Waste to wealth concept: Disposable RGO filter paper for flexible temperature sensor applications

We have developed a flexible reduced graphene oxide (RGO) temperature sensor on filter paper based cellulose substrate using vacuum filtration method. One of the most commonly used synthesized methods for RGO thin films is vacuum filtration process. It has several advantages such as simple operation and good controllability. The structural analysis was carried out by FE-SEM, in which the surface morphology images confirm the formation of RGO nanostructures on the filter paper substrate. It was observed that the pores of the filter paper were completely filled with the RGO material during the filtration process, subsequently the formation of continuous RGO thin films. As a results, the RGO films exhibits a piezoresistive property. The resulted RGO based films on the filter paper reveals the semiconducting behavior having sensitivity of 0.278 Omega/degrees C and negative temperature coefficient (NTC) about -0.00254 Omega / Omega /degrees C. Thus, we demonstrate a simplified way for the fabrication of RGO films on filter paper that possesses better and easier measurable macroscopic electrical properties. Our approach is for easy way of electronics, cost-effective and environment friendly fabrication route for flexible conducting graphene films on filter paper. This will enable for the potential applications in flexible electronics in various fields including biomedical, automobile and aerospace engineering

Supercapacitor based approach towards development of Graphene Sensors

Graphene has been extensively studied and used in energy storage applications like Supercapacitors owing to its high Electric Double Layer Capacitance (EDLC). However, this property of Graphene has not been used in Sensor technology. We report a novel approach for the development of Graphene Capacitive sensors by adopting the Supercapacitor property of Graphene. Graphene was synthesized by Electro-exfoliation process followed by Hydrazine hydrate reduction. The obtained material was characterized using XRD and FE-SEM to ensure structural and morphological properties. An Interdigitized Electrode (IDE) pattern was prepared with reduced Exfoliated Graphene (rEG) as electrode and PVA-H2SO4 electrolytic gel was used to realize EDLC. The fabricated strain sensing device was found to have a gauge factor of 97.3. This low cost, flexible, highly sensitive and easy to fabricate device opens up a new area of capacitance based sensors with wide applications in the chemical & automotive industry, healthcare, robotics, aerospace, mining etc

Graphene-Nickel Composite Films on Flexible PCB for Temperature Monitoring

This paper presents a novel method to fabricate temperature sensor arrays by screen printing Graphene - Nickel (Ni) nanocomposite film on flexible printed circuit board (PCB). Screen printing is a cost effective fabrication technique to get uniform thickness film on a substrate. The fabricated temperature sensor array, each having sensing thickness of around 50 mu m is studied for the temperature response. The synthesized RGO nanosheets and RGO-Ni nanocomposite were characterized by XRD and FE-SEM for structural and compositional analysis. Temperature variation is measured in terms of change in resistance. It is observed that resistance decreases with the increase in temperature showing NTC (Negative Temperature Coefficient) behavior. The calculated response of the sensor in terms of sensitivity is around 2.455 Omega / K and temperature coefficient of resistance (TCR) is around 2.635 x10(-3) Omega / Omega / K. Our approach shows a very simple fabrication process for making mass production of sensors on PCB that can be easily integrated with electronic devices and as a wearable body temperature sensor

PDMS Encapsulated Graphene-Nickel Composite Film as Flexible Tactile Sensor

We report the fabrication of a flexible tactile sensor using Graphene-Ni composite film encapsulated in Polydimethylsiloxane (PDMS). Synthesis of Graphene was carried out by modified Hummer's method. The composite material was characterized by XRD and FE-SEM to analyze their structural and morphological properties. PDMS films were formed using spin coating of liquid PDMS on a metal substrate. Graphene - Ni composite film was screen printed on PDMS. The sensor, encapsulated in PDMS, was found to be highly flexible, cost effective and involved simple fabrication procedure. In the present work, this sensor was used to monitor wrist movement. The device was found to be highly sensitive with a reported gauge factor of 8.08. The piezoresistive device can be used to monitor wide range of muscle movements with high sensitivity. The sensor finds potential applications in healthcare, robotic applications and consumer electronics

High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications

This paper presents development and performance assessment of an innovative and a highly potent graphene-electrolyte capacitive sensor (GECS) based on the supercapacitor model. Although graphene has been widely researched and adapted in supercapacitors as electrode material, this combination has not been applied in sensor technology. A low base capacitance, generally the impeding factor in capacitive sensors, is addressed by incorporating electric double layer capacitance in GECS, and a million-fold increase in base capacitance is achieved. The high base capacitance (similar to 22.0 mu F) promises to solve many inherent issues pertaining to capacitive sensors. GECS is fabricated by using thermally reduced microwave exfoliated graphene oxide material to form interdigitated electrodes coated with solid-state electrolyte which forms the double layer capacitance. The capacitance response of GECS on subjecting to strain is examined and an enormous operating range (similar to 300 nF) is seen, which is the salient feature of this sensor. The GECS showed an impressive device sensitivity of 11.24 nF kPa-1 and good immunity towards noise i.e. lead capacitance and stray capacitance. Two regimes of operation are identified based on the procedure of device fabrication. The device can be applied to varied applications and one such biomedical application of breath pattern monitoring is demonstrated

Highly sensitive, scalable reduced graphene oxide with palladium nano-composite as strain sensor

We report a novel strain sensor based on reduced graphene oxide (rGO) with palladium (Pd) nano-composite. The sensor was fabricated on the SS304 stainless-steel substrate using a screen-printing method. Graphene oxide was synthesized using a modified Hummer's method and reduced using a chemical route. Field emission-scanning electron microscope, x-ray diffraction and Raman spectroscopy were used to characterize the as-synthesized nano-composite. The as-fabricated strain sensor was tested for tensile strain using Micro-universal Test Machine and the change in resistance for different strains was recorded. The sensor response was observed to be stable and linear within the applied strain range of 0-3000 microstrains, and an average gauge factor of 42.69 was obtained in this range