New Sensor Harnesses Energy From Movement for Human-machine Interfaces

May 20, 2022 by Antonio Anzaldua Jr.

Solar, thermal, and wind are common sources of energy harvesting. Now, a triboelectric tactile sensor draws energy from movement to power wearables.

On April 25, 2022, researchers at Northumbria University (NPU) in China announced a newly-developed triboelectric tactile sensor that harvests energy from typical day-to-day movements of the human body and converts it into usable energy. 


The tactile hydrogel sensors

The tactile hydrogel sensors were placed on individual fingers and could power the movements of the robotic hand, giving the HMI system enough power for low-power actions. Image used courtesy of Advanced Science


Researchers hope this device will give rise to a new generation of wearable fitness trackers and smartwatches powered by bending, stretching, and twisting motions. 


Harvesting Motion for Energy

Energy-harvesting devices receive power continuously, periodically, or on-demand without external components or power supplies. Industry-standard energy harvesting devices typically rely on thermal, wind, or solar power—but not on physical movement. Now, however, researchers around the world are exploring movement as a form of energy that will not add additional weight or size to systems. 

Triboelectric nanogenerators (TENGs) harvest energy from friction applied to a wearable device. The main challenge facing TENGs falls on the production side since TENG based-sensors for wearables are not easily deformable to a wrist or ankle band. It's also difficult to fabricate a sensor thin enough to be shaped while also withstanding environmental elements and perspiration.


Components of a TENG that affect triboelectric energy generation

Components of a TENG that affect triboelectric energy generation. Image used courtesy of NPG Asia Materials

The research at NPU led by Professor Richard Fu involves a tactile hydrogel sensor (THS) that detects subtle pressure changes by measuring changes in triboelectric output signal without any external power supply. 

The new method relies on friction between a pyramid-patterned material and a silicone polymer called polydimethylsiloxane (PDMS). The friction between these two surfaces creates triboelectricity, which provides more available energy to a wearable device. 


NPU Research to Harvest Movement

The sensor prototype from NPU includes a feature that TENG-based sensors lack: hydrogels. Hydrogel offers anti-dehydrating and anti-freezing properties that help the sensor power through outside elements. The researchers used the new sensor as part of a human-machine interface (HMIs), a user interface or dashboard that connects a person to a machine system or device. 


Different movement voltages

Examples of the different activities that generate energy. Image (modified) used courtesy of Advanced Science

The HMI setup was rigged in three sections: the tactile sensors, a signal processing system (threshold module), and the robotic hands. When applied to robotic hands, the hydrogel sensor could generate usable power through extending, compressing, and rotating hand movements. Small movements and minor simulations provided the HMI with an output range of 5 V to 26.9 V peak voltage. These minor movements included individual finger motions.

The sensor could also withstand temperatures of -20°C to 60°C and high levels of humidity. The main applications for these sensors, according to researchers, is to detect health conditions and measure performance in active sports.