KEYWORDS: Scanning electron microscopy, Aerodynamics, Biomimetics, Current controlled current source, Foam, Photography, Atomic force microscopy, Polishing, Electron microscopes, Adhesives
Primary feathers allow birds to fly; however, morphology and material properties of theses feathers vary in different bird
species. We therefore analysed both morphology and material properties of primary feathers in two raptor species, the
peregrine falcon (Falco peregrinus) which is the fastest vertical flyer known, and the kestrel (Falco tinnunculus), using
scanning electron microscopy (SEM) and nanoindentation. The program AutoCAD was used for the computation of the
moments of inertia. The reduced E-modulus of the cortex of the rachis of the first, fifth, and tenth primary were
measured at proximal (10% of total rachis length), central (50%) and distal (75%) cross-sections. In all cross sections the
kestrel showed higher E-moduli than the peregrine falcon (values varied between 6.7 and 9.1 GPa). In the primaries,
values increased from proximal to central but decreased distally. Looking at the hardness, the kestrel had higher values
than the peregrine falcon yet again. The main differences occurred in the first primary. Values ranged between 0.17 and
0.4 GPa. SEM studies revealed that the tenth primary was more stable in the peregrine falcon, featuring more hamuli
than the kestrel at all analysed positions and longer hamuli at the distal positions. The higher moments of inertia found in
the peregrine falcon caused a much higher bending stiffness in this species. Values were 4.4 to 9.1 times larger in the
peregrine falcon than in the kestrel. Because the given structures are responsible for the stability of the feather face it
seems that the feathers of F. peregrinus are more robust than those of F. tinnunculus. Even when considering the higher
body mass of the peregrine falcon compared to the kestrel (3.4 times), the determined stability of the feather
compensates for this problem.
The beetle Melanophila acuminata is highly dependent on forest fires. The burned wood serves as food for the larvae
and the adults copulate on the burned areas to put their eggs in the freshly burned trees. To be able to detect forest fires
from great distances the beetle developed a highly sensitive infrared receptor which works according to a photomechanical
principle. The beetle has two pit organs, one on each lateral side, of which each houses around 70 dome
shaped infrared receptors. These IR-receptors consist of a hard outer cuticular shell and an inner microfluidic core.
When IR-radiation is absorbed, the pressure in the core increases due to the thermal expansion. This results in a
deflection of a dendritic tip of a mechanosensitiv neuron which generates the signal.
This biological principle was transferred into a new kind of un-cooled technical infrared receptor. To demonstrate the
functional principle and the feasibility of this IR-sensor a macroscopic demonstrator sensor was build. It consisted of an
inner fluid filled cavity (pressure chamber), an IR-transmissive window and a membrane. The deflection of the
membrane due to the absorbed IR-energy was measured by a sensitive commercial capacitive sensor. In the experiments
ethanol with added black ink, a mix of ethanol and glucose with additional absorber, air with additional absorber and
water were used as fillings of the cavity and compared against each other. In order to get insights into the physics of the
results of the experiments accompanying simulations using FEM methods and analytical calculations have been
performed.
The results showed that ethanol and air as fillings of the cavity caused the largest deflection of the membrane.
Furthermore it turned out that the thermal expansion of the sensor housing material has an important influence. The
comparison of the measured deflection with calculated deflections showed a good concordance.
Beetles of the genus Melanophila and certain flat bugs of the genus Aradus approach forest fires. For the detection of
fires and of hot surfaces the pyrophilous species of both genera have developed infrared (IR) receptors, which have
developed from common hair mechanoreceptors. Thus this type of insect IR receptor has been termed photomechanic
and shows the following two special features: (i) the formation of a complex cuticular sphere consisting of an outer
exocuticular shell as well as of a cavernous microfluidic core. (ii) The enclosure of the dendritic tip of a
mechanosensitive neuron inside the core in a liquid-filled chamber. Most probably a photomechanic IR sensillum acts as
a microfluidic converter of infrared radiation into an increase in internal pressure inside the sphere, which is measured by
a mechanosensitive neuron.
A simple model for this biological IR sensor is the Golay sensor, which is filled with a liquid instead of gas. Here the
absorbed IR radiation results in a pressure increase of the liquid and the deflection of a thin membrane. For the
evaluation of this model analytical formulas are presented, which permits the calculation of the pressure increase in the
cavity, the deformation of the membrane and the time constant of an artificial leak to compensate ambient temperature
changes. Some organic liquids with high thermal expansion coefficients may improve the deflection of the membrane
compared to water.
Insect cuticle has a broad range of mechanical properties. As it has to provide a very efficient and lightweight skeleton,
cuticle is a highly interesting composite-material and may serve as a natural model for new biomimetic materials.
However, the water content of insect cuticle is of great importance for its material properties. Here, we present a
new method to perform nano-indentation experiments in cuticle which has its full water content. Parts of the exoskeleton
of Locusta migratoria were investigated to determine the elastic modulus (Er) and hardness (H) of the cuticle. Cuticle
sections were measured in air and then submerged and measured in water. As insect cuticle is an anisotropic material,
we performed nano-indentation in the normal as well as in the transverse direction and also tested different cuticle layers
within each sample (exo-, meso- and endo-cuticle).
It turned out that a change of the water content has a dramatic impact on the material properties of the cuticle.
For example, the Er of submerged endo-cuticle turned out to be 75% lower than of endo-cuticle samples measured in air.
Further, the proportion of material property values between different cuticle layers within a sample change dramatically
after addition of water.
For the detection of forest fires the "fire-loving" (pyrophilous) jewel beetle Melanophila acuminata uses a pair of sensor
arrays each consisting of about 90 infrared (IR) receptors which are located on either sides of the body. The IR receptors
most likely have evolved from common contact hair mechanoreceptors. Compared to a mechanoreceptor, an IR receptor
shows the following special features: (i) the formation of a complex cuticular sphere instead of the bristle; the sphere
consists of a hard outer exocuticular shell as well as of an inner softer and spongy mesocuticular core. (ii) The enclosure
of the dendritic tip of the mechanosensitive neuron inside the sphere in a fluid-filled inner pressure chamber which is
connected with the system of microcavities and nanocanals in the mesocuticular core. Hence we propose that an IR
sensillum most probably acts as a microfluidic converter of infrared radiation into an increase in internal pressure inside
the sphere which is measured by the mechanosensitive neuron. Because the miniaturized receptors respond within a few
milliseconds to a brief pulse of IR radiation an approach is made to develop technical IR sensors based on the
Melanophila IR receptors. Numerical simulations of sensor performance suggest that the sensitivity of a single IR
receptor is in the range of 15 mW/cm2. Theoretical calculations which are based on a hypothetical fire of defined
temperature and size demonstrate that a beetle should be able to detect a forest fire from a distance of 10 km. A fluidfilled
Golay cell was taken as a basis for the design of a first sensor prototype.
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