A research team has developed an automatic drawing machine that uses pens and pencils to draw metamaterials onto paper.

“Metamaterials, especially those used as absorbers, generally need to be thin, lightweight, wide, and strong, but it isn’t easy to create thin and lightweight devices using traditional substrates,” said research team leader Dr. Junming Zhao, Department of Electronic Engineering, School of Electronic Science and Engineering, Nanjing University. “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.” Plastic Sheet Extrusion Line

The drawing machine uses pens with ink containing conductive material or regular mechanical pencils with varying graphite content. It has three stepper motors — two control the movement of the horizontal-plane pen or pencil, while the other lifts or drops the vertical-plane drawing tool. A computer controls the parameters of the drawing machine.

“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,” said Zhao. “After some testing, we found the best performance came from using paper that is 0.22 mm thick, which is easy to obtain and very compatible with the pencils and conductive ink.”

The team designed and fabricated three different paper-based metamaterials — a polarization converter, an absorber, and a conformal coding metasurface. The work showed that the polarization converter could rotate linear polarization by 90 degrees at a conversion efficiency of more than 90 percent from 3.1 to 6.6 GHz. Their absorber had a mass of just 58.3 grams and achieved 90-percent absorptivity between 2.1 GHz and 10.5 GHz.

The researchers also created a conformal coding metasurface for use with radar cross-section reduction — used to hide the radar signal in military aircraft and ships. This metasurface had two structural units with a 180-degree reflection phase difference to each other, which allowed them to act as ‘0’ and ‘1’ elements for 1-bit coding. When bent around a curved surface, this metasurface achieved a 10-dB radar cross-section reduction over a frequency band from 8.94 to 11.59 GHz.

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“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,” said Zhao. “We also plan to design mechanically reconfigurable metamaterials that take advantage of the fact that paper can be bent and folded.”

Here is a Tech Briefs interview with Zhao, edited for clarity.

Tech Briefs: What inspired the research?

Zhao: Metamaterial absorbers generally need to meet the following four requirements — thin, light, wide, and strong. The first two requirements mean that the thickness and weight of the absorbers should be as small as possible. But it is difficult to satisfy these two requirements using the traditional dielectric substrates. Therefore, we focus on paper, which has the advantages of lightness and thinness, and it has found applications in some areas like sensing and engineering.

To draw structures on paper, we introduced an automatic drawing machine, which makes the fabrication process quick and accurate. As a result, paper-based metamaterial absorbers fabricated by the automatic drawing machine can easily meet the requirements of thinness and lightness, and the fabrication process is more environmentally friendly, easy, and flexible.

Tech Briefs: What were the biggest technical challenges you faced?

Zhao: We did a lot of tests on the performance of paper, pencils, and conductive ink pens before we officially started sample fabrications, because we needed to make sure that they can work well with each other and also have good electromagnetic responses. After many tests, we chose the kind of paper, conductive ink pen, and pencil we use now, which can guarantee good performance.

Tech Briefs: Can you explain in simple terms how the technology works?

Zhao: The drawing machine has a pen holder that can hold any kind of pens for drawing. And it has three stepper motors, two of which control the movement of the pen in the horizontal plane, while the other controls the lifting and dropping of the pen. The paper we use is a very common type of paper with a thickness of 0.22 mm. We mainly use two kinds of pens, conductive ink pens and pencils.

The conductive ink pens can be used to draw structures with good conductivity, such as metallic resonant structures. And the pencils can be used to draw structures with a certain resistance, such as resistors or resistive films. Therefore, we can use a computer to control the drawing machine to draw the designed structures of paper-based metamaterials.

Tech Briefs: What’s the next step with regards to your research/testing?

Zhao: The next step of the current research is to design mechanically reconfigurable metamaterials based on the property that paper can be bent and folded, and to fabricate samples using the drawing technique.

Tech Briefs: Do you have any advice for engineers to bring their ideas to market?

Zhao: We think that the ideas should solve practical problems and have economic value.

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