Stealth Sumo Robots with IR Flock Sheet: Cutting IR Sensor Detection Range from 40 cm to 5 cm
On August 1, we went to watch the Kanto regional championship of the All Japan Robot Sumo Tournament for high schools, held at a shopping mall in Kawaguchi, Saitama. Watching robots find their opponent in an instant and push each other out of the ring is gripping every time. Each split-second charge holds months of design and tuning by the students.
In short
A team from a technical high school in Saitama, Japan covered its 500 g autonomous sumo robots with IR Flock Sheet. An infrared distance sensor (850 to 940 nm) that normally detected the robot at about 40 cm only reacted at about 5 cm. The school took first, second and third place in the 500 g autonomous class.
A clean sweep of the podium
The team that drew the biggest cheers was from a technical high school in Saitama, Japan. The school entered four robots in the 500 g autonomous class, and they not only won but took all three places on the podium. We had been cheering for them because they use our IR Flock Sheet to make their robots "stealthy." It is rare to see one school take the whole podium, and the crowd was clearly impressed. The result reflects their hours of practice and constant improvement. Congratulations to the whole team!
The material: IR Flock Sheet
The robots were covered with IR Flock Sheet, our flocked fabric. It combines a special dye with carbon-loaded pile fibers, so it absorbs not only visible light but also near-infrared light, including the InGaAs sensor range.
| Wavelength | Reflectance of IR Flock Sheet |
|---|---|
| 550 nm (visible) | 0.26% |
| 850 to 940 nm (typical IR distance sensors) | 0.27 to 0.33% |
| 400 to 1500 nm | below 0.5% |
| Up to 2500 nm | below 1% |
Total hemispherical reflectance at 8° incidence, measured by an external testing laboratory. Typical values, not guaranteed.
IR Flock Sheet is used for stray-light control in LiDAR and automated driving systems, for reducing measurement noise in R&D, and in space-related testing. Through a near-infrared camera, it looks completely black because it absorbs the light.
From 40 cm to 5 cm
All four robots in the 500 g autonomous class used adhesive-backed IR Flock Sheet, applied around the sensors or over the whole body.
At the venue, we had the chance to talk with a teacher from the school's electronics and mechanics department. What stood out most was the change in detection range with an infrared digital distance sensor (850 to 940 nm band) of the kind mounted on the robots.
Normally the sensor reacted to a robot at about 40 cm. With IR Flock Sheet applied, it only reacted at about 5 cm, a reduction of 35 cm.
In robot sumo, when and at what distance a robot can locate its opponent has a big effect on the result. A longer detection range gives the opponent more time to find you and track your position. If the near-infrared absorption of IR Flock Sheet helped keep the opponent from detecting the robot until it was too late to react, and played even a small part in this result, nothing could make us happier. Of course, the result depends above all on the team's skill in design and tuning.
Good luck at the national championship!
The national championship is scheduled for December, usually held at the Ryogoku Kokugikan in Tokyo. We look forward to seeing what the team does next, and we are cheering for them all the way.
For another robot sumo case, using FINESHUT KIWAMI XX, see A Stealth Revolution in Robot Sumo with Infrared-Absorbing Sheets.
Flocked fabric with NIR dye and carbon-loaded fibers. Adhesive-backed version available. Laser Cut Service
Don't want to cut it yourself? Order precision-cut pieces ready to apply.
Originally published in Japanese on August 26, 2026. Translated into English in October 2026.
Related: Why Black Materials Reflect Near-Infrared, and 3 Ways to Build a True NIR Absorber
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