Printable textiles cool, detect motion and generate electricity

Although clothing is a fundamental human need, it does not seem to advance as quickly as many others. That said, scientists have created a printable fabric that can cool, detect motion, and generate electricity without external systems or multiple layers.

Researchers at the University of Illinois Grainger College of Engineering have created a zirconium oxide (ZrO₂) nanocomposite textile material that combines passive cooling and biomechanical energy harvesting.

The material uses radiative cooling to reflect 96% of incoming solar radiation, keeping the wearer cool outdoors, plus it can also radiate the wearer’s thermal energy. Additionally, the material detects movement by detecting the triboelectricity generated when the user moves against the fabric. This extremely small amount of electricity can serve as a signal for embedded technologies. According to researchers, it can also be used to power small portable devices.

We spend almost 100% of our lives dressed. It follows that they should do more than just protect us from the elements. It is this line of thinking that has led scientists to invent clothing with health monitoring, climate adaptation, interactive control and self-healing, among other features. The problem is that most of these functions require active and complex systems and, in many cases, multiple layers assembled with different functions.

The solution from researchers at the University of Illinois avoids these requirements by combining multiple functionalities in a single 3D printed fabric. At its core is a zirconium oxide (ZrO₂) nanocomposite. It turns out that zirconia has two properties that researchers can exploit at once. Optically, its high refractive index makes it very good at dispersing sunlight. Electrically, its dielectric properties help it accumulate triboelectric charge when it makes and breaks contact with another material.

Therefore, the researchers developed a material useful for both radiative cooling and motion-driven electricity generation. Additionally, the material can be printed using direct ink writing, a form of extrusion-based additive manufacturing.

Unlike normal fabric that absorbs a significant amount of the sun’s heat and transfers it to the wearer’s body, the new fabric reflects 96% of incoming solar radiation. Additionally, the material has 97% emissivity in the mid-infrared, making it very effective at radiating the wearer’s body heat in the form of infrared radiation. Under outdoor sunlight, the researchers measured the tissue at about 3-6°C below ambient air temperature. For context, humans can detect 1°C (1.8°F) differences in air temperature under normal conditions.

The material’s other potential functions lie in its ability to generate electricity.

You know that little static discharge you can get after rubbing your feet on a rug? That is true electricity. The same happens with the new fabric, as the user moves and their skin rubs against it. Repeated mechanical motion generates a detectable electronic pulse. The article, published in the magazine Advanced scienceIt reports a maximum power density of approximately 47 mW/m² and stable electrical output for more than 30,000 operating cycles.

While this amount of electricity is not enough to charge your phone remotely, it is useful for many other applications, including sensing. Connected to the right sensor, that small electrical signal can indicate when the user is moving. The signal level can also indicate how much movement is occurring. The fabric can also be connected to a control system, where the signal acts as a trigger.

The researchers demonstrated this functionality by combining the fabric with an underlying conductive textile layer to create an adaptive thermal management system. When the user was stationary, passive radiative cooling kept things cool. Instead, when they moved, the triboelectricity generated a signal that triggered the underlying conductive layer to begin heating.

Important clarification: The ZrO₂ material did not generate the heat itself, but simply provided the signal that activated the underlying layer. The conductive layer came with its own electronics, including heating elements, a DC power supply, a solid-state relay, and an Arduino microprocessor.

It seems somewhat contradictory that the heating is activated when the user is moving, a state that in turn generates body heat. However, the researchers designed this setup as an intentional experiment. The triboelectricity generated can be applied to several other systems. For example, fabric sewn into sleepwear can trigger alarms when it detects a predetermined amount of movement.

Source: University of Illinois, Urbana-Champaign