A Method of Measuring Acoustic Wave Attenuation in the Laboratory

Abstract

The measurement of attenuation is performed by directly determining the attenuation operator (or the impulse response of the medium) in the time domain. In this way, it is possible to separate the attenuation operator from other non-attenuation effects, e.g. reflections. The Wiener filtering technique, or the damped least-squares, is used to calculate the attenuation operator. For the damped least squares, we have corrected for the effect due to the addition of the damping constant using a perturbation method. Numerical tests are carried out to illustrate the technique. The geometric beam spreading of ultrasonic waves generated by a source of finite size can strongly affect the result of attenuation measurements. Corrections are made by equating the received signal to the average pressure over the receiver surface. The technique is used to measure ultrasonic attenuation in water, glycerol and mud. The measurement in water offers a test of the corrections made for the geometric beam spreading. The measurement in glycerol and mud shows that, in the frequency range of 0.2-1.5 MHz, the attenuation of glycerol increases rapidly with frequency, whereas the attenuation of mud is proportional to frequency, exhibiting a constant Q behavior. The measurements show that the technique used here is an effective approach to the measurement of attenuation.