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Effects of the microstructure and density profiles on wave propagation across an interface with material properties
摘要： The characterization of the interphase condition between two materials is current in mechanics. In general, its modeling is achieved by considering an interface with only purely elastic properties. In this paper, following previous works, also inertial interface properties are taken into account. For sufficiently low-frequency regime, we investigate two density profiles (affine and quadratic), for the interphase. Moreover, the interface and the interphase are placed between two solids with different characteristics. The first one is non-dispersive, while for the second one three cases are considered: (a) solid without microstructure, i.e., a Cauchy continuum, (b) solid with microstructure characterized by normal dispersion, i.e., a strain gradient continuum, and (c) by anomalous dispersion. The reflection coefficients are plotted for each case. These results are evaluated with respect to a benchmark finite elements simulation of the finite heterogeneous interphase, and the error is discussed. It is shown that the effects of microstructure can be appreciated at higher frequencies and that the proposed model results to be accurate.
关键词： Strain gradient,Reflection coefficient,Interface,Interphase,Density profiles,Wave propagation
更新于2025-09-23 15:23:52
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Raman analysis of strained graphene grown on dewetted cobalt
摘要： Graphene grows onto cobalt by means of diffusion of carbon atoms during the isothermal stage of exposure to hydrocarbon precursor, followed by precipitation during cooling. This method, largely applied with nickel catalyst, is known to produce continuous, but not uniform, layers with the concurrent presence of mono‐ and poly‐graphene areas. With the aid of Raman mapping of graphene still lying onto its catalyst, we are able to consider the possible origins for the observed distortions of the phonon modes with respect to the well‐known picture of the monolayer material. Optical effects, doping, the presence of multi‐layered islands, and strain are kept into account. It is shown that some isotropic observations can be interpreted in terms of the occurrence of strain with the uniaxial component superimposed at the metal discontinuities. Strain is proposed to originate from the difference between the thermal expansion coefficients of graphene and cobalt. The present paper shows that inhomogeneities in graphene grown onto catalysts with high C solubility are not always directly related to excess of precipitation. The observation of strain in as‐grown graphene opens the possibility of tailoring the electronic density of states via strain engineering directly during growth.
关键词： strain,graphene,micro‐Raman,cobalt,chemical vapor deposition
更新于2025-09-23 15:23:52
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Speckle tracking echocardiography in healthy children: comparison between the QLAB by Philips and the EchoPAC by General Electric
摘要： Speckle tracking echocardiography (STE) has become a useful tool in cardiology but remains scarcely developed in pediatrics. We aimed to evaluate the feasibility of STE analyses in healthy children and compare reliability of STE for left and right ventricles (LV, RV) between the EchoPAC (GE Healthcare) and the QLAB (Philips Healthcare) software systems. Healthy children were screened for this prospective cross-sectional study. Analyses were performed upon five levels of variability: intra/inter-ultrasound system, intra/inter-sonographer and intra/inter-analyzer. The feasibility was measured, and the tracking quality informed. The study included 156 healthy children. Mean age was 7.6 ± 5 years [1 month–16.8 years]. Conventional echocardiography variables were similar in both ultrasound systems. For both software brands, the tracking quality was excellent in the LV longitudinal and circumferential displacements, but more limited in the RV free wall longitudinal strain. Inter-ultrasound system correlation was poor for global longitudinal and circumferential LV strain (ICC of 0.34 [IC95% 0.06–0.57]) and 0.12 [IC95% ? 0.18 to ? 0.40], respectively). We observed poor inter-sonographer reliability for both global LV longitudinal strain and global LV circumferential strain with the two software systems. Inter-analyzer variability was good especially for the global LV circumferential strain using Philips software (ICC of 0.78 [IC95% 0.52–0.91]). In pediatrics, the Philips/GE inter-vendor level of variability in STE analysis is mainly due to inter ultrasound systems and inter sonographers’ differences. These results need to be taken into account when using STE analysis in the follow-up of cardiac children. Clinicaltrials.gov: NCT02056925.
