Microphone based on SPIDERS could make mobile conversations clearer


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A new kind of sensor based on the way spiders detect the vibrations of their prey could lead to mobile phones that are able to cancel out wind noise during calls.

Current handsets have highly sensitive microphones that allow people to chat on tiny handsets that can even be used from the other side of a room.

But this also brings a frustrating side-effect when outside in even the lightest of breezes - conversations can be completely obscured by the noise of the air rushing past the microphone.

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The wandering spider is thought to have one of the most sensitive vibration detectors in the natural world and has provided the inspiration for a new kind of microphone that could be used to reduce background noise

The wandering spider is thought to have one of the most sensitive vibration detectors in the natural world and has provided the inspiration for a new kind of microphone that could be used to reduce background noise

But now scientists in South Korea have found a solution that could make calls clearer by copying a sensory organ used by spiders to detect tiny vibrations created by their prey and other spiders.

The researchers have mimicked the spiders' lyriform organ, which is thought to be one of nature's most sensitive vibration detectors.

This organ, also known as the slit organ, features parallel cracks that look like the strings of a lyre which move and deform in response to tiny changes in air pressure or movement on plants.

WHAT IS THE SPIDER SLIT ORGAN?

Brazilian wandering spiders and their relatives all have slit organs that essentially allow them to hear what is going on around them.

These organs are formed of tightly packed grooves that run down the exoskeleton of their their legs.

These form what is known as a slit organ, or lyriform organ. 

With dense clusters of nerves endings around theses groves, scientists initially thought these were used by spiders to 'smell' their surroundings with a sort of chemosensor.

However, further research has shown that these organs, which feature parallel slits that look like the strings of a lyre, were actually used to detect vibrations in the air and of vegetation.

Due to the stiffness of their exoskeleton, the slits deform in response to these vibreations while the nerves carry signals of these movements to the spider's brain.

They are so sensitive that wandering spiders can detect and distinguish different males rubbing their mouths on a leaf from several metres away.

The wandering spider - Cupiennius salei - is thought to have one of the most sensitive lyriform organs, as they use them to sense and distinguish tiny vibrations that are created during a bizarre mating ritual in which the male spiders scratch leaves with their mouths and abdomen.

The spiders are able to detect these tiny vibrations and distinguish between them. 

In an attempt to copy this, the scientists built a thin platinum and plastic film that had microscopic cracks along it in the same way as the slit organ in spiders.

These platinum cracks then deform and stretch in response to vibrations from sound waves, altering an electrical current through the platinum each time the cracks change shape. 

Tests using the new sensor showed that it could then be used to record sounds from musical instruments and human voices far more accurately than commercial microphones.

The device helped to produce far clearer recordings even with background noise that was equivalent to standing 50 feet from a pneumatic drill at roadworks.

Professor Mansoo Choi, an engineer who led the work at Seoul National University in South Korea, said the device could lead to a new range of microphones and medical sensors.

He said: 'The accuracy of simple word recognition for our nanoscale crack sensor was approximately 97.5% even with noise. 

'Another test was done to confirm that our sensor could successfully pick up complicated voice patterns from a song by attaching our sensor to the diaphragm of a loudspeaker while the song was played in a noisy environment. 

The new spider inspired sensor was created by putting a layer of cracked platinum on top of soft plastic and was able to detect vibrations so small that it could record the sound of a ladybird (blue box) beating its wings

The new spider inspired sensor was created by putting a layer of cracked platinum on top of soft plastic and was able to detect vibrations so small that it could record the sound of a ladybird (blue box) beating its wings

Spiders have organs in their legs called slit organs that detect vibrations in the air and plants around them

Spiders have organs in their legs called slit organs that detect vibrations in the air and plants around them

Nanoscale cracks in the platinum layer change the electrical conductivity of the sensor
The sensor was able to detect the vibrations created by human speech without picking up annoying background noise

Nanoscale sized cracks in the platinum layer change the electrical conductivity of the sensor so that it could detect the vibrations created by human speech without picking up annoying background noise

'The device is reversible, reproducible, durable and mechanically flexible and thus can be easily mounted on human skin.'

The cracks in the platinum were created by layering it on top of a soft polymer substrate so that when it was vibrated, the cracks changed shape.

This altered the electrical resistance of the platinum layer, allowing the scientists to convert the vibrations into an electrical signal, which could then be recorded as digital signals.

Professor Choi, whose work is published in the journal Nature, said the resulting microphone was so sensitive that it was able to detect a ladybird beating its wings close to the sensor.

The researchers also attached the device to a violin, close to the f-hole where vibrating air emerges and found they were able to see the cracks in the sensor vibrate in time to Edward Elgar's Salut d'Amour.

They then attached the sensor to the necks of 10 human volunteers and asked them to say the words 'go', 'jump', 'shoot' and 'stop' as commands in a video game.

When they compared recordings made by the sensor to those made by a microphone, they found the sensor was able to accurately record the commands even in a noisy environment.

They played background noises at 92dB yet still obtained clear recordings of speech as it was able to filter out the unnecessary background noise.

The researchers also used their sensor to monitor volunteer's pulse by attaching it to their wrists.

They also tried to build gold-plated sensors but found the platinum seemed to perform best, perhaps because it is stiffer than the gold and so responds better to vibrations.

Wind and other background noise can make mobile phone calls almost inaudible with current microphones
Gusts of wind can leave some mobile phone users adopting odd strategies to shield their phones from the wind

Wind and other background noise can make mobile phone calls almost inaudible with current microphones that can leave some users adopting odd strategies during a conversation to shield their phones from the wind

The scientists found the cracks in their platinum layer deformed as vibrations created strain across the layer, which altered the electrical conductivity of the metal and so allowed them to selectively record sounds

The scientists found the cracks in their platinum layer deformed as vibrations created strain across the layer, which altered the electrical conductivity of the metal and so allowed them to selectively record sounds

Currently the sensor needs to be held close to the neck or attached to the skin of the neck to record human speech, meaning it could be used to make handsfree microphones.

However, with some tweaks, the scientists believe they could make it more accurate and create microphones that can be used in normal handsets.

It could also be used to make new medical sensors to monitor patients vital signs.

Peter Fratzl, a materials scientist at the Max Planck Institute in Germany who was not involved in the research said the device could have many applications and could be improved further .

He said: 'There are so many vibrations we'd like to monitor. The ultrasensitivity … is really what makes the difference. 

'Despite these impressive practical applications, the analogy with the spider's lyriform sensor is not complete. The only feature translated into the authors' system is geometric amplification.

'The biological sensing mechanism is entirely different - it is based on the firing of neurons rather than the measurement of electrical resistivity, and many other aspects of the spider's organ, such as its tunable sensitivity to different vibration-frequency ranges, are not reproduced.'

 



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