Spatially variant regularization of lateral displacement measurement using variance

The purpose of this work is to confirm the effectiveness of our proposed spatially variant displacement component-dependent regularization for our previously developed ultrasonic two-dimensional (2D) displacement vector measurement methods, i.e., 2D cross-spectrum phase gradient method (CSPGM), 2D autocorrelation method (AM), and 2D Doppler method (DM). Generally, the measurement accuracy of lateral displacement spatially varies and the accuracy is lower than that of axial displacement that is accurate enough. This inaccurate measurement causes an instability in a 2D shear modulus reconstruction. Thus, the spatially variant lateral displacement regularization using the lateral displacement variance will be effective in obtaining an accurate lateral strain measurement and a stable shear modulus reconstruction than a conventional spatially uniform regularization. The effectiveness is verified through agar phantom experiments. The agar phantom [60 mm (height) × 100 mm (lateral width) × 40 mm (elevational width)] that has, at a depth of 10 mm, a circular cylindrical inclusion (dia. = 10 mm) of a higher shear modulus (2.95 and 1.43 × 10⁶ N/m², i.e., relative shear modulus, 2.06) is compressed in the axial direction from the upper surface of the phantom using a commercial linear array type transducer that has a nominal frequency of 7.5-MHz. Because a contrast-to-noise ratio (CNR) expresses the detectability of the inhomogeneous region in the lateral strain image and further has almost the same sense as that of signal-to-noise ratio (SNR) for strain measurement, the obtained results show that the proposed spatially variant lateral displacement regularization yields a more accurate lateral strain measurement as well as a higher detectability in the lateral strain image (e.g., CNRs and SNRs for 2D CSPGM, 2.36 vs 2.27 and 1.74 vs 1.71, respectively). Furthermore, the spatially variant lateral displacement regularization yields a more stable and more accurate 2D shear modulus reconstruction than the uniform regularization (however, for the regularized relative shear modulus reconstructions, slightly accurate, e.g., for 2D CSPGM, 1.51 vs 1.50). These results indicate that the spatially variant displacement component-dependent regularization will enable the 2D shear modulus reconstruction to be used as practical diagnostic and monitoring tools for the effectiveness of various noninvasive therapy techniques of soft tissue diseases (e.g., breast, liver cancers). Application of the regularization to the elevational displacement will also increase the stability of a three-dimensional (3D) reconstruction.     

CVD synthesis and radial deformations of large diameter single-walled CNTs

Single-walled carbon nanotubes (CNTs) were synthesized by a chemical vapor deposition (CVD) method on transmission electron microscopy (TEM) silica coated nickel grids using carbon monoxide as carbon source and iron nanoparticles as catalyst. The produced CNTs were as large as 11 nm in diameter. Investigations on the CNT deformations based on high-resolution TEM images showed that the deformation of CNTs due to their interaction with the substrate occurs at diameters larger than 2.7 nm. Small deformation of free standing tubes was found to occur at diameters above approximately 4.5 nm.     

Sequential beamforming for synthetic aperture imaging

Synthetic aperture sequential beamforming (SASB) is a novel technique which allows to implement synthetic aperture beamforming on a system with a restricted complexity, and without storing RF-data. The objective is to improve lateral resolution and obtain a more depth independent resolution compared to conventional ultrasound imaging. SASB is a two-stage procedure using two separate beamformers. The initial step is to construct and store a set of B-mode image lines using a single focal point in both transmit and receive. The focal points are considered virtual sources and virtual receivers making up a virtual array. The second stage applies the focused image lines from the first stage as input data, and take advantage of the virtual array in the delay and sum beamforming. The size of the virtual array is dynamically expanded and the image is dynamically focused in both transmit and receive and a range independent lateral resolution is obtained. The SASB method has been investigated using simulations in Field II and by off-line processing of data acquired with a commercial scanner. The lateral resolution increases with a decreasing F#. Grating lobes appear if F# ⩽ 2 for a linear array with λ-pitch. The performance of SASB with the virtual source at 20 mm and F# = 1.5 is compared with conventional dynamic receive focusing (DRF). The axial resolution is the same for the two methods. For the lateral resolution there is improvement in FWHM of at least a factor of 2 and the improvement at −40 dB is at least a factor of 3. With SASB the resolution is almost constant throughout the range. For DRF the FWHM increases almost linearly with range and the resolution at −40 dB is fluctuating with range. The theoretical potential improvement in SNR of SASB over DRF has been estimated. An improvement is attained at the entire range, and at a depth of 80 mm the improvement is 8 dB.     

