In-plane Resonance Measurement of Cracked Photovoltaic Cell Substrates using Electronic Speckle Pattern Interferometry
|關鍵字:||電子光斑干涉術;太陽能電池;面內共振模態量測;裂縫偵測;Electronic speckle pattern interferometry;Photovoltaic cell;In-plane resonant modes;Detection of crack|
The trend of silicon-based photovoltaic cells is toward increasing wafer size and decreasing substrate thickness. However, silicon has high stiffness and low toughness. Micro-defects having tiny crack width are frequently generated in the brittle cell substrates during manufacture and results in catastrophic failure in module process or later application. It is very time consuming to detect those defects by human eyes or machine vision technology. This thesis develops a full-field optical nondestructive technique to detect defects in cell substrates by application of electronic speckle pattern interferometry (ESPI) to measure its in-plane resonant vibration. The modal density of out-of-plane resonant vibration is high for a planar structure. It is of difficulty to identify the influence of cracks in accordance with out-of-plane resonance. The in-plane resonance featuring clear modal separation has potential to detect the crack and its position. An active fiber composite adhered to one edge of the cell substrate is used to actuate in-plane vibration. Lower in-plane resonant modes are measured by the amplitude-fluctuation ESPI method. Numerical analysis of in-plane vibration for the integrated photovoltaic cells has been validated by experimental measurement. The cracked cell substrate has lower resonant frequency for in-plane vibration than the integrated one due to lower stiffness. The discontinuous displacement field across the crack faces characterizes the appearance of defect. Further, the speckle fringes intensively moving toward the crack could be an indication of the crack position.
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