Evaluation of gallium-indium alloy as an acoustic couplant for high-impedance, high-frequency applications

Materials are investigated for coupling ultrasound between solid piezoelectric transducers and solid targets having acoustic impedances ranging between 10-20 MRayl. The majority of available acoustic couplants have impedances below 5 MRayl, leading to large surface reflections and acoustic losses. The desired couplant is preferably liquid or semiliquid with good conformability and low attenuation. This study examines the acoustic properties of various couplants, including gallium-indium alloys. Transmission tests were conducted at 19 MHz, concluding that these alloys are most appropriate for the stated application, with low attenuation, high acoustic impedance (17.4 MRayl), and a measured compressional velocity of 2740 m/s. (C) 2005 Acoustical Society of America.