Total-Focus Ultrasonic Imaging of Defects in Solids Using a PZT Piezoelectric Micromachined Ultrasonic Transducer Array.

This work demonstrates the ultrasonic imaging ability of piezoelectric micromachined ultrasonic transducer (PMUT) for the detection of defects deep in solids by total-focus imaging algorithm. The 3-MHz PMUT array uses thin-film PZT as the material for energy transformation because of its high piezoelectric coefficient. Six columns with 12 PMUT units each exhibit an acoustic pressure of 137 kPa measured in water at 1 cm away when driven by a 27-Vpp input. Butter is chosen experimentally as the coupling agent to solids because of its low noise level and short cycling down. Through multilevel processing of echoes and total-focus algorithm, the 2-D image of a graphite plant was obtained with four holes identified based on our customized impedance-matched imaging system. The 16 columns of PMUT array with an area of 5.8 mm ×4.2 mm exhibit the imaging ability of an area of 40 mm ×40 mm in the graphite plant with identified defects deep as 3 cm. These results indicate that PMUT has the detection and imaging ability for defects deep in solids, not merely surface within hundreds of micrometers, and it has the potential for 3-D imaging, especially those occasions in limited space.

Design, Characterization, and Analysis of PZT Micromachined Piezoelectric Ultrasonic Transducers With Good Coupling to Solids.

This article presents the piezoelectric micromachined ultrasonic transducer (PMUT) and its arrays that were based on a sputtered PZT/Si diaphragm structure and prototyped from an SOI substrate. Due to the high piezoelectric coefficient of PZT, polarization tuning pretreatment, and membrane thickness optimization, the PMUT shows high transmitting sensitivity in air and good coupling capability to liquid and solid. The PMUT transmitter exhibited a high sensitivity of 809, 190, and 135 nm/V at a resonant frequency of 0.450, 0.887, and 1.689 MHz, respectively, in air. The 5 ×5 array of 0.5-MHz PMUTs' acoustic output in water was measured as 42.4 Pa at a distance of 3 cm with a 10.0- [Formula: see text] input. Thickness-measuring ability in solids was evaluated with an 8 ×8 array of 1-MHz PMUTs as transmitter providing 8.0- [Formula: see text] input and another single PMUT of identical frequency response as receiver showing 0.2 [Formula: see text] (after 20 times magnification) output when the acoustic wave was transmitted through a 5-cm-thick graphite plate. Meanwhile, the time response of the receiver through different thicknesses of graphite plates is in reasonable agreement with predication from the analytical calculation. This high-performance PMUT with good coupling to solids will be utilized in various applications for solid-state sensing and detecting or as an alternative to the bulk piezoelectric ceramic transducers in the near future.