High-resolution 3D ultrasonic imaging using high-frequency piezoelectric transmitter and ultra-multiple laser 2D scanning

In this paper, we extend a piezoelectric and laser ultrasonic system (PLUS) to a high-frequency version for high-sensitivity three-dimensional (3D) ultrasonic imaging by utilizing a unique characteristic of PLUS. PLUS combines a piezoelectric transmitter and a two-dimensional (2D) scan of a laser Doppler vibrometer (LDV). A high frequency can be used simply by adopting a high-frequency piezoelectric transmitter with a center frequency, such as 15 MHz, since the LDV has a broad bandwidth reception of 0–25 MHz. Furthermore, a 2D array receiver with a small interelement pitch can be achieved by precisely scanning a small laser irradiation spot. We experimentally demonstrate its 3D imaging capability for flat-bottom-hole and fatigue-crack specimens.