A novel polarization splitter in ZnTe tellurite glass three-core photonic crystal fiber

A kind of polarization splitter in ZnTe tellurite glass three-core photonic crystal fiber has been proposed. The polarization splitter is based on the phenomenon of resonant tunneling. We use the finite element method and the full-vector beam propagating method to analyze the characteristics of three-core photonic crystal fiber. Compare with the silica glass three-core PCF, the ZnTe tellurite glass three-core PCF have higher extinction ratios and lower coupling loss, the extinction ratios ERA = ? 164.2681 dB and ERC = ? 37.1742 dB at the wavelength λ = 1.55 μm, and the coupling loss is lower than 0.02 dB. The 8.7983-mm-long splitter is proposed to achieve extinction ratio better than ? 20 dB and a bandwidthof 20 nm.     

Novel optical add-drop multiplexer based on dual racetrack resonators

In this paper, we designed and fabricated a four-channel optical add-drop multiplexer (OADM) based on dual racetrack resonators. The size of the fabricated device is only 2400 μm × 500 μm. The fabricated device can effectively and perfectly realize the signals upload and download. The free spectral range (FSR) of OADM is about 15.2 nm. We take the spectral responses near 1555 nm as an example. When the device acts as an optical drop multiplexer, the minimum insertion loss is 4.481 dB and the maximum extinction ratio is 31.931 dB. The maximum adjacent channels crosstalk is -9.845 dB. When the device acts as an optical add multiplexer, the minimum insertion loss is 0.944 dB and all of the extinction ratios are bigger than 25 dB. The maximum crosstalk is -16.531 dB which indicates the crosstalk can be neglected.     

In-situ strain localization analysis in low density transformation-twinning induced plasticity steel using digital image correlation

The effect of deformation temperature on the strain localization has been evaluated by an adapted digital image correlation (DIC) technique during tensile deformation. The progress of strain localization was traced by the corresponding strain maps. The electron backscatter diffraction analysis and tint etching technique were utilized to determine the impact of martensitic transformation and deformation twinning on the strain localization in both elastic and plastic regimes. In elastic regime the narrow strain bands which are aligned perpendicular to the tension direction were observed in temperature range of 25 to 180 °C due to the stress-assisted epsilon martensite. The strain bands were disappeared by increasing the temperature to 300 °C and reappeared at 400 °C due to the stress-assisted deformation twinning. In plastic regime strain localization continued at 25 °C and 180 °C due to the strain-induced alfa-martensite and deformation twinning, respectively. The intensity of plastic strain localization was increased by increasing the strain due to the enhancement of martensite and twin volume fraction. The plastic strain showed more homogeneity at 300 °C due to the lack of both strain-induced martensite and deformation twinning.     

Ab initio study of shear strain effects on ferroelectricity at PbTiO3 thin films

Ferroelectric thin film with the perovskite ABO₃ structure have been widely used in technology applications, e.g., actuators in MEMS/NEMS and nonvolatile random access memories (FeRAM). In order to clarify the effect of the shear strain on the ferroelectricity, the PbTiO₃ thin film as a typical one is chosen. The focus of this study is to put on the PbO-terminated (1? × ?1) and c(2? × ?2) surfaces and the TiO₂-terminated (1? × ?1) surface. Based on ab initio density functional theory calculations with the local density approximation, we have found out that in both the PbO and TiO₂-terminated (1? × ?1) models, the ferroelectricity in the PbO layers was enhanced under the positive shear strain while it was suppressed under the negative one. For the TiO₂ layers, the ferroelectricity was slightly enhanced and sharply suppressed under the positive and negative shear strains, respectively. In the PbO-terminated (2? × ?2) model, the AFE phase was suppressed by the FE phase under the positive shear strain while the opposite trend was found under the negative shear strain. For the PbO layers, the ferroelectricity was enhanced under the positive and negative shear strains. For the TiO₂ layers, the influence of the negative shear strain on the ferroelectricity was larger than that of the positive one. In addition, the ideal strength of the PbTiO₃ thin film with the different terminations was investigated as well.     

