Turning Old Smartphones into Battery-free, Biodegradable Ecosystem Monitors

If the goal of monitoring our natural resources is to protect the environment, shouldn't the technology involved be sustainable as well? That's what VP Nguyen, assistant professor in the University of Massachusetts Amherst's Manning College of Information and Computer Sciences (CICS), is aiming to achieve under a $600,000 grant from the U.S. National Science Foundation to repurpose old smartphones into cameras and sensors that monitor the environment using renewable energy, battery-free computing and biodegradable materials.

"We want to make sure that the impact of our system to the environment is minimal," he says. "We reuse what people throw away, and then we make sure that in its afterlife, the device will not hurt the environment."

People change out their phones every two to three years, on average, resulting in a lot of technological waste-or potential, from Nguyen's perspective. Even an old phone that no longer holds a charge likely has a camera that is more powerful than current monitoring cameras, and costs between $50 and $75, instead of $200 or more.

It's the battery that is the limiting factor. Batteries are excellent for storing energy, but they have a limited number of recharging cycles. "Buying new batteries defeats the whole purpose, because a new battery is expensive, and eventually, you have to replace the battery again," he explains. "If you keep buying batteries and then replacing them, that's not a very environmentally friendly solution either."

As an alternative, his team, which also includes Deepak Ganesan and Hui Guan from UMass CICS, proposes a battery-free computing system. Instead, the system will have a capacitor array that collects power from solar and wind harvesters built into the phone case. Also, the capacitor array and case can be biodegradable.

"What we are developing is basically a phone case," he says. "That phone case will connect to the solar panels and also the wind energy harvester. And the entire material for that phone case is biodegradable so, after we finish, it will dissolve into the environment."

One of the challenges of using a capacitor array and renewable energy is that it does not provide the robust and consistent stream of power that a battery would.

"The amount of energy in a capacitor is very small, so the computational technology needs to be extremely efficient," says Nguyen. "With that amount of energy, you have to make computing really efficient. That's a difficult challenge in computer science, but it's also what we enjoy-every problem gives us a chance to invent something new."

The other technique Nguyen plans to integrate into the design is energy-aware computing strategies, so that his device can take advantage of a smartphone's AI integration, even when electricity to run AI techniques on the edge is intermittent, like when the sun isn't shining or the wind isn't blowing.

This technology will be evaluated and deployed in real-world settings through collaboration with two partners. The PhenoCam network, created by Northern Arizona University, is a series of cameras that track the impact of climate change, particularly on trees. The second partner, GaugeCam, created by the University of Nebraska at Lincoln, does similar monitoring but of rivers. In partnering with existing efforts, Nguyen ensures that this technology will be rapidly deployable and scale quickly.