A High Sensitivity Transparent Ultrasound Transducer Based on PMN-PT for Ultrasound and Photoacoustic Imaging

We recently introduced piezoelectric lithium niobate (LN) based transparent ultrasound transducers (TUT) as a new platform for developing multimodal optical, ultrasound, and photoacoustic imaging (PAI) systems. However, LN based TUT is limited in its signal-to-noise ratio due to material's low piezoelectricity (
$d_{33}$
). In this letter, we report, for the first time, a 0.2-mm-thick transparent lead magnesium niobate-lead titanate (PMN-PT) based TUT (PMN-PT-TUT) for ultrasound and photoacoustic applications and compared its performance with a 0.25-mm-thick transparent LN based TUT (LN-TUT). To improve the ultrasound energy transmission efficiency, TUTs were fabricated with a two-matching-layer design. This resulted in a dual frequency response with center frequencies of 7.8 MHz/13.2 MHz and corresponding bandwidths of 28.2%/66.67% for PMN-PT-TUT, as well as center frequencies of 7.2 MHz/11.8 MHz and bandwidths of 36.1%/62.7% for LN-TUT. The optical transmission rate of PMN-PT-TUTs and LN-TUTs are measured as
$\sim$
73 and
$\sim$
91%, respectively, at 532 nm optical wavelength. The PMN-PT-TUT exhibited higher sensitivity compared to LN-TUT with a nearly threefold higher pulse echo amplitude and more than twofold higher photoacoustic amplitude. Furthermore, optical resolution photoacoustic microscopy experiments on phantom targets demonstrated lateral resolutions of 7 and 5.1
$\mu$
m and axial resolutions of 285.6 and 375.9
$\mu$
m for PMN-PT-TUT and LN-TUT, respectively. These results indicated that PMN-PT is a viable alternative to LN for developing TUT based multimodal ultrasound and PAI systems.