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 Swinburne University developed a graphene-based highly efficient solar absorbing film that absorbs sunlight with minimal heat loss. The film rapidly heats up in an open environment and has great potential in solar thermal energy harvesting systems - in addition to other applications such as thermophotovoltaics (directly converting heat to electricity), solar seawater desalination, light emitters and photodetectors.
This is the 2nd-generation material developed by the same group - now with a thickness of only 30 nm and improved performance and longer lifetime. The researchers have now created a first prototype and also suggest a scalable low-cost manufacturing process.
A new graphene-based sensor that measures stress via cortisol in sweat could be used by NASA to gauge the anxiety levels of astronauts.
Developed by Caltech assistant professor of medical engineering, Wei Gao, the device features a plastic sheet etched with a laser to generate a 3D graphene structure with tiny pores in which sweat can collect. Those pores create a large amount of surface area in the sensor, which makes it sensitive enough to detect compounds in the sweat that are only present in very small amounts. Those tiny pores are also coupled with an antibody sensitive to cortisol, allowing the sensor to detect the compound.
A team of researchers at the University of Michigan, led by Zhaohui Zhong, Jeffrey Fessler and Theodore Norris of the Department of Electrical Engineering and Computer Science, has created a 3D camera made from a stack of transparent graphene photodetectors that can capture and focus on objects that are different distances away from the camera lens. The device might find use in applications as diverse as biological imaging, driverless cars and robotics.
Most of today’s optical imaging systems use a flat optical detector to record the intensity of light reflected from an object at each pixel. However, since these systems detect light in only one plane, all the information concerning the direction of the light rays is lost. This means that the recorded images are simple 2D projections of the actual 3D object being imaged.
In April 2018, researchers at the India-based Uttarakhand Residential University, RI Instruments and Innovationin developed a graphene-based technology to prevent vehicles from operating if the driver is drunk. Now, the same team produced a prototype that will be based on graphene generated from waste products and wild grasses as one of the components.
Graphene has an important role in the device as graphene-coated electrodes can catalyze the process of oxidation of ethyl alcohol into acetic acid. The concentration of alcohol will automatically disconnect the device, the team explained. The driver, while at the driving seat, has to blow the graphene sensor on the device to start the vehicle. This will immediately activate the sensor that will analyze and estimate the liquor content present in the blood of the driver.
The Graphene Flagship has announced the launch of eleven new "Spearhead Projects", each developed to take graphene-enabled prototypes to commercial applications. Now, the Graphene Flagship has committed €45 million to invest in eleven commercialization projects led by key industrial partners in Europe such as Airbus, Fiat-Chrysler Automobiles, Lufthansa Technik, Siemens, and ABB. Notably, the project partners will also co-fund the projects with a further combined contribution of €47 million, showing their interest in the development of graphene-enabled products.
The newly launched projects combine the results of the Graphene Flagship's innovative scientific research with the ambitions of commercial partners for marketable applications. This initiative will bring the number of companies involved in the Graphene Flagship to 78, which makes up nearly half of the whole consortium.