Deconvolution of vibroacoustic images using a simulation model based on a three dimensional point spread function

Vibro-acoustography (VA) is a medical imaging method based on the difference-frequency generation produced by the mixture of two focused ultrasound beams. VA has been applied to different problems in medical imaging such as imaging bones, microcalcifications in the breast, mass lesions, and calcified arteries. The obtained images may have a resolution of 0.7–0.8 mm. Current VA systems based on confocal or linear array transducers generate C-scan images at the beam focal plane. Images on the axial plane are also possible, however the system resolution along depth worsens when compared to the lateral one. Typical axial resolution is about 1.0 cm. Furthermore, the elevation resolution of linear array systems is larger than that in lateral direction. This asymmetry degrades C-scan images obtained using linear arrays. The purpose of this article is to study VA image restoration based on a 3D point spread function (PSF) using classical deconvolution algorithms: Wiener, constrained least-squares (CLSs), and geometric mean filters. To assess the filters’ performance on the restored images, we use an image quality index that accounts for correlation loss, luminance and contrast distortion. Results for simulated VA images show that the quality index achieved with the Wiener filter is 0.9 (when the index is 1.0 this indicates perfect restoration). This filter yielded the best result in comparison with the other ones. Moreover, the deconvolution algorithms were applied to an experimental VA image of a phantom composed of three stretched 0.5 mm wires. Experiments were performed using transducer driven at two frequencies, 3075 kHz and 3125 kHz, which resulted in the difference-frequency of 50 kHz. Restorations with the theoretical line spread function (LSF) did not recover sufficient information to identify the wires in the images. However, using an estimated LSF the obtained results displayed enough information to spot the wires in the images. It is demonstrated that the phase of the theoretical and the experimental PSFs are dissimilar. This fact prevents VA image restoration with the current theoretical PSF. This study is a preliminary step towards understanding the restoration of VA images through the application of deconvolution filters.     

A surface-plasmon-polariton wavelength splitter based on a metal–insulator–metal waveguide

A surface-plasmon-polariton (SPP) wavelength splitter based on a metal–insulator–metal waveguide with multiple teeth is proposed. Using the transfer-matrix method, a plasmonic band gap is identified in the multiple-toothed structure, and the splitting wavelength of the SPP splitter can be easily adapted by adjusting the widths of the teeth and the gaps. The proposed wavelength splitter is further verified through finite-difference time-domain (FDTD) simulations, in which SPPs with incident wavelengths of 756 nm and 892 nm are successfully split and guided in opposite directions in the waveguide, with extinction ratios of 30 dB and 29 dB, respectively.     

Multispectral 3D phase-encoded turbo spin-echo for imaging near metal: Limitations and possibilities demonstrated by simulations and phantom experiments

To see improvements in the imaging performance near biomaterial implants we assessed a multispectral fully phase-encoded turbo spin-echo (ms3D-PE-TSE) sequence for artifact reduction capabilities and scan time efficiency in simulation and phantom experiments.For this purpose, ms3D-PE-TSE and ms3D-TSE sequences were implemented to obtain multispectral images (± 20 kHz) of a cobalt-chromium (CoCr) knee implant embedded in agarose. In addition, a knee implant computer model and the acquired ms3D-PE-TSE images were used to investigate the possibilities for scan time acceleration using field-of-view (FOV) reduction for off-resonance frequency bins and compressed sensing reconstructions of undersampled data. Both acceleration methods were combined to acquire a + 10 kHz frequency bin in a second experiment.The obtained ms3D-PE-TSE images showed no susceptibility related artifacts, while ms3D-TSE images suffered from hyper-intensity artifacts. The limitations of ms3D-TSE were apparent in the far off-resonance regions (±[10–20] kHz) located close to the implant. The scan time calculations showed that ms3D-PE-TSE can be applied in a clinically relevant timeframe (~ 12 min), when omitting the three central frequency bins. The feasibility of CS acceleration for ms3D-PE-TSE was demonstrated using retrospective reconstructions before combining CS and rFOV imaging to decrease the scan time for the + 10 kHz frequency bin from ~ 10.9 min to ~ 3.5 min, while also increasing the spatial resolution fourfold. The temporally resolved signal of ms3D-PE-TSE proved to be useful to decrease the intensity ripples after sum-of-squares reconstructions and increase the signal-to-noise ratio.The presented results suggest that the scan time limitations of ms3D-PE-TSE can be sufficiently addressed when focusing on signal acquisitions in the direct vicinity of metal implants. Because these regions cannot be measured with existing multispectral methods, the presented ms3D-PE-TSE method may enable the detection of inflammation or (pseudo-)tumors in locations close to the implant.     

