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During air bending of sheet metals, the correction of punch stroke for springback control is always implemented through repeated trial bending until achieving the forming accuracy of bending parts. In this study, a modelling method for correction of punch stroke is presented for guiding trial bending based on a data-driven technique. Firstly, the big data for the model are mainly generated from a large number of finite element simulations, considering many variables, e.g., material parameters, dimensions of V-dies and blanks, and processing parameters. Based on the big data, two punch stroke correction models are developed via neural network and dimensional analysis, respectively. The analytic comparison shows that the neural network model is more suitable for guiding trial bending of sheet metals than the dimensional analysis model, which has mechanical significance. The actual trial bending tests prove that the neural-network-based punch stroke correction model presents great versatility and accuracy in the guidance of trial bending, leading to a reduction in the number of trial bends and an improvement in the production efficiency of air bending.

In this paper, a sapphire-derived fiber (SDF) with a core diameter of 10 μm and a cladding diameter of 125 μm is fabricated by the melt-in-tube method, and fiber Bragg gratings (FBGs) with reflectivity over 80% are prepared by the femtosecond laser point-by-point direct writing method. By analyzing the refractive index distribution and reflection spectral characteristics of the SDF, it can be seen that the SDF is a graded refractive index few-mode fiber. In order to study the element composition of the SDF core, the end-face element distribution of the SDF is analyzed, which indicates that element diffusion occurred between the core and the cladding materials. The temperature and stress of the SDF gratings are measured and the highest temperature is tested to 1000 °C. The temperature and strain sensitivities are 15.64 pm/°C and 1.33 pm/με, respectively, which are higher than the temperature sensitivity of the quartz single-mode fiber. As a kind of special fiber, the SDF expands the application range of sapphire fiber, and has important applications in the fields of high-temperature sensing and high-power lasers.

Background Two-dimensional speckle-tracking echocardiography (2D-STE) enables objective assessment of left atrial (LA) deformation through the analysis of myocardial strain, which can be measured by different speckle-tracking software. The aim of this study was to compare the consistency of 3 different commercially available software, which include vendor-specific software for measuring left ventricle (VSSLV), vendor-independent software packages for measuring LV strain (VISLV) and vendor-independent software packages for measuring LA strain (VISLA). Methods Sixty-four subjects (mean age: 44 ± 16 years, 50% males) underwent conventional echocardiograms using a GE Vivid 9 (GE Ultrasound, Horten, Norway) cardiac ultrasound system. Standard apical 4 and 2 chamber views of the left atrium were obtained in each subject with a frame-rate range of 40–71 frames/s. LA strain during the contraction phase (Sct), conduit phase (Scd), reservoir phase (Sr = Sct + Scd) were analyzed by 2 independent observers and 3 different software. Results Sct, Scd, Sr were, respectively, − 11.26 ± 2.45%, − 16.77 ± 7.06%, and 28.03 ± 7.58% with VSSLV, − 14.77 ± 3.59%, − 23.17 ± 10.33%, and 38.23 ± 10.99% with VISLV, and − 14.80 ± 3.88%, − 23.94 ± 10.48%, and 38.73 ± 11.56% when VISLA was used. A comparison of strain measurements between VSSLV and VIS (VISLV and VISLA) showed VIS had significantly smaller mean differences and narrower limits of agreement. Similar results were observed in the coefficient of variation (CV) for measurements between VSSLV and VIS (VISLV and VISLA). Comparison of the intra-class correlation coefficients (ICCs) indicated that measurement reliability was weaker with VSSLV (ICC 0.9). For intra-observer ICCs, VISLA > VSSLV = VISLV. For inter-observer ICCs, VSSLV > VISLA > VISLV. Conclusions Software measurement results of LA strain vary considerably. We recommended not measuring LA strain across vendor platforms. Electronic supplementary material The online version of this article (10.1186/s12947-019-0158-y) contains supplementary material, which is available to authorized users.

