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2000 Microphones Used to Unlock Mystery of Why Hummingbirds Hum


Anna’s Hummingbird / Becky Matsubara, CC license

The hummingbird is named after its pleasant humming when it hovers in front of flowers to feed. But only now has it become clear how the wing generates the hummingbird’s namesake sound when it beats rapidly at 40 beats per second.

Researchers from Eindhoven University of Technology, Stanford University and Sorama meticulously observed hummingbirds using 12 high-speed cameras, six pressure plates and 2,176 microphones. The engineering team managed to measure the precise origin of the sound generated by the flapping of a flying animal’s wings for the first time.

They found that the soft and complex feathered wings of hummingbirds generate a sound similar to that of the simpler wings of insects. The new insights could help make devices like fans and drones quieter.

The hum of the hummingbird originates from the pressure difference between the top and bottom of the wings, which changes in both magnitude and orientation as the wings move back and forth. These pressure differences on the wing are essential, because they provide the net aerodynamic force that allows the hummingbird to take off and glide.

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Unlike other species of birds, a hummingbird’s wing generates a strong upward aerodynamic force during the downward and upward wing stroke, that is, twice per beat. While the pressure differences due to lift and drag force acting on the wing contribute, it turns out that the upward lift pressure difference is the main source of the hum.

The difference between whining, humming and barking

Professor David Lentink of Stanford University said: “This is why birds and insects make different sounds. Mosquitoes buzz, bees buzz, hummingbirds buzz, and larger birds go ‘woosh.’ Most birds are relatively quiet because they generate most of the lift only once during their flapping on the downstroke. Hummingbirds and insects are louder because they do it twice per wingbeat. “

To arrive at their model, the scientists examined six Anna’s hummingbirds, the most common species at Stanford.

One by one, they made the birds drink sugar water from a fake flower in a special flight chamber. Around the camera, not visible to the bird, cameras, microphones and pressure sensors were installed to accurately record each wingbeat as it moved in front of the flower.

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During a follow-up experiment, six highly sensitive pressure plates finally managed to record the lift and drag forces generated by the wings as they moved up and down, for the first time.

The researchers finally managed to condense all of their various results into a simple 3D acoustic model, taken from the world of airplanes and mathematically adapted by flapping of wings. Predict the sound of flapping wings radiating, not just hummingbird buzzing, but also buzzing from other birds and bats, buzzing and whining from insects, and even wing beating robots.

Making drones quieter?

Although it was not the focus of this study, published in March in the daily eLife—The knowledge gained can also help improve aircraft and drone rotors, as well as laptop fans and vacuum cleaners. New knowledge and tools can help make designed devices that generate complex forces, as animals do, quieter.

This is exactly what Sorama aims to do: “We make sound visible to make household appliances quieter. Noise pollution is becoming a growing problem. And a decibel meter alone is not going to solve that. You need to know where the sound is coming from and how it is produced in order to eliminate it. That’s what our sound cameras are for. This hummingbird wing research provides us with a completely new and highly accurate model as a starting point, so that we can do our job even better, ”concludes CEO and researcher Rick Scholte of Sorama, a spin-off from Eindhoven University of Technology. .

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If the movements of hummingbirds can give us a quieter technology in the future? Well, we are absolutely here for it.

(WATCH the researchers’ video of hummingbirds humming)

Source: Eindhoven University of Technology

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