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Showing papers on "Beam (structure) published in 1994"


Journal ArticleDOI
TL;DR: In this paper, a spiral phaseplate can convert a TEM00 laser beam into a helical wavefront beam with a phase singularity at its axis, and the diffractive-optical effect of the spiral phase plate is implemented by index matching a macroscopic structure in an optical immersion.

1,393 citations


Journal ArticleDOI
TL;DR: In this article, a double conical scanning system was designed to collect a large data set of integrated intensities that were more suitable for structure determination by electron diffraction, both by removing excitation errors due to curvature of the Ewald sphere and also by reducing non-systematic dynamical effects.

640 citations


Journal ArticleDOI
TL;DR: In this paper, a cracked, simply supported uniform beam is treated for either bending or axial vibrations, and the crack is simulated by an equivalent spring connecting the two segments of the beam.

381 citations


Journal ArticleDOI
TL;DR: In this paper, a simple propagation law is found for light beams of various orders and their field distribution across the waist plane is similar to that produced by an ordinary gaussian beam except that the central region is flattened.

335 citations


Patent
17 Mar 1994
TL;DR: In this article, a substrate is mounted on an x-y stage to provide at least one degree of freedom while the substrate is being scanned by the charged particle beam, and an optical alignment system for initially aligning the substrate beneath the particle beam.
Abstract: A method and apparatus for a charged particle scanning system and an automatic inspection system, including wafers and masks used in microcircuit fabrication. A charged particle beam is directed at the surface of a substrate for scanning that substrate and a selection of detectors are included to detect at least one of the secondary charged particles, back-scattered charged particles and transmitted charged particles from the substrate. The substrate is mounted on an x-y stage to provide at least one degree of freedom while the substrate is being scanned by the charged particle beam. The substrate is also subjected to an electric field on it's surface to accelerate the secondary charged particles. The system facilitates inspection at low beam energies on charge sensitive insulating substrates and has the capability to accurately measure the position of the substrate with respect to the charged particle beam. Additionally, there is an optical alignment system for initially aligning the substrate beneath the charged particle beam. To function most efficiently there is also a vacuum system for evacuating and repressurizing a chamber containing the substrate. The vacuum system can be used to hold one substrate at vacuum while a second one is being loaded/unloaded, evacuated or repressurized. Alternately, the vacuum system can simultaneously evacuate a plurality of substrates prior to inspection and repressurize the same plurality of substrates following inspection. In the inspection configuration, there is also a comparison system for comparing the pattern on the substrate with a second pattern.

324 citations


Journal ArticleDOI
TL;DR: In this paper, reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam.
Abstract: In this study, the reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam The plate thickness is varied to assess the premature failure initiated at the plate curtailment zone due to the high concentration of shear and peeling stresses Different repair and anchoring schemes were conducted in an effort to eliminate such failures and insure ductile behavior The results indicated that the flexural strength of the repaired beams is increased The ductile behavior of the repaired beams is inversely proportional to the plate thickness The use of an I-jacket plate provided a proper anchorage system and improved the ductility of beams repaired with plates of large thickness

319 citations


Journal ArticleDOI
TL;DR: In this article, the spring constants of a V-shaped atomic force microscopy cantilever beam are given in terms of the beam geometry and material properties, and the normal and longitudinal stiffness are obtained from a few simple equations.
Abstract: For a V‐shaped atomic force microscopy cantilever beam, the spring constants in the three principal directions are given in terms of the beam geometry and material properties. For the lateral stiffness, a closed‐formed expression is presented. Also, the normal and the longitudinal stiffness are obtained from a few simple equations. The results are compared with a finite element study and found to be very accurate. All spring constants depend strongly on the cantilever thickness, which is difficult to measure. In addition, the lateral and longitudinal stiffness are sensitive to the location and the height of the attached pyramid.

318 citations


Journal ArticleDOI
TL;DR: In this article, it was shown by use of a simple model that in general the state of polarization of a light beam generated by a partially coherent source changes as the beam propagates in free space.
Abstract: It is shown by use of a simple model that in general the state of polarization of a light beam generated by a partially coherent source changes as the beam propagates in free space.

