A group of engineering students from Rice University designed a knee brace that generates power from the simple act of walking and stores it in a lithium-ion battery. The energy-generating knee brace is the third iteration of a multi-year project that was brought to Rice by Cameron International, a private company that challenged the students to power artificial hearts. Similar technology has previously been developed for military applications, and this version would be used for doctors who need electricity for medical care in remote areas.
When a person wears the brace, each knee bend creates energy that spins a motor that is attached to the joint of the brace. The motor’s electricity then travels through a cable to battery that clips onto a belt. In previous years, Rice students harnessed piezoelectric energy from small devices that attached to shoes. Although they were much less bulky than the knee brace, the shoe version didn’t produce enough power. So in this round, the students decided that although a knee brace is more cumbersome, it is worth the inconvenience because rotational energy is much more powerful.
The students say the biggest breakthrough in their design process was when they added a capacitor. Walking energy is extremely variable, so it would create a dangerous safety hazard if fed directly into the battery. The capacitor solves this problem by storing the variable energy in the short-term and then delivering it to the battery in a regulated amount so that it can safely charge without risking explosion.
The brace produces 4 watts of energy, which isn’t quite enough energy for the artificial heart that Cameron International challenged them to power. However, the students have made many improvements over the past year and they are hopeful that future versions of the brace will be powerful enough to take the rotational energy from walking and use it to power medical devices.