Research at the Li-Fi Centre at the University of Edinburgh
We often see a warning sign in a petrol station, `Do not use mobile phones’. You might ask how can a mobile phone cause an explosion?
Some research shows that mobile phones pose no hazard for petrol stations. However, in physics, the antenna of a mobile phone receives radio frequency (RF) electromagnetic radiation in order to induce the RF current for communications. When the current circulates in the antenna, it may cause electric sparks. If there is some corrosion or poor connections in the antenna, the probability of electric sparks will greatly increase. When the duration of the electric sparks is more than 1 micro-second and the power is more than 6 micro Watt, the sparks will ignite the mixed gas of methane and air. In practice, both the density of the gas and the power of the spark are lower than the level of ignition. Thus, in a petrol station, mobile phones have a low probability of causing an explosion. We need to be careful about it but do not need to worry about it excessively.
However, in other situations, the possibility of RF electromagnetic radiation causing an explosion is a real risk, for example, in natural gas extraction. In a gas well downhole monitoring system, RF communications can easily cause an explosion for the following reasons. Firstly, the reason for the downhole monitoring system in the gas well is to have continuous data on the gas pressure, temperature and density. The gas well is a long pipe of over 1,000 metres, and sometimes, longer than 10,000 metres. In order to transmit signals in such long pipes, the power requirement of the transmitter antenna is much more than that of mobile phones, and thus the probability of the generation of electric sparks is increased. Secondly, in the downhole monitoring system, communications with the surface should always be maintained. This will increase the duration of the electric sparks. Thirdly, the gas density in the gas well is much higher than in a petrol station, and this creates a good environment for an explosion. For these three reasons a RF communication system can easily cause explosions in the gas well.
Unlike RF, in visible light communications (VLC), instead of antennas, the optical signal is transmitted by a light-emitting diode (LED) and is received by a photodiode (PD). As there is no RF current in the VLC system, the generation of the electric sparks is avoided. Hence, there is no danger of causing explosions. Thus, at the Li-Fi Centre at the University of Edinburgh, we are currently undertaking research into and providing solutions for using VLC in downhole monitoring systems.
PhD Research Student