Batteryless IoT Sensor to be used underwater and in outer space

What do you think is humankind’s final frontier? It’s not outer space - The way things stand, there are over 2000 artificial satellites orbiting the Earth. And, this number is expected to quintuple over the course of this decade. Come July 2020, it will be 41 years since Neil Armstrong and Buzz Aldrin landed on the moon.Man-made ships have orbited Jupiter, Saturn, Mercury and Venus. There’s a lot of talk about a certain South African emigre drawing up plans to send a million people to Mars in the next 30 years!  So, space is very much within our reach now. However, the depths of our oceans continue to remain unexplored and shrouded in all kinds of mystery. The ocean floor of our very own planet, it would seem, is our final frontier!

Unknown depths

Over 70% of our planet’s surface is covered by its oceans. That’s not news to anybody. After all, we are not called the blue planet for no reason. However, what might shock a lot of people is how much of this “world ocean” is still largely beyond the purview of science. That’s right - For all our computing wizardry and rocketing expertise, about 90% of our oceans remain unmapped and unstudied. As things presently stand, we only have about 5-15% of the world’s ocean floor mapped and that too from various disparate sources. 

If you need additional perspective to make sense of that, here goes - We have much more reliable and detailed maps of Mars, than we do of our oceans!

Batteryless 

The world is a radically different place, today, than it was even a decade ago. The IoT revolution has managed to make the world a super-connected place. Far from being a fringe phenomenon, the Internet of Things has truly come of age! We have dramatically reduced the complexity of hundreds of thousands of processes using our unprecedented ability to collect and process data. Today, we are able to gather information, using various kinds of sensors, from all sorts of machines, tools and other everyday objects and use this information to build better systems and optimise outcomes. This is no mean feat! It wouldn’t be an overstatement to say that our continued survival as a species depends on us continuing down this path.

A team of researchers at MIT wanted to design a system of sensors, based on the same principle. The system would collect data from the ocean floor and relay it back to the surface - a deep-sea IoT, if you will! However, they were faced with a pressing challenge - how do you power a complex system of sensors that are to be placed several kilometres below sea level? 

Batteries could hardly be an option, considering that the researchers were planning on building a complex system containing dozens of sensors. Moreover, these sensors were meant to stay underwater for extended periods of time. The researchers were also mindful of the fact that using batteries would pollute the ocean. Not to mention the costs and hassle that hauling sensors back up and replacing them would entail - all in all, using batteries just wasn’t an option. 

The researchers wanted to find a solution that would allow the sensors to collect and send data without needing an external source of power. 

The researchers did manage to create a solution that fit the bill - an ultra-low power underwater communication system that autonomously harvests energy and uses it to transmit bursts of data. 

What is this system meant to do?

The team behind this system designed it to be used in extreme conditions. The system is built to monitor sea temperatures, in a bid to study the controversial effects of climate change and track it’s impact on marine flora and fauna, over a long duration of time. Moreover, the researchers claim that the system could also be deployed in space missions to test samples of water from far flung planets. 

Another left-field application for this system could be monitoring large pools of brine that form in ocean basins. These “brine pools” tend to be quite arduous to monitor on a long-term basis. Studying these pools, say for instance, the ones on the Antarctic Shelf, could help us shed light on how melting ice affects marine biodiversity in these areas. 

The science behind the self-powered sensor

The system was presented at the SIGCOMM conference in Beijing, China, where it won the “best paper” award. It makes use of two main phenomena - the piezoelectric effect and backscatter. 

So, what is the piezoelectric effect you ask? It’s pretty simple - some materials (conveniently called piezoelectric materials) have the ability to generate an electric charge when they are subjected to mechanical stress. A wide variety of ceramics, crystals and semiconductors exhibit this property. 

And now for backscatter - backscatter refers to the technique of bouncing wireless signals off a tag and back onto a reader. This phenomenon is widely employed in RFID tags. 

“Basically, we can communicate with underwater sensors based solely on the incoming sound signals whose energy we are harvesting.” 

-  Fadel Adib, co-author & Asst.Prof at MIT

How does the batteryless sensor work?

