Once again, man is imitating nature for the best. A team of Dutch physicists has created artificial cricket hairs, which are among the most sensitive sound detectors on Earth. These artificial sensory hair systems will help to develop sensor arrays useful for a variety of applications. For example, these sensor arrays could be used to visualize airflow on surfaces, such as an aircraft fuselage. But more importantly, this "could lead to a new generation of cochlear implants, for people with severe hearing problems." Even if it doesn't happen overnight, the low energy consumption and costs of fabrication are excellent news for deaf people. Read more...
First, let's look at how real crickets are using their hairs.
Crickets spend most of their lives on the ground, making them vulnerable to wandering and flying predators. Species such as the wood cricket Nemobius sylvestris have developed a pair of hairy appendages at the abdominal end of their body called cerci, which are incredibly good at detecting small fluctuations in air currents -- the kind that might be caused by the beating of a wasp’s wings or the jump of an attacking spider.
On the figure below, you can see the sensory hairs of the cricket (Credit: University of Twente, The Netherlands).
The sensory hairs of the cricket are situated on the back of the cricket’s body on appendices called cerci. [...] Each hair is lodged in a socket, guiding the hair to move in a preferred direction. The hair is held in its socket by an elastic material surrounding the base. Airflow causes a neuron to be fired, by rotation of the hair base. The cricket is able to pinpoint low-frequency sound from any given direction, by using the combined neural information of all sensory hairs.
Now, let's focus on how these Dutch physicists have created artificial cricket hairs.
Physicists at the University of Twente in the Netherlands have now succeeded in building artificial sensory hair systems, which they hope will enable them to unravel the underlying process and develop sensor arrays with a variety of important applications.
The Twente team built a mechanical array with up to a few hundred artificial hairs using technologies often referred to as MEMS technology. The sensors are made by depositing and structuring various thin layers of electrically insulating and conducting materials, creating structured electrodes on a suspended membrane. The structured electrodes form two capacitors with the underlying substrate.
Below is a picture of an array of spiral-suspended sensory hairs, obtained through "a relatively simple fabrication process" (Credit: University of Twente, The Netherlands).
The news release gives some more details, but for more information, the research work has been published on June 20, 2005 by the Journal of Micromechanics and Microengineering under the name "Artificial sensory hairs based on the flow sensitive receptor hairs of crickets." Here is a link to the abstract.
This paper presents the modelling, design, fabrication and characterization of flow sensors based on the wind-receptor hairs of crickets. Cricket sensory hairs are highly sensitive to drag-forces exerted on the hair shaft. Artificial sensory hairs have been realized in SU-8 on suspended SixNy membranes. The movement of the membranes is detected capacitively. Capacitance versus voltage, frequency dependence and directional sensitivity measurements have been successfully carried out on fabricated sensor arrays, showing the viability of the concept.
And if you're a registered member of the Institute of Physics, here is a link to the full paper (PDF format, 7 pages, 686 KB) (you can register for free from the abstract link). The above illustrations were extracted from this paper.
Finally, you can find other technical information on the CICADA project page at the University of Twente -- CICADA standing for " Cricket Inspired perCeption and Autonomous Decision Automata."
Sources: Institute of Physics news release, June 20, 2005; and various web sites
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