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  • 1.
    Ashraf, Shakeel
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Niskanen, Ilpo
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Finland.
    Kanyathare, Boniphace
    Electronics and Telecommunications Department, Dar es salaam Institute of Technology, Tanzania.
    Vartiainen, Erik
    LUT School of Engineering Science, Lappeenranta University of Technology, Finland.
    Mattsson, Claes
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Heikkilä, Rauno
    Faculty of Technology, Structures and Construction Technology, University of Oulu, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Determination of complex refractive index of SU-8 by Kramers-Kronig dispersion relation method at the wavelength range 2.5 – 22.0 μm2019In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 224, p. 309-311Article in journal (Refereed)
    Abstract [en]

    Accurate determination of the complex refractive index of SU-8 epoxy has significant for the wide variety of applications in optical sensor technology at IR range. The complex refractive index of SU-8 is determined by recording the transmission of light spectra for the wavelength range of 2.5 – 22.0 μm.  The data analysis is based on the Kramers-Kronig dispersion relation method. The method has several merits, such as ease of operation, non-contact technique, measurement accuracy, and rapid measurement. The present method is not restricted to the case of SU-8 but it is also proposed to be applicable across a broad range of applications, such as assessment of the optical properties of paints and biomedical samples.

  • 2.
    Niskanen, Ilpo
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Oulu, Finland.
    Forsberg, Viviane
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences. KTH.
    Zakrisson, Daniel
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Reza, Salim
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Hummelgård, Magnus
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Andres, Britta
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Natural Sciences.
    Fedorov, Igor
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Suopajärvi, Terhi
    University of Oulu, Oulu, Finland.
    Liimatainen, Henrikki
    University of Oulu, Oulu, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Determination of nanoparticle size using Rayleigh approximation and Mie theory2019In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 201, no 29, p. 222-229Article in journal (Refereed)
    Abstract [en]

    Accurate determination of the size of nanoparticles has an important role in many different scientific and industrial purposes, such as in material, medical and environment sciences, colloidal chemistry and astrophysics. We describe an effective optical method to determine the size of nanoparticles by analysis of transmission and scattering of visible spectral range data from a designed UV-Vis multi-spectrophotometer. The size of the nanoparticles was calculated from the extinction cross section of the particles using Rayleigh approximation and Mie theory. We validated the method using polystyrene nanospheres, cellulose nanofibrils, and cellulose nanocrystals. A good agreement was achieved through graphical analysis between measured extinction cross section values and theoretical Rayleigh approximation and Mie theory predictions for the sizes of polystyrene nanospheres at wavelength range 450 - 750 nm. Provided that Rayleigh approximation's forward scattering (FS)/back scattering (BS) ratio was smaller than 1.3 and Mie theory's FS/BS ratio was smaller than 1.8. A good fit for the hydrodynamic diameter of nanocellulose was achieved using the Mie theory and Rayleigh approximation. However, due to the high aspect ratio of nanocellulose, the obtained results do not directly reflect the actual cross-sectional diameters of the nanocellulose. Overall, the method is a fast, relatively easy, and simple technique to determine the size of a particle by a spectrophotometer. Consequently, the method can be utilized for example in production and quality control purposes as well as for research and development applications.

  • 3.
    Niskanen, Ilpo
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. Univ Oulu, Oulu Min Sch, Oulu, Finland.
    Räty, Jukka
    Univ Oulu, Unit Measurement Technol MITY, Finland.
    Peiponen, Kai-Erik
    Univ Eastern Finland, Joensuu, Finland.
    On the Immersion Liquid Evaporation Method Based on the Dynamic Sweep of Magnitude of the Refractive Index of a Binary Liquid Mixture: A Case Study on Determining Mineral Particle Light Dispersion2017In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 71, no 7, p. 1586-1592Article in journal (Refereed)
    Abstract [en]

    This is a feasibility study of a modified immersion liquid technique for determining the refractive index of micro-sized particles. The practical challenge of the traditional liquid immersion method is to find or produce a suitable host liquid whose refractive index equals that of a solid particle. Usually, the immersion liquid method uses a set of immersion liquids with different refractive indices or continuously mixes two liquids with different refractive indices, e.g., using a pumping system. Here, the phenomenon of liquid evaporation has been utilized in defining the time-dependent refractive index variation of the host liquid. From the spectral transmittance data measured during the evaporation process, the refractive index of a solid particle in the host liquid can be determined as a function of the wavelength. The method was tested using calcium fluoride (CaF2) particles with an immersion liquid mixed from diethyl ether and diffusion pump fluid. The dispersion data obtained were consistent with the literature values thus indicating the proper functioning of the proposed procedure.

