Power Your Smartphone by Your Sweat

Anyone can power a smartphone by manually running a small electric generator. Without a doubt, some will sweat in the process. However, this technology is somewhat different. Here, a small tattoo will detect whether you are sweating (for whatever reasons) and generate power directly from your sweat.

Researchers at the University of California in San Diego have developed a sensor to monitor a person’s progress when he or she is exercising. Although this is not something new, but the sensor is in the form of a temporary tattoo and it also doubles as a bio-battery. It can detect when the person is perspiring and produce power from it.

According to one of the researchers, Wenzhao Jia, when a person sweats, one of the naturally occurring chemicals is lactate. The sensor detects and responds to lactate, which is a very important indicator of how the person is progressing with the exercise. That is because with more intense exercise, the body produces increasing amounts of lactate. With strenuous physical activity, the body activates a process called glycosis, which produces energy and lactate.

Professional athletes test their performance by monitoring the levels of lactate they produce. This is one of the ways they evaluate their training program and their fitness. Moreover, some conditions cause abnormally high lactate levels in the body such as lung or heart diseases. Doctors measure the lactate levels during exercise testing of their patients. However, lactate testing is intrusive because it needs blood samples of the person to be collected at different times during exercising and then analyzed. Therefore, the current process is inconvenient.

The team led by Joseph Wang, of which Jia is a member, has developed a faster, easier and more comfortable way of measuring lactate during exercise. They imprinted the biosensor onto a temporary tattoo paper. The sensor has an enzyme that strips electrons from the lactate produced during the workout and generates a weak electrical current.

In practice, the tattoo is applied to the upper arm of the person exercising. When the person exercises on a stationary bicycle, it is easy to monitor the performance against increasing resistance levels. The researchers were able to monitor 10 health volunteers for 30 minutes and checked the lactate levels in their sweat over time and with changes in intensity of their exercise.

One of the startling discoveries from the research was that different people produced different amounts of electricity. Surprisingly, people who exercised less than once per week and hence were less fit produced more power as compared to moderately fit people who exercised between one and three times per week. Those who were the most fit, working out more than three times per week, produced the least amount of power.

According to the researchers, less-fit people become fatigued sooner and glycosis kicks in earlier for them. Therefore, they produce more lactate because of their increased fatigue. In the low-fitness group, the maximum amount of energy produced by a person was 70μW for every square cm of skin. Although the power generated is not very high, the researchers are confident of eventually increasing it to power small gadgets.