Ultrasonic wave attenuation and phase velocity in a paper-fibre suspension

An ultrasonic pulse-echo technique has been used to investigate whether ultrasonic wave attenuation and phase velocity can be employed to measure fiber mass fraction in a paper fibre suspension, . Attenuation and phase velocity has been determined using Fourier transform and cross-correlation techniques. Measurements have been carried out in the frequency range from 250 kHz to 3 MHz. The mass fraction of dispersed fibres varied between 0% to 1.0%. It has been shown that the attenuation varies linearly with fibre mass fraction, and that attenuation is proportional to frequency. Phase velocity is found to correlate weakly with fibre mass fraction, and is also independent of frequency, in the range covered. It is concluded that mass fraction of fibres in a paper fibre suspension can be measured via its attenuation of ultrasonic pulses.