Ambient radiation used to power battery-free temperature sensor

Researchers at the U of A and the University of Michigan have reported the creation of a graphene-based energy harvester that uses ambient radiation to run ultra-low-power temperature sensors. This is the second sensor created by the team whose overall goal is development of autonomous sensor systems that draw power from multiple sources in the environment — solar, thermal, acoustic, kinetic, nonlinear and ambient radiation.  

The team previously reported successful development of graphene-based solar cells that can be used to power temperature sensors.  

The team has three requirements for these sensors: they must use locally harvested energy, they must have a long unattended service life (potentially decades) and they must be able to operate at nanowatt-scale power. All three requirements have been met in the latest sensor utilizing ambient radiation.  

MD Rezaul Kabir, a Ph.D. candidate in the Materials Science and Engineering Program at the U of A, was first author on the paper, but graphene energy harvesters are the invention of U of A physics professor Paul Thibado, who began studying graphene's unique properties more than a decade ago and is the corresponding author.  

Harnessing Ambient Radiation 

Thibado noted that ambient radiation is everywhere in modern life, especially radiating from the electrical wiring of our homes (though the wires running through the walls could be better arranged to take advantage of this waste radiation). The temperature sensor systems created by Thibado's group focused on the standard 60 Hertz electrical frequency commonly used in the U.S. The sensor uses a graphene inductor to harvest energy from the magnetic fields created by these power lines. The inductor's signal feeds into a custom circuit that  converts the AC signal to DC, which charges the capacitors in the sensor.  

"The inductor adds charge to these capacitors at a slow rate," Thibado explained, "but it's faster than the rate the sensor uses up the charges from the capacitors. So even if the power went out, it can still pull a charge from the capacitors. The way ours are set up, it can easily last 24 hours — probably a week even." 

While Thibado's research group is working with temperature sensors as a proof of concept, Thibado imagines a wide range of uses for long-lasting, low-power sensors, such as tracking products, atmospheric monitoring, logistical fleet management, soil and wearable fitness monitoring, and medical tracking, to name just a few niches where he sees commercial opportunities.  

Because the sensors don't require batteries, you can "set it and forget it," as Thibado explains, reducing the cost, effort and waste associated with replacing old batteries.  

The end goal is development of multi-modal (utilizing more than one of the above power sources) sensors utilizing the energy harvesting capability of graphene that can last decades and help realize the Internet of Things, in which smart technology is literally woven into the fabric of daily life. So a sensor may harvest energy from ambient radiation and kinetic movement, providing a backup power source in the event there is interruption in one (such as a power outage). 

The paper was published in the Journal of Vacuum Science and Technology B. Co-authors from the U of A included Ashadsuzzaman, Tamzeed Bani Amin, Jim Magnum and S.M. Rahman, all doctoral students. Co-authors from the University of Michigan included Hung Do, Gordon Carichner and David Blaauw, a professor of electrical engineering and computer science who specializes in low-power wireless sensors and embedded systems.  

Patent and Licensing 

NTS Innovations, a company specializing in nanotechnology, owns the exclusive license to develop graphene energy harvesters into commercial products. The company has provided funding for patenting, creating business plans, finding business partners and customer discovery. 

NTS Innovations' role over the course of the grant is to engage with customers on acceptance criteria, such as the minimum power levels needed for inclusion in products. Currently, more than 60 parties have expressed interest in testing the technology and working with Thibado and his colleagues to integrate it into their applications.