In this paper, an energy regulation method based on the combination of a half-wave plate (HWP) and a polarization beam splitter (PBS) is proposed for the fabrication of apodized fiber gratings, which can effectively improve the side lobe suppression ratio of high-reflectivity fiber Bragg gratings (FBGs) fabricated by femtosecond laser. The apodized FBGs prepared by this method has good repeatability and flexibility. By inputting different types of apodization functions through the program, the rotation speed of the stepping motor can be adjusted synchronously, and then the position of the HWP can be accurately controlled so that the laser energy can be distributed as an apodization function along the axial direction of the fiber. By using the energy apodization method, the gratings with a reflectivity of 75% and a side lobe suppression ratio of 25 and 32 dB are fabricated in the fiber with a core diameter of 9 and 4.4 μm, respectively. The temperature and strain sensitivities of the energy-apodized fiber gratings with a core diameter of 4.4 μm are 10.36 pm/°C and 0.9 pm/με, respectively. The high-reflectivity gratings fabricated by this energy apodization method are expected to be used in high-power narrow-linewidth lasers and wavelength division multiplexing (WDM) systems.

A simple method for adjusting a chirped fiber Bragg gratings (CFBGs) with an external heater is proposed and demonstrated in experimental. A fiber grating is set in the heater that is composed with a series of resistance coils. Uniform or gradient temperature field around the grating is implement by designing the radius of resistance coils fixed or varied along the heater. The properties of the grating can be accurately tuned when varying the voltage applied to the resistance coils. In particular, the chirp and the central wavelength of the grating that is set in two different heaters can be adjusted separately by controlling the voltage in each of these heaters. The group delay of the CFBG is measured.

In this letter a simple method for fabricating tunable sampled nonlinearly chirped fiber Bragg gratings (SNCFBGs) is demonstrated experimentally. A SNCFBG is formed when tension is applied to an etched sampled fiber Bragg grating (SFBG), whose cross-section area's reciprocal varies along the length of the SFBG. The chirp of the grating period and the sampled period can be tuned by adjusting the strain gradients, and the dispersion and dispersion slope can also be compensated.

We present a new bend sensor which can measure the curvature using an etched fiber Bragg grating (FBG) embedded into a beam. The reflection power of the grating detected by an optical power meter varies linearly with the curvature of the beam. This sensor is in- dependent of temperature. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 414 - 417, 2004; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.20486

and 5.48 GHz, respectively. Obviously, both resonant frequencies significantly decrease. Taking another point of view, the area of the proposed semi-microstrip is much less than that of the conventional circular antenna, which operates at the fixed frequencies. The measured far-field radiation patterns at the two resonant frequencies for the case of S/R 0.5 are plotted in Figures 4 and in 5. Both the 1 st and 2 nd resonant frequencies have orthogonal polarization planes and broadside radiation patterns. However, the cross-polarization levels are different. Good cross-polarization levels for two principle planes at 4.26 GHz are obtained. But for 2.75 GHz, the H-plane cross-polarization is quite high. The different radiation patterns come from the difference of the surface current distributions of the two operating frequencies. From the simulation by IE3D, the current distribution of the 2 nd resonant frequency on the shorting plane has a direction similar to that of the semicircular patch. But for the first resonant frequency, the current distribution of the antenna is distorted. 3. CONCLUSION A semicircular microstrip antenna has been successfully implemented. The remarkable feature of the proposed antenna is dual frequency with a good impedance matching. As the width of the shorting plane decreases, the two operating frequencies are significantly reduced. Comparing with a conventional circular patch, the proposed antenna is smaller in size.

A novel temperature-independent strain sensor based on a fiber Bragg grating is demonstrated. The front section of the fiber Bragg grating is fixed to a crystal plate, and the other section is lin- early etched in HF acid. The reflected power of the grating varies lin- early with strain and is insensitive to temperature variation. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 324 -326, 2004; Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/mop.20458

In this paper, we report on high quality two-level phase-type Fresnel zone plates (FZPs) produced by femtosecond laser two-photon polymerization of the resin SU-8. The optical focusing property was tested using a simple experimental setup. Moreover, the lens imaging functions 'JLU' and '' (English and Chinese abbreviations for Jilin University) were also demonstrated. In order to further enhance the diffraction efficiency, four-level and eight-level FZPs were designed using theoretical calculation and rapidly realized by point-to-point femtosecond laser scanning. In this way, the diffractive efficiency was enhanced from 35.8% for the two-level phase lens to 67% for the four-level phase lens and 73.9% for the eight-level phase lens, which are the largest values reported so far.