- Thermal sensors measure the temperature. No big deal. We have thermometer in our homes, and we have thermal sensors to send a signal to the heating system to pump some heat because it is getting cold or to the air conditioning to cool down the ambient. The water faucet in our shower contains a thermal sensor to mix cold and hot water to our liking. In the past thermal sensor technology exploited the expansion of a material as the temperature increased. By measuring the expansion one could derive the data on the temperature. Today most thermal sensors use technologies that are refined “versions” of those used in the past, having discovered better materials and using two or more in combination to increase the precision. However, thermal sensors can be very sophisticated, much more sophisticated that the ones we are using at home. There are sensors that can detect a variation of 0.02° C in 1/40 of a second using nanotechnology coating the detecting surface with carbon nanotubes. Interestingly this technology is mimicking the scales on the Morpho butterfly that are very sensitive to temperature changes and deflect lights to help stabilizing the temperature on the wings.
Thermal sensors can make buildings and cities more secure by providing earlier warning of possibile fire. They can also be used for traffic monitoring since they are not adversely affected by light or darkeness as videocamera are.
Thermal sensors are part of the Array of Things initiative in Chicago where hundreds of nodes on light poles will provide data on temperature, barometric pressure, light, vibration, carbon monoxide, nitrogen dioxide, sulfur dioxide, ozone, ambient sound intensity, pedestrian and vehicle traffic, and surface temperature.
- Spatial sensors are a broad category providing data on location, speed and acceleration. They utilise a variety of technologies from GPS location to lasers and gyroscopes. The sensing part is complemented by sophisticated software to analyse the raw data captured (such as the delay in signal reception in the case of GPS where different satellites are beaming to Earth their radio signals: knowing where each satellite is and the different timing their signals are received it is possible to calculate with a very good precision where the receiver is on the Earth surface).
More and more vehicles have a GPS receiver on board to pinpoint their location. So do most smartphones and a growing number of digital cameras. Even a few smart watches are starting to have a GPS receiver. Smart phones all have an accelerometer and a few also have a gyroscope. These data are often shared as embedded information inside a photo we are sending to a friend or posting on Facebook. It is most likely that most objects, either directly or indirectly, will have a way to “know” where they are, whether they are standing still or moving and in which direction. Radio signals can also be used to localise a smartphone (or a cellphone) based on triangulation and by measuring the signal power emission. Accelerometers nowadays are mostly based on MEMS and laser. They have achieved a very high sensitivity and precision. An HP inertial accelerometer developed in 2010 as part of HP project CeNSE (Central Nervous System for the Earth) can detect acceleration in the order of 1/1000 of G (gravity). It is measuring the displacement of a particle of silicon suspended at the center of the chip and is able to detect movement of the order of 1/10000 of a billionth of meter (a billionth times tinier than a human hair). This sort of accelerometers can detect all sort of vibration and software for signal processing can analyse those vibration to find the signature of the objects vibrating, that is the unique way an object vibrate so that it can be distinguished from other objects. One can detect if rails in an underground line are getting loose and need fixing, if a train has problem with its braking system and so on… Indeed, one can look at something similar to CeNSE to create a nervous system for a Smart City.
Cities can leverage on these sensors to get information on traffic and using software make forecast on the evolution reassigning resources as needed.