Biomimetics - Biologically Inspired Technologies - Yoseph Bar Cohen Episode 2 Part 3 ppt

13.10 Riot Control Agent 358 13.10.1 Chemical Mace 358 13.11 Operational 359 13.11.1 Long-Term Disablement 359 13.11.2 Passive Deterrents 359 13.12 Physiological 359 13.12.1 Neurochemical 359 13.12.2 Diversion 360 13.13 Surveillance 360 13.13.1 Electrosensing 360 13.14 Conclusions 361 References 361 13.1 INTRODUCTION Whilst there are several proposed uses of biomimetics in defense or attack (martial, general law enforcement) systems, at present they seem to be mostly development of novel materials (occa- sionally novel mechanisms) in an established context. Examples are armor, personal or otherwise, made of analogs of silk, mother-of-pearl (nacre), or wood. I do not intend to rehearse this topic further. Camouflage is another area that has been examined, especially adaptive camouflage, but since there is still much to be learned about camouflage techniques in nature (which I take to include mimicry — camouflage is ‘deception’), I have included it. In general, camouflage and armor are inimical; the tendency is for the more primitive ( ¼ evolutionarily older) animals of any particular phylum to be well armored but slow and relatively easily seen, whereas the more highly evolved ones are less well armored, or have no armor at all, but are fast-moving, or very well camouflaged, or both. Thus they rely on speed and behavioral adaptiveness and subtlety for their safety. The inevitable conclusion is that nature often employs guerrilla techniques rather than what we think of as ‘‘conventional’’ ones. This may be related to the perceived financial investment. In human warfare, an infantryman is seen as more expendable than the combination of a pilot and aircraft. Indeed a significant reason for having a pilot is as a hostage to the aircraft’s expensive technology, so that it is brought back in one piece from a sortie. The preparation of a chapter like this is especially difficult since I could not think of a suitable narrative to cover all the possibilities that exist in nature. Also, I have little understanding of the techniques that are available to, or desired by, the military and police (the obvious users of defense mechanisms). I decided, therefore, to adopt a classificatory approach, and to use an existing military classification as my template (Alexander et al., 1996). I have removed the obviously nonbiological techniques that involve explosives, lasers, etc., have retained others which, although biology does not present us with the same resource, are obvious functional analogs, and have included some that seemed to be missing from Alexander’s list but are present in biology. These latter are presented without citations. Man has many martial devices that have their reflections in nature, but the similarities have either not been recognized or have not been developed. And since the outcome in nature is, mostly for all parties, in an intraspecific encounter to live to fight another day (or at least live), perhaps we have still much to learn. As for the rest, I suspect we have an untapped resource for biomimicry; I have mostly left the extrapolation from biology to technology to the reader, otherwise this chapter would have been too long. But most of the examples quoted either have a technological counterpart or could be realized without much difficulty. The Department of Defense defines (non-lethal) weapons as designed and deployed so as to incapacitate people or their weapons and other equipment, rather than destroying them; also to Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 342 21.9.2005 11:51pm 342 Biomimetics: Biologically Inspired Technologies have minimal effects on the environment. Unlike conventional, lethal, weapons that destroy their targets principally through blast, penetration and fragmentation, non-lethal weapons have rela- tively reversible effects and affect objects differently (Alexander et al., 1996). 13.2 ACOUSTICS 13.2.1 Blast Wave Projector Energy generation from a pulsed laser that will project a hot, high pressure plasma in the air in front of a target. It creates a blast wave with variable but controlled effects on hardware and troops (Alexander et al., 1996). This could be akin to cavitation bubbles that are the loudest source of sound from ship propellers. Snapping shrimps (Stomatopods or mantis shrimp) are very noisy; it has been long assumed that the noise was caused by their claws closing. In Odontodactylus scyllarus, the sound is caused by the collapse of cavitation bubbles due to the high speed at which the claw moves, powered by a highly elastic part of the exoskeleton. The shrimps appear to use cavitation to stun their prey (small crabs, fish, and worms); it certainly wreaks havoc with the shrimp’s own exoskeleton. Although the claw is highly mineralized, its surface becomes pitted and damaged; stomatopods moult frequently and produce a new smashing surface every few months (Patek et al., 2004). 