All-fiber intermodal Mach–Zehnder interferometer based on a long-period fiber grating combined with a fiber bitaper

We report a novel all-fiber narrow-bandwidth intermodal Mach–Zehnder interferometer (MZI) based on a long-period fiber grating (LPFG) combined with a fiber bitaper, and the MZI has no special limit for the resonant wavelength of the LPFG. Its responses to temperature and axial strain are studied theoretically and experimentally. Experimental results indicate that the temperature sensitivity is 0.0585 nm/°C within the temperature range from 30 °C to 90 °C and the axial strain sensitivity of 0.00013 nm/με can be neglected. Furthermore, as only the common single-mode fiber (SMF) is required during the fabrication process, the proposed device is cost effective and has good practicability in the optical sensing systems.     

Feasibility of MR elastography of the intervertebral disc

Low back pain (LBP) is a costly and widely prevalent health disorder in the U.S. One of the most common causes of LBP is degenerative disc disease (DDD). There are many imaging techniques to characterize disc degeneration; however, there is no way to directly assess the material properties of the intervertebral disc (IVD) within the intact spine. Magnetic resonance elastography (MRE) is an MRI-based technique for non-invasively mapping the mechanical properties of tissues in vivo. The purpose of this study was to investigate the feasibility of using MRE to detect shear wave propagation in and determine the shear stiffness of an axial cross-section of an ex vivo baboon IVD, and compare with shear displacements from a finite element model of an IVD motion segment in response to harmonic shear vibration. MRE was performed on two baboon lumbar spine motion segments (L3–L4) with the posterior elements removed at a range of frequencies (1000–1500 Hz) using a standard clinical 1.5 T MR scanner. Propagating waves were visualized in an axial cross-section of the baboon IVDs in all three motion-encoding directions, which resembled wave patterns predicted using finite element modeling. The baboon nucleus pulposus showed an average shear stiffness of 79 ± 15 kPa at 1000 Hz. These results suggest that MRE is capable of visualizing shear wave propagation in the IVD, assessing the stiffness of the nucleus of the IVD, and can differentiate the nucleus and annulus regions.     

A gain-clamped-semiconductor-optical-amplifier combined with a distributed Raman-fiber-amplifier: a good candidate as an inline amplifier for WDM networks

A gain-clamped semiconductor optical amplifier (SOA) is used as an inline amplifier in combination with a distributed Raman fiber amplifier. The combined amplifier has 20 dB gain and a noise figure below 2.7 dB. The optical signal to noise ratios after five spans of 20 dB loss, equivalent to 5 × 80 km, are over 25.2 dB for eight-channel transmissions. In addition, the potentially compact amplifier shows negligible transients under dynamic add-drops.     

Modeling and deformation analyzing of InSb focal plane arrays detector under thermal shock

A higher fracture probability appearing in indium antimonide (InSb) infrared focal plane arrays (IRFPAs) subjected to the thermal shock test, restricts its final yield. In light of the proposed equivalent method, where a 32 × 32 array is employed to replace the real 128 × 128 array, a three-dimensional modeling of InSb IRFPAs is developed to explore its deformation rules. To research the damage degree to the mechanical properties of InSb chip from the back surface thinning process, the elastic modulus of InSb chip along the normal direction is lessened. Simulation results show when the out-of-plane elastic modulus of InSb chip is set with 30% of its Young’s modulus, the simulated Z-components of strain distribution agrees well with the top surface deformation features in 128 × 128 InSb IRFPAs fracture photographs, especially with the crack origination sites, the crack distribution and the global square checkerboard buckling pattern. Thus the Z-components of strain are selected to explore the deformation rules in the layered structure of InSb IRFPAs. Analyzing results show the top surface deformation of InSb IRFPAs originates from the thermal mismatch between the silicon readout integrated circuits (ROIC) and the intermediate layer above, made up of the alternating indium bump array and the reticular underfill. After passing through both the intermediate layer and the InSb chip, the deformation amplitude is reduced firstly from 2.23 μm to 0.24 μm, finally to 0.09 μm. Finally, von Mises stress criterion is employed to explain the causes that cracks always appear in the InSb chip.     

The geometries of coadsorbate layers of O and H on Ru(0 0 1): How well can quantitative LEED see hydrogen atoms?

Using a CCD LEED system for the collection of IV data with low beam damage, and full dynamical as well as tensor LEED calculations, we have determined the geometries of the (2 × 2)-(O + 3H) and the (2 × 2)-(O + H) coadsorbate structures on Ru(0 0 1). We show that here quantitative LEED can locate the H atoms very well. Not only their sites (hcp in the first, fcc in the second case), but also the Ru–H spacings and changes in the first two substrate layers are clearly determined. We argue that this success is due to the relatively large data range and to the smaller H mobility compared to pure H layers caused by their repulsive lateral interactions with the oxygen atoms.     