294 citations


Journal ArticleDOI
TL;DR: In this paper, a simple and sensitive method for detecting small forces applied to an optically trapped microsphere utilizes the transmitted beam of the trapping laser to monitor micro-sphere deflections within the potential well of the trap.
Abstract: A simple and sensitive method for detecting small forces applied to an optically trapped microsphere utilizes the transmitted beam of the trapping laser to monitor microsphere deflections within the potential well of the trap. The rms dynamic displacement detection sensitivity measured in the frequency range from 1 Hz to 10 kHz is ∼1 nm in the radial direction and ∼10 nm along the z (optic) axis. Radiation trapping force constants were calibrated against viscous drag on microspheres in the range between the Rayleigh (r<0.2λ) and Mie (r≫λ) size regimes. For a 1‐μm‐diam polystyrene sphere trapped with a 60 mW beam the rms spontaneous thermal motion limits the force sensitivity to better than 10−12 N and lateral spatial resolution to ∼10 nm in a frequency range from 1 Hz to the viscous rolloff frequency ∼1 kHz. The measured maximum trapping efficiencies are compared with the theoretical predictions of the ray‐optics approximation.

241 citations


Journal ArticleDOI
TL;DR: In this paper, the static deformation of micromachined beams under prescribed in-plane compressive stress is studied through analytical and experimental means over the prebuckling, transition, and postbuckling load ranges.
Abstract: The static deformation of micromachined beams under prescribed in-plane compressive stress is studied through analytical and experimental means over the prebuckling, transition, and postbuckling load ranges. The finite amplitude of the beam in its postbuckled state is predicted by modeling the non-linear dependence of the out-of-plane deformation on the compressive stress. In addition, the model explicitly considers the net effect of slight imperfections, which can include fabrication defects, geometric irregularities, or non-ideal loading, on the beam's behavior in the near-buckling regime. As an application, clamped-clamped silicon dioxide beams are fabricated through conventional bulk micromachining, and their deflected profiles are measured through three-dimensional optical profilometry. The measurements are compared to the postbuckled amplitudes and shapes that are predicted by the model, and by existing simpler models that do not include the effects of either non-linearity or imperfection. As borne out by the data, when imperfections are considered, the beams exhibit continuous growth of the out-of-plane amplitude during transition from the prebuckled state to a postbuckled one, in contrast to sudden bifurcation at a critical load. By accounting for this behavior, the estimate of residual stress in the thin film from which the beams are fabricated can be improved, and the amplitude of common postbuckled micromachined structures can be predicted during the design phase.

212 citations


Journal ArticleDOI
TL;DR: This paper focuses on trade-offs among the above four aspects of beam forming and relate them to system parameters such as aperture size, f-number (the ratio between focal length and aperture diameter), central frequency (wavelength), system bandwidth and sidelobes.
Abstract: The principles of biomedical ultrasound beam forming control the quality of diagnostic imaging. Beam parameters associated with imaging quality are: (1) lateral and axial resolutions; (2) depth of field; (3) contrast and (4) frame rate. In this paper, we review some of the current beam forming techniques and their principles. We focus on trade-offs among the above four aspects of beam forming and relate them to system parameters such as aperture size, f-number (the ratio between focal length and aperture diameter), central frequency (wavelength), system bandwidth and sidelobes. Methods for steering conventional and limited diffraction beams with array transducers are also reviewed.

Patent
02 Jun 1994
TL;DR: In this paper, an array detector such as a charge coupled device is used to acquire an at least one dimensional digital image of a region of an object using an optical source which outputs a first optical beam having a short coherence length.
Abstract: An apparatus and method for acquiring an at least one dimensional digital image of a region of an object using an optical source which outputs a first optical beam having a short coherence length. A splitter splits the first optical beam into a reference beam and an object beam. The reference beam travels to a reference scatterer and the object beam is directed toward the region of the object. An array detector such as a charge coupled device receives a portion of the object beam and a portion of the reference beam and detects the resulting incident intensity over the at least one dimension and outputs a signal. Since the coherence length of the source is short, the signal output from the detector array corresponds to one or more dimensional slice of the object which represents the above region.

Journal ArticleDOI
TL;DR: In this paper, a series of reinforced concrete beams were tested in four-point bending to determine the ability of externally bonded composite fabrics to improve the beams' flexural capacity and stiffness.

