LEDs could provide better data transmission under water

Experts in underwater wireless communication have found a novel application in sports science for monitoring swimmers.

They are working on a device that will gather measurements on movements such as stroke count and then send it wirelessly in real time to a heads-up goggle display and poolside coach.

Underwater wireless communication is a particularly challenging area, with potential applications in tsunami and earthquake monitoring, marine archaeology, and search and rescue.

The problem is that electromagnetic signals such as radio frequencies cannot propagate effectively through water, while the acoustic sources currently used are limited by the speed of sound and experience path losses.

The current project began with sports engineers at Griffith University in Australia who wanted to extend the remote monitoring of athletes — for which there are now a number of commercial devices — to the pool environment. They turned to a research team at the Helmut Schmidt University in Germany, led by Dr Thomas Fickenscher.

‘From the combinations of many turns and different axes, you can process the real movements of the swimmer and get a lot of data from that — more than just stroke rate,’ Fickenscher told The Engineer.

To transmit this data, the German team saw the potential in exploiting the relatively new field of wireless optical communication with modified LEDs, which can propagate through water effectively over short distances with quite a high bandwidth in relation to acoustic sources.

Their device setup includes accelerometer and gyroscope sensors mounted on a chip, which performs data processing in situ for signal conversion to a near-infrared emitter that operates in the 850–900nm spectral range.

‘Underwater optical researchers normally use blue or green light, because the attenuation is lowest, however, for short distances, the attenuation shouldn’t be high if the water isn’t dirty, so it’s better to go to red to make a cheap and very functional system — this is something a lot of people don’t consider,’ Fickenscher said.

So far, the group has successfully tested the transmission of data in a sectioned-off experimental pool-based setup. They will now look to develop the heads-up goggle display.

Fickenscher explained that there are still challenges to overcome, such as ambient light that acts as a noise source; bubbles that can interfere with the signal; and the fact that transmission has to be consistent over three regimes: water-water; water-air and air-air.