Superior Noise Characteristics Research Articles

CoFeBX layers for MgO-based magnetic tunnel junction sensors with improved magnetoresistance and noise performance

Magnetoresistive sensors have been enthusiastically selected for applications requiring magnetic field detection with small footprint sensors. The optimisation of the sensor response includes using soft magnetic free layers, based on CoFeB and NiFe alloys. Here we report the TMR and noise performance of magnetically saturated in-plane MTJ sensors including CoFeBTa and CoFeSiB soft magnetic films as free layers (FL). Assessing magneto-crystalline anisotropy μ0Hk values of 2.1 and 0.7 mT in CoFeB 2.5 (nm)/Ru 0.2/CoFeBTa 4 and CoFeB 3/Ru 0.2/CoFeSiB 4 compared to 1.7 mT in CoFeB 2.5/Ru 0.2/NiFe 4, together with an improved magnetoresistance of 230% in CoFeBSi comparing with 170% (NiFe) with superior noise characteristics, with Hooge parameter of αH = 7 × 10−11 μm2.

Low-noise octave-spanning mid-infrared supercontinuum generation in a multimode chalcogenide fiber.

We demonstrate the generation of a low-noise, octave-spanning mid-infrared supercontinuum from 1700 to 4800 nm by injecting femtosecond pulses into the normal dispersion regime of a multimode step-index chalcogenide fiber with 100 µm core diameter. We conduct a systematic study of the intensity noise across the supercontinuum spectrum and show that the initial fluctuations of the pump laser are at most amplified by a factor of three. We also perform a comparison with the noise characteristics of an octave-spanning supercontinuum generated in the anomalous dispersion regime of a multimode fluoride fiber with similar core size and show that the normal dispersion supercontinuum in the multimode chalcogenide fiber has superior noise characteristics. Our results open up novel perspectives for many practical applications such as long-distance remote sensing where high power and low noise are paramount.

Infrared Degenerate Four-wave Mixing with Upconversion Detection for Quantitative Gas Sensing.

We present a protocol for performing gas spectroscopy using infrared degenerated four-wave mixing (IR-DFWM), for the quantitative detection of gas species in the ppm-to-single-percent range. The main purpose of the method is the spatially resolved detection of low-concentration species, which have no transitions in the visible or near-IR spectral range that could be used for detection. IR-DFWM is a nonintrusive method, which is a great advantage in combustion research, as inserting a probe into a flame can change it drastically. The IR-DFWM is combined with upconversion detection. This detection scheme uses sum-frequency generation to move the IR-DFWM signal from the mid-IR to the near-IR region, to take advantage of the superior noise characteristics of silicon-based detectors. This process also rejects most of the thermal background radiation. The focus of the protocol presented here is on the proper alignment of the IR-DFWM optics and on how to align an intracavity upconversion detection system.

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

MO‐PIS‐Exhibit Hall‐01: Imaging: CT Dose Optimization Technologies I

Pulsed-ASE-seeded DWDM optical system with interferometric noise suppression

We propose and demonstrate a 10-Gb/s dense wavelength-division-multiplexing (DWDM) optical system based on a pulsed-seed-light source employing a fiber-based Mach-Zehnder interferometer (F-MZI) as an intensity noise suppressor. The transmission results show that the required injection power into a reflective modulator was as low as -18 dBm. The F-MZI can accommodate the polarized seed-light with superior noise characteristics so that the supported DWDM systems double using a single conventional unpolarized seed-light. In addition, an allowable length of the drop fiber is investigated to show the system flexibility.

유연 복합재료 프로펠러 제작개선 및 성능분석

It is well known that flexible composite material propeller has superior radiation noise characteristics with outstanding damping effects. In this paper, three flexible composite material propellers were produced using compression molding process, and their hydrodynamic performances and radiation noise characteristics were measured. One propeller, C1, was made up from carbon/epoxy composite laminates, and the other two ones, G1 and G2, from glass/epoxy ones. Their fiber arrays were selected by the progressive damage structural analysis of propellers using composite material model MAT_162 (Composite_DMG_MSC) linked with LS-DYNA code. Carbon/epoxy and glass/epoxy composite specimen tests were performed, their damage mechanisms were figured out, and their parameters were calibrated by their progressive damage structural analysis according to their damage criteria.

