Broadband transparent ultrasound transducer design via matching-free composite approach

• The lithium niobate 1–3 composite material with a low volume fraction was successfully developed and demonstrated for the transparent ultrasound transducer application. • The low acoustic impedance, high piezoelectric voltage constant and electromechanical coefficient of the composite material contribute to a substantial bandwidth exceeding 100%, of the transparent ultrasound transducer, achieved without the need for additional matching layers. • The broad bandwidth enables a high axial resolution, comparable to that of transparent ultrasound transducers operating at higher frequencies. • This work represents the first practical implementation of a lithium niobate 1–3 composite transducer in biomedical imaging. Photoacoustic imaging (PAI) combines the high optical contrast of light with the deep tissue penetration of ultrasound, making it a powerful modality for functional biomedical imaging. Transparent ultrasound transducers (TUTs) have been developed to facilitate co-axial illumination and detection in PAI systems by enabling light transmission directly through the transducer. However, the performance of TUTs has been limited by the significant acoustic impedance mismatch between conventional transparent piezoelectric single crystals/ceramics and biological tissues. In this study, a lithium niobate (LN) single crystal-based 1–3 composite piezoelectric material is employed for the first time in a practical biomedical imaging application as the active layer of a TUT. Leveraging its intrinsically high piezoelectric voltage constant ( g 33 ) and electromechanical coupling coefficient ( k t ), the 1–3 composite structure with a reduced volume fraction of LN possesses a lower acoustic impedance. This results in an improved acoustic transmission coefficient at the interface between TUT and biological tissues. Experimental results demonstrate that the LN 1–3 composite TUT achieves an ultra-wide bandwidth exceeding 100% without the use of a matching layer, enabling improved axial resolution that outperforms comparable reported TUTs. Additionally, the device exhibits superior receiving sensitivity when benchmarked against transducers fabricated using piezoelectric polymers. The imaging performance of the developed TUT was validated in a PAI system using phantom imaging, confirming its potential for high-performance biomedical imaging applications.