Showing papers on "Beam (structure) published in 1987"

Diffraction-free beams.

Abstract: It was recently predicted that nondiffracting beams, with beam spots as small as a few wavelengths, can exist and propagate in free space. We report the first experimental investigation of these beams.

Use of piezoelectric actuators as elements of intelligent structures

Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.

Spatial dissipative structures in passive optical systems

Abstract: We consider a nonlinear, passive optical system contained in an appropriate cavity, and driven by a coherent, plane-wave, stationary beam. Under suitable conditions, diffraction gives rise to an instability which leads to the emergence of a stationary spatial dissipative structure in the transverse profile of the transmitted beam.

Gaussian beam tracing for computing ocean acoustic fields

Abstract: The method of Gaussian beam tracing has recently received a great deal of attention in the seismological community. In comparison to standard ray tracing, the method has the advantage of being free of certain ray‐tracing artifacts such as perfect shadows and infinitely high energy at caustics. It also obviates the need for eigenray computations. The technique is especially attractive for high‐frequency, range‐dependent problems where normal mode, FFP, or parabolic models are not practical alternatives. The Gaussian beam method associates with each ray a beam with a Gaussian intensity profile normal to the ray. The beamwidth and curvature are governed by an additional pair of differential equations, which are integrated along with the usual ray equations to compute the beam field in the vicinity of the central ray of the beam. We have adapted the beam‐tracing method to the typical ocean acoustic problem of a point source in a cylindrically symmetric waveguide with depth‐dependent sound speed. We present an overview of the method and a comparison of results obtained by conventional ray‐tracing, beam‐tracing, and full‐wave theories. These results suggest that beam tracing is markedly superior to conventional ray tracing.

Nonlinear Beam Kinematics by Decomposition of the Rotation Tensor

Abstract: A simple matrix expression is obtained for the strain components of a beam in which the displacements and rotations are large. The only restrictions are on the magnitudes of the strain and of the local rotation, a newly-identified kinematical quantity. The local rotation is defined as the change of orientation of material elements relative to the change of orientation of the beam reference triad. The vectors and tensors in the theory are resolved along orthogonal triads of base vectors centered along the undeformed and deformed beam reference axes, so Cartesian tensor notation is used. Although a curvilinear coordinate system is natural to the beam problem, the complications usually associated with its use are circumvented. Local rotations appear explicitly in the resulting strain expressions, facilitating the treatment of beams with both open and closed cross sections in applications of the theory. The theory is used to obtain the kinematical relations for coupled bending, torsion extension, shear deformation, and warping of an initially curved and twisted beam.

Ultrasound Doppler Probing of Flows Transverse with Respect to Beam Axis

Abstract: It is an accepted fact that transverse Doppler effects of the first order in v/c are nonexistent for all physical wave phenomena, including acoustics, i.e., the Doppler effect is zero for radiation normal to the direction of motion. However, this statement assumes that the incident field is a plane wave, which is not true in general for finite aperture sources. Consequently, the probing of flows transverse to the axis of finite diameter beams, particularly focused beams, is feasible. This geometry will be advantageous in many applications where the classical orientation of the sound beam, oblique to the flow, is not possible. With this motivation in mind, the theory and experimental feasibility of measuring Doppler spectra in transverse geometries is presently investigated.

Laser spray nozzle and method

Abstract: A laser spray nozzle assembly includes a nozzle body with first and second spaced apart end portions. A beam passageway extends between the end portions and permits a laser beam to pass therethrough. A housing surrounds the second end portion. The housing is spaced from the second end portion and forms an annular passage. The housing has an opening coaxial with the beam passageway for permitting the laser beam to pass therethrough. A cladding powder supply system is operably associated with the passage for supplying cladding powder thereto so that the powder exits the opening coaxial with the beam.

Beam Loading in Plasma Accelerators

Abstract: Acceleration of particles in high-phase-velocity plasma waves is attractive because of the extremely high accelerating gradients that can be obtained. 3 However, a high gradient is only one important benchmark for an accelerator. It is also important to know how many particles can be accelerated (i.e., luminosity), what will be the beam quality (i.e., emittance), and what will be the overall efficiency of the device. In this paper, we address these issues for plasma-wave accelerators. The results apply to both the beat-wave ,4 and wake-field,s,6 accelerator schemes. Previous work by R. Ruth et al. 5 has addressed emittance matching in plasma wake fields driven by unshaped electron bunches. S. Van der Meer? has considered specialized shaping of an accelerated beam to reduce its energy spread. Here we consider simultaneously the constraints on emittance and energy spread. These lead to quantitative estimates of the maximum number of particles that can be accelerated in plasma waves and the resulting efficiency. We augment the analysis with self-consistent particle-in-cell computer simulations. In order to find the maximum number of particles that can be accelerated by a plasma wave, we first review the wake field generated by a relativistic chargedparticle bunch of arbitrary shape (Section 2). The beam-loading problem can then be analyzed by applying linear superposition of the bunch wake field and the accelerating plasma-wave field. This is done for a one-dimensional approximation in Section 3 and for three dimensions in Section 4.

