Disposable, 3D-Printed Sensor to Revolutionize Large-Area Environmental Monitoring

During crisis situations, such as industrial chemical and gas leaks and forest fires, large area environmental monitoring might have a vital role in the mitigation efforts. Each year, thousands of lives are lost globally due to forest fires. Loss of lives and long-term health issues could also be caused due to exposure to the unmonitored emission of toxic gases in remote and industrialized regions.

Prevalent early warning environmental monitoring systems are dependent on watchtowers, satellite monitoring, or high-cost fixed sensors. Although fixed network infrastructure can be executed in a few areas, implementing such networks over vast areas is not feasible because the installation cost turns out to be excessively high, specifically in remote areas.

A research team, headed by Associate Professor of Electrical Engineering Atif Shamim, from KAUST has developed an inexpensive, 3D-printed reliable node system to overcome the high cost and environmental impacts. The system functions by saturating areas at high risk with disposable sensor nodes that are wirelessly connected to a few fixed nodes that set up an alarm. The smart sensor system has the potential to detect changes in humidity and temperature as well as noxious gases, thereby revolutionizing environmental monitoring.

“The main idea was to create inexpensive, disposable, wireless sensors that 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,” stated Shamim.

Low cost in real-time

The node, designed by Muhammad Farooqui, a PhD student at KAUST, has been investigated in both the laboratory as well as in the field. It remains undamaged upon being dropped and withstands temperatures of nearly 70 °C, which, according to Shamim, “is good enough to give an early warning in cases of wildfire.” He is confident that it is the first “low-cost, fully integrated, packaged, 3D-printed wireless sensor node for real-time environmental monitoring.”

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 do disposable low-cost sensors, and at KAUST, we have access to a variety of excellent printers that can print on inexpensive materials like plastic, different types of paper and other kinds of material. Before coming to KAUST, I was working in Canada on traditional wireless electronics that are rigid, bulky and expensive,” noted Shamim. “When I came to KAUST, I saw a printer in the Core Labs 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—3-D printing, inkjet printing and screen printing. In our lab—the IMPACT Lab—we like to do flexible, disposable, wearable and stretchable wireless sensing systems.

Atif Shamim, Associate Professor of Electrical Engineering, KAUST

Utilizing cutting-edge technology

With their progressive research works, Shamim and Farooqui have discovered that inkjet and 3D printing can be distinctively combined to achieve a low-cost, completely integrated wireless sensor node.

The inkjet-printed antenna and sensors are developed on the walls of a 3D-printed cubic package, incorporating the microelectronics created on a 3D-printed circuit board. Inkjet-printing of these small-node sensors were performed on a 3D-printed node measuring 2 cm³ and including a battery and a microelectronic circuit board with an antenna that can transmit in any direction. The sensors have been developed on the walls of the 3D-printed package to be exposed to the environment. The capacitive humidity sensor has also been developed in a similar way, including an externally exposed air channel. As the sensor will be distributed in random locations in the environment, the sensors have to be covered with a protective coating to prevent the impact of rainwater, dust, and so on. In the case of the H₂S and humidity sensor, a porous membrane can be developed by adopting inkjet printing, permitting just gas molecules to pass through it.

Tailor-made microelectronics that could be incorporated into a single chip can be used for further reducing the cost and size of the sensor node. Capabilities for harvesting ambient energy, such as RF harvesting and solar cells, can also be integrated into the sensor package to develop a self-sustained system and to minimize the need for batteries of higher capacity.

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 the 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 done through molding 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.

Atif Shamim, Associate Professor of Electrical Engineering, KAUST

Inventive low-cost problem solving

The wireless sensor node of the cube was 3D printed in two parts. Following inkjet printing of the sensors and the antenna on the wall, the battery and microelectronics were incorporated into the cube sensor. The manufacturing cost involved in developing the smart sensor cubes was maintained very low because the custom inks and additive manufacturing were made in-house. The ease in developing this kind of sensor and its low cost could lead others to presume that the team compromised on performance or in other areas. However, Shamim asserted that the sensors were investigated and passed the most extreme performance criteria and tests.

“We tested the selectivity and sensitivity—two important things for sensors. Sensitivity is the ability of the sensor to detect very small changes and selectivity is the ability to differentiate between stimuli from the thing it was designed to detect and other stimuli. 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,” he further stated.

The study shows that fully integrated and packaged electronic devices could be developed through 3D inkjet printing. It is anticipated that printers with the ability to simultaneously deposit dielectric and metal will be available shortly. These printers will considerably decrease the steps and time needed to create these sensors.

Interconnectivity to aid emergency

The sensor nodes also have the ability to transmit and “talk” to one another from a distance of nearly 100 m. Evaluations have demonstrated that the sensor can convey readings of humidity, temperature, and H₂S levels up to a considerable distance. The familiar location of the fixed network nodes can be used to determine the sensor locations. An appropriate algorithm can be created and programmed in the microcontroller of the sensor node to ascertain its location and to wirelessly transfer it over the network.

This interconnectivity can be valuable in developing a map to assist emergency response teams during any given environmental incident. For instance, during a gas leak, one can lift a feedback mechanism that would remotely sense a gas or many gases, which would result in instantaneous switching off of a grid or gas line. 3D-printed drones can be used to distribute the sensor nodes in remote locations and also to gather data from these nodes. Therefore, the humidity and temperature monitoring over a huge, remote area, such as forests, can assist during fire incidents by providing early warnings and transmitting the precise location of the early fire incident before it could spread to a vast area.

“This information can be relayed back to a control room, office or person where all of the sensors at the same time can be monitored to make a judgment call. This could create a map like a heat map, a moisture map, a gas map or whatever map you want—its large area monitoring made very easy,” emphasized Shamim.

A drive toward the Internet of things

Shamim, whose deals with wireless electronics, considers that the sensor nodes are part of a thrust 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,” he stated. An IoT strategy can be devised for real-time environmental monitoring over a large area, thereby ensuring healthy and safe living.

“What is the most important character for the non-living things to have for them to behave like humans? It is sensing something and then communicating that information, and these are the two main areas we worked on—sensing and integrated wireless communication,” he stated.

“Eventually, the 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 as ‘Smart Living’,” he further stated.

Harnessing wireless energies

The team’s following move would be to perform smart sensing study to include an energy source that will render 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 do harvesting of energy from the environment to charge the 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 the 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. Though this energy is being used for communications, the question is: Can we take part of it? We would take the part of the environment that is not being used and harvest it to power small devices such as these sensor nodes. Another future step is to make these sensor nodes through mass-producible customized chips (in place of the commercial circuit boards). This would take the cost of each sensor node to below a dollar.

Atif Shamim, Associate Professor of Electrical Engineering, KAUST

Building for a smart future

The KAUST team is confident that there are no restrictions in terms of applications of the smart sensing nodes developed by them. Shamim is of the view that the technology developed by his team could transform into a crucial environmental monitoring device in the future—to make wise decisions and develop an efficient and positive environmental impression for advanced, smart cities.

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 and that can show how much methane we’re inhaling when air levels drop to unsafe levels, etc.. Our research can change how we integrate things—how we monitor things—how we live. This technology can affect our day-to-day lives because it can bring an untold smartness into the way we live.

Atif Shamim, Associate Professor of Electrical Engineering, KAUST