Study on the carrier frequency of Carrier-wave electronic speckle pattern interferometry

The choice of carrier frequency choice for Carrier-wave electronic speckle pattern interferometry (CESPI) is one of the key factors which affect the quality of carrier correlation fringe images and the result of measuring. Through researching systematically the carrier frequency requests of the spectral separation and measurement sensitivity, the rules of carrier frequency choice were generalized. According to the rules, an improved spatial modulation method which was based on deflection of reference mirror was proposed. The modulation principle theory was analyzed by setting up a geometric optical model. The results of examples showed that the modulation method could overcome the shortage that the speckle size limited carrier frequency. It could increase the carrier frequency effectively that was propitious to scrub out the carrier frequency spectrum part including shape change information from the low frequency part including background information. The modulation method is particularly applicable to measure out-of plane displacement caused by big-load with high precision.