Mechanical characteristics of harbor seal (Phoca vitulina) vibrissae under different circumstances and their implications on its sensing methodology

In this paper, the mechanical properties of harbor seal vibrissae immersed in various solutions are investigated. As there are no nerves along the length of the vibrissae, all the perturbations have to be transmitted to their bases for sensing. Hence, quantification and understanding of the mechanical properties of the vibrissae are essential in determining the perturbations transmitted to the base of the vibrissae. Two experimental setups are devised for measurements of the different properties of the vibrissae. The first experimental setup is performed with a dynamic mechanical analysis machine. The measured properties in these experiments are the modulus of elasticity and the damping of the vibrissae. Dry, saline water-immersed, water-immersed and Hanks' balanced salt solution (HBSS)-immersed vibrissae are tested to determine the effects of these solutions on the properties of the vibrissae. Tests on the duration of immersion are also performed with saline water-immersed vibrissae. The second experimental setup is performed with a mini-shaker connected to a clamp, which rigidly holds the vibrissae at their bases. The measured properties in these experiments are the natural frequencies of the vibrissae. The results indicate that the moduli of elasticity of the vibrissae are found to decrease along their lengths. However, their damping does not vary along the lengths. HBSS-immersed and saline water-immersed vibrissae show similar characteristics on their properties. An analytical model for predicting the natural frequencies of the vibrissae is also derived. Strong agreement with previous studies on the underwater sensing principle of the harbor seal is also established.