor cables. In addition, new opportunities provided by distributed fibre optic sensors in road engineering are discussed.

Practical guidelines for cell segmentation models under optical aberrations in microscopy

Cell segmentation is essential in biomedical research for analyzing cellular morphology and behavior. Deep learning methods, particularly convolutional neural networks (CNNs), have revolutionized cell segmentation by extracting intricate features from images. However, the robustness of these methods under microscope optical aberrations remains a critical challenge. This study evaluates cell image segmentation models under optical aberrations from fluorescence and bright field microscopy. By simulating different types of aberrations, including astigmatism, coma, spherical aberration, trefoil, and mixed aberrations, we conduct a thorough evaluation of various cell instance segmentation models using the DynamicNuclearNet (DNN) and LIVECell datasets, representing fluorescence and bright field microscopy cell datasets, respectively. We train and test several segmentation models, including the Otsu threshold method and Mask R-CNN with different network heads (FPN, C3) and backbones (ResNet, VGG, Swin Transformer), under aberrated conditions. Additionally, we provide usage recommendations for the Cellpose 2.0 Toolbox on complex cell degradation images. The results indicate that the combination of FPN and SwinS demonstrates superior robustness in handling simple cell images affected by minor aberrations. In contrast, Cellpose 2.0 proves effective for complex cell images under similar conditions. Furthermore, we innovatively propose the Point Spread Function Image Label Classification Model (PLCM). This model can quickly and accurately identify aberration types and amplitudes from PSF images, assisting researchers without optical training. Through PLCM, researchers can better apply our proposed cell segmentation guidelines. This study aims to provide guidance for the effective utilization of cell segmentation models in the presence of minor optical aberrations and pave the way for future research directions.

Cryogenic Digital Image Correlation as a Probe of Strain in Iron-Based Superconductors

Abstract Uniaxial strain is a powerful tuning parameter that can control symmetry and anisotropic electronic properties in iron-based superconductors. However, accurately characterizing anisotropic strain can be challenging and complex. Here, we utilize a cryogenic optical system equipped with a high-spatial-resolution microscope to characterize surface strains in iron-based superconductors using the digital image correlation method. Compared with other methods such as high-resolution X-ray diffraction, strain gauge, and capacitive sensor, digital image correlation offers a non-contact, full-field measurement approach, acting as an optical virtual strain gauge that provides high spatial resolution. The results measured on detwinned BaFe2As2 are quantitatively consistent with the distortion measured by X-ray diffraction and neutron Larmor diffraction. These findings highlight the potential of cryogenic digital image correlation as an effective and accessible tool for probing the isotropic and anisotropic strains, facilitating the application of uniaxial strain tuning in the study of quantum materials.

Geomechanics Modeling of Strain-Based Pressure Estimates: Insights from Distributed Fiber Optic Strain Measurements