Design Of A Long Trace Surface Profiler

Abstract: The design of a long-trace surface profiler for the non-contact measurement of surface profile, slope error and curvature on cylindrical synchrotron radiation (SR) mirror is pre-sented here. The optical system is based upon the concept of a pencil-beam interferometer with an inherent large depth-of-field. The key feature of the optical system is the zero-path-difference beam splitter, which separates the laser beam into two colinear, variable-separation probe beams. A linear array detector is used to record the interference fringe in the image, and analysis of the fringe location as a function of scan position allows one to reconstruct the surface profile. The optical head is mounted on an air bearing slide with the capability to measure 38" long aspheric optics, typical of those encountered in SR applications. A novel feature of the optical system is the use of a transverse "outrigger" beam which provides information on the relative alignment of the scan axis to the cylinder optic symmetry axis.

Shear and moment capacity of reinforced steel-fibre-concrete beams

Abstract: Synopsis An analytical approach for predicting the shear and moment capacity of reinforced steel-fibre-concrete (RSFC) beams is proposed. Recent plasticity analyses for shear capacity of reinforced concrete beams are extended to RSFC beams by including the contribution of the fibres. Moment capacity is derived using the usual sectional analysis and fully plasticized stress blocks and forces. By establishing relevant capacities for a given beam loaded over a range of span/depth ratios, the capacity and governing mode of failure can be predicted. The observed failure loads and modes of failure for 22 test beams agree well with the predictions. Data presented in the literature are also analysed and compared. The present approach allows for direct comparison between the efectiveness of stirrups and fibres as shear reinforcement. The results suggest that fibres can replace stirrups partially or wholly as long as parity in the shear reinforcement factor is maintained.

Active vibration control of a simply supported beam using a spatially distributed actuator

Abstract: The application of a spatially shaped distributed actuator for the vibration control of a simply supported beam is studied both analytically and experimentally. The actuator consists of a layer of polyvinylidene fluoride (PVF 2 ) bonded to one face of the beam. A summary of the underlying theory is presented, with emphasis on how controllability requirements affect the choice of the film's spatial distribution. The requisite film controller has a linearly varying spatial distribution that facilitates the control of both even- and odd-order vibrational modes. Experimental results are presented for the control of the beam's first three modes, using both the linearly varying as well as a uniform spatial distribution. The linearly varying distribution is shown to be effective in controlling both even- and odd-order modes, serving to increase the modal loss factors by up to a factor of 4.5. In addition, the experimental results are found to corroborate a simplified computer model of the controller.

Influence of age of loading, water-cement ratio and rate of loading on fracture energy of concrete

Abstract: The applicability of linear elastic fracture mechanics to a composite material such as concrete has always been questioned. Recently, a new approach to describe failure of concrete has been developed. In this context a material is characterized by its fracture energy and the shape of the descending branch of the strain softening diagram. So far little work has been done to determine experimentally major influences on these material parameters. In this contribution results of test series to study the influence of age of loading, water-cement ratio, and rate of loading are presented. It is shown that a detailed evaluation of the test data necessitates appropriate computer programs. Essentials of these modules are briefly described. It is shown that failure of a beam under three-point bending mode can be predicted in a realistic way if valid material parameters are incorporated in a numerical analysis. Finally, it is pointed out that further studies are needed before a general application of the new approach can be recommended.

Effect of Curvature on Stability of Curved Beams

Abstract: This paper intends to derive the nonlinear differential equations of equilibrium for a horizontally curved I‐beam. Based on the principle of virtual displacements, the equilibrium of a bar is established for its deformed or buckled configuration using a Lagrangian approach. Central to the consideration of the effect of curvature is the expression of various quantities in cylindrical coordinates and the incorporation of radial stresses in the virtual work statement. The governing differential equations are obtained for the curved beam as the Euler‐Lagrange equations of the functional using a variational procedure. Rationality of the present theory is demonstrated for some typical examples, where the sources of errors in existing theories are traced. Also illustrated is the inconsistency involved in a conventional finite element analysis in which a curved beam is represented by several straight beam elements.

