Mechanoluminescent (ML) materials, which emit light when mechanically stressed without needing an external power source, hold great promise for advanced technologies like bite-controlled interfaces, health monitoring, and precise force sensing. However, a challenge with these materials is their broad light emission spectrum, which can decrease sensitivity and introduce unwanted noise – hindering their effectiveness in sensing applications.
Addressing the Challenge with Color Filtration
Researchers from South Korea and the UK, led by Professor Hyosung Choi of Hanyang University, have developed a new approach to enhance ML sensor resolution. Their work, published in Advanced Materials, involves coating the ML material, zinc sulfide doped with copper (ZnS:Cu), with a special polymer shell. This shell, made of poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), acts as a color filter, selectively reducing light emissions below 490 nanometers. This narrowing of the light spectrum from 94 nm to 55 nm significantly improves the ability to distinguish between different signals.
A Novel Dual-Functionality: Light Compensation
Typically, color filtration reduces the overall intensity of light emitted. However, in this innovative system, the F8BT polymer’s own light emission, triggered by mechanical pressure, compensates for this loss. This dual functionality — acting as both a filter and a light source — is a key advantage. By filtering out unwanted colors while maintaining strong blue light emission, the system minimizes spectral noise and boosts resolution in practical haptic controllers.
Proof of Concept: Color Tracking System
To demonstrate the system’s capabilities, the researchers created a proof-of-concept color tracking system using ZnS:Cu coated with F8BT. This system accurately distinguished between blue and green ML signals, showcasing the high spectral resolution achieved through their chromatic filtration strategy.
Implications for Future Applications
This technology opens up exciting possibilities for a range of applications:
- Wearable Sensors for Space Environments: Quantifying crew activity in space, requiring lightweight, power-efficient monitoring solutions.
- Mouthpiece-Type Controllers: Enabling wheelchair operation via chewing gestures, where specific movements (left, center, right) trigger different actions.
- Elderly Health Care: Addressing the growing need for power-free stress sensing technologies for motion monitoring and assistive robotics, particularly as populations age.
“As the aging society accelerates, there will be an increasing demand for eco-friendly, power-free stress sensing technologies that are directly linked to elderly health care,” said Prof. Choi.
Long-Term Vision: Eco-Friendly Sensors and Energy Harvesting
Beyond immediate applications, this technology has the potential to advance energy-harvesting sensors and interfaces that convert mechanical energy into light. This provides an eco-friendly alternative to traditional battery-powered devices, significantly reducing battery dependence and electronic waste. The high color purity and reliable optical decoding allow for long periods of operation without external power, activated and read with cameras or photodiodes, making it ideal for power-constrained environments such as disaster zones, remote infrastructure, deep sea exploration, and space missions. Within the next five to ten years, this innovation is expected to lead to battery-free, high-resolution sensor networks in displays, wearables, and industrial safety equipment.
