Influence of electrical source impedance on phase shift of sound wave in the ultrasonic velocity measurement

In acoustic velocity measurement using ultrasonic waves, the composite resonator method with the sample and the transducer becomes a source of error. This phenomenon is considered as a phase shift at the boundary between the transducer and the sample and is analyzed by numerical simulation. From the result, it is found that the phase shift depends on the electrical source impedance and that the phase shift can be minimized by setting the electrical source impedance equal to the reactance of the transducer at resonance, depending on the acoustic condition of the backing of the transducer. The results of experiments with a varying electrical source impedance are found to be similar to those of simulations. Further, it becomes possible to measure the acoustic velocity of water with a discrepancy of less than 0.1% from the referenced value if the phase shift is eliminated by taking the propagation time difference in two samples with different lengths.