Magnetics Business & Technology - November/December 2024 - 17

RESEARCH & DEVELOPMENT
infers whether to turn the sensor on or off, take a measurement,
or kick the harvester into a higher gear so it can gather more
energy for more complex sensing needs.
" Just like when you change gears on a bike, the energy management
interface looks at how the harvester is doing, essentially
seeing whether it is pedaling too hard or too soft, and then it varies
the electronic load so it can maximize the amount of power it
is harvesting and match the harvest to the needs of the sensor, "
Monagle explains.
Self-powered sensor
Using this design framework, they built an energy management
circuit for an off-the-shelf temperature sensor. The device
harvests magnetic field energy and uses it to continually sample
temperature data, which it sends to a smartphone interface using
Bluetooth.
The researchers used super-low-power circuits to design the
device, but quickly found that these circuits have tight restrictions
on how much voltage they can withstand before breaking down.
Harvesting too much power could cause the device to explode.
To avoid that, their energy harvester operating system in the
microcontroller automatically adjusts or reduces the harvest if the
amount of stored energy becomes excessive.
They also found that communication - transmitting data gathered
by the temperature sensor - was by far the most power-hungry
operation.
" Ensuring the sensor has enough stored energy to transmit data
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STANDARD AND FULLY-CUSTOMIZED
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is a constant challenge that involves careful design, " Monagle
says.
In the future, the researchers plan to explore less energyintensive
means of transmitting data, such as using optics or
acoustics. They also want to more rigorously model and predict
how much energy might be coming into a system, or how much
energy a sensor might need to take measurements, so a device
could effectively gather even more data.
" If you only make the measurements you think you need, you
may miss something really valuable. With more information, you
might be able to learn something you didn't expect about a device's
operations. Our framework lets you balance those considerations, "
Leeb says.
" This paper is well-documented regarding what a practical
self-powered sensor node should internally entail for realistic
scenarios. The overall design guidelines, particularly on the coldstart
issue, are very helpful, " says Jinyeong Moon, an assistant
professor of electrical and computer engineering at Florida A&M
University-Florida State University College of Engineering who
was not involved with this work. " Engineers planning to design a
self-powering module for a wireless sensor node will greatly benefit
from these guidelines, easily ticking off traditionally cumbersome
cold-start-related checklists. "
The work is supported, in part, by the Office of Naval Research
and The Grainger Foundation.
By Adam Zewe | MIT News
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Magnetics Business & Technology - November/December 2024

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