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Large area environmental monitoring can play a crucial role in dealing with crisis situations, such as forest fires or industrial gas and chemical leaks. Forest fires alone are responsible for thousands of fatalities worldwide every year and exposure to the unmonitored emission of toxic gases in industrialised and remote regions can also lead to fatalities and lifelong health issues.
Existing early warning environmental monitoring systems rely on satellite monitoring, watchtowers or expensive fixed sensors. Fixed network infrastructure can be implemented in specific areas, but installing such networks over large areas is not practical as the cost of installation becomes unreasonably high, especially in remote areas.
A group of researchers at the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia are seeking to address these environmental and high-cost concerns through the development of an attractive solution in the form of a low-cost, 3D printed reliable node system. The system, developed by a research team led by Associate Professor of electrical engineering Atif Shamim, works by saturating high-risk areas with disposable sensor nodes that are linked wirelessly to a few fixed nodes that raise the alarm. The smart sensor system is capable of detecting noxious gases and changes in temperature and humidity that could revolutionise environmental monitoring.
“The main idea was to create inexpensive, disposable, wireless sensors, which can sense and send the data out. We wanted to prove that you don’t need traditional fixed expensive sensors for environmental monitoring. We want to make sensors, that are low cost, disposable, variable, and dispersible,” Shamim noted.
Creating low-cost real-time environmental monitoring
Designed by KAUST Ph.D. student Muhammad Farooqui, the node has been tested in both the laboratory and in the field. It survives being dropped from a height and subjected to temperatures up to 70°C, which, says Shamim, “is good enough to give an early warning in cases of wildfire.” He believes it is the first “low-cost, fully integrated, packaged, 3D-printed wireless sensor node for real-time environmental monitoring.”
“these small node sensors were inkjet-printed onto a 3D-printed, 2-cm3 node containing a battery and microelectronic circuit board along with an antenna that transmits in any direction”
“We call this additive manufacturing. With our design, we wanted to stay completely digital so there is no material wasted because we only print material when it’s required. That is why it is called additive manufacturing. The key is to make disposable low-cost sensors, and at KAUST we have access to a variety of excellent printers which can print on inexpensive materials, like plastic, different types of paper and other kinds of material,” said Shamim.
“Before coming to KAUST, I had been working in Canada on traditional wireless electronics which are rigid, bulky and expensive. I still work on traditional wireless electronics such as CMOS based, but I also started to do printed electronics because I wanted to make flexible and inexpensive electronics that can be worn by a human or be mounted on non-planar objects. When I came to KAUST, I saw a printer in the core lab facilities and that is where my journey with printed electronics started. In the last five years, we have established a great printed electronics setup with the generous support provided by KAUST.
We have been involved in all kinds of printing, 3D printing, inkjet printing and screen printing. In our lab (IMPACT), we like to do flexible, disposable, wearable and stretchable wireless sensing systems,” he added.
Utilising cutting-edge technology
Through their ongoing studies, Shamim and Farooqui have found that 3D printing and inkjet printing can be uniquely combined in order to realise a cheap, fully integrated wireless sensor node.
The inkjet-printed sensors and antenna are realised on the walls of a 3D-printed cubic package which encloses the microelectronics developed on a 3D-printed circuit board. These small node sensors were inkjet-printed onto a 3D-printed, 2-cm3 node containing a battery and microelectronic circuit board along with an antenna that transmits in any direction. The sensors have been realised on the walls of the 3D-printed package so that they are exposed to the environment.
This is also the case for the capacitive humidity sensor whose air channel is exposed externally. Since the sensor will be dispersed in the environment in random locations, a protective coating is required on these sensors so that they are not affected by dust, rainwater etc. For the H2S and humidity sensor, a porous membrane can be made using inkjet printing, which will allow only gas molecules to pass through it.
The size and cost of the sensor node can be further reduced by using customised microelectronics which can be integrated into a single chip. Ambient energy harvesting capabilities, such as solar cells, RF harvesting can also be incorporated in the sensor package to make the system self-sustained and reduce the high capacity battery requirements.
“for the H2S and humidity sensor, a porous membrane can be made using inkjet printing, which will allow only gas molecules to pass through it”
“The electronics are inside this small cube which acts as the package for the electronics. We printed the antenna and the sensors on the walls of the package so this package becomes functional and part of the system (unlike traditional electronics packages which only act as protectors for electronics but add no functionality). That is why we call it a System-on-Package (SoP). Moreover, we have 3D printed the package, which is different from typical packaging that is done through moulding or other techniques, but additive manufacturing is not used. We created specified inks for temperature, humidity and gas sensing. In this study, we are sensing H2S gas as a proof of concept, but we have the capability to sense other gases as well. This is the direction of our future work in this area to enhance the number of sensors, and have the capability to sense multiple gases,” Shamim said.
Inventive low-cost problem solving
The cube’s wireless sensor node was 3D printed in two parts. After inkjet printing the antenna and sensors on the wall, the microelectronics and battery were enclosed in the cube sensor. Due to additive manufacturing and custom inks made in-house, the manufacturing costs of creating these smart sensor cubes was kept extremely low. It could be assumed, due to the ease and low-cost involved in creating these type of sensors, that the researchers compromised on performance or other areas, however, Shamim insists that the sensors were tested and passed to the highest performance tests and criteria.
