MIT researchers have developed a battery-free, self-powered sensor that may harvest energy from its environment.
Since it requires no battery that should be recharged or replaced, and since it requires no special wiring, such a sensor could possibly be embedded in a hard-to-reach place, like contained in the inner workings of a ship’s engine. There, it could routinely gather data on the machine’s power consumption and operations for long periods of time.
The researchers built a temperature-sensing device that harvests energy from the magnetic field generated within the open air around a wire. One could simply clip the sensor around a wire that carries electricity — perhaps the wire that powers a motor — and it’ll routinely harvest and store energy which it uses to observe the motor’s temperature.
“That is ambient power — energy that I haven’t got to make a selected, soldered connection to get. And that makes this sensor very easy to put in,” says Steve Leeb, the Emanuel E. Landsman Professor of Electrical Engineering and Computer Science (EECS) and professor of mechanical engineering, a member of the Research Laboratory of Electronics, and senior creator of a paper on the energy-harvesting sensor.
Within the paper, which appeared because the featured article within the January issue of the IEEE Sensors Journal, the researchers offer a design guide for an energy-harvesting sensor that lets an engineer balance the available energy within the environment with their sensing needs.
The paper lays out a roadmap for the important thing components of a tool that may sense and control the flow of energy continually during operation.
The versatile design framework is just not limited to sensors that harvest magnetic field energy, and might be applied to people who use other power sources, like vibrations or sunlight. It could possibly be used to construct networks of sensors for factories, warehouses, and industrial spaces that cost less to put in and maintain.
“We have now provided an example of a battery-less sensor that does something useful, and shown that it’s a practically realizable solution. Now others will hopefully use our framework to get the ball rolling to design their very own sensors,” says lead creator Daniel Monagle, an EECS graduate student.
Monagle and Leeb are joined on the paper by EECS graduate student Eric Ponce.
A how-to guide
The researchers had to satisfy three key challenges to develop an efficient, battery-free, energy-harvesting sensor.
First, the system must have the opportunity to cold start, meaning it may fan the flames of its electronics with no initial voltage. They achieved this with a network of integrated circuits and transistors that allow the system to store energy until it reaches a certain threshold. The system will only activate once it has stored enough power to totally operate.
Second, the system must store and convert the energy it harvests efficiently, and with out a battery. While the researchers could have included a battery, that may add extra complexities to the system and will pose a hearth risk.
“You may not even have the luxurious of sending out a technician to exchange a battery. As an alternative, our system is maintenance-free. It harvests energy and operates itself,” Monagle adds.
To avoid using a battery, they incorporate internal energy storage that may include a series of capacitors. Simpler than a battery, a capacitor stores energy within the electrical field between conductive plates. Capacitors might be made out of a wide range of materials, and their capabilities might be tuned to a variety of operating conditions, safety requirements, and available space.
The team fastidiously designed the capacitors in order that they are large enough to store the energy the device must activate and begin harvesting power, but sufficiently small that the charge-up phase doesn’t take too long.
As well as, since a sensor might go weeks and even months before turning on to take a measurement, they ensured the capacitors can hold enough energy even when some leaks out over time.
Finally, they developed a series of control algorithms that dynamically measure and budget the energy collected, stored, and utilized by the device. A microcontroller, the “brain” of the energy management interface, continuously checks how much energy is stored and infers whether to show the sensor on or off, take a measurement, or kick the harvester into a better gear so it may gather more energy for more complex sensing needs.
“Similar to once you change gears on a motorcycle, the energy management interface looks at how the harvester is doing, essentially seeing whether it’s pedaling too hard or too soft, after which it varies the electronic load so it may maximize the quantity of power it’s 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 repeatedly 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 will withstand before breaking down. Harvesting an excessive amount of power could cause the device to blow up.
To avoid that, their energy harvester operating system within the microcontroller routinely adjusts or reduces the harvest if the quantity of stored energy becomes excessive.
In addition they found that communication — transmitting data gathered by the temperature sensor — was by far probably the most power-hungry operation.
“Ensuring the sensor has enough stored energy to transmit data is a relentless challenge that involves careful design,” Monagle says.
In the long run, the researchers plan to explore less energy-intensive technique of transmitting data, akin to using optics or acoustics. In addition they wish to more rigorously model and predict how much energy could be coming right into a system, or how much energy a sensor might have to take measurements, so a tool could effectively gather much more data.
“For those who only make the measurements you think that you wish, it’s possible you’ll miss something really useful. With more information, you would possibly have the opportunity to learn something you didn’t expect a couple of device’s operations. Our framework allows you to balance those considerations,” Leeb says.
The work is supported, partly, by the Office of Naval Research and The Grainger Foundation.
