“I have long admired bats for their uncanny ability to navigate complex natural environments based on ultrasound and suspected that the unusual mobility of the animal’s ears might have something to do with this,” said Virginia mechanical engineer Rolf Mueller.
According to Mueller, bats do something that humans cannot – waggle the pinna of their ears to add Doppler information. This, combined with the complex shape of pinna, encodes angle-of-arrival information into the sound entering a single ear.
The team made a soft artificial pinna, inspired by horseshoe and Old-World leaf-nosed bats, and attached it to a motor via a string (photo) to twitch it.
A microphone picked up the resulting Doppler and geometrically modified sound, and this, plus the direction of a moveable sound source, were used as input data to train a deep neural network.
Once trained, they mounted the ear and its twitching mechanism on a rotating platform alongside a laser pointer to test it – exposing it to sound from a mobile loudspeaker and measuring how accurately the laser pointed to the sound source.
“Once the direction of the sound was determined, the control computer would rotate the rig so that the laser pointer hit a target attached to the loudspeaker, pinpointing location within half a degree,” according to the university. “Human hearing typically determines location within 9 degrees with working with two ears, and the best technology has achieved location within 7.5 degrees.”
“The capabilities are completely beyond what is currently in the reach of technology, and yet all this is achieved with much less effort,” said Mueller. “Our hope is to bring reliable and capable autonomy to complex outdoor environments, including precision agriculture and forestry; environmental surveillance, such as biodiversity monitoring; as well as defence and security-related applications.”
This Virginia Tech bat ear YouTube video is well worth a look