24-11-2020 | | By Liam Critchey
There has been a strong interest in the development of autonomous vehicles, and they are starting to become more and more advanced as the years go on. To function effectively and safely, the vehicles must possess an advanced control system design which requires continuous feedback and analysis from sensors located around the vehicle.
It’s thought that up to 10 million self-driving cars could be on our roads in the future, and such a large scale of autonomous vehicles is going to require a precise control and communication subsystem for them to meet safety standards. One of the aspects of autonomous vehicles are going to be crucial for meeting these safety standards is the tyres, and smart tyres with continuous monitoring capabilities are now being designed.
The tyre on any vehicle interacts with the driving space, i.e. the road. Hence, this aspect must be monitored if autonomous vehicles are going to be safe and reliable for everyday use. This has led to smart tyres—which are integrated with strain sensors—being developed that can continuously sense and monitor dynamic parameters, as these smart tyres can combine strain sensing monitoring with essential tyre functions. The ability to analyse these parameters, and utilise the obtained data, is also critical for the intelligent controls that are present in autonomous vehicles.
Smart tyres are still an aspect that is undergoing significant development, and some of the issues are still trying to be ironed out. For example, smart tyres ideally need self-powered sensors to be embedded within the tyres, so that they can measure and securely transmit data at high frequencies and provide a high degree of real-time control. In practice, many of the tyre developments do not have a seamless integration of sensors into the tyre, increasing the cost of these tyres beyond large-scale commercial feasibility and increasing the amount of regular upkeep required.
A lot of effort is going into making smart tyres in general, as well as ways to integrate wireless sensors better. To date, alongside a complex and time-consuming integration process, a lot of these sensors are much more rigid than they should be for use within tyres and many require an external power source (which is not the ideal scenario). Nevertheless, the research and development of smart tyres are on the rise, and it has come to the fore recently that graphene could a way of negating many of these issues within smart tyres.
When it comes to electronic devices, graphene has so far found the most use in sensors, and for a good reason. It’s small size, with its large relative surface area, provides a very large sensing surface while keeping the sensor itself small. Moreover, it has some of the highest electrical conductivity and charge carrier mobility properties in existence, which provides them with very high sensitivity. So, when a change in the environment is sensed, it changes these properties across the graphene sheet, providing a detectable response. Because these properties are so high, it means that minute changes can be detected.
This is an ideal set of properties for strain sensors, especially in autonomous vehicles, as it allows very small strain changes in the tyre environment to be detected. These changes can then be relayed to the central data analysis system in real-time, and the car’s AI can make decisions. Aside from this high sensitivity, graphene strain sensors are also highly flexible thanks to the inherent thinness and flexibility of the graphene itself, and this in itself offers a flexible alternative option to the more rigid sensors being used today.
As mentioned, the inherent flexibility of graphene makes it an ideal choice for strain sensors in tyres compared to other (more rigid) materials. When coupled with its high sensitivity, graphene strain sensors can provide very accurate real-time data. This is a key parameter for smart tyres and is why graphene is being trialled as a strain sensor within smart tyres, but recent research also goes beyond this to tackle some of the other issues found with many smart tyres.
A new approach has been to 3D print graphene strain sensors directly onto the surface of a tyre, using a graphene-based ink as the printing medium. To function as a complete system, the graphene strain sensor was connected to a piezoelectric energy harvesting device and a secure wireless data transfer electronics which were also embedded within the tyre. The data system was also connected to a machine learning system so that it could perform predictive data analysis.
This multi-disciplinary approach, taking aspects of nanotechnology, 3D printing, data transfer methods, and many more in between, solves one of the key issues when it comes to most smart tyre’s inability to self-power. Not only this, but the high cost and multi-step integration processes are both negated by this approach. The ability to print the sensor is not only much simpler, but the estimated cost per sensor is roughly 2.7 US cents, making it a much more cost-effective option than the status quo.
Aside from addressing the key issues and finding ways to overcome them, the sensor and subsequent data analysis protocols are also very efficient and accurate. By being printed on the surface of the tyre, the sensor was able to obtain a range of environmental information regarding the tyre and transmit it via a secure network at a desired frequency. This approach enabled several tyre-road interactions to be measured at varying driving speeds, loads and tyre pressure.
Aside from monitoring these interactions, it also enabled the tyre pressure to be analysed in real-time, something which needs to be monitored to ensure tyre and vehicle safety are meeting the required standards. Overall, these sensing systems are not only effective and solve key challenges, but they are also something which could be key to ensuring that vehicles meet the required safety standards—at least where the safety of the tyres is concerned.