Patent
10 Feb 1994
TL;DR: In this paper, a beam guide element is provided with a beam detector for detecting the degree of wetting of a multi-layer transparent pane, made in particular of glass, by an, in particular, drop-shaped precipitation.
Abstract: A sensor device for detecting the degree of wetting of a multi-layer transparent pane, made in particular of glass, by an, in particular, drop-shaped precipitation. The sensor device is provided with a beam guide element which comprises two beam windows and cooperates with a beam transmitter and a beam receiver. In order to prevent spurious beams caused by an extremely thin intermediate layer located in the pane from having a noticeable influence on the signal used to control the windscreen wiper system, the beam guide element comprises a further beam exit window in the central region of its rear surface facing away from the pane. The region is located between the two beam windows. The further beam exit window is allocated to the measuring path and cooperates with an additional beam detector. Only those irrelevant beams reflected at the extremely thin metallic intermediate layer located in the pane exit therefrom. The signal resulting from the existing irrelevant beams which is detected by the additional beam detector is used to correct the signal supplied by the actual beam detector. Alternatively; signal correction can be achieved by an electrical circuit.

Patent
19 May 1994
TL;DR: In this paper, a composite laminate beam for an automotive body construction has an outer structural portion an an inner tube portion separated by a thin layer of structural foam, and a method of making the beam is also disclosed.
Abstract: A composite laminate beam for an automotive body construction has an outer structural portion an an inner tube portion separated by a thin layer of structural foam. The beam may take the form of a radiator support structure, a windshield pillar, a rocker assembly or a drive shaft or similar structures. A method of making the beam is also disclosed.

Patent
30 Sep 1994
TL;DR: In this article, a blind crack is formed by an incident beam of radiation being effected to a temperature short of its softening point, with the rate of relative displacement of the beam and of the material, and the region of the heated zone which is locally cooled being selected to form the blind crack in the material.
Abstract: A method of cutting non-metallic materials, specifically glass, resides in the heating of the material by an incident beam of radiation being effected to a temperature short of its softening point, with the rate of relative displacement of the beam and of the material, and the region of the heated zone which is locally cooled being selected to form a blind crack in the material. The method provides for increasing substantially the cutting speed and accuracy, and also for controlling the depth, shape and angle of the cut face formed by the crack. The method can be employed in the automotive industry for making glass windows and mirrors, in the electronics industry for making precision backings and substrates for LED indicator panels and masks, magnetic and optomagnetic disks, in watch-making for making protective glasses, in the aircraft and space industry for making structural optics components, in construction and architecture for dimensional pattern-cutting of glass, including its integration in the glass manufacturing technology, and also in other fields of production and technologies where precision of non-metallic materials are made.

Book
01 Jan 1994
TL;DR: Generation of the electron beam and its behavior on penetrating metal Welding parameters and advice on welding practice The weldability of metallic materials preparation of the workpiece Beam and machine control Electron beam welding machines and equipment Quality levels and acceptable variations in electron beam welds Examples of electron beam welding components Personnel qualifications and machine testing Standards and regulations Other methods of working materials with electron beams A comparison of electronbeam and laser welding as discussed by the authors.
Abstract: Generation of the electron beam The behaviour of the electron beam on penetrating metal Welding parameters and advice on welding practice The weldability of metallic materials Preparation of the workpiece Beam and machine control Electron beam welding machines and equipment Quality levels and acceptable variations in electron beam welds Examples of electron beam welded components Personnel qualifications and machine testing Standards and regulations Other methods of working materials with electron beams A comparison of electron beam and laser welding

Journal ArticleDOI
TL;DR: In this article, a hybrid damping design that integrates active and passive dampings through intelligent constrained layer (ICL) treatments is proposed, which consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped.
Abstract: This paper is to propose a viable hybrid damping design that integrates active and passive dampings through intelligent constrained layer (ICL) treatments. This design consists of a viscoelastic shear layer sandwiched between a piezoelectric constraining cover sheet and the structure to be damped. According to measured vibration response of the structure, a feedback controller regulates axial deformation of the piezoelectric layer to perform active vibration control. In the meantime, the viscoelastic shear layer provides additional passive damping. The active damping component of this design will produce adjustable and significant damping. The passive damping component of this design will increase gain and phase margins, eliminate spillover, reduce power consumption, improve robustness and reliability of the system, and reduce vibration response at high frequency ranges where active damping is difficult to implement. To model the dynamics of ICL, an eighth-order matrix differential equation governing bending and axial vibrations of an elastic beam with the ICL treatment is derived. The observability, controllability, and stability of ICL are discussed qualitatively for several beam structures. ICL may render the system uncontrollable or unobservable or both depending on the boundary conditions of the system. Finally, two examples are illustrated in this paper. The first example illustrates how an ICL damping treatment, which consists of an idealized, distributed sensor and a proportional-plus-derivative feedback controller, can reduce bending vibration of a semi-infinite elastic beam subjected to harmonic excitations. The second example is to apply an ICL damping treatment to a cantilever beam subjected to combined axial and bending vibrations. Numerical results show that ICL will produce significant damping.