In this MIT-designed system, a transmitter first sends acoustic waves through water towards a sensor, in which data is stored. This sensor is made of a piezoelectric material. Therefore, when the waves from the transmitter hit the piezoelectric sensor, the material starts vibrating and stores the electrical charge that is generated. 

The sensor then uses this stored energy to reflect or not reflect a wave back to a receiver (on the surface). Reflected and non-reflected waves correspond to bits of data transmitted in binary code, i.e. when the receiver receives a reflected wave, it reads a 1 and when there is no reflected wave, it reads a 0. 

Do not let the simplicity of the concept fool you - all manner of data can be transmitted in the form of 1s and 0s. In fact, the device on which you are reading this had to convert all this information from binary into English. 

In the words of co-author Fadel Adib who is an Assistant Professor of Electrical Engineering and Computer Science at the MIT Media Lab and the founding director of the Signal Kinetics Research Group, “Once you have a way to transmit 1s and 0s, you can send any information”. He goes on to add, “Basically, we can communicate with underwater sensors based solely on the incoming sound signals whose energy we are harvesting.”

The team successfully demonstrated their piezoelectric, backscatter system in an MIT campus pool. They used the sensor system to collect water temperature and pressure measurements. It was able to accurately transmit about 3 kilobits of data per second over a distance of 10 metres. (Check the video below)

Sensors in space

Adib and his team have huge plans for the signalling system. They feel that the potential applications of this system could extend well beyond the scope of our planet. Recently, we discovered an ocean under the surface of Saturn’s largest moon - Titan. In fact, NASA has announced an unmanned mission to this moon in 2026, aiming to sample water sources and other sites. 

This batteryless sensor system, says Adib, could well be used to collect data on this mission. 

“How can you put a sensor under the water on Titan that lasts for long periods of time in a place that’s difficult to get energy?” says Adib who co-authored the paper with JunSu Jang. “Sensors that communicate without a battery open up possibilities for sensing in extreme environments.”

“Internet-of-things (IoT) devices could help with that research, but underwater you can’t use Wi-Fi or Bluetooth signals and you definitely don’t want to put batteries all over the ocean, because that raises serious issues with pollution.” 

Design inspired by nature

Adib says he got inspired to build his system while he was engrossed in an episode of Blue Planet, the lushly shot marine documentary series. “It occurred to me how little we know of the ocean and how marine animals evolve and procreate,” he says. 

“Internet-of-things (IoT) devices could help with that research, but underwater you can’t use Wi-Fi or Bluetooth signals and you definitely don’t want to put batteries all over the ocean, because that raises serious issues with pollution.”

On the face of it, there is nothing groundbreaking about using piezoelectric materials - they have been in use for over a century. They have been used in various devices over the years, including microphones. When they are subjected to vibrations, they produce a small voltage, but here is the cool part - the reverse is also true! I.e. if you apply a voltage, the material deforms. When placed underwater, this property (the deforming) produces a pressure wave that is able to travel through the water. 

“This reversibility is what allows us to develop a very powerful underwater backscatter communication technology,” Adib says. 

The system contains, at its core, a submerged node, a circuit board which contains a piezoelectric resonator, an energy harvesting unit and an MCU. The microcontroller allows any type of sensor to be integrated into the system. An acoustic transmitter and an underwater hydrophone (receiver) form the rest of the system’s components. 

The design of the system has attracted praise for its simplicity and ingenuity, although consensus is that it needs more experimentation. The next step for the researchers is to test if the system can also transmit sound and low-res images.  

Energy harvesting for the win

It has been clear within the IoT world, for quite some time now, that the next wave of mass IoT adoption could only be made possible by embracing energy harvesting technologies such as RF-energy (radio frequency harvesting) and piezoelectric energy harvesting. 

The scenario of an astronomically high number of IoT edge devices that was forecasted just a few years ago could actually come to be, but only if these IoT sensors are to be powered by batteryless MCUs . 

This incredible piece of sensing technology is no doubt going to pave the way for more sustainable, economical and high-tech innovations, in what is surely the age of IoT.