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Lateral-line inspired UAV detection: Part 7

Potential methodologies
Electrical
Bees
Bees are able to use electroreception for the detection of flowers containing pollen, and for additional communications during the characteristic waggle dance. The electroreception used by bees is unique in that unlike the sharks and monotremes, it is used whilst flying through the dry air.

In the case of the waggle dance communications, the dancing bee emits both low and high frequency electrical fields. These fields induce a passive antennal movement in nearby stationary bees in accordance with Coulomb’s Law. Coulomb’s Law describes the force interacting between statically charged particles. It states that the magnitude of the electrostatic force between two point charges (i.e. the dancing bee and the antennas of the observing bee) is directly proportional to the product of the magnitudes of charges, and inversely proportional to the square of the distance between them. If the two charges have the same sign, the electrostatic force between them is repulsive. If they have opposing charges, the force is attractive. This means that depending on the polarity of the dancing bee, the observing bee’s antennas are either drawn towards the dancer or repelled. The bees are then able to interpret this movement in a meaningful way alongside the rest of the dance. It has been found that the bases of the antennas in bees act as mechanoreceptors, allowing for this sensing to take place.

In the case of pollen detection, when a naturally charged bee lands on a flower, the natural floral electric field is changed. Future bees are able to discern between flowers which have recently been visited by other bees and those which have not, avoiding the former . It was found that electrical charges may passively induce movement in both the body hairs and the antennas of bees. These were found to have quite different resonant frequencies, and tests showed that bees only reacted to the movement of body hairs. The hairs move like stiff rods, and pivot on their bases which were found to contain mechanosensory neurons. Hairs were found to respond to charges of as little as 25mV, whereas antennas would only respond to charges of at least 500mV. Sharks however are able to detect changes of as little as 5nV, meaning that sharks are approximately 5 million times more sensitive to electrical field changes than bees are. However, bees are still able to detect tiny changes, considering that they operate within an electrical insulator (the air).

As was highlighted previously, quite a lot of cross-wind is experienced in flights. It appears that a combination of the tiny scale of the bees and the incredibly high sensitivity of the Johnston’s organ (the organ that transduces mechanical deflection in hairs to an electrical analogue in bees) may be the reason that bees are able to still detect electrical fields within these conditions. In the study which discerned the difference in response between antennas and hairs to electrical fields, the bees used within the research were already dead. This means that direct observation of hair deflection within flight was not possible, and so data taken from another study of hair deflection in crickets was used. It was found that the Johnston’s organs of bees respond to hair deflections of around 4×10-2 degrees, which is the deflection induced by electrical fields. In the studied crickets, air currents were found to induce a hair deflection of between 5×10-3 and 5×10-2 degrees. It may be possible that Johnston’s organs are able to filter out deflects of the wrong size, causing only the electrically induced deflections to be interpreted. It may be possible also that the tightly packed tiny stiff hairs somewhat support each other, meaning that cross winds are not able to induce much movement. Perhaps if tiny, highly sensitive artificial Johnston’s organs/tiny hair combinations could be created, these would enable to some electric field sensing capability to be added to UAVs.

Published inBiomimeticsUAVs

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