Sound velocity and attenuation measurements of perfluorocarbon liquids using photoacoustic methods

A method to measure the phase velocity and attenuation of liquids over a frequency range of 100-1000 MHz using a photoacoustic method is presented. A pulsed laser directed at a thin gold or ink layer was used to create a broadband ultrasonic wave and was used as the source. An ultrasound transducer (375 or 750 MHz center frequency) positioned above the source was used as the receiver. The phase and amplitude spectra of signals transmitted through a liquid between the photoacoustic source and ultrasound receiver were used to determine the phase velocity and attenuation as a function of frequency. The method was first validated using water, ethanol and castor oil. The phase velocity and attenuation were similar to published values. Water and ethanol showed no dispersion with frequency, while castor oil increased from 1508 m/s at 200 MHz to 1561 m/s at 700 MHz. Three perfluorocarbon (PFC) liquids (perfluorohexane, perfluoroheptane and FC-77) were then measured. The phase velocity was 480, 516 and 557 m/s at 200 MHz for perfluorohexane, perfluoroheptane and FC-77, respectively, and increased by approximately 1.5% at 700 MHz. The attenuation was similar for all three PFC liquids at 0.352f^1.56 dB/cm/MHzⁿ.