332 IEEE SENSORS JOURNAL, VOL. 12, NO. 2, FEBRUARY 2012 Structural Characterization of the Whisker System of the Rat Danja Voges, Kathrin Carl, Gertrud J. Klauer, René Uhlig, Cornelius Schilling, Carsten Behn, and Hartmut Witte Abstract—Vibrissae or tactile hairs, commonly known as whiskers, are the mechanical gates of special mechano-sensitive organs. In terrestrial mammals, they carry various functions, especially object determination and texture discrimination. We hypothesise that the characteristic morphology and structure of whiskers is a primary morphological condition for their mechano-sensitive functions. To constitute mathematical models on the systematic but different mechanical behavior of the main types of whisker hairs (micro vibrissae, macro vibrissae, strad- dlers), information is lacking on the distribution of properties in a field of all three types of hairs, taken from one and the same animal. Referring to sets taken from five individuals, geometry data is provided as one complete set for a female rat (Rattus norvegicus). Due to measurements of diameters along the length, the shape of whiskers in rats is confirmed to resemble a cone, which may be overlaid by some convexity or concavity. Addition- ally, the surface and internal structure of different vibrissae were examined by scanning electron microscopy. The cuticle of the rat whisker consists of flat scales, overlapping like roofing slates. A cross section reveals up to 20 superposed layers of cuticular scales. The longitudinal dimension of one scale is shorter in whiskers compared with body hairs. A hollow medulla is observed from the base to approximately half of the overall length, which is then partially filled by compact tissue, until it disappears completely near the tip. An extraordinarily thick cortex probably rules the characteristic bending features, and the multilayer cuticle prob- ably has a mainly protective function. Index Terms—Biomimetics, rat vibrissae, structure, tactile sen- sors, whiskers. I. INTRODUCTION V IBRISSAE form the first mechanical element of a com- plex mechano-sensitive organ, which beneath a lot of other hypothetized functions allows mammals to localize ob- jects and to discriminate their surface structure (cf. the overview in [20]). To understand the observed physiological behavior of whiskers, the underlying control laws acting on the follicle sinus complexes (FSCs) as active bearings of the hairs, and at last at biomimetic transfer into technical sensor principles, we try to constitute mathematical models of the mechanical behavior of vibrissae. Manuscript received October 20, 2010; revised April 30, 2011; accepted May 19, 2011. Date of publication July 12, 2011; date of current version December 07, 2011. The associate editor coordinating the review of this paper and ap- proving it for publication was Prof. Raul Martin-Palma. D. Voges, K. Carl, C. Schilling, R. Uhlig, C. Behn, and H. Witte are with the Ilmenau University of Technology, D-98693 Ilmenau, Germany (e-mail: Hartmut.Witte@tu-ilmenau.de). G. J. Klauer is with Senckenbergische Anatomie, Institut der Anatomie III, Johann Wolfgang Goethe-Universität, Frankfurt/Main, Germany. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2011.2161464 Fig. 1. Morphological designation of mystacial vibrissae. The individual of Rattus norvegicus described owned four rows of macro vibrissae numbered 1 to 4 from occipital to rostral, and five arcs of macro vibrissae called A (near Dorsum nasi) to E (near the mouth). Straddlers situated occipital between the rows of macro vibrissae are identified by Greek letters Alpha to Delta corre- sponding to the next nasal row of macro vibrissae. Micro vibrissae are named following an analogous sequence from MicroA to MicroE. From literature, no set of data necessary for this task, de- scribing morphology, structure, and material properties of a complete array of mystacial vibrissae of a terrestrial/arboreal mammal is available. Thus, in a first step, we provide data on the outer and inner geometry of mystacial vibrissae of a rat, addressed via their location in the fields of macro vibrissae, micro vibrissae, and straddlers (see Fig. 1 for that terminology). The morphological features of various types of hair are used for their characterization in widely varying branches of science [17]. In addition to the macroscopic features of form, size, pro- file and color, microscopic characteristics are gaining in signifi- cance, an observation that applies both to the distinction of dif- ferent hair types of one species and the comparison of those of different species [21]. The crucial characteristics are the shape, the varying cross section, and the surface texture. To micro- scopic characteristics belong the form and size of the cutic- ular scales, as well as the nature of the medulla. The properties of any hair are modified by a number of environmental influ- ences which complicate general characterization, such as cli- mate, habitat, ectoparasites, or nutrition [9]. Latzke [11] suggests a structural classification: • cross-sectional shape: round or with another profile (e.g., angular, lobed, dentate, etc.); • cross-sectional shape: filled (solid) or hollow (mono- or multitubular); 1530-437X/$26.00 © 2011 IEEE