Simple yet universal fabrication strategy for a focused photoacoustic transmitter.

Aiming to address existing technical challenges and explore a simple yet effective and universal solution for making a polydimethylsiloxane (PDMS)-based focused photoacoustic transmitter, a novel fabrication strategy is proposed. Different from the traditional technical route based on direct photoacoustic layer coating on a rigid concave substrate, it works by utilizing an elastomeric molding process, through which the originally flat photoacoustic conversion layer, consisting of PDMS-candle soot nanoparticles/PDMS-PDMS composite, is transformed into a concave contour with controllable radius of curvature and finally merged into a soft PDMS substrate. For proof-of-concept demonstration, two types of focused photoacoustic transmitters (6.3 mm and 8 mm focal lengths) operating at 5.3 MHz with -6  dB bandwidth of 134% are successfully fabricated, showing both distinct acoustic focusing capability and high energy conversion efficiency. Moreover, different from conventional focused counterparts, acoustic signals with nearly symmetric bi-polar waveform can be obtained at the focuses, facilitating ultrasound cavitation-based applications.