He said: “We tested the selectivity and sensitivity, the two important things for sensors. Sensitivity is the ability of the sensor to detect very small changes and selectivity is if it is sensitive to only that thing for which it is designed. For example, if there is a gas leak and multiple gases are in the environment, our sensor can focus on one specific gas like H2S; it focuses solely on that gas. The selectivity and the sensitivity of our cubes are as good as the commercial (expensive) sensors – these factors were very important to us.”
This research at KAUST demonstrates that it is possible to develop fully integrated and packaged electronic devices using 3D inkjet printing. It is expected that printers which can deposit metal and dielectric at the same time will be available in the near future. Such printers will greatly reduce the time and steps that are required to develop these sensors.
Interconnectivity to aid emergency
The sensor nodes can also transmit and “talk” to each other for distances of up to 100 metres. Measurements have shown that the sensor can communicate readings of temperature, humidity, and H2S levels up to a significant distance. The sensor locations can be determined based on the known location of the fixed network nodes. A suitable algorithm can be developed and programmed in the microcontroller of the sensor node to determine its location and wirelessly send it over the network.
This interconnectivity can help to create a map to aid emergency response teams in the event of any given environment incident. For example, if there is a gas leak, you could lift a feedback mechanism, which would remotely sense a gas or gases, which would then instantaneously action the switching off of gas line or grid. 3D-printed drones can be used to disperse the sensor nodes in remote locations and also to collect data from these nodes. Therefore, the monitoring of temperature and humidity over a large remote area, such as forests, can help with fire incidents by issuing early warnings and providing a precise location of the early fire incident before it spreads to a large area.
“3D-printed drones can be used to disperse the sensor nodes in remote locations and also to collect data from these nodes”
“This information can be relayed back to a control room or office or person who can then monitor all of these sensors at the same time and make a judgment call. This could create a map. Like a heat map, like a moisture map, like a gas map, whatever map you want. It’s large area monitoring made very easy,” Shamim said.
A drive towards IoT
Shamim, whose background is in wireless electronics, sees these sensor nodes as part of a drive toward an internet of things (IoT), “Where non-living things connected to the internet make smart decisions for humans. Similar to the internet being used by humans at present where two humans are on either side of the internet whether it is an email or a chat message, in IoT this communication will be between two machines.” An IoT approach can be developed for large area real-time monitoring of an environment to ensure safe and healthy living.
“What is the most important character for the non-living things to have for them to behave like humans? Sensing something and then communicating that information. These are the two main areas we worked on, sensing and integrated wireless communication. Eventually, these sensors connected to each other in a network could be dispersed remotely to give us gas leakage information, pollution or temperature information, etc. This is also useful for our home and office automation, such as controlling temperatures, monitoring door locks, assessing our groceries and re-ordering them, etc. These and many other such small decisions by machines will enable what we call ‘Smart Living’” he added.
The next step
The next step in the team’s smart sensing research is to incorporate an energy source which will make the nodes self-sustainable in remote locations. “A traditional way to charge or change a discharged battery is a no-no for this kind of concept. We can disperse the sensors, but going into the forest or oceans to swap out batteries constantly is not practical. What we want to do is to replace the need for constant battery changing and instead harvest energy from the environment to charge these batteries. By removing the need for changing the discharged batteries, the life of these nodes can be extended considerably. For this, we need to harvest energy from the environment to charge these batteries at their respective locations through renewable sources.
“I would say 50 percent of this development is done, but it remains a major target for the team – we want to enable self-powering for these sensor nodes, There is wireless energy all around us, for example, your mobile phone is working from the tower, there’s GSM, there’s WiFi, there’s GPS, there’s 3G, 4G, Bluetooth – a complete spectrum of wireless energy is out there. Although this energy is being used for communications, the question is can we take part of it? The part of the environment that is not being used and harvest it to power small devices such as these sensor nodes,” said Shamim.
He added: “Another future step is to make these sensor nodes through mass-producible customised chips in place of the current commercial circuits boards. This will take the cost of each sensor node to below a dollar.”
Building for a smart future
Since publishing their paper, Shamim and his team have been approached by many collaborators and industrial peers. The KAUST researchers believe that the sky’s the limit for future applications for their smart sensing nodes. Shamim feels that his team’s technology can become an essential environmental monitoring device of the future – a device that can help to make informed decisions and create a positive, efficient, environmental footprint for our modern smart cities.
“our research can change how we integrate things, how we monitor things, how we live”
“I want the device to be able to monitor all gases that cause environmental pollution. Our sensors can provide cutting-edge information for a smart city. Information that can be delivered and acted upon in real time. The goal is to continue to create a technology that can measure the composition of pollutant gases that can tell me how much methane we’re inhaling daily and when our air levels drop to unsafe levels,” he said.
Shamim concluded: “Our research can change how we integrate things, how we monitor things, how we live. This technology can affect our day-to-day living because I think our smart sensing device can bring an untold smartness into the way we live – it can save hundreds of thousands of lives.”
