The project deals with three key aspects in THz technology, which can have a significant scientific impact on the understanding and characterization of properties of wood and cellulose based materials:

Anisotropic optical properties of wood

As the anisotropic optical properties of wood and cellulose correlate strongly with the cellulose microfibril orientation, THz radiation is an excellent medium for probing the spatial structure of wood relevant to mechanical properties. In light of a more efficient and advanced use of wood, a better insight into structure-mechanics relationships and into wood-water interaction are needed.

Publications:

• Zolliker P., Rüggeberg M., Valzania L. & Hack E. "Extracting Wood Properties from Structured THz Spectra: Birefringence and Water Content". IEEE Transactions on Terahertz Science and Technology, 2017, 7(6), 722-731.
• Cao J., Rüggeberg M., & Zolliker P. Towards detection of helical orientated cellulose structures in wood using THz time-domain spectroscopy. In Proceedings of the 44th international conference on infrared, millimeter and terahertz waves IRMMW-THz 2019. Paris, France (2019).

THz imaging of wood

THz radiation is very sensitive to humidity and water. Due to the different spectral properties of water compared to those of the cell wall polymers it allows for a spatially and temporally resolved measurement of water content and diffusion in wood. Our goal is to build and use a spectroscopic THz imaging setup in a humidity controlled environment. This will allow performing advanced research by in-situ imaging of wood structure and diffusion processes.

Publications:

• Zolliker, P., Shalaby, M., Söllinger, E., Mavrona, E., & Hack, E. "Real-Time High Resolution THz Imaging with a Fiber-Coupled Photo Conductive Antenna and an Uncooled Microbolometer Camera", Sensors 2021, 21, 3757.

Exploring wood and cellulose based materials as THz devices

The strong anisotropic properties of wood mainly caused by the preferred orientation and inhomogeneous distribution of cellulose fibers motivates to synthesize cellulose based materials with tailored optical properties for THz devices (half wave plates, quarter wave plates, polarizers)

Publications:

• Zolliker, P., Mavrona, E., Hack, E., Markus Rüggeberg, M., Zeng, Z., Siqueira, G., & Nyström, G. "Wood: base material for optical elements for terahertz waves?" In 2020 45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2020.
• Zeng, Z., Mavrona, E., Sacré, D., Kummer, N., Cao, J., Müller L., Hack, E., Zolliker, P. & Nyström, G. "Terahertz Birefringent Biomimetic Aerogels Based on Cellulose Nanofibers and Conductive Nanomaterials", ACS Nano 15 (4), 7451-7462, 2021.

External funding:

SNF project 200021_179061 "Revealing key properties of wood and cellulose with spectroscopic THz imaging" http://p3.snf.ch/project-179061

Contributors and collaborators

Peter Zolliker, Elena Mavrona, Jingming Cao, Daniel Sacré, Laboratory for Transport at Nanoscale Interfaces, Empa

Markus Rüggeberg, Institute for Wood Technology, TU Dresden

Ingo Burgert, Wood Materials Science Laboratory, Institute for Building Materials, ETH Zürich

Gustav Nyström Laboratory for Cellulose & Wood Materials, Empa