Using high frequency acoustic micro imaging to detect defects in artificial micro void specimens

We have studied the acoustic characteristics of echoes reflected from micro void areas. Artificial-defect samples with air gap widths of 30, 50, and 70 μm were developed. Echo signals from the samples were obtained in a pulse-echo experiment with a high-frequency ultrasonic probe (center frequency: 200 MHz). Wave propagation for an artificial-defect model was also simulated by using a finite element method. Calculation and experimental results confirmed that phase shifts and ringing are useful for distinguishing between normal and defective samples. Simulation results show that defect detection is possible for gap widths of less than 10 μm.