Measurement of strain and strain rate by echocardiography - Ready for prime time?

Strain and strain rate (SR) are measures of deformation that are basic descriptors of both the nature and the function of cardiac tissue. These properties may now be measured using either Doppler or two-dimensional ultrasound techniques. Although these measurements are feasible in routine clinical echocardiography, their acquisition and analysis nonetheless presents a number of technical challenges and complexities. Echocardiographic strain and SR imaging has been applied to the assessment of resting ventricular function, the assessment of myocardial viability using low-dose dobutamine infusion, and stress testing for ischemia. Resting function assessment has been applied in both the left and the fight ventricles, and may prove particularly valuable for identifying myocardial diseases and following up the treatment response. Although the evidence base is limited, SR imaging seems to be feasible and effective for the assessment of myocardial viability. The use of the technique for the detection of ischemia during stress echocardiography is technically challenging and likely to evolve further. The clinical availability of strain and SR measurement may offer a solution to the ongoing need for quantification of regional and global cardiac function. Nonetheless, these techniques are susceptible to artifact, and further technical development is necessary.

Simultaneous temperature and strain measurement with enhanced resolution up to 20 times by using a compact hybrid optical waveguide Bragg grating

A hybrid waveguide Bragg grating in optical fiber was fabricated and characterized, showing thermal responsivity of 211pm/°C. Proposed being used in fiber sensor, it demonstrates enhanced resolution by 20x and 2x for temperature and strain.

Effectively simultaneous temperature and strain measurement utilising a dual-grating sensor formed by type IA and type IIA FBGs

In this paper, we report a systematic investigation of the dependence of both temperature and strain sensitivities on the jiber Bragg grating (FBG) type, including the wellknown Type I, Type IIA, and a new type which we have designated Type 1.4, using both hydrogen-Ji-ee and hydrogenated B/Ge codoped jibers. We have identijed distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, duul-parameter sensor device. Three dual-grating sensing schemes with different combinations of gruting types have been constructed and compared. The Type IA-Type IIA combination exhibits the best pe$ormance and is superior to that of previously reported gruting-based structures. The characteristics of the measurement errors in such dualgrating sensor systems is also presented in detail.

Simultaneous temperature and strain measurement with enhanced resolution up to 20 times by using a compact hybrid optical waveguide Bragg grating

A hybrid waveguide Bragg grating in optical fiber was fabricated and characterized, showing thermal responsivity of 211pm/°C. Proposed being used in fiber sensor, it demonstrates enhanced resolution by 20x and 2x for temperature and strain.

Simultaneous measurement of strain and temperature using the first- and second-order diffraction wavelengths of Bragg gratings

A method of discriminating between temperature and strain effects in fibre sensing using a conventionally written, in-fibre Bragg grating is presented. The technique uses wavelength information from the first and second diffraction orders of the grating element to determine the wavelength dependent strain and temperature coefficients, from which independent temperature and strain measurements can be made. The authors present results that validate this matrix inversion technique and quantify the strain and temperature errors which can arise for a given uncertainty in the measurement of the reflected wavelength.

Simultaneous measurement of temperature and strain: cross sensitivity considerations

Interferometric sensors using optical fibers as a transduction medium have been shown to be sensitive to a variety of physical measurands. A result of this is that the resolution of a system designed to sense strain, for example, may be compromised by fluctuations in the temperature of the environment. The possibility of simultaneously determining the strain and temperature applied to the same piece of highly birefringent fiber is discussed. Second-order effects are shown to be important for long sensing lengths or in the presence of high strains or temperature changes. The results of experiments carried out to verify the theoretical predictions are also described.

Direct measurement of coherency limits for strain relaxation in heteroepitaxial core/shell nanowires

The growth of heteroepitaxially strained semiconductors at the nanoscale enables tailoring of material properties for enhanced device performance. For core/shell nanowires (NWs), theoretical predictions of the coherency limits and the implications they carry remain uncertain without proper identification of the mechanisms by which strains relax. We present here for the Ge/Si core/shell NW system the first experimental measurement of critical shell thickness for strain relaxation in a semiconductor NW heterostructure and the identification of the relaxation mechanisms. Axial and tangential strain relief is initiated by the formation of periodic a/2 〈110〉 perfect dislocations via nucleation and glide on {111} slip-planes. Glide of dislocation segments is directly confirmed by real-time in situ transmission electron microscope observations and by dislocation dynamics simulations. Further shell growth leads to roughening and grain formation which provides additional strain relief. As a consequence of core/shell strain sharing in NWs, a 16 nm radius Ge NW with a 3 nm Si shell is shown to accommodate 3% coherent strain at equilibrium, a factor of 3 increase over the 1 nm equilibrium critical thickness for planar Si/Ge heteroepitaxial growth. © 2012 American Chemical Society.