Patent
08 Dec 1994
TL;DR: In this article, the effects of a defective electromechanical pixel 20 having a beam 30 and a hinge 32,34 are mitigated by applying a voltage sufficient to damage the hinge or beam of the pixel.
Abstract: Methods are disclosed by which the effects of a defective electromechanical pixel 20 having a beam 30 and a hinge 32,34 are mitigated. These methods may damage the hinge 32,34 or the beam 30 and comprise the step of applying a voltage sufficient to damage the hinge 32,34 or beam 30 of said electromechanical pixel 20 by mechanical overstress, thermal overstress, electrochemical reaction, or thermally induced chemical reaction. Other methods are also disclosed.

Journal ArticleDOI
TL;DR: An iterative pencil beam algorithm for optimization of multidimensional radiation therapy dose plans has been developed and a quantity termed the generalized fluence vector is introduced, combining fluences and energy fluences from external beams as well as the radiation source densities of intracavitary and interstitial sources or external source distributions.
Abstract: An iterative pencil beam algorithm for optimization of multidimensional radiation therapy dose plans has been developed. The algorithm allows the use of both physical and radiobiological treatment objective functions and allows arbitrary sampling such as straight Cartesian grids with linear or nonlinear sampling functions or random sampling. The algorithm can account for and optimally combine almost all the degrees of freedom at an advanced radiotherapy clinic, such as different beam modalities and spectra, beam directions, beam fluence distributions, and time-dose fractionations. The algorithm allows for external charged and neutral beams as well as intracavitary and interstitial sources to be optimally combined. A quantity termed the generalized fluence vector is introduced, combining fluences and energy fluences from external beams as well as the radiation source densities of intracavitary and interstitial sources or external source distributions. The positivity constraint on the generalized fluence can therefore be applied directly during the optimization procedure. The convergence properties and the required iteration time of the algorithm are discussed. Several examples with combinations of photon and electron beams of different energies and directions of incidence are presented. The optimization has been made with the treatment objective to maximize the probability of achieving tumor control without causing severe complications in healthy normal tissues.

Patent
09 Mar 1994
TL;DR: In this paper, a merged MR head is provided which has vertically aligned sidewalls so as to minimize side-fringing and improve off-track performance, and the bottom pole piece P1, which comprises the second shield layer S2 of the read head, has a pedestal pole tip with a short length dimension.
Abstract: A merged MR head is provided which has vertically aligned sidewalls so as to minimize side-fringing and improve off-track performance The bottom pole piece P1, which comprises the second shield layer S2 of the read head, has a pedestal pole tip with a short length dimension A pedestal pole tip with a length as short as two times the length of the gap layer G optimally minimizes the sidewriting and improves off-track performance The bottom pole tip structure of the write head is constructed by ion beam milling using the top pole tip structure as a mask The ion beam milling is directed at an angle to the sidewalls of the top pole tip structure which causes the bottom pole tip structure to be milled with sidewalls which align with the top pole tip structure The ion beam milling can comprise two angled beams, either sequentially or simultaneously, the first beam performing primarily a cutting operation and some clean up work while the second beam primarily conducts clean up work of the redeposition of the debris caused by the cutting In another embodiment, a single angled ion beam can be employed, provided its angle is within a particular range

Journal ArticleDOI
TL;DR: A paraxial wave equation for an azimuthally polarized field propagating in free space is developed and the propagation characteristics of the azIMuthal Bessel-Gauss beam solution are compared with a solution of the more familiar scalar paraxIAL wave equation, the linearly polarized Bessel - Gauss beam.
Abstract: We develop a paraxial wave equation for an azimuthally polarized field propagating in free space. The equation's beamlike solution is composed of a plane-wave propagation factor multiplied by a Bessel function of the first kind, of order one, and a Gaussian factor, which describe the transverse characteristics of the beam. We compare the propagation characteristics of the azimuthal Bessel-Gauss beam solution with a solution of the more familiar scalar paraxial wave equation, the linearly polarized Bessel-Gauss beam.

Journal ArticleDOI
TL;DR: The optical trapping of microscopic metal particles with a fixed Nd:YAG laser beam of TEM00 and TEM01* modes is demonstrated and consideration of a simple model on the basis of ray optics indicates that a fixed single beam itself can produce a force that will pull the particle into the beam axis.
Abstract: The optical trapping of microscopic metal particles with a fixed Nd:YAG laser beam of TEM00 and TEM01* modes is demonstrated. Three kinds of metal particles (bronze, silver, and gold) used in the experiments were trapped two-dimensionally only when the laser beam focus was located near the bottom of the particle. Consideration of a simple model on the basis of ray optics indicates that a fixed single beam itself can produce a force that will pull the particle into the beam axis. A linear focal pattern also was applied to trap several particles simultaneously.

