Spatially Dependent Mechanical Properties Of Rat Whiskers For Tactile Sensing
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Spatially Dependent Mechanical Properties Of Rat Whiskers For Tactile Sensing E. K. Herzog, D. F. Bahr, C. D. Richards, R. F. Richards, and D. M. Rector* School of Mechanical and Materials Engineering, PO Box 642920 Washington State University, Pullman WA 99164 *Department of Veterinary and Comparative Anatomy, Pharmacology, and Physiology, PO Box 7010 Washington State University, Pullman WA 99164 ABSTRACT A new generation of sensors based on biologically inspired whisking action will help determine the presence and location of solid objects and fluid vortices similar to mechanisms used by whisker bearing animals such as rats and seals. By using nanoindentation, we demonstrate that mechanical properties are essentially uniform by cross section, but vary longitudinally from the whisker base (a 3.9 GPa elastic modulus) to the tip (a 3.1 GPa elastic modulus). Several recent studies show propagation of high frequency information through whiskers that are tuned by their physical properties. In order to fully understand and model these properties, this study demonstrates a more complex whisker structure than previously assumed. INTRODUCTION Harbor seals routinely perform hydrodynamic detection and following with extreme sensitivity. In an experimental context, seals are able to track a small model submarine from great distances in the absence of olfactory, auditory, or visual cues [1]. These authors conclude that whiskers are sensitive to persistent vortices set up in the water by the trail of a herring from 180 meters. Similarly, rats can distinguish between fine grades of sandpaper using only their whiskers [2,3]. By investigating, understanding and simulating the mechanical and sensory systems that mediate such sensitivity, we will greatly enhance the development of sensitive tactile sensors. At least some of the sensitivity of the whisker system and the resulting neurological signals can be attributed directly to the mechanical properties of the whiskers themselves [4,5]. Whiskers can resonate with external stimuli at high frequencies (100 - 1000 Hz) and neural mechanisms can respond with action potentials in a one to one relationship towards these high frequencies [1]. As research into whisker stimulation – barrel cortex activity continues, relating the mechanical response to the neurological response will require a complete understanding of the links between external stimuli and the measured electrical response in the sensing regions of the brain, and the various transfer functions between these levels. We are currently creating artificial sensing systems based on whisking models, but this project requires the knowledge of the properties of the actual whiskers prior to fabricating micro machined structures to mimic these systems. In this study, an alpha-keratin fiber of a rat vibrissa (a whisker) was tested using nanoindentation to find the mechanical properties as a function of position on the whisker. Instead of treating the fibers as a uniform structure, the vibrissa was tested as a function of bot
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