Self-focusing high-frequency ultrasonic transducers for non-destructive testing applications

Focused high-frequency acoustic waves are utilized in industrial non-destructive testing (NDT) on account of their exceptional spatial resolution and high sensitivity. However, the majority of the focusing methods currently adopted for high-frequency transducers are mechanical pressure focusing and lens focusing, which may inflict mechanical damage on piezoelectric elements and give rise to low transmission efficiency. In this paper, an efficient approach to achieving self-focusing at high frequency is proposed. This is accomplished by utilizing half-concave piezoelectric elements. Through the employment of a precise micro-nano processing technology, a self-focusing half-concave ultrasonic transducer operating at a high frequency (62.7 MHz) was designed, fabricated, and characterized. This device exhibits excellent lateral resolution (39 μm) and a - 6 dB bandwidth (76.6%). The outstanding imaging performance was manifested using a multilayer circuit board and a chip. The results imply that the self-focusing half-concave high-frequency ultrasonic transducer has a prospective potential in industrial NDT, especially for defect detection in chip packaging.