Chemical composition and physical features of harbor seal (Phoca Vitulina) vibrissae for underwater sensing application

Harbor seals are known to be able to detect wakes of fish underwater by using only their vibrissae. In this study, we examine the composition of the harbor seal vibrissae, to establish their vibratory properties, and the physical features (such as roughness, and morphology), which may significantly affect the flow around the vibrissae and influence its flow detection ability. The analysis is performed a using Scanning Electron Microscope (SEM) with an Energy Dispersive Spectrometer (EDS) to identify the overall chemical composition of the seal vibrissae as well as to quantify the roughness feature of the seal vibrissa. Analysis on the surface composition of the seal vibrissae using X-ray Photoelectron Spectrometer (XPS) reveals similar composition to the overall composition. The composition obtained from the test results reveal that the seal vibrissae are composed of approximately 69% carbon atoms as compared to human hair consisting of approximately 50% carbon atoms. The roughness features are found to be small as compared to the geometrical dimension of the seal vibrissa, approximately 1000 times smaller than the undulations of the vibrissa diameters. A cavity is also found in the middle of the cross section of the vibrissa. Traces of nerves are not visible in the region, which is in agreement with previous reports that no nerves exist along the vibrissae. Hence, mimicking the seal whisker does not require special treatment on the material and the surface features. Ensuring the existence of undulations on both minor and major axes will be crucial for the study on the seal's hydrodynamic tracking ability.