Novel Sensor System Can Detect Force and Direction of Touch

Researchers in South Korea have developed a novel approach to touch-based sensors that combines high sensitivity with the ability to analyze dynamic forces instantly.

In a research paper entitled Behavioral Biometric Optical Tactile Sensor for Instantaneous Decoupling of Dynamic Touch Signals in Real Time, the scientists detail a new kind of sensor designed to measure and separate different types of touch signals quickly and accurately. Developed by researchers in South Korea, this optical tactile sensor is unique because it can detect both the pressure (normal force) and the direction of motion (shear force) in real-time, all from a single image. Traditional sensors generally measure only one type of force or require multiple readings to estimate dynamic forces.

Inspired by the way human skin senses touch, the sensor is built to amplify and transmit touch signals effectively. It is made of layered materials that mimic the skin’s structure, using thermoplastic polyurethane (TPU) and polydimethylsiloxane (PDMS) with tiny embedded crystals called upconversion nanocrystals (UCNs).

The UCNs emit a specific type of light when touched and exposed to infrared light. This light emission pattern varies depending on the type of force applied: a symmetrical pattern appears under steady pressure, while an asymmetrical pattern is produced when there is movement across the sensor. By reading these patterns, the sensor can distinguish between vertical pressure and side-to-side motion.

This precise force detection opens up many new possibilities, particularly for applications in biometric recognition, where individual behaviors—like the way someone touches or moves their hand—can be unique identifiers. The researchers showed that the sensor could be used for verifying handwriting styles by capturing the unique pressure and motion patterns of different individuals. Unlike traditional handwriting recognition, which relies on analyzing shapes and spacing, this sensor adds another layer of security by capturing the speed and pressure used in real-time, making it very hard to imitate.

The sensor also demonstrates promise in other areas. For instance, it can recognize detailed surface textures, such as those found on golf balls or small screws, with remarkable clarity. This high-resolution touch recognition could be useful in manufacturing or quality control, where identifying small surface defects is essential.

In another example, the researchers used the sensor to build a Braille-to-Speech (BTS) system that converts Braille patterns into audio. This ability to detect tiny raised dots makes the sensor a valuable tool for accessibility applications.

Another impressive aspect of the sensor is its adaptability. It was tested to maintain accuracy even after thousands of cycles and under various temperatures, showing that it can withstand frequent use in different environments. Its rapid response time, less than ten milliseconds, allows it to keep up with real-time demands, such as in security systems or robotics.

It can also operate with affordable camera technology, which means it could be used in more everyday products and devices without high costs.

The sensor could play an essential role in advancing biometric technology, particularly for secure authentication and user recognition applications. Its ability to capture both the pressure and movement of touch opens up new possibilities for personalized, secure interactions across various fields, from consumer electronics and accessibility tools to high-tech security and industrial quality control.

Source: Nature Communications

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October 28, 2024 – by Cass Kennedy