Topic
Beam (structure)
About: Beam (structure) is a research topic. Over the lifetime, 155735 publications have been published within this topic receiving 1420731 citations.
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TL;DR: It is shown that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.
Abstract: Cylindrical-vector beams are of increasing recent interest for their role in novel laser resonators and their applications to electron acceleration and scanning microscopy. In this paper, we calculate cylindrical-vector fields, near the focal region of an aplanatic lens, and briefly discuss some applications. We show that, in the particular case of a tightly focused, radially polarized beam, the polarization shows large inhomogeneities in the focal region, while the azimuthally polarized beam is purely transverse even at very high numerical apertures.
1,472 citations
TL;DR: In this article, an active vibration damper for a cantilever beam was designed using a distributed-parameter actuator and distributedparameter control theory, and preliminary testing of the damper was performed on the first mode of the beam.
Abstract: An active vibration damper for a cantilever beam was designed using a distributed-parameter actuator and distributed-parameter control theory. The distributed-parameter actuator was a piezoelectric polymer, poly (vinylidene fluoride). Lyapunov's second method for distributed-parameter systems was used to design a control algorithm for the damper. If the angular velocity of the tip of the beam is known, all modes of the beam can be controlled simultaneously. Preliminary testing of the damper was performed on the first mode of the cantilever beam. A linear constant-gain controller and a nonlinear constant-amplitude controller were compared. The baseline loss factor of the first mode was 0.003 for large-amplitude vibrations (± 2 cm tip displacement) decreasing to 0.001 for small vibrations (±0.5 mm tip displacement). The constant-gain controller provided more than a factor of two increase in the modal damping with a feedback voltage limit of 200 V rms. With the same voltage limit, the constant-amplitude controller achieved the same damping as the constant-gain controller for large vibrations, but increased the modal loss factor by more than an order of magnitude to at least 0.040 for small vibration levels.
1,408 citations
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
TL;DR: In this article, a detailed theoretical analysis of the frequency response of a cantilever beam that is immersed in a viscous fluid and excited by an arbitrary driving force is presented.
Abstract: The vibrational characteristics of a cantilever beam are well known to strongly depend on the fluid in which the beam is immersed. In this paper, we present a detailed theoretical analysis of the frequency response of a cantilever beam, that is immersed in a viscous fluid and excited by an arbitrary driving force. Due to its practical importance in application to the atomic force microscope (AFM), we consider in detail the special case of a cantilever beam that is excited by a thermal driving force. This will incorporate the presentation of explicit analytical formulae and numerical results, which will be of value to the users and designers of AFM cantilever beams.
1,359 citations
TL;DR: In this article, a structural mechanics approach to modeling the deformation of carbon nanotubes is presented, where the primary bonds between two nearest-neighboring atoms act like loadbearing beam members, whereas an individual atom acts as the joint of the related beam members.
1,266 citations