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Anisotropic reflectance from paper: measurements, simulations and analysis
Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. (FSCN)
2006 (English)Report (Other academic)
Abstract [sv]

Arbetet innehåller en grundläggande teoretisk och experimentell undersökning av anisotrop (icke-diffus) reflektans från papper. Fenomenet kopplas till papperets ljusabsorptionsgrad, fenomenets effekt på standardiserade reflektansmätningar utreds, och orsaker till fenomenet redovisas.

Abstract [en]

An overview of the theory describing light scattering in paper is given. It is investigated

experimentally and theoretically how the anisotropy of light reflected from paper depends on the

paper absorption and thickness. This is done by measuring the angular resolved reflectance from

a series of handsheets containing different amounts of dye and filler and varying in grammage.

The theoretical investigation is done by using the angular resolved model DORT2002.

Measurements and simulations both show that the anisotropy increases with increased

absorption and is higher for lower grammages. The relative amount of light scattered into larger

polar angles increases for these cases. It is shown that the range of exact validity of the Kubelka‐

Munk model is limited to a case where an infinitely thick non‐absorbing medium is illuminated

diffusely, since this is the only situation where the reflectance is isotropic. It is also shown that the

reflectance from what is intuitively thought to be a perfect diffusor strongly depends on the

illumination conditions, meaning that a bulk scattering medium that reflects light diffusely

independently of the illumination conditions does not exist.

 

It is investigated how the anisotropy affects d/0° measurements. The DORT2002 model is

adapted to the d/0° instrument to allow for inverse calculations starting from d/0° measurement

data. This gives access to the objective parameters used in the DORT2002 model through an

instrument originally not designed for this purpose. It is shown that this method can explain

more than 50 % of the widely investigated anomalous parameter dependence of the Kubelka‐

Munk model.

 

The causes of anisotropic reflectance are investigated and it is shown, using analytical methods

and the Monte Carlo model Grace, that it depends on the relative contribution from near‐surface

bulk scattering. The reflectance in larger polar angles is higher from near‐surface bulk scattering

than it is from scattering deeper inside the medium. Near‐surface bulk scattering dominates in

strongly absorbing media since the remaining light is absorbed and in optically thin media since

the remaining light is transmitted. Obliquely incident illumination causes the light to scatter

closer to the surface, and this also causes the relative contribution from near‐surface bulk

scattering to increase.

 

Comment

This master's thesis was done by Magnus Neuman as the final part of a Master of Science

program in Engineering Physics at Umeå University. The work was done at M‐Real Technical

Center in Örnsköldsvik and at Digital Printing Center (DPC), Mid Sweden University in

Örnsköldsvik. Supervisors were Nils Pauler, Senior Research Scientist at M‐Real and Assistant

Professor at Mid Sweden University, and Per Edström, Lecturer and Researcher at Mid Sweden

University.

 

Place, publisher, year, edition, pages
Sundsvall: Mittuniversitetet, FSCN , 2006. , p. 37
Series
Rapportserie FSCN, ISSN 1650-5387 ; 2006:38
Series
FSCN-rapport ; R-06-67
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:miun:diva-9265OAI: oai:DiVA.org:miun-9265DiVA, id: diva2:227065
Projects
DPC - Digital printing centerAvailable from: 2009-07-09 Created: 2009-07-09 Last updated: 2017-11-29Bibliographically approved

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