The garment is made from a combination of electronic parts. All are flexible, washable, and have been screen-printed in a special arrangement to optimize the amount of energy they can accumulate. A simple T-shirt can thus become a portable microgrid that collects and stores energy directly from the human body, with which it can power small electronic devices. The key is the combination of three elements biofuel cells that recharge with sweat, devices that use friction and movement to generate energy, and supercapacitors capable of storing it.
This electrical microgrid has been developed by a team of engineers specialized in nanobioelectronics from the University of California San Diego (UC) and is part of a new generation of flexible and integrated fabrics that seek to revolutionize both the feeding of gadgets and wearables and the way they the one we use them. Just as an urban microgrid integrates various sources of local and renewable energy, a wearable microgrid integrates devices that collect energy locally in different parts of the body explains Lu Yin, a Ph.D. student at UC and co-author of a paper that appeared this week in the journal Nature Communications.
Once the user begins to perspire, the batteries located on the inside of the shirt, at chest height begin to generate energy, as they are equipped with enzymes that cause the exchange of electrons between lactate and oxygen molecules present in sweat. On the other hand, the pieces that convert movement energy into electricity triboelectric generators are placed on the outside of the shirt on the forearms and the sides of the torso, near the waist, to collect activity when walking or running. thanks to the friction that occurs.
Taking advantage of both movement and perspiration allows the microgrid to power the devices on a sustained basis. By adding the two elements, you make up for each other’s deficiencies, Yin explains. They are complementary and synergistic and allow fast starting and continuous power. Each element provides a different type of energy: biofuel cells generate a low, continuous voltage while triboelectric generators provide high-voltage pulses. For the system to be able to harness the energy correctly, the voltages must be combined and regulated into one stable one.
This is the role of the supercapacitors, located outside the shirt, also at chest level. They act as a reservoir that temporarily stores energy from both sources and can discharge it when needed. You can say that biofuel stacks are a kind of slow-flowing tap and that triboelectric generators are like a hose that squirts water, Yin describes. “The supercapacitors would be the reservoir that both feed.
The engineers put the microgrid to the test in 30-minute sessions (10 minutes of exercise on a stationary bike or running and 20 minutes of rest). The system was able to power an LCD clock or a small electrochromic screen a device that changes color in response to an applied voltage in each session.
Although there are other applications, the system is especially useful for athletes, who would be charging their devices with the energy of each workout. But we are not limited to a single design, we can adapt the system by selecting different types of energy collectors for different scenarios, says Yin. Specifically, the team is already working on other models that can store energy even while the user is sitting, or walking slowly outside.
And while in San Diego engineers are working on garments capable of powering electronic devices, in Shanghai another team of researchers is working on the integration of these gadgets into fabrics. This Wednesday Chinese scientists describe in Nature the creation of a textile that serves as a screen. Flexible and resistant, its creators have had to solve an added difficulty since the conventional materials used in the screens are in principle incompatible with the natural deformation that occurs with the use of garments.
But this new design spins conductive fibers, luminescent fibers, and cotton fibers into a flexible fabric screen, making it a material with endless practical uses. The screen is materialized thanks to the electroluminescent units that are formed at the intersection between the conductive and luminescent fibers. The authors state that in the tests the vast majority of the light units remained stable even after 1,000 flexings, stretching, and pressing cycles. Also, they point out that the brightness of these units remained stable after 100 washing and drying cycles.
Engineers target several potential applications for the fabric, such as a navigation tool that displays an interactive map or a communication tool that can send or retrieve messages via a Bluetooth connection with a smartphone. They can be used for biomedical fields, for example; we can make them emit blue light, which is used to treat some diseases like neonatal jaundice more safely and effectively, explains Huisheng Peng, an engineer at Shanghai Fudan University and lead author of the article in Nature. Also, they can be used for smart homes or toys. Peng explains that this technology can already be produced on a large scale, some products are already being tested by companies for real applications.
The fabric can also be integrated with a touch-sensitive keyboard and its own power supply (in this case, solar batteries). And we can also make the power unit textile, creating a completely self-powered system, he stresses. We don’t really need other technology to complete our device.