The role of damage-softened material behavior in the fracture of composites and adhesives

Abstract: Failure mechanisms of materials under very high strain experienced at and ahead of the crack tip such as the formation, growth and interaction of microvoids in ductile materials, microcracks in brittle solids or crazes in polymers and adhesives are represented by one-dimensional, nonlinear stress-strain relations possessing different post-yield softening (strain-softening) behavior. These reflect different ways by which the material loses capacity to carry load up to fracture or total separation. A DCB type specimen is considered in this study. * The nonlinear material is confined to a thin strip between the two elastic beams loaded by a wedge. The problem is first modelled as a beam on a nonlinear foundation. The pertinent equation is solved numerically as a two-point boundary value problem for both the stationary and the quasi-statically propagating crack. A finite element model is then used to model the problem in more detail to assess the adequacy of the beam model for the use of experimental data to determine in-situ properties of the thin interlayer.

Electron beam propagation in the ion‐focused regime

Abstract: In this paper the features of propagation of intense relativistic beams are discussed in the environment of low‐density (≲1 Torr), partially ionized gas. Beam phenomena in this ion‐focused regime (IFR) are found to be analogous to those at much higher density. Several instabilities and dissipative mechanisms have been identified and are compared to their high‐density counterparts. Scaling laws are derived for quantitative estimation of these effects. In general, it is found that long propagation distances are possible in the laboratory suggesting that this regime may be useful for controlled beam transport and conditioning.

Lightweight composite automotive door beam and method of manufacturing same

Abstract: A lightweight, composite beam for reinforcing a vehicle door is provided. The reinforcing beam comprises an open channel-shaped metal member having a longitudinal cavity which is filled with a reinforcing polymeric material which in one aspect is a thermoset or thermoplastic resin-based material. The composite beam includes end pieces which are adapted to be mounted to a vehicle door panel in a door cavity by spot-welds or the like. The horizontally mounted beam provided substantially increased resistance to side impacts to the vehicle door in the event of a collision. In one embodiment, the beam is mounted between the window glass space and the inner door panel for flush-glass vehicle doors. In another configuration, one surface of the beam is sculptured to mate with a concise outer door panel.

Impact behaviour of concrete beams

Abstract: An instrumented impact machine was used to carry out impact tests on concrete beams, 100×125 mm in cross-section and 1400 mm long. The simply supported beams were struck at their midpoints by a 345 kg mass impact hammer, dropped from various heights. The instrumentation included strain gauges mounted on the striking end of the hammer, strain gauges mounted on one support anvil, and three accelerometers placed at various locations along the beam. The data were collected using a 5-channel data acquisition system. Normal strength, high strength, and fibre reinforced concrete beams were tested. In general, it was found that the properties of concrete under the high stress rates associated with impact loading could not be predicted from conventional static tests.

Large displacement analysis of naturally curved and twisted composite beams

Abstract: This paper presents an efficient procedure for analyzing naturally curved and twisted beams undergoing large displacements and rotations but small strains. Special care is taken to accurately model the structural behavior of the beam: shearing deformations as well as torsion-related warping are taken into account. The various elastic couplings (e.g., bending-twisting or extention-twisting) that can arise in composite beams are also modeled in a rational fashion. The equations are derived in curvilinear material coordinates, and Euler angles are used to represent the arbitrarily large rotations. The strain energy in the beam is reduced to a quadratic expression by means of a quasilinearization procedure. This expression of the strain energy is the basis for a finite-element analysis of the structure, and standard iteration techniques are used to obtain nonlinear solutions to the problem. The predictions of this model are found to be in good agreement with the experimental results, and the computational efficiency is greatly improved as compared with other available analyses.

The ion-ion acoustic instability

Abstract: This paper considers the linear theory of ion-acoustic-like instabilities in a homogeneous Vlasov plasma with two ion components, a less dense beam and a more dense core, with a relative drift velocity. Numerical solutions of the full electrostatic dispersion equation are presented, and the properties of the ion-ion acoustic instability are studied in detail. At relatively cold beam temperatures, the instability is fluid-like, but it becomes a beam resonant kinetic instability as the beam temperature becomes of the order of the core temperature; if the mode is unstable, its threshold lies well below the threshold of the electron-ion acoustic instability. An electron temperature anisotropy enhances the instability, and at sufficiently large beam-core relative drift speeds, electron magnetization can either detract from or enhance the instability.

