Off-axis Sensitivity Research Articles

Wall shear stress measurement using a zero-displacement floating-element balance

The floating-element (FE) principle, introduced nearly a century ago, remains one of the most versatile direct wall shear stress measurement methods. Yet, its intrinsic sources of systematic error, associated with the flow-exposed gap, off-axis load sensitivity, and calibration, have thus far limited its widespread application. In combination with the lack of standard designs and testing procedures, measurement reliability still hinges heavily on individual judgement and expertise. This paper presents a framework to curb these limitations, whereby the design and operation of a FE balance are leveraged by an analytical model that attempts to capture the behaviour and predict the relative contribution of the systematic sources of error. The design is based on a parallel-shift linkage and a zero-displacement force-feedback system. The FE has a surface area of 200×200\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$200\ imes 200\\,$$\\end{document} mm, and measurement sensitivity is adjustable depending on the surface condition and the Reynolds number. It is thus suitable for application in a wide range of low-speed, boundary-layer wind tunnels, small or large scale. Measurements of the skin friction coefficient over a smooth wall show a remarkable agreement with oil-film interferometry, especially for Reθ>1.3×104\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\rm Re}_{\ heta } > 1.3 \ imes 10^4$$\\end{document}. The discrepancy relative to the empirical Coles–Fernholz relation (κ=0.39\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\kappa = 0.39$$\\end{document} and C=4.352\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$C = 4.352$$\\end{document}) is within 0.5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.5\\,$$\\end{document}%, and the level of uncertainty is below 1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1\\,$$\\end{document}% for a confidence interval of 95\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$95\\,$$\\end{document}%.

The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog

The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ∼65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ∼120 ks and an outer 0.35 deg2 area with an exposure of ∼60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ∼8000 X-ray point sources. The survey design employs a grid of 36 heavily (∼50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

Quantitative Determination of Surface Morphology of Red Blood Cell

In this study, the determination of the surface morphology of red blood cell (RBC) from interferogram image obtained by quantitative phase imaging (QPI) method is presented. QPI, is an optical measurement method fre-quently used in recent years, allows to obtain quantitative data for different samples (cell, thin film surface, etc.). Many measurement setups at the micrometer level and with nanometer precision have been designed for quantita-tive surface determination. Among these, white light diffraction phase microscopy (WDPM) is a design that combines the advantages of off-axis holography-specific speed and phase sensitivity associated with common path interferometry. Interferogram image of RBCs have been formed by the WDPM setup. Analysis of this image has been carried out by Fourier transform. As a result of this analysis, three-dimensional (3D), dynamic (observable from all angles) and height-known profiles of RBCs have been created. From the height profiles, the parameters related to the morphology of RBCs as the projected surface area (PSA), diameter (D), mean corpuscular volume (MCV) and total surface area occupied by the cell (SA), have been determined quantitatively. In addition, two-dimensional images, obtained by examining blood samples with light microscopy and scanning electron micros-copy (SEM), have been compared with the data achieved by WDPM. The advantages and disadvantages of WDPM and light microscopy and SEM, which are commonly used in biomedical measurements, are discussed through the results. In this way, it was possible to see the difference between QPI and traditional methods used to imaging the cell surface.

Microphone vibration sensitivity: What it is, why it is important, and how to measure it

Microphones are designed to respond to acoustic pressure fields, but they can also be excited by external sources of mechanical vibration. In hearing aids, feedback is a difficult problem to resolve due to the high gain used to amplify sounds. The problem is worsened by the location of microphones and loudspeakers in close proximity, coupling both the acoustic and mechanical feedback paths. The first proposals of microphone vibration measurement techniques and definitional structure were published by Mead Killion in the 1970’s. Significant improvements in measurement technique have been published over the last 10 years. This talk will focus on a new measurement technique that allows for direct measurement of the “intrinsic vibration sensitivity”. The technique gives the ideal zero acoustic pressure condition at the microphone port and isolates room acoustic noise from the desired vibration signal. The noise floor of the new technique is 30 dB below previous methods, allowing for exceptionally clean measurement of primary-axis vibration sensitivity up to 10 kHz. Improvements are robust enough to enable the clean measurement of off-axis sensitivity of the microphone, which is often below 50 dBspl equivalent at 9.81 m/s2 of acceleration.

