Sensors of Polymers

Being Green in I&M

Bruno Andò

Green small measurement devices for a green world! This is the message we would like to offer to our readership through this special issue of Instrumentation and Measurement Magazine. Outcomes of these realizations can be observed from several perspectives. Green means to protect the environment, but green also means to recycle materials and to let new materials come into play in the field of electronics and sensors.  Moreover, it would also allow users to be protected from hazardous and dangerous materials. But “green” means much more that this… 

These are risks we are now facing in the IT age. Many researchers are providing strong efforts to reduce the negative impact of electronics on the environment. This is because the fabrication of such products needs amounts of hazardous substances to be wasted in the environment. Let’s think to the current idea of “smart dust.” Thousands of small and autonomous sensors are dispersed in the environment to collect data. This is a strategic approach, especially in cases when the intensive monitoring of hostile environments, maybe as a consequence of a natural disaster, is the target to be reached. And in fact it is! However, such devices will never be collected back, and hence it would be terrific to spread out green pieces of materials. 

Talking about green materials, a fascinating example is bacterial cellulose. It is amazing, and I would never imagine that bacteria would be able to produce convenient substrates for the development of electronic components, including sensors. Considering the wide use and the nowadays spreading of Information and Communication Technology and subsequent need to monitor thousands of devices, to process signals and to transmit data gathered by sensors, the availability of green substrates would be really strategic. And, it will be also useful for the fast prototyping of sensors and electronic components. I perfectly remember the first time I printed out my first strain gauge on a flexible substrate by using a desktop inkjet printer and a functional ink. It was a very fast pathway from the layout to the device, and it was a real joy to see the sensor working and really measuring stress. That was not so green, I must say, but the idea of fast prototyping green and inexpensive sensors is a real challenge to be addressed by the scientific community. 

I would like to thank the Guest Editor who did an excellent job in publicizing this issue, and thus was able to collect such interesting contributions. He is a real expert in the field of polymeric sensors and actuators, and thanks to his outstanding work, he is now a well-recognized landmark in the framework of green sensors.

Have a time nice reading!


Guest Editorial - Polymeric Sensors for Smart Systems

Salvatore Graziani

Our society is undergoing deep changes, and new electronic systems are required for amplifying our capacity of sensing and acting on the surrounding environment. 

About the new challenges imposed by the internal changes in our society, it is enough to consider that Western society is undergoing a significant aging phenomenon. Old and/or elderly people will need artificial systems to check their level of comfort or the sudden need for assistance so that improved quality of life and their longer active life can be assured. Such systems not only will increase the quality of life of elderly people but will also reduce the costs of health and social care.

Another relevant field of application of smart systems will be the monitoring of human heritage and large structures. Our society recognizes the fundamental role of human heritage as part of our identity. Nevertheless, human heritage largely consists of very fragile buildings and/or natural environments that need continuous monitoring, to control the adverse effects produced by human presence and/or climate changes. The same need is shared by the surveillance of strategic structures. Mobility structures (such as airports, railroads, motorways), and facility infrastructures (such as freshwater reservoirs, oil pipes, communication systems) need to be constantly monitored against accidents. Last but not least important, many such systems could be the object of terroristic attacks with dramatic, and even irreversible, consequences to our safety and quality of life. 

Smart systems will also be required because of the changes in agricultural and industrial production processes: think, e.g., to the new need imposed by Precision Agriculture and Industry 4.0. Sensing will be an enabling functionality of smart systems. Such systems will require a distributed working principle as a way to fit the distributed sensing and acting behavior of many biological systems and, eventually, guarantee for functional redundancy, robustness and graceful degradation of performance in case of faults. Further constraints, such as the need for system miniaturization and/or biocompatibility, will come from the envisaged applications, because of the need to develop both implanted and external smart systems, working in very tight, unstructured environments.

It is not possible to face such changes only by mass production of low-cost sensors, fabricated by using conventional technologies. Though improvements can still occur in the framework of the Moore Law’s, i.e., a continuous growth of electronics performance, in terms of speed increment and size reduction, we need to develop “More than Moore” solutions that complement silicon-based devices with new technologies, based on novel materials, to obtain significant diversification. 

The pervasive diffusion envisaged for smart systems raises significant issues about electronics’ afterlife fate: greener production processes are required, if we do not want to be submerged by broken, non-degradable devices, which, if not adequately recycled or disposed of, can release pollutants into the environment. 

Polymeric materials represent a promising class of materials for sensors realization. Polymeric systems can be realized to be scalable, light-weight, and flexible, with applications ranging from stretchable smart skin to bendable displays, photovoltaic systems, batteries, and, of course, sensors, just to mention a few. Eventually, the availability of low-cost materials will make it possible to have mass production of disposable devices suitable for consumer markets. Last, but not less important, will be the possibility to develop environmentally friendly production procedures and devices that can be easily recycled or disposed of. 

This issue of I&M Magazine focuses on this two-fold evolution toward polymeric and greener sensing devices, where the request for new functionalities can even conflict with that of sustainable economics and greener devices. I schematized this evolution in the reported figure, where some available technologies are, also reported, referring to the field of ionic electroactive polymers. These, of course, are not to be considered as the one available technology. They are only examples of the evolution of a class of compounds that I, personally, have the opportunity to work with. 

The fulfillment of such ambitious objectives will be possible only if a multidisciplinary approach is pursued, where competencies from material sciences, electronics, and mechanics, just to mention the main ones, will cooperate. Papers in the present issue are examples of such complex research activity, giving a nice view of the mixture of contributions coming from different research fields that aim to both study new sensing approaches and develop new applications. 

This is for sure evident in the contribution by Maurizio Porfiri, where the long-lasting modeling activity of his research group in the field of ionic polymer-metal composites is devoted to better understanding the transduction mechanisms of this class of material. But, as you will notice, the focus is also on possible applications, including power harvesting, which is a relevant issue if autonomous systems are of interest. 

The same interesting mixture between theoretical investigation and relevant applications can be found in the contribution by Ximing He et al., where the focus is on pressure sensors, which we need in view of smart systems development. It is quite interesting how in this contribution the understanding of working phenomena is used to drive the engineering of new geometries for realizing better sensors. 

Both of these contributions give evidence of the attention that researchers play on showing that polymeric based compounds could give in the realization of meaningful application. This gives me the opportunity to introduce the contribution by Moupali Chakraborty et al., where a sensing system using polymethyl methacrylate (PMMA) in soil moisture sensing is described. Do we need to spend any more words to convince ourselves about the importance of measuring the level of humidity in the soil? I believe that is a nice contribution showing how polymeric based sensors can be used to face challenges posed to agriculture by climatic changes and drought. 

All applications mentioned so far can be the object of large-scale production, and this is why, in the contribution by my research group, the focus is on the evolution of the “first generation” compounds toward greener polymeric sensors. I believe that this is one of the main challenges with polymeric sensing systems and I am glad that I have the opportunity to work in this exciting research field. Finally, further evidence about how much new technologies and solutions are needed for sensing in everyday life is given in the research described in the contribution by Pelumi W. Oluwasanya et. al., where the focus is new platforms for assessing air quality (is it not nice that of two of the contributions in this issue deals with soil and air?). As the last comment on this contribution, a flexible substrate is used, and of course, flexibility is one of the most demanded properties of new sensing systems.


The print magazine includes a schematic illustration.