Sound dispersion and attenuation in the thickness direction of paper materials

Abstract

A through-transmission, dry-contact ultrasonic technique aimed at investigating sound propagation in the thickness direction of paper materials is presented. The method uses piezoelectric ceramic transducers immersed in fluid-filled rubber wheels. Thickness and longitudinal velocity are determined from time domain measurements for several commercial paper specimens between 40 and 1750 gum. Dispersion and attenuation are reported at frequencies up to 1.5 MHz. Dispersion is less than 10% between 0.25 and 1.25 MHz. Amplitude calculations are used to evaluate the attenuation coefficient versus the frequency. Using a nearly local form of the Kramers-Kronig relationships, the attenuation coefficient is also obtained from the phase information. By comparing the amplitudeand phase-determined attenuation coefficients, an apparent reflection coefficient is predicted. It is shown that the Kramers-Kronig relationships can be applied to papers thicker than 200 gm under dry coupling conditions. The attenuation coefficient is inversely related to the elastic stiffness for homogeneous specimens. A linear relationship is observed between the loss attenuation, and the thickness. The apparent reflection coefficient correlates to the apparent surface roughness; of paper.

Contact and Noncontact Ultrasonic Nondestructive Test in Reinforced Concrete Beam

“…Air-coupled sensors were developed in the 1970s and were mainly used for inspection of wood and quality control of paper, art objects, and advanced composite materials used in the aerospace industry [3]. Quality tests in paper focused on sound dispersion and attenuation and estimation of its surface roughness can be monitored [4,5]. In construction building materials, this method is now being developed for noncontact detection of surface waves in concrete [3].…”

Novel Stylus Method for Measuring Papers Topography

“…in terms of economical and computational terms. On the other hand, the ultrasonic methods consist of measuring ultrasonic impedance and mass specific ultrasonic attenuation provided by paper surface which can be correlated to surface roughness (28 = Brodeur et al, 1993). Most common off-line analysis technique is stylus tracking method, beside the microscopy, pneumatic and light scattering.…”

Measurement of acoustic dispersion using both transmitted and reflected pulses

“…Determination of acoustic dispersion ͑phase velocity as a function of frequency͒ in the frequency domain using a broadband transmission method has recently found many applications. Since introduced by Sachse and Pao in 1978, this method has been used to study the dispersion properties of metal ͑Sachse and Pao, 1978͒, epoxy resin ͑Rokhlin et al, 1986͒, paper materials ͑Brodeur et al, 1993͒, polymeric materials ͑Zellouf et al, 1996͒, and ultrasound contrast agent ͑Mobley et al, 1998͒, as well as to verify Kramers-Kronig relationship for acoustic waves ͑Lee et Brodeur et al, 1993͒. Determination of dispersion using the above transmission method requires the measurements of a reference velocity-usually the sound speed in water, the thickness of the specimen, and the phase spectra of two transmitted ultrasound pulses. Since the magnitude of dispersion for most materials is very small ͑less than 1% within the frequency range of 1-10 MHz͒, minimizing measurement uncertainties is particularly important in such applications.…”