AstroSat-CZTI as a hard X-ray pulsar monitor

The Cadmium Zinc Telluride Imager (CZTI) is an imaging instrument onboard AstroSat. This instrument operates as a nearly open all-sky detector above ~60 keV, making possible long integrations irrespective of the spacecraft pointing. We present a technique based on the AstroSat-CZTI data to explore the hard X-ray characteristics of the $\gamma$-ray pulsar population. We report highly significant ($\sim 30\sigma$) detection of hard X-ray (60--380 keV) pulse profile of the Crab pulsar using $\sim$5000 ks of CZTI observations within 5 to 70 degrees of Crab position in the sky, using a custom algorithm developed by us. Using Crab as our test source, we estimate the off-axis sensitivity of the instrument and establish AstroSat-CZTI as a prospective tool in investigating hard X-ray characteristics of $\gamma$-ray pulsars as faint as 10 mCrab.

A Laterally Driven MEMS Inertial Switch With Double-Layer Suspended Springs for Improving Single-Axis Sensitivity

A novel laterally driven inertial switch with double-layer springs has been proposed and fabricated by surface micromachining technology for improving single-axial sensitivity. The symmetrical distribution of double-layer suspended springs and the constraint structures limits the displacement of the proof mass in the off-axis sensitive direction under an acceleration disturbance. The ANSYS simulation results reveal that compared with the inertial switch with one layer springs, the symmetrical distribution of double-layer serpentine springs effectively reduces the displacement of the proof mass in the off-axis direction. The design of symmetrical distribution of double-layer serpentine springs plays an important role in resisting small acceleration disturbance from the off-axis sensitive $z$ -direction, and the constraint structures can resist the large acceleration disturbance. The modal analysis, contact time, and the collision response in the inertial switch have also been simulated and discussed. Finally, the proposed inertial switch has been fabricated successfully, and the prototype is tested by a dropping hammer system. The test results show that the threshold level of the fabricated inertial switch is 272 g with 20- $\mu \text{s}$ contact time. The combined efforts of double-layer suspended springs and constraint structures effectively lower off-axis sensitivity and improve the single-axis sensitivity of the microelectromechanical system inertial switch.

Sensitivity to Off-Axis Vector Components of Typical Wire Wound Flat H-Coil Configurations

Power loss in magnetically soft magnetic materials can be measured by detecting magnetic field strength H and flux density B. H can be detected with the so-called H-coil sensor, which is an induction coil wound on a thin flat non-magnetic former. The accuracy of H measurement directly affects the measurement of power loss. For alternating (uni-directional) magnetization, H is applied mainly along the symmetry axis of the sample under test and the normal component is small due to magnetically closed circuit. So any off-axis H components usually have small amplitude and do not cause significant errors. However, under 2-D or rotational magnetization, the H-coils are exposed to strong H in all directions. It is shown in this paper that such off-axis H components can introduce significant amplitude and phase errors, which contribute to the differences in the calculated clockwise and anticlockwise power loss values. Theoretical analysis of order of magnitude of such off-axis sensitivity is given in this paper for three typical configurations of H-coils (with the return wire positioned along one side, diagonally and through the center). Experimental verification is also presented for the side wire configuration.

Fiber-optic annular detector array for large depth of field photoacoustic macroscopy

We report on a novel imaging system for large depth of field photoacoustic scanning macroscopy. Instead of commonly used piezoelectric transducers, fiber-optic based ultrasound detection is applied. The optical fibers are shaped into rings and mainly receive ultrasonic signals stemming from the ring symmetry axes. Four concentric fiber-optic rings with varying diameters are used in order to increase the image quality. Imaging artifacts, originating from the off-axis sensitivity of the rings, are reduced by coherence weighting. We discuss the working principle of the system and present experimental results on tissue mimicking phantoms. The lateral resolution is estimated to be below 200μm at a depth of 1.5cm and below 230μm at a depth of 4.5cm. The minimum detectable pressure is in the order of 3Pa. The introduced method has the potential to provide larger imaging depths than acoustic resolution photoacoustic microscopy and an imaging resolution similar to that of photoacoustic computed tomography.

