We report on a novel kind of accelerating beams that follow parabolic paths in free space. This accelerating peculiar polygon beam (APPB) not only exhibits autofocusing property, but also possesses two types of accelerating intensity maxima, i.e., the cusp and spot structure. We also provide a detailed insight into the theoretical origin and characteristics of this spatially accelerating beam through catastrophe theory. Moreover, experimental results confirm the peculiar features presented in the theoretical findings, and the APPB is further verified to exhibit self-healing property during propagation with either obstructed cusp or spot-like main lobe reconstructing after a certain distance. This accelerating beam with multiple types of main lobes has never been achieved previously, and we anticipate that APPB will facilitate the applications in the areas of biomedical manipulation and optofludics.
To explore the effect of the incident polarization on achieving polarization-controllable multifocal arrays (MFAs), the polarization-controllable MFAs generated by radially polarized (RP) and azimuthally polarized (AP) beams are compared in this work. Four phase filters for the numerical aperture (NA) of 0.80, 0.85, 0.90 and 0.95 are respectively designed to generate the polarization-controllable MFAs under the illumination of RP and AP beams. The intensity comparison demonstrates that the polarization-controllable MFAs generated by AP beams have the higher uniformity, smaller focal spots and more stable intensity distributions for the same NA. The polarization comparison demonstrates that the polarization properties of the polarization-controllable MFAs generated by AP beams are more consistent with the desired target. Therefore, the AP incident beam is the better choice to realize a polarization-controllable MFA by a phase filter.
The destruction of spatial complex tubular joints may lead to failure of the whole tubular structure, thus it is necessary to analyze the mechanical properties of spatial complex tubular joint. In this paper, a novel method based on close range photogrammetry to accurately measure the three-dimensional (3D) deformation of spatial complex tubular joints during loading test is proposed. Artificial targets are pasted on the deformation area before loading. The 3D coordinates of these targets are reconstructed by analyzing the images captured at each stage, and the coordinate systems of different stages are registered together by means of global transformation points. The whole field 3D deformation under different load levels is then obtained by tracking the homonymous targets among different stages. It is helpful for further analysis of the mechanical properties. Two different precision evaluation experiments indicate that the proposed method could achieve accuracy of 0.1mm/m. Two full scale tubular joints are tested and a feasible solution for improving the load carrying capacity of the tested tubular joints is thus obtained as per the measured results. For comparison, finite element analysis is employed to predict the deformation in a traditional way. The deformation tendency measured by two methods agrees well.
KEYWORDS: Calibration, 3D image processing, Digital image correlation, Cameras, Imaging systems, Stereoscopic cameras, 3D acquisition, Detection and tracking algorithms, 3D image reconstruction, Experimental mechanics
A three-dimensional (3-D) digital image correlation system for deformation measurement in experimental mechanics has been developed. The key technologies applied in the system are discussed in detail, including stereo camera calibration, digital image correlation, 3-D reconstruction, and 3-D displacement/strain computation. A stereo camera self-calibration algorithm based on photogrammetry is proposed. In the algorithm, the interior and exterior orientation parameters of stereo cameras and the 3-D coordinates of calibration target points are estimated together, using the bundle adjustment technique, so the 3-D coordinates of calibration target points are not needed in advance to get a reliable camera calibration result. An efficient image correlation scheme with high precision is developed using the iterative least-squares nonlinear optimization algorithm, and a method based on a seed point is proposed to provide a reliable initial value for the nonlinear optimization. After the 3-D coordinates of the object points are calculated using the triangulation method, the 3-D displacement/strain field could then be obtained from them. After calibration, the system accuracy for static profile, displacement, and strain measurement is evaluated through a series of experiments. The experiment results confirm that the proposed system is accurate and reliable for deformation measurement in experimental mechanics.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.