Summary Rayleigh frequency shift distributed strain sensing (RFS-DSS) has been demonstrated as a potential technology for characterizing fracture geometries and optimizing the completion design in unconventional reservoirs. The combination of RFS-DSS strain and pressure gauge measurements has been reported recently in field applications (Dhuldhoya and Friehauf 2022; Haustveit and Haffener 2023) to characterize conductive fracture dimensions and production profiles. Haustveit and Haffener (2023) demonstrated a novel technique that uses RFS-DSS strain change during production, measured from a far-field observation well, to monitor the drain profile of a horizontal multistage well. The strain change and pressure change were strongly related during production, and this relationship was applied to continuously estimate pressure drawdown along the full length of the well. However, the sensitivity or influencing factors of the relationship between strain change and pressure change along the fiber are not yet fully understood. Therefore, the main objective of this study is to investigate the relationship between strain change and pressure change under various fractured reservoir conditions and provide guidelines for better utilizing this novel strain-pressure relationship to estimate conductive fractures and pressure profiles. We use a coupled geomechanics and fluid flow model to simulate the strain and pressure changes in the near-well and far-field regions during stable production and shut-in periods. A linear relationship is used to fit the strain change and pressure change data obtained from both producing and monitoring wells. We analyze the impact of various fracture properties [size and permeability of the stimulated reservoir volume (SRV) around fractures, fracture conductivity, fracture area, and skin factor] on the linear relationship based on the R2 value and fitting error. The relationship between the strain change and pressure change during the stable production obtained by our numerical study is consistent with the field measurements. The slope of strain change vs. pressure change during one day of production is significantly influenced by fracture properties. Overall, the monitoring well shows a stronger linear relationship than the producing well during both stable production and shut-in periods. A better linear relationship between the strain change and pressure change is associated with a larger fracture conductivity or larger fracture spacing scenario on both producing and monitoring wells during the stable production period. The cluster spacing affects the linear relationship between strain and pressure change during rock deformation. When cluster spacing is reduced, the nonlocal effect of deformation becomes more pronounced, resulting in a weaker linear relationship. During the shut-in period, the monitoring well exhibits a stronger linear relationship with a high R2 value and small fitting error compared to the producing well. The linear relationship obtained during the shut-in period is less reliable for the producing well. In cases of homogeneous fractures, where the fracture properties are uniform, the strain change and pressure change are similar, except for two outer fractures. This study provides a better understanding of the relationship between strain change and pressure change measured in the near-well and far-field regions during stable production and shut-in periods. The results of our study also demonstrate the potential for utilizing the RFS-DSS strain measurement to characterize the effective fracture and drainage dimensions.

Structural Diagnosis of Solid Rocket Motors Using Neural Networks and Embedded Optical Strain Sensors

The main failures that could deteriorate the reliable operation of solid rocket motors (SRMs) and lead to catastrophic events are related to bore cracks and delamination. Current SRMs’ predictive assessment and damage identification practices include time-consuming and cost-demanding destructive inspection techniques. By considering state-of-the-art optical strain sensors based on fiber Bragg gratings, a theoretical study on the use of such sensors embedded in the circumference of the composite propellant grain for damage detection is presented. Deep neural networks were considered for the accurate prediction of the presence and extent of the defects, trained using synthetic datasets derived through finite element analysis method. The evaluation of this combined approach proved highly efficient in discriminating between the healthy and the damaged condition, with an accuracy higher than 98%, and in predicting the extent of the defect with an error of 2.3 mm for the bore crack depth and 1.6° for the delamination angle (for a typical ~406 mm diameter grain) in the worst case of coexistent defects. This work suggests the basis for complete diagnosis of solid rocket motors by overcoming certain integration and performance limitations of currently employed dual bond stress and temperature sensors via the more scalable, safe, sensitive, and robust solution of fiber optic strain sensors.

Distributed fiber optic temperature and strain sensing in cementing and water injection: Insights to well integrity monitoring and multisensing optical fiber cable design

In this study, we installed two fiber optic cables with different designs into a new well, a soft-flat cable and a stainless-steel cable, for distributed fiber optic sensing in cementing and water injection. The two fiber cables were cemented behind casing and the soft-flat cable was used for temperature sensing in cementing as well as cement curing period. The high-speed Rayleigh scanning successfully visualized the cement front tracking from the combined effects of temperature and pressure changes by cement pumping. The temperature variations in cement curing reveled the cement volume and have the potential to identify defects in annular cement and formation damage caused by cementing. The water injection test for strain sensing was carried out with increasing injection rate from 100 L/min to 200 L/min. Strain profiles from the two fiber cables suggested that the strain responses reveal alternation of sand and silt, and reservoir heterogeneity. The water injection results showed that the measured strains of the two cables matched fairly well and the stainless-steel cable showed a high strain sensitivity responding to injection pressure (1 με/5 kPa). Comparison of strain measurement results of the two cables provided valuable insights for future strain fiber cable design. Strain sensing results also indicated a high capability to capture small pressure changes in the heterogeneous layers. Thus, our results demonstrate the high potential of using strain sensing for leak detection and well integrity monitoring in fluid injections, particularly for the long-term monitoring at CO2 storage site.

