Smart phones and the features they offer have become an essential part of daily life. Yet their short battery life, which is approximately three-fourths of a day, leaves many frustrated, especially if power cords and chargers have been misplaced or forgotten. However, according to a new invention from the University of Wisconsin-Madison (UW-Madison), the frustration of a forgotten charging device may soon become a relic of the past. A novel energy collection and storage technology, which was developed by mechanical engineers at UW-Madison, could allow users to charge their phone’s battery through their footwear.
Mechanical Engineer and Researcher J. Ashley Taylor and Professor of Mechanical Engineering Tom Krupenkin described their work in a paper published in the journal Scientific Reports last year. Krupenkin and Taylor claim their device is particularly apt for capturing the energy of human motion.
According to Krupenkin, human walking carries a lot of energy. It has been estimated that walking can produce up to 10 watts per shoe. This is a significant amount of energy, especially when compared to the amount necessary to charge a typical smart phone. According to Krupenkin, smart phones usually require less than two watts to charge, leaving an excess of energy that could be used to power flashlights, laptops, tablets or other small mobile devices.
Logistically, Krupenkin and Taylor’s system works through the sole of a shoe and involves an energy harvester that sits inside a carefully crafted piece of footwear. Since research has shown that traditional approaches to energy collection and conversation have not worked well with large footfalls and small displacements, Taylor and Krupenkin have developed a new method of directly converting mechanical motion into electrical energy. Their innovative method, coined “reverse electrowetting,” uses a nanofilm-coated surface to convert mechanical energy directly into electrical energy when a conductive liquid interacts with this surface.
Yet this novel technique is not enough to adequately coincide with the low-frequency disjointed walking styles of most people. Because reverse electrowetting requires continuous quick vibrating or rotating, this method alone is not a viable technology for producing electricity through walking.
Yet Krupenkin and Taylor did not give up. Instead, they pioneered another new mechanism, called “bubbling,” to solve this problem. In its most basic form, bubbling works by using pressurized gas to produce bubbles in a conductive liquid.
Within the compartment of the shoe that would create electricity, two flat plates, one on top of the other, would be separated by a small gap filled with conductive liquid. The bottom plate has many tiny holes through which pressurized gas is able to make bubbles. These bubbles expand until they are collapsed by the top plate, causing the system to begin again. It is this continuous disturbance that allows Taylor and Krupenkin’s reverse electrowetting to succeed.
The two scientists believe their technology could be used for a diverse set of activities and people, from military personnel to individuals living in developing countries that lack adequate power grids.
