Showing papers on "Beam (structure) published in 1992"

Dependence of the quality factor of micromachined silicon beam resonators on pressure and geometry

Abstract: An experimental study of damping and frequency of vibrating small cantilever beams in their lowest eigenstate is presented. The cantilever beams are fabricated from monocrystalline silicon by means of micromachining methods. Their size is a few millimeters in length, a few 100 µm in width, and a few 10 µm in thickness. Damping and resonance frequency are studied as a function of the ambient pressure p (1–105 Pa) and the geometry of the beam. The purpose of this research was to obtain design rules for sensors employing vibrating beams. The analysis of the experimental results in terms of a semiqualitative model reveals that one can distinguish three mechanisms for the pressure dependence of the damping: viscous, molecular, and intrinsic. For viscous damping a turbulent boundary layer dominates the damping at high pressures (105 Pa), while at smaller pressure laminar flow dominates. In the latter region, this leads to a plateau for the quality factor Q and in the former to Q p. The pressure pc at which the transition from laminar flow dominated damping to turbulent flow dominated damping occurs depends on the geometry of the beams. pc is independent on the length and decreases with both, the width and the thickness of the beams.

High‐Order Theory for Sandwich‐Beam Behavior with Transversely Flexible Core

Abstract: A general high-order theory based on variational principles is presented for the bending behavior of a sandwich beam with a core that is vertically flexible. The theory embodies a rigorous and systematic approach to the analysis of such structures, which have high-order effects caused by the nonlinearity of the longitudinal and the transverse deformations of the core through the height. As such, it improves on the available classical and superposition theories. Beam construction consists of the upper and lower skin, metallic or composite laminated symmetric, with nonidentical mechanical and geometrical properties, and a soft core made of foam or honeycomb. The formulation uses a beam theory for the skins and a two-dimensional elasticity theory for the core. The behavior is presented in terms of internal resultants and displacements in skins, peeling and shear stresses in skin-core interfaces, and stress and displacement fields in the core, even in the vicinity of concentrated loads. The method is applicable to any type of loading exerted on the skins and to any type of boundary or continuity conditions, including cases in which at the same section the conditions at the upper skin are different from those at the lower. Some typical cases are studied numerically.

Transparent boundary condition for the beam propagation method

Abstract: A new boundary condition is presented for use in beam propagation calculations that passes outgoing radiation freely with minimum reflection coefficient (as low as 3*10/sup -8/). In conjunction with a standard Crank-Nicholson finite difference scheme, the assumption that the radiation field behaves as a complex exponential near the boundary is shown to result in a specific transparent boundary condition algorithm. In contrast to the commonly used absorber method, this algorithm contains no adjustable parameters, and is thus problem independent. It is shown to be accurate and robust for both two- and three-dimensional problems. >

Strengthening of RC beams with epoxy-bonded fibre-composite materials

Abstract: Strengthening of concrete beams with externally bonded fibre-reinforced plastic (FRP) materials appears to be a feasible way of increasing the load-carrying capacity and stiffness characteristics of existing structures. FRP-strengthened concrete beams can fail in several ways when loaded in bending. The following collapse mechanisms are identified and analysed in this study: steel yield-FRP rupture, steel yield-concrete crushing, compressive failure, and debonding. Here we obtain equations describing each failure mechanism using the strain compatibility method, concepts of fracture mechanics and a simple model for the FRP peeling-off debonding mechanism due to the development of shear cracks. We then produce diagrams showing the beam designs for which each failure mechanism is dominant, examine the effect of FRP sheets on the ductility and stiffness of strengthened components, and give results of four-point bending tests confirming our analysis. The analytical results obtained can be used in establishing an FRP selection procedure for external strengthening of reinforced concrete members with lightweight and durable materials.

