Scientists from the United States and Canada have developed a power-generating device that can be attached to a person’s knee. This device harvests energy lost when a person walks, generating enough electricity to charge up to 10 mobile phones. Arthur Guo, an engineer at the University of Michigan in the U.S., says the device’s power-generation principle is similar to that of electric bicycles that rely on braking to generate electricity. According to him, when a pedestrian takes a step, the knee naturally applies a slight brake. At this moment, some energy is lost—but the “knee generator” can capture this lost energy and convert it into electrical power. Researchers believe this power-generating device has numerous potential applications. Travelers and soldiers facing a shortage of power sources could use it as an emergency solution. Surgeons might even integrate it into prosthetic limbs. Before the “knee generator” was developed, researchers had already created power-generating devices that could be fitted onto shoes and backpack-mounted generators. However, both of these earlier devices had their own drawbacks: the shoe-mounted generator produced too little power, while the backpack-mounted generator was excessively heavy. By contrast, the new device manages to capitalize on the strengths of each while avoiding their weaknesses. If both feet are fitted with these devices and the user walks briskly on a treadmill at a speed of 3.5 kilometers per hour, the generator can produce up to 5 watts of electricity. Still, the generator weighs 1.20 kilograms, making it somewhat inconvenient to use.