Bismuth Silicon Oxide Receiver for Low Frequency Ultrasound from a Liquid Metal Transducer with Carbon Nanofibers

Advanced structures like nuclear and solar power plants produce energy in extreme environments at high temperatures, or with strong radiation, and thus require advanced sensors for monitoring. Robust and durable materials are required for effective structural monitoring. The integrity of structures is often monitored using ultrasound, generated by piezoelectric materials or lasers. The baseline test of Bismuth Silicon Oxide (Bi<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf>SiO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</inf>; BSO) as a transmitter and receiver was promising for high sensitivity and accuracy. In a previous work, our lab used a combination of liquid Fields metal (Bi-In-Sn; FM) and carbon nanofibers (~ 25μm thick; CNF) to produce low frequency laser induced ultrasound at roughly 200 kHz. In this work, a BSO sensor was used to receive ultrasound from 1) a FM-CNF laser ultrasound transmitter, and 2) a BSO transmitter. The CNF's were used to increase the optical absorbance of the FM transducer, which normally has low optical absorbance (<20%), and thus increase the overall photoacoustic efficiency. The CNF's have high optical absorbance and high thermal diffusivity, ideal for dispersing thermal energy converted from the laser light into heat. This results in thermal expansion from the FM which generates and acoustic wave. Ultimately, pulsed laser light is used with the FM-CNF combination to produce ultrasound. A comparison was made to determine which transducer was more effective at generating ultrasound at ~200 kHz. The FM-CNF and BSO results were comparable, situated at a distance of 420 mm and 360 mm from the receiver, producing signals of 53.6 mV<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</inf> and 43 mV<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">pp</inf>, respectively.