13.2.2 Infrasound Very low-frequency sound that can travel long distances and easily penetrate most buildings and vehicles. Transmission of long wavelength sound creates biophysical effects; nausea, loss of bowels, disorientation, vomiting, potential internal organ damage or death may occur. Superior to ultrasound because it is ‘‘in band’’ meaning that its does not lose its properties when it changes mediums such as from air to tissue. By 1972 an infrasound generator had been built in France that generated waves at 7 Hz. When activated it made the people in range sick for hours (Alexander et al., 1996). Whales are certainly able to generate low frequencies (15 to 30 Hz) which they use for communication over long distances (the capercaillie, a ground-living bird of the Scottish wood- lands, uses low frequencies for the same reason) but they have not been tested for any damaging effects (Croll et al., 2002). Although it does not really belong to ‘‘infrasound,’’ animals (e.g., frogs, birds, and deer) advertize a false impression of exaggerated size by making low frequency sounds (Reby and McComb, 2003). The implication for other animals is that a low noise can only come from a large resonant cavity, so the animal producing the noise is probably large and therefore probably strong. Producing low frequency vibrations is therefore a premium especially if the animal cannot be seen and the assessment of size can be made only from the frequency range of the noise. 13.2.3 Squawk Box Crowd dispersal weapon field tested by the British Army in Ireland in 1973. This directional device emits two ultrasonic frequencies which when mixed in the human ear become intolerable. It produces giddiness, nausea or fainting. The beam is so small that it can be directed at specific individuals (Alexander et al., 1996). There are many reports of dolphins using a similar technique, either when hunting or when swearing at a human experimenter. In a U.K. radio programme some years ago, a researcher recounted playing back its own sounds to a dolphin to see what it would do, including listening Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 343 21.9.2005 11:51pm Defense and Attack Strategies and Mechanisms in Biology 343 to the dolphin’s response with a hydrophone. The dolphin was quite amenable to this game and cooperated well. But by mistake the experimenter sent the dolphin a rather loud signal to which the dolphin obviously objected. The dolphin looked at the experimenter through the walls of the aquarium, then went to the hydrophone and blasted into it before the experimenter could rip off his earphones. The experimenter experienced much pain! The implication is that we could probably learn about physiologically damaging noise from dolphins and other cetaceans that are also much more experienced with the technique, having been using it for longer than we have. 13.3 ANTILETHAL DEVICES 13.3.1 Body Armor Many animals have a hard outer covering that serves as armor, but there are many different ways in which the function is realized. Whereas the armor developed for individuals or vehicles is based on the inevitability of attack, and relies on resisting by strength, biological armor can come in many guises. Obvious ones are armadillo and tortoise, although nobody seems to have made any measurements of the protection that is given. The same is not true of ankylosaurs (Figure 13.1) and their relatives, herbivorous dinosaurs that grew to 10 m long during the late Jurassic and Cretaceous. They had centimeter-sized osteodermal plates that covered back, neck, head, and also protected the eyes. In polarized light, sections of the plates show where collagen — a normal precursor of bone and an essential component of skin — was incorporated. Comparing similar dermal bones from stegosaurus and crocodile, the polocanthids had extra collagen fibres that may have stabilized the edges of the bony plates. But in nodosaurids — which also had plates between 2 and 5 cm thick, the collagen fibres ran parallel and perpendicular to the surface, and then at 458 to each of these axes, providing reinforcement in all directions. Ankylosaurids had thinner plates that were 0.5 to 1.0 cm thick, convex shaped, which will have increased their stiffness in bending, and with the collagen fibres randomly arranged. The dinosaur structure seems to be repeated in the bone-free collagenous skin of the white rhinoceros, which is three times thicker and contains a dense and highly ordered three-dimensional array of relatively straight and highly crosslinked collagen fibres. The skin of the back and sides of the animal is therefore relatively stiff (240 MPa) and strong (30 MPa), with high breaking energy (3 MJ m À3 ) and work of fracture (78 kJ m À2 ). These properties fall between those of tendon and skin as would be expected from a material with a large amount of collagen (Shadwick et al., 1992). Figure 13.1 An ankylosaur. Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 344 21.9.2005 11:51pm 344 Biomimetics: Biologically Inspired Technologies Unfortunately the data on ‘‘soft’’ body armor (e.g., Kevlar) does not quote performance in these units, preferring to equate energy of an incoming threat to depth of penetration through the armor. Presumably one has to go to reports from the old big game hunters to get similar information about the rhinoceros. However, leather is still tougher than Kevlar, although nobody really understands why, since the collagen fibres are not dissimilar from Kevlar in general morphology. A concept that is entirely alien to the current design of man-made armor is the porcupine quill, although the pikestaff of the medieval infantryman might be considered analogous, and parts of mediaeval armor and their weapons were equipped with spikes to keep the enemy at bay. The porcupine has several different types of quill; those with a length-to-diameter ratio greater than about 25 are mostly rattles to warn enemies that there are quills here. Those with a lower length- to-diameter ratio (15 or less) act as columns when they meet an end load, and with the sharp tip, can easily penetrate flesh. They are sometimes brittle and the tip can break off, but they also have weak roots in the porcupine’s skin and so can easily be pulled out when the impaled attacker moves away. The quills are filled with a variety of reinforcing foams, struts, and stringers, so that they rarely break when buckled (Vincent and Owers, 1986). Quills are modified hairs and are made of keratin. In general, plants have totally passive defense mechanisms, which is energetically probably much cheaper. They are thus built to survive a certain amount of damage due to grazing, and may even grow more vigorously in response. Many plants, especially those living under dry conditions, such as the acacia, have spines, thorns, or hooks that cause pain to the animals attacking them. Presumably the giraffe, which feeds on such plants, has a reinforced surface to its tongue so that it can cope with the abuse. Many of the grain-bearing plants (Graminae) have silica particles — sometimes as much as 15% of the dry weight — which wears down the teeth of the animals feeding on them. Indeed the performance of the teeth is frequently dependent on such wear, exposing a complex of self-sharpening cutting and grinding surfaces (Alexander, 1983). The literature on plant–animal interactions is large, mostly concerned with how plants control the ease with which they can be grazed, commonly by limiting crack propagation with inhomogeneities such as embedded fibres; and their chemical defenses which range from repulsive taste or smell, through manipulation of the digestion or behavior of the grazer (by psychoactive drugs) to lethal chemicals, mostly in those plants which cannot afford to be eaten since they grow so slowly. In both plants and animals, spines and thorns are passive and are of use only at close quarters. The closest equivalent is barbed wire which many claim to be biomimetic. Horns and antlers can be used for both attack and defense, an unusual concept for technology — the closest analogy is the sword, which can be used both to deliver a blow and to parry one. The utility of antlers (dead, made of bone, replaced each season, grown from the tip) and horns (living, made of a thick keratin sheath over a bone core, incremented each season, grown from the base) has been questioned by animal behaviorists who find difficulty coping with the wide range in sizes of horns and antlers, and the range in forces imposed on them during fighting. These problems were largely resolved by Kitchener, who showed that there is a linear relationship between the second moment of area at the base of the horn or antler and the body weight of the animal, and that this relationship is constant for any single style of fighting. Most styles are ritualistic and akin to wrestling; sheep and goats are far more agonistic, throwing themselves at each other resulting in more random forces being exerted on their horns (Kitchener, 1991). Ever since their discovery in the 16th century, the enormous antlers of the extinct Irish elk or giant deer (Megaloceros giganteus) have attracted scientific attention. Mechanical analysis of the antlers of the Irish elk shows that they are massively over-designed for display (for which, as John Currey pointed out, they really only need to be made of waterproof cardboard) because the force exerted by gravity acting on the antlers is less than 1% of their strength. In contrast, the antlers seem to be optimally designed for taking the maximum estimated forces of fighting, that are more than 50% of the strength of the antler, as would be expected for a biological structure of this kind. However, this analysis assumes that the mechanical properties of the bone of the Irish elk antlers and living deer are similar. It would be unwise to measure directly the mechanical properties of Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 345 21.9.2005 11:51pm Defense and Attack Strategies and Mechanisms in Biology 345 Irish elk antler after more than 10,000 years in a peat bog. Instead, neutron diffraction, which measures the degree of preferred orientation of the hydroxyapatite crystals that comprise bone, showed that the orientation of the hydroxapatite is predictable from the presumed forces generated during fighting. Thus on the tensile faces of the antler, the orientation was along the length of the antler, whereas on the compressive faces, the orientation was more orthogonal to the long axis — exactly what the theory of fibrous composite materials predicts (Kitchener et al., 1994). 