关键词： Variability,Pediatrics,Inter-vendor,Pediatric cardiology,2D strain
更新于2025-09-23 15:23:52
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Study on sliding-window length based on Rayleigh backscattering spectrum correlation in distributed optical-fiber strain measurement
摘要： A theoretical model is established for estimating the strain measurement error based on the Rayleigh backscattering spectrum correlation in distributed optical fiber strain measurements. Assuming the signal is much larger than the noise, the theoretical model predicts the strain measurement error using noise variance and the defined quality factor Q of the Rayleigh backscattering spectrum. Furthermore, an algorithm based on the quality factor Q is proposed to select an optimized sliding-window. The sliding-window length can be obtained by calculating the threshold value of the quality factor using a theoretical model corresponding to the required strain measurement accuracy. Compared with the traditional method where the sliding-window length is defined by the user based on spatial resolution requirements or an empirical definition, the sliding-window length determined by the algorithm is more reasonable and can be automatically defined, alleviating the requirement for user inputs. To verify the correctness of the theoretical model, two experiments are set up: a self-correlation experiment, that analyzes the effect of the quality factor on the strain measurement accuracy, and a virtual experiment of the noise influence, which analyzes the effect of different noise variances. The experimental results are in good agreement with those of the model.
关键词： Distributed optical fiber strain measurement,Rayleigh backscattering spectrum correlation,Optical frequency domain reflectometer
更新于2025-09-23 15:23:52
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Impact of Substrate Characteristics on Stretchable Polymer Semiconductor Behavior
摘要： Stretchable conductive polymer films are required to survive not only large tensile strain but also stay functional after the reduction in applied strain. In the deformation process, the elastomer substrate that is typically employed plays a critical role in the response of the polymer film. In this study, we examine the role of a PDMS elastomer substrate on the ability to achieve stretchable PDPP-4T films. Specifically, we consider the adhesion and near surface modulus of the PDMS tuned through UV/ozone treatment on the competition between film wrinkling and plastic deformation. We also consider the role of PDMS tension on the stability of films under cyclic strain. We find that increasing the near-surface modulus of the PDMS and maintaining the PDMS in tension throughout the cyclic strain process promotes plastic deformation over film wrinkling. In addition, the UV/ozone treatment increases film adhesion to the PDMS resulting in significantly reduced film folding and delamination. For 20 min UV/ozone treated PDMS, we show that a PDPP-4T film RMS roughness is consistently below 3 nm for up to 100 strain cycles with a strain range of 40 %. In addition, while the film is plastically deforming, the microstructural order is largely stable as probed with grazing incidence X-ray scattering and UV-visible spectroscopy. These results highlight the importance of the neighboring elastomer characteristics on the ability to achieve stretchable polymer semiconductors.
关键词： Yield strain,Stretchable electronics,Deformability,Polymer semiconductors,Adhesion energy
更新于2025-09-23 15:23:52
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Superstructure Fiber Bragg Gratings for Simultaneous Temperature and Strain Measurement
摘要： A new and simple fiber optic sensor based on a superstructure fiber Bragg grating (SFBG) for simultaneous temperature and strain measurement is proposed. The SFBG is a superimposed grating for which a long period fiber grating (LPG) and a fiber Bragg grating (FBG) is written in the same section of a Corning SMF-28 fiber. The reflection spectrum of the SFBG possesses two resonant peaks and a trough. By measuring the wavelength shift of the main resonant peak and the reflection power change of the trough, temperature and strain can be determined simultaneously. The accuracy of the sensor in measuring strain and temperature is estimated to be ±13.01 με in a range from 0 με to 1000 με and ±0.75 ℃ from 20 ℃ to 100 ℃, respectively.
关键词： CO2 laser,SFBG,simultaneous measurement of temperature and strain,fiber optic sensor
更新于2025-09-23 15:23:52
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Thermally-stable large strain in Bi(Mn0.5Ti0.5)O3 modified 0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3 ceramics
摘要： A N U S C RIP T (1-x)[0.8Bi0.5Na0.5TiO3-0.2Bi0.5K0.5TiO3]-xBi(Mn0.5Ti0.5)O3 (x = 0 ~ 0.06, BNKMT100x) lead-free ferroelectric ceramics were prepared via solid state reaction method. Bi(Mn0.5Ti0.5)O3 induces a structure transition from rhombohedral-tetragonal morphotropic phases to pseudo-cubic phase. Moreover, the wide range of compositions within x = 0.03 ~ 0.055 exhibit large strain of 0.31% ~ 0.41% and electrostrictive coefficient of 0.027 ~ 0.041 m4/C2. Especially, at x = 0.04, the large strain and electrostrictive coefficient are nearly temperature-independent in the range of 25 ~ 100 °C. The impedance analysis shows the large strain and electrostrictive coefficient originate from polar nanoregions response due to the addition of Bi(Mn0.5Ti0.5)O3.
