In a study published in Nature Communications, a team led by Prof. ZHENG Hairong, Prof. QIU Weibao, and Prof. LIU Chengbo from the Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences, collaborating with Prof. LI Fei's team from Xi'an Jiaotong University, developed an ultrasensitive, broadband transparent ultrasonic transducer based on a novel transparent piezoelectric single crystal, and achieved high-resolution, large-field-of-view, and rapid photoacoustic microscopic imaging.

Owing to the synergistic benefits of optical and acoustic imaging, photoacoustic imaging and acoustic-optical multimodal imaging have emerged as frontier technologies with great potential in the biomedical fields. However, traditional ultrasonic transducers, being opaque, bring spatial coupling challenges between the optical and acoustic pathways, resulting in complex imaging systems and issues such as near-field blind spots.

Transparent ultrasonic transducers offer a solution by enabling dense integration of acoustic and optical modules, which is crucial for advancing photoacoustic and acoustic-optical multimodal imaging techniques. However, the existing transparent ultrasonic transducers often underperform the traditional transducers, significantly impacting image quality and thus restricting their practical application.

In this study, researchers used a novel transparent PIN-PMN-PT piezoelectric single crystal which was developed through an AC polarization process as the piezoelectric layer of the transparent ultrasonic transducers. They developed an innovative double-layer acoustic matching system utilizing quartz glass and epoxy resin, and refined the fabrication process of these acoustic layers, which led to a significant enhancement in ultrasonic transmission efficiency between the transparent transducer and the human body. 

In addition, researchers introduced a novel wiring strategy and enhanced the performance of Indium Tin Oxide (ITO) transparent electrodes, contributing to overall improvements in device functionality and effectiveness.

Owing to these optimizations, new transparent ultrasonic transducers achieve ultra-high sensitivity (two-way insertion loss of -17.6dB) and – 6dB bandwidth (approximately 80%). Compared with those of the current state-of-the-art transparent transducers, the sensitivity of these transducers is 3.5 times higher, and the bandwidth 1.3 times broader, representing an advancement in the performance capabilities of such devices.

Furthermore, researchers developed an optical-resolution photoacoustic microscopic imaging system (OR-PAM) based on new transparent transducers, enabling first-time continuous dynamic imaging of a mouse's cortical microvascular during an epileptic seizure. This system provides high-resolution (micrometer level), large-field-of-view (millimeter scale), and fast (frame rate of 0.8Hz) imaging of living animals.

This work paves the way for biomedical applications of photoacoustic and acoustic-optical multimodal imaging based on transparent transducers.