13.3.2 Passive Camouflage Many American hunters recommend that more effort should be put into the research on camou- flage, and that body armour should be a second priority to finding effective concealment. The logic is that what you can’t see, you can’t hit. Body armour is required only when you can be seen and identified. Many animals and plants, especially insects, can look like inert objects such as bits of wood or stones (e.g., the succulent South American plant Lithops). Because of their colored wings, many moths can conceal themselves when placed against a suitable background such as the bark of a tree. The peppered moth (Biston betularia) in industrial areas of England has been held as a classic example of natural selection, with birds eating those moths that they could see only when they were sitting on an unsuitably colored bark. In this instance the moth was originally light with small black speckling, but pollution produced in the early industrial revolution blackened the trees, so an initially rare dark form of the moth was selected by being less easily seen and eaten (Kettlewell, 1955). Later, with reduced pollution and clearing of the woods, the bark was lighter and better lit and the lighter-colored form again predominated. Similarly many nesting birds are difficult to see; ground-nesting birds have camouflaged eggs and chicks. Many insects, especially grasshoppers, have bright hind wings which disappear when the insect stops flying, settles, and folds its wings thus becoming camouflaged. This sudden change makes it difficult to spot the insect. Another basic component of passive camouflage, well known to technology, is countershading, in which, those parts of the body that are normally well illuminated are darkly colored, and those that are normally shaded lightly colored . This is seen in both terrestrial and aquatic animals; the corollary is the larva of the privet hawk moth (Sphinx ligustri) which is dark on the underside and light on the upperside, and habitually hangs inverted beneath its twig. The effect is to flatten the aspect of the animal, making it difficult to judge its size and how far away it is. The literature of camouflage in biology is very large (Wickler, 1968). 13.3.3 Warning Coloration The announcement that you are strong or dangerous is useful since it can deter an enemy from attacking, and gains its best effect by the strong making themselves easily seen. But one can also pretend strength. This is not novel, and has been used for hundreds of years with armies making themselves appear larger than they are with hats on sticks, unattended guns protruding through the battlements, and soldiers circulating past a small gap for the enemy to see . . . Many animals and plants (especially fruits) advertize that they are poisonous or that they have a very nasty sting or bite. Typical warning colors are bright, for instance red and yellow associated with black, mutually arranged to maximize contrast and visibility (aposematic coloration). There is a vast amount of literature on this aspect of coloration, which includes mimicking of an unpalatable animal by a palatable one (Batesian mimicry) and mimicry of palatable mimics of unpalatable animals (Mu ¨ llerian mimicry). Such mimicry is probably commonest amongst butterflies, where the main selection agent is predatory birds and the habitat is thick forest or woodland (Wickler, 1968). Thus, the predatory bird probably only ever gets a fleeting glimpse, poorly illuminated of its prospective prey, and with this minimal information it has to decide whether or not to attack. It Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 346 21.9.2005 11:51pm 346 Biomimetics: Biologically Inspired Technologies is imaginable that under these conditions even a slight resemblance to an unpleasant species is enough to convince a bird not to attack. Most insects, in particular beetles, butterflies, and moths, get their noxious chemicals from the plants they feed on. The first bird to be discovered with warning coloration and toxic feathers is the Pitohui of New Guinea (Dumbacher et al., 2004). The source of the alkaloids, also found in poison- dart frogs, is Melyrid beetles. 13.3.4 Active Camouflage Created by dynamically matching the object to be camouflaged to its background colors and light levels thus rendering it virtually invisible to the eye. This is conceptually the same camouflage process as that used by a chameleon. This is accomplished through a sophisticated color and light sensor array that detects an object’s background color and brightness. This data is then computer matched and reproduced on a pixel array covering the viewing service of the object to be camouflaged. Pattern control is achieved by flatfish such as the plaice (Pleuronectes platessa) that can change its shading and patterns to suit a variety of backgrounds — including a chequer board! However, it can manage only black and white, and then only slowly, over a matter of minutes, since its color- change