Reviewed by Alex SmithOct 14 2022
Researchers have created an automatic drawing machine that transfers metamaterials onto paper using pens and pencils. Making three metamaterials that can be utilized to control the microwave portion of the electromagnetic spectrum served as their example of the new methodology.
Researchers developed a new method for drawing metamaterials onto paper. They used it to make three different types of metamaterials capable of manipulating the microwave region of the electromagnetic spectrum. Image Credit: Junming Zhao, Nanjing University
Metamaterials are synthetically created composite materials whose structured microstructures, rather than the materials’ chemical components, determine their properties.
The structures can be utilized to alter electromagnetic waves in ways that are not conceivable with ordinary materials due to their precise shape, geometry, size, orientation, and arrangement.
Metamaterials, especially those used as absorbers, generally need to be thin, lightweight, wide, and strong, but it is not easy to create thin and lightweight devices using traditional substrates. Using paper as the substrate can help meet these requirements while also lending itself to metasurfaces that conform to a surface or that are mechanically reconfigurable.
Junming Zhao, Research Team Leader, Nanjing University
The researchers explain their innovative method, which uses mechanical pencils to make resistors and resistive coatings and a ballpoint pen with conductive ink to create conductors, in the journal Optical Materials Express. They mechanized and improved this procedure by incorporating it into a computer-controlled drawing machine.
Zhao added, “Although paper-based metamaterials have been made previously using inkjet printing technology, our drawing technique is lower cost, simpler, and more flexible. Our method could be useful for making reconfigurable antennas and metalenses as well as metamaterial devices that absorb incident electromagnetic energy from cell phones or other sources.”
Automated Drawing
The innovative drawing device utilizes mechanical pencils with changing graphite contents or conductive ink-containing pens.
Three stepper motors are used; two are used to move the pen or pencil in a horizontal plane, and the third is used to lift or lower the writing instrument in a vertical plane. A computer regulates the drawing machine’s characteristics, including movement speed.
“Some of the paper we tried was not very compatible with the pencils or conductive ink pens, resulting in poor conductivity of the drawn patterns. After some testing, we found the best performance came from using paper that is .22 mm thick, which is easy to obtain and very compatible with the pencils and conductive ink,” Zhao added.
The patterns that the researchers drew on paper with the conductive ink pen had a good conductivity of 3×106 Siemens per meter. To understand how drawing times, drawing pressures, and pencils with different amounts of graphite affected electrical resistance, researchers also examined these variables.
As a result, they could determine the prerequisites for creating patterns with a particular resistance.
Creating Paper Metamaterials
The researchers created three distinct paper-based metamaterials: a polarization converter, an absorber, and a conformal coding metasurface using their unique drawing technique. They demonstrated that the polarization converter could rotate linear polarization by 90° between 3.1 and 6.6 GHz with a conversion efficiency of over 90%.
An absorber was created that weighed only 58.3 gm and had 90% absorptivity between 2.1 GHz and 10.5 GHz.
A conformal coding metasurface was also developed for radar cross-section reduction, a technique for concealing the radar signal in ships and aircraft utilized by the military.
This metasurface contained two structural units that were 180° apart in terms of the reflection phase, allowing them to serve as the “0” and “1” elements for 1-bit coding. When twisted around a curved surface, the metasurface reduced the radar cross-section by 10 dB for the frequency range of 8.94 to 11.59 GHz.
We hope that in the future, we can use the drawing technology to design and fabricate meta-devices that could be carried or applied to the skin to achieve electromagnetic shielding and other functions. We also plan to design mechanically reconfigurable metamaterials that take advantage of the fact that paper can be bent and folded.
Junming Zhao, Research Team Leader, Nanjing University
Journal Reference:
Zhu, K., et al. (2022) Directly drawing metamaterials on paper based on an automatic drawing machine. Optical Materials Express. doi:10.1364/OME.472866.