As our need for electronic gadgets and sensors grows, scientists are coming up with new ways to keep devices powered on longer with less power.
The latest sensor invented in the lab can run for an entire year on a single burst of energy, aided by a physical phenomenon known as a quantum tunnel.
The tunnel look means that with the help of a 50 million electron jumpstart, this simple, inexpensive device (consisting of just four capacitors and two transistors) can continue for an extended period of time.
The quantum rules of physics, applied at the smallest atomic scales, mean that electrons can behave both like particles and waves, and scientists have been able to tap into this behavior to precisely control the flow of electrons to ‘one side of a circuit to the other.
“If you want to get to the other side, you have to physically climb the hill,” says electrical engineer Shantanu Chakrabartty of Washington University in St. Louis.
“The quantum tunnel is more like crossing the hill”.
In order to generate current, devices need to be able to give electrons a strong enough push – this is called threshold energy, because that push needs to exceed a certain threshold. When you’re trying to make devices that run on as little energy as possible, reaching this threshold can be tricky.
This is where the quantum mechanical part comes in: by taking certain approaches to shape the “hill” or barrier that needs to be overcome, it is possible to control the flow of electrons in different ways.
In this case, the “hill” is what is called a Fowler-Nordheim tunnel barrier, less than 100 atoms thick. By building the barrier this way, the scientists were able to slow the flow of electrons while keeping the system (and device) stable and turned on.
“Imagine there is an apple hanging from a tree,” Chakrabartty says. “You can shake the tree a bit, but the apple doesn’t fall. You have to give it enough pressure to shake the apple.”
“This is the minimum amount of energy needed to move an electron over a barrier.”
Inside the device are two dynamic systems, one with a transducer (energy converter). The team had to work backwards to shape their hill or barrier, measuring the movement of electrons first and then fine-tuning the Fowler-Nordheim setup accordingly.
The researchers were left with a device that uses the interaction between the two internal systems to detect and record the data without any additional power. Something like this could be used to monitor blood glucose, for example, or to measure temperature for vaccine transport – batteries are not needed.
In this case, the transducer used was a piezoelectric accelerometer, which detected and was powered by ambient motion, but the basic principles of long life and high efficiency system can also be applied to other types of energy recovery.
“Right now the platform is generic,” says Chakrabartty. “It just depends on what you pair with the device. As long as you have a transducer capable of generating an electrical signal, it can self-power our sensor-datalogger.”
The research was published in Nature communications.