The importance of the sensor field and, in particular, gas sensors is undeniable: they play a fundamental role in industrial emissions, environmental pollution, medical diagnosis, food processing, to name but a few. For example, the monitoring of NOx is necessary, among other reasons, to control the environmental pollution coming from combustion or automotive emissions.
The number of electronic devices employed in our daily life is exponentially increasing, especially the number of sensors required to monitor our environment and well-being. This situation is leading to drastically increased in the amount of electronic wastes and energy consumption to power up the systems by using the conventional fabrication techniques and devices. SELFSENS has explored a different approach to produce sensors with environmental friendly processes and materials as well as energy harvesters to produce the desired electronic systems in a sustainable way.
The ultimate goal of this project is to achieve an autonomous printed system for environmental monitoring.
The objectives pursued in this project are described below:
1. To develop selective and low-power gas sensors. One of the main challenges is to find a selective solution, that is to say, a sensor system capable of discriminating among different vapour species. Looking at the attractive characteristics of reduced graphene oxide (rGO), SELFSENS has looked for their functionalization in order to increase their selectivity to a concrete gas while decreasing it to others. Furthermore, the design of sensor arrays together with pattern recognition algorithms have been investigated in order to develop a truly selective sensory device. Moreover, the sensor response is desired to be recovered over time. An easy way to achieve this is to heat the active layer to force the trapped molecules to be desorbed. This strategy and others (e.g. current flow) have been studied, selecting the most appropriate one in terms of power demand. The manufacturing of these sensors have been done by laser scribing and printing techniques because of the large number of features that these technologies offer to electronics circuits.
2. To design printed and efficient energy harvesters. The inclusion of an energy harvesting solution has been investigated in order to reduce the total consumption of the sensor module or even to achieve a full autonomous sensory system. In particular, solar energy and radiofrequency have been explored as harvester solutions. Moreover, a storage element based on rGO technology is desired to enhance energy management. For this purpose, a laser-scribed supercapacitor have been designed so that its integration in the fabrication process of the system is immediate.
3. To implement self-powered sensor nodes. These two elements (sensors and harvesters) have been included in a larger system, adding other already developed printed sensors –such as temperature sensors- with the aim of performing environmental monitoring in different scenarios, such as industry or comfort in buildings. To do that, some basic circuitry have been designed, including resistors, and capacitors.
4. To find a compatible and stackable manufacturing process. A key point of this strategy is to use the same fabrication processes for the circuitry as well as the harvester part as employed for the manufacturing of the gas sensors, looking at the compatibility of materials and processes, as well as, the possibilities of stackable procedures.
