Wireless-powered telemetry system monitors dragonflies

Dragonflies combine delicate horizontal and vertical maneuvering to capture their prey in mid-flight, intriguing scientists at the Howard Hughes Medical Institute (HHMI), who want to better understand the insects’ complex flight control system. The HHMI researchers gather information by attaching tiny electrodes to individual cells in the dragonfly’s nerve cord and recording the electrical activity of the neurons and muscles. But how to instrument and gather the electrical data?  Because existing systems are so heavy, experiments to date have been carried out with immobilized dragonflies, hardly an accurate model of how dragonflies actually move within their environment.

So Duke University electrical engineers led by Prof. Matt Reynolds developed a wirelessly-powered telemetry system that is light-weight and powerful enough to allow scientists to study the neurological activity of dragonflies as they capture prey on the wing. The new system uses no batteries; its power is beamed wirelessly to the flying dragonfly.

The wireless power transmitter works within a flight arena used for the experiments, equipped with nature scenes on the walls, a pond and fruit flies for the dragonflies to chase and eat. The plan is ultimately to synch the neuronal data gathered from the chip with high-speed video taken while the insect is in flight and preying on fruit flies.

“The average weight of the dragonfly species involved in these studies is about 400 milligrams, and … an individual dragonfly can carry about one-third of its weight without negatively impacting its ability to fly and hunt. Currently, most multi-channel wireless telemetry systems weigh between 75 and 150 times more than a dragonfly, not counting the weight of the battery, which rules them out for most insect studies…. [An older] battery-powered version of the insect telemetry system… weighs 130 milligrams -- liftable by a foraging dragonfly but with difficulty.”

The telemetry system, based on a custom IC developed by Reynolds and his team, uses the same wireless power source to send back data at over 5Mbits/sec. The chip weighs 38 milligrams, less than half the weight of a postage stamp. Sporting two hair-thin antennae, the chip will be attached to the belly of the dragonfly and out of the way of its wings. I assume the same antenna both harvests RF energy and transmits the data? Also, how much power the telemetry system requires, and what the maximum power is that the transmitter system can practically provide.

Reynolds, an assistant professor of electrical and computer engineering at Duke’s Pratt School of Engineering, presented his work today at the annual Biomedical Circuits and Systems Conference, held by the IEEE in San Diego.

What about the communications method as well as power usage? Reynolds answers questions about the communication protocol and the power used by the telemetry system at the PowerSource blog.