High frequency printing mechanism

Abstract: The present invention provides an ink-jet ejection device which is capable of ejection or ink (including hot melt ink) jet frequencies greater than 50,000 Hz. A cantilevered beam of selected shape is mounted at its base to a piezoelectric element which oscillates the base. The beam is shaped so that its moment of inertia is reduced toward its free end. The element is activated by an oscillating electrical signal the frequency of which is equal to or close to a natural frequency of oscillation of the beam. In the preferred embodiment herein a third or higher modal frequency is utilized. Because of the structural configuration of the cantilevered beam and the selected frequency of oscillation thereof, the tip of the beam oscillates over an amplitude which is significantly greater than the oscillation amplitude of the base. The beam is highly damped and made of low density material so that the tip amplitude is extremely responsive to variations in the base amplitude. The tip of the beam is provided with an aperture which is preferably tapered in cross-section. One opening of the tapered aperture is in fluid communication with a reservoir of ink and the other opening of the aperture is positioned at an appropriate distance from a recording medium such as paper towards which individual droplets of ink from the reservoir are to be propelled. When the tip amplitude is above a predetermined threshold the solid-fluid interaction between the tapered aperture and the ink causes a drop of ink to accelerate through the aperture and be ejected upon each excursion of the tip of the beam toward the printing media.

Non-linear vibration of a traveling tensioned beam

Abstract: Free non-linear vibration of an axially moving, elastic, tensioned beam is analyzed over the sub- and supercritical transport speed ranges. The pattern of equilibria is analogous to that of Euler column buckling and consists of the straight configuration and of non-trivial solutions that bifurcate with speed. The governing equations for finite local motion about the trivial equilibrium and for motion about each bifurcated solution are cast in the standard form of continuous gyroscopic systems. A perturbation theory for the near-modal free vibration of a general gyroscopic system with weakly non-linear stiffness and/or dissipation is derived through the asymptotic method of Krylov, Bogoliubov, and Mitropolsky. The method is subsequently specialized to non-linear vibration of a traveling beam, and of a traveling string in the limit of vanishing flexural rigidity. The contribution of non-linear stiffness to the response increases with subcritical speed, grows most rapidly near the critical speed, and can be several times greater for a translating beam than for one that is not translating. In the supercritical speed range, asymmetry of the non-linear stiffness distribution biases finite-amplitude vibration toward the straight configuration and lowers the effective modal stiffness. The linear vibration theory underestimates stability in the subcritical range, overestimates it for supercritical speeds, and is most limited in the near-critical regime.

Quasi-optical techniques

Abstract: The basic theory of quasi-optical Gaussian beam propagation and beam transformation by simple optical elements is summarized, and coupling to and between Gaussian beams is briefly discussed Guidelines for Gaussian optics system design are reviewed, the most important being beam truncation and matching Passive components in the terahertz frequency range based on quasi-optical propagation, including polarization processors, filters, diplexers, and ferrite devices, are examined Some active quasi-optical devices, including multielement oscillators, frequency multipliers, and phase shifters, are described Some specific applications of quasi-optical systems are briefly described >

Using light as a lens for submicron, neutral-atom lithography.

Abstract: We show that light can be used as a lens to focus a collimated neutral atomic beam to submicron dimensions during deposition onto a substrate. We have used an optical standing wave at 589 nm as an array of cylindrical lenses to focus a perpendicular sodium beam into a grating on a substrate, with a periodicity of 294.3\ifmmode\pm\else\textpm\fi{}0.3 nm. This result is the first direct evidence of submicron focusing of atoms by light, and represents a fundamentally new scheme for submicron lithography.

Free vibrations of delaminated beams

Abstract: Free vibration of laminated composite beams is studied. The effect of interply delaminations on natural frequencies and mode shapes is evaluated both analytically and experimentally. The equation of motion and associated boundary conditions are derived for the free vibration of a composite beam with a delamination of arbitrary size and location. A generalized variational principle is used to formulate the equation of motion, taking into account the interlaminar stress concentration at the crack-tips. This is accomplished by introducing a 'crack function' into the beam's compatibility relations. This function has its maximum value at the crack tip and decays exponentially in the longitudinal direction. The rate of exponential decay is determined by a least-square fit with the experimental results. The effect of coupling between longitudinal vibration and bending vibration is considered in the present study. This coupling effect is found to significantly affect the natural frequencies and mode shapes of the delaminated beam.

Observation of quantum frequency conversion

Abstract: Quantum frequency conversion, a process with which an input beam of light can be converted into an output beam of a different frequency while preserving the quantum state, is experimentally demonstrated for the first time. Nonclassical intensity correlation (\ensuremath{\simeq}3 dB) between two beams at 1064 nm is used as the input quantum property. When the frequency of one of the beams is converted from 1064 to 532 nm, nonclassical intensity correlations (\ensuremath{\simeq}1.5 dB) appear between the up-converted beam and the remaining beam. Our measurements are in excellent agreement with the quantum theory of frequency conversion. The development of tunable sources of novel quantum light states seems possible.

