Tag Archives: Ninja

Blank paper on ninja history wins top grades — it was written in invisible ink

A Japanese student of ninja history handed in a blank paper and still passed with flying colors. Her secret? Invisible ninja ink.

Eimi Haga.
Image via BBC.

Eimi Haga, a student at the Mie University in Japan, wrote her paper using the ninja technique of “aburidashi.” Apart from the time she used to research and write her assignment, Haga also spent hours soaking and crushing soybeans to make the ink, she told the BBC. Luckily, her professor eventually heated the paper over a gas stove to reveal the text, otherwise, her grades might not have reflected her commitment to the task.

Hidden in plain sight

“It is something I learned through a book when I was little,” Ms Haga told the BBC. “I just hoped that no-one would come up with the same idea.”

Her interest in ninjas, the infamous spies and assassins of medieval Japan, first sprouted during her childhood from watching animated TV shows. For her class on ninja history, the first-year student was asked to write about a visit to the Ninja Museum of Igaryu.

“When the professor said in class that he would give a high mark for creativity, I decided that I would make my essay stand out from others,” she said.

“I gave a thought for a while, and hit upon the idea of aburidashi.”

She created the ink by soaking soybeans overnight, crushing them, and squeezing them through a cloth. She then mixed the soybean extract with water, spending two hours to get the concentration just right to create the ink. The final step was to write her essay with a fine brush on “washi” (thin Japanese paper).

The essay, showing the heated and unheated sections.
Image via BBC.

After the ink dried, it became invisible. To make sure she wouldn’t be dismissed out of hand, she left a note (with normal ink) for her professor to “heat the paper”. The professor, Yuji Yamada, told the BBC he was “surprised” when he saw the essay.

“I had seen such reports written in code, but never seen one done in aburidashi,” he said. “To tell the truth, I had a little doubt that the words would come out clearly. But when I actually heated the paper over the gas stove in my house, the words appeared very clearly and I thought ‘Well done!’

He added that although he didn’t read the full paper — “I thought I should leave some part of the paper unheated, in case the media would somehow find this and take a picture” — he didn’t hesitate to give it full marks.

The art of the ninja is a tradition going back hundreds of years to Japan’s feudal era. Ninjas didn’t serve in battles directly, but they did operate akin to the special forces of today, gathering intel, taking out key individuals, and even helping to shape strategy. Techniques such as aburidashi allowed them to share information covertly and protect it from prying eyes.

Origami battery that runs on a few drops of water could revolutionize biosensors

An engineer from Binghamton University, State University of New York designed a new disposable battery that could power biosensors and other small devices in areas where conventional batteries are just too expensive. The battery only uses one drop of dirty water to generate energy. But the best part — it folds up like an origami ninja star.

Image credit: Jonathan Cohen/Binghamton University.

Seokheun Choi, assistant professor of computer and electrical engineering at Binghamton University, working with two of his students developed the new device that’s powered by the bacteria found in dirty water. This isn’t Choi’s first origami battery — his first design was shaped like a matchbox and consisted of four modules stacked together. The star version is made out of eight small batteries connected in a series, measures in at around 6.35 centimeters (2.5 inches) wide and has a better power output and increased voltage than the first one.

“Last time, it was a proof of concept. The power density was in the nanowatt range,” said Choi. “This time, we increased it to the microwatt range. We can light an LED for about 20 minutes or power other types of biosensors.”

Paper-based biosensors are currently used for pregnancy and HIV tests, but their sensitivity is limited says Choi. His battery could allow these sensors to employ fluorescent or electrochemical biosensors with a much better accuracy, even in developing countries.

“Commercially available batteries are too wasteful and expensive for the field,” he said. “Ultimately, I’d like to develop instant, disposable, accessible bio-batteries for use in resource-limited regions.”

The battery unfolds into a star with one inlet at its center and the electrical contacts at the points of each side. After adding a few drops of dirty water on the inlet and the device can be opened into a Frisbee-like shape, allowing each of the eight fuel cells to function. Each module is a sandwich of five functional layers with its own anode, proton exchange membrane and air-cathode.

While Choi’s first battery could be produced for about 5 US cents, the star is a bit more expensive — roughly 70 US cents. This is because the battery is also made with carbon cloth for the anode and copper tape in addition to the filter paper. The team plans to produce a fully paper-based device that has the power density of the new design with lower price tag.