Everyone talks about energy as a major crisis in the world. Renewable energy over non-renewable energy, electric cars vs IC engines, the dangers of nuclear energy, the lacking efficiency in Solar energy etc. are major problems tackled by many renowned names around the world.
However, a tiny aspect of the energy sector hasn’t gotten the attention it deserves. I am talking about devices that need a small amount of energy to run, minuscule in fact and might just seem negligible in the grand scheme of energy utilization, however, as they say, every drop makes an ocean.
It is this nothingness that we must harvest energy from and effectively use and store to have a sustainable future driven by technology.
So, what exactly am I talking about here?
Let us start at the beginning. Thomas Alva Edison in 1879 filed a patent that would go on to revolutionize the very way that we live. I am talking of the light bulb of course.
Everyone wanted to find ways to power the light bulb, and so many devices were built along the course of a century and a half. Batteries, traditional energy, renewable energy sources, supercapacitors were all built as a viable power source.
They served their own purposes and had their own disadvantages, and soon enough they couldn’t keep up with the demand of the electronics industry. Though the electronics research continued in reducing the power consumption of devices, new sources had to be found.
This is when researchers turned their eyes to a source of energy that should definitely be harnessed. Imagine, that you can power your watch with just your pulse, and I am talking about smartwatches. Or you can charge your phone just by placing it in your pant pockets and went for your morning run.
We are a source of energy by just being alive, and now we have enough progress in science and technology to store and use this energy. Devices called as nanogenerators are being developed, to convert “wasted” mechanical energy into electrical energy.
There are three main approaches to nanogenerators, I will focus on the piezoelectric approach( also called PENG) in this article:
Piezoelectric Nanogenerators
Essentially these nanogenerators are a bunch of nanowires placed like a comb, but thousands of them would essentially fit in a single strand of hair. Nanowires are just nanometre size strands of a certain material.
It is worth talking about the unique properties of nanowires. One very interesting property about nanowires is in their conductivity. They are ballistic conductors.
In classical conductors, electrons collide with other electrons as they travel through a conductor, therefore producing heat, which is a waste of energy and can be harnessed too, but more on that later. Nanowires are so tiny, that these electrons can travel without any collision, there they effectively conduct without any heat dissipation.
So how do we create energy with these tiny structures? We make nanowires of piezo-resistive ceramic materials (the methods of production for nanowires are beyond the scope of this article), and then when we bend this nanowire, it will produce an electric charge.
So, we stack up 1000s of these nanowires on a suitable electrode ( usually silicon) and we are good to go. Any physical pressure will flex the nanowires, they will produce electricity, the electrode will carry the charge to the rest of the circuit.
Simple, right?! Not quite. Let us look at actual numbers. So far, the maximum energy that a nanogenerator of any type has been able to produce is 55.07 microWatts or the equivalent of lighting up 39 LEDs. That is a very small amount of energy and to power, a smartwatch from the kinetic energy created from your jogging is going to take quite some time.
However, there is hope to cultivate all the energy we expend for nothing. Together with supercapacitors, devices that store energy very efficiently, we can begin to build batteries that work on mechanical vibrations.
Conclusion
The other two types of nanogenerators are triboelectric and pyroelectrical in nature. Triboelectric nanogenerators( TENG) work on the triboelectric effect, which is basically the creating of electric charges because a material loses contact with another material, and pyroelectric nanogenerators(PyENG) harness thermal energy ( told you we wouldn’t waste heat too) into electrical energy. It relies on the Seebeck effect. A combination of these types has also proved to be useful and effective.
Although you can’t quite charge your phone as you run to your morning class yet, sensors are being developed that are powered by nanogenerators, providing many wireless solutions and with the ongoing drive for IoT devices, it is evident that nanogenerators are the way to go for small energy.
– Article by Pravan Omprakash, 3rd Year Metallurgical and Materials Engineering.