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Bats’ skill with echolocation—pinpointing prey on the wing and in the dark—has long been a source of inspiration for scientists and engineers, resulting in advances that include novel medical devices for the visually impaired and sophisticated radar systems. Now researchers have created a 3D sonar system that, when combined with high-speed cameras, makes it easier to “see” bat echolocation in action. The new tech, which could reveal more valuable insights into echolocation and predator-prey interactions, is described in a study published 8 January in IEEE Sensors Letters. It could also potentially pave the way for even more bat-inspired technologies in the future.
Moths and bats have been locked in an evolutionary arms race for generations. As bats evolve more sophisticated echolocation tactics, moths have responded by evolving their own arsenal of defenses. For example, some moths have evolved a unique thin layer of scales that absorb sound, and others have learned ways to emit their own ultrasonic sounds to jam bats’ echolocation signals, like a biological radio jammer.
Observing these battle tactics in the field is no easy task, in part because both bats and moths move quickly and agilely in their dim environments.
Jan Steckel is an associate research professor at Cosys-Lab at the University of Antwerp, in Belgium. During his Ph.D. work in the early 2000s, he did some measurements on various aspects of insect echo generation, which involved both stationary and fluttering insects. Over the years, colleagues increasingly approached Steckel, asking for better technology that could be used to study bat-insect interactions in the field.
Pairing Light and Sound to Study Bat Echolocation
This prompted Steckel and his colleagues to create their novel sensor system, called the flutter real-time imaging sonar (FL-RTIS), which integrates a high-speed camera with a 3D sonar sensor to investigate insects’ ability to fill an area with sound (a process called ensonification).
“The FL-RTIS is the first sensor that can measure the echo dynamics of fluttering insects both in 3D and at a high speed at the same time,” Steckel says, noting that other systems either take minutes to complete a full 3D sound scan, or quickly record unidirectional sound—but have yet to capture 3D sound fast.
In particular, the system is able to capture the echoes of fluttering insects at a rate of 100 hertz, a pulse repetition frequency often used by bats as they home in on their prey at close distances (a technique called the “terminal buzz phase“).
FL-RTIS is a fully embedded sensor system using an array of microphones, a broadband ultrasonic speaker, and an embedded GPU for processing.
The system uses an approach to process the sound data called minimum variance distortionless response beamforming, which can help enhance target detection and tracking while suppressing interference and noise from other sources. The technique allows for better spatial resolution of acoustic images without requiring large microphone arrays.
Meanwhile, a random electrical signal recorded by the microphone array and a blinking LED light help sync up the high-speed camera and 3D sound-recording devices with microsecond precision. This high degree of synchronicity provides temporal consistency between the acoustic and visual data streams.
The researchers tested the new system first in the lab by recording rotating fans and overlaying the echo signals onto the images, before doing similar tests in the lab with luna moths. They also took their new FL-RTIS system into the field, taking multiple measurements of roughly 200 insect specimens in the rain forests of Ecuador and Mozambique.
While these initial field experiments demonstrated that FL-RTIS can capture the sound and visual data of moving insects, the tool is now being used by biologists to uncover predator-prey interactions of bats and moths in Ecuador. That data is currently being analyzed but should be available in the near future, Steckel says.
In the meantime, Steckel is interested in continuing to develop unique tech like the FL-RTIS, which he notes is “a niche technology that has been neglected by the sensing community for too long.”
This article appears in the April 2025 print issue as “Sonar Scope “Sees” Bat Echolocation.”
Michelle Hampson is a freelance writer based in Halifax. She frequently contributes to Spectrum's Journal Watch coverage, which highlights newsworthy studies published in IEEE journals.