Anisotropic size effect law for notched strength of unidirectional carbon/epoxy laminates – Part 2: Comparison with experiment

The multiaxial quasi-brittle failure criterion for notched orthotropic composites that was formulated in the first part of this study is evaluated on the basis of the off-axis notched strength of a unidirectional carbon/epoxy composite. Static tension tests are first carried out on center circular hole specimens of different hole diameters and fiber orientations to examine the notch size effect as well as the fiber orientation effect on the off-axis notched strength of the unidirectional composite. Experimental results show that the tensile strength in the fiber direction is more notch-sensitive than that in the transverse direction. The notch sensitivity in off-axis strength increases as the off-axis angle increases from the 0° fiber direction to about 10° off-axis direction, but it turns to decrease monotonically as the off-axis angle increases further in the range up to 90°. Then, the analytical formulas to predict the off-axis notched strength, off-axis notch sensitivity, off-axis intrinsic equivalent mode-I fracture toughness, and off-axis apparent equivalent mode-I fracture toughness of unidirectional composites are established on the basis of the multiaxial quasi-brittle failure criterion. These analytical formulas succeed in efficiently predicting both the effects of notch size and fiber orientation on the off-axis notched strength of the unidirectional composite. It is also shown that the intrinsic and apparent off-axis equivalent mode-I fracture toughness values predicted for brittle failure and quasi-brittle failure, respectively, correlate well with the experimental results.

A surface-micromachining-based inertial micro-switch with compliant cantilever beam as movable electrode for enduring high shock and prolonging contact time

A novel laterally-driven inertial micro-switch with two L-shaped elastic cantilever beams as the movable electrode, which is attached to the proof mass, is proposed in this paper. The advantage of this design is that the contact time of the inertial micro-switch can be prolonged. Meanwhile, the micro-switch can withstand a higher shock than the traditional designs whose cantilever beams are attached to the fixed electrode. The designed inertial micro-switch was simulated and optimized with ANSYS software and fabricated on a quartz substrate by surface micromachining technology. The simulated result demonstrates that the threshold acceleration (aths) under stable switch-on state is about 288g and the contact time is about 198μs when the pulse width of acceleration loads is 1ms. At the same time, it indicates that the threshold acceleration, the response time and the contact time of designed micro-switch all increase with the pulse width of acceleration loads. The simulation of impact process in non-sensitive direction shows that the introduced constraint sleeve structure in the novel inertial micro-switch can lower the off-axis sensitivity. The fabricated micro-switch prototype has been tested by a standard dropping hammer system under shock accelerations with various amplitudes and pulse widths. The experimental measurements show that the contact time is about 150μs when the threshold acceleration is about 288g. It also indicates that the response time and the contact time both increase with the pulse width, which is consistent with the simulation ones.

Design and fabrication of a laterally-driven inertial micro-switch with multi-directional constraint structures for lowering off-axis sensitivity

This paper proposes a novel laterally-driven inertial micro-switch with multi-directional compact constraint structures for lowering off-axis sensitivity and improving shock-resistibility. The design utilizes constraint sleeve and reverse stop-block structures to limit too much displacement of proof mass in the micro-switch and avoid damage to the device under a high shock load. The dynamic contact simulation indicates that the designed inertial micro-switch can limit the movement of proof mass and lower the off-axis sensitivity by constraint sleeve and reverse block structures. The first collision response time between proof mass and constraint structures in the z-direction has been analyzed theoretically and simulated, which have indicated that the collision response time mainly depends on geometric parameters, applied shock acceleration amplitude and the inherent frequency of the mass-spring inertial system. Simulated dynamic response curves under applied reverse directional shock accelerations show the proposed inertial micro-switch also has a good shock-resistibility. The inertial micro-switch fabricated by surface micromachining technology has been evaluated using a drop hammer system. The test results indicate that spurious triggering is more likely to occur in the inertial micro-switch without constraint structures, and the designed constraint structures can effectively lower the off-axis sensitivity and improve the shock-resistibility.

Design and simulation of a high-performance Z-axis SOI-MEMS accelerometer

This paper presents a new micromachined z-axis accelerometer as well as a new method to sense the out-of-plane displacement capacitively via comb finger arrays. The new design built the z-accelerometer using eight folded beam suspension to minimize the off axis sensitivities in both the x- and y- directions. The proposed method implements the sensing electrode as a comb finger arrays surrounding the sensor. This method enables the realization of the sensor by bulk micromachining process, increases the sense capacitance and reduces the off-axis sensitivity. This process allows building the micromachined accelerometer with large inertial mass. This work introduces the design and simulation for this accelerometer. The introduced method results in a high sense capacitance as well as high sensitivity. The simulated sense capacitance is 19.6627 pF. The sensor sensitivity is 2.037 μm/g with a very small total noise equivalent acceleration of 3.096 μg/$$ \sqrt {Hz} $$.