  • 4.
    Niskanen, Ilpo
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Oulu, Finland.
    Suopajärvi, Terhi
    University of Oulu, Oulu, Finland.
    Liimatainen, Henrikki
    University of Oulu, Oulu, Finland.
    Fabritius, Tapio
    University of Oulu, Oulu, Finland.
    Heikkilä, Rauno
    University of Oulu, Oulu, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Determining the complex refractive index of cellulose nanocrystals by combination of Beer-Lambert and immersion matching methods2019In: Journal of Quantitative Spectroscopy and Radiative Transfer, ISSN 0022-4073, E-ISSN 1879-1352, Vol. 235, p. 1-6Article in journal (Refereed)
    Abstract [en]

    Nanocelluloses have received significant interest due to their unique structural, mechanical, and optical properties. Nanocellulose refractive indices can be used to indicate many crucial characteristics, such as crystallinity, transparency, and purity. Thus, accurate measurement is important. This study describes a new method to determine the wavelength dependent complex refractive index of cellulose nanocrystals (CNCs) by the measurement of light transmittance with a spectrophotometer. The data analysis is based on a combination of the Beer-Lambert and immersion liquid matching equations. The immersion liquid method's main advantage is that it is independent of particle shape and size. Moreover, the measurement is easy and relatively quick to perform. The present procedure is not restricted to the nanocellulose and could potentially be applied to other nanomaterials, such as hyphenate nanoparticle-based, lignin nanoparticles, nanopigments, biological entities, structural elements of dielectric metamaterials, and nanoparticle-based composites. 

  • 5.
    Niskanen, Ilpo
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Oulu, Finland.
    Sutinen, Veijo
    University of Oulu, Kajaani, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Räty, Jukka
    University of Oulu, Kajaani, Finland.
    Image Information Obtained Using a Charge-Coupled Device (CCD) Camera During an Immersion Liquid Evaporation Process for Measuring the Refractive Index of Solid Particles2018In: Applied Spectroscopy, ISSN 0003-7028, E-ISSN 1943-3530, Vol. 72, no 6, p. 908-912Article in journal (Refereed)
    Abstract [en]

    The refractive index is a fundamental physical property of a medium, which can be used for the identification and purity issues of all media. Here we describe a refractive index measurement technique to determine simultaneously the refractive index of different solid particles by monitoring the transmittance of light from a suspension using a charge-coupled device (CCD) camera. An important feature of the measurement is the liquid evaporation process for the refractive index matching of the solid particle and the immersion liquid; this was realized by using a pair of volatile and non-volatile immersion liquids. In this study, refractive indices of calcium fluoride (CaF2) and barium fluoride (BaF2) were determined using the proposed method.

  • 6.
    Soetedjo, Hariyadi
    et al.
    The University of Ahmad Dahlan,Yogyakarta, Indonesia.
    Niskanen, Ilpo
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design. University of Oulu, Oulu, Finland.
    Rautkari, Lauri
    Aalto University, Aalto, Finland.
    Altgen, Michael
    Aalto University, Aalto, Finland.
    Hiltunen, Eero
    Aalto University, Aalto, Finland.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Zakrisson, Daniel
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Räty, Jukka
    University of Oulu, Kajaani, Finland.
    Determining the degree of heat treatment of wood by light polarization technique2018In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 76, no 4, p. 1359-1362Article in journal (Refereed)
    Abstract [en]

    Thermal modification of wood enables the use of non-durable wood species in exterior applications, but quality control methods are required to monitor the product variability. This study tests the potential of a light polarization technique where visible light (400–500 nm) is directed through a linear polarizer to the surface of thermally modified wood to measure the reflectance. Besides an effect of the grain direction, the reflectance decreased with increasing temperature during the thermal modification process. The technique could be used for quality control, but further studies are required to understand its modes of action. 

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