Effectively simultaneous temperature and strain measurement utilising a dual-grating sensor formed by type IA and type IIA FBGs

In this paper, we report a systematic investigation of the dependence of both temperature and strain sensitivities on the jiber Bragg grating (FBG) type, including the wellknown Type I, Type IIA, and a new type which we have designated Type 1.4, using both hydrogen-Ji-ee and hydrogenated B/Ge codoped jibers. We have identijed distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, duul-parameter sensor device. Three dual-grating sensing schemes with different combinations of gruting types have been constructed and compared. The Type IA-Type IIA combination exhibits the best pe$ormance and is superior to that of previously reported gruting-based structures. The characteristics of the measurement errors in such dualgrating sensor systems is also presented in detail.

Simultaneous measurement of strain and temperature using the first- and second-order diffraction wavelengths of Bragg gratings

A method of discriminating between temperature and strain effects in fibre sensing using a conventionally written, in-fibre Bragg grating is presented. The technique uses wavelength information from the first and second diffraction orders of the grating element to determine the wavelength dependent strain and temperature coefficients, from which independent temperature and strain measurements can be made. The authors present results that validate this matrix inversion technique and quantify the strain and temperature errors which can arise for a given uncertainty in the measurement of the reflected wavelength.

Simultaneous measurement of strain and curvature using superstructure fibre Bragg gratings

We report the first demonstration of the simultaneous measurement of strain and curvature, with temperature compensation, using a single superstructure fibre Bragg grating (SFBG). The SFBG exhibits the properties of both the fibre Bragg grating (FBG) and the long period fibre grating (LPG) such that its spectral response facilitates strain measurement from the wavelength shift of the FBG-like characteristic, and independent measurement of curvature from the LPG-like mode-splitting characteristic. The dependence of the LPG mode-splitting on the mode order has also been investigated and utilised for the measurement of very small curvatures.

Simultaneous strain and temperature measurement of advanced 3-D braided composite materials using an improved EFPI/FBG system

Simultaneous strain and temperature measurement for advanced 3-D braided composite materials using fibre-optic sensor technology is demonstrated, for the first time. These advanced 3-D braided composites can virtually eliminate the most serious problem of delamination for conventional composites. A tandem in-fibre Bragg-grating (FBG)/extrinsic Fabry-Perot interferometric sensor (EFPI) system with improved accuracy has been used to facilitate simultaneous temperature and strain measurement in this work. The non-symmetric distortion of the optical spectrum of the FBG, due to the combination of the FBG and the EFPI, is observed for the first time. Experimental and theoretical studies indicate that this type of distortion can affect the measurement accuracy seriously and it is mainly caused by the modulation of the periodic output of the EFPI. A simple method has been demonstrated to improve the accuracy for detection of the wavelength-shift of the FBG induced by temperature change. A strain accuracy of ∼ ±20 με and a temperature accuracy of ∼ ±1 °C have been achieved, which can meet the requirements for practical applications of 3-D braided composites. © 2002 Elsevier Science Ltd. All rights reserved.

Fiber grating type dependence of temperature and strain coefficients and application to simultaneous temperature and strain measurement

Although fiber Bragg gratings (FBGs) have been widely used as advanced optical sensors, the cross-sensitivity between temperature and strain has complicated independent measurement procedures for these two measurands. We report here, for the first time to our knowledge, the results of a systematic investigation of the dependence of both temperature and strain sensitivities on the grating type, including the well-known Type I, Type IIA, and a new type which we have designated Type IA, using both hydrogen-free and hydrogenated B/Ge codoped fibers. We have identified distinct sensitivity characteristics for each grating type, and we have utilised them to implement a novel dual-grating, dual-parameter sensor device with performance superior to that of previously reported grating-based structures.

Phase-shifted fiber Bragg grating for strain measurement at extreme conditions

In this work, a phase-shifted fiber Bragg grating is proposed for strain sensing at extreme temperatures. The grating structure is written in bare standard single mode fiber, using the point-by-point femtosecond laser technique. Strain measurements are performed at temperatures ranging from room temperature up to 900°C. By subjecting the sensor to such extreme conditions, the wavelength of the grating increases. © 2014 OSA.

Direct measurement of intrinsic atomic scale magnetostriction

Using differential x-ray absorption spectroscopy (DiffXAS) we have measured and quantified the intrinsic, atomic-scale magnetostriction of Fe(81)Ga(19). By exploiting the chemical selectivity of DiffXAS, the Fe and Ga local environments have been assessed individually. The enhanced magnetostriction induced by the addition of Ga to Fe was found to originate from the Ga environment, where lambda(gamma,2)(approximate to (3/2)lambda(100)) is 390 +/- 40 ppm. In this environment, < 001 > Ga-Ga pair defects were found to exist, which mediate the magnetostriction by inducing large strains in the surrounding Ga-Fe bonds. For the first time, intrinsic, chemically selective magnetostrictive strain has been measured and quantified at the atomic level, allowing true comparison with theory.