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Sea turtles are remarkable creatures for a number of reasons, including the way they hear underwater—not through openings in the form of ears, but by detecting vibrations directly through the skin covering their auditory system. Inspired by this ability to detect sound through skin, researchers in China have created a heart-monitoring system, which initial tests in humans suggest may be a viable for monitoring heartbeats.
A key way in which doctors monitor heart health involves “listening” to the heartbeat, either using a stethoscope or more sophisticated technology, like echocardiograms. However, these approaches require a visit to a specialist, and so researchers have been keen to develop alternative, lower cost solutions that people can use at home, which could also allow for more frequent testing and monitoring.
Junbin Zang, a lecturer at the North University of China, and his colleagues specialize in creating heart-monitoring technologies. Their interest was piqued when they learned about the inner workings of the sea turtle’s auditory system, which is able to detect low-frequency signals, especially in the 300- to 400-hertz range.
“Heart sounds are also low-frequency signals, so the low-frequency characteristics of the sea turtle’s ear have provided us with great inspiration,” explains Zang.
At a glance, it looks like turtles don’t have ears. Their auditory system instead lies under a layer of skin and fat, through which it picks up vibrations. As with humans, a small bone in the ear vibrates as sounds hit it, and as it oscillates, those pulses are converted to electrical signals that are sent to the brain for processing and interpretation.
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But sea turtles have a unique, slender T-shaped conduit that encapsulates their ear bones, restricting the movement of the similarly T-shaped ear bones to only vibrate in a perpendicular manner. This design provides their auditory system with high sensitivity to vibrations.
Zang and his colleagues set out to create a heart monitoring system with similar features. They created a T-shaped heart-sound sensor that imitates the ear bones of sea turtles using a tiny MEMS cantilever beam sensor. As sound hits the sensor, the vibrations cause deformations in its beam, and the fluctuations in the voltage resistance are then translated into electrical signals.
The researchers first tested the sensor’s ability to detect sound in lab tests, and then tested the sensor’s ability to monitor heartbeats in two human volunteers in their early 20s. The results, described in a study published 1 April in IEEE Sensors Journal, show that the sensor can effectively detect the two phases of a heartbeat.
“The sensor exhibits excellent vibration characteristics,” Zang says, noting that it has a higher vibration sensitivity compared to other accelerometers on the market.
However, the sensor currently picks up a significant amount of background noise, which Zang says his team plans to address in future work. Ultimately, they are interested in integrating this novel bioinspired sensor into devices they have previously created—including portable handheld and wearable versions, and a relatively larger version for use in hospitals—for the simultaneous detection of electrocardiogram and phonocardiogram signals.