cells (melanophores) are hormonally controlled. They change color by moving pigment around inside the cell going from ‘‘concentrated’’ (the pigment is centered making the cell white or translucent) to ‘‘dispersed’’ (the pigment is spread around the cell which now appears dark) (Fuji, 2000; Ramachandran et al., 1996). Color control in octopus and squid (cephalopod — literally ‘‘head-footed’’ — molluscs) is managed by colored cells — chromatophores — that are found in the outer layers of the skin. Each comprises an elastic sac containing pigment to which is attached radial muscles. When the muscles contract, the chromatophore is expanded and the color is displayed; when they relax, the elastic sac retracts. The chromatophore muscles are controlled by the nervous system. Differently colored (red, orange, and yellow) chromatophores are arranged precisely with respect to each other, and to reflecting cells (iridophores producing structural greens, cyans and blues, and leucophores, reflect incident light of whatever wavelength over the entire spectrum) beneath them. Neural control of the chromatophores enables a cephalopod to change its appearance almost instantaneously (Hanlon et al., 1999), a key feature in some escape behaviors and during fighting signalling. Amazingly the entire system apparently operates without feedback from sight or touch (Messenger, 2001). The primary function of the chromatophores is to match the brightness of the background and to help the animal resemble the substrate or break up the outline of the body. Because the chroma- tophores are neurally controlled, the animal can, at any moment, select and exhibit one particular body pattern out of many, which presumably makes it difficult for the predator to decide or recognize what it is looking at. When this is associated with changes in shape or behavior, the prey can become totally confusing. Consider this performance by an octopus found in Indo- Malaysian waters. It is seen on the seabed as a flatfish and swims away with characteristic ‘‘vertical’’ (remember the flatfish swims on its side) undulations. As it does so it changes into a poisonous zebra fish. It then dives into a hole and sends out two arms in opposite directions to mimic the front and back ends of a poisonous banded sea snake (videos of these behavior patterns are available to download with the paper by Norman et al.). It also sits on the sea bed with its arms raised, possibly in imitation of a large poisonous sea anemone. Or it can sink slowly through the water column apparently imitating a jellyfish (Norman et al., 2001). Each of these types of animal requires a different response on the part of the predator, which presumably is totally confused. Such dynamic mimicry is seen only in cephalopods and the films of the Marx Brothers. Countershading in animals is widespread and cephalopods are no exception. On the ventral surface, the chromatophores are generally sparse, sometimes with iridophores to enhance reflec- tion; dorsally the chromatophores are much more numerous and tend to be maintained tonically Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 347 21.9.2005 11:51pm Defense and Attack Strategies and Mechanisms in Biology 347 expanded. More remarkably, however, cephalopods can maintain countershading when they become disorientated. The countershading reflex ensures that chromatophores on the ventral surface of the entire body expand when the animal rolls over on its back: a half-roll elicits expansion of the chromatophores only on the upper half of the ventral body. Such a response is, of course, possible only in an animal whose chromatophores are neurally controlled (Ferguson et al., 1994). When matching brightness, the chromatophores act like a half-tone screen; color matching is achieved with the chromatophores, iridophores, and leucophores (Hanlon and Messenger, 1988). On variegated backgrounds, a cuttlefish will adopt the disruptive body pattern, whose effect is to break up the ‘‘wholeness’’ of the animal (Figure 13.2). Disruptive coloration is a concealment technique widespread among animals. Octopus vulgaris has conspicuous frontal white spots; loliginid squids show transverse dark bands around the mantle that probably render the animal less conspicuous, and the harlequin octopuses have bold black-and-white stripes and spots. Although many animals use patterning for concealment, it is nearly always a fixed pattern. Because they control their chromatophores with nerves and muscles, cephalopods can select one of several body patterns to use on a particular background. Cephalopods also produce threatening or frightening displays. In its extreme form, the animal spreads and flattens, becoming pale in the middle and dark around the edges, creating dark rings around the eyes and dilating the pupil, and in sepioids and squids, creating large dark eyespots on the mantle. This effect is extremely startling. The animal also seems to get bigger. 