Design Overview of a Three Kilowatt Recuperated Ceramic Turboshaft Engine

A three kilowatt turboshaft engine with a ceramic recuperator and turbine has been designed for small unmanned air vehicle (UAV) propulsion and portable power generation. Compared with internal combustion (IC) engines, gas turbines offer superior reliability, engine life, noise and vibration characteristics, and compatibility with military fuels. However, the efficiency of miniature gas turbines must be improved substantially, without severely compromising weight and cost, if they are to compete effectively with small IC engines for long-endurance UAV propulsion. This paper presents a design overview and supporting analytical results for an engine that could meet this goal. The system architecture was chosen to accommodate the limitations of mature, cost-effective ceramic materials: silicon nitride for the turbine rotors and toughened mullite for the heat exchanger and turbine stators. An engine with a cycle pressure ratio below 2:1, a multistage turbine, and a highly effective recuperator is shown to have numerous advantages in this context. A key benefit is a very low water vapor-induced surface recession rate for silicon nitride, due to an extremely low partial pressure of water in the combustion products. Others include reduced sensitivity to internal flaws, creep, and foreign object damage; an output shaft speed low enough for grease-lubricated bearings; and the potential viability of a novel premixed heat-recirculating combustor.

An InGaP/GaAs HBT Based Differential Colpitts VCO with Low Phase Noise

An InGaP/GaAs HBT based differential Colpitts voltage control oscillator(VCO) is presented in this paper. In the VCO core, two switching transistors are introduced to steer the core bias current to save power. An LC tank with an inductor quality factor(Q) of 11.4 is used to generate oscillation frequency. It has a superior phase noise characteristics of -130.12 dBc/Hz and -105.3 at 1 MHz and 100 kHz frequency offsets respectively from the carrier frequency(1.566 GHz) when supplied with a control voltage of 0 volt. It dissipates output power of -5.3 dBm. Two pairs of on-chip base collector (BC) diodes are used in the tank circuit to increase the VCO tuning range(168 MHz). This VCO occupies the area of <TEX>$1.070{\times}0.90mm^2$</TEX> including buffer and pads.

Extending Three-Dimensional Weighted Cone Beam Filtered Backprojection (CB-FBP) Algorithm for Image Reconstruction in Volumetric CT at Low Helical Pitches

A three-dimensional (3D) weighted helical cone beam filtered backprojection (CB-FBP) algorithm (namely, original 3D weighted helical CB-FBP algorithm) has already been proposed to reconstruct images from the projection data acquired along a helical trajectory in angular ranges up to [0, 2 π]. However, an overscan is usually employed in the clinic to reconstruct tomographic images with superior noise characteristics at the most challenging anatomic structures, such as head and spine, extremity imaging, and CT angiography as well. To obtain the most achievable noise characteristics or dose efficiency in a helical overscan, we extended the 3D weighted helical CB-FBP algorithm to handle helical pitches that are smaller than 1: 1 (namely extended 3D weighted helical CB-FBP algorithm). By decomposing a helical over scan with an angular range of [0, 2π + Δβ] into a union of full scans corresponding to an angular range of [0, 2π], the extended 3D weighted function is a summation of all 3D weighting functions corresponding to each full scan. An experimental evaluation shows that the extended 3D weighted helical CB-FBP algorithm can improve noise characteristics or dose efficiency of the 3D weighted helical CB-FBP algorithm at a helical pitch smaller than 1: 1, while its reconstruction accuracy and computational efficiency are maintained. It is believed that, such an efficient CB reconstruction algorithm that can provide superior noise characteristics or dose efficiency at low helical pitches may find its extensive applications in CT medical imaging.

A new reconstruction algorithm based on ordered projection subset and divided pixel subset

Statistical iterative methods for image reconstruction like maximum likelihood expectation maximization are more vigorous and feasible than analytical inversion methods and allow for accurately modelling the counting statistics and the photon transport during acquisition. The maximum likelihood approach provides images with superior noise characteristics compared to conventional algorithms, but it has huge computation burden. The objection of this paper is to develop a new algorithm, which modifies the number of projections and the step size for each iteration in order to recover various frequency components. In the present method, the number of projections in a subset increases and the step size decreases when all the subsets have been processed. In addition, the pixel data are divided into subsets to accelerate image reconstruction. The experimental results demonstrate that this algorithm converge faster than any other reconstruction algorithms and can provide high quality of reconstructed images.