Characteristics of polysilicon resonant microbeams

Abstract: Polysilicon resonant microbeams can be used as strain-sensitive elements to replace conventional silicon piezoresistors in precision sensor applications, such as pressure sensors and accelerometers. These elements are combined with conventional silicon diaphragms or flexures with a proof mass to convert pressure or acceleration directly into a frequency output. Vacuum-enclosed resonant microbeam elements 200 or 400 μm long, 45 μm wide and 1.8 μm thick have been fabricated using LPCVD mechanical-grade polysilicon at the University of Wisconsin. Q-values determined using gain/phase analysis are typically over 25 000. Lower Q-values are primarily the result of residual gas in the cavity. Closed-loop operation from −60 to 180°C using piezoresistive sensor and electrostatic drive has been achieved with automatic gain control (AGC) to prevent overdrive. The characteristic resonance frequencies of the beams have been measured, with 550 kHz, 1.2, 2.2 and 5.2 MHz being typical of the frequencies of the one-dimensional bending modes for the 200 μm length. These measurements of the multiple resonance frequencies of a single beam provide a means of testing mathematical models of the dynamic behavior as well as determining the residual beam stress. The one-dimensional (1D) differential equation of motion of a doubly clamped single-span beam with an axial load can be solved analytically for lateral natural frequencies and mode shapes. These 1D solutions have been verified by 3D finite-element methods. In addition, the finite-element models are used to identify both lateral and torsional modes. The closed-form solutions agree closely with the numerical results and the experimental data.

Reinforced Concrete Beams with Plates Glued to their Soffits

Abstract: Reinforced concrete beams can be strengthened and stiffened by gluing steel plates to the tension face of the beam. However, experimental tests show that shear and flexural forces can cause these externally bonded plates to peel away before the design load is reached. In this paper, peeling due to shear forces and the interaction between shear peeling and flexural peeling is studied, and the results are used to formulate a design procedure to prevent debonding due to peeling for reinforced concrete beams that have been strengthened or stiffened by gluing steel plates to their soffits. It is shown that this system is better suited for the strengthening of reinforced concrete slabs than reinforced concrete beams, although it enhances the serviceability requirements of both types of structures.

Digital flexure beam accelerometer

Abstract: Acceleration is measured using an array of micro-machined elements. The array is configured so each successive element is deflected by a higher acceleration. For each acceleration there will be a set of elements that is deflected. By determining the transition point between deflected and undeflected elements, the acceleration can be measured.

Method of treatment room selection verification in a radiation beam therapy system

Abstract: The present invention is directed to a method of treatment room selection verification in a radiation beam therapy system. The method compares treatment room beam request signals with a beam path configuration signal from a switchyard which controls the path of beam travel from an accelerator to one of the treatment rooms. Upon agreement of the request and beam path signals, beam transport to a selected treatment is authorized.

Differential-pencil-beam dose calculations for charged particles

Abstract: The use of a convolution or differential‐pencil‐beam (DPB) algorithm has been studied for charged‐particle dose calculations as a means of more accurately modeling the effects of multiple scattering. Such effects are not reflected in current charged‐particle dose calculations since these calculations rely on depth‐dose data measured in homogeneous water‐equivalent phantoms and use ray‐tracing techniques to calculate the water‐equivalent pathlength from patient CT data. In this study, isodose plots were generated from three‐dimensional dose calculations using Monte Carlo, DPB, and standard ray‐tracing methods for a 4‐cm modulated 150‐MeV proton beam incident on both homogeneous and heterogeneous phantoms. To simulate therapy conditions with charged particles, these studies included cases where compensating boluses were introduced to modify the particle range across the treatment field. Results indicate that multiple‐scattering effects, including increased penumbral width as a function of beam penetration and the ‘‘smearing’’ of isodose distributions downstream from complex heterogeneities, are well modeled by the DPB algorithm. The DPB algorithm may also be used to obtain more useful estimates of the dose uncertainty in regions near the end of the beam’s range downstream from complex heterogeneities than can be derived from standard ray‐tracing calculations.

