There is a decent chance that you’re reading this story with a battery powered device either on or near you. If so, it’s likely that one or several of those devices lose battery power at infuriatingly fast rates. What’s less probable is that you’re near the charger required to power these devices. Thankfully, a high tech energy harvester developed by two engineers could provide you and your devices with emergency power by harvesting—and storing—the energy created by walking.

The genesis of the technology began in 2011 when Dr. Tom Krupenkin, a mechanical engineering professor at the University of Wisconsin-Madison, and Dr. J. Ashley Taylor, a senior scientist in the university’s Mechanical Engineering Department, set out to uncover a new method for converting mechanical energy into electrical energy. More specifically, they wanted to create a method that makes the conversion using human and machine motion.

Krupenkin and Taylor developed their method, known as “reverse electrowetting,” in 2011.

“In reverse electrowetting the mechanical energy is converted to electrical energy by using a micro-fluidic device consisting of thousands of liquid micro-droplets interacting with a novel nano-structured substrate,” Krupenkin explained. “The motion of the droplets with respect to the substrate creates electrical charge which, in turn, generates electrical current that can be used to power the electronic devices.”

Though the development of the method was a huge accomplishment, the team still needed to create a device that could utilize the conversion. As a result, the team created Bubbler, which as Krupenkin describes, “is a microfluidic  device that allows one to convert an energy of the fluid flow into an electrical energy without having any moving parts.”

The shoe

After creating Bubbler, Krupenkin and Taylor wanted to develop  an application that would best capture the mechanical energy produced by walking, an act that results in roughly 7 to 10 watts of  mechanical power lost as heat.

“There is so much more energy in the walking process than you have in other types of human motion,” Taylor said.

Krupenkin added, “So, if one can capture even some small percentage of it, that’s plenty enough to power most of the mobile electronics.”

Through their startup “InStep NanoPower,” Krupenkin and Taylor started building energy harvesters to be used in a partnership with Vibram, an Italian footwear manufacturer which specializes in rubber soles. Vibram takes these harvesters and builds shoe soles that the harvester and battery can be embedded into. Those soles are then placed into a boot prototype, also made by Vibram.

Once placed inside the shoe sole, the battery is connected to  the harvester. When a person walks, the energy is transferred from the harvester to the battery. As a result, the wearer always has a partially charged battery.

Krupenkin and Taylor said the harvester can be used for smartphones and other popular mobile electronics, but they suggest this should only be viewed as an emergency charging option. A better use for the technology, they explained, are electronics that are embedded into the shoe.

Three of the top possible in-shoe applications for the technology, according to Krupenkin and Taylor are:

Global Positioning System

GPS’ and other positional tracking systems are a great tool. They help people from being lost in an unfamiliar location. Unfortunately, these systems are usually incapable of operating inside buildings, which can cause a dangerous issue for some.

“For a lot of people this is just an inconvenience, but some people depend on this,” Krupenkin said. “Firefighters going inside an industrial building filled with smoke will very easily lose their way. Military and police have pretty much the same problem as they often have to go into an unknown environment where a GPS signal is not available.”

Krupenkin and Taylor’s proposal would use inertia-based navigation systems that  elevates users of these frustrations. By putting the system in the shoe, you allow the inertia  sensors  to recalibrate each time that your foot becomes affixed to the floor, ensuring that you have an accurate positioning.

Inertia-based navigation  units that strap onto the foot already exist, and, if you pick the right one, they can be very accurate. However, the issue with these devices is that they’re inconvenient. As Krupenkin explained, every time the battery nears low levels, the user has to take it off the piece of footwear, plug it in, and then reattach the charged device to the shoe. Forgetting any of these steps could leave the wearer with an empty battery while on the job—a potentially dangerous situation. Having a GPS unit inside the shoe with a contestant charge removes these possible mishaps.

Emergency Beacon

Another application that Krupenkin and Taylor are interested is an in-shoe emergency beacon that could be used to monitor the health conditions of individuals—especially during a serious medical emergency.

The emergency beacon could track the location and condition of an individual anytime that they are wearing the shoe or boot if they so choose. Since the device is in the shoe and is always in mechanical and thermal contact with the foot, it provides a very accurate indication of the wearer’s condition.

“If somebody has a heart attack and is basically laying on the ground that would often reflect in the abnormalities of the temperatures of the foot,” Krupenkin said.

The two engineers said the shoe sole would have an electronic system that is connected to the cell phone network , which when set up to do so, could send the coordinates of the individual to the emergency alert service they subscribe to. It could also contact the cell phone of a loved one or any other person that the wearer chooses to provide as a contact.

The emergency alert system would also greatly aid search and rescue personal following a natural disaster. For example, if a person lost in debris caused by an earth quake is wearing a shoe equipped with the device, emergency personal would be able to tell if a victim is still alive and pinpoint exactly where they’re trapped within the rubble.

Wi-Fi Hot Spot

Footwear equipped with Krupenkin and Taylor’s device could also become an instant Wi-Fi hotspot through its connection with a cell network.

When the device is used as a Wi-Fi hotspot there are two connections associated with the system. One connection would occur between the cell tower and Wi-Fi hotspot. The other connection would be between the phone or other device and the Wi-Fi hotspot via Bluetooth. Such a system is beneficial because it frees users of the need to link an electronic device straight to the tower operated by the user’s service provider—a connection that uses up about 10 times more power than a Bluetooth connection, according to Krupenkin

“All of a sudden your cellphone does not expend power nearly as much when making a call or browsing the internet,” Krupenkin said. He added that a user’s phone would receive the same quality of internet surfing and phone calling capabilities that it had when it was connected straight to the cell tower.

Taylor and Krupenkin, along with two others, profiled Bubbler in a paper published Nov. 16, 2015, in the journal Scientific Reports. For more information on InStep NanoPower, visit the company’s website at https://instepnanopower.com/.