What is a sensor?
A sensor is a device that detects events that occur in the physical environment (like light, heat, motion, moisture, pressure, and more), and responds with an output, usually an electrical, mechanical or optical signal. The household mercury thermometer is a simple example of a sensor - it detects temperature and reacts with a measurable expansion of liquid. Sensors are everywhere - they can be found in everyday applications like touch-sensitive elevator buttons and lamp dimmer surfaces that respond to touch, but there are also many kinds of sensors that go unnoticed by most - like sensors that are used in medicine, robotics, aerospace and more.
Traditional kinds of sensors include temperature, pressure (thermistors, thermocouples, and more), moisture, flow (electromagnetic, positional displacement and more), movement and proximity (capacitive, photoelectric, ultrasonic and more), though innumerable other versions exist. sensors are divided into two groups: active and passive sensors. Active sensors (such as photoconductive cells or light detection sensors) require a power supply while passive ones (radiometers, film photography) do not.
Where can sensors be found?
Sensors are used in numerous applications, and can roughly be arranged in groups by forms of use:
- Accelerometers: Micro Electro Mechanical technology based sensors, used mainly in mobile devices, medicine for patient monitoring (like pacemakers) and vehicular systems.
- Biosensors: electrochemical technology based sensors, used for food and water testing, medical devices, fitness tracker and wristbands (that measure, for example, blood oxygen levels and heart rate) and military uses (biological warfare and more).
- Image sensors: CMOS (Complementary Metal-Oxide Semiconductor) based sensors, used in consumer electronics, biometrics, traffic and security surveillance and PC imaging.
- Motion Detectors: sensors which can be Infrared, Ultrasonic or Microwave/Radar technology. They are used in video games, security detection and light activation.
What is graphene?
Graphene is a two-dimensional material made of carbon atoms, often dubbed “miracle material” for its outstanding characteristics. It is 200 times stronger than steel at one atom thick, as well as the world’s most conductive material. It is so dense that the smallest atom of Helium cannot pass through it, but is also lightweight and transparent. Since its isolation in 2004, researchers and companies alike are fervently studying graphene, which is set to revolutionize various markets and produce improved processes, better performing components and new products.
Graphene and sensors
Graphene and sensors are a natural combination, as graphene’s large surface-to-volume ratio, unique optical properties, excellent electrical conductivity, high carrier mobility and density, high thermal conductivity and many other attributes can be greatly beneficial for sensor functions. The large surface area of graphene is able to enhance the surface loading of desired biomolecules, and excellent conductivity and small band gap can be beneficial for conducting electrons between biomolecules and the electrode surface.
Graphene is thought to become especially widespread in biosensors and diagnostics. The large surface area of graphene can enhance the surface loading of desired biomolecules, and excellent conductivity and small band gap can be beneficial for conducting electrons between biomolecules and the electrode surface. Biosensors can be used, among other things, for the detection of a range of analytes like glucose, glutamate, cholesterol, hemoglobin and more. Graphene also has significant potential for enabling the development of electrochemical biosensors, based on direct electron transfer between the enzyme and the electrode surface.
Graphene will enable sensors that are smaller and lighter - providing endless design possibilities. They will also be more sensitive and able to detect smaller changes in matter, work more quickly and eventually even be less expensive than traditional sensors. Some graphene-based sensor designs contain a Field Effect Transistor (FET) with a graphene channel. Upon detection of the targeted analyte’s binding, the current through the transistor changes, which sends a signal that can be analyzed to determine several variables.
Graphene-based nanoelectronic devices have also been researched for use in DNA sensors (for detecting nucleobases and nucleotides), Gas sensors (for detection of different gases), PH sensors, environmental contamination sensors, strain and pressure sensors, and more.
Commercial activities in the field of graphene sensors
In June 2015, A collaboration between Bosch, the Germany-based engineering giant, and scientists at the Max-Planck Institute for Solid State Research yielded a graphene-based magnetic sensor 100 times more sensitive than an equivalent device based on silicon.
In August 2014, the US based Graphene Frontier announced raising $1.6m to expand the development and manufacturing of their graphene functionalized GFET sensors. Their “six sensors” brand for highly sensitive chemical and biological sensors can be used to diagnose diseases with sensitivity and efficiency unparalleled by traditional sensors.
In September 2014, the German AMO developed a graphene-based photodetector in collaboration with Alcatel Lucent Bell Labs, which is said to be the world’s fastest photodetector.
In November 2013, Nokia’s Cambridge research center developed a humidity sensor based on graphene oxide which is incredibly fast, thin, transparent, flexible and has great response and recovery times. Nokia also filed for a patent in August 2012 for a graphene-based photodetector that is transparent, thin and should ultimately be cheaper than traditional photodetectors.
The latest graphene sensor news:
Researchers from Sweden and Germany (from KTH Royal Institute of Technology, RWTH Aachen University and Research Institute AMO GmbH, Aachen) have developed the smallest graphene-based accelerometer ever reported. This achievement has been referred to as "a breakthrough for body sensor and navigation technologies".
For the past few decades microelectromechanical systems (MEMS) have been the basis for research and innovations. Now there is a move to the next level – nano-electromechanical systems, or NEMS. Xuge Fan, a researcher in the Department for Micro and Nanosystems at KTH, says that the unique material properties of graphene have enabled them to build these ultra-small accelerometers. “Based on the surveys and comparisons we have made, we can say that this is the smallest reported electromechanical accelerometer in the world,” Fan said.
Chinese researchers from the Shanghai Institute of Microsystem and Information Technology, under the Chinese Academy of Sciences, have developed a new type of graphene porous fibers decorated with nanoballs and high gauge factors to improve the sensitivity of wearable sensors. The team produced a structural design to reduce the contact area between the graphene and polymer to enhance sensitivity.
The team explained that wearable textile strain sensors, perceiving and responding to human stimuli, are essential parts of wearable electronics. But subtle strains detection on human bodies is still limited to low sensitivity within current sensors.
Riptron, a spin-out company from the University of Manchester, has entered a partnership with China-based Tunghsu Optoelectronics to advance graphene sensors designed to measure the quality of air. The graphene-based sensors are expected to enter mass production shortly following the partnership between the two companies.
In this context, Riptron will secure around £1 million investment over two stages from Tunghsu Optoelectronics.
Novel device architecture based on graphene Schottky diode varactors shows potential for optoelectronics applications
Researchers from Bar-Ilan University in Israel and Yale University in the U.S have reported on a novel device architecture comprising graphene Schottky diode varactors. The team assessed that such devices have great potential for optoelectronics applications.
The team has shown that graphene varactor diodes exhibit significant advantages compared with existing graphene photodetectors, including elimination of high dark currents and enhancement of the external quantum efficiency (EQE).
Project "HEA2D", which started in 2016 and set out to investigate the production, qualities, and applications of 2D nanomaterials, recently demonstrated end-to-end processing chain of two-dimensional nanomaterials. The project is a collaboration between AIXTRON, AMO, Coatema, Fraunhofer and Kunststoff-Institut für die mittelständische Wirtschaft (K.I.M.W.).
It was stated that the "HEA2D" consortium successfully demonstrated an end-to-end processing chain of two-dimensional nanomaterials as part of its results. 2D materials integrated into mass production processes have the potential to create integrated and systemic product and production solutions that are socially, economically and ecologically sustainable. Application areas for the technologies developed and materials investigated in this project are mainly composite materials and coatings, highly sensitive sensors, power generation and storage, electronics, information and communication technologies as well as photonics and quantum technologies.