VTT Technical Research Centre of Finland, Espooi, Finland. matti.kankainen@helsinki.fi|VTT Technical Research Centre of Finland, Espooi, Finland. matti.kankainen@helsinki.fi|VTT Technical Research Centre of Finland, Espooi, Finland. matti.kankainen@helsinki.fi|VTT Technical Research Centre of Finland, Espooi, Finland. matti.kankainen@helsinki.fi