High power with high efficiency in a narrow single‐lobed beam from a diode laser array in an external cavity

Abstract: High output power (700 mW) in a nearly diffraction‐limited (07°) single‐lobed nonsteering output beam is obtained from a gain‐guided diode laser array in a novel, easily fabricated external cavity configuration The laser output beam is collimated in both lateral and vertical directions Differential quantum efficiency as high as 70% has been measured along with excellent linearity of the optical power versus current characteristic The power and efficiency are the highest reported for a coupled‐stripe laser array emitting a narrow single‐lobed beam

Optical beam integration system

Abstract: An improved optical beam integration system for homogenizing a nonuniform radiant energy beam having a nonuniform beam intensity profile characteristic. The optical beam integration system comprises a first crossed lenticular cylindrical lens structure, a second crossed lenticular cylindrical lens structure, and a focusing lens interposed between a radiant energy source and an image or work plane. The nonuniform radiant energy beam from the radiant energy source refracts sequentially through the first and second crossed lenticular cylindrical lens structures and the focusing lens so as to produce a homogenized beam which forms an image in the work plane. The work plane is at a constant distance from the optical beam integration system. Preferably, the optical beam integration system is adjustable for selectively setting the size of the image produced by the homogenized beam in the work plane. The optical beam integration system is also preferably adjustable so that the aspect ratio of the image produced by the homogenized beam in the work plane can be selectively set. As a result, the effectiveness and flexibility of semiconductor processing by means of an ultraviolet excimer laser, for example, are substantially improved.

Analysis of radiation focusing and steering in the free-electron laser by use of a source-dependent expansion technique.

Abstract: In the free-electron laser the resonant interaction between the radiation field and electron beam can result in radiation focusing (optical guiding) If the centroid of the electron beam is transversely displaced off axis, the radiation field, under certain conditions, will follow and be steered by the electron beam The effect of a spatial modulation on the electron-beam envelope can also modify the propagation characteristics of the radiation These and other phenomena are analytically and numerically studied using a novel source-dependent Laguerre-Gaussian modal representation of the fully three-dimensional radiation field Unlike the vacuum Laguerre-Gaussian modal expansion, the longitudinal spatial dependence of the radiation waist and curvature are determined and characterized by the source term in the wave equation Among the advantages of this general source-dependent expansion approach is that few modes are needed to accurately describe the radiation Hence, fast and accurate numerical solutions of the fully three-dimensional free-electron laser problem can be obtained over distances of many Rayleigh lengths Furthermore, this expansion enables us to drive an envelope equation for the radiation beam as well as an expression for the centroid of the beam

An Adaptive Multiple Beam System Concept

Abstract: An adaptive multiple beam system, which has flexibility to adapt beam power to varying beam traffic, is proposed. The multiple beam transmitter, which is called "hybrid transponder" in this paper, consists of a pair of multiport hybrids and a set of amplifying elements. Power combining, isolation, and intermodulation characteristics of this multiport network are analyzed. Also, a new interbeam exchange and feeder link connection concept, which serves as the basis for an adaptive multiple beam system, is proposed. Finally, characteristics of an experimental 8-amplifier 8-port hybrid transponder are described.

Method and apparatus for optically detecting surface states in materials

Abstract: A method and apparatus is disclosed for detecting defect surface states in any material and in particular semiconductors. In the subject device, a periodic localized excitation is generated at the surface of the sample with an intensity modulated pump laser beam. A probe laser beam is directed to the surface of the sample and changes in the probe beam which are in phase with the modulated pump frequency are detected. In the preferred embodiment, periodic changes in the optical reflectivity of the surface of the sample induced by an intensity modulated excitation beam are detected by measuring the corresponding modulations in the reflected power of the probe beam. Any time dependence of the probe beam modulated reflectance signal is monitored. An evaluation of defect surface states is then made by investigating the time dependence of the magnitude and/or phase of this probe beam modulated reflectance signal.

Ion beam scanning method and apparatus

Abstract: An ion beam scanning method and apparatus produces a parallel scanned ion beam (12) with a magnetic deflector (26) having in one instance wedge-shaped pole pieces (28, 30) that develop a uniform magnetic field A beam accelerator (68) for the scanned beam has a slot-shaped passage (42a, 44a) which the scanned beam traverses The beam scan and the beam traverse over a target object (64) are controlled to attain selected beam current, and correspondingly ion dose, on a target object

Nonlinear Control of a Distributed System: Simulation and Experimental Results

Abstract: A nonlinear active vibration damper has been developed which uses a spatially distributed piezoelectric actuator, polyvinylidene flouride, to achieve active vibration control of a cantilever beam. The control algorithm was derived using Lyapunov’s Second Method. All modes of the beam can be controlled simultaneously if the angular velocity of the tip of the beam is known. A simulation algorithm was developed to predict the effect of the control on the free decay of a single mode. A parameter study for the first mode was performed and compared to experimental results. The active damper has been tested successfully on two different scale structures.