The Auto-Focus Method on Scanning Acoustic Microscope Based on Wavelet Analysis

Scanning acoustic microscope (SAM) has been rapidly developed and widely used in nondestructive detection for composites, chip manufacturing, bio-pharmaceuticals and so on. Due to the geometrical features of high frequency transducer, the precision of focus has already become the key factor for the digital imaging and defect detecting. However, the process of focusing has been relying on manual operation without great development until now. To improve the speed and accuracy of the focusing, we proposed a quick auto-focus method based on wavelet analysis. Auto-focus has two steps. The first is auto-focusing on upper surface, the second is auto-focusing on the interlayer base on V(z) curve model. In order to eliminate the effect of superposition and get the amplitude of reflected echo, the deconvolution base on wavelet has been applied on A-scan signal. The auto-focus method based on wavelet analysis has been integrated into our SAM. Its validity has been approved by simulation and practical experiments.