关键词： large strain,thermal stability,composition-insensitivity,lead-free,electric property
更新于2025-09-23 15:23:52
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The evolution of phase structure, dielectric, strain, and energy storage density of complex-ions (Sr1/3Nb2/3)4+ doped 0.82Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3 ceramics
摘要： Lead-free Bi0.5(Na0.82K0.18)0.5Ti1-x(Sr1/3Nb2/3)xO3 (abbreviated as BNKT-xSN, x = 0.02–0.045) ceramics were fabricated via the conventional ceramic process, and the (Sr1/3Nb2/3)4+ complex-ions were used to modify the phase transition and multifarious electrical responses of BNKT-xSN ceramics. The SN complex-ions absolutely incorporate into the lattice of BNKT matrix to form perovskite structure. The grain morphologies and size are almost unaffected by SN complex-ions. The phase transition concerning ferroelectric type transforming into ergodic relaxor happens with increasing SN content, and the corresponding critical point is x = 0.035. The phase transformation process results in the improvement of energy storage density (W = 0.754 J/cm3) at 80 kV/cm and a high bipolar strain (S = 0.25%) with small hysteresis. The dielectric constant at Tm peaks gradually decreases with increasing SN content, and the ferroelectric-relaxor transition temperature (TF-R) is depressed to room temperature. The evolution behaviors might facilitate our cognition about the mechanism between phase structure and multiple electrical properties of BNT-based ceramics.
关键词： BNT-BKT,(Sr1/3Nb2/3)4+,Phase transition,Field-induced strain,Energy storage
更新于2025-09-23 15:23:52
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An interferometric structure with a dual-resonance long period grating for strain sensing
摘要： Spectral characteristics and amplitude tunability of a long period grating with a dual-resonance inside fiber loop mirror are studied in terms of applied stress caused by elongation. Inserting the polarization controller between grating and part of polarization maintaining fiber in the loop structure enables tuning of resonance and interferometric peaks. The maximum sensitivity of demonstrated sensor is of 1.943 dB/mε for the range of 1.1–4.4 mε. Combination of these two optical components allows to measure strain in a wider range comparing with sensors based on standard long period grating.
关键词： Fiber loop mirror,Polarization controller,Polarization maintaining fiber,Strain sensor,Long period grating
更新于2025-09-23 15:23:52
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The role of dipole structure and their interaction on the electromechanical and actuation performance of homogeneous silicone dielectric elastomers
摘要： Grafting polar groups onto elastomer chains has proven to be an effective method to achieve high performance homogenous dielectric elastomers (DE). Up to now, there still lacks an in-depth understanding of the effect of structure and content of these grafted dipoles on the electromechanical properties of the modified DE. In this study, three kinds of polar groups including carboxyl (COOH), hydroxyl (OH), and ester (COOCH3) are grafted onto Polymethylvinylsiloxane (PMVS) by using a photochemical thiol-ene reaction to prepare PMVS-COOH, PMVS-OH and PMVS-COOCH3 DE. Three grafting degrees (15%, 50% and 95%) were prepared for each kind of modified PMVS. Interestingly, although the dipolar moment of COOH is higher than that of OH and COOCH3, at the same grafting degree, the dielectric constant of PMVS-OH is much higher than that of PMVS-COOCH3 and PMVS-COOH. At high grafting degree (50% and 95%), the actuated strain at a specific electric field of PMVS-OH is significantly higher than that of PMVS-COOH and PMVS-COOCH3. The actuated train at a 15 kV/mm sharply increases from 0.2% for PMVS to 9.1% for PMVS-OH with the grafting degree of 95%, higher than that of the commercial silicone DE and the new structured silicone DE reported previously. These dielectric, mechanical and actuated properties are affected by the combined effects of moment, mobility and interactions of these dipoles, which have been deeply discussed. The present study provides guidance for the preparation of high-performance homogeneous DE by rational designing the dipolar structure and content.
关键词： Polymethylvinylsiloxane,dipoles,electromechanical properties,thiol-ene click chemistry,dielectric elastomers,actuated strain
更新于2025-09-23 15:23:52