13.3.5 Translucent Camouflage The best way to avoid being seen is to be invisible and so cast no shadow. The equivalent of translucence is to present the observer with the scene which the object is blocking out. In a technical world this can be done using a camera to film the scene that is blocked and presenting it to the observer in front of the object. Whole animals (e.g. pelagic marine organisms such as jelly fish, sea gooseberries, and many larval forms) or parts of animals (e.g. the cornea of the eye) can be translucent and therefore nearly invisible. To be translucent, reflection of incident light must be kept to a minimum and light must be neither scattered nor absorbed as it passes through the body. Scattering is caused by variations in refractive index. Animal tissue normally has many variations in refractive index (cells, fibres, nuclei, nerves, and so on). The most important factors are the distribution and size of the components; refractive index is less important; the shape of the components is least important. For instance, if a cell requires a certain volume of fat to survive but must scatter as little light as Figure 13.2 (See color insert following page 302) A cuttlefish (Sepia officinalis) can change its appearance according to thebackground. Here theanimal changes its bodypattern when moved from a sandy or gravelsubstrate to one with shells. (Courtesy of Roger T. Hanlon, Senior Scientist, Marine Biological Laboratory, Woods Hole, MA.) Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 348 21.9.2005 11:51pm 348 Biomimetics: Biologically Inspired Technologies possible, it is best to divide the fat into many very small droplets. Slightly worse is to divide it into a few large droplets, but the very worst is to divide it into drops about the size of the wavelength of light (Johnsen, 2001). Variations in refractive index do not always cause scattering. If the refractive indices vary by less than half the wavelength of light, the scattered light is eliminated by destructive interference and the light waves overlap in such a way that they cancel each another. This happens in the cornea of the eye, which is constructed of an orthogonal array of collagen fibres. Many organisms living in the deeper ocean, where there is little or no ambient light to be reflected or by which camouflage color can be seen, produce their own light. The organs that do this — photophores — can be mounted on mechanisms which rotate them so that they face the body and are effectively obscured, hence can be modulated and switched on and off (Johnsen et al., 2004). 13.3.6 Reflecting Camouflage If an object can simply reflect the color and pattern of its surroundings, then it will be adaptive. But if it merely reflects the sky when looked at from above, or the ground when looked at from below, this will be ineffective. The geometry of the reflecting surface is crucial. In deep water, the laterally scattered light is equal in intensity from a range of angles. Looking up, one sees brightness; looking down there is dim blue-green. A perfect mirror suspended vertically in the water would be invisible since the light from the surface is reflected to a viewer below, making the mirror appear translucent. Many fish have platelets of guanine in their scales arranged vertically, thus generating such a mirror independently of the shape of the section of the body. The fish is also countershaded. Viewed laterally the fish is a reflector and therefore invisible. Viewed from the top, it is dark like the depths below it. Viewed from below it is silvery white like the surface. The most difficult view to camouflage is that from directly below when the fish obscures light from above. Many clupeids, such as the threadfin shag Dorosoma petense, are thin and come to a sharp edge at the belly. This allows light from above to be reflected vertically downwards over the entire outline (Johnsen, 2002). Another form of reflecting camouflage is provided by the cuticle of some scarab beetles. The cuticle is made of structures that look like liquid crystals, mainly nematic and cholesteric. Thus, of the incident light on the cuticle, the right circularly polarized component can be reflected and the left circularly polarized light can penetrate the helicoidally structured cuticle. However, at a certain depth, there is a layer of nematic structure that acts as a half-wave plate, reversing the sense of polarization of the light, which is then reflected when it reaches the next layer of helicoidal structure, has its sense of polarization reversed again by the nematic layer, and continues back out through the helicoidal cuticle with very little loss. The refractive index of the cuticle is increased by the addition of uric acid. Thus the cuticle is an almost perfect reflector, making the beetle appear the same green as its surroundings. This system will work only when the color and light intensity are the same in all directions (Caveney, 1971). 