Numerical analysis of a direct UV-written 1 × 8 double smooth octagon microrings resonant wavelength demulti/multiplexer

A microring resonant wavelength demulti/multiplexer (MRRWDM) based on UV-written technology is designed. By using a double smooth octagon microrings structure, a 1 × 8 device around the central wavelength of 1550.918 nm with the wavelength spacing of 1.4 nm is presented. Analytical results based on coupled mode theory show that the 3 dB bandwidth is about 0.22 nm, the insertion loss is less than 0.7 dB, and the crosstalk is below ?47 dB for every output channel of the designed device without tolerances.     

V-band directional tandem coupler of monolithic uniplanar structure

We present a uniplanar coplanar-waveguide 3-dB tandem coupler operating at V-band frequencies. The uniplanar structure is monolithically fabricated by using two-section parallel-coupled lines and air-bridge crossovers replacing the conventional multilayer or bonded structures. Due to an optimized tandem structure and non-bonded crossovers minimizing the parasitic components, a maximum coupling of 2.5 dB is measured at 62 GHz with a 2 dB bandwidth of 83%, while a high directivity factor of 33 dB is simultaneously obtained at 58–62 GHz. Over the entire design frequency range of 30–90 GHz, we achieve good phase unbalance of 90 ± 6.0°, as well as return loss and isolation lower than −23 and −16 dB, respectively.     

56 dB Gain EYDFA with improved noise figure with dual-stage partial double pass configuration

An efficient erbium/ytterbium co-doped fiber amplifier (EYDFA) is demonstrated by using a dual-stage partial double pass structure with a band pass filter (BPF). The amplifier achieves the maximum small signal gain of 56 dB and the corresponding noise figure of 4.66 dB at 1536 nm with an input signal power and total pump power of ?50 dBm and 140 mW, respectively. Compared with a conventional single-stage amplifier, the maximum gain enhancement of 16.99 dB is obtained at 1544 nm with the corresponding noise figure is improved by 2 dB. The proposed amplifier structure only uses a single pump source with a partial double pass scheme to provide a high gain and dual-stage structure to provide the low noise figure.     

Polarization-independent rapidly tunable optical add-drop multiplexer utilizing non-polarizing beam splitters in Ti:LiNbO3

A polarization-independent four-port wavelength-tunable optical add drop multiplexer (OADM) that utilizes non-polarizing relaxed beam splitters has been analyzed and demonstrated in Ti:LiNbO₃ at the 1530 nm wavelength regime. The design utilizes an asymmetric interferometer configuration with strain induced index grating for polarization coupling along its arms that are shifted in position relative to each other. Experimental results of the filter response agree with theoretical predictions. Electrooptic tuning over a range of 15.7 nm at a rate of 0.08 nm/V has been measured. A temporal response < 46 ns to a 20 V step change in tuning voltage has been demonstrated. Fiber-to-fiber insertion loss is ~ 6.5 dB.     

FPGA implementation of real-time SENSE reconstruction using pre-scan and Emaps sensitivities

Sensitivity Encoding (SENSE) is a widely used technique in Parallel Magnetic Resonance Imaging (MRI) to reduce scan time. Reconfigurable hardware based architecture for SENSE can potentially provide image reconstruction with much less computation time. Application specific hardware platform for SENSE may dramatically increase the power efficiency of the system and can decrease the execution time to obtain MR images. A new implementation of SENSE on Field Programmable Gate Array (FPGA) is presented in this study, which provides real-time SENSE reconstruction right on the receiver coil data acquisition system with no need to transfer the raw data to the MRI server, thereby minimizing the transmission noise and memory usage. The proposed SENSE architecture can reconstruct MR images using receiver coil sensitivity maps obtained using pre-scan and eigenvector (E-maps) methods. The results show that the proposed system consumes remarkably less computation time for SENSE reconstruction, i.e., 0.164 ms @ 200 MHz, while maintaining the quality of the reconstructed images with good mean SNR (29 + dB), less RMSE (< 5 × 10^− 2) and comparable artefact power (< 9 × 10^− 4) to conventional SENSE reconstruction. A comparison of the center line profiles of the reconstructed and reference images also indicates a good quality of the reconstructed images. Furthermore, the results indicate that the proposed architectural design can prove to be a significant tool for SENSE reconstruction in modern MRI scanners and its low power consumption feature can be remarkable for portable MRI scanners.