The advent of inexpensive wearable sensors that can monitor heart rate, body temperature, and levels of blood sugar and metabolic byproducts has allowed researchers to monitor human health in ways never before possible. But like all electronic devices, these wearable sensors need a source of power. Batteries are an option but are not necessarily ideal because they can be bulky, heavy, and run out of charge.
Researchers have now developed a way to power wireless wearable sensors by harvesting kinetic energy that is produced by a person as they move around. This energy harvesting is done with a thin sandwich of materials (Teflon, copper, and polyimide) attached to the person’s skin. As the person moves, these sheets of material rub against a sliding layer made of copper and polyimide and generate small amounts of electricity. The effect, known as triboelectricity, is perhaps best illustrated by the static electric shock a person might receive after walking across a carpeted floor and then touching a metal doorknob.
The triboelectric generator (nanogenerator) has a stator that is fixed to the torso and a slider that is attached to the inside of the arm. The slider slides against the stator during human motion and an electrical current is generated at the same time. The nanogenerator was made with commercially available flexible circuit boards.
The nanogenerator does not create a lot of electricity; one would need a device with 100 square meters of surface area to power a 40-watt light bulb. The wearable sensors have low power requirements and the system stores generated electricity in a capacitor until there is enough charge to take a reading from the sensor and wirelessly send the data to a cellphone through Bluetooth. The more a person moves, the more often the sensor can collect data. Even if the person is fairly sedentary, however, the sensor eventually will accumulate enough power to operate.