Silicone sheet reveals 3D shape when folded

A sheet of silicone developed by MIT researchers can display the 3D shape of a folded object almost immediately. The team, including graduate students Qifan Yu and Nina Cao, along with assistant professor Kaitlyn Becker, embedded fourteen rubber optical fibers into a thin silicone sheet. This innovation could be used in clothing to track body movements.

Optical fibers detect bending and direction

The researchers modified traditional optical fibers by replacing the glass core with a soft, transparent rubber and coating it with black rubber. One side of the core was made rough to help detect how the fiber bends. Light scatters more when the fiber bends toward the rough side, allowing the team to determine both the direction and the degree of the bend.

Fibers arranged in two layers for accuracy

The fourteen fibers were placed in two layers of seven each. Each fiber is lit from one end by an LED and ends at a light sensor. The data collected by these sensors is processed by an external board, and an algorithm then translates the information into a 3D shape.

Simulations show high accuracy even with some malfunctions

In their experiments, the researchers found that angling the fibers improved precision more than adding more fibers. Even when three out of fourteen fibers failed, the error in the reconstructed shape was less than 0.3 centimeters. On 3D-printed molds, the difference between the actual sheet and its reconstruction was between 0.28 and 0.45 centimeters.

MIT's method matches existing sensor accuracy

Existing rigid sensor systems have an error range of about 1 to 2 centimeters, but the MIT team's results are "at least on par with existing technologies," according to Qifan Yu. The team describes the reconstruction as "almost in real time," achieving about three reconstructions per second in MATLAB, including all measurement and display steps.

Comparison with Steam Frame's motion tracking

The Steam Frame from Valve, launched in September, uses cameras and two controllers to detect movement. However, its algorithm is too slow for video games and struggles to track the wrist and elbow accurately. In an experimental mode, the image is refreshed up to 144 times per second, but the shape of the sheet would only update on screen once every 48 images.

Flexibility and challenges in tracking joint movement

According to Tom's Hardware, the silicone sheet is fully flexible but does not stretch as a whole. The skin stretches at the wrist and elbow, which challenges the shape-tracking algorithm. To address this, the researchers used a simplified method to estimate the angles of these joints. One of the authors personally performed all the body-mounted demonstrations.

Future improvements and applications

The sheet is sensitive to pressure on the forearm, even without calibrated force measurement, and the team processes this separately from shape tracking. Currently, the fibers are 1 millimeter thick, but with new manufacturing techniques, the researchers believe they could reduce the thickness to less than a hair's width. This would allow more fibers to be integrated into clothing, potentially aiding in patient rehabilitation tracking. Kaitlyn Becker noted that such sheets could help physiotherapists more accurately compare evaluations over time.