J043032 平織CFRP積層板の非主軸切欠強度とその寸法効果に及ぼす破壊機構の影響([J04303]高分子基複合材料の加工と評価(3))

The off-axis notched strength of a plain woven roving fabric CFRP laminate has been studied with emphasis on its fiber orientation dependence and dominant failure mode. Static tension tests were carried out on center hole specimens with different diameters of a hole and different fiber orientations, respectively. The off-axis notch sensitivity of the woven composite was elucidated on the basic of the experimental results obtained. The three-dimensional digital image correlation (DIC) method with two CCD cameras was used to measure full-field displacement filed and its variation during each tension test until rupture occurs. Local strain distribution, which was calculated on the displacement field measured by the 3D-DIC method, was used to identify dominant failure modes that are responsible for ultimate tensile failure in off-axis notched specimens of the woven CFRP laminate. To prediction of the off-axis notched strength of the woven CFRP laminate, applicability of the anisotropic notch size effect law that takes into account both the effects of fiber orientation and notch size was also discussed.

Development of a Novel MEMS Inertial Switch With a Compliant Stationary Electrode

A novel microelecromechnical system (MEMS) inertial switch based on the surface micromachining technology was developed, which mainly consists of a proof mass as the movable electrode and a compliant stationary electrode above the proof mass, whose deformation during the contact process would enhance the contact effect and prolong the switch-on time. Based on the original design which had already realized the enhancing effect to some extent, the device structure was redesigned as a centrosymmetric structure with the stationary electrode changed from two bridge-type beams to one cross beam in order to reduce the off-axis sensitivity. More importantly, a contact point was installed on top of the proof mass, changing the effective contact area of the stationary electrode from its end to the center, which undergoes the largest deformation. Therefore, the contact effect would be improved further, which has been confirmed by the ANSYS transient simulation. This simulation combined with the Simulink dynamic simulation described the device behavior, which were in agreement with the drop hammer tests. The threshold acceleration of the redesigned inertial microswitch was around 70 g, and the tested switch-on time reached 30 mus, more satisfactory than the original design.

S0406-2-4 一方向CFRPの高温における非主軸圧縮切欠強度とその切欠寸法依存性(プラスチック基複合材料の加工と評価(2))

The notch size effect in the off-axis compressive strength of a unidirectional CFRP at high temperature (100℃) has been studied. This study also aims to develop engineering methods for predicting the off-axis notched strengths. Static compression tests were carried out on center hole (CH) specimens with different hole diameters and different fiber orientations. Experimental results showed that the off-axis compressive strengths of the CH specimens become smaller with increasing hole diameter, except for the 0° and 10° specimens. It was also found that the compressive notch sensitivity depends on the ultimate failure mode of the specimens, and it is likely to be lower as the out-of-plane shear failure becomes more appreciable. The off-axis compressive notched strengths were predicted using the off-axis notch sensitivity model and the Feddersen model. These engineering models can efficiently predict the off-axis notch sensitivity, but they fail to predict the off-axis notched strengths distributed in the vicinity of the notch insensitive line.

Design and fabrication of a new miniaturized capacitive accelerometer

A novel mercury-based capacitive accelerometer has been designed and fabricated. The accelerometer features a highly symmetrical cubic structure and capacitive coupling of the high-frequency input voltage, which uses a mercury drop for spring material and flexible interconnection layer between the capacitor plates. The device is mounted on a standard IC package with dimensions of 5 mm × 5 mm × 5 mm. The structure, working principle, fabrication, and mathematical model of the accelerometer are presented. Since the accelerometer uses a mercury drop as its sensitive electrode instead of a solid, which is commonly used in traditional accelerometers, the conflict between the requirements of high shock and high sensitivity is solved. The measurement results show a sensitivity of 0.2 mV (m s −2) −1 with a corresponding resolution of 0.01 ms −2, off-axis sensitivity of <5% and good linearity in the output voltage for accelerations up to at least 10 m s −2.

