Ninja noise cancelling? High school students tackle the mystery of ninja tools March 3 at 21:16

A ninja who made full use of various tools and was active in all directions.

Many of the tools that are said to have been used by ninjas are now unknown in their use and effectiveness due to their secret tradition.

One of these mysterious tools is a metal plate that fits in the palm of your hand.

When a high school student in Yamaguchi Prefecture tried to solve the mystery scientifically, he made a surprising discovery.

(Yamaguchi Bureau Ritsuko Tamura)

Mysterious ninja tools found

By chance, the mystery of ninja tools was tackled by the science club of Tokuyama High School in Shunan City, Yamaguchi Prefecture.

The members of the club who were enrolled at the time liked ninjas, and while researching books, they learned about a mysterious tool.

That is "Saokokigane". It is a brass plate with a length of 7 cm, a width of 3 cm, and a thickness of about 3 mm.

This tool is also recorded in ninjutsu books of the Edo period.

In the modern translation of this book, "Kanhon Ninja Secret Den" (Kokusho Shuppankai), it is speculated that it is a tool to amplify the sound by eavesdropping on the voices of the next room.

Unravel the mystery

But does such a small board really amplify the sound? Wondering, the students began to experiment.

With the cooperation of ironworks in the city, we reproduced and prototyped the "Konon Kin".

Using a device called an "oscilloscope" that expresses the loudness and pitch of sound in waveforms, we repeated the experiment by applying noise and rain sounds to the replica's noise hearing.

In order to prevent the surrounding noise from affecting the data, they once gathered on the ground at 5 a.m. for experiments.

However, no matter how many times it is repeated, the result is not that the sound is amplified.

Second-year student Michiryu Tsurumaru:
"The seniors experimented many times, but it was different from what we expected because it didn't seem to amplify."

This was a surprise even for the teacher who serves as an advisor to the science department.

Teacher Kenji Suetani:
"I think it was very valuable to be able to confirm that the conventional wisdom was different, and although it was really difficult to repeat the experiment many times, both I and the students strongly felt that there was no way that useless things could be conveyed, so we were able to continue the experiment."

Actually, the principle is "noise cancellation"

Students who can't give up. In order to find out the principle, we repeated experiments in which sounds collided.

Then I discovered that a phenomenon was happening. A phenomenon in which noise disappears instead of amplifying sound.

It was a "noise canceling effect" that is also used in modern earphones.

It is said that when the sound was measured by applying the sound to the sound hearing, the higher the sound, the lower the volume.

It was found that "diffraction," in which sound wraps around the sound hearing, is less likely to occur at high pitches, and that "interference" occurs when sounds collide and cancel each other.

It is said that this was the secret to making it easier to hear sounds with a small sound listening money.

Finally understood!? use

After further experiments, the "noise-canceling effect" was supported by data by second-year students Michiryu Tsurumaru and Yuto Shibasaki.

So, what is the use of disappearing treble? Here's how they thought of using the money.

A ninja listens to the wall and tries to do espionage. However, the sound of insects disturbs me around me, and I can't hear the voice behind the wall very well.

So, what I brought to my ears was a small sound listening gold.

Ambient noise is suppressed, and you can hear your voice clearly.

According to the results of the experiment, the ease of hearing has almost doubled.

Second-year student Yuto Shibasaki
: "I think they wanted to silence the surrounding environmental sounds, such as the sound of rain and the sound of bell insects, and I was very surprised that ninjas had been using this principle ahead of time for hundreds of years."

"Secrets" are still in the present day

"I want to make use of ninja technology in the modern era," and the two developed a device using a 2D printer using this principle.

When attached to the microphone, the noise was removed and the speech was picked up more clearly.

In December last year, the two presented their research results at JSEC12 (the 2th High School and Technical College Students Science and Technology Challenge), a contest in which high school and technical college students compete for the results of their independent research, and won a prize.

It was praised not only for providing scientific support for ninja tools, but also for their application to modern times.

Expert "More ingenuity is needed for modern use"

High school students from the science department tackled the mystery of ninja tools.

We asked Hajime Suzuki, director of the Japan Acoustics Research Institute, about the results of this research.

"Considering the size of the tonal sound, we can expect the effect of actually reducing the treble, and if the size is further increased, it is thought that it will be possible to cut the treble. In order to be able to use it even today, it will be necessary to further devise such as changing the size of the tools."

I want to appeal "Ninja was a scientist" to the world

This research was highly evaluated, and Shibasaki and Tsurumaru, have been selected to represent Japan at the International Student Science and Technology Fair (ISEF), one of the world's largest high school science competitions, to be held in Dallas, USA, next month.

I am required to give a presentation in English, so I am busy preparing for it.

The two are looking forward to showcasing their ninja on the international stage.

Yuto Shibasaki
: "I think ninja is a topic that attracts a lot of attention worldwide, so when I present it in the United States, I would like to make a presentation in English so that I can meet those expectations."

Michiryu Tsurumaru:
"I think the fact that ninjas used logical techniques and tools in this way is something that is not well recognized, and I want to tell the world that ninjas were scientists."

Ritsuko
Tamura, a reporter at Yamaguchi Broadcasting Station, joined the bureau in 2019After working in charge of police justice, she is currently covering a wide range of administrative and local topics at the
Shunan Bureau, and
when she was in elementary school,
she was good at making shurikens with origami.