Towards strain gauge 2.0: Substituting the electric resistance routinely deposited on polyimide film by the optimal pattern for full‐field strain measurement

AbstractThe checkerboard constitutes the best pattern for full‐field strain measurement because it maximizes image gradient. In the experimental mechanics community, employing this pattern is currently strongly limited because depositing it on the surface of specimens raises practical difficulties. A recent study shows, however, that it is technically possible by using a laser engraver. The present paper aims to push this solution forward by printing a checkerboard pattern on a thin polymeric film and then gluing the resulting laser‐engraved film on the specimen surface. The underlying idea is to separate the manufacturing process of this optical strain gauge on the one hand and its use on the other hand to help spread this strain measuring tool in the experimental mechanics community. The polymeric film employed here is the same as that used in the manufacturing process of classic electrical gauges, so one can rely on the know‐how of classic strain gauge bonding to glue this optical strain gauge on the specimen surface. The main difference between the proposed tool and classic electrical gauges is that the strain field beneath the polymeric support is measured instead of localized strain values. The paper is a proof of concept for this strain field measuring tool. The manufacturing and bonding processes are described in the paper. The localized spectrum analysis, a spectral technique developed for processing images of periodic patterns, is used to retrieve the strain fields from checkerboard images. Through two complementary examples, we show the ability of this new type of strain gauge to detect and quantify local details in the strain field beneath. A simplified 1D model is also proposed to assess the minimum width of the strain peak that can reliably be measured with this technique.

Real-time monitoring of rock fracture by true triaxial test using fiber-optic strain monitoring in adjacent wells

The real-time monitoring of fracture propagation during hydraulic fracturing is crucial for obtaining a deeper understanding of fracture morphology and optimizing hydraulic fracture designs. Accurate measurements of key fracture parameters, such as the fracture height and width, are particularly important to ensure efficient oilfield development and precise fracture diagnosis. This study utilized the optical frequency domain reflectometer (OFDR) technique in physical simulation experiments to monitor fractures during indoor true triaxial hydraulic fracturing experiments. The results indicate that the distributed fiber optic strain monitoring technology can efficiently capture the initiation and expansion of fractures. In horizontal well monitoring, the fiber strain waterfall plot can be used to interpret the fracture width, initiation location, and expansion speed. The fiber response can be divided into three stages: strain contraction convergence, strain band formation, and postshutdown strain rate reversal. When the fracture does not contact the fiber, a dual peak strain phenomenon occurs in the fiber and gradually converges as the fracture approaches. During vertical well monitoring in adjacent wells, within the effective monitoring range of the fiber, the axial strain produced by the fiber can represent the fracture height with an accuracy of 95.6% relative to the actual fracture height. This study provides a new perspective on real-time fracture monitoring. The response patterns of fiber-induced strain due to fractures can help us better understand and assess the dynamic fracture behavior, offering significant value for the optimization of oilfield development and fracture diagnostic techniques.

Magnet-free electromagnetic nonreciprocity in two-dimensional materials

In this Tutorial, we overview recent developments to break and manipulate electromagnetic nonreciprocity in two-dimensional (2D) materials without relying on magnetic fields. To this purpose, we provide a general conductivity model to describe gyrotropic metasurfaces that exhibit nonreciprocity through different physical mechanisms enabled by 2D materials, including optical pumping, drifting electrons, ferromagnetic monolayers, mechanical strain, and spatiotemporal modulation. We describe in detail the resulting systems, focusing on near-field phenomena, associated to nonreciprocal bulk and edge surface plasmon propagation, and on far-field responses, related to Faraday/Kerr rotation and optical dichroism of waves propagating in free-space. Additionally, we review and contextualize recent advancements in magnet-free nonreciprocal devices based on 2D materials, ranging from Faraday rotators and optical dichrosim, to plasmonic and photonic isolators, hyperlenses, and tunable optical traps. We conclude by providing our outlook for the future development of this technology and its potential applications in areas such as communications, sensing, wave generation, and spectroscopy, among others.

