Numerical study of centroid detection accuracy for Shack-Hartmann wavefront sensor

2006 ◽  
Vol 38 (8) ◽  
pp. 614-619 ◽  
Author(s):  
Zhiling Jiang ◽  
Shunsheng Gong ◽  
Yang Dai
2009 ◽  
Vol 45 (6) ◽  
pp. 2736-2739 ◽  
Author(s):  
S. Hashi ◽  
S. Yabukami ◽  
H. Kanetaka ◽  
K. Ishiyama ◽  
K.I. Arai

2021 ◽  
Author(s):  
Zhe Wang ◽  
Xuedong Chen ◽  
Zhichao Fan ◽  
Wei Chen ◽  
Jingwei Cheng ◽  
...  

Abstract Electromagnetic acoustic transducer (EMAT) gradually becomes the main excitation method for surface wave, which is suitably used in periodic inspection or long-term monitoring of pressure equipment. However, the corroded surfaces appearing on the pressure pipes and vessels can cause an increase of background noise and remarkable attenuation of the echo wave, which restrict the improvement of detection accuracy of surface crack. In this paper, a finite element model of EMAT-Generated surface wave inspection for steel plate with rough surface is established based on the constitutive equation of ferromagnetic materials. Considering the Lorentz force and magnetostrictive effect, the influences of rough surface on energy conversion of multiple fields in the excitation and propagation process of electromagnetic acoustic surface wave are separately investigated. The surface wave responses of cracks characterized by rectangular groove on corroded rough surface have been analyzed further. The numerical results indicate that the rough surface of the excitation region below the transducer with a center frequency of 330 kHz has a slight effect on the surface wave energy, while the surface roughness of the propagation region attenuates echo signal of crack significantly. The reflection coefficients of echo signals can be utilized to quantitatively characterize the depth of crack on the corroded surface with roughness less than λ/15 (λ is wavelength of surface wave).


2010 ◽  
Vol 09 (03) ◽  
pp. 123-133
Author(s):  
XIAOMING YIN ◽  
LIPING ZHAO ◽  
XIANG LI ◽  
ZHONGPING FANG

Shack–Hartmann wavefront sensor splits the incident wavefront into many subsections and transfers the distorted wavefront detection into the centroid measurement. The accuracy of the centroid measurement determines the accuracy of the SHWS. In this paper, we have presented an automatic centroid measurement method based on the image processing technology for practical applications of the digital SHWS in surface profile measurement. The method can detect the centroid of each focal spot accurately and robustly by eliminating the influences of various noises. Based on this centroid detection method, we have developed a digital SHWS system which can automatically detect centroids of focal spots, reconstruct the wavefront, and measure the 3D profile of the surface. The experimental results demonstrate that the system has good accuracy, repeatability and compatibility to optical misalignment. The system is suitable for online applications of surface measurement.


2016 ◽  
Vol 23 (4) ◽  
pp. 615-631 ◽  
Author(s):  
Hao Xu ◽  
Zhongqing Su ◽  
Li Cheng ◽  
Jean-Louis Guyader

A damage identification method named virtual vibration deflection (VVD) was developed, the principle of which was formulated based on the “weak” modality of the pseudo-excitation (PE) approach previously established. In essence, VVD is based on locating structural damage within a series of “sub-regions” divided from the entire structure under inspection, and each sub-region was considered as a “virtual” structure undergoing independent vibration. The corresponding vibration deflection of the “virtual” structure was then used to derive the damage index of VVD. Besides various advantages inheriting from the PE approach, for example, capability of detecting damage without baseline signals and pre-developed benchmark structures, VVD exhibits improved detection accuracy and particularly enhanced noise immunity compared with the PE approach, attributed to a hybrid use of multi-types of vibration signatures (MTVS). As a proof-of-concept investigation, a beam model was used in a numerical study to examine the philosophy of VVD. And the influences from different factors (i.e., level of measurement noise and measurement density) on the detection accuracy of VVD were discussed based on the numerical model. An experiment was carried out subsequently to identify the locations of multiple defects contained in an aluminum beam-like structure. Identification results constructed by the PE approach, VVD using single-type of vibration signatures, and VVD using MTVS, were presented, respectively, for the purpose of comparison.


2002 ◽  
Author(s):  
Sung-Hoon Baik ◽  
Seung-Kyu Park ◽  
Cheol-Jung Kim ◽  
Young-Seok Seo ◽  
Young-June Kang

2010 ◽  
Vol 426-427 ◽  
pp. 638-642
Author(s):  
C. Liang ◽  
W.H. Liao ◽  
J.X. Sheng

The principle of Hartmann-Shack wavefront sensor decided that the distance between micro-lens array and the CCD is the essence of reconstruction algorithm. Because of lacking way to measure the parameter and the existing of assembly error, it will obviously cause error by using the micro-lens focus instead of actual parameter. After analyzing the Zernike polynomial for describing wavrfront aberration, a new Self-reference method is given in this paper to calibrate the parameter. The method is based on the truth that the primary aberration of point light source is defocusing amount. Through this way, the requirement of sensor assembly-precision is reduced, and the detection accuracy of Hartmann-Shack sensor is also improved in the meanwhile. Satisfying results has been achieved under the normal experimental condition using the method given in this paper.


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