A modified OSEM algorithm for PET reconstruction using wavelet processing

Ordered subset expectation-maximization (OSEM) method in positron emission tomography (PET) has been very popular recently. It is an iterative algorithm and provides images with superior noise characteristics compared to conventional filtered backprojection (FBP) algorithms. Due to the lack of smoothness in images in OSEM iterations, however, some type of inter-smoothing is required. For this purpose, the smoothing based on the convolution with the Gaussian kernel has been used in clinical PET practices. In this paper, we incorporated a robust wavelet de-noising method into OSEM iterations as an inter-smoothing tool. The proposed wavelet method is based on a hybrid use of the standard wavelet shrinkage and the robust wavelet shrinkage to have edge preserving and robust de-noising simultaneously. The performances of the proposed method were compared with those of the smoothing methods based on the convolution with Gaussian kernel using software phantoms, physical phantoms, and human PET studies. The results demonstrated that the proposed wavelet method provided better spatial resolution characteristic than the smoothing methods based on the Gaussian convolution, while having comparable performance in noise removal.

Statistical dynamic image reconstruction in state-of-the-art high-resolution PET

Modern high-resolution PET is now more than ever in need of scrutiny into the nature and limitations of the imaging modality itself as well as image reconstruction techniques. In this work, we have reviewed, analysed and addressed the following three considerations within the particular context of state-of-the-art dynamic PET imaging: (i) the typical average numbers of events per line-of-response (LOR) are now (much) less than unity, (ii) due to the physical and biological decay of the activity distribution, one requires robust and efficient reconstruction algorithms applicable to a wide range of statistics and (iii) the computational considerations in dynamic imaging are much enhanced (i.e., more frames to be stored and reconstructed). Within the framework of statistical image reconstruction, we have argued theoretically and shown experimentally that the sinogram non-negativity constraint (when using the delayed-coincidence and/or scatter-subtraction techniques) is especially expected to result in an overestimation bias. Subsequently, two schemes are considered: (a) subtraction techniques in which an imagenon-negativity constraint has been imposed and (b) implementation of random and scatter estimates inside the reconstruction algorithms, thus enabling direct processing of Poisson-distributed prompts. Both techniques are able to remove the aforementioned bias, while the latter, being better conditioned theoretically, is able to exhibit superior noise characteristics. We have also elaborated upon and verified the applicability of the accelerated list-mode image reconstruction method as a powerful solution for accurate, robust and efficient dynamic reconstructions of high-resolution data (as well as a number of additional benefits in the context of state-of-the-art PET).

A fast image reconstruction algorithm based on penalized-likelihood estimate

Statistical iterative methods for image reconstruction like maximum likelihood expectation maximization (ML-EM) are more robust and flexible than analytical inversion methods and allow for accurately modeling the counting statistics and the photon transport during acquisition. They are rapidly becoming the standard for image reconstruction in emission computed tomography. The maximum likelihood approach provides images with superior noise characteristics compared to the conventional filtered back projection algorithm. But a major drawback of the statistical iterative image reconstruction is its high computational cost. In this paper, a fast algorithm is proposed as a modified OS-EM (MOS-EM) using a penalized function, which is applied to the least squares merit function to accelerate image reconstruction and to achieve better convergence. The experimental results show that the algorithm can provide high quality reconstructed images with a small number of iterations.

Gate-alloy-related kink effect for metamorphic high-electron-mobility transistors

Gate-metal-related kink effects in InAlAs ∕ InGaAs ∕ GaAs metamorphic high-electron-mobility transistors have been investigated. Improvements on the kink effect have been observed by using the higher Schottky barrier height gate alloys, including Ti∕Au, Ni∕Au, and Pt∕Au, as compared to the use of the conventional Au gate metal. In comparison with gate alloy combinations, the devices with Ti∕Au alloy exhibit superior noise characteristics, whereas those with Ni∕Au alloy demonstrate the highest power characteristics. With the gate dimensions of 1.2×200μm2, the device minimum noise figure, NFmin, is 1.17dB at 2.4GHz by using Ti∕Au and the output power is 13.14dBm at 2.4GHz by using Ni∕Au. Significant rf characteristics have also been improved upon that with Au gate.

An Improved Maximum Likelihood Approach to Image Reconstruction Using Ordered Subsets and Data Subdivisions

Iterative algorithms such as maximum likelihood expectation maximization (ML-EM) algorithm are rapidly becoming the standard for image reconstruction in emission computed tomography. The maximum likelihood approach provides images with superior noise characteristics compared to conventional filtered backprojection algorithm. A major drawback of the iterative image reconstruction methods is their high computational cost. In this paper, we develop a new algorithm called the improved ordered subset expectation maximization (IOS-EM) algorithm. This algorithm modifies the number of projections in each subset and the step size (i.e., the relaxation factor) for each iteration in order to recover various frequency components in early iteration steps. In the method presented in this paper, the number of projections in a subset increases and the step size decreases after each iteration. In addition, pixel data are grouped into subdivisions to accelerate image reconstruction. Experimental results show that the IOS-EM algorithm can provide high quality reconstructed images at a small number of iterations.