Method and apparatus for evaluating the thickness of thin films

Abstract: A method and apparatus is disclosed for measuring the thickness or other optical constants of a thin film on a sample. The apparatus includes a laser for generating a linearly polarized probe beam. The probe beam is tightly focused on the sample surface to create a spread of angles of incidence. The reflected probe beam is passed through a quarter-wave plate and linear polarizer before impinging on a quad cell photodetector. The output signals from the photodetector represent an integration of the intensity of individual rays having various angles of incidence. By taking the difference between the sums of the output signals of diametrically opposed quadrants, a value can be obtained which varies linearly with film thickness for very thin films. The subject device can be used in conjunction with other prior devices to enhance sensitivity for thicker films.

Theoretical study of crack-induced eigenfrequency changes on beam structures

Abstract: The theoretical relationships between eigenfrequency changes and magnitudes and the locations of crack-induced damage are developed for beam structures with either simply supported or cantilever boundary conditions. For uniform beams, a physical model of a massless rotational spring is used to represent the local flexibility introduced by the crack. A characteristic equation is derived as a base for the development of the relationship. A symbolic computational package, MACSYMA, is used to facilitate the computations of the higher-order determinant and the corresponding derivatives involved in the characteristic equations. For nonuniform beams, the concept of receptance is used for a system linked with two coordinates (axial and rotational coordinates). Numerical experiments involving the use of a finite-element program, SAP, to determine the eigenfrequencies of both uniform and nonuniform beams with a variety of damage scenarios are used to validate the derived theoretical relationships. The comparisons between the predicted and simulated damage conditions are satisfactory. Two important assumptions are involved in the derived relationship: one is that the structure is considered to behave linearly, and the other one is that the elastic properties of the structure member are time-invariant. The application of the theoretical model is discussed at the end of the paper.

Optical dispersion technique for time-delay beam steering

Abstract: A simple technique for steering the microwave radiation beam of a phased-array antenna is proposed and analyzed. Chromatic dispersion in equal-length fibers is used.

Multi-point pyrometry with real-time surface emissivity compensation

Abstract: A multi-point non-invasive, real-time pyrometry-based temperature sensor (200) for simultaneously sensing semiconductor wafer (22) temperature and compensating for wafer emissivity effects. The pyrometer (200) measures the radiant energy that a heated semiconductor wafer (22) emits and coherent beams of light (224) that the semiconductor wafer (22) reflects. As a result, the sensor (200) generates accurate, high-resolution multi-point measurements of semiconductor wafer (22) temperature during a device fabrication process. The pyrometer (200) includes an infrared laser source (202) that directs coherent light beam (203) into beam splitter (204). From the beam splitter (204), the coherent light beam (203) is split into numerous incident coherent beams (210). Beams (210) travel via optical fiber bundles (218) to the surface of semiconductor wafer (22) within the fabrication reactor (80). Each optical fiber bundle (218) collects reflected coherent light beam and radiant energy from wafer (22). Reflected coherent light beam (226) and radiant energy (222) is directed to a detector (240) for detecting signals and recording radiance, emissivity, and temperature values. Multiple optical fiber bundles (218) may be used in the sensor (200) for high spatial resolution multi-point measurements of wafer (22) temperature for precision real-time process control and uniformity optimizations.

Beam-beam phenomena in linear colliders

Abstract: The beam-beam interaction in electron-positron linear colliders shows very di erent aspects from that in storage rings. The single-pass nature of the linear colliders allows drastic deformation of the bunch shape during one collision. Also, under the very strong electro-magnetic eld together with the high beam energy, phenomena which are not important in storage rings come into play, namely the phenomena involving the quantum eld theory. The synchrotron radiation in the beam-beam eld, called beamstrahlung, becomes extremely energetic. The strong eld can even create electronpositron pairs from the beamstrahlung photons. In the present lecture note both the classical and quantum phenomena are described. KEK Preprint 91-2, April 1991 Lecture at 1990 US-CERN School on Particle Accelerators, Nov.7-14, 1990, Hilton Head Island, So. Carolina, USA. Lecture Notes in Physics 400. Frontiers of Particle Beams: Intensity Limitations, Springer Verlag, pp. 415-445. Revised Nov. 1992. Printed. April 7, 1995 BEAM-BEAM PHENOMENA IN LINEAR COLLIDERS Kaoru Yokoya and Pisin Cheny Natinal Laboratory for High Energy Physics, Oho, Tsukuba-shi, Ibaraki, 305, Japan yStanford Linear Accelerator Center, Stanford University, Stanford, CA94309, USA

Catadioptric reduction projection optical system

Abstract: In a cata-dioptric optical system having a combination of a reflection system and a refraction system for reduction-projecting an object on a first plane onto a second plane, a polarization beam splitter and a quarter wavelength plate are provided to split the incident light and the reflected light. The light beam directed to the polarization beam splitter is converted to a substantially collimated light beam by a first group of lenses. A second group of lenses are arranged between the polarization beam splitter and a concave reflection mirror to diverge the light beam. The light reflected by the concave reflection mirror is directed back to the polarization beam splitter with a substantially collimated state by the second group of lenses. The light beam from the second group of lenses transmitted through the polarization beam splitter is focused by a third group of lenses having a positive refraction power to form a reduced image.