Correction of pixel sensitivity variation and off‐axis response for amorphous silicon EPID dosimetry

The aim of this work is to determine the pixel sensitivity variation and off-axis dose response of an amorphous silicon electronic portal imaging device (EPID), and develop a correction method to improve EPID dosimetry. The uncorrected or raw pixel response of the aS500 amorphous silicon EPID shows differences in response (sensitivity) of individual pixels as well as a large off-axis differential response with respect to an ion chamber in water. Both can be corrected by division of raw images by the flood-field (FF) image. However, this leads to two problems for dosimetry: (1) the beam profile is present in both the raw image and FF image, and hence is "washed out" of the corrected image, and (2) any mismatch of EPID position between dosimetry and FF calibration means that the beam profile and off-axis response in the raw image and FF are misaligned. This causes artifacts in FF division and dosimetric errors. A method was developed to measure the off-axis response and pixel sensitivity variation separately to allow correction of images at any EPID position while retaining beam profile information. The pixel sensitivity variation is applied to the imager plane and is independent of imager position. The off-axis response depends on the imager plane position relative to the beam central axis. The pixel sensitivities were derived from multiple images of the same symmetric field acquired with the detector displaced laterally between each image. The off-axis response was measured by acquiring off-axis raw images (FF correction removed) and dividing out the off-axis beam fluence and previously determined pixel sensitivity differences. The dosimetric errors due to lateral and vertical detector displacement with the conventional FF calibration method were measured and compared to the new method. Corrected EPID profiles were then compared to beam profiles measured with ion chamber in water for open fields. The EPID was found to have a large off-axis differential response with respect to an ion chamber in water, particularly for 6 MV. This increased to 13% at 15 cm off-axis for 6 MV, and 3.5% for 18 MV at the isocenter plane. The dosimetric errors introduced by detector displacement with conventional FF calibration were found to be approximately 1% per centimeter of lateral detector displacement and 0.1% per centimeter of vertical displacement. These were reduced to less than 1% for any position with the new correction method. Corrected EPID images agreed with ion-chamber measurements to within 2% (excluding penumbra and low-dose areas outside the field) for various field sizes. The new correction method gives consistent dosimetry for any EPID position and retains beam profile information in the image.

Real-time rectilinear volumetric imaging using a periodic array

Current real-time phased array volumetric scanners use a 2-D array to scan a pyramidal volume comprised of many sector scans stacked in the elevation direction. This scan format is primarily useful for cardiac imaging to avoid interference from the ribs. However, a real-time rectilinear volumetric scan with a wider field-of-view (FOV) close to the transducer could prove more useful for abdominal, breast or vascular imaging. In our previous work, a 94 × 94 Mills cross array operating at 5 MHz was fabricated, and the first real-time rectilinear volumetric images were made using a 2-D array and the Duke real-time 3-D scanner. The FOV for the Mills cross was 30 × 8 × 60 mm. Despite reasonable success with the Mills cross array, the array had limitations of poor off-axis sensitivity and a smaller FOV in one direction. To overcome these limitations, a new rectilinear array containing over 65,500 elements was developed with a periodic geometry to increase the FOV to 30 mm × 30 mm × 60 mm and improve the off-axis sensitivity. Images of tissue-mimicking phantoms and the carotid artery in vivo were obtained. In addition, spectral and color flow Doppler results from a pulsatile flow phantom were obtained. (E-mail: jesse.yen@duke.edu)

Observation of Magnetic Fine Structures by Electron Differential Microscopy

New techniques for electron differential interferometry and microscopy that are free from the effect of distorted reference waves have been developed using an electron trapezoidal prism. This new prism, which replaces an electron biprism, makes a hologram with the object wave inclined and the reference wave perpendicular to the image plane. A differential interferogram can be produced from one double-exposed hologram. A differential phase image from two independently recorded holograms can also be easily achieved. These two techniques retain the advantages of conventional off-axis electron holography, that is, resolution and sensitivity. Their performance is evaluated by reconstructing the electrostatic potential around a charged polystyrene latex particle and by the observation of magnetic fine structures in a permalloy thin film. A two-dimensional vector map of the magnetic flux density enables an interpretation of the contrast of the Lorenz micrograph of the same specimen area.

Electron differential microscopy using an electron trapezoidal prism

The new technique of electron differential interferometry and microscopy which is free from the effect of distorted reference waves has been achieved using an electron trapezoidal prism. This new prism, which replaces an electron biprism, makes a hologram with the object wave inclined and the reference wave perpendicular to the image plane. A differential interferogram can be produced from one double-exposed hologram while retaining the advantages of conventional off-axis electron holography, i.e. resolution and sensitivity. A differential phase image from two independently recorded holograms can also be easily achieved.The performance of this technique is shown by reconstructing the electrostatic potential around a charged polystyrene latex particle.