FEATURE SENSORS AND DETECTORS ➤ Smart cities
It is evident that this type of monitoring infrastructure – be it tunnels, bridges, roads, railways, or buildings – can help with engineering, maintaining and upgrading the key elements that keep a city running. It’s all part of what governments in Europe, and
across the world, are trying to achieve in creating ‘smart cities’ – a concept whereby traditional networks and services are made more efficient with the use of digital and telecommunication technologies.
A smart city translates into better public services for citizens, better use of resources and less impact on the environment, through the creation of smarter urban transport networks, upgraded water supply and waste disposal facilities, safer public spaces, and more efficient ways to light and heat buildings. The European Union is investing in ICT research and innovation and developing policies to improve the quality of life of citizens and make cities more sustainable in view of Europe’s 20-20-20 targets (20 per cent increase in energy efficiency, 20 per cent reduction of CO2
emissions, and 20 per cent
renewables by 2020). Smart sensors require the synchronisation of many different technologies, not least of all sensing, communication and computing. A smart sensor obtains data from the physical
environment and uses built-in compute resources to process and transmit data, and even perform predefined functions. At the very least, these sensors contain a detector, a microprocessor and communication technology. ‘One challenge in designing these types of sensors is that they often require a multidisciplinary team to work together due to the multiple physics involved in the design,’ said Christopher Boucher, technical product manager of Ray Optics at simulation software company Comsol. ‘And… the integration of communication devices in real life may not be described by one ideal environmental condition.’ One tool aiding designers in creating these more complex sensors is simulation software. ‘Comsol Multiphysics and its Application Builder provides simulation experts with the tools needed to turn their detailed physics and mathematical models into easy-to-use simulation apps for use by everyone in their organisation, so that different teams can have easy access to the analysis results,’ Boucher added.
24 ELECTRO OPTICS l JUNE 2016
The MEMS-FPI spectrum sensor from Hamamastu incorporates a Fabry-perot Interferometer tunable filter, which allows near-IR or mid-IR spectroscopy in a compact and low cost set-up
Smart
An example of where optical sensors are being used for ‘smart’ applications is for measuring air quality, according to Jack Bennett, senior sales engineer at Hamamatsu Photonics. ‘Air quality… is of interest for smart cities. For example, cyclists could be notified via an app of areas of poor air quality and take a different route, or even autonomous vehicles could use this data to organise the routes everyone is taking,’ he said. ‘Buildings could detect health hazards and react to them. Monitoring air quality does not actually improve the air quality, but clearly it makes people aware of the problem and offers ways to intelligently start to improve the overall air quality.’ Researchers from CEA-Minatec, a research facility based in Grenoble, France, have designed a demand-controlled ventilation (DCV) system containing silicon-based MEMS CO2
sensors. These
sensors require the synchronisation of many different technologies, not least of all sensing, communication and computing
systems monitor occupancy levels and air quality so that the ventilation system draws in only the amount of fresh air actually needed. Such methods can often drop energy consumption associated with ventilation by more than half compared to a fixed rate of air intake.
For these CO2 sensors
to function, a filament is heated to a specific temperature so that it emits most of its infrared radiation near a specific wavelength. The ambient CO2
absorbs much of this energy while the
remaining infrared radiation is detected to allow calculation of CO2
.
The main focus of the CEA-Minatec’s research was to find the optimum geometry for an energy- efficient filament, the sensor’s primary energy consumer, and Comsol Multiphysics was used
for optimising the design of the filament to avoid hot spots on the freestanding micro hotplate. This helped in making the CO2
sensors smaller,
less expensive, and run on a very low current so that they can be left in a building for many years without the need to replace batteries. Absorption spectroscopy is another common technique for analysing the quantity of gasses in the air, which is being made possible by more affordable, efficient and long lifetime mid-infrared LEDs, as well as cheaper and more eco-friendly InAsSb detectors, Bennett said. Hamamatsu supplies such components, as well as tunable filter technology, which allows near-IR or mid-IR spectroscopy in a compact and low cost set-up. The MEMS-FPI spectrum sensor, for example, incorporates this tunable filter technology and a compound infrared detector such as InGaAs. The fibre optic sensors in the James Dyson building are not technically ‘smart’ yet, as they do not contain onboard technologies to process or transmit data – measurements are taken at set times and compared. According to de Battista, it would be possible to incorporate onboard processors or WiFi in the future, but these technologies will have to improve somewhat in cost, efficiency and performance before they are used. ‘In the future [the fibre optic network] could
be turned into an online, continuous monitoring system, because the fibre optic sensors are going to be there throughout the whole life of the building,’ he noted. ‘The technology of the fibre optics will not change; it’s the technology of the instrumentation that you put on the outside of the fibre optics that will improve. ‘The fibre optic sensors have also been designed with future technology in mind, technology that we do not know of yet. But as the other technology improves we can add more functionality into the sensing system.’ l
@electrooptics |
www.electrooptics.com
Hamamatsu
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