Bending of gel beams: method for characterizing elastic properties and permeability

Abstract: When a saturated gel is deformed, its mechanical response is profoundly influenced by the flow of liquid in its pores. For example, if a gel bar is suddenly deformed in 3-point bending, the liquid cannot immediately flow out of the pores, so the gel initially responds incompressibly; consequently, its deflection provides a measure of its shear modulus, G p , rather than Young's modulus, E p . In this paper, the kinetics of deformation of such a rod are analyzed, showing that it is possible to obtain the permeability, D , of the gel from the time-dependence of the load, as well as finding both G p and E p . Analyses are presented for the time dependence of the load at constant deflection for a square and cylindrical beam, and for load at constant deflection rate for a square beam. The method is applied to determine G p , E p , and D for a silica gel made from tetraethoxysilane.

Semiconductor laser device

Abstract: PURPOSE:To accurately feed back to a laser driving circuit by forming a photodiode film for monitoring directly or through a film for regulating a reflectivity on a back beam emitting end face. CONSTITUTION:In a semiconductor laser, electrodes 2, 2 are formed on the upper and lower surfaces of a laser diode chip 1 formed of an n-type region 1a, a p-type region 1b and a waveguide 1c, a thin film 3 for reducing the reflectivity is formed on the front end of the chip 1, a thin film 4 is formed on the rear end face, a photodiode film 5 is formed on the film 4, and a metal film 6 is further formed on the film 5. When a current flows to the chip 1, electrons are fed from the region 1a to the waveguide 1c, holes are fed from the region 1b to the waveguide 1c to generate a light, the generated laser light is propagated through the waveguide 1c to be irradiated from the front end of the chip 1 as a front beam 7, the other part is absorbed to the film 5 to generate a monitoring current. A laser driving circuit is controlled based on the monitoring current to control the front beam.

Method and apparatus for diagnostic imaging in radiation therapy

Abstract: An apparatus for diagnostic and verification imaging in radiation therapy that consists of attachments for standard radiotherapy equipment comprising an x-ray tube and an x-ray detector placed on opposite sides of a patient along the main axis of the beam produced by the treatment unit. The detector is placed on a plane orthogonal to the axis of the treatment beam and between the beam source and the patient, while the x-ray tube is placed on the other side of the patient, coaxially with the treatment beam and facing the detector. As a result of this configuration, the radiographic view of the x-ray beam, as seen on the detector, is equivalent to the view produced on the same detector by the therapeutic beam, varied only by parallax deviations that can be corrected by geometrical calculations. Accordingly, x-ray exposures and real-time verification of the position of a patient can be obtained with the same unit used for treatment and without requiring movement of either patient or equipment. In addition, the apparatus enables a user to produce diagnostic images that can be used directly to manufacture shielding blocks in conventional shielding-block cutters.

The Theory of Spiral Laser Beams in Nonlinear Media

Abstract: The analytical theory governing the propagation of spiral laser beams in nonlinear media is developed. It is shown that, taking into account the saturation effect in a Kerr medium, spiral beams have a tube-like structure with a periodicity along the axis of a nonlinear autoguide. In the case of the absence of saturation mechanism the collapse of spiral beams is described. It is found that critical autoguide power depends on the topological charge of the spiral beam. The stability of a circular symmetry structure of the beam is investigated. The analytical results are in good agreement with the numerical experiment.

Dynamic boundary control of a Euler-Bernoulli beam

Abstract: A flexible beam, clamped to a rigid base at one end and free at the other end is considered. To stabilize the beam vibrations, a dynamic boundary force control and a dynamic boundary torque control applied at the free end of the beam are proposed. It is proved that with the proposed controls, the beam vibrations decay exponentially. The proof uses a Lyapunov functional, based on the energy functional of the system. >