Analysis of the Anisotropic Cyclic Material Behavior of EN AW-1050A H24 Derived from Strain-Controlled Testing Using a Clip-On Extensometer and an Optical System

Due to its good conductive properties, unalloyed (pure) aluminum, such as EN AW-1050A H24, finds new fields of application in electromobility. To optimize components, the cyclic material behavior must be understood and described precisely as a foundation of a proper fatigue life estimation. Various cyclic tests were performed to not only derive the cyclic parameters to describe the material but also to find the most suitable procedure to deal with the challenges faced during the experiments. The main point of interest is the comparison between a surface-mounted clip-on extensometer and an optical system both used for strain control in cyclic tests. For the analysis of the anisotropic behavior of EN AW-1050A H24, un-notched flat specimens were extracted from sheet metal lengthways and crossways in respect to the rolling direction. While the cyclic material behavior for specimens of both directions of extraction is characterized by cyclic softening in general, the specimens extracted crossways show a strain-amplitude-dependent cyclic softening with strong strain localization especially at the contact points of the knives of the clip-on extensometer leading to an increased quantity of invalid experiments as well as sudden fractures. In the study, it was possible to show the benefits of a contactless optical strain control system when dealing with very soft metallic materials such as EN AW-1050A H24.

The Impact of Liquids and Saturated Salt Solutions on Polymer-Coated Fiber Optic Sensors for Distributed Strain and Temperature Measurement.

The application of distributed fiber optic strain and temperature measurement can be utilized to address a multitude of measurement tasks across a diverse range of fields, particularly in the context of structural health monitoring in the domains of building construction, civil engineering, and special foundation engineering. However, a comprehensive understanding of the influences on the measurement method and the sensors is essential to prevent misinterpretations or measurement deviations. In this context, this study investigated the effects of moisture exposure, including various salt solutions and a high pH value, on a distributed strain measurement using Rayleigh backscattering. Three fiber optic sensors with different coating materials and one uncoated fiber were exposed to five different solutions for 24 h. The study revealed significant discrepancies (∼38%) in deformation between the three coating types depending on the surrounding solution. Furthermore, in contrast to the prevailing literature, which predominantly describes swelling effects, a negative deformation (∼-47 με) was observed in a magnesium chloride solution. The findings of this study indicate that corresponding effects can impact the precision of measurement, potentially leading to misinterpretations. Conversely, these effects could be used to conduct large-scale monitoring of chemical components using distributed fiber optic sensing.

Oversampling for Enhanced Spatial Resolution of Zebrafish by Top-Hat IR-MALDESI-MSI.

Mass spectrometry imaging (MSI) has become a significant tool for measuring chemical species in biological tissues, where much of the impact of these platforms lies in their capability to report the spatial distribution of analytes for correlation to sample morphology. As a result, enhancement of spatial resolution has become a frontier of innovation in the field, and necessary developments are dependent on the ionization source. More particularly, laser-based imaging sources may require modifications to the optical train or alternative sampling techniques. These challenges are heightened for systems with infrared (IR) lasers, as their operating wavelength generates spot sizes that are inherently larger than their ultraviolet counterparts. Recently, the infrared matrix-assisted laser desorption electrospray ionization (IR-MALDESI) source has shown the utility of a diffractive optical element (DOE) to produce square ablation patterns, termed top-hat IR-MALDESI. If the DOE optic is combined with oversampling methods, smaller ablation volumes can be sampled to render higher spatial resolution imaging experiments. Further, this approach enables reproducible spot sizes and ablation volumes for better comparison between scans. Herein, we investigate the utility of oversampling with top-hat IR-MALDESI to enhance the spatial resolution of measured lipids localized within the head of sectioned zebrafish tissue. Four different spatial resolutions were evaluated for data quality (e.g., mass measurement accuracy, spectral accuracy) and quantity of annotations. Other experimental parameters to consider for high spatial resolution imaging are also discussed. Ultimately, 20 μm spatial resolution was achieved in this work and supports feasibility for use in future IR-MALDESI studies.