Optical observation method for ultrasonic field using the shadowgraph introducing pulse inversion averaging

The pulse inversion averaging (PIA) method is introduced to the shadowgraph imaging system to visualize the second-harmonic component of the ultrasonic field. The principle of the PIA method is summarized and the method is customized for observing an second-harmonic ultrasonic field. An experiment of a shadowgraph with PIA using a 1-MHz concave focused transducer is conducted to evaluate the system. The fundamental component of 1MHz is suppressed more than 30 dB with respect to the second-harmonic component. With this system, both a normal shadowgraph image and a second-harmonic image are visualized in real time.