Fast EM-like methods for maximum "a posteriori" estimates in emission tomography.

The maximum-likelihood (ML) approach in emission tomography provides images with superior noise characteristics compared to conventional filtered backprojection (FBP) algorithms. The expectation-maximization (EM) algorithm is an iterative algorithm for maximizing the Poisson likelihood in emission computed tomography that became very popular for solving the ML problem because of its attractive theoretical and practical properties. Recently, (Browne and DePierro, 1996 and Hudson and Larkin, 1994) block sequential versions of the EM algorithm that take advantage of the scanner's geometry have been proposed in order to accelerate its convergence. In Hudson and Larkin, 1994, the ordered subsets EM (OS-EM) method was applied to the ML problem and a modification (OS-GP) to the maximum a posteriori (MAP) regularized approach without showing convergence. In Browne and DePierro, 1996, we presented a relaxed version of OS-EM (RAMLA) that converges to an ML solution. In this paper, we present an extension of RAMLA for MAP reconstruction. We show that, if the sequence generated by this method converges, then it must converge to the true MAP solution. Experimental evidence of this convergence is also shown. To illustrate this behavior we apply the algorithm to positron emission tomography simulated data comparing its performance to OS-GP.

General noise analysis of recirculating delay line structures

Recirculating delay lines have value notably as sensors and optical signal processors. One of their main limitations is that phase noise from the source is converted to amplitude noise at the detector and that intensity noise is also filtered by the system. An expression is derived for the filtering effect that a recirculating delay line topology has on both the source noise and amplified spontaneous emission from in-line amplifiers. From these expressions it is shown that some delay line topologies have far superior noise characteristics compared to others.

Aeroacoustic properties of a supersonic diamond-shaped jet

The potential for using a novel diamond-shaped nozzle, which may allow superior mixing and noise characteristics of supersonic jets without significant thrust losses, is explored. Flow visualization and pressure measurements indicate the presence of distinct structures in the shear layers, not normally observed in shear layers of ideally expanded axisymmetric and rectangular jets. The characteristics of these features suggest that they are a manifestation of significant streamwise vorticity in the shear layers. Despite the distinct nature of the flowfield structure of the diamond jet, the far-field noise characteristics are quite similar to those of the corresponding axisymmetric jet, except moderate mixing-noise reduction in the aft quadrant. Furthermore, the global shear-layer growth rates are also very similar to those of the axisymmetric and two-dimensional counterparts. These observations lead one to believe that the presence of streamwise vorticity may not play a significant role on the overall mixing and noise generation of a supersonic jet.

Iterative image reconstruction for positron emission tomography: a study of convergence and quantitation problems

Iterative reconstruction techniques have been shown to have superior noise characteristics compared to conventional filtered backprojection (FB). The main drawbacks of the iterative methods are the increased computational burden and the difficulty in establishing a stopping criterion and ensuring proper quantitation in different imaging situations. Using a combination of techniques, it has been possible to reduce the time required for iterative reconstruction to a few times that of FB. The quantitation properties of FB have been compared to those of additive and multiplicative iteration formulas, including the maximum likelihood method. Without acceleration, all three tested methods gave quantitative results after 40 iterations, regardless of the number of counts in the data. However, with noisy data, the best images in a least-squares sense were typically obtained after 10-20 iterations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An infrared beam port for the SRS at daresbury

Plans will be presented for the construction and operation of an infrared beam port at the Synchrotron Radiation Storage Ring recently opened at Daresbury, U.K. The beam port incorporates a special metal coated silicon carbide mirror collecting 90 mrad (horizontal) × 100 mrad (vertical) of radiation from an extended source along with focusing and collimating optics which present a parallel beam (7 cm in diameter) to our Martin-Puplett far infrared interferometer. The interferometer will allow radiometric and absorption (or reflection) measurements to be made in the 2–300 cm −1 region with a resolution of ⪖0.1 cm −1. In this region we expect that the SRS will provide at least two orders of magnitude more photon flux than a conventional source lamp with superior noise characteristics and a well-defined time structure. An outline of possible uses of such an IR source will be given, with emphasis on applications in chemical physics, biology and materials science.