MIT develops a sensor that can power itself without batteries

北京莱森泰克

MIT develops a sensor that can power itself without batteries [Copy link]

　　MIT researchers have developed a battery-free, self-powered sensor that harvests energy from the environment. Because it requires no batteries that must be charged or replaced, and no special wiring, the sensor can be embedded in hard-to-reach places, such as the innards of a ship's engine. There, it can autonomously collect data about the machine's power consumption and operation over long periods of time.

　　Researchers have created a temperature-sensing device that harvests energy from the magnetic field generated in the open air around electrical wires . Simply clip the sensor around a live wire (perhaps one that powers a motor), and it automatically harvests and stores the energy to monitor the motor's temperature.

　　“This is ambient power — power that I can get without having to make a specific solder connection,” said Steve Leeb, professor of electrical engineering and computer science (EECS) and professor of mechanical engineering, a member of the Research Laboratory of Electronics. “This makes this sensor very easy to install.”

　　In the paper, which appears in the January issue of the IEEE Sensors Journal, the researchers provide a design guide for energy-harvesting sensors that allows engineers to balance the available energy in the environment with their sensing needs.

　　The paper lays out a roadmap for key components of devices that can continuously sense and control energy flows during operation.

　　This versatile design framework is not limited to sensors that harvest magnetic field energy, but can also be applied to sensors that use other power sources, such as vibration or sunlight. It can be used to build sensor networks for factories, warehouses, and commercial spaces that are cheaper to install and maintain.

　　"We've provided an example of a battery-free sensor that does something useful and demonstrated that it's a viable solution. Hopefully, others will be able to use our framework to design their own sensors."

　　John Donnal, an associate professor of weapons and control engineering at the U.S. Naval Academy who studies technology to monitor ship systems, said getting power on a ship is difficult because there are few outlets and strict restrictions on what devices can be plugged in.

　　“For example, continuously measuring the vibrations of a pump can provide the crew with real-time information on the health of bearings and brackets, but powering the added sensors often requires so much additional infrastructure that it is not worth the investment,” Donnell said. “Energy harvesting systems like this could enable the addition of a variety of diagnostic sensors to a vessel, significantly reducing overall maintenance costs.”

　　The researchers had to address three major challenges to develop an effective, battery-free energy-harvesting sensor.

　　First, the system must be able to cold start, meaning it can start up an electronic device without the initial voltage. They achieved this using integrated circuits and a network of transistors that allow the system to store energy until a certain threshold is reached. Only when the system has stored enough energy to be fully operational will it turn on.

　　Second, the system must efficiently store and convert the harvested energy without using batteries. While researchers could add batteries to the system, this would increase complexity and could introduce a fire risk.

　　To avoid using batteries, they use internal energy storage technology, including a series of capacitors. Simpler than batteries, capacitors store energy in an electric field between conductive plates . Capacitors can be made from a variety of materials, and their functionality can be tailored to suit a variety of operating conditions, safety requirements and available space.

　　The team carefully designed the capacitor to be large enough to store the energy needed for the device to turn on and start harvesting power, but small enough that the charging phase didn't take too long.

　　And because the sensor might not be turned on for measurements until weeks or even months later, they want to make sure the capacitor can hold enough energy, even if some of it leaks away over time.

　　Finally, they developed a series of control algorithms that dynamically measure and budget the energy collected, stored, and used by the device. The microcontroller is the "brain" of the energy management interface, constantly checking how much energy is stored and inferring whether to turn sensors on or off, take measurements, or shift the machine into a higher gear to collect more energy for more complex sensing needs.

Self-Powered Sensors

　　Using this design framework, the researchers built an energy management circuit for an off-the-shelf temperature sensor. The device harvests magnetic field energy and uses it to continuously sample temperature data, which it then sends via Bluetooth to a smartphone interface.

　　The researchers designed the device using ultra-low-power circuits, but soon discovered that there were strict limits on the voltage these circuits could withstand before breaking down. Harvesting too much power could cause the device to explode.

　　To avoid this, their energy harvester operating system in a microcontroller automatically adjusts or reduces the amount of harvested energy when too much stored energy is available. They also found that communication -- transmitting the data collected by the temperature sensor -- is by far the most power-hungry operation. Ensuring that the sensor has enough stored energy to transmit data is a persistent challenge that requires careful design.

　　In the future, the researchers plan to explore less energy-intensive means of transmitting data, such as using optics or acoustics. They also hope to more rigorously model and predict the amount of energy that goes into a system, or the amount of energy required for a sensor to make a measurement, so that the device can efficiently collect more data.

　　“If you only take the measurements you think you need, you might miss something really valuable. If you have more information, you might learn something about the device operation that you didn’t expect. Our framework lets you balance these considerations,” Leeb said.

　　This work was supported in part by the Office of Naval Research and the Grainger Foundation.