Pore Structure Sensor
The porous structure of a sheet is of great importance for many applications. For example, porosity is often very important property for sack paper. The porous structure also influences the printability of a sheet. The Innventia Pore Structure sensor is a new non-contacting, on-line measurement system.
 
Traditionally a sheet has been considered homogeneous to transmitted sound waves 1. According to a new theoretical approach there are two transmission routes for the sound through the sheet, one via the fibres and one through the air in the voids. The waves are both subject to damping and a phase shifting occurs on their way through the sheet. But after the passage the two combine into one single wave with the frequency of the emitted signal.
 
It is thus impossible to differentiate between the two mechanisms by a simple amplitude measurement on the other side of the sheet. Yet a new on-line measurement system for measuring the porous structure of a sheet has been realized applying the theories of Biot.
 
Sample of measurement performed with the Innventia pore structure sensor
 

Output signal from the Innventia pore structure applied to filter paper with varying pore sizes.

 
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Publications

On the verification of the applicability of the orthotropic plate wave theory to paper
Pettersson, T. and Anttila, J.
Ultrasonics 39:617-622 (2002).