20 December 2023

High-frequency terahertz waves have great potential for a number of applications including next-generation medical imaging and communication. Researchers at Linköping University, Sweden, have shown, in a study published in the journal Advanced Science, that the transmission of terahertz light through an aerogel made of cellulose and a conducting polymer can be tuned. This is an important step to unlock more applications for terahertz waves.

Crecent-shaped aerogel with water droplets.
Aerogel can obtain high hydrophobicity by simple chemical modifications. Thor Balkhed

The terahertz range covers wavelengths that lie between microwaves and infrared light on the electromagnetic spectrum. It has a very high frequency. Thanks to this, many researchers believe that the terahertz range has great potential for use in space exploration, security technology and communication systems, among other things. Laser shines on black aerogel.Conducting polymer-cellulose aerogel and optic measuring set-up. Photo credit Thor Balkhed In medical imaging, it can also be an interesting substitute for X-ray examinations as the waves can pass through most non-conductive materials without damaging any tissue.

However, there are several technological barriers to overcome before terahertz signals can be widely used. For example, it is difficult to create terahertz radiation in an efficient way and materials that can receive and adjust the transmission of terahertz waves are needed.

Adjustable filter

Researchers at Linköping University have now developed a material whose absorption of terahertz signals can be turned on and off through a redox reaction. The material is an aerogel, which is one of the world’s lightest solid materials.Two persons in labcoats and facemasks.Qilun Zhang and Chaoyang Kuang, researchers at the Laboratory of Organic Electronics. Photo credit Thor Balkhed

“It’s like an adjustable filter for terahertz light. In one state, the electromagnetic signal will not be absorbed and in the other state it can. That property can be useful for long-range signals from space or radar signals,” says Shangzhi Chen, postdoc at the Laboratory of Organic Electronics, LOE, at Linköping University.

The Linköping researchers used a conducting polymer, PEDOT:PSS, and cellulose to create their aerogel. They also designed the aerogel with outdoor applications in mind. It is both water-repellent (hydrophobic) and can be naturally defrosted via heating by sunlight.

Large modulation range

Conducting polymers have many advantages over other materials used to create tunable materials. Among other things, they are biocompatible, durable, and have a great ability to be tuned. The tunability comes from the ability to change the charge density in the material. Close up of aerogel.Enlarged image of conducting polymer-cellulose aerogel, showing macrostructure of aerogel with various pores. The PEDOT:PSS and cellulose were homogeneously distributed in the aerogel. Photo credit Thor Balkhed The great advantages of cellulose are the relatively low production cost compared to other similar materials and that it is a renewable material which is key for sustainable applications.

“The transmission of terahertz waves in a broad frequency range could be regulated between around 13 % and 91 %, which is a very large modulation range,” says Chaoyang Kuang, postdoc at LOE.

A finger compress a black spunge (areogel).The aerogel in this study is elastic and the thickness of the aerogel can completely recover after each pressing. Photo credit Thor Balkhed The study was funded by, among others, the Swedish Research Council, the Foundation for Strategic Research, the Foundation for Internationalization of Higher Education and Research, the Knut and Alice Wallenberg Foundation, the Wallenberg Wood Science Centre, and through the Swedish government’s strategic initiative in new functional materials, AFM, at Linköping University.

Article: Switchable Broadband Terahertz Absorbers Based on Conducting Polymer-Cellulose Aerogels; Chaoyang Kuang, Shangzhi Chen, Min Luo, Qilun Zhang, Xiao Sun, Shaobo Han, Qingqing Wang, Vallery Stanishev, Vanya Darakchieva, Reverant Crispin, Mats Fahlman, Dan Zhao, Qiye Wen, Magnus P. Jonsson; Advanced Science, published online November 23, 2023. DOI: 10.1002/advs.202305898

Facts: The terahertz range covers the wavelengths that lie between microwaves and infrared light on the electromagnetic spectrum. The waves have a width of between 0.1 and 1 millimetre and the frequency is at least 0.3 terahertz and at most 30 terahertz. 1 terahertz means that 1000 billion waves are sent or received in one second.

Two pipettes poring liquids on to a disk.Mixing raw materials PEDOT:PSS and cellulose. The aerogels are fabricated using aqueous solutions and do not require complex fabrication procedures, thereby holding great promise for large-scale sustainable production at a low cost. Photo credit Thor Balkhed

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