13.3.7 Motion Camouflage This is included here since it is a way of observing and approaching an object without making it obvious to an observer or the object that it is being observed. The technique might have been unintentionally deployed by attacking fighter aircraft, and is currently in development for disguis- ing the intended target of guided missiles. An everyday equivalent, converted to the acoustic environment, would be that if you are following someone closely, make sure that the noise of your footfall is in synchrony with that of your quarry. This is a stealth shadowing technique used by, for instance, the dragonfly approaching its prey on the wing. The dragonfly follows a path such that it always lies on a line connecting itself and a fixed point. Then the only visual cue to the dragonfly’s approach is its looming (i.e., the increase in Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 349 21.9.2005 11:51pm Defense and Attack Strategies and Mechanisms in Biology 349 the size of its image as it closes in on the object). The observer of the object thus sees no movement away from the direction of the fixed point. The fixed point could be a part of the background against which the dragonfly is camouflaged, or the initial position of the dragonfly, in which case the dragonfly appears not to have moved from its starting point (Anderson and McOwan, 2003). 13.3.8 False Target Generation A device that creates and presents an image of a target that causes a weapon to aim at a false target. Used as a countermeasure to precision guided weapons (Alexander et al., 1996). This is a common ploy in insects; for instance, butterflies have eye spots on the trailing edge of the hind wing. Predating birds tend to aim for the eyes rather than the body of the insect, and so the insect escapes with relatively slight damage to the hind wing. Similarly fish can have an eyespot on the tail fin with the true eye concealed in a dark marking across the head. A number of moth larvae have a false ‘‘head’’ at the tail end which can simply be eye spots or an image of the head of another animal such as a snake. The advantage then is not just that the attack will be at the ‘‘wrong’’ end of the animal, thus protecting the nervous system, but that the animal will apparently move backwards in order to escape. A more sophisticated false target is generated by autotomy of part of the animal. A well-known example is the salamander which leaves the end of its tail behind. A more sophisticated example is provided by certain opilionids (harvestmen), which can autotomize a leg which will continue to move and thus confuse and divert the predator whilst the putative prey makes its escape (Gnaspini and Cavalheiro, 1998). Since the opilionid has eight legs (at least at the start of the chase) it can employ this subterfuge a number of times. However, studies on wolf spiders (which play a similar trick) show that the loss of a leg slows them down (Amaya et al., 1998). 13.4 BARRIERS 13.4.1 Slick Coating Teflon lubricants that create a slippery surface because of their chemical properties. These chemical agents reduce friction with the intent to inhibit the free movement of the target. In the 1960s Riotril (‘‘Instant Banana Peel’’) was applied as an ostensibly inert white powder to a hard surface and wetted down. It then became like an ice slick. It is virtually impossible for an individual to move or stand up on a hard surface so treated; tyres skid. Riotril, if allowed to dry, can easily be peeled away or, because it’s water-soluble, can be washed away (Alexander et al., 1996). A similar phenomenon is found in the carnivorous pitcher plants (Figure 13.3). Several mechanisms have been proposed for the way they capture insects, mostly slippery surface wax crystals. But the important capture mechanism is due to the surface properties of the rim of the pitcher, which has smooth radial ridges. This surface is completely wettable by nectar secreted by the rim, and by rain water, so that a film of liquid covers the surface when the weather is humid. The rim is then slippery both for soft adhesive pads (the liquid sees to that) and for the claws, due to the surface topography. This dual system starts sliding ants down the slippery slope (Bohn and Federle, 2004). 13.4.2 Sticky Coating Polymer adhesives used to bond down equipment and human targets. Also known as stick’ems’ and superadhesives (Alexander et al., 1996). The best known biological adhesives are those occurring in spiders’ webs and those on the leaves of the sundew, Drosera. Neither adhesive has yet been characterized. Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 350 21.9.2005 11:51pm 350 Biomimetics: Biologically Inspired Technologies The Peripatus (the velvet worm, Figure 13.4) shoots out sticky adhesive threads that entangle its prey. The threads contain protein, sugar, lipid, and a surfactant, nonylphenol. The proteins are the principal component of the slime; the amino acid composition suggests collagen. The original function of the secretion was probably defense, developing into attack as the viscosity, amount, and distance that the substance could be expelled all increased. This defensive substance would in turn be also useful for hunting, if the original condition consisted of capturing prey directly using mandibles, as when onychophorans handle small prey. The adhesive substance probably allows the entanglement of larger and therefore more nutritious prey (Benkendorff et al., 1999). When in danger, some species discharge sticky threads that can entangle predators. Some like the sea cucumber can even expel their internal organs, which they regrow causing it no harm at all. Although the mechanical properties of the threads have not been measured, they are obviously very Figure 13.3 A pitcher plant trap, which is a modified leaf. The rim of the trap is curled over, forming a slippery platform onto which insects can walk. Figure 13.4 The velvet worm, Peripatus capensis. It lives in damp places and has no external armor. However, it can shoot sticky threads several times its body length. Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 351 21.9.2005 11:51pm Defense and Attack Strategies and Mechanisms in Biology 351 [...]... Vol 21 3 (1987), pp 621 – 639 Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 36 3 21 .9 .20 05 11:51pm Defense and Attack Strategies and Mechanisms in Biology 36 3 Kitchener A.C., The evolution and mechanical design of horns and antlers, in: Rayner J M.V and R J Wootton (eds.) Biomechanics in Evolution, Cambridge University Press, Cambridge, MA (1991), pp 22 9 25 3 Kitchener... America, Vol 101 (20 04), pp 14 138 –141 43 Bar- Cohen : Biomimetics: Biologically Inspired Technologies 3 62 DK31 63_ c0 13 Final Proof page 3 62 21.9 .20 05 11:51pm Biomimetics: Biologically Inspired Technologies Caveney S., Cuticle reflectivity and optical activity in scarab beetles: the role of uric acid, Proceedings of the Royal Society B, Vol 178 (1971), pp 20 5 22 5 Croll D.A., C.W Clark, A Acevedo, B Tershy,... : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 36 4 21 .9 .20 05 11:51pm Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c014 Final Proof page 36 5 6.9 .20 05 12: 41pm 14 Biological Materials in Engineering Mechanisms Justin Carlson, Shail Ghaey, Sean Moran, Cam Anh Tran, and David L Kaplan CONTENTS 14.1 Introduction 36 5 14 .2 Comparisons:... flying towards you, with friendly intent! Figure 13. 6 A bola spider (an American species, Mastophora, is shown here), waiting for a prey insect to fly past Bar- Cohen : Biomimetics: Biologically Inspired Technologies 35 8 DK31 63_ c0 13 Final Proof page 35 8 21 .9 .20 05 11:51pm Biomimetics: Biologically Inspired Technologies 13. 8 .2 Cloggers Polymer agents, sticky-soft plastics, used in burst munitions to clog... have contacted the prey, the stalks often buckle (Kier and Thompson, 20 03) Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 35 3 21 .9 .20 05 11:51pm Defense and Attack Strategies and Mechanisms in Biology 35 3 13. 4.5 Smoke A thick, disorienting ‘‘cold smoke’’ that can be generated in areas from 2, 000 to 50,000 cubic feet It restricts an intruders eye–hand coordination... cocktail A similar system operates in caterpillars The urticating hairs or spines of the larva of the moth Bar- Cohen : Biomimetics: Biologically Inspired Technologies 35 4 DK31 63_ c0 13 Final Proof page 35 4 21 .9 .20 05 11:51pm Biomimetics: Biologically Inspired Technologies Figure 13. 5 A nettle sting, about 1-mm long The tip is highly silicious and brittle, so that when it breaks off it leaves a sharp end like.. .Bar- Cohen : Biomimetics: Biologically Inspired Technologies 3 52 DK31 63_ c0 13 Final Proof page 3 52 21.9 .20 05 11:51pm Biomimetics: Biologically Inspired Technologies tough since the Palauan people of the south Pacific squeeze the sea cucumber until it squirts out its sticky threads,... to 2 km A great many insects produce repellant chemicals (q.v.) 13. 12 PHYSIOLOGICAL 13. 12. 1 Neurochemical There are many neurotoxins For instance, a sea anemone uses its tentacles to capture prey and defend itself against predators Every tentacle is covered with thousands of tiny stinging capsules Bar- Cohen : Biomimetics: Biologically Inspired Technologies 36 0 DK31 63_ c0 13 Final Proof page 36 0 21 .9 .20 05... silk as an antiparallel hydrogen bonded b-sheet The unit cell parameters in the silk II structure (the spun Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c014 Final Proof page 36 8 6.9 .20 05 12: 41pm 36 8 Biomimetics: Biologically Inspired Technologies form of silk that is insoluble in water) are: 0.94 nm (interchain), 0.697 nm (fiber axis), 0. 92 nm (intersheet) These unit cell dimensions... for new materials: (a) silk proteins used by spiders and silkworms to construct composite encasements (cocoons) or strong and 36 5 Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c014 Final Proof page 36 6 6.9 .20 05 12: 41pm 36 6 Biomimetics: Biologically Inspired Technologies functional webs to entrap prey; (b) organic–inorganic composite structures found in sea shells to form highly engineered, . Thompson, 20 03) . Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 3 52 21.9 .20 05 11:51pm 3 52 Biomimetics: Biologically Inspired Technologies 13. 4.5 Smoke A. al., 19 92) . Figure 13. 1 An ankylosaur. Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 34 4 21 .9 .20 05 11:51pm 34 4 Biomimetics: Biologically Inspired Technologies Unfortunately. destroying them; also to Bar- Cohen : Biomimetics: Biologically Inspired Technologies DK31 63_ c0 13 Final Proof page 3 42 21.9 .20 05 11:51pm 3 42 Biomimetics: Biologically Inspired Technologies have minimal