A Photoacoustic Sensing Probe Based on Silicon Acoustic Delay Lines

In this paper, we report new photoacoustic sensing (PAS) probe design based on silicon acoustic delay lines (SADLs). It consists of an optical fiber for light delivery and two SADLs for detecting/relaying the generated PA signals to an outside receiving transducer. Ultrasound testing shows that acoustic signals can be transmitted along the SADLs with low loss up to 17~20 MHz. To improve the PA excitation efficiency, a beveled tip is formed at the distal end of the optical fiber to align the optical illumination region with the acoustic detection zone of the SADLs. New polymer micro linkers fabricated with high-resolution 3-D printing are used to maintain the mechanical stability and acoustic isolation within the probe assembly. For demonstration, a prototype SADL-PAS probe was designed and fabricated. Its PA sensing performance (e.g., sensitivity, linearity, and depth resolution) is characterized. Testing results show that the SADL-PAS probe provides superior sensitivity with considerable high-frequency improvement. Ex-vivo tests in the chicken breast are conducted to demonstrate the PA target detection in biological tissues.