Printed flexible sensors: fabrication, characterization and implementation

Flexible sensors have showed immense potential to be used in the field of healthcare, environment and industrial applications. The full-blown utilisation of these types of sensors is yet to be done to have an impact on the quality of life of people. The presented work shows a great dynamicity in the utilisation of sensors in the application world. Among the different types of techniques that can be used to develop the flexible sensors differing in terms of size, cost and resolution, the use of printing technology had been done to large extent. The work on printed flexible sensors has been continuously growing due to their advantages of low-cost, enhanced electrical and mechanical properties. In this research, novel flexible printed sensors were developed using the laser cutting technique. Four different types of printed flexible sensor prototypes were fabricated, characterised and implemented for different applications. The idea behind the development of each of these sensor prototypes can be attributed to their low-cost, simple operating principle and multi-functional characteristics. The electrical behaviour of the electrodes was based on the capacitive principle due to their interdigitated structures. Electrochemical Impedance Spectroscopy was used in conjunction with the sensor prototypes to determine the output with respect to the changes in the input. The differences among these prototypes lied in their characteristics due to the different raw materials used to develop them. Multi-Walled Carbon Nanotubes, Graphene, Graphite are some of the conductive materials that were used to develop the electrodes of the sensor prototypes due to their light weight, high electrical conductivity, durability and high aspect ratio. Polydimethylsiloxane, Polyethylene Terephthalate and Polyimide are some of the polymers that were used to develop the substrates due to their low-cost, biocompatibility, low Young's modulus and ability to form flexible bilayer-structured devices. The sensor prototypes were used for different fields like monitoring of limb and other body part movements, respiration and taste sensing for healthcare, salinity and nitrate sensing for environment, and tactile and low-force sensing for industrial applications. The futuristic applications of the developed sensors could involve their real-time applications for chemical and biological sensing of proteins, different gases, temperature, humidity, etc. Due to their small size and biocompatible nature, they can also be considered as implantable sensors to determine the anatomical changes happening inside the body. They can also be used for national purposes, for example., in military and defences, where their minuscular forms would be attached to the wings with adaptive feedback systems to determine their active flutter suppressions.