Patent
17 Aug 1994
TL;DR: In this paper, a multiple beam laser sintering device with a focal point at a powder bed and at least one defocussed laser beam 116 incident on a region near the focal point of the focussed beam is considered.
Abstract: A multiple beam laser sintering device includes a sintering beam 64 having a focal point at a powder bed 68 and at least one defocussed laser beam 116 incident on a region near the focal point of the focussed beam 64. The sintering beam 64 raises the temperature of the powder 84 to the sintering temperature. The defocussed beam 116 raises the temperature of the material surrounding the sintering beam 64 to a level below the sintering temperature, thereby reducing the temperature gradient between the sintering location and the surrounding material. Thermal radiation may be measured from one or both beams and used to control the power of one or both beams and the power of one or both beams may be controlled to maintain the temperature at a desired level. Alternatively, a plurality of defocussed beams may be used to provide either a plurality of thermal gradient steps, or to control the temperature of each region around the sintering point independently.

Journal ArticleDOI
TL;DR: In this article, a variable-domain beam finite element, whose number of elements is fixed, while the sizes of the elements change with time, is derived for axially moving materials.

Journal ArticleDOI
TL;DR: In this paper, the generalized Lorenz-Mie theory is used to compute the radiation pressure force components on a particle arbitrarily located in a Gaussian beam, and the influence of the Gaussian character of the beam on resonance structures is discussed.

Journal ArticleDOI
TL;DR: In this article, the authors derived the equation of motion and associated boundary conditions for a uniform Bernoulli-Euler beam containing one single-edge crack and evaluated the rate of exponential decay from finite element calculations.

Patent
14 Apr 1994
TL;DR: In this article, a broadband visible and ultraviolet beam (42) is split into a sample beam (46) and a reference beam (48) to determine the relative reflectance spectrum of the observed sample.
Abstract: An improved method and apparatus for measuring the relative reflectance spectra of an observed sample (3) and method and apparatus for autofocussing the sample (3). A broadband visible and ultraviolet beam (42) is split into a sample beam (46) and a reference beam (48). The sample beam (46) is reflected off the surface of the sample (3), and the spectrum of the reflected sample beam (46) is compared to the spectrum of the reference beam (48) to determine the relative reflectance spectrum of the sample (3). A video camera (96) is provided for viewing the sample (3). The autofocus system has a course-focus mode and a fine-focus mode. In the course-focus mode, the sample (3) is focused when the centroid of the sample image is centered on a position sensitive detector (99). In the fine-focus mode, the sample is focused when the intensity of light reaching the detector (99) is minimized.

Journal ArticleDOI
TL;DR: In this paper, an attempt was made to determine if vibration frequencies of prestressed concrete members can be used to determine prestress losses, and the measured frequencies for both the bridge and the beam showed that, as the prestress force decreased, more microcracks opened and the members softened.
Abstract: This study was an attempt to determine if vibration frequencies of prestressed concrete members can be used to determine prestress losses. An actual post-tensioned bridge and a post-tensioned laboratory specimen were subjected to free vibration. Because the prestresses in the bridge and the beam were known, it was possible to determine if the changes in the measured frequencies would correlate with the prestress forces. The theoretical prediction for homogenous members was that, as the prestress force decreases, the frequency would increase because a reduction in the axial compressive load should stiffen the element. In contrast, the measured frequencies for both the bridge and the beam showed that, as the prestress force decreased, more microcracks opened and the members softened. Based on the measured data for the laboratory specimen, an empirical equation was developed that accounts for the effect of axial force on the rigidity of the element. This expression was used for an actual bridge and led to a reasonable estimate of the fundamental frequency at different prestress forces.

Journal ArticleDOI
TL;DR: In this paper, a simple holographic technique is used to generate a nondiverging hollow beam, which is similar to a Bessel beam, obtained from a Gaussian beam with a high conversion efficiency.
Abstract: A simple holographic technique is used to generate a nondiverging hollow beam, which is similar to a ${\mathit{J}}_{1}$ Bessel beam. The hollow beam is obtained from a Gaussian beam with a high conversion efficiency (greater than 50%). We describe briefly the merit of this hollow beam, which has potential applications in particle collimation.